JPH0766487A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To use a semiconductor laser device as a coherent light source for optical FDMs by largely changing the oscillation wavelength of the laser device at high speed. CONSTITUTION:A semiconductor laser device is provided with an ntype InGaAsP clad layer 2 which is formed on an n-type InP substrate, has a coefficient of thermal conductivity smaller than the substrate 1 has, and has a projecting section, strained quantum well active/optical waveguide layer 4 which is formed on the projecting section of the layer 2 and works as a light emitting layer and optical waveguide layer, p-type InP clad layer 5 which is formed on the layer 4, holds the layer 4 together with the layer 2, and has a width narrower than that of the substrate 1, and diffraction grating which is provided in the waveguide of the laser light generated from the layer 4 and works as a distributed feedback resonator.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device, and more particularly to a semiconductor laser device capable of varying an oscillation wavelength.

[0002]

2. Description of the Related Art Conventionally, research and development of optical communication technology have been actively conducted. This is because optical signal transmission is superior to electrical signal transmission in terms of transmission speed and interference between signals. Under these circumstances, an optical frequency division multiplexing system (optical FDM) has been receiving attention in recent years. This is an optical FDM
Can be applied to various fields such as large-capacity optical communication systems, optical interconnection, optical switching, and optical computing.

By the way, as a coherent light source for optical FDM, a compact, reliable, electrically tunable semiconductor laser device is being developed. In order to realize a large capacity optical FDM, it is necessary to develop a semiconductor laser device having a wide wavelength variable range.

Further, in order to multiplex a large number of frequency channels with high density within a predetermined wavelength range, it is necessary to narrow the frequency range occupied by each channel, that is, narrow the oscillation wavelength spectrum width. is necessary. In particular, in a promising coherent optical transmission system for optical FDM, an extremely narrow linewidth light source is required to obtain a received signal due to interference between signal light and local oscillation light.

Wavelength tunable semiconductor laser devices currently being studied are (1) multi-electrode distributed Bragg reflection (DBR) semiconductor laser device (2) twin guide type semiconductor laser device (3) super-periodic structure type or mode interference type Semiconductor laser device (4) Temperature control type semiconductor laser device (5) Multi-electrode distributed feedback (DFB) semiconductor laser device

In the multi-electrode DBR semiconductor laser device of (1), carriers are injected into the Bragg reflection region to largely change the Bragg wavelength. However, although the wavelength tunable range is wide, since carriers are injected into the passive Bragg waveguide, the oscillation line width increases to 10 MHz or more due to internal carrier density fluctuations, making it difficult to apply to coherent optical transmission. Is. Moreover, since the wavelength changes while jumping among many modes, the wavelength range that can be continuously changed is small. Furthermore, since multiple modes are used, in order to switch to any wavelength, instead of simply controlling the reference value of the feedback loop, adjust the current flowing through each electrode to the set value stored in memory in advance. It was necessary to take the method of. Therefore, the wavelength switching speed is limited by the processing speed. In addition, even if the relationship between the oscillation wavelength and the stored set value deviates even a little, it becomes inoperable, and therefore, stricter stability of current vs. wavelength and reliability are required as compared with the conventional case.

The twin guide type semiconductor laser device of (2) independently controls the currents flowing through the active layer and the optical waveguide layer which are laminated in close proximity to each other. It can be considered that the region is divided in the layer direction instead of dividing the region in the multi-electrode DBR semiconductor laser device, and the operation mode is similar to that of the multi-electrode DBR semiconductor laser device. However, even in this case, it is difficult to apply the twin guide type laser device to the coherent optical transmission because of the limitation of the oscillation spectrum line width.

The super periodic structure type or mode interference type semiconductor laser device of (3) is, for example, a sampled grating.
Type, super structure garting (SSG) type, vertical
Although there is a coupled grating (VCF) type or the like, it is difficult to apply this type of semiconductor laser device to coherent optical transmission due to the limitation of the oscillation spectrum line width during wavelength tuning operation.

The temperature controlled semiconductor laser device of (4) is
A heating means is provided near the active region so that the temperature of the active layer can be raised. In general, by raising the temperature of the active layer, the oscillation wavelength can be shifted to the longer side (red shift), and the oscillation wavelength can be largely changed while maintaining the narrow line width. However, if the oscillation wavelength is greatly changed, the time until the oscillation wavelength stabilizes becomes long, which is several milliseconds. Therefore, it is difficult to use it for switching the channels of the optical FDM at high speed such as an optical LAN.

In the multi-electrode DFB semiconductor laser device of (5), the DFB semiconductor laser device is divided into a plurality of regions in the cavity direction, the carrier density distribution and the temperature distribution are changed, and the oscillation wavelength is changed. .

FIG. 6 shows a schematic structure of a three-electrode DFB semiconductor laser device as an example of a multi-electrode DFB semiconductor laser device. In the figure, 51 indicates an n-type InP substrate, and an n-type InP clad layer 53 is formed on the n-type InP substrate 51.
Are formed. A striped strained quantum well active / optical waveguide layer 54 having a width of about 1 μm is formed on the narrowed portion of the n-type InP cladding layer 53. Also,
The thinned portion of the n-type InP clad layer 53 is a p-type I
It is embedded by the nP layer 57 and the n-type InP layer 58.

A p-type InP clad layer 55 and a p-type InGaAsP ohmic contact layer 56 are sequentially formed on the strained quantum well active / optical waveguide layer 54. A p-side ohmic electrode 59 is provided on the p-type InP clad layer 56,
An n-side ohmic electrode 60 is provided on the n-type InP substrate 51.

Although not shown, p-type InGa
The AsP ohmic contact layer 56 and the p-side ohmic electrode 59 are separated into three regions, that is, a central portion and both end portions, so that a current can flow independently in each region. Furthermore, a single-mode DFB oscillation is realized by a first-order diffraction grating (not shown) formed on the strained quantum well active / optical waveguide layer 54.

According to the three-electrode DFB semiconductor laser device configured as described above, the current is increased by increasing the current while balancing the currents flowing in the three regions so as to maintain the single-mode oscillation state. As the temperature in the vicinity of the strained quantum well active / optical waveguide layer 54 rises, a red shift of several nm can be caused. Moreover, since the entire region is active, the carrier density fluctuation during current injection is small and a narrow line width can be realized.

However, since the response speed of the thermal effect is slow as it is, if this semiconductor laser device is used in an optical FDM system in which a large number of wavelength channels are switched at high speed, the time required for wavelength switching is long, which is extremely high. There is a problem that the system becomes inefficient.

[0016]

As described above, various wavelength tunable semiconductor laser devices have been conceived and their performances have been recognized, but their drawbacks become remarkable, and coherent for optical FDM. There is no favorite light source.

The present invention has been made in consideration of the above circumstances, and a problem to be solved by the invention is a semiconductor laser device capable of changing the oscillation wavelength at a high speed and greatly and being usable as a coherent light source for an optical FDM. To provide.

[0018]

In order to achieve the above object, a semiconductor laser device of the present invention (claim 1) is provided on a substrate, has a thermal conductivity smaller than that of the substrate, and has a convex shape. A first clad layer, an active layer provided on the convex portion of the first clad layer and serving as a light emitting layer and an optical waveguide layer, and provided on the active layer, the active layer together with the first clad layer. A second clad layer sandwiching the layer and a diffraction grating provided as a waveguide of the laser light generated in the active layer and functioning as a distributed feedback resonator are provided.

Here, the thermal conductivity of the substrate is K _s [w /
(M · K)], the thermal conductivity of the first cladding layer is K ₁
[W / (m · K)], its thickness is d ₁ [m], the second
Where W [m] is the width of the clad layer and h [m] is the height above the first clad layer, 1.5 × 10 ¹¹ · h <K ₁ / d ₁ <K _s / It is preferable to satisfy (2W) ... (I).

In order to achieve the above object, the following semiconductor laser device of another invention may be used. That is, a heat flow delay layer provided on the substrate and having a smaller thermal conductivity than the substrate, and a heat flow delay layer provided on the heat flow delay layer, having a larger thermal conductivity than the heat flow delay layer, and having a width wider than that of the heat flow delay layer. Of the first clad layer, an active layer provided on the first clad layer and serving as a light emitting layer and an optical waveguide layer, and an active layer provided on the active layer together with the first clad layer. It is also possible to use a semiconductor laser device including a second clad layer that holds the laser beam and a diffraction grating that is provided in the waveguide of the laser light generated in the active layer and that functions as a distributed feedback resonator.

Here, the thermal conductivity of the substrate is K _s [w /
(M · K)], and the thermal conductivity of the heat flow delay layer is K ₀ [w / (m
K)], its thickness is d ₀ [m], the width of the first cladding layer is W [m], and the height above the heat flow delay layer is h.
When it is [m], it is preferable that 1.5 × 10 ¹¹ · h <K ₀ / d ₀ <K _s / (2W) ... (II) is satisfied.

[0022]

According to the present invention (claim 1), since the thermal conductivity of the first cladding layer is smaller than that of the substrate, when current is injected into the active layer and the active layer generates heat, the active layer causes the substrate to flow. Heat flow to and from is blocked by the first cladding layer. Therefore, the temperature of the active layer rises due to the heat accumulated in the first cladding layer and the upper portion thereof. Moreover, the active layer and the second
Since the clad layer has a narrow width, its heat capacity is small. Therefore, the temperature of the active layer can be greatly changed in a short time,
The oscillation wavelength can be greatly changed in a short time.

According to another aspect of the present invention, since the thermal conductivity of the heat flow delay layer is smaller than that of the substrate and the first cladding layer, when current is injected into the active layer and the active layer generates heat, the active layer is activated. Heat flow from the layer to the substrate is impeded by the heat flow retardation layer. Therefore, the temperature of the active layer rises due to the heat accumulated in the heat flow delay layer. Moreover, since the width above the first clad layer is smaller than that of the substrate, the heat capacity is small. Therefore, the temperature of the active layer can be largely changed in a short time, and the oscillation wavelength can be largely changed in a short time.

The inequality sign on the left side of the formulas (I) and (II) is
The condition that the time constant is sufficiently small (<< 10 μs), and the inequality sign on the right is the condition that the temperature difference between the first cladding layer and the heat flow delay layer, which have low thermal conductivity, is sufficiently larger than the temperature difference of the substrate. It is shown in.

[0025]

Embodiments will be described below with reference to the drawings. 1 and 2 are sectional views showing a schematic configuration of a three-electrode DFB semiconductor laser device according to a first embodiment of the present invention, and FIG. 1 is a sectional view perpendicular to a stripe direction of an active layer, FIG. 2 shows a sectional view parallel to the stripe direction of the active layer.

In the figure, 1 indicates an n-type InP substrate,
On this n-type InP substrate 1, as shown in FIG. 1, an n-type InGaAsP cladding layer 2, a p-type InP layer 7, and an n-type I
nP layer 8, p-type InP clad layer 5 and p-type InGa
Consists of AsP ohmic contact layer 6 with a width of about 7μ
m mesa portions 12 are formed.

The upper portion of the n-type InGaAsP cladding layer 2 is finely processed. Specifically, the thickness is 3.5
μm, of which 0.5 μm in the upper part is processed to have a width of 1 μm, which is the same as the active layer 4. Also, InGaAsP
The composition ratio of is such that the band gap corresponds to a wavelength of 1.05 μm.

On the narrowed portion of the n-type InGaAsP cladding layer 2, a strained quantum well active / optical waveguide layer 4 having a width of 1 μm is formed. In addition, n-type I
The thinned portion of the nGaAsP cladding layer 2 is a p-type I
It is embedded by the nP layer 7 and the n-type InP layer 8.

Here, the reason why the strained quantum well structure is introduced into the active layer is that it lowers the oscillation threshold and improves the temperature characteristics, so that the adverse effect due to the rise in the temperature of the active layer during normal operation is exerted. This is to reduce. Note that a simple quantum well structure may be used instead of the strained quantum well structure.

The strained quantum well active / optical waveguide layer 4 has a thickness of 1
A μ-type p-type InP clad layer 5 and a 0.5-μm-thick p-type InGaAsP ohmic contact layer 6 are sequentially formed. The p-type InGaAsP ohmic contact layer 6 is provided with a p-side ohmic electrode 9, and the n-type InP substrate 1 is provided with an n-side ohmic electrode 10. Although not shown in the drawing, a plateau is formed on both sides of the mesa portion 12 with a groove therebetween, and a bonding pad and a p-side ohmic electrode formed on the plateau via an insulating film. 9 is connected by bridge wiring. Here, the height of the mesa portion 12 is 5.2 μm.

Further, as shown in FIG. 2, p-type InGaA
sP ohmic contact layer 6 and p-side ohmic electrode 9
Are separated by a semi-insulating InP layer 16 into three regions, that is, a first current injection region 17 in the central portion and a second current injection region 18 and a third current injection region 19 at both ends.

On the strained quantum well active / optical waveguide layer 4,
A first-order diffraction grating 13 is formed. This diffraction grating 1
The Bragg wavelength of 3 is set near the gain peak wavelength of the laser. A phase (quarter wavelength) shift region 14 is formed in the center of the resonator of the diffraction grating 13.

Further, on both end faces formed by cleavage,
A low reflection film 15 made of SiNx and having a reflectance of 1% or less is coated. Therefore, the Fabry-Perot mode oscillation is suppressed, and stable single-mode oscillation with a spectral line width of 2 MHz or less is realized in a wide current setting range.
The dimensions of this semiconductor laser chip are about 1 mm in length, 300 μm in width and 80 μm in thickness. The length of the current injection region 17 in the central portion is about 400 μm, and the current injection regions 1 at both ends are
The lengths of 7 and 18 are both about 300 μm.

The semiconductor laser chip is fixed by AuSn solder on the metal heat sink 11 serving as a ground electrode. The metal heat sink 11 is controlled so as to be kept at a constant temperature by, for example, temperature control means including a temperature sensor and a Peltier element. Also,
Each electrode pad is connected to a power supply line formed on the ceramic substrate by bonding, and the currents at the central portion and both end portions can be independently controlled. These are mounted in a module together with a lens system, an optical isolator, a beam splitter, a frequency discrimination etalon, a monitor / photodiode, a drive control IC, a pigtail, and the like.

FIG. 3 is a diagram showing the thermal conductivity of III-V group semiconductor mixed crystals. In general, a semiconductor mixed crystal of ternary or higher has a much lower thermal conductivity than that of a binary mixed crystal. For example, In
The thermal conductivity of P is about 70 W / (m · K) at room temperature, while that of In _0.53 Ga _0.47 As is about 4 W / (m · K).
K) and an order of magnitude smaller. On the other hand, the difference due to the difference in the composition of the specific heat of these semiconductors is small.
It is 0 ⁶ J / (m ³ · K).

In the case of this embodiment, the n-type InGaAsP cladding layer 2 is made of a quaternary semiconductor mixed crystal, and its thermal conductivity is n.
The value is smaller than that of the InP substrate 1 and about 10 W / (m · K) or less.

Therefore, the strained quantum well active / optical waveguide layer 4
When a current is injected into the strained quantum well active / optical waveguide layer 4 to generate heat, the strained quantum well active / optical waveguide layer 4 passes through the n-type In
The heat flow to the P substrate 1 is blocked by the n-type InGaAsP cladding layer 2. As a result, the temperature of the mesa portion 12 including the strained quantum well active / optical waveguide layer 4 rises due to the heat accumulated in the n-type InGaAsP cladding layer 2 and the mesa portion 12 above it. Moreover, since the width of the mesa portion 12 is as narrow as about 7 μm and the height is as low as 5.2 μm, its heat capacity is small. That is, K _s = 70, K ₁ = 10, d ₁ = 3.5
× 10 ^-6 , W = 7 × 10 ^-6 , h = 5.2 × 10 ^-6 , which satisfies the formula (I).

Therefore, the temperature of the strained quantum well active / optical waveguide layer 4 can be largely changed in a short time, and the oscillation wavelength can be greatly changed in a short time. Hereinafter, the three-electrode DFB semiconductor laser device of the present embodiment will be described in more detail by comparing it with the operation of the related art shown in FIG.

FIG. 4 shows how the temperature of the active layer changes with time when the current flowing through the strained quantum well active / optical waveguide layers (hereinafter simply referred to as active layers) 4 and 54 is increased stepwise. Is.

Since the laser is processed into a mesa shape, the current rise time due to the parasitic CR limitation is about 1 nanosecond. The increase in the current causes a wavelength red shift through the increase in the refractive index due to the temperature increase in the optical waveguide region. Here, it is assumed that the main heat sources are the active layers 4 and 54. The change in refractive index due to temperature rise can be regarded as instantaneous compared to the rate of temperature change. The rate of wavelength change due to temperature rise in the optical waveguide region is about 0.1 nm / ° C.

In the figure, the characteristic curve a is the conventional three-electrode D of FIG.
The FB semiconductor laser device is shown, and it can be seen that it takes 200 μs until the temperature becomes constant and the time until the temperature changes by 90% is as long as 20 μs. For this reason, even if automatic frequency control (AFC) is applied, only control on the order of tens of microseconds is possible, and in an optical FDM system that accesses different frequency channels every tens of microseconds, about half is required for wavelength tuning. It will be dead time.

The characteristic curve b is the three-electrode DF of this embodiment.
B semiconductor laser device is shown, and the time until the temperature reaches a constant value is the same as that of the conventional example, but from 100 nsec to 1
It can be seen that the temperature greatly changes in the range of 0 μsec.

That is, although the time over which the temperature distribution of the entire substrate changes (several hundreds of microseconds) does not change much, the heat capacity is small, and the n-type InGaAsP cladding layer 2 causes the n-type I
It only takes about 10 microseconds for the temperature distribution of only the mesa portion 12 thermally separated from the nP substrate 1 to reach equilibrium. Also, the time until the temperature changes by 90% is as short as 8 μsec, and AFC of several μsec order is possible. Moreover,
The change in current for obtaining a predetermined change in wavelength is also small, and the change in carrier density that causes a change in wavelength in the opposite direction due to current injection can be suppressed small.

Therefore, according to this embodiment, the optical FDM that accesses different frequency channels every tens of microseconds.
In the system, the dead time can be reduced to 1/10 or less.

The characteristic curve c shows the case where an n-type InP clad layer is used instead of the n-type InGaAsP clad layer 2 in the semiconductor laser device having the same shape and size as this embodiment. In this case, a temperature change of the order of several microseconds appears, but the magnitude is much smaller than that of the present embodiment, and it can be seen that the effect cannot be expected. In this case, K
₁ = 70, which does not satisfy the right inequality sign of the formula (I).

The characteristic curve d is shown in FIG. 6 as the n-type InP cladding layer 53 of the conventional three-electrode DFB semiconductor laser device.
Instead of the above, the case where the same n-type InGaAsP cladding layer as in the present embodiment is used is shown. In this case, although the overall temperature rise is large due to the increase in the thermal resistance, it can be seen that the temperature change component having the time constant on the order of several microseconds does not appear because there is no mesa portion having a small heat capacity.

The characteristic curve e is the n-type InGaAsP
The case where the thickness of the cladding layer 2 is reduced from 3.5 μm to 1.5 μm (d = 1.5 × 10 ⁻⁶ ) is shown. In this case, although there is a time constant component on the order of several microseconds, it can be seen that such a large effect cannot be obtained. That is, in order to obtain the effect, n also has a function of delaying the heat flow flowing from the strained quantum well active / optical waveguide layer 4 to the n-type InP substrate 1.
It is necessary to make the type InGaAsP cladding layer 2 thick enough to satisfy the formula (I).

The characteristic curve f shows the case where the width of the mesa portion 12 is narrowed to 4 μm in this embodiment.
In this case, since the heat capacity of the mesa portion 12 is reduced, the effect of the present invention is further enhanced, and the time until the temperature of the active layer changes by 90% is 6 μsec. Thus, if the width of the mesa portion 12 is narrowed, the n-type In
The thickness of the GaAsP cladding layer 2 can be made thinner. However, if the mesa portion 12 is raised, the time required for the temperature change of the mesa portion 12 becomes longer.

FIG. 5 is a sectional view showing a schematic structure of a three-electrode DFB semiconductor laser device according to the second embodiment of the present invention. This corresponds to FIG. 1 and shows a sectional view perpendicular to the stripe direction of the active layer. In addition, 3-electrode DFB
Semiconductor laser device The parts corresponding to those in FIG. 1 are designated by the same reference numerals as those in FIG. 1, and detailed description thereof will be omitted.

In the first embodiment, the n-type InGaAsP clad layer 2 has the roles of both the clad layer and the heat flow delay layer, but in the present embodiment, these roles are provided in separate semiconductor layers. I have it.

That is, in this embodiment, n-type InGaA is used.
The one corresponding to the sP clad layer 2 is an n-type InGaAs mixed crystal semiconductor layer 3a (heat flow delay layer) having a thickness of 1.5 μm,
It is composed of an n-type InP clad layer 3b having a thickness of 1.5 μm. The n-type InGaAs mixed crystal semiconductor layer 3 a is not formed in the mesa portion 12 but is formed on the surface of the n-type InP substrate 1. Of course, the n-type InGaAs mixed crystal semiconductor layer 3a
The same effect can be obtained by providing the inside of the mesa portion 12. The width of the mesa portion 12 is 4 μm and the height is 3.2 μm.

According to the three-electrode DFB semiconductor laser device of this embodiment, the n-type InGaAs mixed crystal semiconductor layer 3a having a smaller thermal conductivity than the n-type InP substrate 1 and the n-type In cladding layer 3b is the n-type InP substrate. 1 and the n-type InP clad layer 3b, the strained quantum well activity /
When a current is injected into the optical waveguide layer 4 and the strained quantum well active / optical waveguide layer 4 generates heat, the heat flow from the strained quantum well active / optical waveguide layer 4 to the n-type InP substrate 1 is n-type InGaAs.
It is hindered by the mixed crystal semiconductor layer 3a.

Therefore, by the heat accumulated in the n-type InGaAsP mixed crystal semiconductor layer 3a and the mesa portion 12 above it,
The temperature of the mesa portion 12 including the strained quantum well active / optical waveguide layer 4 rises. Moreover, since the mesa portion 12 is narrower in width and smaller than the n-type InP substrate 1, the heat capacity of the mesa portion 12 is small. Therefore, the temperature of the strained quantum well active / optical waveguide layer 4 can be largely changed in a short time, and the oscillation wavelength can be largely changed in a short time.

The temperature response of the three-electrode DFB semiconductor laser device of this embodiment is shown by the characteristic curve g in FIG. n-type InGaA
Since the s mixed crystal semiconductor layer 3a has a low thermal conductivity of about 4 W / (m · K), the temperature is similar to that of the characteristic curve f (the width of the mesa portion 12 is narrow) even when the thickness is 1.5 μm. A response is obtained. This example satisfies the formula (II).

In this embodiment, an n-type I is used as the heat flow delay layer.
Although the nGaAs mixed crystal semiconductor layer 3a is used, one made of another material such as metal may be used. When a metal layer is used as the heat flow delay layer, for example, epitaxial lift-off is used.

That is, finally, a mesa portion is epitaxially grown on a semiconductor substrate different from the substrate holding the laser, and the mesa portion is peeled off by lift-off to remove a metal layer having a low thermal conductivity on the surface. High substrate (eg,
(Si, diamond, AlN, BN, Cu, etc.) are bonded and integrated to form the characteristic structure of the present invention. Of course, a heat flow delay layer is formed in the mesa with a semiconductor mixed crystal layer, and these are bonded to a metal substrate having a high thermal conductivity or a substrate coated with a metal layer by epitaxial lift-off,
May be integrated. By using the substrate itself as a heat sink, it is possible to suppress temperature changes with a large time constant.

The present invention is not limited to the above embodiment. For example, in the above embodiment, the multi-electrode D
Although the three-electrode DFB semiconductor laser device has been described as the FB semiconductor laser device, the present invention can be applied to a multi-electrode DFB semiconductor laser device having two electrodes or four or more electrodes or a normal DFB semiconductor laser device.

Further, instead of forming the mesa portion over the entire laser as in the above-described embodiment, the portion mainly acting as the gain region is made into a planar structure having good thermal characteristics, and the mesa portion is mainly provided only in the portion acting as the wavelength variable region. May be formed.

Furthermore, a structure having a region having another function such as phase control in the resonator direction, a structure asymmetric with respect to the resonator, a structure in which an active layer, a diffraction grating, a sectional structure, etc. are changed for each region, a phase For various variations such as a structure without a shift structure, a structure with dispersed phase shift regions, a structure with a window region without an active layer on the end face, and an inclined end face structure in which the emitting surface is not perpendicular to the active layer stripe. Also has the same effect.

Furthermore, the buried structure is not limited to the above structure, and it can be applied to a so-called photonic IC integrated with other elements and a laser array. In addition, various modifications can be made without departing from the scope of the present invention.

[0061]

As described above in detail, according to the present invention, the heat escaping from the active layer to the semiconductor substrate can be utilized for heating the active layer, the temperature of the active layer can be largely changed in a short time, and the oscillation can be performed in a short time. The wavelength can be changed greatly.

[Brief description of drawings]

FIG. 1 is a sectional view perpendicular to a stripe direction of a three-electrode DFB semiconductor laser device according to a first embodiment of the present invention.

FIG. 2 is a sectional view parallel to the stripe direction of the three-electrode DFB semiconductor laser device according to the first embodiment of the present invention.

FIG. 3 is a diagram showing the thermal conductivity of a III-V group semiconductor mixed crystal.

FIG. 4 is a diagram for explaining a temperature change of an active layer due to heat generation.

FIG. 5 is a cross-sectional view perpendicular to the stripe direction of a three-electrode DFB semiconductor laser device according to a second embodiment of the present invention.

FIG. 6 is a sectional view of a conventional three-electrode DFB semiconductor laser device perpendicular to the stripe direction.

[Explanation of symbols]

1 ... n-type InP substrate 2 ... n-type InGaAsP clad layer (first clad layer) 3a ... n-type InGaAs mixed crystal semiconductor layer (heat flow delay layer) 3b ... n-type InP clad layer (first clad layer) 4 ... Strained quantum well active / optical waveguide layer (active layer) 5 ... p-type InP cladding layer (second cladding layer) 6 ... p-type InGaAsP ohmic contact layer 7 ... p-type InP layer 8 ... n-type InP layer 9 ... p-side Electrode 10 ... N-side electrode 11 ... Heat sink 12 ... Mesa part 13 ... Diffraction grating 14 ... Phase shift region 15 ... Low reflective film 16 ... Semi-insulating InP layer 17 ... First current injection region 18 ... Second current injection region 19 ... Third current injection region

Claims (1)

[Claims] 1. A first clad layer provided on a substrate, having a thermal conductivity smaller than that of the substrate, and having a convex shape, and a light emitting layer and an optical waveguide provided on the convex portion of the first clad layer. An active layer serving as a layer, a second clad layer provided on the active layer and sandwiching the active layer together with the first clad layer, and a waveguide for laser light generated in the active layer, A semiconductor laser device comprising: a diffraction grating acting as a distributed feedback resonator.