JP3311238B2 - Optical semiconductor device and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical semiconductor device such as a low threshold semiconductor laser and an optical integrated device used for optical communication, optical information processing, and the like, and a method of manufacturing the same.

[0002]

2. Description of the Related Art A short cavity laser having a short cavity has been studied as a low threshold laser. As this type of laser, a surface emitting laser (Vertical Cavity Sur) that emits a laser beam perpendicular to the substrate surface is used.
face Emitting Laser: VCSEL)
R & D has been promoted. In recent years, the threshold value of laser oscillation has been drastically reduced, and is about 1 mA at room temperature continuous oscillation (CW) in an oscillation wavelength band of 980 nm. In addition, progress has been made in arraying and fiber coupling methods,
It is expected to be applied to optical communication and optical information processing fields.

On the other hand, short-cavity lasers having a resonator extending in a direction parallel to the substrate are being developed. For example, a multi-reflection microcavity laser in which a large number of etching mirrors are formed, or a DBR laser as shown in FIG.
1099, M.P. Hamasaki et al.
30a-ZG-8; C. Shin, et
al. 30a-ZG-9) and the like have been proposed. In addition, when such an etching mirror is used, the roughness of the mirror surface causes a decrease in reflectance. Therefore, a regrowth is performed in a lateral direction on an etching surface perpendicular to the substrate, and the growth surface is considered to be a mirror end surface. (M. Goodd
a et al. , J. et al. Crystal Grow
th145, p. 675 (1994)).

[0004]

However, in the case of the former substrate vertical type (VCSEL), the structure for reducing the leakage current is important because the area of the active region is small, so that the manufacturing process becomes complicated and the yield is reduced. There is a limit to lowering the threshold. In addition, while a two-dimensional array can be easily realized on the same surface, a spatial mounting arrangement (for example, an arrangement for spatially aligning two-dimensional arrays) is difficult.

On the other hand, in the case of the latter substrate horizontal type, the current confinement structure can be performed in the same process as the conventional long cavity laser, so that the process is simplified and a lower threshold value can be realized. There is. Further, it is relatively easy to integrate a plurality of short-cavity lasers on the same substrate and couple them with an optical waveguide, and there is an advantage that the mounting of an optical integrated circuit for optical information processing is simplified.

However, at present, the horizontal cavity type short-cavity laser cannot reduce the threshold value because the reflectance does not increase due to the roughness of the etching mirror even if the coating is highly reflective. In addition, a highly efficient DB formed by a semiconductor heterojunction as realized by a VCSEL.
There is no means to produce R reflector, so form a DBR in a periodic reflector by etching, ya Ri There etch <br/> ring end face of the problems, the threshold can not be reduced.

[0007] In view of such problems, the object of the present invention will be described below corresponding to each claim. An object of 1) is to provide a horizontal optical semiconductor device having a periodic heterostructure having a smooth surface perpendicular to the optical waveguide in order to improve the reflectivity of the end face of the optical waveguide formed by etching.
A structure having a reflector area, wherein an active layer and a reflector area are provided.
Longitudinal Mode Oscillation with a Mechanism that Can Inject Current Independently
Possible structure of distributed reflection laser and distributed feedback laser
It is to provide a structure for realizing it . The purpose of 2) is to enable single longitudinal mode oscillation in the optical semiconductor device as in 1).
To provide an efficient distributed reflection laser. 3) eyes
The target is an optical semiconductor device having the structure as in 1) above, with a single vertical mode.
It is an object of the present invention to provide a distributed feedback laser capable of oscillation.
The purpose of 4) is to make the surface perpendicular and smooth to the optical waveguide described above.
To provide a method for producing a layer structure having

[0008]

The principle of the present invention will be described with reference to specific examples. First, a stripe-shaped buried heterostructure is manufactured as in a normal long-cavity laser. Next, an etching mirror is formed. Where Ch
Utilizing the fact that a smooth crystal plane appears when grown on the mirror surface of the side wall by the electronic beam epitaxy (CBE) method. The conditions at that time are, for example, a substrate temperature of 550 ° C., a V / III ratio of about 2, and a growth rate of about 0.6 μm / hour. For example, when a sidewall is grown in the <0-11> and <01-1> directions using a (100) InP substrate, a smooth surface perpendicular to the substrate appears. This is shown in FIG. In FIG. 2, reference numeral 201 denotes a region formed at the end face by etching, 202 denotes a waveguide layer, and 203 denotes a laterally grown layer. If there is a large deviation from this condition, other crystal orientations will appear and the plane will not be perpendicular to the substrate, or the etching roughness will be emphasized and will not be smooth.

In this lateral growth, for example, if a periodic multilayer heterojunction is formed, it can function as a DBR reflector. For example, the active layer (see 104 in FIG. 1) is a rectangular buried heterostructure having a width of 1.5 μm and a length of 0.7 μm, and is processed so as to have a resonator length of 10 μm.
When the surface is selectively grown in the lateral direction with a mask made of a dielectric film such as SiO ₂ , the structure shown in FIG. 1 is obtained. Then, (see 107 in FIG. 1 (b)) a layer grown on the substrate bottom surface kept sufficiently taking etch height as negligible. Also, when growing in the lateral direction, as shown in FIG.
Since the growth occurs above the plane 02 and it is difficult to form a planar structure, the mask 402 is previously configured to overhang on both sides as shown in FIG. Such a shape can be formed by using wet etching together. In FIG. 3, reference numeral 301 denotes a region formed by etching, 302 denotes a selection mask, 303 denotes a layer laterally grown, 304 denotes a waveguide layer, and in FIG. 4, 401 denotes a region formed by etching and 402 denotes a region. Selection mask, 4
03 is a laterally grown layer, and 404 is a waveguide layer.

In the case of a 1.55 μm wavelength band in an InP system, the multilayer hetero layer may be grown so that InP / InGaAsP (bandgap wavelength λg = 1.3 μm) is periodically formed at a pitch of 240 nm.

With such a configuration, in a short cavity laser, since the reflectance is large and the leakage current is small, a laser having a low threshold value and performing single longitudinal mode oscillation can be provided. By integrating a large number of such optical elements on the same substrate, it is possible to provide an optical communication element, an optical information processing element, and the like, which are easy to mount.

In such a short-cavity laser, the sectional shape of the waveguide can be freely set. Forming a shape close to a square as shown in FIG. 1 is advantageous when coupling to another optical element such as an optical fiber because the emission angle of the laser is small and the beam shape is close to a circle. Also, since the difference between the confinement coefficients of the two polarization modes of the waveguide, TE mode and TM mode, is small, the wavelength difference and gain difference between the two modes are small. Therefore, when functioning as an optical amplifier, the amplifier can operate as a polarization-independent amplifier having a small gain difference with respect to polarization. When functioning as a laser,
It can be operated as an optical bistable element that can switch between two polarization modes. In this case, when a DBR reflecting mirror having a periodic hetero structure is provided, the absence of polarization dependence of the reflectivity at the end face has an advantageous effect on polarization switching. For a waveguide having a shape close to a square, it is difficult to reduce the threshold value because the current injection efficiency of a long-cavity laser is reduced. Therefore, a short-cavity laser using lateral growth as in the present invention should be used. Thus, it is possible to realize a lower threshold value while using a waveguide close to a square.

Means and actions for achieving the object corresponding to each claim are summarized as follows. 1) CBE
By performing the growth under the conditions as described above by law, while smoothing the end surface formed by etching, it is growing a layer in the lateral direction having a periodic heterostructure Chi lifting the optical waveguide and substantially vertical surface . That is, the optical semiconductor device that achieves the object of 1) is an optical waveguide having an end face formed by etching, and an optical waveguide formed by lateral crystal growth on the end face of the optical waveguide formed by etching, which is substantially perpendicular to the optical waveguide. Reflector region having a periodic heterostructure having a smooth surface
And current can be independently injected into the active layer and the reflector area
It has a mechanism .

[0014]

2 ) having a laser active layer in the optical waveguide portion,
If a periodic heterostructure is formed by smooth lateral growth as in 1 ), the laser can oscillate as a distributed reflection laser.
That is, in the optical semiconductor device that achieves the object 2 ), the optical waveguide has a gain with respect to light, the periodic heterostructure functions as a distributed reflector, and can oscillate as a distributed reflective laser. Features . If the Bragg wavelength is changed by injecting a current into this periodic heterostructure, the oscillation wavelength of the distributed reflection laser can be changed.

3 ) If a configuration is adopted in which a current is injected into the above-mentioned periodic heterostructure to give a gain to light, a single longitudinal mode oscillation is possible as a gain-coupled distributed feedback laser.

[0017]

[0018]

[0019]

[0020]

[0021]

[0022]

[0023]

[0024]

[0025]

[0026]

[0027]

4 ) Stable and smooth crystal growth can be performed stably by defining the plane orientation in which the lateral growth is performed on the end face as described above, and a selective mask is projected from the end face to improve the lateral growth.
Control the vertical growth of
Wear. That is, the manufacture of the optical semiconductor device which achieves the object of 4).
The method is such that, on the end face of the optical waveguide formed by etching,
By the crystal growth in the lateral direction, the optical waveguide is substantially perpendicular and flat.
The method of forming a layer having a smooth surface is based on a dielectric selection method.
Disk from the end face of the optical waveguide for crystal growth.
Thus, the growth in the vertical direction during the crystal growth in the horizontal direction is suppressed.
Control .

[0029]

[0030]

[0031]

[0032]

[0033]

[0034]

[0035]

[0036]

[0037]

[0038]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment A first embodiment according to the present invention will be described. FIG. 1A is a sectional perspective view of a substrate horizontal emission type short cavity DBR laser according to the present invention. In this figure, a part of the substrate and the lower electrode are omitted. FIG. 1B is a sectional view taken along line AA ′ of FIG.
(C) also shows a BB ′ cross-sectional view.

In these laser structure diagrams, reference numeral 105 denotes nI
An nP substrate 104 is a well layer i-In _0.28Ga_0.72As
(Thickness 10 nm) and barrier layer i-In Ga AsP (λg
= 1.15 μm, thickness 15 nm) and a pair of S layers
CH layer i-In Ga AsP (λg = 1.15 μm, thickness
200 nm) multiple quantum well (MQW) structure
Layer 103 is p-In P clad layer, 102 is p-I
n_0.53Ga_0.47As contact layer, 109 is high resistance In
P buried layer, 101 is a p-side electrode Cr / AuZ
An nNi / Au layer 108 is AuGeN which is an n-side electrode.
i / Au layer. 106 is undoped InP
(Thickness: 120 nm) / InGaAsP (λg = 1.3 μm)
m, 120 nm thick) were grown in 20 pairs in the lateral direction.
It is a BR reflector. Reference numeral 07 denotes a component of the DBR reflecting mirror 106.
It is a layer grown simultaneously on the surface of the substrate 105 when it is long,
It is a layer that has no functional relationship.

The active layer 104 is a structure having a tensile strain to the well layer, TM mode and the gain spectrum and the wavelength of the gain peak of TE mode substantially equal, the wavelength of 1.5
At 5 μm, the Bragg wavelength determined by the DBR reflector 106 is set at 1.55 μm. However, in the case of a short resonator as in the present embodiment, the oscillation wavelength greatly depends on the length of the resonator. In the present structure, the thickness of the active layer 104 is about 0.7 μm, the stripe width when the buried structure is about 1.5 μm, and there is almost no difference in the effective refractive index between the TE mode and the TM mode. Have almost the same oscillation wavelength. In addition, since the emission angle of the guided light is about 15 degrees in both width and height at half width, the light reflected by the DBR reflector 106 is sufficiently coupled to the active layer 104.

A brief description will be made on a method of manufacturing the present apparatus. n-I
A buffer layer (not shown), an active layer 10
4, CB in the order of the cladding layer 103 and the contact layer 102
It grows by E method. Next, the <0-11> direction with a width of 2 μm
SiO in the direction of the stripe_TwoForm a mask and RIBE
Etching to the n-InP substrate 105 by M
OCVD (metal-organized chem)
ical vapor deposition) method
A high resistance buried layer 109 is grown, as shown in FIG.
State. After removing the mask, the stripe and 90 degrees
In the rotated <011> direction, a stripe shape with a width of 15 μm
New SiO_TwoA mask is formed and similarly etched by RIBE.
Switch. The etching depth is the same when
Sometimes, the layer 107 growing on the bottom surface of the substrate 105 prevents light emission.
The thickness is set to be as deep as about 6 μm so as not to be disturbed. Ma
To make the overhang of the disk, make InP HCl aqueous solution
In the liquid, In Ga As and In Ga AsP to H_TwoSO_Four+
H_TwoO_Two+ H_TwoPerform wet etching with O mixed solution,
Side etching is caused by about 2 μm (see FIG. 4).
(See step 402). Therefore, the actual resonator length is about 11 μm (1
5-2 × 2). When lateral growth is performed in this state,
The growth layer above the contact layer 102 is not
4 (see the growth layer 403). This
Is grown by the CBE method at a substrate temperature of 550 ° C. and V / III.
The ratio is about 2, and the growth rate is about 0.6 μm / hour.
P / In Ga AsP multi-layer growth shows smooth surface
It functions as the DBR reflecting mirror 106. In addition, smooth
The same applies to the single layer of InP and the heterostructure as described above.
You can do it. Therefore, first, a smooth surface with a single layer of InP
Then, multi-layer growth may be performed.

The electrode 10 is formed on the entire surface of the n-InP substrate 105 side.
8 and the electrode 101 is formed only in the resonator region on the p side.
The orientation of the stripe is the same as the direction described above (<011>
Direction) and a direction rotated by 90 degrees is also possible. Although a short resonator is used for lowering the threshold value, the stripe width (in the <0-11> direction in FIG. 1A) is increased in the growth of CBE.
, There is almost no dependence, and the length of the resonator for lateral growth can be freely selected, and may be several hundred μm or the like.

Next, the operating characteristics of the device according to the present invention will be described. FIG. 5 shows current-light output characteristics. Threshold is room temperature C
It is about 1 mA in W operation. In this embodiment, as described above, the gains of the TE mode and the TM mode are designed to be substantially equal, and the polarization is switched midway as shown in FIG. Hysteresis having a width of 2 mA centered at about 15 mA is observed, indicating that bistable operation is possible. Therefore, it is possible to switch polarization by current pulse or polarization by injection of light pulse.

[0044] For example, the bias current I _B is fixed to 15 mA, when the applied digital signal △ I amplitude 4mA, it is polarization modulated in TE / TM. FIG. 6 shows the time waveform at this time. 1) is a modulation current waveform, 2) is laser output light, 3) is TM-polarized light (emitted when the modulation current is 17 mA), and 4) is TE-polarized light (modulation current is 13).
(emitted at mA). As shown in FIG. 5, the laser output light does not change significantly due to the modulation.
It can be seen that after the polarization separation, they are modulated in opposite phases. At this time, the modulation band was DC to 10 GHz. When transmitting this modulated light, for example, a polarizer may be placed on the laser emission end face, and either the TE mode or the TM mode may be selected and extracted as intensity modulated light. At this time, dynamic fluctuation of the oscillation wavelength, that is, chirping is 0.0
It was 1 nm or less.

In this embodiment, it is possible to provide a laser which can perform high-efficiency and high-speed modulation at a low threshold value and has low chirping. This laser is suitable for constructing a low-cost wavelength multiplexing optical LAN system.

Here, the active layer is a multiple quantum well having tensile strain (amount of strain: about -1%) for efficient polarization switching, but may be an active layer having a single crystal composition.
Also, by controlling the amount of distortion and controlling the gain difference between the TE mode and the TM mode, the polarization switching point can be set freely. Furthermore, by making the gain of either polarization mode superior, laser oscillation in a single polarization mode is of course also possible.

Although a DBR reflecting mirror is manufactured by lateral growth, a Fabry-Perot laser may be formed by performing only smoothing with a single crystal composition. In both the DBR type and the Fabry-Perot type, when the HR (High Reflection) coating with a dielectric multilayer film, a metal thin film, or the like is applied to the end face, the threshold value can be further reduced.

Second Embodiment In the first embodiment, after the buried growth of the laser waveguide (see the buried layer 109 in FIG. 1) is performed, D by lateral growth is obtained.
Although a BR reflector was manufactured, the steps are reversed in this embodiment.

That is, a stripe pattern having a width of 15 μm is formed, and a DBR reflector is formed by lateral growth.
All the portions not embedded and grown including the DBR side surfaces are masked and etched down to the substrate, and the stripe width is about 2 μm.
Buried growth. As the active layer, a tensile strained MQW structure having a total thickness of about 0.7 μm is used for the purpose of polarization switching as in the first embodiment, but another structure may be used.

The pn junction of the DBR reflector may be formed in the direction perpendicular to the substrate as in the first embodiment, or may be formed in the direction horizontal to the substrate 701 as shown in FIG. At this time, a semi-insulating InP substrate 701 is used, and all the growth layers are grown non-doped. One of the buried layers 704 and 705 diffuses Zn to form a p-electrode 7
06 and the other is diffused with Si to form an n-electrode 707. Thus, current flows in the lateral direction. Active area 702
And Zn so that current can be independently injected into the DBR region 703.
If the diffusion region 704 and the electrode 706 are separated, wavelength tuning can be performed. In order to increase the separation resistance, a buried layer between the separation electrodes may be etched to form a separation groove having a width of about 2 μm.

In this configuration, the confinement of light at the DBR reflecting mirror 703 is also stronger than in the first embodiment, so that the reflectance increases and the threshold value can be lowered.

The operation characteristics of the present apparatus will be described. Active area 70
FIG. 8 shows the oscillation characteristics when the current injected into the DBR region 2 is I ₁ and the current injected into the DBR region 703 is I ₂ . FIG.
(A) is a figure of a contour display of an optical output. Increasing the I _2, the threshold of laser oscillation is increased for I ₁ and the amount of detuning increases from the effective refractive index is changed by the gain peak emission wavelength is shifted to the short-wave. I ₁ = 1
It can be seen that the polarization switching occurs around 5 mA. Hysteresis exists near this as in the first embodiment. On the other hand, FIG. 8B shows the oscillation wavelength characteristics. It can be seen that the wavelength shifts to a short wave with an increase in I ₂ , and a tune of several nm can be achieved. When the polarization switches, there is a slight wavelength jump due to the difference in effective index of refraction (approximately 0. 0).
1 nm). Note that the resonator length is short (about 10
μm), the longitudinal mode interval as a Fabry-Perot resonator is about 38 nm, and a wavelength tune without a wavelength jump can be performed.

In the first embodiment, oscillation is performed only at a fixed wavelength in the oscillation mode determined by the short resonator. However, in this device, variable wavelength and polarization modulation can be realized simultaneously.

Third Embodiment Up to now, the laterally grown layer functions as a DBR reflector having no gain, but a DFB laser may be provided with a gain. The structure is, for example, an entirely embedded type as shown in FIG. The lateral growth layer is made of undoped InP / InGaAs.
If a multilayer structure of P (λg = 1.55 μm) is used, a current of I ₂ will flow to have a periodic gain, and a DFB laser of a gain coupling type will be obtained. A portion having a cavity length of about 10 μm (a portion 702 in FIG. 7) serving as a source of lateral growth has a role of assisting the gain, but can oscillate as a DFB laser without the active layer in this portion.

Further, in order to strengthen the light confinement, FIG.
Structure 9 in which the entire upper side of the 2 μm stripe is buried as shown in FIG.
04. In FIG. 9, reference numeral 901 denotes a substrate;
2 is an active layer, 903 is a cladding layer, 905 is a p-type buried region formed by Zn diffusion, 906 is an n-type buried region formed by Si diffusion, 907 is a periodic hetero layer of a lateral growth layer, 908 is a p electrode, 909 is an n-electrode. Also in the configuration of FIG. 9, the polarization switching and the wavelength tunable can be achieved simultaneously as in the second embodiment. In this embodiment, the gain coupling DFB
By the laser, particularly the return light without oscillation mode is disturbed, it can provide a narrow oscillation scan Bae spectrum linewidth.

Fourth Embodiment Although the operation as a laser device has been described in the previous embodiments, it has almost the same structure as the first to third embodiments and operates as an optical wavelength filter or an optical amplifier. You can also.

In the case of the DBR type, it operates as a wavelength variable filter. Taking the laser of the second embodiment in FIG. 7 as an example,
A bias current is caused to flow immediately before oscillation at about I ₁ = 1 mA, and the selected wavelength is set at I ₂ . When light is incident from the outside, it has transmission characteristics as shown in FIG. It can be seen that the transmission gain is as narrow as 1 nm and the transmission gain is about 10 dB. Wavelength tunable range is several nm as in the second embodiment, so that the status at the same time the threshold immediately before changing the selected wavelength, can wavelength tuning while the transmission gain constant by adjusting the I _1.

In this apparatus, the difference in effective refractive index between the TE mode and the TM mode is small, and the difference in Bragg wavelength is 0.1 mm. Since it is less than 1 nm and the difference in gain between the two modes is reduced by introducing tensile strain into the active layer, the optical filter operates as a polarization-independent optical filter. Therefore, it is effective as a receiving filter for high-density wavelength division multiplexing transmission.

In order to realize a Fabry-Perot laser structure by performing only smoothing with a single crystal composition, the lateral growth layer is formed by DBR.
With a structure without a reflecting mirror, it can operate as a polarization-independent optical amplifier.

Fifth Embodiment FIG. 11 shows an optical-electrical converter (node) connected to each terminal when polarization-modulated optical transmission using a semiconductor laser according to the present invention is applied to a wavelength division multiplexing optical LAN system. FIG. 12 shows a configuration example of an optical LAN system using the node.

Using the optical fiber 1101 connected to each unit as a medium, an optical signal is taken into a node,
Part of the light enters the receiving device 1103 provided with the tunable filter according to the present invention. With this receiver, only an optical signal of a desired wavelength is extracted and signal detection is performed. On the other hand, when transmitting an optical signal from a node, the wavelength tunable DFB laser or the wavelength tunable DFB
The laser 1104 is polarization-modulated, and the light converted into intensity modulation by the polarizer 1105 is transmitted through the branching unit 1107 to the optical transmission line 1.
101. At this time, an isolator (not shown) may be inserted to avoid the influence of the return light to the laser. In the device according to the invention, these optical nodes can be integrated on a single substrate. The waveguides connecting the corner devices and the branch portions 1102 and 1106 may be made of a semiconductor, or may be made of an organic waveguide (such as polyimide). As the polarizer 1105, a waveguide type can be integrated.

In some cases, only a single wavelength needs to be transmitted, depending on the terminal. In this case, the D in the first embodiment is used.
A BR laser or the like is used. Conversely, if it is necessary to further widen the wavelength tunable range, a plurality of wavelength tunable lasers may be provided. In addition, since the laser and the filter can have the same structure, both transmission and reception operations can be performed by only one device according to the present invention.

As a network of the optical LAN system,
FIG. 12 shows a bus type in which nodes are connected in directions A and B, and a large number of networked terminals and centers can be installed. However, in order to connect a large number of nodes, it is necessary to install an optical amplifier in series on the transmission line 1101 in order to compensate for optical attenuation.

In the polarization modulation according to the present invention, as described in the first embodiment, the wavelength fluctuation at the time of the modulation is 0.001 nm or less, and the transmission half-value width of the filter is about 0. Since it is 1 nm, when the wavelength variable width is 3 nm, an optical network system by high-density wavelength division multiplexing transmission of 3 / 0.1 = 30 channels can be constructed.

As a form of the network, FIG.
It may be a loop type connecting A and B, a star type, or a combination of them.

Sixth Embodiment In this embodiment, a short resonator type polarization modulation DBR according to the present invention is used.
The laser is monolithically integrated and used as an optical information processing device.

The TE / TM switching shows a bistable characteristic as shown in FIG. That is, the polarization is switched by a current pulse or light incidence when fixing the injection current to the center I _B of the bistable point. For current pulses,
When a negative pulse is given at an amplitude number mA, the signal is switched to TE, and when a positive pulse is given, the signal is switched to TM. However, if the original state is the same, the switch is naturally not switched (that is, for example, TM
Even if a positive pulse is applied to the oscillation state, the state remains in the TM oscillation state). On the other hand, in the case of light incidence, when light in a polarization mode different from the oscillating polarization mode is incident, the light is switched to the same polarization mode as the incident light. FIG. 13 shows these timing charts.

Therefore, as shown in FIG. 14, the short-cavity polarization-modulated DBR lasers according to the present invention are integrated in parallel and in series to function as an ultra-high-speed optical information processing device. FIG.
In 140, 1401 is a substrate, 1402 is a periodic hetero layer grown in the lateral direction, 1403 is an active layer, 1404 is an electrode, and 1405 is an electrode separation part. The switching response time in light injection is about 10 psec, and the switching response time in current injection is about 100 psec.

If an optical amplifier is integrated at the output end, it can be used as a light source for optical communication by coupling to an optical fiber. Further, if the polarization splitting waveguide is integrated to divide the TE / TM mode light, the degree of freedom when constructing the optical interconnection is further increased. When the DBR laser according to the present invention is used, D
If the Bragg wavelength of the BR is tuned, ON / OFF of light injection into the DBR laser can be controlled by the same principle as that of the optical filter.

The integration in the serial direction is easier than in the case of constructing an optical information processing apparatus using a VCSEL.

[0071]

As described above, the present invention has the following effects corresponding to the claims. According to 1 ), in a horizontal substrate type optical semiconductor device, it is possible to provide a structure having a smooth surface perpendicular to the optical waveguide and having improved reflectivity at the end face of the optical waveguide formed by etching. According to 2 ), a distributed reflection laser capable of oscillating in a single longitudinal mode can be provided with the optical semiconductor device having the structure as in 1 ). 3)
If an optical semiconductor device having the structure shown in 1) is used,
The present invention can provide a distributed feedback laser capable of laser oscillation. 4)
In this case, a structure having a smooth surface perpendicular to the optical waveguide described above
A manufacturing method of the structure can be provided .

[Brief description of the drawings]

FIG. 1 is a sectional perspective view of a short cavity DBR laser according to a first embodiment of the present invention, and a sectional view in a resonance direction and a lateral direction.

FIG. 2 is a view for explaining that an end face becomes smooth by lateral growth.

FIG. 3 is a view for explaining that vertical growth occurs simultaneously with horizontal growth depending on a method of forming a mask.

FIG. 4 is a view for explaining suppression of vertical growth by overhang of a selection mask;

FIG. 5 is a diagram illustrating a bistable operation of polarization switching.

FIG. 6 is a diagram illustrating a modulation signal and a polarization modulation waveform.

FIG. 7 is a perspective view of a lateral injection type tunable DBR laser according to a second embodiment of the present invention.

FIG. 8 is a diagram showing the oscillation characteristics of a tunable DBR laser.

FIG. 9 is a sectional perspective view of a lateral injection type DFB laser having an entire buried structure according to a third embodiment of the present invention.

FIG. 10 is a diagram showing transmission characteristics of the wavelength tunable filter according to the present invention.

FIG. 11 is a block diagram of an optical node according to a fifth embodiment of the present invention.

FIG. 12 is a diagram illustrating a configuration of an optical LAN system according to a fifth embodiment.

FIG. 13 is a view for explaining a timing chart when a polarization switch is performed by a current pulse or an optical pulse in a sixth embodiment according to the present invention.

FIG. 14 is a diagram showing an integrated optical information processing apparatus according to a sixth embodiment of the present invention.

FIG. 15 is a diagram showing a conventional example of a substrate horizontal short-cavity DBR laser.

[Explanation of symbols]

1, 105, 701, 901, 1401 Substrate 2, 4, 103, 903 Cladding layer 3, 104, 902, 1403 Active layer 102 Contact layer 101, 108, 706, 707, 908, 909, 1
404 Electrode 109, 904 Buried layer 106, 703, 907, 1402 Periodic hetero layer 107 grown laterally Layers 201, 301, 401, 702 grown simultaneously during lateral growth Regions 202, 304, 404 formed by etching Wave layers 203, 303, 403 Layers 302, 402 grown laterally Selection mask 704, 905 P-type buried region formed by Zn diffusion 705, 906 N-type buried region formed by Si diffusion 1101 Optical fiber (optical transmission line) 1102; 1106 Optical power divider (branching unit) 1103 Optical receiving device consisting of optical filter and photodetector 1104 Polarizable switchable laser 1105 Polarizer 1405 Electrode separating unit

Claims (4)

(57) [Claims] 1. An optical semiconductor device, comprising: an optical waveguide having an end face formed by etching and including an active layer;
A reflecting mirror region having a periodic heterostructure formed by lateral crystal growth on the end face of the optical waveguide, and having a mechanism capable of independently injecting current into the active layer and the reflecting mirror region. Optical semiconductor device. 2. The optical waveguide according to claim 1, wherein said optical waveguide has a gain with respect to light, and said periodic heterostructure functions as a distributed reflection mirror and can oscillate as a distributed reflection laser. Optical semiconductor device. 3. The device according to claim 1, wherein said periodic heterostructure portion is configured to have a gain with respect to light by injecting current, and can oscillate as a distributed feedback laser. Optical semiconductor device. 4. A step of forming a waveguide including an active layer by etching, a step of forming a reflector region having a periodic heterostructure on an end face of the optical waveguide by lateral crystal growth, Forming a mechanism capable of independently injecting current into the reflecting mirror region, wherein the step of forming the reflecting mirror region includes the step of forming a mask protruding from the end face of the optical waveguide on the optical waveguide. After forming
A method of manufacturing an optical semiconductor device, wherein the method is performed while suppressing vertical growth during the horizontal crystal growth.