JPH07312457A - Semiconductor laser device - Google Patents

Abstract

(57) [Abstract] [Purpose] To reduce the dark current when a semiconductor laser is used as a photodetector and to increase the optical coupling efficiency in direct coupling with an optical fiber. [Structure] On a surface of a semiconductor substrate 1, there is provided a laminated film in which at least one conductivity type semiconductor layers 21 and 22, a core layer 3 made of a semiconductor, and another conductivity type semiconductor layer 4 are sequentially formed, and one end side of the substrate is provided. The transparent waveguide part is formed by using the core layer as a waveguide, and the laser oscillating part is formed on the other end side of the substrate following the transparent waveguide part and uses the core layer as a photomultiplier layer. A first slit section in which a slit formed by cutting at least the core layer in each of the waveguide section and the laser oscillation section is filled with a semiconductor layer having a wider band gap than the core layer.
91 and the second slit portion 92, the first electrode 5 formed on the back surface of the substrate, and the second electrode 61 formed on the laminated film between the first slit portion and the second slit portion. Laser device having a.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device, and more particularly to a semiconductor laser device which performs transmission / reception by using one device for both laser and photodetector in time division.

[0002]

FIG. 21 shows a conventional semiconductor laser. FIG. 21 is a sectional view of Conventional Example 1.

In the figure, 1 is a semiconductor substrate, 2 is an n-type cladding layer, 3 is a core layer, 4 is a p-type cladding layer, 5 is an n-side electrode, 6 is a p-side electrode, and 7 is exposed at the laser end. The pn junction, 8 is the incoming and outgoing light beam.

This semiconductor laser comprises a n-type cladding layer 2 and a core layer 3, or a core layer 3 and a p-type cladding layer 4.
A pn junction is formed between and, and the pn junction is exposed on the end face.

When this semiconductor laser is used as a laser, a forward bias voltage is applied to the pn junction, and when it is used as a photodetector, a reverse bias voltage is applied to the pn junction.

In the semiconductor laser of Conventional Example 1, the n-side electrode 5
When a voltage is applied between the p-side electrode 6 and the p-side electrode 6, an electric field is also applied to the pn junction 7 exposed at the laser end. Since the surface of the laser edge is electrically unstable, when a reverse bias voltage is applied,
There is a problem that the leakage current when light is not incident (hereinafter referred to as dark current) becomes large and the sensitivity deteriorates when used as a photodetector.

FIG. 22 is a sectional view of Conventional Example 2. The conventional example 2 has a structure in which the laser end face is embedded as a window portion with a transparent semiconductor layer in order to eliminate the drawbacks of the conventional example 1. When this structure is applied to a Fabry-Perot type laser, the feedback rate of the light reflected from the end face to the active layer of the laser decreases, and the oscillation threshold value increases. Therefore, this structure is mainly used for a distributed feedback laser (DFB laser) mainly having a diffraction grating.

A laser having this window portion is manufactured as follows. Each layer constituting a laser is grown on a wafer, each layer at a portion corresponding to the end of each laser chip is removed by etching to form a groove, and a buried layer including a current limiting layer is buried therein. Then, the surface of the buried layer is scribed at a diamond point or the like and cleaved along the scribe line to divide each laser chip.

At this time, the accuracy of the cleavage position is worse than ± 5 μm. Therefore, the length of the window in the waveguide direction is 5
It becomes as large as about 15 μm. FIG. 23 shows a case where the laser is abutted against the single mode optical fiber 11 having a flat tip in this case to optically couple.
As shown in the figure, in a normal semiconductor laser, the distance from the surface of the laser to the core layer 3 is 2 μm or less, and the diameter of the core 14c of the optical fiber is 8 to 10 μm. Therefore, the portion which can be coupled to the waveguide of the laser is only the portion indicated by reference numeral 14 in the drawing. Further, the light is spread with the propagation due to the diffraction effect, and the coupling efficiency is further reduced for the two reasons that the distance between the waveguide and the tip of the fiber 11 is increased because of the window portion 13.

Even if the distance from the surface of the laser to the core layer 3 is increased as shown in FIG. 24, since the optical electric field distribution 12 in the laser is localized in a narrow region of 2 μm or less, the laser conduction is reduced. The portion that can be coupled to the waveguide is limited to the portion indicated by reference numeral 14 in the figure. Therefore, if there is the window portion 13, the optical coupling efficiency is lowered due to the influence of the spread of light due to the diffraction effect.

Further, as shown in FIG. 25, when optical coupling is performed by abutting with an optical fiber having a lens processed at the tip,
Since the distance between the tip of the optical fiber and the beam waist is less than 5 μm, the light is coupled to the laser waveguide in the state where the beam waist is formed in the window and spreads from it.

As described above, when the optical terminal device is directly connected to the optical fiber in order to reduce the cost, the window length is about 15 μm at maximum, which causes a problem that the optical coupling efficiency is lowered. .

[0013]

SUMMARY OF THE INVENTION It is an object of the present invention to reduce the dark current when a semiconductor laser is used as a photodetector and to increase the optical coupling efficiency when directly coupling with an optical fiber.

[0014]

[Means for Solving the Problems] 1) (See FIG. 1, FIG. 6 (A) and FIG. 14) The above-mentioned problems can be solved by first forming at least one layer on the surface of a semiconductor substrate (1).
First semiconductor layer (2) layered with a semiconductor of the conductivity type
And a core layer (3) composed of at least one semiconductor layer of any conductivity type and a semiconductor layer of at least one semiconductor layer of a second conductivity type different from the first conductivity type. An optical device having a laminated film in which two semiconductor layers (4) are sequentially formed, and the first semiconductor layer (2) and the second semiconductor layer (4) serve as clad layers and the core layer (3) serves as a core. In a semiconductor laser device having a waveguide and having a waveguide structure in which at least two types of optical waveguides having different properties are arranged in series in the optical axis direction with a common optical axis, the following (a), (b) ), (C) and (d) are requirements for the semiconductor laser device.

(A) One end of the optical waveguide is a portion that oscillates the laser using the core layer (3) as an optical amplification layer (hereinafter, this is referred to as a laser oscillating portion (B)) and the other end of the optical waveguide is located. Indicates that the light absorption coefficient of the core layer (3) is smaller than the light absorption coefficient of the core layer (3) of the laser oscillator (hereinafter, the optical waveguide portion including the core layer having a relatively small light absorption coefficient. Is referred to as a transparent optical waveguide section (A or A1 and A2).

(B) Both the transparent optical waveguide portion (A or A1 and A2) and the laser oscillation portion (B) are slit-shaped, and the slit intersects the optical axis of the optical waveguide, and at least the core layer (3) is formed. It has a slit-like first slit portion (91) made of a semiconductor having a wider bandgap than the core layer and having a cutting depth.

(C) A slit is formed at the end of the laser oscillator (B) on the side remote from the transparent waveguide, and the slit intersects the optical axis of the optical waveguide, and at least the core layer (3).
It has a slit-like second slit portion (92) made of a semiconductor having a wider bandgap than the core layer.

(D) A first electrode (5) is provided on the back surface of the semiconductor substrate (1), and a first electrode (5) is formed on the laminated film between the first slit portion (91) and the second slit portion (92). Two electrodes (61)
Or a semiconductor laser device having 2) (see FIG. 15 and FIG. 7 (A)) at least one or more first layers on the surface of the semiconductor substrate (1).
First semiconductor layer (2) layered with a semiconductor of the conductivity type
And a core layer (3) composed of at least one semiconductor layer of any conductivity type and a semiconductor layer of at least one semiconductor layer of a second conductivity type different from the first conductivity type. An optical device having a laminated film in which two semiconductor layers (4) are sequentially formed, and the first semiconductor layer (2) and the second semiconductor layer (4) serve as clad layers and the core layer (3) serves as a core. In a semiconductor laser device having a waveguide and having a waveguide structure in which at least two types of optical waveguides having different properties are arranged in series in the optical axis direction with a common optical axis, the following (a), (b) ), (C) and (D), a semiconductor laser device characterized by including the following:
(A) One end side of the optical waveguide is a transparent optical waveguide section (A1 and A2) having the core layer (3) as a core, and the other end side of the optical waveguide is the core layer (3) as an optical amplification layer. It is a laser oscillator (B).

(B) The transparent optical waveguide portion (A or A1 and A2) has a slit shape and the slit is perpendicular to the optical axis of the optical waveguide and has a slit shape having a depth to cut at least the core layer (3). Further, it has a first slit part (91) and a second slit part (92) made of a semiconductor having a wider band gap than that of the core layer. (C) The first electrode (5) on the back surface of the semiconductor substrate (1). And a third electrode (63) on the laminated film between the first slit portion (91) and the second slit portion (92), and on the laminated film of the laser oscillation portion (B). (D) Lamination of the third oscillation electrode (63) formed on the laminated film between the first slit portion (91) and the second slit portion (92), which has the electrode (62), and the laser oscillation portion. Semiconductor laser which is electrically separated from the electrode (62) formed on the film Location or 3) (FIGS. 16 and 11 (A) refer) first or at least one layer on the surface of the semiconductor substrate (1),
First semiconductor layer (2) layered with a semiconductor of the conductivity type
And a core layer (3) composed of at least one semiconductor layer of any conductivity type and a semiconductor layer of at least one semiconductor layer of a second conductivity type different from the first conductivity type. An optical device having a laminated film in which two semiconductor layers (4) are sequentially formed, and the first semiconductor layer (2) and the second semiconductor layer (4) serve as clad layers and the core layer (3) serves as a core. In a semiconductor laser device having a waveguide and having a waveguide structure in which at least two types of optical waveguides having different properties are arranged in series in the optical axis direction with a common optical axis, the following (a), (b) ), (C) and (D), a semiconductor laser device characterized by including the following:
(A) A laser in which one end side of the optical waveguide is a transparent optical waveguide section (A) having the core layer (3) as a core, and the other end side of the optical waveguide has the core layer (3) as an optical amplification layer. Oscillator (B)
Have.

(B) The core layers of the transparent optical waveguide portion (A) and the laser oscillation portion (B) are slit-shaped, the slits are perpendicular to the optical axis of the optical waveguide, and at least the depth at which the core layer (3) is cut is cut. (C) The present semiconductor laser device on the opposite side of the transparent optical waveguide part (A), which is separated by a first slit part (91) made of a semiconductor having a slit shape and a wider band gap than the core layer. The core layer in contact with the end face of the laser oscillator and the core layer of the laser oscillating portion (B) are slit-shaped, and the slit is perpendicular to the optical axis of the optical waveguide, and has a slit-like shape having a depth to cut at least the core layer (3); Separated by a second slit portion (92) made of a semiconductor having a wider band gap than the core layer, (d)
A first electrode (5) is provided on the back surface of the semiconductor substrate (1), and a fourth electrode (64) is provided on the laminated film between the first slit part (91) and the second slit part (92). Or a semiconductor laser device according to 4) (see FIGS. 11D and 16) 3), characterized in that the semiconductor laser device satisfies the following requirements (a) and (b): A laser device, that is, (a) an optical waveguide having the same sectional structure in the waveguide of the transparent waveguide section (A) and the waveguide of the laser oscillation section (B) (that is, when the sections are compared, the thickness and composition of each layer are the same. An optical waveguide), and a fifth electrode (65) is formed on the laminated film of the portion (A) to be a transparent waveguide,
(B) A semiconductor laser device capable of injecting a current through the fifth electrode (65) to the core layer (3) below the fifth electrode, or 5) (see FIGS. 14, 15 and 16) ) The semiconductor layer (2) of the first conductivity type is formed of at least two semiconductor layers (21, 22) having different refractive indexes, and a diffraction grating (23) is formed on the boundary surface between the two semiconductor layers of the laser oscillator. )
Forming a distributed Bragg reflector laser that the diffraction grating and the distributed reflector (D istributed F eed b ack
A Laser (abbreviated as DFB Laser),
A semiconductor laser device according to any one of 1) to 4), characterized in that a laser oscillation portion is formed between the first slit portion and the second slit portion, or 6) (see FIGS. 14 and 15) 7. The semiconductor laser device according to 1) to 5), characterized in that the core layer (3) of the transparent optical waveguide portion (A or A1 and A2) is thinner than the core layer (3) of the laser oscillation portion. ) (See FIGS. 14 and 15) The core layer (3) of the transparent optical waveguide portion (A or A1 and A2) has a thickness distribution such that the core layer (3) gradually becomes thinner toward the end face 1) to 1). 5) The semiconductor laser device according to 5), or 8) (see FIG. 1). The thickness of the core layer (3) of the transparent optical waveguide portion (A or A1 and A2) is in contact with the first slit portion (91). The thickness is constant on the part and the end face 7) or 9) (see FIGS. 1 and 2), the core layer (3) includes a multi-quantum well layer, and the thickness of the multi-quantum well layer tends to change. 6), 7) or 8) characterized by the same tendency as the change in layer thickness
Or the semiconductor laser device according to 10) (see FIG. 13 (A)) at least one first layer on the surface of the semiconductor substrate (1).
First semiconductor layer (2) layered with a semiconductor of the conductivity type
And a core layer (3) composed of at least one semiconductor layer of any conductivity type and a semiconductor layer of at least one semiconductor layer of a second conductivity type different from the first conductivity type. An optical device having a laminated film in which two semiconductor layers (4) are sequentially formed, and the first semiconductor layer (2) and the second semiconductor layer (4) serve as clad layers and the core layer (3) serves as a core. In a semiconductor laser device having a waveguide, an optical waveguide having a structure in which at least two types of optical waveguides having different properties are arranged in series in the optical axis direction with the optical axis in common are provided. ), (C), (d) and (e) are requirements for the semiconductor laser device.

(A) Both sides of the optical waveguide are the core layer (3)
Is a transparent optical waveguide part (A or A1, A2, and E or E1, E2) having a core as a core, and the central part of the optical waveguide is an optical amplification part (B) having the core layer (3) as an optical amplification layer. is there.

(B) The transparent optical waveguide portion (A or A1 and E or E1) is formed up to the end face. (C) One transparent optical waveguide part (A or A1 and A2)
A first slit portion made of a semiconductor which is slit-shaped and has a depth which intersects the optical axis of the optical waveguide and which has a depth for cutting at least the core layer (3) and which is wider in band gap than the core layer. (91) is formed.

(D) The other transparent optical waveguide portion (E or E1)
And E2) which is slit-shaped and has a slit that intersects the optical axis of the optical waveguide and has a depth that cuts at least the core layer (3) and that is made of a semiconductor having a wider band gap than the core layer. Slit part (9
2) has been formed.

(E) A first electrode (5) is provided on the back surface of the semiconductor substrate (1), and a first electrode (5) is formed on the laminated film between the first slit portion (91) and the second slit portion (92). Four electrodes (64)
11) (See FIG. 13 (A), FIG. 13 (B) and FIG. 13 (C)) Transparent optical waveguide part (A or A1 and E or E1) far from the laser oscillating part 1 is used as the mirror surface of the Fabry-Perot resonator and the optical amplification section (B) is used as the amplification section for laser oscillation 1
0) or 12) (see FIGS. 13 (A) and 13 (B)), the core layer (3) of the transparent optical waveguide section (A, A1 and E, E1) is an optical amplifier. The semiconductor laser device according to 10) or 11), which is thinner than the core layer (3) of the part (B), or 13) (see FIGS. 13A and 13B). Optical waveguide part (A or A1, A2 and E or E
1, E2) the core layer (3) has a thickness distribution such that the core layer (3) becomes gradually thinner toward the end face, 10) or 11), or 14) (FIG. 13 ( A) and FIG. 13B)) The transparent optical waveguide portion (A or A1, A2 and E or E)
The thickness of the core layer (3) of (1, E2) is constant at the portion in contact with the first slit portion (91) and the second slit portion (92) and at the very end face 13).
15) (See FIGS. 2, 13 (A), and 13 (B)) The core layer (3) includes a multiple quantum well layer, and the thickness of the multiple quantum well layer. The thickness is changed in the same manner as the thickness of the core layer (3), thereby making the waveguide portions (A or A1, A2 and E or E1, E2) to be transparent transparent. ), 12), 13) or 1
4) The semiconductor laser device according to 4), or 16) (see FIG. 11A). The semiconductor substrate (1) has at least one first layer on the surface thereof.
First semiconductor layer (2) layered with a semiconductor of the conductivity type
And a core layer (3) composed of at least one semiconductor layer of any conductivity type and a semiconductor layer of at least one semiconductor layer of a second conductivity type different from the first conductivity type. An optical device having a laminated film in which two semiconductor layers (4) are sequentially formed, and the first semiconductor layer (2) and the second semiconductor layer (4) serve as clad layers and the core layer (3) serves as a core. In a semiconductor laser device having a waveguide, an optical waveguide having a structure in which at least two types of optical waveguides having different properties are arranged in series in the optical axis direction with the optical axis in common are provided. ) And (c) are satisfied, that is, (a) both ends of the optical waveguide are transparent optical waveguide portions (A and E) having the core layer (3) as a core. And the central part of the optical waveguide optically amplifies the core layer (3) An optical amplifier unit (B) to,
(B) Transparent optical waveguide section (A and E) and optical amplification section (B)
A slit-shaped first slit portion made of a semiconductor having a slit shape which is perpendicular to the optical axis of the optical waveguide and has a depth to cut at least the core layer (3) and which has a wider band gap than the core layer. (91) and second
(C) The first electrode (5) is provided on the back surface of the semiconductor substrate (1) separated by the slit part (92) of
A semiconductor laser device having a fourth electrode (64) on the laminated film between the slit part (91) and the second slit part (92), or 17) (see FIG. 11 (A)) transparent optical waveguide 16. The semiconductor laser device according to 16), wherein the end faces of the parts (A and E) farther from the optical amplification part (B) are used as the mirror surface of the Fabry-Perot resonator and the optical amplification part (B) is used as the amplification part for laser oscillation. 18) (See FIGS. 13 (A) and 11 (B)) The energy gap of the semiconductor forming the core layer of the transparent optical waveguide section (A and E) is the same as that of the semiconductor forming the core layer of the optical amplifying section (B). Larger than energy gap 1) to 5) and 10), 11), 16)
And a semiconductor laser device selected from the group of semiconductor laser devices according to 17) or 19) (see FIGS. 13A and 11D) 16) or 17). At
A semiconductor laser device having the following requirements (a) and (b), that is, (a) a transparent waveguide section (A)
And E) and the optical amplification section (B) are waveguides having the same sectional structure (that is, the optical waveguides having the same thickness and composition of each layer when the sections are compared) are used as transparent optical waveguide sections. A fifth electrode (65) and a sixth electrode
(B) a semiconductor capable of injecting current into the core layer (3) of this portion by injecting current into the fifth and sixth electrodes (65 and 66) Laser device, or 20) (see FIG. 1) selected from the semiconductor laser devices described in 1) to 19), characterized in that the slit portions (91, 92) are formed of non-doped semiconductor crystal. Semiconductor laser device of No. 1 or 21) (see FIG. 1) The slit portion (91, 92) has a semiconductor layer (2) having the first conductivity type and a semiconductor layer (4) having the second conductivity type. 1) to a semiconductor laser device selected from the semiconductor laser devices described in 1) to 19), or 22) (see FIG. 19) below. 1) A semiconductor laser device selected from the semiconductor laser devices described in 1) to 21), characterized in that it has the requirements of (b) and (c), that is, (a) the transparent waveguide. Section (A1, A2, A, E1, E2 or E) and laser oscillation section (B) or optical amplification section (B)
Is formed so as to have a mesa shape and a stripe shape (hereinafter referred to as a mesa stripe shape waveguide (3
1)), (b) the mesa stripe waveguide (3
1) is filled with a semiconductor crystal having an energy band gap larger than that of the core layer (3) (so-called BH
Structure (Buried-heterostructure)
e)), (c) The stripe width of the mesa stripe-shaped waveguide (31) of the transparent waveguide portion (A1, A2, A, E1, E2 or E) is toward the end face. A semiconductor laser device having a stripe width distribution that becomes gradually wider, or 23) (see FIG. 19) characterized by having the following requirements (a), (b) and (c) 1) to 21. 1) a semiconductor laser device selected from the semiconductor laser devices described in 1), that is, (a) the transparent waveguide section (A1, A2, A, E1, E2 or E) and the laser oscillation section (B) or optical amplification. Department (B)
The optical waveguide of is a mesa striped waveguide (31),
(B) The mesa striped waveguide (31) is embedded with a semiconductor crystal having an energy band gap larger than that of the core layer (3) (so-called BH structure (Bur structure)).
ied-heterostructure)), and (c) the transparent waveguide section (A1,
A semiconductor laser device having a stripe width distribution such that the stripe width of the mesa stripe waveguide (31) of A2, A, E1, E2 or E) becomes gradually narrower toward the end face, or 24) (see FIG. 20). ) The stripe width of the mesa stripe-shaped waveguide (31) of the transparent optical waveguide section (A1, A2, A, E1, E2 or E) is constant at the portion in contact with the first slit section (91) and the end face. 22) or 23), or 25) (see FIG. 19), the mesa-stripe-shaped conductor at the tip of the transparent optical waveguide portion (A1, A2, A, E1, E2, or E). 23. The semiconductor laser device according to 23), characterized in that the waveguide (31) has a square cross-sectional shape, or 26) (no reference diagram) the transparent optical waveguide section (A1, 2, A, E1, E2 or E), wherein the stripe width of the mesa stripe waveguide (31) is constant at the portion in contact with the first slit portion (91) and at the very end face. Semiconductor laser device, or 27) (see FIG. 1) selected from the semiconductor laser devices described in 1) to 26), characterized in that the first slit portion (91) reaches the semiconductor substrate (1). No. 1 semiconductor laser device or 28) (see FIG. 1) first slit portion (91) and second slit portion (92)
Both of them reach the semiconductor substrate (1), which is achieved by one semiconductor laser device selected from the semiconductor laser devices described in 1) to 26).

[0025]

According to the present invention, a laser (photodetector)
Since the pn junction at the end is covered with the slit, the dark current is reduced.

Further, since the tip of the waveguide is provided on the laser end face, the optical fiber can be brought close to the optical fiber, and the optical coupling efficiency is improved. In particular, as shown in FIG. 25, in coupling with a fiber having a lens-processed tip, the beam waist and the waveguide end can be surely aligned with each other, so that the optical coupling efficiency is improved. Since it is easy to set the thickness (length in the waveguide direction) of the slit portion of the present invention to 5 μm or less, the loss of the slit portion is the loss in the window portion of the laser having the conventional window layer (from a manufacturing problem. Window thickness is 5μ
It is smaller than m).

[0027]

EXAMPLE 1 FIG. 1 is an explanatory view of Example 1 of the present invention and is a cross-sectional view of an optical waveguide of a semiconductor laser device taken along the optical axis.

In the figure, 1 is a semiconductor substrate, 2 is an n-type semiconductor layer, 23 is a diffraction grating, 3 is a core layer, 4 is a p-type semiconductor layer, 5 is a first electrode, 61 is a second electrode, and 91 is The first slit portion and 92 are second slit portions. N here
The shaped semiconductor layer 2 is formed by stacking 21 and 22 semiconductor layers having different compositions. Each part is specifically 1 for n-I
nP semiconductor substrate (thickness 100 μm), 21 is n-InP
The semiconductor layers (thickness: 1.5 μm), 22 are n-InGaAsP semiconductor layers (having a flat portion thickness of 0.
3 μm), 23 is a diffraction grating with a pitch of about 200 nm (grating depth 0.15 μm), 3 is a SCH (Separat)
e-confinement heterostruc
MQW (Mul
Ti quantum well)) core layer (detailed structure will be described later), 4 is a p-InP semiconductor layer (thickness 3 μm at the tip of the transparent waveguide portion), 5 and 61 are electrodes formed by laminating Ti / Au, 91 And 92 are Fe-doped high resistance I
It is an nP semiconductor (slit thickness 4 μm).

The region indicated by A corresponds to the transparent waveguide portion (length 300 μm), the region indicated by B corresponds to the laser oscillation portion (length 250 μm), and the total length is 600 μm. Further, in this embodiment, the thickness of the core layer 3 is changed so as to become thinner from the laser oscillation portion toward the transparent waveguide portion in the region C (length 220 μm). Although not shown, both the transparent waveguide section and the laser oscillation section of this laser have a stripe width of 2
It has a BH structure of μm or less. In forming the BH structure, both sides of the stripe are filled with p-InP semiconductor.

Next, FIG. 2 is a diagram showing a band diagram of a semiconductor constituting the core layer 3. Here, the horizontal axis is the position in the thickness direction, and the portions indicated by 2, 3 and 4 are shown in FIG.
It corresponds to the 3rd and 4th parts. Ec, Ev, and Eg represent the position of the conduction band edge and the valence band edge, and the energy gap, respectively. The core layer 3 of the laser oscillating portion is composed of non-doped InGaAsP (λg = 1.3 μm) in order from the n-type semiconductor layer side.
m, thickness 18.8 nm), non-doped InGaAs (thickness 7.04 nm), non-doped InGaAsP (λg =
1.3 μm, thickness 18.8 nm), undoped InGa
As (thickness 7.04 nm), non-doped InGaAsP
(Λg = 1.3 μm, thickness 18.8 nm), non-doped InGaAs (thickness 7.04 nm), non-doped InG
It is a multiple quantum well of aAsP (λg = 1.3 μm, thickness 18.8 nm).

Further, in the region C, all the semiconductor layers included in the core have a uniform thickness change, and the thickness is reduced to 1/4 at the termination. In such a waveguide, as shown in FIG. 3, a mask 10 made of a silicon dioxide (SiO ₂ ) film having a window whose width is changed is formed on an InP substrate 1, and a core layer 3 is formed thereon. It is manufactured by epitaxially growing a multi-layered semiconductor (reference document 1993 Autumn Meeting of the Institute of Electronics, Information and Communication Engineers, Proceedings 4-262 (hereinafter referred to as Reference 1)). A more detailed manufacturing method of this structure is described in the specification of the invention of Japanese Patent Application No. 05-216006 (hereinafter referred to as Document 2). If the semiconductor layer 23 is also selectively grown on the substrate of FIG.
The thickness of # 2 also changes, and the mode size conversion effect described later becomes greater.

According to this embodiment, since the pn junction including the laser oscillator B is covered with the slits (91 and 92), there is an effect of reducing the dark current when it is operated as a photodetector. Further, since the laser according to the present embodiment has the waveguide at the end, the optical fiber can be brought close to the laser, and the effect of improving the optical coupling efficiency can be obtained. Especially Figure 2
As shown in Fig. 5, when a fiber whose tip is processed into a lens shape is used, the beam waist can be aligned with the end face, so that the optical coupling efficiency is significantly improved.

Next, another effect of this embodiment will be described with reference to FIG. FIG. 4 is a view showing a state in which the optical fibers 11 are butted and optically coupled to each other, and shows the tip of the optical fiber and the tip of the transparent optical waveguide portion of the semiconductor laser according to the present embodiment. In the semiconductor laser according to the present embodiment, since the core layer 3 at the tip portion is very thin, the electric field of the light guided to the optical waveguide of this laser is greatly exuded and distributed to the substrate 1 side as indicated by reference numeral 12 in the figure. ， The mode size becomes large. Therefore, the optical coupling efficiency becomes highest when the center O of the optical fiber is moved slightly to the substrate side. This effect is qualitatively explained as follows. FIG. 5 shows a case where the mode size (ω ₂ ) of the light guided in the optical waveguide of the laser changes and the single mode optical fiber (the mode size (ω ₁ ) of the guided light is 1
It is a figure explaining the change of the optical coupling efficiency of 0 micrometer. Since the mode size of the optical fiber is fixed at 10 μm,
When the mode size of the light guided to the waveguide is 10 μm, the modes match and the coupling efficiency becomes maximum (approximately 100%). Then, as the difference in mode size increases, the coupling efficiency deteriorates. Since the mode size (ω ₂ ) of the conventional laser is about 2 μm (1), the coupling efficiency is limited to about 10%, but the mode size (ω) of the laser according to the present embodiment is limited.
₂ ) is expanded to about 5 μm or more, and (2) high coupling efficiency is obtained. Focusing only on the direction perpendicular to the bonding, specifically, it is possible to obtain a coupling efficiency of 90% or more (Reference 1, Reference 2 and Reference Conference of).
Integrated Photonics Res
search, Technical digest, P
ostdeadline papers PD3-1 ~
PD3-4, (1994) (hereinafter referred to as Reference 3)
It is described in). As another effect, when the spot diameter of the light guided to the waveguide becomes large, the coupling loss due to the diffraction that occurs when the light passes through the slit portion (the mode mismatch occurs when the light is coupled to the waveguide again because it spreads by diffraction). The resulting reduction in coupling efficiency) is also obtained.

It is known from the above-mentioned document that the optical coupling efficiency of the laser can be improved by making the core layer 3 thin, but a slit portion (91) having a high resistivity is used for the laser having such a high coupling efficiency. And 92), the photodetector has a small dark current, and the portion contacting the slit portion (the left and right portions contacting the slit portion in FIG. 1) has a thin core to increase the mode size. It is an effect peculiar to the present invention that the loss due to diffraction of passing light is reduced.

Next, essential requirements for the present invention will be described, and then some specific embodiments will be shown and described as other examples. FIG. 6 illustrates only the essential requirements of the present invention. Here, A1 and A2 are transparent waveguide portions, B is a laser oscillation portion, D is a portion on the end face side of the waveguide separated by the second slit, and A is a portion (A1 + A2) added with A1 and A2. , Ps1 and Ps2 are symbols indicating the positions of the first slit portion and the second slit portion, respectively. This structure is equivalent to the one schematically showing the main part of the first embodiment shown in FIG.

The essential requirement of the first embodiment of the present invention is shown in FIG.
As shown in (a), the transparent waveguide A1, the first slit portion 91, and the transparent waveguide portion A are sequentially arranged on the semiconductor substrate 1 from the left.
2, the laser oscillator B and the second slit 92 are arranged,
To have electrodes (5 and 61). Here, the laser oscillation part and the transparent waveguide part are formed by a double heterojunction, and the BH structure is used in the direction perpendicular to the plane of the drawing. Further, as described above, the structure in which Ti / Au is laminated is used for the electrodes, and the high resistance semiconductor such as non-doped semiconductor or Fe-doped InP is used for the slit portion. For example, a slit is formed by dry etching so as to form a slit perpendicular to the optical axis of the waveguide, and then the semiconductor is embedded and grown to form a slit portion. If the wet etching is performed for a short time after the dry etching, the surface layer damaged by the dry etching can be removed.

Next, FIGS. 6 (B) to 6 (E) extract only the waveguide portions of the transparent waveguide portion A and the laser oscillation portion B. The transparent waveguide portion is formed by changing the thickness by forming the core layer 3 with multiple quantum wells as shown in FIG. 6 (B) or FIG. 6 (C) or by changing the thickness of the transparent waveguide portion as shown in FIG. 6 (D). It is formed by making the energy gap of the semiconductor of the core layer 3 larger than the energy gap of the semiconductor of the core layer 3 of the laser oscillation part. 6 (B) and 6 (C) are one specific example of a method of making the energy gap of the semiconductor of the core layer 3 of the transparent waveguide portion larger than the energy gap of the semiconductor of the core layer 3 of the laser oscillation portion. You can also

The difference between FIG. 6 (B) and FIG. 6 (C) is the core layer 3
It is only the difference in the thickness of the material that changes temporarily or suddenly. Further, when the structure of FIG. 6 is used, it is necessary to form the corrugations 23 in the laser oscillation portion as shown in FIG. 6 (E). Although FIG. 6 (E) is an example of a DFB laser,
It suffices that a laser oscillation unit has an equivalent to a mirror.
It goes without saying that the object can be achieved by forming other mirrors such as a g reflector structure.

Next, FIGS. 7 and 8 extract and show the essential requirements of another configuration of the present invention. As shown in FIG. 7 (A), the essential requirements of this example are as follows: a transparent waveguide portion A1, a first slit portion 91, a transparent waveguide portion A2, a second slit portion 92, on the semiconductor substrate 1 in order from the left. That is, the laser oscillators B are arranged and have electrodes (5, 62 and 63). Here, the requirements for the waveguide, electrodes, and slits of each part are the same as in the case of FIG.

Here, FIG. 7 (B) to FIG. 7 (D) and FIG.
Is a schematic diagram showing the transparent waveguide portion A and the waveguide portion of the laser oscillation portion, and Ps1 and Ps2 are symbols showing the positions where the first and second slit portions are formed, respectively. In this configuration, a part A2 of the transparent waveguide portion is used as a detector. At this time, multiple quantum wells are used for the core layer 3 and the structure shown in FIGS.
As described above, the core layer (3) of the transparent waveguide portion is thinned to be transparent. FIG. 7 (B) shows a case where the thickness of the core layer is sharply changed and the second slit portion is formed at the boundary between the transparent waveguide portion and the laser oscillation portion, and FIG. 7 (C) shows the thickness of the core layer. FIG. 7 (D) shows a case in which the thickness of the core layer is changed for a while and the second slit portion is formed in the transparent waveguide portion by abrupt change.
8 is one in which the slit portion is formed in the transparent waveguide portion, and FIG. 8 uses a semiconductor having a relatively large energy gap in the core layer of the transparent waveguide portion. Figure 7 (B) and Figure 7
(D) and when using the laser in Figure 8 as a detector, a reverse bias voltage is applied to the pn junction of the transparent waveguide (A1), and the resulting optical absorption due to the quantum Stark confinement effect and Franz-Keldysh effect Used as a detector. When the BH structure is used for this laser, it is desirable to make the stripe width of the laser oscillation part and the part used as the detector constant. However, the width of the laser oscillator and the portion used as the detector need not necessarily be the same.

In the structure of FIG. 8, for example, a waveguide structure is formed as shown in FIG. 9 (A), and then a part of the core layer 3 is removed by etching, and epitaxial growth is performed again as shown in FIG. 9 (C). Then, the core layer 3 and the upper semiconductor layer 4 may be formed.

Using this structure (FIGS. 7 to 9), the following effects are brought about by dividing the laser portion and the detector portion. First, since a laser-dedicated drive circuit and a detector-dedicated receiver circuit are used, the circuit design is facilitated, and the cost of the electronic circuit can be reduced and the electronic circuit can be optimized for high performance. Secondly, it is possible to improve the performance of this device by optimally designing the laser section and the detector section. For example, by designing the depletion layer in the detector portion to be thick, the junction capacitance is reduced and the detector becomes faster. Furthermore, the junction capacitance decreases and the detector becomes faster. Thirdly, there is an effect of reducing crosstalk between transmission and reception. In another embodiment (for example, FIG. 1), the laser driving device and the reception preamplifier are connected to the semiconductor laser device by a common wiring, so that a switch unit (usually a FET switch is used) for switching between transmission and reception. For this reason, isolation tends to deteriorate, and crosstalk between transmission and reception is likely to occur, but the problem can be solved by using the semiconductor laser according to the present embodiment.

Further, as shown in FIG.
The optical coupling efficiency is improved by adopting a structure in which the transparent waveguide portion A that functions as a detector and the transparent waveguide portion F that functions as a mode size expansion waveguide are connected. The stripe width at F becomes narrower toward the tip (for example, FIG. 19).
Alternatively, it may be changed such that it spreads toward the tip (for example, FIG. 20). Even in the configurations shown in FIGS. 7, 8, 9 and 10, the laser section requires an optical feedback structure such as a diffraction grating (corresponding to a mirror).

Next, FIG. 11 shows the essential requirements of another structure of the present invention extracted. The essential requirement of this example is shown in FIG.
As shown in (A), a transparent waveguide portion A, a first slit portion 91, a laser oscillator portion B, and a second slit portion 92 are arranged in order from the left on the semiconductor substrate 1, and electrodes (5 and 64) are arranged. Is to have. There are cases where the portion indicated by the symbol E is a transparent waveguide portion and there is an opaque waveguide portion. Also in this case, the requirements for the waveguide, the electrode, and the slit portion of each portion are the same as those in the case of FIG.

As described above, the means for making the portion indicated by A in the figure transparent is such that the energy gap of the semiconductor of the core layer 3 is made relatively large (FIG. 11B), and the core layer 3 is made relatively large. There is a method of making thin multiple quantum wells (Fig. 11 (C)).
Further, as shown in FIG. 11 (D), using the core layer 3 having the same composition,
The electrode 65 may be formed only in the portion to be the transparent optical waveguide and the current Ii may be injected. By injecting a current, a population inversion is formed in the core layer 3 and the waveguide becomes transparent. When the current injection level becomes higher, it has an optical amplification gain.

In the case where only the side indicated by the symbol A in FIG. 11 is made transparent, mirrors such as a diffraction grating are formed in the laser oscillation part, but the waveguides at the left and right ends (portions A and E) are made transparent. This is not necessary when using an optical waveguide. This is because the mirror is formed by cleaving the end face. If the reflectance of the end face of the semiconductor laser of FIG. 11C is reduced, a laser amplifier with a traveling waveform in which optical coupling is easy can be obtained. Needless to say, the semiconductor laser shown in FIG. 11D can also be used as a photodetector with a laser amplifier.
If the core layer 3 is a multiple quantum well and has a structure having a thickness distribution as shown in FIG. 12, a photodetector (portion B) having a beam spot size conversion waveguide (portion G) and a laser amplifier (portion H) is provided. It goes without saying that

Next, FIG. 13 shows the essential requirements of another configuration of the present invention extracted. The essential requirement of this example is shown in FIG.
As shown in (A), the transparent waveguide portion A1, the first slit portion 91, and the transparent waveguide portion A are sequentially arranged on the semiconductor substrate 1 from the left.
2, the optical amplification section B, the transparent waveguide section E2, the second slit section 92, and the transparent waveguide section E1 are arranged and electrodes (5 and 64) are provided. Also in this case, the requirements for the waveguide, the electrode, and the slit portion of each portion are the same as those in the case of FIG. As described above, the energy gap of the semiconductor of the core layer 3 is made relatively large in order to make the transparent waveguide part transparent (see FIG. 1).
3 (b)), the core layer 3 is formed into a relatively thin multiple quantum well (FIG. 13 (c)), and the core layer 3 having the same composition is used as shown in FIG. 13 (d) to form a transparent optical waveguide. There is a method in which electrodes (65 and 66) are formed only in the power part and the current Ii is injected. Also in this case, a mirror such as a diffraction grating is required in the laser oscillation part when only one side of the transparent waveguide parts indicated by A and E is made transparent, but when both are transparent, the cleaved end face is made a mirror. It becomes possible to do. Further, the semiconductor laser of 13 (C) becomes a laser amplifier with a traveling waveform in which optical coupling is easy when the reflectance of the end face is reduced, and the semiconductor laser of FIG. 13 (D) can also serve as a photodetector with a laser amplifier. Is the same as in.

FIG. 14 is a sectional view of the second embodiment of the present invention. In the figure, 1 is a semiconductor substrate, 21 is an n-type semiconductor layer,
22 is an optical guide layer, 23 is a diffraction grating, 3 is a core layer, 4 is a p-type semiconductor layer, 5 is a first electrode, 61 is a second electrode, and 91 is a first electrode.
Is a second slit portion, and 92 is a second slit portion.

In the figure, the left half shows the transparent waveguide portion, and the right half shows the laser oscillation portion / photodetector portion. This example
The transparent waveguide section is provided with a first slit section 91, and the laser oscillation section is provided with a second slit section 92. These slits are filled with a non-doped semiconductor layer having a wider bandgap than the core layer (or a high resistance semiconductor layer having a wider bandgap than the core layer), and the second electrode is provided between both slits.
Form 61.

Here, when a reverse bias voltage is applied between the first electrode 5 and the second electrode 61, the ends of the reverse-biased pn junction are protected by the semiconductors of the slits 91, 92. The dark current becomes smaller.

FIG. 15 is a sectional view of the third embodiment of the present invention. In the figure, 1 is a semiconductor substrate, 21 is an n-type semiconductor layer,
22 is an optical guide layer, 23 is a diffraction grating, 3 is a core layer, 4 is a p-type semiconductor layer, 5 is a first electrode, 62 is a laser section dedicated electrode, 63
Is a third electrode, 91 is a first slit portion, and 92 is a second slit portion.

In the figure, the left half shows the transparent waveguide portion (also the photodetector portion), and the right half shows the laser oscillation portion. In this example, the first slit portion 91 and the second slit portion 92 are provided in the transparent waveguide portion. These slits are filled with a non-doped semiconductor layer having a wider band gap than the core layer (or a high resistance semiconductor layer having a wider band gap than the core layer), and the third electrode 63 is formed between both slits.
Further, the laser section dedicated electrode 62 is also provided in the laser oscillation section.

Here, a reverse bias voltage is applied between the first electrode 5 and the third electrode 63, and Franz-Keldysh (Fra
The nz-Keldysh) effect and quantum confined Stark (Stark) effect increase the optical absorption of the core layer of the transparent waveguide part, and this part is also used as a photodetector. At this time, the dark current becomes small because the ends of the reverse-biased pn junction are protected by the semiconductor of the slits 91 and 92.

In this example, the electrode 62 of the laser oscillator is connected to the laser drive circuit, and the third electrode 63 is connected to the front end of the receiver. In this case, since it is connected to each dedicated circuit, the configuration of the electric circuit becomes simpler than that of the first embodiment and the conventional example. Also, since the transmission and reception circuits are separated, crosstalk is reduced.

In the first and second embodiments, since the waveguide from the left end of the laser to the slit portion 91 is transparent, if the light beam 8 is made to enter and exit from this transparent end, the light guide at the entrance / exit portion will be obtained. The propagation loss of light in the waveguide is reduced. Further, the space between the first slit portion 91 and the second slit portion 92 can be used as an electroabsorption type optical modulator.

FIG. 16 is a sectional view of the fourth embodiment of the present invention. In the figure, 1 is a semiconductor substrate, 21 is an n-type semiconductor layer,
22 is an optical guide layer, 23 is a diffraction grating, 3 is a core layer, 4 is a p-type semiconductor layer, 5 is a first electrode, 64 is a fourth electrode, and 65 is a fifth electrode.
Electrode, 91 is the first slit portion, and 92 is the second slit portion.

In the figure, a laser oscillation section (also a photodetector section) is provided between both slit sections. In this example, the conventional semiconductor laser has a first slit portion 91 and a second slit portion.
92 is provided. These slits are filled with a non-doped semiconductor layer having a wider gap than the core layer (or a high resistance semiconductor layer having a wider gap than the core layer), and the fourth electrode 64 is provided between both slits at one end of the laser, for example, The fifth electrode 65 is formed between the left end and the first slit portion 91.

Here, when a reverse bias voltage is applied between the first electrode 5 and the fourth electrode 64, the ends of the reverse biased pn junction are protected by the semiconductor of the slits 91, 92. The dark current becomes smaller. Then, when a forward bias voltage is applied between the first electrode 5 and the fourth electrode 64, this portion becomes a laser amplifier, and the propagation loss of the light beam 8 is reduced.

FIG. 17 is a sectional view of the fifth embodiment of the present invention. In the figure, 1 is a semiconductor substrate, 2 is an n-type semiconductor layer,
3 is a core layer, 4 is a p-type semiconductor layer, 5 is a first electrode, 64 is a fourth electrode, 65 is a fifth electrode, 66 is a sixth electrode, 91 is a first slit portion, and 92 is The second slit portion.

In the figure, a space between both slit portions is an optical amplification portion (also a photodetector portion). This example has a structure in which the diffraction grating 23 and the light guide layer 22 are removed and the sixth electrode 66 is added to the laser shown in the third embodiment.

Here, when a forward current is simultaneously applied between the first electrode 5 and the fourth electrode 64, the fifth electrode 65, and the sixth electrode 66, laser oscillation occurs even without a diffraction grating. Therefore, manufacturing becomes easy.

By using any of the first to fifth embodiments, the semiconductor laser can be used as a photodetector with a low loss and a small dark current. Next, the materials used in the above Examples 2 to 5 will be described.

The semiconductor substrate 1 is an InP substrate, the n-type semiconductor layer 21.
Is the InP layer, the optical guide layer 22 is the InGaAsP layer with a wavelength-converted energy bandgap (λg) = 1.2 μm, the core layer 3 is the InGaAsP layer with λg = 1.55 μm, and the p-type semiconductor layer 4 is InP.
Semiconductor embedded in layers and slits has λg = 1.1 μm
InGaAsP layer.

The length of the transparent waveguide portion in FIG. 14 is 100 μm,
The length of the laser oscillation portion is 250 μm, the length from the laser left end to the first slit 91 is 50 μm, the length from the laser right end to the second slit 92 is 50 μm, and the thickness of the n-type semiconductor layer 21 is 1 μm. The light guide layer 22 has a thickness of 0.3
μm, the core layer 3 has a thickness of 0.1 μm, the p-type semiconductor layer 4 has a thickness of 1.8 μm, and the first and second slits 91 and 92 have a lateral width of 4 μm and a depth of 4 μm.

The length of the transparent waveguide portion in FIG. 15 is 270 μm,
The length of the laser oscillation part is 200 μm, the length from the laser left end to the first slit 91 is 50 μm, the length from the laser left end to the second slit 92 is 250 μm, and the thickness of the n-type semiconductor layer 21 is 1 μm. The thickness of the light guide layer 22 is 0 in the part without unevenness.
3 μm, the core layer 3 has a thickness of 0.1 μm, the p-type semiconductor layer 4 has a thickness of 1.8 μm, and the first and second slits 91 and 92 have a width of 4 μm in the left-right direction and a depth of 4 μm.

The total length of the laser in FIG. 16 is 300 μm, the length from the laser left end to the first slit 91 is 50 μm, the length from the laser right end to the second slit 92 is 50 μm, and the thickness of the n-type semiconductor layer 21 is Is 1 μm, the thickness of the light guide layer 22 is 0.3 μm in the part without unevenness, and the thickness of the core layer 3 is 0.1 μm, p
The thickness of the type semiconductor layer 4 is 1.8 μm, the widths of the slits 91 and 92 are 4 μm in the left-right direction, and the depth is 4 μm.

Next, an example of forming a waveguide having a core layer of a multiple quantum well structure in Examples 2 and 3 is shown in FIG. 18A and 18B are explanatory views of an example of forming the waveguide of the embodiment.

In the figure, a 1 μm thick layer is formed on the InP substrate 1.
After growing the InP layer 21, the diffraction grating 23 is formed by interference exposure using a He—Cd laser, photolithography, and wet etching. At this time, the growth of the InP layer 21 was omitted,
The diffraction grating may be formed directly on the InP substrate. Then, λ
An InGaAsP layer 22 of g = 1.2 μm is grown, then a silicon dioxide (SiO ₂ ) film 10 is grown by a thermal vapor deposition (CVD) method, and patterned by photolithography and wet etching as shown in the figure. The width between patterns is 20μ
m.

Then, the InGaAsP layer 22a with λg = 1.3 μm,
Multiple quantum well (MQW) core layer in which InGaAs layers and InGaAsP layers with λg = 1.3 μm are alternately stacked 3, λg = 1.3 μm
InGaAsP layer 41a and InP clad layer 4 are sequentially grown. In such a laminated structure, the MQW well layer of the transparent waveguide core layer is thinned to form a wide bandgap core.

Next, each layer 21, 22, 22a, 3, 41a, 4 is mesa-etched in a stripe shape, and the periphery thereof is filled with InP. In Examples 2 and 3 (FIGS. 14 and 15), the thickness of the core layer 3 is shown to change abruptly. However, in actual crystal growth, the thickness changes via a transition region of 30 μm to 100 μm. Therefore, such a core layer 3 may be used. The length of the formed transition region changes depending on the crystal growth conditions. In Example 3 (FIG. 15), when there is a transition region, it is desirable to avoid the transition region and form the second slit.

Example 1 (FIG. 1) or Example 2 (FIG. 1)
When the transparent waveguides are formed on the left and right in 4),
The laser has the structure shown in (c). As already mentioned,
In this case, since the diffraction grating is unnecessary, the diffraction grating 23
It goes without saying that the semiconductor layer 22 becomes unnecessary. When the semiconductor layer 22 is eliminated, the light confinement is weakened, and the effect of increasing the mode size at the end of the waveguide is increased.

At the time of this mesa etching, as shown in FIG. 19, the mesa at the end of the waveguide is made so that the section perpendicular to the optical axis of the portion where the layers 22a, 3 and 41a at the end of the waveguide are overlapped becomes a square. The narrower the width, the smaller the polarization dependence of the optical transport loss. Such a stripe shape is particularly advantageous for optical coupling with an optical fiber whose tip is lens-processed.

On the other hand, when the shape of the mesa-shaped stripe (31) is as shown in FIG. 20, the coupling efficiency with the optical fiber having a flat tip is improved. Here, FIG. 20 is a plan view of the semiconductor laser device, and 31 is a contour line drawn for explaining the pattern of the mesa stripe. Needless to say, it does not look like this because the electrodes are actually formed on the surface and the periphery is embedded.

The right end of the laser of FIGS. 14 and 16 for explaining the second and fourth embodiments (the end on which light does not enter and exit)
Instead of the slit portion, a window structure may be used as in the second conventional example.

Next, a numerical example showing the effect of the embodiment will be described. When a reverse bias of 2 V was applied with the lasers of Examples 1 to 5, the dark current was 10 μA in the case of the conventional example without the slit portion.
Compared with the above, it is less than 1 nA, and it is possible to prevent deterioration of sensitivity when used as a photodetector.

The laser of the third embodiment can also oscillate as a Fabry-Perot laser without the diffraction grating 23. In addition, in the laser of Example 2, the second
By providing an electrode between the slit 92 and the right end of the laser and injecting a forward current, it is possible to oscillate as a Fabry-Perot laser without the diffraction grating.

[0077]

According to the present invention, it is possible to reduce the dark current when a semiconductor laser is used as a photodetector and to increase the optical coupling efficiency when directly coupling with an optical fiber.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a first embodiment of the present invention.

FIG. 2 is a diagram showing a band diagram of a semiconductor forming a core layer.

FIG. 3 is a diagram showing an example of a substrate for selective growth.

FIG. 4 is a diagram showing a state in which an optical fiber is butted and optically coupled.

FIG. 5 is a diagram showing an effect of the embodiment (a diagram showing a relationship between a beam spot diameter in a waveguide and optical coupling efficiency).

FIG. 6 is a diagram (1) illustrating an embodiment of essential requirements and components of the present invention.

FIG. 7 is a diagram (2) for explaining the essential requirements of the present invention and an embodiment of constituent elements;

FIG. 8 is a diagram showing an example of a waveguide structure according to the present invention (1).

FIG. 9 is a diagram illustrating a method of manufacturing an optical waveguide.

FIG. 10 is a diagram showing an example of a waveguide structure according to the present invention (2).

FIG. 11 is a diagram (3) for explaining the essential requirements of the present invention and an embodiment of constituent elements;

FIG. 12 is a diagram (3) showing an example of a waveguide structure according to the present invention.

FIG. 13 is a diagram (4) for explaining the essential requirements of the present invention and an embodiment of constituent elements;

FIG. 14 is a sectional view of a second embodiment of the present invention.

FIG. 15 is a sectional view of a third embodiment of the present invention.

FIG. 16 is a sectional view of a fourth embodiment of the present invention.

FIG. 17 is a sectional view of a fifth embodiment of the present invention.

FIG. 18 is an explanatory diagram of an example of forming the waveguide of the example.

FIG. 19 is an explanatory diagram of a waveguide.

FIG. 20 is a plan view of a mesa stripe waveguide.

FIG. 21 is a sectional view of Conventional Example 1.

FIG. 22 is a cross-sectional view of Conventional Example 2.

FIG. 23 is an explanatory view (1) of the problem of Conventional Example 2;

FIG. 24 is an explanatory diagram (2) of the problem of Conventional Example 2

FIG. 25 is an explanatory diagram (3) of the problem 2 of the conventional example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Semiconductor substrate 100 Semiconductor laser 2 1st semiconductor layer (n-type semiconductor layer) 21 Semiconductor layer (n-type semiconductor layer) 22 Semiconductor layer (light guide layer) 23 Diffraction grating 3 Core layer 31 Mesa stripe waveguide 4 2nd Semiconductor layer (p-type clad layer) 5 first electrode (n-side electrode) 6 p-side electrode 61 second electrode 62 electrode (laser oscillator electrode) 63 third electrode 64 fourth electrode 65 fifth Electrode 66 sixth electrode 7 pn junction exposed at the laser end 8 incident light beam 91 first slit portion 92 second slit portion 10 SiO ₂ mask 11 optical fiber 11c optical fiber core 12 electric field intensity distribution 13 window Part 14, 14a Light beam A, A1, A2 Transparent optical waveguide part B Optical waveguide (may be a laser oscillating part or optical amplifying part) E, E1, E2 Optical waveguide (transparent (In some cases, there is a clear optical waveguide and in other cases, it is not transparent)

Claims (28)

[Claims] 1. A first semiconductor layer (2) formed by layering at least one layer of a semiconductor of a first conductivity type on a surface of a semiconductor substrate (1) and a semiconductor of at least one layer of any conductivity type. A core layer (3) consisting of layers and at least one or more first layers
A second semiconductor layer (4) formed of a semiconductor layer of a second conductivity type different from that of the first semiconductor layer (2). A semiconductor laser device comprising an optical waveguide in which the second semiconductor layer (4) serves as a clad layer and the core layer (3) serves as a core, and at least two types of optical waveguides having different properties are used as a common optical axis. In a semiconductor laser device having a waveguide structure arranged in series in the direction, the following (a), (b), (c) and (d)
A semiconductor laser device having the requirements of (1). (A) One end of the optical waveguide is a portion that oscillates with the core layer (3) as an optical amplification layer (hereinafter referred to as a laser oscillating portion (B)), and the other end of the optical waveguide has the core. The light absorption coefficient of the layer (3) is smaller than the light absorption coefficient of the core layer (3) of the laser oscillator (hereinafter, the optical waveguide portion including the core layer having a relatively small light absorption coefficient is referred to as transparent light Waveguide portion (referred to as A or A1 and A2). (B) Depth in which both the transparent optical waveguide portion (A or A1 and A2) and the laser oscillation portion (B) are slit-shaped, the slit intersects the optical axis of the optical waveguide, and at least cuts the core layer (3). And a first slit portion (91) made of a semiconductor having a slit shape and having a wider band gap than the core layer. (C) A slit shape is formed at the end of the laser oscillating portion (B) on the side remote from the transparent optical waveguide portion, the slit intersects the optical axis of the optical waveguide, and at least the depth at which the core layer (3) is cut is provided. It has a slit-like second slit portion (92) made of a semiconductor having a wider bandgap than the core layer. (D) A first electrode (5) is provided on the back surface of the semiconductor substrate (1), and a first slit portion (91) and a second slit portion (9) are provided.
The second electrode (61) is provided on the laminated film between 2). 2. A first semiconductor layer (2) layered on the surface of a semiconductor substrate (1) with at least one semiconductor layer of the first conductivity type and at least one semiconductor layer of any conductivity type. A core layer (3) consisting of layers and at least one or more first layers
A second semiconductor layer (4) formed of a semiconductor layer of a second conductivity type different from that of the first semiconductor layer (2). A semiconductor laser device comprising an optical waveguide in which the second semiconductor layer (4) serves as a clad layer and the core layer (3) serves as a core, and at least two types of optical waveguides having different properties are used as a common optical axis. In a semiconductor laser device having a waveguide structure arranged in series in the direction, the following (a), (b), (c) and (d)
A semiconductor laser device having the requirements of (1). (A) One end side of the optical waveguide is a transparent optical waveguide section (A1 and A2) having the core layer (3) as a core, and the other end side of the optical waveguide is the core layer (3) as an optical amplification layer. It is a laser oscillator (B). (B) The transparent optical waveguide portion (A or A1 and A2) is slit-shaped and has a slit shape that intersects the optical axis of the optical waveguide and has a depth that cuts at least the core layer (3). It has a first slit portion (91) and a second slit portion (92) made of a semiconductor having a wider band gap than the layer. (C) A first electrode (5) is provided on the back surface of the semiconductor substrate (1), and a first slit portion (91) and a second slit portion (9) are provided.
The third electrode (63) is provided on the laminated film between 2), and the electrode (62) is provided on the laminated film of the laser oscillator. (D) The third electrode (6) formed on the laminated film between the first slit portion (91) and the second slit portion (92).
3) and the electrode (6
It is electrically separated from 2). 3. A first semiconductor layer (2) layered on the surface of a semiconductor substrate (1) with at least one semiconductor layer of the first conductivity type and at least one semiconductor layer of any conductivity type. A core layer (3) consisting of layers and at least one or more first layers
A second semiconductor layer (4) formed of a semiconductor layer of a second conductivity type different from that of the first semiconductor layer (2). A semiconductor laser device comprising an optical waveguide in which the second semiconductor layer (4) serves as a clad layer and the core layer (3) serves as a core, and at least two types of optical waveguides having different properties are used as a common optical axis. In a semiconductor laser device having a waveguide structure arranged in series in the direction, the following (a), (b), (c) and (d)
A semiconductor laser device having the requirements of (1). (A) A laser in which one end side of the optical waveguide is a transparent optical waveguide section (A) having the core layer (3) as a core, and the other end side of the optical waveguide has the core layer (3) as an optical amplification layer. Oscillator (B)
Have. (B) The core layers of the transparent optical waveguide portion (A) and the laser oscillation portion (B) are slit-shaped, and the slits intersect the optical axis of the optical waveguide and have a depth at least cutting the core layer (3). It is separated by a first slit portion (91) made of a semiconductor having a slit shape and a wider bandgap than the core layer. (C) The core layer in contact with the end face of the semiconductor laser device on the opposite side of the transparent optical waveguide part (A) and the core layer of the laser oscillation part (B) are slit-shaped, and the slit intersects the optical axis of the optical waveguide. Moreover, it is separated by a second slit portion (92) made of a semiconductor having a slit-like shape having a depth to cut at least the core layer (3) and having a wider band gap than the core layer. (D) A first electrode (5) is provided on the back surface of the semiconductor substrate (1), and a first slit portion (91) and a second slit portion (9) are provided.
The fourth electrode (64) is provided on the laminated film between 2). 4. The semiconductor laser device according to claim 3, wherein the semiconductor laser device has the following requirements (a) and (b). (A) An optical waveguide having the same thickness and composition of each layer of the sectional structure is used for the waveguide of the transparent waveguide section (A) and the laser oscillation section (B), and A fifth electrode (65) is formed on the laminated film. (B) It has a structure capable of injecting a current through the fifth electrode (65) to the core layer (3) below the fifth electrode. 5. The semiconductor layer (2) of the first conductivity type is composed of at least two semiconductor layers (21, 22) having different refractive indexes.
And a diffraction grating (23) is formed on the boundary surface between the two semiconductor layers of the laser oscillating portion, and the diffraction grating is used as a distributed reflector to form a distributed reflection laser. 5. A semiconductor laser device selected from the semiconductor laser devices according to claim 1, wherein a laser oscillation part is formed between two slit parts. 6. The core layer (3) of the transparent optical waveguide section (A or A1 and A2) is thinner than the core layer (3) of the laser oscillation section (B). One semiconductor laser device selected from the semiconductor laser devices described. 7. The core layer (3) of the transparent optical waveguide portion (A or A1 and A2) has a thickness distribution such that the core layer (3) gradually becomes thinner toward the end face.
A semiconductor laser device selected from the semiconductor laser devices according to 1. 8. The core layer (3) of the transparent optical waveguide portion (A or A1 and A2) has a first slit portion (9).
8. The semiconductor laser device according to claim 7, wherein the portion contacting with 1) and the end face have a constant thickness. 9. The core layer (3) includes a multi-quantum well layer, and the tendency of the thickness change of the multi-quantum well layer is similar to the tendency of the thickness change of the core layer (3). 9. The semiconductor laser device according to claim 6. 10. A first layer formed of at least one semiconductor layer of a first conductivity type on the surface of a semiconductor substrate (1).
A semiconductor layer (2) and a core layer (3) comprising at least one semiconductor layer of any conductivity type, and at least one semiconductor layer of a second conductivity type having a conductivity type different from the first conductivity type. A second semiconductor layer (4) formed of a layer and a laminated film in which the second semiconductor layer (4) is sequentially formed, and the first semiconductor layer (2) and the second semiconductor layer (4) serve as a clad layer and a core layer (3 ) Is a semiconductor laser device having an optical waveguide serving as a core, and the semiconductor laser device has an optical waveguide having a structure in which at least two types of optical waveguides having different properties are arranged in series in the optical axis direction with the optical axis in common. (A), (b), (c),
A semiconductor laser device having the requirements (d) and (e). (A) Both sides of the optical waveguide are transparent optical waveguide portions (A or A1, A2, and E or E whose core is the core layer (3).
1, E2) and the central portion of the optical waveguide is an optical amplification section (B) using the core layer (3) as an optical amplification layer. (B) Transparent optical waveguide part (A or A1 and E or E1)
Is formed to the end face. (C) One transparent optical waveguide part (A or A1 and A2)
A first slit portion made of a semiconductor which is slit-shaped and has a depth which intersects the optical axis of the optical waveguide and which has a depth for cutting at least the core layer (3) and which is wider in band gap than the core layer. (91) is formed. (D) The other transparent optical waveguide part (E or E1 and E2)
A second slit portion made of a semiconductor which is slit-shaped and has a depth which intersects the optical axis of the optical waveguide and which cuts at least the core layer (3) and which is wider in band gap than the core layer. (92) is formed. (E) A first electrode (5) is provided on the back surface of the semiconductor substrate (1), and a first slit portion (91) and a second slit portion (9) are provided.
The fourth electrode (64) is provided on the laminated film between 2). 11. A transparent optical waveguide section (A or A1 and E).
11. The semiconductor laser device according to claim 10, wherein the end face on the side farther from the optical amplification unit of E1) is used as the mirror surface of the Fabry-Perot resonator and the optical amplification unit (B) is used as the amplification unit for laser oscillation. 12. The core layer (3) of the transparent optical waveguide section (A, A1 and E, E1) is thinner than the core layer (3) of the optical amplification section (B). 11. The semiconductor laser device according to item 11. 13. The transparent optical waveguide section (A or A1, A
12. The semiconductor laser device according to claim 10, wherein the core layer (3) of 2 and E or E1, E2) has a thickness distribution that becomes gradually thinner toward the end face. 14. The transparent optical waveguide portion (A or A1, A
2 and E or E1, E2) has a thickness of the core layer (3) of the first slit portion (91) and the second slit portion (9).
14. The semiconductor laser device according to claim 13, wherein the portion contacting with 2) and the end face have a constant thickness. 15. The core layer (3) includes a multi-quantum well layer, and the thickness of the multi-quantum well layer is changed in the same manner as the change of the thickness of the core layer (3), thereby making it transparent. Waveguide portion (A or A1, A2 and E or E1, E2)
15. The transparent structure according to claim 11, wherein:
The semiconductor laser device according to 1. 16. A first semiconductor layer (2) layered on the surface of a semiconductor substrate (1) with at least one semiconductor layer of the first conductivity type and at least one semiconductor layer of any conductivity type. A core layer (3) composed of layers, and a second semiconductor layer (4) formed of a semiconductor layer of a second conductivity type having a conductivity type different from that of the first conductivity type of at least one layer in order. A semiconductor laser device having an optical waveguide having a laminated film, the first semiconductor layer (2) and the second semiconductor layer (4) are clad layers, and the core layer (3) is a core.
A semiconductor laser device having an optical waveguide having a structure in which optical waveguides of different kinds are arranged in series in the optical axis direction with a common optical axis having the following requirements (a), (b) and (c): A semiconductor laser device. (A) Light in which both ends of the optical waveguide are transparent optical waveguide portions (A and E) having the core layer (3) as a core, and the central portion of the optical waveguide has the core layer (3) as an optical amplification layer. Amplification unit (B)
Is. (B) Transparent optical waveguide section (A and E) and optical amplification section (B)
A slit-shaped first slit portion made of a semiconductor which has a slit shape and has a depth which intersects the optical axis of the optical waveguide and which cuts at least the core layer (3) and which has a wider band gap than the core layer. (91) and second
Are separated by a slit portion (92). (C) A first electrode (5) is provided on the back surface of the semiconductor substrate (1), and a first slit portion (91) and a second slit portion (9) are provided.
The fourth electrode (64) is provided on the laminated film between 2). 17. The laser oscillation is performed by using the end surface of the transparent optical waveguide section (A and E) farther from the optical amplification section (B) as the mirror surface of the Fabry-Perot resonator and the optical amplification section (B) as the amplification section. The semiconductor laser device according to 1. 18. The energy gap of the semiconductor forming the core layer of the transparent optical waveguide section (A and E) is larger than the energy gap of the semiconductor forming the core layer of the optical amplifying section (B). One semiconductor laser selected from the semiconductor lasers according to claims 1 to 5 or claim 10 or claim 11 or claim 16 or claim 17.
The semiconductor laser device according to 1. 19. A semiconductor laser device according to claim 16 or 17, wherein the following requirements (a) and (b) are satisfied. (A) For the waveguides of the transparent waveguide section (A and E) and the optical amplification section (B), optical waveguides having the same thickness and composition of each layer of the cross-sectional structure are used, and A fifth electrode (65) and a sixth electrode (66) are formed on the laminated film. (B) The core layer (3) in this portion has a structure capable of injecting a current by injecting a current into the fifth and sixth electrodes (65 and 66). 20. One semiconductor laser device selected from the semiconductor laser devices according to claim 1, wherein the slit portion (91, 92) is formed of a non-doped semiconductor crystal. 21. The slit portions (91, 92) are formed of a semiconductor crystal having a higher resistance than the semiconductor layer (2) having the first conductivity type and the semiconductor layer (4) having the second conductivity type. Claims 1 to 19 characterized in that
A semiconductor laser device selected from the semiconductor laser devices according to 1. 22. One semiconductor laser device selected from the semiconductor laser devices according to any one of claims 1 to 21, characterized in that the following requirements (a), (b) and (c) are satisfied. (A) The transparent waveguide section (A1, A2, A, E1, E2
Alternatively, E) and the optical waveguide of the laser oscillating unit (B) or the optical amplifying unit (B) are formed in a mesa-stripe shape and in a stripe shape.
Have. (B) The mesa striped waveguide (31) is filled with a semiconductor crystal having an energy band gap larger than that of the core layer (3). (C) The transparent waveguide portion (A1, A2, A, E1, E2
Alternatively, the stripe width of the mesa stripe waveguide (31) of E) has a distribution such that the stripe width gradually increases toward the end face. 23. One semiconductor laser device selected from the semiconductor laser devices according to any one of claims 1 to 21, characterized in that the following requirements (a), (b) and (c) are satisfied. (A) The transparent waveguide section (A1, A2, A, E1, E2
Alternatively, the optical waveguide of E) and the laser oscillator (B) or the optical amplifier (B) is a mesa stripe waveguide (31).
Is. (B) BH structure (Buried-h) in which the mesa stripe-shaped waveguide (31) is filled with a semiconductor crystal having an energy band gap larger than that of the core layer (3).
ETROSTRUCTURE). (C) The transparent waveguide portion (A1, A2, A, E1, E2
Alternatively, the stripe width of the mesa stripe waveguide (31) of E) has a distribution such that the stripe width becomes gradually narrower toward the end face. 24. The transparent optical waveguide portion (A1, A2,
The mesa-stripe-shaped waveguide (31) of A, E1, E2, or E) has a constant stripe width at a portion in contact with the first slit portion (91) and at an extreme end surface thereof. Semiconductor laser device. 25. The transparent optical waveguide portion (A1, A2,
24. The semiconductor laser device according to claim 23, wherein the cross section of the mesa stripe waveguide (31) at the tip of A, E1, E2 or E) is square. 26. The transparent optical waveguide portion (A1, A2,
26. The semiconductor according to claim 25, wherein the stripe width of the mesa striped waveguide (31) of A, E1, E2 or E) is constant at the portion in contact with the first slit portion (91) and the end face. Laser device. 27. One semiconductor laser device selected from the semiconductor laser devices according to claims 1 to 26, characterized in that the first slit portion (91) reaches the semiconductor substrate (1). 28. The semiconductor laser device according to claim 1, wherein both the first slit portion (91) and the second slit portion (92) reach the semiconductor substrate (1). One selected semiconductor laser device.