JPH1168221A - Semiconductor laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor laser wherein the disturbance of a far-field pattern at a gain region side end surface is suppressed. SOLUTION: A constant-thickness active layer 3, extending in stripe in a specified direction, which comprises a gain region 3a having a constant width and a spot size conversion region 3b wherein its width becomes succeedingly narrower as going against the gain region 3a, a diffraction grating 13 which is, lattice-arrayed toward extension of the active layer 3, provided along the gain region 3a of the active layer 3 of an upper clad layer 4, and a reflection preventing film 14 provided above the end surface on the side of spot size conversion region 3b, are provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser, and more particularly to a semiconductor laser with a spot size converter, which is used mainly in the field of optical communication to increase the efficiency of optical coupling with an optical fiber. .

[0002]

2. Description of the Related Art In a conventional semiconductor laser (hereinafter abbreviated as LD) having an active layer having a uniform width and a uniform thickness over all portions from the front end face to the rear end face of a laser resonator end face. Since the spot size of the laser beam emitted from the front end face is smaller than the spot size of the optical fiber, the coupling loss when the LD is directly coupled to the optical fiber is large. Therefore, in a conventional LD, a function of increasing the spot size of light guided and emitted by giving a thickness distribution to a part of the active layer or giving a distribution to the width of the active layer. A so-called LD with a spot size converter, which is an LD with a built-in spot size converter, has been considered.

FIG. 5 shows a conventional L with a spot size converter.
FIG. 1D is a perspective view of D, wherein 1 is a p-type (hereinafter referred to as p-) InP semiconductor substrate, 2 is a p-InP lower cladding layer, 3 is an InGaAsP well layer sandwiched between upper and lower InGaAsP light confinement layers. And an InGaAsP barrier layer. The active layer 3 has a uniform thickness and has a multilayer structure. The active layer 3 extends in a stripe shape in a predetermined direction, and has two regions in the extending direction. A gain region 3a having a uniform width, that is, a length in a direction perpendicular to the laser resonator length direction, and a planar shape having a width gradually decreasing as approaching one of the end faces away from the gain region 3a. Spot size conversion area 3
b. 4 is an n-type (hereinafter referred to as n-) InP
Upper cladding layer, 5 is a p-InP current blocking layer, 6 is n
In the -InP current blocking layer, the p-InP current blocking layer 5 and the n-InP current blocking layer 6 form a current constriction structure. 7 is an n-InP contact layer,
Reference numeral 8 denotes an LD anode electrode, 9 denotes an LD cathode electrode, and 10 denotes a SiO ₂ insulating film having an opening in a region on the gain region 3a for enabling the cathode electrode 9 to contact the contact layer 7 on the gain region 3a. , 11 is a front reflection film provided on the front end face, and 12 is a rear high reflection film provided on the rear end face.

FIG. 6 is a cross-sectional view of the conventional LD with a spot size converter shown in FIG. 5 taken along a laser resonator length direction at a position including an active layer. Indicates the same or corresponding parts.

FIG. 7 is a plan view for explaining the operation of the conventional semiconductor laser. The same reference numerals as those in FIG. 5 denote the same or corresponding parts. Is shown.

The gain region 3a of the conventional semiconductor laser
Has a light amplifying action like the active layer of a normal LD,
As the width of the active layer 3 decreases, the spot size conversion region 3b extends in the vertical direction, that is, in the height direction of the substrate 1, and in the horizontal direction, that is, in the direction perpendicular to the height direction of the substrate 1, and in the direction in which the active layer 3 extends. It has the function of expanding the spot size of light by utilizing the weakening of vertical light confinement. That is, in this semiconductor laser, when a voltage is applied between the electrode 8 and the electrode 9, holes and electrons are injected into the gain region 3a of the active layer 3, light-emitting recombination occurs, and light 20 is generated. Then, this light 20 is guided along the active layer 3,
As shown in FIG. 7, laser oscillation occurs when light reciprocates between the front end face and the rear end face. At this time, as described above, since the width of the spot size conversion region 3b is tapered, the confinement of light is weakened, and the guided light 20 spreads in this region. As a result, the laser light spreads and is emitted from the end face on the spot size conversion region 3b side, which is the front end face of the LD, and laser light with a wide spot size can be obtained.

[0007]

However, since the light is spread and guided in the spot size conversion region 3b, as shown in FIG. A portion 21 of the laser light propagating toward the rear of the spot size conversion region 3b, that is, toward the gain region 3a, is guided in the radiation mode, that is, in the direction in which the active layer 3 extends. As a result, the light interferes with the main beam, thereby disturbing the far-field image obtained from the end surface on the gain region 3a side, which is the rear end surface. In addition, the far-field image is disturbed particularly with temperature fluctuation. For this reason, for example, a laser beam emitted from the rear end face is received by a photodiode, the amount of current injected into the LD is adjusted based on the light intensity, and a so-called APC (Automatic Power Control) that keeps the light intensity emitted from the front end face constant. Power C
In operation, since the ratio of the light incident on the photodiode varies due to the disturbance of the far-field image, the intensity of the laser beam emitted from the front end face controlled based on the variation varies, and the It was a big problem. Therefore, an LD structure capable of suppressing the disturbance of the far-field image on the rear end face has been demanded.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to provide a semiconductor laser capable of suppressing disturbance of a far-field image on an end face on a gain region side.

[0009]

A semiconductor laser according to the present invention comprises a first conductive type lower clad layer formed on a first conductive type semiconductor substrate, and a fixed width disposed on the lower conductive layer. An active layer having a constant thickness extending in a stripe direction in a predetermined direction, comprising an active region having a gain region having a width and a spot size conversion region having a width gradually decreasing as the distance from the active region is increased; A current constriction structure provided in contact with the surface, a second conductivity type upper cladding layer disposed on the active layer, a second conductivity type contact layer disposed on the upper cladding layer, Either the clad layer or the upper clad layer, provided at positions along the entire gain region of the active layer, diffraction gratings arranged in a lattice in a direction in which the active layer extends; To the direction A pair of end faces which are directly provided, in which as and a anti-reflection film provided on the end face of the spot size conversion area side.

Further, the diffraction grating is a refractive index coupling type diffraction grating in which semiconductor materials having different refractive indexes are alternately arranged.

Further, the diffraction grating is a gain-coupled diffraction grating in which semiconductor materials having different gains are alternately arranged.

Further, the diffraction grating is a λ / 4 shift type diffraction grating (where λ is the wavelength of guided light).

A semiconductor laser according to the present invention has a first conductivity type lower cladding layer formed on a first conductivity type semiconductor substrate, and a gain region having a constant width disposed on the lower cladding layer. And an active layer having a constant thickness extending in a predetermined direction in a stripe shape, comprising a spot size conversion region having a width gradually reduced as the distance from the gain region increases, and contacting both side surfaces of the active layer. The provided current constriction structure, a second conductivity type upper cladding layer disposed on the active layer, a second conductivity type contact layer disposed on the upper cladding layer, and the lower cladding layer or Either one of the cladding layers, provided only at a position along the area on the spot size conversion region side in the gain region of the active layer, a diffraction grating arranged in a lattice in the direction in which the active layer extends, Activity A pair of end faces provided perpendicular to the direction in which the laser beam extends, the gain area side being a laser resonator end face, and an antireflection film provided on the end face on the spot size conversion area side. It was made.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 FIG. FIG. 1 is a plan view showing the structure of the semiconductor laser according to the first embodiment of the present invention as viewed from above the substrate (FIG.
(a)), a cross-sectional view taken along the line Ib-Ib of FIG.
(b)) and a cross-sectional view taken along line Ic-Ic in FIG. 1 (a) (FIG. 1 (c))
In the figure, 1 is a p-type (hereinafter referred to as p−) In
The semiconductor substrate 2 composed of P is formed of p-
The InP lower cladding layer 3 is formed on the lower cladding layer 2 and has a multilayer structure in which InGaAsP well layers and InGaAsP barrier layers are alternately stacked on top and bottom of which are sandwiched between InGaAsP light confinement layers. The active layer 3 is a uniform active layer over the entire area. The active layer 3 extends in a stripe shape in a predetermined direction, and has two widths in the extending direction, that is, a width, that is, a length perpendicular to the laser resonator length direction. The gain region 3a has a uniform diameter, and the spot size conversion region 3b has a tapered planar shape whose width gradually decreases as approaching one of the end faces, away from the gain region 3a. The active layer 3 may be a single-layer active layer or an active layer made of another material. Reference numeral 4 denotes an n-type (hereinafter referred to as n-) InP upper cladding layer disposed on the active layer 3, and the upper cladding layer 4, the active layer 3, and the lower cladding layer 2 have a mesa shape extending in the laser cavity length direction. have. 13 is provided near the gain region 3a of the active layer of the upper cladding layer 4.
Diffraction gratings arranged in a lattice pattern in the direction in which the active layer 3 extends. Here, the diffraction gratings are arranged at a constant period so as to be parallel to the surface of the active layer 3 and extend in a stripe shape in the width direction of the semiconductor laser. n-In _0.798 Ga _0.202 As
_A refractive index coupling type diffraction grating is used in which a plurality of buried layers 13a made of a material having a different refractive index to InP, such as a _{0.491P 0.559} layer, are buried in the n-InP upper cladding layer 4. 13c is a refractive index coupling layer made of the same material as the buried layer 13a used to form the plurality of buried layers 13a, and 5 and 6 are buried in the mesa-shaped portions so as to be in contact with both side surfaces of the active layer 3. The p-InP current blocking layer 5 and the n-I
A current constriction structure is formed by the nP current block layer 6. 7 is an n-InP contact layer, 8 is an LD anode electrode, 9 is an LD cathode electrode, 10 is a cathode electrode 9
Is an SiO ₂ insulating film having an opening in a region on the gain region 3a so that the contact layer 7 can be brought into contact with the contact layer 7 only on the gain region 3a. The provided anti-reflection film (AR film) 12 is a rear high reflection film provided on the rear end surface which is the end surface on the gain region 3a side, and this high reflection film 12 may not be provided if necessary. .

FIG. 2 is a plan view for explaining the operation of the semiconductor laser according to the first embodiment. In FIG. 2, the same reference numerals as those in FIG. The light is guided through the layer 3.

FIG. 3 is a perspective view for explaining the method of manufacturing the semiconductor laser according to the first embodiment of the present invention. In the figure, the same reference numerals as those in FIG. 1 denote the same or corresponding parts. Reference numerals 4a and 4b denote first and second upper cladding layers. The first and second upper cladding layers 4a and 4b are laminated to form the above-mentioned upper cladding layer 4. Reference numeral 15 denotes a resist film, and 16 denotes an insulating film.

The semiconductor laser according to the first embodiment has a gain region 3a having a uniform width and having a light amplifying effect, and a width gradually decreasing in a tapered shape as the distance from the gain region increases. In the semiconductor laser provided with the active layer 3 composed of the spot size conversion region 3b having the function of expanding the spot size, the refractive index coupling type diffraction grating 13 is provided near the upper or lower part of the gain region 3a, and the reflection is made on the front end face thereof. An anti-reflection film (AR film) 14 is coated.

Next, the manufacturing method will be described. First, as shown in FIG. 3A, a lower cladding layer 2, an active layer 3, a first upper cladding layer 4a, and a refractive index coupling layer 13c are sequentially epitaxially grown on a substrate 1 in a wafer state. Next, a resist film 15 is applied on the refractive index coupling layer 13c, and is patterned by a photoengraving technique using an interference exposure method, as shown in FIG. A plurality of stripe-shaped resist patterns extending at a predetermined interval and extending in a direction perpendicular to a certain direction are formed, and the refractive index coupling layer 13 is selectively used as a mask.
By etching c, as shown in FIG. 3 (c), a plurality of buried layers 13a arranged at a constant period and extending in a stripe shape in the width direction of the semiconductor laser are obtained. Then, after removing the resist film 15, as shown in FIG. 3D, the second upper cladding layer 4b is grown on the first upper cladding layer 4a so as to bury the burying layer 13a. A diffraction grating 13 is formed near the active layer 3 of FIG.

Subsequently, the gain region 3 is formed on the upper cladding layer 4.
The insulating film 16 is formed in a stripe shape having a constant width on the region where the a is formed, and a taper shape in which the width is gradually reduced on the region where the spot size conversion region 3b is formed. As shown in e), using this as a mask, the upper portions of the upper cladding layer 4, the active layer 3, and the lower cladding layer 2 are selectively etched to form a mesa shape.
The current blocking layers 5 and 6 are buried and grown using the insulating film 16 as a mask so as to bury the mesa-shaped portion, and after the insulating film 16 is removed,
As shown in FIG. 3F, a crystal of the contact layer 7 is grown. Note that a patterned resist film may be used instead of the insulating film 16.

Thereafter, an insulating film 10 is formed on the contact layer 7, and an opening is provided in a region of the insulating film 10 on the side of the gain region 3a.
A cathode electrode 9 is formed on the region including the opening, an anode electrode 8 is formed on the back side of the substrate 1, and each element is separated from the wafer to form a pair of end faces perpendicular to the direction in which the active layer 3 extends. After the formation, an anti-reflection film 14 is coated on the spot size conversion region 3b side of this end surface, and a high reflection film 12 is formed on the end surface on the gain region 3a side as necessary. Get a laser.

Next, the operation will be described. When a voltage is applied between the anode electrode 8 and the cathode electrode 9, holes and electrons are injected into the gain region 3 a of the active layer 3, and radiative recombination occurs to generate light 22. As shown in FIG. 5, since the laser beam is subjected to Bragg reflection by the diffraction grating 13, the laser beam basically reciprocates in the gain region 3a as in a normal distributed feedback laser. Oscillation occurs, a part of which proceeds to the spot size conversion area 3b side, and is emitted from the end face. At this time, in the spot size conversion region 3b, the width is tapered and the confinement of light is weakened, so that the guided light 22 is spread and guided in this region. The laser light spreads and is emitted from the end face, so that a laser light with a wide spot size can be obtained.

At this time, since the antireflection film 14 is provided on the end face on the spot size conversion area 3b side, the gain area 3a
Most of the light traveling from the end surface to the spot size conversion region 3b is not reflected at this end surface, and the amount of laser light returning from the end surface to the gain region 3b is very small. Therefore, the radiation mode that advances to the end face on the gain area 3a side is also reduced, and the far-field image of the end face on the gain area 3a side is clean and free from disturbance like a semiconductor laser having no ordinary spot size conversion area. It becomes stable with temperature. As a result, APC (Auto P
power control), stable operation is possible.

Further, since the anti-reflection film 14 is formed on the front end face, the reflection of the laser light on the front end face is reduced. Therefore, even if the laser light propagating in the spot size conversion region 3b is reduced, the front end face is not affected. The intensity of the laser light radiated from the LD can be the same as that of the LD having the above-mentioned conventional spot size converter.

As described above, according to the first embodiment, the gain region 3a having a fixed width and the spot size conversion region 3b whose width gradually decreases as the distance from the gain region increases, are determined. Active layer 3 having a certain thickness extending in a stripe shape in the direction, and active layer 3 of upper cladding layer 4.
A diffraction grating 13 provided at a position along the gain region and arranged in a lattice in the direction in which the active layer 3 extends, and an antireflection film 14 provided on the end face on the spot size conversion region 3b side. Therefore, laser oscillation can be performed only in the gain region of the active layer, and reflection of light guided through the active layer on the end surface on the side of the spot size conversion region can be prevented. There is an effect that a laser can be provided.

In the first embodiment, the buried layer 13 made of a material having a different refractive index is formed in the upper cladding layer 4.
Embedded grating is used, but the upper cladding layer is formed by laminating two semiconductor layers having different refractive indices, the interface of which is a diffraction grating shape. The vicinity of the interface between the layers may be used as a diffraction grating.

In the first embodiment, the case where the diffraction grating is provided near the active layer 3 of the upper cladding layer 4 has been described. However, in the present invention, the diffraction grating is provided near the active layer of the lower cladding layer. It may be provided, and in such a case, the same effect as in the first embodiment can be obtained.

Here, in the first embodiment, the spot size conversion region 3b having a distribution in width is formed by the active layer 3
In the semiconductor laser in which the spot size can be enlarged by providing the diffraction grating 13 in the vicinity of the gain region 3b and the non-reflection film 14, the disturbance of the far-field image is eliminated. In a semiconductor laser in which a spot size conversion region having a tapered distribution in thickness is provided in an active layer to increase the spot size of light, a diffraction grating and an anti-reflection film are provided, and It is conceivable to obtain the same effect.

However, such a semiconductor laser requires a step of selectively growing an active layer having a partially different thickness using a mask provided with openings having different widths in the manufacturing process. When the active layer is formed by such selective growth, the height of the active layer surface is not constant, particularly on the stripe formation region, and the surface becomes uneven on the wafer, and the resist used when forming the diffraction grating is formed. It is difficult to apply a uniform thickness to the active layer, and patterning by photolithography cannot be performed accurately, and the spacing between the diffraction gratings may vary. A slight layer thickness distribution also occurs in the gain region, and this slight distribution changes the effective refractive index for light even at a position in the gain region, Results pitch of effective diffraction grating or changed, it becomes difficult to form a good diffraction grating, single-mode oscillation is difficult in the gain region, problems such as noise caused occurs. In addition, it is difficult to control the thickness distribution of the spot size conversion region, and the boundary between the spot size conversion region and the gain region becomes unclear, and a partial diffraction grating is formed on the spot size conversion region. Or Therefore, in the case of such a structure, a semiconductor laser having high quality as in the present application cannot be obtained.

On the other hand, the semiconductor laser according to the first embodiment does not have such a problem because the active layer thicknesses of the spot size conversion region and the gain region are both uniform. In the semiconductor laser according to the first embodiment, since the active layer width is controlled by photolithography and etching, control of the active layer width is easy and highly accurate, and the gain region and the spot size conversion region are completely formed. And a diffraction grating can be easily formed only in the gain region.

Embodiment 2 FIG. FIG. 4 is a cross-sectional view in the laser cavity length direction showing the structure of a semiconductor laser according to a second embodiment of the present invention. In the drawing, the same reference numerals as those in FIG. 1 denote the same or corresponding parts. A refractive index coupling type diffraction grating having a sufficiently high coupling efficiency is provided only in the upper part of the gain region 3a near the region in contact with the spot size conversion region 3b. The structure of the diffraction grating 33 is long in the laser resonator length direction. Has a structure similar to that of the diffraction grating 13 except that the difference is that the material composition is adjusted to obtain a coupling efficiency sufficient to reflect light.
The diffraction grating 13 is manufactured by the same manufacturing method as that described in the first embodiment. In the second embodiment, the end face on the gain region 3a side is formed by cleavage or the like so as to be a resonator end face capable of reflecting light, and a sufficient reflectance is obtained.

The semiconductor laser according to the second embodiment is
In the semiconductor laser according to the first embodiment, instead of providing the refractive index coupling type diffraction grating 13 on all the regions of the gain region 3a, only the upper part of the gain region 3a near the region in contact with the spot size conversion region 3b is provided. By providing the diffraction grating 33, light generated in the gain region 3a is reflected between the diffraction grating 13 and the end face on the gain region 3a side, thereby causing laser oscillation.

In the second embodiment, the same effect as that of the first embodiment can be obtained, and the diffraction grating 33 having the increased coupling efficiency can be used in the spot size conversion region 3.
Since the reflectivity for the light traveling from b to the gain region 3a is sufficiently high, light propagating from the spot size conversion region 3b to the gain region 3a by reflection at the front end face on the spot size conversion region 3b side is minimized. Gain area 3
This has the effect of preventing entry into a.

Embodiment 3 FIG. 8 is a sectional view showing the structure of the semiconductor laser according to the third embodiment of the present invention. In the figure, reference numeral 43 denotes a diffraction grating, and 43a denotes, for example, In _0.53 Ga.
_The buried layer is made of a material having a different gain from the material of the upper cladding layer 4, such as _0.47 As.

The third embodiment is different from the semiconductor laser shown in the first embodiment in that the buried layer 13a having a different refractive index from the upper cladding layer 4 has a different gain from the upper cladding layer 4. The diffraction grating provided on the gain region 3a by using the buried layer 43a is a gain-coupled diffraction grating 43. In the third embodiment, the same effect as that of the first embodiment is obtained. And by using the gain-coupled diffraction grating 43,
The difference in threshold gain between the main mode and the sub mode can be increased, and mode hopping noise due to return light from the front end face on the spot size conversion area 3b side can be reduced.

Embodiment 4 FIG. FIG. 9 is a sectional view showing the structure of a semiconductor laser according to the fourth embodiment of the present invention. In the figure, reference numeral 53 denotes a λ / 4 shift type diffraction grating (where λ is a light guided in the gain region 3a). The diffraction grating 53 adjusts the arrangement period of the buried layer 13a, divides the diffraction grating into two at the center of the gain region 3a in the laser resonator length direction, and arranges the arrangement period of one of the gratings. Can be easily formed by being shifted by λ / 4 with respect to the other.

The fourth embodiment is different from the semiconductor laser shown in the first embodiment in that the refractive index-coupled diffraction grating 1
3 by adjusting the period of the lattice arrangement of the buried layer 13a.
This is a four-shift type diffraction grating 53. In such a fourth embodiment, the same effect as in the first embodiment can be obtained, and the diffraction grating formed on the gain region 3a can be shifted by λ / 4. By using a diffraction grating of the type, it is possible to increase the side mode suppression ratio of the laser beam to increase the difference between the peaks of the main mode and the submode, and to obtain a stable main mode. .

In the first to fourth embodiments, a semiconductor laser made of an InP material using InP as a substrate has been described. However, the present invention is also applicable to a semiconductor laser made of another material such as a GaAs material. Embodiment 1 is applicable to such a case.
The same effect as that of Nos. To 4 is achieved.

In the first to fourth embodiments, the case where the conductivity type of the substrate is p-type has been described. However, in the present invention, the conductivity type of the substrate is n-type, and in each of the above embodiments, the n-type is used. This can be applied to the case where the layer which has been changed to p-type and the layer which has been p-type becomes n-type. In such a case, the same effects as those of the first to fourth embodiments can be obtained.

[0039]

As described above, according to the present invention, a first conductive type lower clad layer formed on a first conductive type semiconductor substrate and a fixed width disposed on the lower conductive layer are provided. A gain area, and a spot size conversion area whose width gradually decreases as the distance from the gain area increases,
An active layer having a certain thickness extending in a stripe shape in a predetermined direction; a current constriction structure provided to be in contact with both side surfaces of the active layer; and a second conductive type upper clad disposed on the active layer A second conductive type contact layer disposed on the upper cladding layer, and one of the lower cladding layer and the upper cladding layer provided at a position along the entire gain region of the active layer. A diffraction grating arranged in a lattice pattern in a direction in which the active layer extends, a pair of end faces provided perpendicular to the direction in which the active layer extends, and a pair of end faces provided on the end face on the spot size conversion region side. With the provision of the antireflection film, laser oscillation can be performed only in the gain region of the active layer, and reflection of light guided through the active layer on the end face on the spot size conversion region side can be prevented. There is an effect capable of providing a turbulence less semiconductor laser of the far field pattern.

Further, according to the present invention, since the diffraction grating is a refractive index coupling type diffraction grating in which semiconductor materials having different refractive indices are alternately arranged, a semiconductor laser with less disturbance in the far-field image is provided. There is an effect that can be done.

Further, according to the present invention, since the diffraction grating is a gain-coupled diffraction grating in which semiconductor materials having different gains are alternately arranged, the threshold gain difference between the main mode and the sub mode is increased. Therefore, there is an effect that a semiconductor laser capable of reducing mode hopping noise caused by return light from the end face on the spot size conversion area side can be provided.

According to the present invention, since the diffraction grating is a λ / 4 shift type diffraction grating, the side mode suppression ratio of the laser beam is increased to reduce the difference between the peaks of the main mode and the submode. This has the effect of providing a semiconductor laser that can be made large and can stably obtain a main mode.

Further, according to the present invention, a semiconductor laser according to the present invention includes a first conductive type lower cladding layer formed on a first conductive type semiconductor substrate, and a constant conductivity type disposed on the lower conductive cladding layer. An active layer having a constant thickness, comprising a gain region having a width of, and a spot size conversion region having a width gradually decreasing as the distance from the gain region increases; A current constriction structure provided to be in contact with both side surfaces of the second conductive type upper clad layer disposed on the active layer, a second conductive type contact layer disposed on the upper clad layer, Either the lower cladding layer or the upper cladding layer, provided only at a position along the area on the spot size conversion region side in the gain region of the active layer, is arranged in a lattice in a direction in which the active layer extends. Time A grating, a pair of end faces provided perpendicular to the direction in which the active layer extends, and the gain area side being a laser resonator end face; and a reflection provided on the end face on the spot size conversion area side. With the provision of the anti-reflection film, laser oscillation can be performed only in the gain region of the active layer, and reflection of light guided through the active layer at the spot size conversion region side end surface is prevented. Along with providing a semiconductor laser with less disturbance of the view field image, the light propagating from the spot size conversion region side to the gain region side by reflection at the end face on the spot size conversion region side is prevented from entering the gain region as much as possible. There is an effect that a semiconductor laser with less disturbance of the far-field image can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram showing a structure of a semiconductor laser according to a first embodiment of the present invention.

FIG. 2 is a plan view for explaining the structure of the semiconductor laser according to the first embodiment of the present invention.

FIG. 3 is a perspective view illustrating a method for manufacturing the semiconductor laser according to the first embodiment of the present invention.

FIG. 4 is a sectional view showing a structure of a semiconductor laser according to a second embodiment of the present invention.

FIG. 5 is a perspective view showing a structure of a conventional semiconductor laser.

FIG. 6 is a sectional view showing a structure of a conventional semiconductor laser.

FIG. 7 is a plan view for explaining a problem of a conventional semiconductor laser.

FIG. 8 is a sectional view showing a structure of a semiconductor laser according to a third embodiment of the present invention.

FIG. 9 is a sectional view showing a structure of a semiconductor laser according to a fourth embodiment of the present invention.

[Explanation of symbols]

1 p-InP substrate, 2 p-InP lower cladding layer, 3
Active layer, 3a gain region, 3b laser spot conversion region, 4n-InP upper cladding layer, 4a first upper cladding layer, 4b second upper cladding layer, 5p-InP current blocking layer, 6n-InP current blocking layer , 7 n-
InP contact layer, 8 LD anode electrode, 9 LD
Cathode electrode, 10 SiO ₂ insulating film, 11 reflective film,
12 high reflection film on the back surface, 13, 33 refractive index coupling type diffraction grating, 13a, 43a buried layer, 13c refractive index coupling layer, 14 antireflection film, 15 resist film, 22 guided light, 43 gain coupling type diffraction grating , 53λ / 4 shift type diffraction grating.

Claims (5)

[Claims] A first conductive type lower cladding layer formed on the first conductive type semiconductor substrate; a gain region having a constant width disposed on the lower conductive layer; An active layer having a constant thickness, which is formed of a spot size conversion region whose width is gradually reduced, and extends in a stripe shape in a predetermined direction; and a current constriction structure provided to be in contact with both side surfaces of the active layer. A second conductivity type upper cladding layer disposed on the active layer, a second conductivity type contact layer disposed on the upper cladding layer, and one of the lower cladding layer and the upper cladding layer; A diffraction grating provided in a position along the entire area of the gain region of the active layer and arranged in a lattice in a direction in which the active layer extends; and a pair of end faces provided perpendicular to the direction in which the active layer extends. And the above spot Semiconductor laser characterized by comprising an antireflection film provided on the end surface of the size conversion region side. 2. The semiconductor laser according to claim 1, wherein said diffraction grating is a refractive index coupling type diffraction grating in which semiconductor materials having different refractive indexes are alternately arranged. 3. The semiconductor laser according to claim 1, wherein said diffraction grating is a gain-coupled diffraction grating in which semiconductor materials having different gains are alternately arranged. 4. The semiconductor laser according to claim 1, wherein said diffraction grating is a λ / 4 shift type diffraction grating (where λ
Is the wavelength of the guided light). 5. A first conductivity type lower cladding layer formed on a first conductivity type semiconductor substrate, a gain region having a constant width disposed on the lower conductivity layer, and a distance from the gain region. An active layer having a constant thickness, which is formed of a spot size conversion region whose width is gradually reduced, and extends in a stripe shape in a predetermined direction; and a current constriction structure provided to be in contact with both side surfaces of the active layer. A second conductivity type upper cladding layer disposed on the active layer, a second conductivity type contact layer disposed on the upper cladding layer, and one of the lower cladding layer and the upper cladding layer; A diffraction grating, which is provided only at a position along the spot size conversion region side in the gain region of the active layer and is arranged in a lattice in a direction in which the active layer extends, with respect to a direction in which the active layer extends. Installed vertically A semiconductor laser comprising: a pair of end faces each having a laser cavity end face on the gain area side; and an antireflection film provided on the end face on the spot size conversion area side.