JP2684930B2 - Phase-lock laser array and manufacturing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a visible light phase-locked laser array used in the fields of optical measurement and optical information processing.

[0002]

2. Description of the Related Art In recent years, demand for semiconductor lasers has increased in many fields, and GaAs-based and InP-based semiconductors have been actively commercialized. Above all, there is a strong demand for higher output, and GaAs-based products with optical output exceeding 50w have been commercialized. However, there is a limit to the light density at the light emitting surface of the material of the semiconductor laser, and if the light density is exceeded, the laser will be destroyed. It determines the light output. Therefore, a stable fundamental transverse mode laser stabilizes the transverse mode by confining light in an optical waveguide with a small cross-sectional area, which is a disadvantageous structure for high output power, and is limited to about 100 mW. .

Therefore, a structure called a phase lock array is adopted in order to achieve both a stable transverse mode and a high output. This is due to the multiple waveguides in close proximity
A stable transverse mode is realized by combining the phases of light in each waveguide. Moreover, since the optical output is the sum of the outputs emitted from the respective waveguides, it is possible to increase the optical output accordingly by increasing the number of the waveguides.

FIG. 5 shows the classification of the phase-locked array according to the main waveguiding mechanism. (A) Gain-guided type, (b) Loss-guided type, (c)
The index guided type is often used. Besides these,
There is an anti-refractive index waveguide type. The anti-refractive index waveguide type is
As shown in FIG. 6 (d), the refractive index of the region having the gain is lower than that of the region having no gain. Different from the refractive index distribution.

In the GaAs semiconductor laser, the gain waveguide type (a)
And the loss waveguide type (b) is often used. These are particularly popular because similar fabrication processes are available for phase-locked arrays. Further, the refractive index guided type (c) can also be realized by a simple ridge stripe structure, and is therefore used relatively often.

By the way, in the phase-locked array, the coupling between the waveguides includes 0 ° phase coupling in which the phase is the same as the adjacent waveguide and 180 ° phase coupling in which the 180 ° phase is different. As shown in FIG. 7 (a), a 0-degree phase coupling produces a single-peaked far-field image, and it is easy to form a parallel beam or focus the beam. On the other hand, 180 ° phase coupling results in a bimodal far-field image as shown in FIG. 7B, which makes it difficult to use.

As shown in FIG. 6, in the loss guiding type (b) or refractive index guiding type (c) structure, the refractive index n1 of the element region is higher than the refractive index n0 of the inter-element region. Therefore, when the structure of the loss guiding type (b) or the refractive index guiding type (c) is used, the effect of basically confining the light in the element region becomes strong, and as shown in FIG. 8 (A-2). The 180 ° phase coupling of the basic mode tends to occur. The reason why 180 ° phase coupling is likely to occur is that the light intensity in the inter-element region is weak and the light intensity becomes zero in the center of the inter-element region as shown in FIG. 8 (A-2).
This is because the 180 ° phase coupling has smaller waveguide loss and is more stable.

In the case of the gain waveguide type (a), the refractive index distribution in the element region is slightly lower as shown in FIG. Therefore, light confinement is weak in the element region, and 0 ° phase coupling is likely to occur. However, it is unstable with respect to temperature and light output because it has a structure that confine light only by gain.

As shown in FIG. 6, the anti-refractive index waveguide type is the same as the gain waveguide type and has a higher refractive index in the inter-element region than in the element region. Furthermore, a good point compared to the gain waveguide type (c) is that due to the large difference in the refractive index between the element region and the inter-element region, strong light coupling occurs between the elements adjacent to each other. As shown in 2), 0 ° phase coupling is easily obtained. More specifically, since the element area has a gain, light is confined,
Further, since the inter-element region has a higher refractive index than the element region, light is confined. As a result, light coupling occurs in the element region and the inter-element region, and 0 ° phase coupling is obtained.

Therefore, the anti-refractive index waveguide type will be considered.
FIG. 9 is a schematic perspective view showing an element structure of a conventional anti-refractive index wave-guiding type phase-locked laser array, and FIG. 10 is an enlarged cross-sectional view of an essential part thereof (amplified fuzzy letters 55 (1)).
Volume 1989: Appl. Phys. Lett. 55 (1), 3 July 1989. ).

The first cladding layer 1 is formed on the GaAs substrate 10.
N-Al0.4Ga0.6As as 1 and Ga as the active layer 12.
As / AlGaAs multiple quantum well layer and second clad layer 1
3 is formed of p-Al0.4Ga0.6As. The second clad layer has an element region in which a current is injected into the active layer by etching into a mesa shape and an element winding region in which a current is not injected into the active layer. Here, the refractive index n1 of the inter-element region is higher than the refractive index n0 of the element region.

In this element, the AlGaAs16 layer is formed on the element region and the inter-element region. Especially, in the inter-element region, the AlGaAs16 layer is used as the optical waveguide layer.
Since it is close to 12 (the AlGaAs 16 layer is separated from the active layer in the element region), the inter-element region has a higher refractive index than the element region as shown in FIG. Moreover, since the difference in the refractive index between the element region and the inter-element region is large, the stability of mode coupling is excellent.

The current is selectively injected only into the element region. Since the radiation loss of the optical mode is large in the inter-element region, oscillation does not occur, and oscillation occurs only in the element region. In order to maximize the coupling between adjacent elements in such a configuration, the width s of the inter-element region is set to be close to one half of the resonance wavelength of the transverse wave of light shown in the following equation. (IEEE J. Quantum Electron 2
See 6.482, 1990. ).

S = λ1 / 2 λ1 = λ / (n12-n02 + (λ / 2d) 2) 1/2 s: Guide region width, d: Stripe width λ: Wavelength, λ1: Transverse wave wavelength n0: Element region Effective refractive index n1: Effective refractive index in the inter-element region If set in this way, the array mode will be in a resonance state,
All the elements are phase-coupled with each other by 0 ° and the array mode gain is the highest (0 ° phase-coupling is the state where oscillation is most likely).

[0015]

However, it is difficult to obtain stable 0 ° phase coupling even in the conventional anti-refractive index guided phase-locked laser array described above. The reason will be described. FIG. 11 shows the gain of each mode with respect to the width s of the inter-element region when the number of elements is 10.

From this figure, it is clear that when s = λ1 / 2, the mode gain of 0 ° phase coupling shown by the solid line is large. However, in addition to the 0 ° phase-coupling mode, there are 180 ° phase-coupling mode and proximity mode shown by the wavy line, and the gain difference Δgp with them cannot be large.
There is also a case where the phase-coupling mode is transferred to the 180-degree phase-coupling mode or the proximity mode. That is, the individual lasers of the phase-locked laser array oscillate in various modes, or the mode (0th mode, 1st mode) selected by the optical output changes as shown in FIG. It will be very unstable.

Therefore, to obtain only 0 ° phase coupling, a Talbot filter or the like is added separately from the phase-locked laser array as described in the literature (Appl.Phys.Lett.55 (1), 3 July 1989). It was necessary to devise something to do.

The first object of the present invention is to increase the radiation loss of the 180 ° phase-coupled mode and the proximity mode to obtain a stable 0 °.
An object of the present invention is to provide a phase-locked laser array capable of obtaining a phase-coupled mode.

A second object of the present invention is to provide a method for providing a refractive index profile in the inter-element region, which is an effective means for a stable 0 ° phase coupling mode.

[0020]

The phase-locked laser array according to claim (1) has a structure in which, in the inter-element region, the refractive index is large in the central portion and small in both end portions.

According to a second aspect of the present invention, there is provided a method of manufacturing a phase-locked laser array, wherein a superlattice optical waveguide layer is formed at a high temperature on a ridge stripe having a (111) A plane as a side surface formed in a highly doped second cladding layer. I decided to grow.

[0022]

The phase-locked laser array according to claim (1) is formed such that in the inter-element region, the refractive index is high in the central part and low in the peripheral part, and the radiation loss of 180 ° phase-coupled mode and adjacent mode is reduced. Can be increased. Therefore, it became possible to obtain a stable 0 ° phase coupling mode.

In the method of manufacturing a phase-locked laser array according to claim (2), the superlattice is disordered by selective self-diffusion from the (111) A plane during growth of the superlattice optical waveguide layer and the third cladding layer. Can be converted. Therefore, it became possible to fabricate an inter-element region in which the refractive index was large in the central portion and small in both end portions.

[0024]

EXAMPLES (Examples) FIG. 1 shows the examples described in claims (1) and (2).

FIG. 1 is a perspective view showing the outline of a phase-locked laser array according to the present invention, and FIG. 2 is an enlarged sectional view of the main part thereof.

The configuration will be described. On the n-GaAs substrate 0, n-AlGaInP first cladding layer 1, active layer 2, p-AlGaInP
The second cladding layer 3 is formed. Second cladding layer 3
Is formed of an element region which is a mesa-shaped ridge stripe 20 by etching, and an inter-element region in which the second cladding layer 3 is removed by etching and the superlattice optical waveguide layer 5 and the n-AlGaInP third cladding layer 6 are embedded. Has been done. Further, the second clad layer 3 and the third clad layer 6 are covered with a p-GaAs cap layer 7, and an anode electrode 21 is formed thereon. N-
A cathode electrode is formed on the GaAs substrate 0.

The point of the construction of the phase-locked laser array of the present invention is that the superlattice optical waveguide layer 5 is formed on the side surface of the ridge stripe 20 in the element region and on the surface of the inter-element region. Since the optical waveguide layer 5 formed on the side surface of the ridge 20 is further away from the active layer, the effective refractive index of the optical waveguide layer 5 is lower than the refractive index of the diffusion region in the inter-element region.

Further, both ends of the optical waveguide layer 5 in the inter-element region are divided into a diffusion region in which impurities are diffused and a non-diffusion region in which impurities are not diffused. In this diffusion region, the superlattice is disordered due to the diffusion of impurities, and the refractive index of this portion is lower than that of the non-diffusion region in which the impurities are not diffused. Therefore, as shown in FIG.
The element region, the diffusion region, and the non-diffusion region have different refractive indexes. Especially in the inter-element region, the refractive index is high in the non-diffusion region, so that light is easily trapped in this portion. By utilizing this phenomenon, 0 ° phase coupling as shown in FIG. 8B-2 can be obtained.

Next, a method for manufacturing the phase-locked laser array shown in FIGS. 1 and 2 will be described with reference to FIG.

As shown in FIG. 3A, n- (Al0.7) was formed on the n-GaAs substrate 0 by the first pressure-reduced metal-organic chemical vapor deposition method.
Ga0.3) InP first cladding layer 1 is 1 μm, GaInP active layer 2 is 0.
06μm, p- (Al0.7Ga0.3) InP second clad layer 3 1μm, p-
The GaInP antioxidant layer 4 is continuously grown to 0.1 μm.

Next, as shown in (b), a stripe-shaped etching mask made of SiO 2 is formed on the crystal surface, and etching is performed with a sulfuric acid-based etchant. The etching stops at about 0.2 μm above the active layer 2. Up to the above, ridge stripe 2 with a stripe width of 3 μm and spacing of 5 μm
0 is formed.

Further, as shown in (c), a GaInP well layer with a film thickness of 60 Å is formed with a film thickness of 100 Å while leaving the stripe mask.
A superlattice optical waveguide layer 5 and an n-AlGaInP third cladding layer 6 separated by an (Al0.5Ga0.5) InP barrier layer are grown. The number of well layers of the superlattice optical waveguide layer 5 is 10.

Since the p- (Al0.7Ga0.3) InP second cladding layer 3 is previously doped with Zn so as to have a carrier concentration of 1 × 10 18 cm −3, the second low pressure metal organic vapor phase epitaxy method is performed. To superlattice waveguiding layer 5 and n- (Al0.7Ga0.3) In
When the P third cladding layer 6 was grown at a temperature of 750 ° C., the second side was formed only from the (111) A plane which was the side surface of the ridge stripe 20.
Zn, which is a dopant of the clad layer 3, is used as the superlattice waveguide layer 5
Spread violently. Then, only the ridge stripe 20 near the superlattice waveguiding layer 5 is disordered and almost (Al0.2Ga0.8)
A mixed crystallized region 30 having an InP composition is formed. However, the remaining flat portion keeps the superlattice waveguiding layer 5 in the original form.

Next, as shown in (d), after removing the stripe mask, the p-GaAs cap layer 7 is grown in the third growth.

Finally, as shown in (e), the anode electrode 2
1. The cathode electrode 22 is formed to complete the device.

In this phase-locked laser array,
Non-diffusion area width s1 and diffusion area width s2 in the inter-element area
Satisfies the following relationship.

S1 + 2 s2 = λ1 / 2 λ1 = λ / (n12-n02 + (λ / 2d) 2) 1/2 s1: non-diffusion region width, s2: diffusion region width, d: inter-element region width λ: wavelength , Λ1: Transverse wave wavelength n0: Effective refractive index of element region n1: Effective refractive index of inter-element region Here, refractive indices n1 and n0 are 3.4396, 3.4292 and wavelength 680n, respectively.
m, element region width 3 μm, total of non-diffusion region width s1 and diffusion region width 2 s2 was 1.2 μm. Here, λ1 / 2 is about 1.2 μm, which is almost the same as s1 + 2s2. Where diffusion area width s2
Is about 0.2 μm, but is sufficiently smaller than the non-diffusion region width s1, so λ1 is the same as when there is no diffusion region.

The effective refractive index in the lateral direction of the phase-locked laser array thus manufactured is high in the non-diffusion region at the center of the inter-element region and low in the diffusion regions at both ends, as shown in FIG. .

In the 0 ° phase coupling having one light intensity peak in the inter-element region, strong coupling occurs between the element regions and high gain can be obtained almost in the same manner as when there is no diffusion region.

On the other hand, in the 180 ° phase coupling mode and the proximity mode, the light intensity distribution exists in the portion close to the inter-element region, so that it is strongly influenced by the diffusion region and radiation loss increases. Therefore, only the 0 ° phase-coupling mode, which always has a mode peak in the center of the inter-element region, is selected and oscillation occurs. Moreover, as described in the conventional example, the relationship of s (= s1 + 2s2) = λ1 / 2 is also satisfied here, so a stable 0 ° phase coupling mode is realized without sacrificing the gain of the oscillation mode. it can.

Although AlGAInP is used as the material of the active layer of the phase-locked laser array in this embodiment, it goes without saying that it is also effective for all materials used for semiconductor lasers.

[0042]

In the phase-locked laser array according to the present invention, a stable 0 ° phase coupling mode can be realized up to a current injection level of 8 times the threshold current.

[Brief description of the drawings]

FIG. 1 is a perspective view of a device structure of a phase-locked laser array according to the present invention.

FIG. 2 is an enlarged sectional view of a device structure of a phase-locked laser array according to the present invention.

FIG. 3 is a sectional view of a manufacturing process of a phase-locked laser array according to the present invention.

FIG. 4 is a diagram showing a lateral effective refractive index profile of a phase-locked laser array according to the present invention.

FIG. 5 is a sectional view of a device structure of a phase-locked laser array having various waveguiding mechanisms.

FIG. 6 is a diagram showing a refractive index distribution of a phase-locked laser array having various waveguide mechanisms.

FIG. 7 is a diagram showing monomodality and bimodality.

FIG. 8 is a diagram showing refractive index distributions of 0 ° and 180 ° phase coupling modes and electric field distributions corresponding thereto.

FIG. 9 is a perspective view of an element structure of a conventional anti-refractive index guided phase-locked laser array.

FIG. 10 is an enlarged cross-sectional view of a device structure of a conventional anti-refractive index waveguide type phase-locked laser array.

FIG. 11 is a diagram showing the mode gain with respect to the inter-element region width s of the anti-refractive index guided phase-locked laser array.

FIG. 12 is a diagram showing electric field intensities of the 0th-order mode and the 1st-order mode of the 0 ° phase coupling and the 1st-order mode of the 180 ° phase coupling with respect to the refractive index distribution.

[Explanation of symbols]

 0 n-GaAs substrate 1 n- (Al0.7Ga0.3) InP first clad layer 2 GaInP active layer 3 p- (Al0.7Ga0.3) InP second clad layer 4 p-GaInP antioxidant layer 5 n- ( Al0.5Ga0.5) InP / GaInP superlattice optical waveguide layer 6 n- (Al0.7Ga0.3) InP third cladding layer 7 p-GaAs cap layer 10 GaAs substrate 10a n-GaAs buffer layer 11 first cladding layer 12 Active layer 13 Second clad layer 14 p-GaAs 15 p-Al0.18Ga0.82As layer 16 p-Al0.4Ga0.6As layer 17 Cap layer 18 Current blocking layer 20 Ridge stripe 21 Anode electrode 22 Cathode electrode 30 Mixed crystal region

Claims (4)

(57) [Claims] 1. A compound semiconductor substrate, a first clad layer, an active layer, a second clad layer formed on the compound semiconductor substrate, a plurality of element regions for injecting current into the active layer, and a plurality of the element regions. And an inter-element region that does not inject current into the active layer, the inter-element region having a non-diffusion region at the center and diffusion regions at both ends thereof. A phase-locked laser array, wherein the refractive index of the non-diffusion region is larger than that of the diffusion region. 2. A step of forming a first clad layer, an active layer, and a second clad layer having a predetermined carrier concentration on a compound semiconductor substrate, and etching the second clad layer so that its side surface is (111). ) A step of forming a ridge stripe to be the A-face, and growing an optical waveguide layer composed of a superlattice between the ridge stripes, while adding impurities doped in the second cladding layer on the side surface of the ridge stripe to the optical waveguide layer. A method of manufacturing a phase-locked laser array, comprising: 3. The carrier concentration of the second cladding layer is 1 × 1018 cm.
-3 or more, The manufacturing method of the phase lock laser array of Claim 2 characterized by the above-mentioned. 4. The method for manufacturing a phase-locked laser array according to claim 2, wherein the optical waveguide layer is grown at a growth temperature of 700 ° C. or higher by a low pressure metal organic vapor phase epitaxy method.