JPH04137783A - Super luminescent diode apparatus - Google Patents

Abstract

PURPOSE:To minimize a spot size of guided beam and maximize diffraction effect of the beam to an window region from an active region in order to realize super low reflectivity by narrowing or widening the width of active layer in the area near the end part of window region. CONSTITUTION:A window region 5 is formed on an element obtained by sequentially forming a lower clad layer 2, an active layer 3 and an upper clad layer 4 on a GaAs substrate 1 by the epitaxial growth method. Moreover, anti- reflection coat films 6a, 6b are provided at both front and rear end faces. A GaAs contact layer 7 is formed thereon and moreover rear surface electrode 8a and front surface electrode 8b are also formed. When the width 2T1 of the active region 9c in the vicinity of the window region 5a is set to give minimized spot size of guided beam in the cross-sectional view indicating the refraction index and width of the area in the vicinity of the active layer in the case where such diode is given the dimensional structure using the equivalent refraction index method, the beam diverging angle becomes large, making small the reflectivity. Namely, since optical damage can be prevented by widening the width of active region 9a, high output operation can be achieved easily.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a superluminescent diode device having high output and wide spectral width, which is used in optical fiber gyros and the like.

[Conventional technology]

Figure 11 shows, for example, the proceedings of the 50th Japan Society of Applied Physics Academic Conference in the fall of 1989 (Heisei 1), 27ρ-ZG-16.
2 is a cross-sectional view showing the conventional window type superluminescent diode device shown in FIG.
I composition ratio X), (3) is the 1GaAs active layer (AI composition ratio 2), (4) is the AlGaAs upper cladding layer (AI composition ratio
(6a) and (6b) are AR coating films on the front end surface and the rear end surface, respectively.

Next, the operation will be explained. GaAs substrate f substrate ll
Upper rad layer (2), active layer (3), upper kraft layer (4)
Wind regions (5
), and further anti-reflective coating (hereinafter referred to as A) is formed on both the front and rear end surfaces.
(referred to as R coat) films (6a) and (6b) are provided. In a superluminescent diode, it is important to reduce the amount of light that feeds back into the active region (3), that is, how to reduce the reflectance. Front end face and rear end face AR coating film (6a), (
Since 6b) alone is insufficient, a part of the active layer (3) is destroyed to provide a window region (5) to further reduce the reflectance. The light that enters the window region (5) from the active layer (3) is diffracted and spread, is partially reflected at the rear end face, and enters the active layer (3) again. Wind area (5
), the light is diffracted and spread, so the amount of light that returns to the active layer (3) becomes smaller and the reflectance decreases.

[Problem to be solved by the invention]

Although the conventional superluminescent diode device was constructed as described above, there was a problem in that the reflectance was insufficiently reduced and a wide spectral width could not be obtained.

This invention was made to solve the above-mentioned problems, and it is possible to create a superluminescent diode device with a sufficiently wide spectral linewidth by sufficiently reducing the feedback of light (and further reducing its reflectance). The purpose is to obtain.

[Means to solve the problem]

The superluminescent diode device according to the present invention minimizes the spot size of guided light by narrowing or widening the active layer width near the edge of the window region, thereby reducing the diffraction effect of light from the active region to the window IF region. This achieves ultra-low reflectance.

[Effect]

In this invention, the active layer with a narrow width or the active layer with a wide width near the edge of the window region has the effect of minimizing the spot size of the guided light propagating in the active layer, and furthermore, the active layer width is sufficient. When multiple waveguide modes are allowed in a wide area, the narrow active layer near the edge of the wind region acts as a mode filter that only allows the transverse fundamental mode.
Enables high output operation.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
In the figure, (7) is a GaAs contact layer, (8a)
and (8b) are a back electrode and a front electrode, respectively. FIG. 2 is a cross-sectional view showing the refractive index and width near the active layer when the superluminescent diode device shown in FIG. 1 is made into a two-dimensional structure using the equipolarized refractive index method. (5a) is a window region (9a) with refractive index nc
) is the active region with width 2To refractive index n1, (9b) is the tapered part of the active region with refractive index n, (9c) is the active region near the edge of the window region with width 2T and refractive index n, and OI is the refraction region. In the cladding region with index n, there is the following (1
) holds true.

Figure 3 shows a structure in which the waveguide structure in a superluminescent diode is simplified and replaced with a three-layer slab waveguide, in which a core region with a refractive index of n1 and a width of 2T has a refractive index of n1,
It has a structure that is intertwined with the craft area. The fundamental modes of the TE wave in this three-layer slab waveguide are as follows (2) to (4)
It can be expressed as the formula.

2 π u”+w”= ()”T2(n+”nz”)−
-(31λ control=u+anu If the spot size of the fundamental mode is -.), this spot size and the field distribution of the fundamental mode can be expressed as shown in Figure 4. From this figure, the following relationship is expressed by equation (5) +61. holds true.

By transforming these equations, the spot size −0
can be expressed as the following equation (71+81).

Given the wavelength λ, the cocoa bandwidth 2T, the refractive index n of the core region and the refractive index n2 of the cladding region, the spot size can be found from the above equations (3), (4), (7) and (8). . Figure 5 shows an example of a wavelength of 0.86 μm.
, refractive index of the core region nt=3.60. Spot size (-0
) and the core area width 2T. At a certain core region width of 2T, the spot size is . It turns out that is the minimum. Here, core region width 2 T =0.49μ
- When -, spot size. -0.46 μm, which is the minimum.

When the electric field distribution of the guided light is assumed to be a Gaussian wave, the spot size -0 and the beam spread angle θ. The following relationship (9) holds true between .

This means that the smaller the spot size -0, the more the beam spread angle θ
. This means that it becomes larger.

Therefore, as shown in FIG. 2, the width 2T of the active region (9c) near the window region (5a) is set to the spot size (Wo
) is minimized, the beam divergence angle increases and the reflectance decreases.

Furthermore, in the active region (2T) where subbo 7) size is the smallest, generally only the fundamental mode is allowed, so even if the width of the active region (9a) is wide enough to allow many higher-order modes, the fundamental mode as a whole is mode (light travels back and forth between the front and rear end surfaces). By widening the width of the active region (9a), optical damage (COD) can be prevented and high output operation can be easily obtained.

FIG. 6 is a cross-sectional view showing the relationship between the refractive index and the width of another embodiment of the present invention, in which the width of the active region (9a) is designed to minimize the spot size -0, and the front end surface is This is a superluminescent diode in which the width of the active region is constant from the to the window region.

FIG. 7 is a cross-sectional view showing the relationship between refractive index and width according to another embodiment of the present invention, in which the width of the active region (9e) is smaller than the width 2T+ which is the minimum spot size ( 2rz). In this case as well, the spot size of the light increases in the active region (9e), so COD can be prevented.

FIG. 8 is a cross-sectional view showing the relationship between the refractive index and the width of yet another embodiment of the present invention, in which the spot size in the crystal lamination direction is minimized. The active layer thickness 2U1 near the window region (5b) is set so that the spot size in the stacking direction is minimized.

Moreover, FIG. 9 is a cross-sectional view showing the relationship between the refractive index and the width, which is still another embodiment of the present invention, in which the active layer (3d)
The active layer (3d
) is a superluminescent diode with a constant thickness.

Moreover, FIG. 10 is a cross-sectional view showing the relationship between the refractive index and the width according to yet another embodiment of the present invention, in which the active layer thickness (20K) near the front end surface is the thickness (20K) that provides the minimum spot size.
2II) is a superluminescent diode when the thickness is thicker than .

In addition, the above-mentioned Noh embodiments (Fig. 8, 9, and 10), one embodiment of the present invention (Fig. 2), and other embodiments (Fig. 6)
7), an even lower reflectance can be achieved.

〔Effect of the invention〕

As described above, according to the present invention, a superluminescent diode is provided with a mechanism in which the spot size is minimized in the stacking direction of crystal growth, in the direction perpendicular to the stacking direction, or in both directions. This has the effect that a superluminescent diode device with high reflectance, wide spectral width, and high output can be easily obtained.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a superluminescent diode device which is an embodiment of the present invention, and FIG. 2 shows the structure of the superluminescent diode shown in FIG.
A cross-sectional view showing the relationship between refractive index and width when a dimensional structure is used. Figure 3 is a structural diagram when the optical waveguide mechanism in a superluminescent diode is simplified to form a three-layer slab waveguide.
Fig. 4 is a waveform diagram showing the relationship between the fundamental mode electric field distribution and spot size, Fig. 5 is a waveform diagram showing the relationship between subbo 7) size and core region width, and Figs. FIG. 11 is a cross-sectional view showing the relationship between refractive index and width of a superluminescent diode device according to an embodiment of the present invention, and FIG. 11 is a cross-sectional view of a conventional superluminescent diode device. In the figure, fl+ is a GaAs substrate, (2) is an AIMG
al-x As lower cladding layer, (3) is Aft Ga1
-z As active layer, (3a) is the active layer (refractive index na, thickness 2Uo), (3b) is the tapered part of the active layer, (3C)
is the active layer near the window edge (refractive index na, thickness 2Ul)
>, (3cl) is the active layer (refractive index na thickness 2tl+)
, (3e) is an active layer having a layer thickness (2[1,) thicker than the thickness 2U+ that gives the minimum spot size, and (4) is ^
l, Ga1-XAs upper cladding layer, (51 is AI,
Ga, -. As window frI area (3'/2), (5a
), (5b) is the window region (refractive index n c )
, (6a) is the front end surface AR coating film, (6h) is the rear end surface AR coating film, (7) is the GaAs:17 tact layer, (8
a) is the back electrode, (8b) is the front electrode, (9a is the active region (radius 2, refractive index na), <9b) is the tapered part of the active region, and (9c) is the area near the edge of the window region. Active region (width 2T1. M refractive index na), (9d) is the core region (radius 2, refractive index n+), (9e) is the active layer having a width (272) narrower than the minimum spot size, radial 2TI. , aOt is the crund region (refractive index nb), <10a
) indicates the cladding region (refractive index nz). In addition, the same reference numerals indicate the same or equivalent parts throughout.

Claims (1)

[Claims] In a structure that has a pair of resonator end faces and has an optical waveguide mechanism inside, and a part of the optical waveguide mechanism is interrupted inside the resonator, an optical waveguide in the vicinity of the disconnection. The electromagnetic field of the light propagating in the adjacent waveguide is made smaller or equal to the electromagnetic field of the light propagating in the other waveguides so as to increase the diffraction angle of the light emitted from the waveguide, or A superluminescent diode device characterized in that the electromagnetic field of light propagating in the waveguide near the interruption is minimized.