JPS6076182A - Semiconductor laser having deflection switching function for beam emission - Google Patents

Abstract

PURPOSE:To realize a deflection switch for emitting stable beams in a semiconductor laser having two independent electrodes for injecting current, by electrically insulating between the electrodes. CONSTITUTION:A deflection switch for emitting stable beams is realized by changing the current ratio to be injected to two electrodes in a state where the current density at the center of an active layer is reduced, oscillation of the basic mode is restrained and only the higher-order mode is allowed to oscillate. The regions of semiconductor layers 4 and 5 directly under the current inlets 9a and 9b are subjected to diffusion or ion implantation of a different kind of material (e.g. zinc) so as to form low resistance layers 10a and 10b. In such a structure, the current injected from the current inlets 9a and 9b tend to concentrate in the low resistance layers 10a and 10b, whereby the insulation between the electrodes 8a and 8b can be improved. As the result thereof, the current distribution in the active layer also has double-humped characteristics, whereby the basic mode oscillation is restrained while the higher-order mode oscillation is promoted. In such a manner, the space between the electrodes is not needed to enlarge much and therefore competitive oscillations between the higher-order modes rarely occur.

Description

DETAILED DESCRIPTION OF THE INVENTION Xylophone φj relates to a semiconductor laser in which the direction of deflection of a radiation beam can be switched by controlling the injection current.

Semiconductor lasers are currently being used as light sources for optical communications as light emitting elements that can be made smaller, have a lower turbulence rate, and have a higher output. Gas lasers were first used as light sources for optical communications, but external modulation elements such as ultrasonic elements and air optics have been used for modulation.

On the other hand, with semiconductor lasers, it is possible to perform so-called direct modulation, which changes the output light intensity by modulating the injected current, making it possible to simplify the system configuration and improve reliability, which is extremely effective in practice. It can be a means.

On the other hand, in contrast to the above-mentioned modulation technology in the time domain, light modulation technology in the spatial domain (beam deflection, scanning, etc.) also
This is an extremely important technology for applications because light is good at two-dimensional information processing technology such as images.

Conventionally, such spatial light modulation techniques include a method of rotating a mirror, a method of using an ultrasonic deflection element, an electro-optical element, and the like.

However, in addition to drawbacks such as the inability to achieve high speed with the method of rotating a mirror, and the inability to obtain a large deflection angle with ultrasonic deflection elements or electro-optical elements, both methods require external modulation. However, there are drawbacks such as a complicated system configuration and the inability to downsize the device. If spatial modulation of light could be directly achieved by controlling the current injected into a semiconductor laser, it would be possible to miniaturize the system and significantly improve reliability, contributing to the development of optical information processing technology. It's a big deal.

Therefore, the inventors of the present invention completed the present invention as a result of intensive research aimed at developing a semiconductor laser that can switch the deflection direction of a radiation beam by controlling the injection current.

The operating principle of the current injection type semiconductor laser will now be explained, and then the principle of the present invention will be explained.

Figure 1 shows an example of the structure of a semiconductor laser called a gain waveguide type. JfI-1, AJyGcL, -yAs active debris 3,
p-AlxGa, -xAs buffer [
4(, p-GaAs layer, 5iCh insulating N6 are laminated in order, furthermore, one side of the 5hot insulating layer 6 is provided with a p-side electrode, and one side of the n-GaAs substrate 1 is provided with a layer for injection current. A pole t is provided on the n-side electrode, and a current injection portion 9 is provided on the n-side electrode S.

Then, the current is injected into the semiconductor layer from the current injection 1ily and 'f
c'vL flow ii, kl-r Ga, -y As h It is converted into light energy in the central part 3α of the columnar layer 3, but it is activated by the low refractive index layers above and below this corner)
3, and the light distribution in the tub direction is determined by the injection redundant current density.

Fig. 2 Transverse fundamental mode (a,
), the first-order mode (b), and the second-order mode (C). Further, FIG. 6 shows a far-field image when these waveguide modes are emitted from the semiconductor laser end facet.

Here, the @ axis is the radiation angle seen from the end face of the semiconductor laser, and the vertical axis is the emitted light intensity. The far-field image (α) of the fundamental mode has a light intensity distribution that has a maximum intensity on the central axis and decreases from the central axis to the periphery, whereas the far-field image (b) of the primary mode has a bimodal light intensity distribution. far-field image of the secondary mode (C)
tj: Shows bimodality with a small central peak and large peaks at both ends. In the case of a chair, the far-field image is also symmetrical about the central axis.

On the other hand, if the injection current density distribution is non-uniform within the active region 3α, the angular distribution of the radiation beam of each waveguide mode will also become asymmetric with respect to the central axis. FIG. 4 shows an example of the distribution of far-field patterns for each waveguide mode when the injection current density is non-uniformly distributed.

Accordingly, there is an essential difference in the way the far-field pattern changes between the fundamental mode and the higher-order mode.

That is, the radiation beam pattern (α) of the fundamental mode exhibits a change in which the maximum intensity angle shifts to the left or right by giving a gradient to the injection current density. 1 for this
In the radiation beam pattern of the next mode (b) and the radiation beam pattern of the second mode (C), the peak position of the bimodal radiation beam intensity hardly changes, but the peak strength of either one decreases. Then, the other peak shows a change with maximum intensity.

This 11. In general, the following conclusions can be drawn from the @- results. That is, when the lateral fundamental mode is excited f' in the active layer of a semiconductor laser, if the injection current density distribution is gradually changed from a uniform distribution to a nonuniform distribution with a certain slope, the emitted beam angle can be varied continuously from the center to the left and right, thus allowing spatial sweeping (scanning) of the radiation beam by varying the injection current distribution.

On the other hand, when higher-order modes are excited in the active layer, if the injected current density distribution has a gradient, the intensity of one of the bimodal peaks as a far-field pattern increases. death,
At the same time, the other peak intensity decreases.

Application of this principle allows polarization switching of the radiation beam.

On the other hand, the basic method for forming a non-uniform distribution of injection current in the active layer of a semiconductor laser is to divide the injection current electrode g into two electrodes ra and b, as shown in FIG.
, tb current injection Mtα,? 6 is buried in the 5i02 insulating layer 6, and this electrode gα has an IF:, structure.

By changing the injection current ratio from tb, the active layer 3
This is to control the current distribution within. However, this structure has a pAlzGa+ XAS buffer layer, 7)-G
Since the lateral composition of the GA8 layer 3 is uniform, the current spreads to the left and right, and in particular, the subcurrent density in the central part 3a of the active layer does not decrease, which tends to cause fundamental mode' oscillation. In order to suppress the fundamental mode oscillation and cause only the higher-order mode oscillation with this structure, it is necessary to widen the electrode gap, but if the gap is widened too much, coupled oscillation will occur between the υ third-order modes. A stable deflection switch is not achieved.

Therefore, in the present invention, in order to realize a stable deflection switch for the emitted beam based on the above principle, in a semiconductor laser having two independent turtle current injection electrodes, the two electrodes are electrically insulated. It is.

With the above configuration, it is possible to reduce the lightning current density in the center of the active layer, suppress the oscillation of the fundamental mode, and excite only the higher-order modes. In this state, by changing the ratio of currents injected into the two electrodes, it is possible to realize a stable deflection switch for the emitted beam.

In the present invention, various methods can be considered for electrically insulating between two independent current injection electrodes.
This is illustrated below.

6 to 9 show this embodiment, and parts common to those in FIGS. 1 and 5 are given the same reference numerals, and explanations thereof will be omitted.

Is the structure in Figure 6 a current injection part? By diffusing or ion-implanting a different material (for example, zinc) into the semiconductor Me, z portion located directly under α, 9b, the low resistance layers 10a, 1
06.

In the above structure, the fc current injected from the current injection portions 9α, 9b tends to concentrate on the low resistance layers 70α, /θb, and the degree of insulation between the electrodes α, tb is improved.

As a result, the current distribution in the active layer also becomes bimodal, suppressing fundamental mode oscillation and making higher-order mode oscillation more likely to occur.

According to this method, since there is no need to widen the electrode gap so much, competitive oscillation between higher-order modes is less likely to occur, and stable deflection beam switching can be realized.

In FIG. 7(α), in order to improve the insulation between Tll and the pole Sα2gb, a groove l/ is formed between the electrodes Sα and gb by boring three parts of the semiconductor layer. Current injection into the central portion 3a is prevented, allowing only higher-order modes to oscillate.

FIG. 7(b) shows an electrode g instead of the groove // in FIG. 7(α).
a.

Perform proton irradiation etc. on the semiconductor J@II, k between 56,
This is an example of a semiconductor laser device structure in which a high resistance #12 is formed here to enable oscillation in only higher-order modes.

The 8th prisoner (a) is the semiconductor layer outside the light emitting region in the device structure of the 7th ←). r can be removed by etching or the like, so that the injected current flows through the current injection parts 9a,
Since the high-order mode oscillation can be efficiently concentrated under tb and the higher-order mode oscillation can be performed more efficiently, it is possible to obtain a semiconductor laser device structure that can achieve high-order mode oscillation.

Figure 8 (6) shows the element structure of Figure 7 (6) in which the semiconductor layer 3 outside the light emitting region is removed by etching, etc. This is an example of an element structure that can efficiently perform the following steps.

FIG. 9 shows a configuration example of a semiconductor laser having a deflection switch function using a p-GaAa substrate saw in contrast to the above embodiment using an fL-GctAa substrate 1. In this configuration, a p-GaAs substrate 12 is used. and” AlzGa, -zAs
A reverse bias layer 13 made of n-G (!AJIM is provided between the buffer layer and the n-Q layer below the electrode ga, 17).
In the αA8 layer/J and the p-GaA3 substrate/J, grooves lda α and ldab are formed by etching or the like. When a current is injected from the electrodes Sα and ff6 in the typical device structure, “-G
aksN73, T) - A reverse bias is applied to the P-N junction part of the GaAs substrate 12, and no current can pass through this region, and the current becomes V@ldaα, /4(
Therefore, the injected current is V groove/4! from b to the substrate/co side. α, /'Active part J in contact with M to Ib
b.

By passing through only 3C, fundamental mode oscillation is suppressed and a semiconductor laser capable of higher-order mode oscillation is formed.
Ru.

Next, we will discuss an application example of the semiconductor laser having a deflection switch function formed as described above. Figure 1θ shows how the optical signal input to the optical fiber is, tt is transferred to the electrodes tα, zab on the semiconductor laser. This figure shows how switching occurs by changing the injection current.

In the case of a semiconductor laser that has a deflection switch function related to the main hole QIm, the angle of the emitted beam is constant, so if the optical fibers /j and /A are installed at predetermined positions, the emitted light from the semiconductor laser is optical fiber /j, /
& is sure to enter one side without causing any leakage of light to the outside.

On the other hand, when the fundamental mode is excited by the beam i and the injection beam is simplified, the beam leaks out of the fiber when it travels from one optical fiber to the other. Put it away.

In addition, in the above-described deflection switch, since the light beam crosses the fiber cross section fc, the rise and fall portions of the pulse signal waveform when performing pulse-like signal switching are distorted by the crossing time. On the other hand, in the semiconductor laser having the deflection switch function of the present invention, the beam position does not change, so the injection current pulse waveform itself becomes a light pulse and is transmitted through the optical fiber. This will be the most important feature in realizing future ultra-high-speed optical switches.

While the deflection angle of a conventional optical deflector using an electro-optic crystal is only 1 to 2 degrees, the semiconductor laser with the deflection switch function of the present invention has a beam deflection angle of 10 degrees in the first mode. After the target, the secondary wave is around 14 to 15 degrees tL, and its practical value is extremely large.

[Brief explanation of the drawing]

Figure 1 is a diagram of the principle configuration of a gain waveguide semiconductor laser with a single-ft pole, and Figure 2 (d), (6), (6)
Figure 5 shows each oscillation mode and lateral light intensity distribution diagram of the same gain-guided semiconductor laser as above, (6), (c)
ti, an example of a far-field image when each of the guided modes as above is emitted from the laser end face, Fig. 4 (5), (6),
(6) is an example of the far-field pattern of the emitted beam for each waveguide mode when the injection current density distribution in the active layer is non-uniform;
Figure 5 shows the principle M4 configuration of a semiconductor laser having two independent fc current injection electrodes to generate a non-uniform injection current distribution in the active layer, and Figure 6 shows the electrical connection between the two TjjL poles of the same. FIGS. 7(a) and 7(6), which are principle configuration diagrams showing one embodiment of the insulated semiconductor laser of the present invention, are other embodiments of the semiconductor laser of the present invention in which the two electrodes are insulated by another method, Figure 7 (the gradient is an example of insulation by providing a groove between both electrodes,
wJ1 Figure (6) is an example of insulation by forming a high resistance layer, Figure 8 (G), (6) is the same as Figure 97 (Q).
, Fig. 8 is a configuration diagram of a semiconductor laser which is an improved example of (6) and which allows high-order mode oscillation to be performed efficiently by etching the outside of the light emitting region of the semiconductor layers Hiroshi and S, respectively. 9 is a block diagram showing another embodiment for electrically insulating between both electrodes, and FIG. 9 is a perspective view showing an example of application of the semiconductor laser of the present invention. In the figure, ga and gb are two independent current injection electrodes, 3
α is the central part of active l1II3. Figure 3 Figure 4 Figure 1 0 Figure 8 7 Procedural Amendment (Method) ■Indication of the Case 1983 Patent Application No. 183.445 2 Title of Invention Semiconductor laser with output beam deflection switch function 3
Relationship with the case of the person making the amendment Patent applicant: 1-114 Kasumikaseki 1-3-1, Chiyoda-ku, Tokyo Director of the Institute of Industrial Technology Kawa 1) Yutaka Department 4 designated agent 5 Date of amendment order 1988 1 Month 31st (Shipping date -
゛) In the specification subject to amendment 6, column 7 for a brief explanation of the drawings Contents of the amendment (1) In the specification, on page 14, line 14, "Figure 8 is" changed to 1
Figure 9 is corrected. (2) Same, p. 14, line 15, “Figure 9 welfare,” was changed to “1
Figure 0 is corrected.

Claims (5)

[Claims] (1) A semiconductor laser that has two independent fc current and current injection fabric poles and switches the deflection of the emitted beam by changing the current ratio injected into the two 17 poles in a higher-order mode oscillation state. By electrically insulating the space between the two electrodes, the current density in the center of the active layer is reduced, suppressing the oscillation of the fundamental mode and excitation of only the higher-order modes. - A semiconductor laser having a characteristic output beam deflection switch function. (2) 1 car! 2. A semiconductor laser according to claim 1, wherein a high resistance layer is formed between the two electrodes by grooves or ion implantation to electrically insulate the two electrodes. (3) Etching the outside of the light emitting area of the semiconductor layer
A semiconductor laser according to claim 2. (4) The semiconductor laser according to item 1, wherein a low resistance layer is formed under both electrodes to electrically insulate between both electrodes. (5) A reverse bias layer is provided between the substrate and the semiconductor layer, and a V-groove is formed in the reverse bias layer and the substrate below both electrodes to electrically insulate both electrodes 1#3J. Semiconductor laser 6 described in Paragraph 1