JPH0482197B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor laser array device.

[Prior Art] High-power semiconductor laser devices are currently being widely used because they can be used as light sources for optical recording systems such as optical disk systems and laser beam printers, as well as for space communications and YAG laser excitation. Research is being conducted. However, when considering the practical lifespan of a normal single semiconductor laser element, the optical output is limited to about 80 mW.

Therefore, research is being carried out on semiconductor laser array devices that can operate at a higher output than a single semiconductor laser element by integrating a plurality of semiconductor laser elements.

A semiconductor laser array device has a structure in which waveguides for a plurality of semiconductor laser elements are arranged on the same substrate, and is divided into the following two types.

One is a phase-locked array in which light propagating in multiple waveguides is optically coupled to each other and has a fixed phase relationship, and the other is a phase-locked array in which each waveguide is optically independent of each other. It is a standalone array. In a phase-locked array, it is possible to focus the output beam to the diffraction limit using a lens, but this is not possible with an independent array, so it is necessary to use a lens to focus the output beam to the diffraction limit. Phase-locked arrays are useful for this application.

A phase-locked array allows multiple transverse modes (array modes) and tends to oscillate in a mode in which the phase of light is inverted by 180 degrees in adjacent waveguides (180 degree phase mode). This is because the 180° phase mode confines light within the waveguide better than other array modes, and the gain required for oscillation is minimized.

However, since the image of the light emitted from the semiconductor laser array device, that is, the far-field image, has a multimodal peak in the 180° phase mode, it cannot be focused into a single spot by a lens. On the other hand, a mode in which the phases of light in each waveguide of a semiconductor laser array device are in-phase (0° phase mode) shows a far-field pattern with a single peak.
A lens can focus light onto a single spot. Therefore, there is a need for a semiconductor laser array device that oscillates in 0° phase mode.

Therefore, in order to obtain the output light in 0° phase mode,
A semiconductor laser array device has been proposed that is configured to convert guided light oscillating in a 180° phase mode into output light in a 0° phase mode at an output end face.

FIG. 4 is a perspective view showing a conventional semiconductor laser array device having a structure in which guided light in a 180° phase mode is converted into a 0° phase mode at the output end face.

This semiconductor laser array device is VSIS (V-
It has a channeled Substrate Inner Stripe) structure and is manufactured as follows.

An n-GaAs current blocking layer 22 is grown on a p-GaAs substrate 21 by a crystal growth method such as LPE growth. Next, V-shaped grooves 30 having a depth reaching the underlying n-GaAs substrate 1 are formed in the p-GaAs current blocking layer 22 in the form of parallel stripes by photolithography and etching techniques. Then, by the LPE method again, a p-Al _x Ga _1-x As cladding layer 2 is formed on the p-GaAs current blocking layer 22
3, p or n-Al _Y Ga _1-Y As active layer 24, n-
An Al _x Ga _1-x As cladding layer 25 and an n ⁺ -GaAs cap layer 26 are grown in sequence. Here, X>Y. Each striped region including the V-shaped groove 30 is referred to as a laser stripe.

Thereafter, in the vicinity of one end face, from the n ⁺ -GaAs cap layer 26 to the p-
The groove 31 is deep enough to reach inside the GaAs substrate 21.
Formed by RIBE (Reactive Ion Beam Etching) method, etc. Both side wall surfaces 32 and 33 of this groove 31 are formed perpendicularly to the laser stripe.

Next, end faces 34 and 35 perpendicular to the laser stripe are formed on both end faces by the cleavage method so that the cavity length is 2509 μm. Further, by photolithography and etching techniques such as RIBE, one end surface 34 is formed into an uneven shape so that the resonator lengths of adjacent stripes differ by a predetermined length l. This surface becomes the laser emitting end surface. Finally, p ^- type electrodes 27 and n
A mold electrode 28 is formed.

When a current is passed between the p-type electrode 27 and the n-type electrode 28 of the semiconductor laser array device manufactured in this manner, the current is injected in a stripe pattern into the region of the active layer 24 corresponding to the V-shaped groove 30. , active layer 2
A striped waveguide is formed in 4.

In this semiconductor laser array device, the difference l between the cavity lengths of adjacent stripes satisfies the following equation.

(2π/λ ₀ )・(Neff-1)・l=(2m-1)π ...(1) Here, λ ₀ is the oscillation wavelength of the laser, Neff is the refractive index of the waveguide, and m is a natural number. .

In this semiconductor laser array device, groove 3
The laser resonator formed from the side wall surface 33 and the end surface 35 of the laser resonator oscillates in a 180° phase mode by obtaining gain. The guided light in the 180° phase mode passes through the phase converter formed by the side wall surface 32 of the groove 31 and the output end face 34, so that the phase of the light in each waveguide is the same. It is converted into mode output light.

[Problems to be Solved by the Invention] However, in the conventional semiconductor laser array device described above, in order to form the resonator end face and to process the emission end face 34, the RIBE
It is necessary to use a dry etching method such as a dry etching method.
At this time, there are problems such as the crystal surface being contaminated by the etching gas, which tends to cause element deterioration, and the crystal surface becoming uneven with a diameter of about 0.1 μm or more, causing light to be scattered and lost. It was hot.

This invention was made to solve the above-mentioned problems, and because there is no need to use an etching method to form the end face, it has a clean and flat end face, and there is no loss due to element deterioration or light scattering. , an object of the present invention is to provide a semiconductor laser array device that can convert 180° phase mode guided light into 0° phase mode output light.

[Means for Solving the Problems] The present invention provides a semiconductor laser array device in which a plurality of waveguides are formed in parallel on a semiconductor substrate, in which the lengths of adjacent waveguides are adjusted to a predetermined length on one end side. an insulating semiconductor material layer is formed on the end face of the plurality of waveguides on the one end side, and a cleavage plane perpendicular to the waveguide is formed in the semiconductor material layer to emit light. It has an end surface.

The predetermined length t is (2π/λ ₀ )・|Neff−n
It is set to satisfy |·t=(2m−1)π, where λ ₀ is the oscillation wavelength of the laser, Neff is the refractive index of the waveguide, n is the refractive index of the semiconductor material layer, and m is a natural number. The refractive index Neff of the waveguide is different from the refractive index n of the semiconductor material layer.

[Function] In the semiconductor laser array device according to the present invention, 180° phase mode oscillation occurs between the cleavage plane formed in the insulating semiconductor material layer and the end face of the other end. This 180° phase mode oscillation light is converted into a 0° phase mode by passing through the semiconductor material layer, and is emitted from the laser emitting end face formed by the cleavage plane.

Since the refractive index of the semiconductor material layer is greater than the refractive index of the atmosphere, the difference between the refractive index of the waveguide and the refractive index of the semiconductor material layer becomes small. Therefore, even if there is uneven damage on the end face of the waveguide, the scattering of light due to the damage is small and can be ignored.

Furthermore, since the difference between the refractive index of the waveguide and the refractive index of the semiconductor material layer is small, it is possible to increase the difference in length between adjacent stripes determined by equation (1). Thereby, the depth of damage to the end face of the waveguide can be made relatively small, and its influence can be eliminated.

In this semiconductor laser array device, since the laser emitting end face can be formed by the cleavage method without using the etching method, the crystal surface is not contaminated by etching gas, and
There is no occurrence of uneven shapes on the crystal surface.
Therefore, there is no loss due to element deterioration or light scattering.

[Example] An example of the present invention will be described below with reference to the drawings.

FIG. 1A is a perspective view showing a main part of an embodiment of a semiconductor laser array device according to the present invention, and FIG. 1B is a sectional view taken along line AA of the semiconductor laser array device of FIG. 1A.

In FIG. 1B, on the n-GaAs substrate 1, an n
-Al _X Ga _1-X As cladding layer 2, n or p-Al _Y
Ga _1-Y As active layer 3, p-Al _x Ga _1-x As cladding layer 4, n-GaAs current blocking layer 5, p-Al _x Ga _1-X
An As clad layer 6 and a p-GaAs cap layer 7 are laminated in this order.

Five V-shaped grooves 8 are formed in the current blocking layer 5 in the form of parallel stripes. This V-shaped groove 8
is formed to a depth that reaches the surface of the underlying cladding layer 4. That is, at the bottom of this V-shaped groove 8, the upper cladding layer 6 and the lower cladding layer 4 are in contact, and a current is injected into the active layer 3 from this region, causing activation corresponding to the V-shaped groove 8. layer 3
A stripe-shaped waveguide is formed. Each striped region of the semiconductor layers 1 to 7 including the V-shaped groove 8 and the waveguide is referred to as a laser stripe.

As shown in FIG. 1A, one end surface of each of the layers 1 to 7 is formed into an uneven shape such that the lengths of adjacent laser stripes differ by a predetermined length t. Then, this end face is covered with insulating Al _Z Ga _1-Z As
A buried layer 9 is formed. A cleavage plane 10 perpendicular to the laser stripe is formed in this buried layer 9.

Note that the difference in length between adjacent laser stripes t
satisfies the following formula.

(2π/λ ₀ )・|Neff−n|・t=(2m-1)π …(2) Here, λ ₀ is the laser oscillation wavelength, Neff is the refractive index of the waveguide, and n is the buried layer The refractive index is 9, m is a natural number.

For example, the cladding layers 2, 4 and the active layer 3
Assuming that the Al mixed crystal ratio is X = 0.42 and Y = 0.14, and the Al mixed crystal ratio of the buried layer 9 is Z = 0.6, Neff = 3.4 and n = 3.265 at the oscillation wavelength λ ₀ = 0.78 μm. The difference in length between adjacent laser stripes is t
=2.9μm.

Next, a method for manufacturing this semiconductor laser array device will be explained with reference to FIG.

First, MOCVD (Metal
_Depending on the organic chemical vapor deposition _{) growth} method, _{n - Al}
A cladding layer 4 and an n-GaAs current blocking layer 5 are grown in sequence. Here, X>Y. Next, using photolithography and etching technology,
Five V-shaped grooves 8 having a depth reaching the cladding layer 4 are formed in the current blocking layer 5 in the form of parallel stripes (see FIG. 1B).

Then, MOCVD is placed on the V-shaped groove 8 again.
A p-Al _x Ga _1-x As cladding layer 6 is buried and grown using a p-Al High Al mixed crystal ratio on top
An Al _0.8 Ga _0.2 As layer 11 is grown.

Next, by photolithography and the RIBE method, a groove 1 is formed which is perpendicular to the laser stripe and has a depth reaching from the Al _0.8 Ga _0.2 As layer 11 into the n-GaAs substrate 1.
form 2. The side wall surface 12a of this groove 12 is formed in an uneven shape so that the lengths of adjacent laser stripes differ by a predetermined length t.

Next, an insulating Al _Z Ga _1-Z As layer is grown by LPE on the surface of the growth layer formed as described above. At this time, Al _0.8 with a high Al mixed crystal ratio
Since no crystal growth occurs in the Ga _0.2 As layer 11,
An Al _Z Ga _1-Z As buried layer 9 is selectively grown only within the trench 12 . Next, the Al _0.8 Ga _0.2 As layer 11 is selectively etched away, and an end face 10 perpendicular to the laser stripe is formed in the center of the buried layer 9 by a cleavage method.

The buried layer 9 becomes a 180° phase conversion part, and the cleavage plane 10
becomes the laser emitting end face of the semiconductor laser array device.

Finally, the n-GaAs substrate 1 and the cap layer 7
forming an n-type electrode and a p-type electrode on the surface of the
The other end face is formed by the cleavage method so that the resonator length is 250 μm, and then it is mounted on a Cu heat sink with In solder with the growth layer side facing down.

When the side wall surface 12a of the groove 12 is formed into an uneven shape, the depth of damage caused to the crystal surface of the side wall surface 12a is approximately 0.1 μm. The degree of light scattering due to damage to the crystal surface is evaluated by the value of K _S determined by the following equation.

K _S =(2π/λ)・Δn・d (3) Here, λ is the wavelength of light, Δn is the refractive index difference between materials, and d is the depth of damage.

In the semiconductor laser array device of the above embodiment, since the buried layer 9 is formed on the waveguide end face, damage to the crystal surface of the waveguide end face is covered with the buried layer 9. As mentioned above, the waveguide refractive index Neff
is 3.4, and the refractive index n of the buried layer 9 is 3.265, so the refractive index difference Δn is 0.135, which is small. λ
= 0.78 μm, K _S =0.03π according to equation (3).

In contrast, in the conventional semiconductor laser array device shown in FIG. 4, the crystal surface of the light emitting end face is damaged. Therefore, damage to the crystal surface comes into contact with the atmosphere. Since the refractive index Neff of the waveguide is 3.4 and the refractive index of the atmosphere is 1, the refractive index difference Δn is as large as 2.4. Therefore, according to equation (3), K _S =0.62π.

In this way, the semiconductor laser array device of the above embodiment has a degree of light scattering that is approximately 1/20th that of the conventional semiconductor laser array device.

Therefore, in the semiconductor laser array device of the above embodiment, even if the waveguide end face is damaged to a depth of about 0.1 μm, the effect of the damage on the laser characteristics of light scattering is small and can be ignored.

Furthermore, in the semiconductor laser array device of the above embodiment, the refractive index difference |Neff−n| (=Δn) is smaller than that of the conventional semiconductor laser array device.
The difference t between the lengths of adjacent laser stripes determined by equation (2) on page 10 can be increased.

Therefore, the semiconductor laser array device of the above embodiment uses the configuration for phase conversion to simultaneously increase the difference t between the lengths of adjacent laser stripes to relatively reduce the damage caused by etching on the side wall surface 12a of the groove 12. Can be made smaller. Thereby,
The effect of etching can be removed.

FIG. 3 is a far-field image of laser light emitted from the emission end face when the semiconductor laser array device manufactured as described above is caused to oscillate;
It shows the light intensity distribution in the direction parallel to the bonding surface.

As shown in the figure, a single peak near the diffraction limit was stably obtained. This is because the 180° phase mode guided light oscillated in each laser stripe passes through the buried layer 9, that is, the 180° phase converter, and is converted into 0° phase mode output light.
At this time, in the above example, the refractive index difference Δn between the buried layer 9 and the waveguide is relatively small, Δn=0.135, so the light reflectance at the interface with the buried layer 9 is approximately 0.04.
%, which can be practically ignored. In addition, since the laser emission end facet is formed by a cleavage plane, the oscillation threshold is increased due to the provision of a 180° phase conversion section in the semiconductor laser array device.
Almost no decrease in quantum efficiency or reliability was observed.

In addition to semiconductor laser array devices using GaAs-AlGaAs semiconductor materials, the present invention also applies to
It is also applicable to semiconductor laser array devices using InP-InGaAsP-based and other semiconductor materials.

Furthermore, the present invention is applicable to semiconductor laser array devices that use either gain-guided or refractive index-guided waveguide structures, and can be applied to both real-refractive index-guided and gain-guided waveguide structures. It is also applicable to the semiconductor laser array device used.

Furthermore, the conductivity types of each layer may be reversed from those in the embodiment.

[Effects of the Invention] As described above, according to the present invention, the laser has a laser emitting end face made of a cleavage plane, converts 180° phase mode guided light into 0° phase mode emitting light, and emits it from the laser emitting end face. This enables stable oscillation and a diffraction-limited unimodal peak far-field pattern even during high-power operation without increasing threshold current, decreasing quantum efficiency, or decreasing reliability. is obtained.

[Brief explanation of the drawing]

FIG. 1A is a perspective view showing the main parts of an embodiment of a semiconductor laser array device of the present invention, FIG. 1B is a sectional view taken along line AA in FIG. 1A, and FIG. 3 is a diagram for explaining the manufacturing method, FIG. 3 is a diagram showing a far-field image of laser light produced by the semiconductor laser array device of the same embodiment, and FIG. 4 is a perspective view showing a conventional semiconductor laser array device. In the figure, 1 is an n-GaAs substrate, 2 is an n-GaAs substrate, and 2 is an n-GaAs substrate.
Al _X Ga 1 _{- X} As clad layer, 3 is Al _Y Ga _1-Y As active layer, 4 is p- _Al
GaAs current blocking layer _, 6 _{p - Al} shows.

Claims (1)

[Scope of Claims] 1. In a semiconductor laser array device in which a plurality of waveguides are formed in parallel on a semiconductor substrate, the lengths of adjacent waveguides differ by a predetermined length t on one end side, and An insulating semiconductor material layer is formed on the end face of the plurality of waveguides on one end side, and the semiconductor material layer is formed with an output end face consisting of a cleavage plane perpendicular to the waveguide. The length t is set to satisfy (2π/λ ₀ )・|Neff−n|・t=(2m−1)π, where λ ₀ is the oscillation wavelength of the laser, and Neff is the refraction of the waveguide. A semiconductor laser array device, wherein n is a refractive index of the semiconductor material layer, m is a natural number, and a refractive index Neff of the waveguide is different from a refractive index n of the semiconductor material layer.