JPH10223966A - Gain coupled distributed feedback semiconductor laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the absorption saturation of an absorbing layer by constituting a waveguide to have a broad section and narrow sections so that the distribution of the sections may cause laser oscillation in the fundamental horizontal mode and may not cause absorption saturation of inductively discharged light from an absorptive diffraction grating. SOLUTION: A waveguide 2 formed on a substrate 3 has a broad section 2a at its central part and narrow sections 2b at its both ends and, in the waveguide 2, a lower clad layer 5, a carrier barrier layer 6, an active layer 7, an upper clad layer 8, and a contact layer 9 are successively laminated upon another within the extent surrounded by a current constricting layer 4. An absorptive diffraction grating 3 in which a plurality of gratings are arranged in parallel is formed between the lower clad layer 5 and carrier barrier layer 9. At the central part of the waveguide 2 in which light density becomes higher, absorption saturation of an absorbing layer can be reduced by reducing the light density at the central part by widening the width of the part. At the time of preventing the absorption saturation, the width of the widened central part is set at 1.5 times of the width of the narrow sections 2b which are provided for stabilizing the lateral mode.

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 used as a light source for an optical disk device, an optical communication device, an optical measuring device, and the like, and more particularly, to a gain-coupled distributed feedback provided with an absorptive diffraction grating near an active layer. Semiconductor laser device.

[0002]

2. Description of the Related Art A semiconductor laser device in which a diffraction grating is provided in the vicinity of an active layer for generating stimulated emission light so as to generate laser oscillation at a single wavelength is called a distributed feedback semiconductor laser device (DFB: Distributed FeedBack). Laser Dio
de). Further, a device in which such single-wavelength laser oscillation is caused by the periodic distribution of the refractive index by the diffraction grating is referred to as a refractive index coupling distribution feedback semiconductor laser device, and is caused by the periodic distribution of the gain and the absorption by the diffraction grating. Is referred to as a gain-coupled distributed feedback semiconductor laser device. The latter one of them is easier to obtain stable single-wavelength laser oscillation and has more excellent characteristics.

FIG. 6 shows a conventional gain-coupled distributed feedback semiconductor laser device with a part thereof cut away. This semiconductor laser device 101 has a ridge-type structure, and includes a lower main body 102 and an upper ridge 103. In this device 101, a lower cladding layer 105, an active layer 106, a carrier barrier layer 107, a first guide layer 1
08, a second guide layer 109, an upper cladding layer 110, a contact layer 111, and an insulating film 112 are sequentially formed, and electrodes 113 and 114 are provided above and below the same.

The upper ridge 103 of the ridge type structure has
The upper cladding layer 110 overlaps the region A having a width of 2 μm.

A first guide layer 108 and a second guide layer 109
An absorptive diffraction grating 116 in which a plurality of gratings are arranged side by side is formed, and a light absorbing layer 117 is provided on each protrusion of the absorptive diffraction grating 116.

The constituent materials, thicknesses, and the like of each part of the semiconductor laser device 101 are as follows. Substrate 104: n-type GaAs, layer thickness 100 μm Lower cladding layer 105: n-type Al _0.6 Ga _0.4 As, layer thickness 1 μm Active layer 106: triple quantum well with no impurity added Al _0.1 Ga _0.9 As well layer Al _0.35 Ga _0.65 As barrier SCH layer Carrier barrier layer 107: p-type Al _0.5 Ga _0.5 As, layer thickness 0.2 μm First guide layer 108: p-type Al _0.3 Ga _0.7 As, layer thickness 0.05 μm (thickest part) Light absorbing layer 117: n-type GaAs, layer thickness 0.03 μm (thickest part) Second guide layer 109: p-type Al _0.25 Ga _0.75 As, layer thickness 0.08 μm (thickest part) Upper cladding layer 110: p-type Al _0.75 Ga _0.25 As, thickness 0.8 [mu] m (realm A only) contact layer 111: p ⁺ -type GaAs, layer thickness 0.5 [mu] m (region A only) insulating film 112: SiNx each electrode 113 and 114: AuZn, AuGe this In such a configuration, when a current is applied to each of the electrodes 113 and 114, stimulated emission light is generated in the active layer 106, and the stimulated emission light is guided along the waveguide 115, that is, along the arrow C. The light is emitted from the end face of the laser device.
Since the light absorbing layers 117 of the respective convex portions of the absorptive diffraction grating 116 are periodically arranged along the waveguide 115, they act as periodic absorption and loss with respect to the stimulated emission light. The gain is periodically distributed and laser oscillation at a single wavelength occurs.

For example, each convex portion of the absorptive diffraction grating 116 (first guide layer 108) is formed at a constant period (pitch 350 nm) along the waveguide direction of the stimulated emission light. An absorption layer 117 is provided. Each light absorbing layer 1
The GaAs constituting 17 has a bandgap smaller than the energy of light stimulatedly emitted from the active layer 106. Therefore, each light absorbing layer 117 functions as an absorptive diffraction grating 116 that periodically absorbs the stimulated emission light having a wavelength of 780 μm generated in the active layer 106, and generates laser oscillation at a single wavelength. .

[0008]

However, in the above-mentioned conventional gain-coupled distributed feedback semiconductor laser device,
When laser oscillation is performed with a high optical output exceeding 10 mW, absorption saturation occurs in the light absorption layer 117 of the absorptive diffraction grating 116. When this absorption saturation occurs, gain coupling by the absorptive diffraction grating 116 is not sufficiently performed.
There is a problem that the laser oscillation characteristics at a single wavelength deteriorate. Also, there is a problem that the characteristics of the optical output with respect to the drive current are not linear.

Accordingly, the present invention is to solve such a conventional problem, and suppresses the influence of absorption saturation of the light absorption layer of the absorptive diffraction grating until the light output reaches a high level. As a result, stable single-wavelength laser oscillation is realized, and the characteristics of the optical output with respect to the drive current are made linear. Despite these advantages, there is no additional characteristic deterioration, and the structure is further improved. It is an object of the present invention to provide a gain-coupled distributed feedback semiconductor laser device that can be manufactured easily and easily.

[0010]

In order to solve the above-mentioned problems, the present invention provides an active layer for generating stimulated emission light, and an active layer formed along the active layer, as described in claim 1 of the claims. In the gain-coupled distributed feedback type semiconductor laser device provided with an absorptive diffraction grating that periodically absorbs the stimulated emission light and a waveguide that guides the stimulated emission light along the absorptive diffraction grating, the waveguide includes: The waveguide has a wide portion and a narrow portion, and the distribution of the wide portion and the narrow portion of the waveguide is such that the laser oscillation occurs in the fundamental horizontal transverse mode, and the stimulated emission light generated by the absorptive diffraction grating. Is set so as not to cause absorption saturation.

That is, according to the present invention, since the waveguide is composed of a wide portion and a narrow portion, the absorption saturation of the absorption layer can be reduced while maintaining stable laser oscillation in the fundamental horizontal and transverse modes. Can be reduced.

According to a second aspect of the present invention, a waveguide includes a main body including an active layer and an absorptive diffraction grating, and a wide portion and a narrow portion adjacent to the absorptive diffraction grating of the main body. In the range where the stimulated emission light reaches, the stimulated emission light is absorbed only by the active layer and the absorptive diffraction grating, and the ridge portion of the ridge type structure has a narrow width. Cut off higher-order horizontal and transverse modes of stimulated emission light.

By adopting such a ridge-type waveguide, it is possible to alleviate the problem that the higher-order horizontal transverse mode is easily excited and to reduce the absorption saturation caused by the absorptive diffraction grating.

As described in the third aspect, the wide portion of the waveguide is provided in a region where the light density in the waveguide tends to increase. For example, since the optical density tends to increase at the approximate center of the waveguide, a wide portion of the waveguide is provided at the approximate center of the waveguide, and the width of the waveguide is reduced. A narrow portion is provided near the laser light emitting end face in the waveguide. This makes it possible to sufficiently achieve the functions and effects based on Claims 1 and 2.

According to a fifth aspect of the present invention, a wide portion of the waveguide is provided substantially at the center of the waveguide and in the vicinity of the laser light emitting end face of the waveguide, and between the wide portions. Alternatively, a narrow portion of the waveguide may be provided.

In this case, since the width of the waveguide is increased near the emission end face of the laser light, the light density does not need to be increased near the emission end face, and the emission end face is damaged by the laser light. You don't have to.

According to a sixth aspect of the present invention, if the length of the wide portion of the waveguide is set to be not less than 20% and not more than 60% with respect to the entire length of the waveguide, 2 and 2 can be sufficiently achieved.

If the wide and narrow portions of the waveguide are smoothly connected as described in claim 7, it is possible to sufficiently achieve the functions and effects according to claims 1 and 2. Become.

According to the present invention, the distribution of the wide portion and the narrow portion of the waveguide is set so that the amount of phase shift of the stimulated emission light is reduced.

Further, as described in claim 9, the length L of at least one of the wide portion and the narrow portion of the waveguide satisfies the relationship of the following equation (1).

Δβ · L = m · π (1) where m = ± 1, ± 2, ± 3,... Δβ is a narrow value of the propagation constant of light propagating in the wide portion of the waveguide. The phase shift amount of the stimulated emission light generated by the distribution of the wide portion and the narrow portion of the waveguide is simply the difference from the propagation constant of the light propagating through the portion. It is set so that laser oscillation at one wavelength is most likely to occur.

According to the eighth, ninth, and tenth aspects, the phase shift of the guided light that occurs when the light propagates through the waveguide having an irregular width is eliminated or set to an appropriate amount.
Even with a waveguide having an irregular width, the laser oscillation characteristic of a single wavelength due to gain coupling is not impaired.

[0023]

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

FIG. 1 shows a first embodiment of a gain-coupled distributed feedback semiconductor laser device according to the present invention, with a part thereof cut away. In the semiconductor laser device 1 of the first embodiment, the width of the waveguide 2 is not constant.
As shown in FIG. 3A, a wide portion 2a at a substantially central portion and narrow portions 2b at both ends are provided.
m, the width Wnarrow of each narrow portion 2b is 1.5 μm.
Further, the length of the waveguide 2 is 300 μm and the wide portion 2a
Is 90 μm.

The waveguide 2 is formed on the substrate 3, and a lower clad layer 5, a carrier barrier layer 6, an active layer 7, an upper clad layer 8, and a contact layer 9 are sequentially laminated in a range surrounded by the current confinement layer 4. Do it. The electrodes 11 and 1 are respectively provided on the lower surface of the substrate 4 and the upper surface of the contact layer 9.
2 are formed.

An absorptive diffraction grating 13 having a plurality of gratings arranged in parallel is formed between the lower cladding layer 5 and the carrier barrier layer 6, and these gratings are provided in respective grooves having a triangular cross section. An absorption layer 14 is provided.

The laser light emitting end face of the semiconductor laser device 1 is not subjected to any special treatment such as coating of a dielectric film.

The constituent materials, thicknesses, and the like of each part of the semiconductor laser device 1 are as follows. In the following notation, for example, “Q (y = 0.5)” means that InP
In _{Ga x In 1-x As y} P 1-y 4 -element mixed lattice-matched to, indicates a y = 0.5.

Substrate 3: n-type InP, layer thickness 100 μm Lower cladding layer 5: n-type InP, layer thickness 1 μm Light absorption layer 14: n-type Q (y = 0.62), layer thickness 0.1 μm (thickest part) ) Carrier barrier layer 6: n-type InP, layer thickness 0.33 μm (thickest part) Active layer 7: impurity-free quadrupole well SCH layer Q (y = 0.065), layer thickness 30 nm Q (y = 0.16), layer thickness 30 nm Q (y = 0.24), layer thickness 30 nm Q (y = 0.33), layer thickness 30 nm well layer Q (y = 0.62), layer thickness 15 nm barrier layer Q ( y = 0.33), layer thickness 15 nm Upper cladding layer 8: p-type InP, layer thickness 1 μm contact layer 9: p ⁺ type InGaAs, layer thickness 0.5 μm Electrodes 11, 12: AuCr, AuGe Current confinement layer 3: High-resistance InP layer doped with Fe In such a configuration, each of the electrodes 11, 12 When a current flows through the active layer 7, stimulated emission light is generated in the active layer 7, and the stimulated emission light is guided along the waveguide 2, and is emitted from the end face of the semiconductor laser device.

Each light absorbing layer 14 of the absorbing diffraction grating 13 is
The stimulated emission acts as a periodic absorption and loss, whereby the gain is periodically distributed and laser oscillation at a single wavelength occurs. For example, the absorption diffraction grating 13
Are formed at a pitch of 0.23 μm. GaInAs constituting these light absorbing layers 14
P has a forbidden band width smaller than the energy of light having a wavelength of 1.3 μm stimulatedly emitted from the active layer 7. Therefore, each light absorbing layer 14 serves as an absorptive diffraction grating 13 that periodically absorbs the stimulated emission light generated in the active layer 7, and generates laser oscillation at a single wavelength.

FIG. 3A shows a laser light output characteristic with respect to a drive current of the semiconductor laser device 1 of the first embodiment. In addition, the graph of FIG. 3B shows a conventional semiconductor laser device (in which the waveguide 2 is set to a constant width of 1.5 μm) for comparison with the first embodiment.
Shows the laser light output characteristics with respect to the drive current of FIG.

As is clear from the graph of FIG. 3A, according to the semiconductor laser device 1 of the first embodiment, the laser light output rises when the driving current is 10 mA, and the laser light output when the driving current is 150 mA. The output reaches 50mW,
During that time, the drive current-laser light output characteristics are linear. Further, within this laser light output range, laser oscillation at a single wavelength based on the period of each light absorbing layer 14 of the absorbing diffraction grating 13 can be obtained.

On the other hand, as is clear from the graph of FIG. 3B, in the conventional semiconductor laser device, the drive current-laser light output characteristic is bent near the laser light output of 10 mW (hereinafter, bent). The position is called a kink point). When the laser light output is lower than the kink point, laser oscillation at a single wavelength can be obtained. However, when the laser light output is higher than the kink point, laser light at two wavelengths can be obtained. Oscillation (two-mode oscillation) occurs.

According to the present inventors, the kink point in the characteristics shown in FIG. 3B occurs because the light density absorbed by each light absorption layer 14 of the absorption diffraction grating 13 increases as the laser light output increases. Was increased, and absorption saturation occurred in these light absorbing layers 14 at the kink point. Especially,
In the device 1 of the first embodiment, since the light density is higher in the central portion of the waveguide 2 than in the vicinity of the laser emission end face, absorption saturation of each light absorbing layer 4 is more likely to occur in this central portion.

In consideration of such considerations, the central portion of the waveguide 2 where the optical density is increased, the width of which is increased, and the optical density at the central portion is reduced is the device 1 of the first embodiment. There is a new effect that the absorption saturation of each light absorbing layer 14 can be avoided by this.

On the other hand, even when the entire waveguide 2 is set to have a constant wide width and the light density is reduced in the entire waveguide 2, the absorption saturation of each light absorbing layer 14 can be avoided, but the height is high. There is a disadvantage that the next horizontal / horizontal mode occurs. In comparison with this, as in the device 1 of the first embodiment, a narrow portion 2b is left in the waveguide 2 to stabilize the horizontal and transverse modes, and a portion with a high optical density, that is, a waveguide It can be seen that it is most preferable to increase the width only by the center of 2 to avoid the absorption saturation of each light absorbing layer 14. In particular, the width of the wide portion provided to prevent absorption saturation needs to be at least 1.5 times the width of the narrow portion provided to stabilize the transverse mode.

In the device 1 of the first embodiment, no special treatment such as coating of a dielectric film is performed on the emission end face of the laser light. It tends to be the highest. On the other hand, for example, when coatings having different reflectivities are applied to the respective exit end faces of the laser light, the distribution of the light density changes, and the position where the light density becomes highest is shifted from the center of the waveguide 2. In this case, the position of the wide portion 2a of the waveguide 2 may be changed so as to overlap the position where the light density becomes highest. Alternatively, when a reflection film having a low reflectance is provided on one of the output end faces facing the laser beam and a reflection film having a high reflectance is provided on the other, the light density is high in the vicinity of the reflection film having a high reflectance. Therefore, it is necessary to increase the width of the waveguide 2 in the vicinity of the emission end on the side provided with the reflection film having high reflectance.

Here, the length of the waveguide 2 is set to 300
The length of the wide portion 2a is set to 90 μm. This is because if the length of the wide portion 2a is not more than 20% of the entire length of the waveguide 2, the effect of avoiding the absorption saturation of each light absorbing layer 14 cannot be obtained. This is because stable laser oscillation in the horizontal / lateral mode cannot be obtained.

Further, in the device 1 of the second embodiment,
The length L of the wide portion of the waveguide 2 is determined based on the following equation (1).

Δβ · L = m · π (1) where m = ± 1, ± 2, ± 3,... Δβ is a narrow value of the propagation constant of light propagating in the wide portion of the waveguide. In this device 1, there is a difference of about 7.3 × 10 ^-3 in the equivalent refractive index between the wide portion 2a and the narrow portion 2b of the waveguide 2. Accordingly, in order not to cause a phase shift of the stimulated emission light between the wide portion 2a and the narrow portion 2b, the distribution of the wide portion 2a and the narrow portion 2b is satisfied so that the above expression (1) is satisfied. Set. In order to compare with this, an apparatus which greatly deviated from the relation of the above equation (1) was manufactured.
Laser oscillation at a single wavelength at the Bragg wavelength could not be obtained.

FIG. 4 shows a gain-coupled distributed feedback semiconductor laser device according to a second embodiment of the present invention, with a part thereof cut away. The semiconductor laser device 21 has a ridge-type structure, and includes a lower body 22 and an upper ridge 23.

The waveguide 24 comprises a main body 22 and a ridge 23
The width of the waveguide 24 at the ridge portion 23 is not constant, and each wide portion 24a near both ends as shown in FIG.
And a narrow portion 24b substantially at the center, and each wide portion 24a
Width Wwide is 3.0 μm and width Wnarrow of narrow portion 24b
Is 1.0 μm, and each wide portion 24a and narrow portion 24
b is smoothly connected. Also, this waveguide 24
Is 300 μm and the length of the narrow portion 24b is 130 μm
m.

In this device 21, the lower clad layer 26, the active layer 27, the carrier barrier layer 28, the first guide layer 29, the second guide layer 30, the upper clad layer 31, the contact layer 32, the insulating film 33 Are sequentially formed, and electrodes 34 and 35 are provided on the upper and lower sides.

The upper ridge portion 23 of the ridge type structure is composed of the upper cladding layer 31 and overlaps the region A having a width of 3 μm.

An absorptive diffraction grating 36 in which a plurality of gratings are arranged in parallel is formed between the first guide layer 28 and the second guide layer 29, and each protrusion of the absorptive diffraction grating 36 (the first guide layer 28) is formed. The portion is provided with a light absorbing layer 37.

The laser light emitting end face of the semiconductor laser device 1 is coated with an Al ₂ O ₃ dielectric film so that the reflectivity of both end faces is 70%.

The constituent materials, thicknesses, and the like of each part of the semiconductor laser device 21 are as follows. Substrate 25: n-type GaAs, layer thickness 100 μm Lower cladding layer 26: n-type Al _0.6 Ga _0.4 As, layer thickness 1 μm Active layer 27: triple quantum well with no impurity added Al _0.35 Ga _0.65 As SCH layer, layer thickness 70 μm Al _0.1 Ga _0.9 As well layer, 8 nm Al _0.35 Ga _0.65 As barrier layer, 8 nm Al _0.35 Ga _0.65 As SCH layer, layer thickness 70 μm Carrier barrier layer 28: p-type Al _0.5 Ga _0.5 As, layer thickness 0 0.2 μm First guide layer 29: p-type Al _0.3 Ga _0.7 As, layer thickness 0.05 μm (thickest part) Light absorption layer 37: n-type GaAs, layer thickness 0.03 μm (thickest part) Second guide layer 30 : P-type Al _0.25 Ga _0.75 As, layer thickness 0.08 μm (thickest part) Upper cladding layer 31: p-type Al _0.75 Ga _0.25 As, layer thickness 0.8 μm (region A only) Contact layer 32: p ⁺ -type GaAs , Layer thickness 0.5μ (Area A only) Insulating film 33: SiNx Each electrode 34, 35: AuZn, AuGe In such a configuration, when a current flows through each electrode 34, 35, stimulated emission light is generated in active layer 27, and this stimulated emission is generated. Light is guided along the waveguide 24 and emitted from the end face of the semiconductor laser device.

The first guide layer 29 (absorbing grating 36) has a constant period (pitch: 350 nm) and a duty ratio of 2
Rectangular unevenness of 0% is formed, and a light absorbing layer 37 is arranged on each convex portion. Ga constituting each light absorbing layer 37
As has an energy gap smaller than the energy of light stimulated emitted from the active layer 27, and serves as an absorptive diffraction grating 36 that periodically absorbs stimulated emission light having a wavelength of 780 μm generated in the active layer 27. It plays a role and generates laser oscillation at a single wavelength.

In the device 21 of the second embodiment,
The width near the end face of the waveguide 24 is increased based on the fact that the internal light density becomes highest near the laser emission end face,
At least in the range up to the drive current of 20 mA, the drive current −
The laser light output characteristic becomes linear, and the kink point as shown in the graph of FIG. 3B does not occur.

Further, a narrow portion 24 substantially at the center of the waveguide 24 is provided.
b serves to cut off the higher-order horizontal / lateral mode, and suppresses the occurrence of this higher-order horizontal / lateral mode.

On the other hand, in the ridge portion 23, the waveguide 24
Is set to a constant wide width, and even when the optical density of the entire waveguide 24 is reduced, the absorption saturation of each light absorption layer 37 can be avoided, but the laser light output is about several mW. Also, higher order horizontal and transverse modes occurred. As in the device 21 of the second embodiment, the narrow width portion 24a is
While stabilizing the horizontal and transverse modes,
Most preferably, a wide portion is provided in 4 to avoid absorption saturation of each light absorbing layer 14.

Further, since the wide portion 24a and the narrow portion 24b of the waveguide 24 are smoothly connected, the absorption saturation can be suppressed particularly effectively. This is because light scattering occurs at the boundary between regions having different widths, especially when the wide portions 24a and the narrow portions 24b are not smoothly connected, and the light density becomes high, so that absorption saturation is easily induced. On the other hand, it can be presumed that the smooth connection does not cause light scattering at the boundary portion, and thus is more effective in suppressing absorption saturation.

Further, since each wide portion 24a of the waveguide 24 is provided at both ends of the waveguide 24, the light density of the laser light near each emission end face is reduced, and damage to each emission end face by the laser light is small. Become.

Also in the device 21 of the second embodiment, the above equation (1) is used so that the phase shift of the stimulated emission light does not occur between the wide portion 24a and the narrow portion 24b of the waveguide 24.
Satisfy the relationship.

In particular, in the case of an intrinsic gain-coupled distributed feedback semiconductor laser device that does not include a component of the refractive index coupling, the necessity of satisfying the relationship of the above equation (1) becomes higher. On the other hand, in the case of a partial gain coupling distributed feedback semiconductor laser device including both refractive index coupling and gain coupling, as proposed by the present inventors in Japanese Patent Application No. Hei 8-92854, gain coupling and refractive index coupling are proposed. It is desirable to appropriately set the phase shift according to the ratio of.

In the device 21 according to the second embodiment, the width of the narrow portion 24b of the waveguide 24 is set to 1.0 μm.
m, and this width is made very narrow so as to cut off the higher-order horizontal / lateral mode.

This is because, in an ordinary semiconductor laser device having a ridge-type structure, the width of the waveguide is set appropriately wide, and the laser oscillation in the basic horizontal transverse mode can be performed without cutting off the higher-order horizontal transverse mode. On the other hand, in the device 21 of the second embodiment, the waveguide 24 has a ridge type structure, and a light absorbing member other than the absorptive diffraction grating 36 is provided between the ridge portion 23 and the active layer 27. This is because a higher-order horizontal / horizontal mode is likely to occur, and this higher-order horizontal / horizontal mode is sufficiently cut off. This will be described in more detail with reference to FIG.

FIG. 5A shows a cross section of the device 21 of the second embodiment, and FIG.
FIG. 5C shows a light density distribution along a ′, and FIG.
4A shows a light density distribution along bb ′ in FIG.

As is clear from FIGS. 5A, 5B, and 5C, the light beams overlapping the absorptive diffraction grating 36 in the regions B on both outer sides are better than those in the region A overlapping the ridge portion 23. Small density. Therefore, the effective absorption coefficient of the absorptive diffraction grating 36 is smaller in the region B, so that the light density distribution is biased toward the region B having a small absorption loss or a higher-order transverse mode is easily generated.

In the device 21 of the second embodiment, it is necessary to arrange a light absorption layer having a very large absorption amount near the active layer for gain coupling. The tendency that a mode is likely to occur is remarkable. If the width of the narrow portion 24b of the waveguide 24 is made sufficiently small and the higher-order horizontal and transverse modes are not reliably cut off, the laser in the basic horizontal and transverse modes is required. Oscillation makes it impossible to obtain even a laser light output of about several mW, which is far from practical use in applications requiring a laser light output of several tens mW or more as a light source, such as long-distance optical communication. Therefore, it is necessary to make the width of the narrow portion 24b of the waveguide 24 sufficiently small.

The present invention is not limited to the above embodiments, but can be variously modified. For example, as shown in FIG. 2C, the waveguide 41 may have three wide portions 41a and two narrow portions 41b. In this case, the absorption saturation is suppressed by the wide portion 41a substantially at the center of the waveguide 41, and the waveguide 4
The wide end portions 41a at both ends of the laser beam 1 prevent the laser light emitting end face from being broken. L in the above equation (1) is given as the sum of the lengths of the portions having the same width.

Further, each width of the waveguide is not set in two steps, but is set in three or more steps, or in FIG.
As shown in (d), both edges of the waveguide 42 may be formed in a curved shape, and the width of the waveguide 42 may be smoothly changed.
In particular, as shown in FIG. 2 (d), when the wide area and the narrow area are smoothly connected by a curve having a large curvature, light scattering at the boundary between the wide area and the narrow area is minimized. Therefore, it was most effective for suppressing absorption saturation.

Further, the material constituting the semiconductor laser device of the present invention or the oscillation wavelength of the laser light is not limited to those exemplified in the above embodiments, but includes Al, Ga, In and the like as Group III elements. And P and A as group V elements
III-V mixed crystal semiconductor materials containing s, N, etc., and II-VI mixed crystal semiconductor materials containing Zn, Mg, Cd, etc. as Group II elements and containing S, Se, Te, etc. as Group VI elements The present invention can also be applied to a gain-coupled distributed feedback semiconductor laser device made of various materials such as. Further, various known techniques are applied as a method of crystal growth, and the semiconductor laser device of the present invention can be manufactured. Alternatively, it is also possible to use a buffer layer (buffer layer) between the substrate and the lower cladding layer in order to improve the crystallinity of each layer constituting the semiconductor laser device.

Various known techniques can be applied to the structure and manufacturing method of the waveguide and the structure and manufacturing method of the absorptive diffraction grating in the semiconductor laser device of the present invention.

Further, although there is no mention in the above embodiments regarding the processing method of the laser light emitting end face or the coating material and its forming method, various known techniques are applied to modify the configuration of the laser device. Things can be done easily.

Further, since the gain-coupled distributed feedback type semiconductor laser device can perform laser oscillation even if the emission end face of the laser beam is not formed by cleavage, it is promising as a monolithic light source in an optical integrated circuit or the like. Has been
The semiconductor laser device of the present invention can be applied not only as a single device described in each of the above embodiments but also as a laser light source of an optical integrated circuit.

The present invention has been described with respect to a gain-coupled distributed feedback semiconductor laser device used as a light source for an optical disk device, an optical communication device, an optical measuring device, and the like. The present invention can also be applied to a wavelength filter or the like to which a grating is applied.

[0068]

As described above, according to the device of the first aspect, since the waveguide is composed of the wide portion and the narrow portion, the waveguide is stable in the basic horizontal and transverse mode. Absorption saturation of the absorption layer can be reduced while maintaining laser oscillation.

Further, according to the device of the second aspect, even if a waveguide having a ridge-type structure is applied, the problem that a higher-order horizontal transverse mode is easily excited can be solved and an absorptive diffraction grating can be obtained. Can reduce absorption saturation.

According to the third aspect of the present invention, the wide portion of the waveguide is provided in a region where the light density in the waveguide tends to be high. If the height tends to be higher, the wide portion of the waveguide is provided substantially at the center of the waveguide, and the narrow portion of the waveguide is emitted from the waveguide. Provided near the end face. This makes it possible to sufficiently achieve the functions and effects based on Claims 1 and 2.

According to the fifth aspect of the present invention, the width of the waveguide is increased near the emitting end face of the laser light so that the light density does not increase near the emitting end face, and the emission of the laser light is prevented. The destruction of the end face can be prevented.

According to the device of the sixth aspect, the length of the wide portion of the waveguide is set to be 2 to the entire length of the waveguide.
It is set between 0% and 60%.
This makes it possible to sufficiently achieve the functions and effects based on Claims 1 and 2.

According to the device described in claim 7, the wide portion and the narrow portion of the waveguide are smoothly connected.
This makes it possible to sufficiently achieve the functions and effects based on Claims 1 and 2.

According to the apparatus described in each of the eighth, ninth, and tenth aspects, the phase shift of the guided light that occurs when the light propagates through the waveguide having an irregular width is eliminated or set to an appropriate amount. Therefore, even if the waveguide has an irregular width, the laser oscillation characteristic of a single wavelength due to gain coupling is not impaired.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a first embodiment of a gain-coupled distributed feedback semiconductor laser device according to the present invention, with a part thereof cut away;

FIG. 2 is a plan view showing a waveguide of the gain-coupled distributed feedback semiconductor laser device according to the present invention when viewed from above, and FIG.
1 shows a waveguide in the device of FIG. 1, (b) shows a waveguide in the device of FIG. 4, (c) shows a modification of the waveguide, and (d) shows another modification of the waveguide.

3A and 3B are graphs showing laser light output characteristics with respect to a drive current of a semiconductor laser device, wherein FIG. 3A shows the characteristics of the semiconductor laser device of FIG. 1 and FIG. 3B shows the characteristics of a conventional semiconductor laser device.

FIG. 4 is a perspective view showing a second embodiment of the gain-coupled distributed feedback semiconductor laser device according to the present invention, with a part thereof cut away;

5A shows a cross section of the device of FIG. 4, FIG. 5B shows a light density distribution along aa ′ in FIG.
(C) shows the light density distribution along bb 'in (a).

FIG. 6 is a perspective view showing a conventional gain-coupled distributed feedback semiconductor laser device with a part thereof cut away.

[Explanation of symbols]

 Reference numerals 1,21 Semiconductor laser device 2,24,41,42 Waveguide 3,25 Substrate 4 Current confinement layer 5,26 Lower cladding layer 6,28 Carrier barrier layer 7,27 Active layer 8,31 Upper cladding layer 9,32 Contact Layers 11, 12, 34, 35 Electrodes 13, 36 Absorbing diffraction grating 14, 37 Light absorbing layer 22 Main body 23 Ridge 29 First guide layer 30 Second guide layer 33 Insulating film

Claims (10)

[Claims] 1. An active layer for generating stimulated emission light, an absorptive diffraction grating provided along the active layer and periodically absorbing the stimulated emission light, and an absorptive diffraction grating along the absorptive diffraction grating. In the gain-coupled distributed feedback semiconductor laser device including the waveguide for guiding the light, the waveguide has a wide portion and a narrow portion, and the distribution of the wide portion and the narrow portion of the waveguide is:
A gain-coupled distributed feedback semiconductor laser device which is set so as to generate laser oscillation in a fundamental horizontal and transverse mode and not to cause absorption saturation of stimulated emission light by an absorptive diffraction grating. 2. A waveguide comprising: a main body including an active layer and an absorptive diffraction grating; a waveguide adjacent to the absorptive diffraction grating of the main body;
It has a ridge-type structure consisting of a ridge having a wide part and a narrow part. Within the range where stimulated emission reaches, stimulated emission is absorbed only by the active layer and the absorptive diffraction grating. 2. The gain-coupled distributed feedback semiconductor laser device according to claim 1, wherein a high-order horizontal transverse mode of stimulated emission light is cut off by a narrow portion of said ridge portion. 3. The wide portion of the waveguide is provided in a region where the optical density in the waveguide tends to increase.
2. A gain-coupled distributed feedback semiconductor laser device according to item 1. 4. The waveguide according to claim 1, wherein a wide portion of the waveguide is provided substantially at the center of the waveguide, and a narrow portion of the waveguide is provided near an emitting end face of the laser light in the waveguide. A gain-coupled distributed feedback semiconductor laser device according to any one of the above. 5. A wide portion of the waveguide is provided substantially at the center of the waveguide and in the vicinity of the emission end face of the laser light in the waveguide, and between the wide portions, the width of the waveguide is reduced. 4. The gain-coupled distributed feedback semiconductor laser device according to claim 1, wherein a narrow portion is provided. 6. The waveguide according to claim 1, wherein the length of the wide portion of the waveguide is set to 20% or more and 60% or less with respect to the entire length of the waveguide. Gain-coupled distributed feedback semiconductor laser device. 7. The gain-coupled distributed feedback semiconductor laser device according to claim 1, wherein a wide portion and a narrow portion of the waveguide are smoothly connected. 8. The gain-coupled distributed feedback semiconductor laser device according to claim 1, wherein distributions of the wide portion and the narrow portion of the waveguide are set so that the amount of phase shift of the stimulated emission light is reduced. . 9. The method according to claim 1, wherein the length L of at least one of the wide portion and the narrow portion of the waveguide satisfies the following expression (1). Gain-coupled distributed feedback semiconductor laser device. Δβ · L = m · π (1) where m = ± 1, ± 2, ± 3,. Is the difference from the propagation constant of the 10. A phase shift amount of stimulated emission light generated by distribution of a wide portion and a narrow portion of a waveguide is set so that laser oscillation at a single wavelength is most easily generated. 10. The gain-coupled distributed feedback semiconductor laser device according to any one of 1 to 9.