JPH0395524A - Bistable semiconductor laser - Google Patents

Abstract

PURPOSE:To enable bistable operation in a wide current area and to provide a light injecting function by providing an optical waveguide between two stripes areas consisting of nonexcitation and excitation areas and providing a light reflecting surface at the other end. CONSTITUTION:A 1st clad layer 11, an active layer 12, a 2nd clad layer 13 and an SiO2 film 14 are formed on a substrate 10, two window are provided in stripes, and Zn is diffused in them to form a 1st excited area 19 and a 1st nonexcitation area 20. Similarly, a 2nd excitation area 21 and a 2nd noexcitation area 22 are formed and the optical waveguides 26 is provided between those two striped areas; and a V-cut end surface 25 is formed at one end and a light reflecting surface 31 is formed at the other end. Those excitation areas 19 and 21 and nonexcitation areas 20 and 22 are made to meet specific requirements and thus the bistable operation is performed in the wide current area; and light is made incident to enable optical switch operation and different- wavelength laser oscillation.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a bistable semiconductor laser used as an optical switch element, an optical logic operation element, etc. in an optical information processing device or the like.

[Conventional technology]

Optical bistable devices with a hysteresis phenomenon in their optical output characteristics have functions such as high-speed optical switches, optical logic operations, and optical memories, and are attracting wide attention as basic optical functional devices for optical information processing equipment, optical computers, etc., and are currently being researched and developed. is in progress.

Double heterojunction (DH
Kawakuchi (H
．． Kaw-acuchi) and G.Iwane
) and Electronics Letters ( Electr
onics Letters) Magazine 1981 Volume 17 16
"Bistable operation in semiconductor lasers with non-uniform excitation" on pages 7-168.
ion in semiconductor wi
th inhomogeneous excitati
The presentation was titled ``on''. As shown in FIG. 9, this bistable semiconductor laser has a hexagonal carrier injection region 61 in the longitudinal direction of the striped resonator.
The cap layer 62 of the aAsP/InP semiconductor laser has a periodically shaped structure by diffusion of zinc (Zn).

[Problem to be solved by the invention]

In the above-mentioned bistable semiconductor laser such as Kawakuchi, the bistable operation fluctuates and is unstable depending on the temperature and the length of the carrier injection region, and its operating region (operating current region) is narrow and lacks reproducibility. Also, since light is emitted from the -1 (wavelength) surface, there is a drawback that it cannot be integrated like a surface-emitting type device.

When processing optical information using a combination of surface-emitting devices, it is necessary to have an element structure that not only emits light from the surface but also emits light in the vertical direction and responds to light injected from the vertical direction. However, such a bistable element has not yet been proposed.

The object of the present invention is to eliminate the above-mentioned drawbacks, and to provide a bistable semiconductor laser which stably produces bistable operation over a wide current range based on the principle of bistable operation, and which also has a function of -5-injection of light in the vertical direction. The goal is to provide the following.

[Means to solve the problem]

A first means provided by the present invention to solve the above-mentioned problem is to have a multilayer structure including at least a double heterojunction structure in which an active layer is sandwiched between semiconductor layers having a wider band gap than the active layer. two stripe-shaped regions that are continuous in the longitudinal direction of the resonator and are composed of a non-excited region and an excited region that have a smaller band gap than the active layer in the active layer, and that have different band gaps from each other; In parallel, an optical waveguide consisting of a double heterojunction structure having an active layer having a wider bandgap than the two striped regions is connected in the resonator length direction of the two striped regions and between the two striped regions. The optical waveguide has a buried structure in which its entirety is buried with a semiconductor layer having a wider band gap than the active layer, and one end surface of the optical waveguide is located at the center of the element, and the stripe is located in the longitudinal direction of the optical waveguide. It has an inclined surface 6 such that the traveling light is reflected in both left and right directions at 90 degrees with respect to the traveling direction, and the end faces located near the center of the element of the two striped regions are located right and left from the end face of the optical waveguide. The optical waveguide is provided with an inclined region so that the light reflected in both directions is reflected by 1J in the longitudinal direction of the stripe of each striped region, and the other end face of the optical waveguide is perpendicular to the element surface, and
Facing the vertical plane, it has a 45-degree slope to the right of the bottom surface of the element, and has a reverse slope that reflects incident light from a direction perpendicular to the element surface at right angles and makes the light enter the guiding waveguide. In each of the two striped regions, the ratio of the total length of the excited region to the total length of the non-excited region is (1-h): h
(0<h<1), and loss α of the entire non-excited region
The loss β normalized using the resonator loss P is β=hα/
The present invention is a bistable semiconductor laser characterized by a ratio ga/gb of a differential gain coefficient ga in an excitation region to a differential gain coefficient g in a non-excitation region and a comparison of Gallia natural lifetime, where P is a differential gain coefficient ga in an excitation region and a differential gain coefficient g in a non-excitation region.

A second means of the present invention is a second means in the first means described above, in which a second portion is provided in the longitudinal direction of the resonator of the optical waveguide and in the vicinity of the other end face of the element.
The light propagating in the longitudinal direction of each stripe is provided with an optical waveguide, and when the other end surface of the two striped regions is located near the center of the element and faces the end surface having the inclined surface, the light traveling in the longitudinal direction of each stripe passes through the second striped region. The second optical waveguide has an inclination with respect to the longitudinal direction of the stripe so as to be contrary to the direction of the optical waveguide, and the end face located inside the element in the second optical waveguide is reflected from the end face of the two striped regions. A sloped area is provided to reflect each light in the longitudinal direction of the second live.
The other end face of the optical waveguide is provided with an inclined surface at an angle of 45 degrees with respect to a plane perpendicular to the element, and the second optical waveguide includes an active layer in contact with the inclined surface in the vertical direction, and is directed to the laser oscillation light. This is a surface-emitting bistable semiconductor device characterized by having holes formed in the device to expose a transparent layer surface.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

1 is a perspective view of this embodiment, FIG. 2 is a top view, and FIGS. 3 and 4 are sectional views taken along line AA' and line BB' in FIG. 1, respectively. FIG. 5 is a perspective view of another embodiment, FIG. 6 is a top view of FIG. 5, and FIG. 7 is a sectional view taken along the line CC' of FIG. The manufacturing method of this embodiment is as shown in FIG.
n-type Aβo4G ao,s A s first on the substrate 10
The cladding layer l1 is 3.0 μm, n-type A (l o.o
s Ga 0.9 5 A S active layer 12 (carrier concentration 3X 10 18 cm-3) is 0.10 μm, n
Shape A R o. h G a o. The aAs second cladding layer 13 is continuously lengthened by 2.0 μm.

SiO2 film 1 on the third n-type second cladding layer 13
4, and in this SiCh film 14, two stripe-shaped windows 15 and 16 with a width of 3 μm and a length of 150 μm are formed using a photoresist technique so that they are parallel to each other and do not touch each other.
Open the μm apart, and then add these two striped windows 1.
5. Width 3 μm 1 length 22 to match the center line of 16
Two striped windows 17 and 18 of 0 .mu.m are formed on the extension of the striped window 15.16, separated by 5 .mu.m from each end (FIG. 8). Zn is diffused at a low concentration through these windows. Diffusion Freon 1 is n-type AA. 、． G
a o. s A S within the first cladding layer 1 , more preferably at the boundary between the first cladding layer 11 and the active layer 12 .

If the concentration of Zn diffused at this time is controlled to 4 x 1018 cm''3, the diffused region in the active layer has a carrier concentration I
It is converted to a p-type of X 1 0 IJcm-3 and is a p-type with impurity compensation. At this time, the band gap of the impurity-compensated active layer was found to be 40 meV smaller than the band gap of the original active layer 12, according to measurements made by the inventor. Here, the impurity-redeemed active layers under the windows 15 and 17 become a first excitation region 9 and a first non-excitation region 20, respectively (FIG. 2).

Next, the striped window 15.17 is covered with a SiO2 film, and Zn is added from the striped window 16.18 to 7×10
Diffuses to the inside of the 18cm-3 active layer. At this time, the concentration of the active layer in the diffused region is 8 x 1 in addition to the above.
According to measurements made by the present inventors, the band gap was 60 meV smaller than that of the original active layer 12. The impurity-compensated active layers under windows 16 and 18 now become second excitation regions 21-10 and second non-excitation regions 22, respectively (FIG. 2).

Next, as shown in FIG. 8, after removing the SiO2 film, the Si
02 film is applied, and between the first stripe portion connecting the Zn diffusion regions from windows 15 and lγ, the second stripe portion connecting the Zn diffusion regions from windows 16 and 18, and the window 17. and 18, each having a width of 6 μm and extending from near each end face of the Zn diffusion region in the direction opposite to the Zn diffusion region.
The SiO2 film in the striped region and the entire vicinity of the end face is left, and the other parts are removed by etching.

The Zn diffusion region end faces of the first and second striped regions have an inclination of 45 degrees with respect to the longitudinal direction of the resonator at the outer side sandwiching the third striped region (the first inclined end face 23, The second inclined end surface 24) allows light entering perpendicular to the end surface to be reflected by 90 degrees and travel within each stripe region toward the resonator (FIG. 2). On the other hand, the end face of the third striped region near the center of the element has a V-shaped cut whose angle is 90 degrees in the longitudinal direction of the resonator, corresponding to the 45-degree inclined surface 23 and 24. A groove is formed (V-shaped notch end face 25) so that the light injected into the third stripe-like region is reflected in a 90-degree direction by this 45-degree inclined surface and is injected into the first and second stripe regions. Make it. This third stripe-shaped area is the optical waveguide 26.
(Figure 2). At this time, etching is performed to the inside of the first cladding layer l1.

Next, apply high resistance AI! o. oa G a O. 9
2A S layer 27 (FIGS. 3 and 4). If the MOVPE method is used in the above-mentioned process, it is possible to lengthen any set of layers with good control of the layer thickness by changing the composition of the mixed gas, since the MOVPE method is a vapor phase growth method using organic metals. can. Furthermore, the high resistance layer 27 can be easily formed by introducing oxygen into the growth gas.

Moreover, if the gas flow rate is controlled at this embedding length, Si
It is possible to lengthen only the etched region without growing on the O2 film. Furthermore, the surface can be gas-etched with HCj7 gas before embedding, and reliability can be further improved.

After the formation of the high resistance layer 27, the Sin2 film is removed, and a p-type ohmic contact 28 is formed in the Zn diffusion region corresponding to the first excitation region l9, and a p-type ohmic contact 29 is formed in the Zn diffusion region corresponding to the second excitation region 21. Attach n-type substrate 10
An n-type ohmic contact 30 is formed on the side.

Next, a photoresist is applied to the surface on which the p-type ohmic contact is attached, and in the region left by the etching near the element end face of the optical waveguide 26, a stripe pattern of about 2 μm in width is formed perpendicular to the longitudinal direction of the resonator. Open a window and perform vertical dry etching on the first cladding layer 11.
Do this to a depth of . Next, photoresist is applied again, and after filling the groove with resist, dry etching is performed adjacent to the groove at an angle of 45 degrees with respect to the end face direction of the optical waveguide. At this time, it is preferable to tilt the element at 45 degrees with respect to the vertical dry etching beam. As shown in FIG. 3 with respect to the thus obtained slope 31, light incident from above is split at right angles by the slope 3l and proceeds into the optical waveguide 26 (FIGS. 2 and 3). .

-13- Thus, the first semiconductor laser of the present invention is obtained (first
(Fig. 2, Fig. 3, Fig. 4).

In the above-mentioned manufacturing process, during etching before high-resistance embedding, a 6-μm wide groove was etched from near the end face of the Zn diffusion region through the windows 15 and 16 in the direction of the resonator length opposite to the optical waveguide 26. 4 striped areas are formed. At this time, the end surfaces of the first and second striped regions are also provided on the outside sandwiching the fourth striped region at an angle of 45 degrees with respect to the resonator direction so as to face the first inclined end surface 23 and the second inclined end surface 24. A third inclined end surface 32 and a fourth inclined end surface 33 forming an angle of (FIG. 6) are formed. On the other hand, the end face of the fourth stripe-like region inside the element forms a V-shaped notch end face 34 similar to the optical waveguide 26, and this fourth stripe-like region becomes a second optical waveguide 35.

In this way, the light traveling through the optical waveguide 26 can be separated into the first and second stripe regions at the end face inside the element, and both can enter the second optical waveguide 35 and travel therein (Fig. 6). ). As shown in Fig. 1, the high resistance layer 27
14 to form p-type and n-type ohmic contacts. Along with the formation of the above-mentioned slope 31, a second optical waveguide 35 is formed on the element end face facing the slope 31.
Also, a slope 36 that is parallel to the slope 31 is formed at an angle of 135 degrees with respect to the inside of the element in the longitudinal direction of the resonator by dry etching. This can be formed simultaneously with the slope 31.

Next, a photoresist film is applied to the substrate side and the second optical waveguide 35 is formed.
A circular window with a radius of 2 μm is formed in the photoresist film, centered on a point perpendicular to the substrate from the center of the active layer where the slope 36 contacts. Next, a hole 37 is drilled in the substrate 10 using dry etching and chemical etching until the surface of the first cladding layer 11 is exposed, and then all the photoresist film is removed. In this way, a laser having another structure of the present invention is obtained (FIGS. 5, 6, and 7).

[Action/Principle]

In the structure of this embodiment, carriers injected from the p-type ohmic contact on each Zn diffusion region are injected into the active region through the Zn diffusion region.

The active region has high resistance in the horizontal and lateral directions A A O. 05 Ga
It has a BH structure sandwiched between O,95A s layers 27. In particular, in this embodiment, the first excitation region l9 and the first non-excitation region 20 are p-type active layers of I x 10 1 acm-3, and their refractive index is equal to the refractive index of the active layer n. =3.555
When the amount of decrease in refractive index due to p-type concentration is taken into account, the effective refractive index becomes 3.550.On the other hand, the high resistance A I!o which is a buried layer
．． o s G a o. o 5 A refractive index n b of the S layer 27 = 3. 5 3 4, so the refractive index difference Δn=1
．． 6X. 10-2, maintaining stable fundamental transverse mode oscillation. On the other hand, the second excitation region 2l and the second non-excitation region 22 are 8
Since it is a p-type active layer of X l O '' cm-3 and the effective refractive index is n,,,,= 3.5 4 3, the refractive index difference Δn=9X10-3, and the stripe width is 3 μm.
The active region can continue to maintain stable fundamental transverse mode oscillation up to high output.

By the way, in the structure of the present invention, the first excitation region 19 and the second excitation region 21 are connected to each other and each has the same p-type dopant.
A non-excited region 20 and a second non-excited region 22 are formed. When carriers are injected into the excitation region to cause laser oscillation, each non-excitation region becomes an absorption region with a loss of 200 cm-' relative to the laser oscillation. Therefore, in the structure of the present invention, an absorption region 20 is formed continuous to the active region 19, and an absorption region 22 is formed continuous to the active region 21.

Therefore, in the structure of the present invention, the striped active region resonator has a non-excited light absorption region in the longitudinal direction of the resonator, which is equivalent to introducing a saturable absorber into the resonator. The relationship between the phenomena that appear in such cases and various parameters is explained in the Journal of -7 Pride Physics (
Journal of Applied Physics
) 1985, Vol. 58, pp. 1689-1692, M. Ueno and R. Lang, ``Condition for Self-sustained Oscillation and Bistability Generation in Semiconductor Lasers J.
stained pulsation and bist
ability in semiconductor
It was announced under the title of ``Lasers''. According to this, the length ratio of the excitation region (region 1) and the absorption region (region 2) is (1-h):h, and the ratio of the differential gain coefficient of the excitation region to the absorption region is g 1 / g 2 1 If the ratio of carrier natural lifetimes in each region is τ1/τ2, then the normalized non-saturated absorption thickness is 171.

According to the embodiment of the present invention, the loss α in the light absorption region is a=
-200cm-' and r'=40cm-
', h=0.4, then β=-2.0. The light absorption region becomes a non-excited region, so the natural lifespan of carriers τ
2 is relatively long τ2 = 4 μm to 5 μm, while in the active region τ. = 1.5 μm to 2.0 μm, so τ1/τ2
=0, 2~0.375, g+/g2=0.8~1
．． Since it is expected to be 0, the above-mentioned conditions for bistable occurrence are fully satisfied, and each bistable operation occurs stably.

Further, the structure of the present invention has a slope 31 and an optical waveguide 26 adjacent thereto, which performs the following optical function operation.

First, in the structure of the present invention, each excitation region 19, 21 is excited to such an extent that laser oscillation does not occur. When light is incident on the slope 31 in this state, the light is reflected by the -18 slope 31, curves at a right angle, and is injected into the optical waveguide 26. Since the optical waveguide 26 has a positive refractive index distribution based on the refractive index difference between the active layer and the high-resistance buried layer, light travels while being confined within the optical waveguide. The optical waveguide 26 has a V-shaped notch end face 25 within the device, and is a square plane that forms angles of 45 degrees and 135 degrees with respect to the center line in the longitudinal direction of the resonator. The traveling light is reflected by this end face 25, divided into two in both left and right directions with respect to the traveling direction, turns at right angles, and begins to travel perpendicular to the center line.

In the structure of the present invention, as shown in FIG. 2, there are a first non-excited region 20 and a second non-excited region 22 in the traveling direction, so the traveling light is absorbed by these non-excited regions and is absorbed by these non-excited regions. It will stimulate your career. As a result, the band gap in the non-excited region is equivalently widened, and the loss is reduced, which is reflected in the first excited region 19 and the first non-excited region 20, and in the second excited region 2l and the second non-excited region 22, respectively. Laser oscillation is started in the resonator.

Furthermore, in the structure of the present invention, each excitation region as well as each non-excitation region has a different bandgap width, which significantly enhances the optical functional operation. That is, when the wavelength of light incident on the slope 3l from the outside is wider than the bandgap between the first and second non-excited regions, the light is absorbed by the first and second non-excited regions, resulting in bistable operation and the first excited region. A wavelength λ1 due to the laser oscillation of 19 and a wavelength λ2 due to the ray→no oscillation of the second excitation region 2 are emitted from each region.

On the other hand, if the wavelength of the incident light is wider than the bandgap of the first non-excited region 20 and narrower than the second non-excited region 22, the incident light is absorbed in the first non-excited region, resulting in bistable operation and the wavelength λ1. Laser oscillation occurs in the first excitation region l9, whereas light passes through the second non-excitation region and the injection oscillation wavelength is λ.

laser light is emitted from the second excitation region 2l. Wavelength λ of incident light. λ from the first and second excited regions if is narrower than the bandgap of the first non-excited region. of laser light is emitted.

As described above, the structure of the present invention not only performs bistable laser oscillation with different wavelengths and emits each laser oscillation light from the same surface, but also has wavelength selectivity.

In the second structure of the present invention (Fig. 5), the laser light oscillated in each active region travels in the longitudinal direction of the resonator, but the end face of each excitation region is at an angle of 45 degrees with respect to the longitudinal direction of the resonator. Since the inclined surface is located at a position sandwiching the second optical waveguide 35 on the inside thereof, the light incident on this inclined end surface is reflected here, the traveling direction is changed by 90 degrees, and the second optical waveguide 35 is formed. into the optical waveguide 35 (FIG. 6). This optical waveguide has a V-shaped notch on its end face, and each side of the V-shaped notch forms an angle of 45 degrees with respect to the longitudinal direction of the resonator, so the light is reflected here and in the direction of propagation. is converted by 90 degrees and proceeds toward the resonator of the second optical waveguide. The end face of the second optical waveguide 35 is a slope 36 inclined at 45 degrees toward the outside of the resonator, so the laser beam is bent at a right angle by the slope 36 and travels perpendicularly toward the substrate. Since there is a hole 37 in the substrate adjacent to this slope 36, light passes through this hole 37 and becomes a surface emitting laser emitted from the back surface of the substrate.

The light that is vertically incident from the upper part of the element undergoes one-length selectivity of the wave 21, and is emitted vertically to the lower part of the element. For optical logic circuits, etc., which are important for optical information processing, methods have been considered in which optical functional elements are integrated and stacked on other stages, and this second structure is particularly effective in this respect. .

As described above, the structure of the present invention performs stable bistable operation, so it has a memory effect and can be used as an optical switching and switching function, making it a key element of optical logic circuits.

〔Effect of the invention〕

The structure of the present invention is not one in which an absorption region is provided due to the difference in carrier injection as in the laser prototyped by Sen. Kawak et al., but a region that absorbs light is formed. It is a laser and has a completely different structure.

The structure of the present invention (1) is capable of bistable operation, has a wide tolerance range, and is unparalleled in terms of controllability and reproducibility compared to conventional structures.

(2) Increase the voltage to near the threshold where bistable operation occurs -2
2, high-speed switching operation can be achieved by vertically incident light. Furthermore, laser oscillations with different wavelengths can be performed in arbitrary numbers depending on the light intensity of the incident light.

(3) Laser oscillation of any wavelength is possible by controlling the wavelength of incident light.

(4) It is a surface emitting type and can be used by stacking it in multiple stages.

(5) The excitation region itself has a positive refractive index guiding mechanism, and further has a light guiding mechanism within the resonator to achieve stable fundamental transverse mode oscillation.

It has the following advantages.

Although this example describes the Aj2GaAs/GaAs double heterojunction crystal material, other crystal materials such as InGaP/AI2InP, InGaAsP/InGa
P, InGaAsP/InP, A4GaAsSb/Ga
The present invention can also be applied to semiconductor lasers made of many crystalline materials such as AsSb.

[Brief explanation of drawings]

FIG. 1 is a perspective view of the first embodiment of the present invention, and FIG. 2 is a perspective view of the first embodiment of the present invention.
The top view of the figure, Figures 3 and 4 are A-A', B- of Figure 1.
B' sectional view, FIG. 5 is a perspective view of the second embodiment, FIG. 6 is a top view of FIG. 5, FIG. 7 is a c-c' sectional view of FIG. FIG. 9 is a perspective view when a window for Zn diffusion is opened in the 8102 film in the manufacturing process of the embodiment, and FIG. 9 is a schematic diagram of a conventional bistable semiconductor laser. In the figure, 10... n-type GaAs substrate, 11...
...n type A j7 o. tG ao. a As first cladding layer, 1 2 − − n type A 4 o. os
G a O, 9 5 AS active layer, 1 3 − −
n-type A j' 0.4 G a o. aAs second cladding layer, 14... SiCh film, 15...
Zn diffusion window, 16...Zn diffusion window, 17...
...Zn diffusion window, 18...Zn diffusion window, l9.
...First excitation region, 20...Lth non-excitation region, 21...Second excitation region, 22...
- Second non-excited region, 23...l-th inclined end surface, 24
...Second inclined end face, 25...V-shaped notch end face, 26...Optical waveguide, 27...High resistance A Il o. o s G a O. 9 2 A
s layer, 2 8 ...- p-type ohmic contact,
29...p type ohmi, sokukontaku l-, 30
...N-type ohmic contact, 31...
...45 degree slope, 32...Third slope end surface, 33
... Fourth inclined end surface, 34 ... V-shaped notch end surface, 35 ... Second optical waveguide, 36 ...
・45 degree slope, 37...hole, are shown respectively.

Claims (2)

[Claims] (1) It has a multilayer structure including at least a double heterojunction structure in which an active layer is sandwiched between semiconductor layers with a wider bandgap than the active layer, and the active layer is continuous in the longitudinal direction of the resonator. is composed of a non-excited region and an excited region having a band gap smaller than that of the active layer, and has two parallel stripe-like regions having different band gaps, and is wider than the two stripe-like regions. An optical waveguide consisting of a double heterojunction structure having an active layer with a bandgap is provided in the cavity length direction of the two striped regions and between them, and the entire optical waveguide is provided with a bandgap smaller than that of the active layer. It has a buried structure filled with a wide semiconductor layer, and one end face of the optical waveguide is located at the center of the element, and the light traveling in the stripe length direction is reflected in both left and right directions at 90 degrees with respect to the traveling direction. The end face, which has an inclined surface and is located near the center of the element of the two striped regions, reflects the light reflected in both left and right directions from the end face of the optical waveguide in the longitudinal direction of the stripe of each striped region. The other end face of the optical waveguide forms a plane perpendicular to the element surface, and opposite to the perpendicular plane, has a slope at an angle of 45 degrees with respect to the bottom face of the element, and this slope is , serves as a reflecting surface that reflects incident light from a direction perpendicular to the element surface at right angles and allows the light to enter the optical waveguide, and in each of the two striped regions, the total length of the excitation region and the total length of the non-excitation region The ratio of (1-h):h(0<h<1
), and the loss α of the entire non-excited region is the resonator loss Γ
When the loss β normalized using is β=hα/Γ, the ratio g_a/g_b of the differential gain coefficient g_a in the excitation region to the differential gain coefficient g_b in the non-excitation region and the ratio τ_a/τ_b of the carrier natural lifetime are g_aτ_a /(g_bτ_b)
A bistable semiconductor laser characterized by having a relationship of <-β/(1-β). (2) In the bistable semiconductor laser according to claim 1, a second optical waveguide is provided in the cavity length direction of the optical waveguide and near the other end face of the element, and the element is provided in the two striped regions. The other end face located near the center and facing the end face having an inclined surface is inclined with respect to the longitudinal direction of the stripe so that light traveling in the longitudinal direction of the stripe is reflected in the direction of the second optical waveguide. The end face of the second optical waveguide located inside the element has an inclined region so as to reflect each light reflected from the end face of the two striped regions in the longitudinal direction of the stripe. However, the other end face of the second optical waveguide is at an angle of 45° with respect to a plane perpendicular to the element.
A hole is formed in the element so as to include an active layer in the vertical direction in which the second optical waveguide and the inclined surface are in contact with each other and expose a layer surface that is transparent to the laser oscillation light. A bistable semiconductor laser characterized by: