JP5460477B2 - Surface emitting laser array element - Google Patents

Description

  The present invention relates to a surface emitting laser array element.

  Conventionally, as a signal light source for optical interconnection, a surface emitting laser array element in which a plurality of surface emitting laser elements are two-dimensionally arranged on a substrate is used. This surface emitting laser array element is configured such that each surface emitting laser element outputs an independent laser light signal.

  On the other hand, a technique using this surface-emitting laser array element as a watt-class high-power laser light source is disclosed (see Non-Patent Document 1). Unlike the case of the signal light source described above, this surface emitting laser array element is configured such that the laser light outputs from a plurality of surface emitting laser elements are integrated and function as one light source. Further, such a surface emitting laser array element is expected to be a highly reliable high output laser light source because there is no optical damage (catastrophic optical damage: COD) of the end face unlike the end face emitting type laser element. Yes. The power conversion efficiency defined by the ratio of the laser light output to the power injected into the element is also reported to be 51% at the maximum in the surface emitting laser array element described in Non-Patent Document 1, and the edge emitting laser element. It is said to be high enough to compete with.

  Here, when the surface emitting laser array element is operated, in the area where there are many other adjacent surface emitting laser elements, such as the central area of the surface emitting laser array element, the heat inflow from the other adjacent surface emitting laser elements. The temperature rise is larger because there are many. On the other hand, in a region where there are few other adjacent surface emitting laser elements, such as the peripheral region of the surface emitting laser array element, the temperature rise is smaller than that in the central region because there is less heat inflow from the other adjacent surface emitting laser elements. . As a result, there is a problem that a temperature difference occurs in the surface emitting laser element between the central region and the peripheral region of the surface emitting laser array element, and the laser oscillation wavelength also varies and becomes non-uniform.

  In Patent Document 1, in order to solve the above problem, a surface emitting laser element is arranged in a region other than the central region of the surface emitting laser array element, or the post diameter of the element in the central region and the peripheral region, or A technique for making the areas of the conductive region and the oxidized region different is disclosed.

JP 2005-216925 A

Jean-Francois Seurin, et al., “High-power high-efficiency 2D VCSEL arrays”, Proc. SPIE, Vol. 6908, 690808 (2008)

  However, in the technique of Patent Document 1, it is difficult to increase the degree of integration of the surface emitting laser elements when the surface emitting laser elements are arranged in a region other than the central region of the surface emitting laser array element, which hinders high output. There was a problem of becoming. In addition, when the post diameter of the element is different between the central region and the peripheral region, the characteristics of the surface emitting laser elements are also different, which causes a problem that the design and configuration become complicated. It was.

  The present invention has been made in view of the above, and an object of the present invention is to provide a surface emitting laser array element having a simple configuration and high output and having a uniform laser oscillation wavelength.

  In order to solve the above-described problems and achieve the object, a surface emitting laser array element according to the present invention is a surface emitting laser array element in which a plurality of surface emitting laser elements are two-dimensionally arranged, The light-emitting laser element optically resonates a temperature compensation layer whose layer thickness is set so that the difference in laser oscillation wavelength due to the temperature difference between the first area where there are many other adjacent surface-emitting laser elements and the second area where there are few is small. It is characterized by having in the vessel.

  The surface emitting laser element according to the present invention is characterized in that, in the above invention, the surface emitting laser element has an intracavity structure.

  In the surface emitting laser array element according to the present invention, the temperature compensation layer functions as a phase adjustment layer in the above invention.

  In the surface emitting laser array element according to the present invention, the temperature compensation layer of the surface emitting laser element disposed in the second region is the surface emitting laser element disposed in the first region. It is thicker than the temperature compensation layer.

  According to the present invention, there is an effect that it is possible to realize a surface emitting laser array element having a simple configuration and high output and having a uniform laser oscillation wavelength.

FIG. 1 is a schematic plan view of a surface emitting laser array element according to an embodiment. FIG. 2 is a cross-sectional view of a surface emitting laser element which is a main part of the surface emitting laser array element shown in FIG. FIG. 3 is a diagram showing an example of the relationship between the center-to-center distance of the surface emitting laser element and the temperature rise in the center region. FIG. 4 is a diagram for explaining an example of a method for changing the layer thickness of the temperature compensation layer for each region.

  Embodiments of a surface emitting laser array element according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

(Embodiment)
FIG. 1 is a schematic plan view of a surface emitting laser array element according to an embodiment of the present invention. As shown in FIG. 1, the surface-emitting laser array element 100 has a plurality of surface-emitting laser elements arranged on a substrate S two-dimensionally and in a triangular lattice shape. Here, the region where the surface emitting laser elements are arranged is divided into a central region A1, an intermediate region A2, and a peripheral region A3. The surface emitting laser element 101 is disposed in the central area A1, the surface emitting laser element 102 is disposed in the intermediate area A2, and the surface emitting laser element 103 is disposed in the peripheral area A3. Regarding the surface-emitting laser element 103, those arranged at the vertices of the hexagon are indicated by white circles, and those arranged at the sides of the hexagon are indicated by hatched circles.

FIG. 2 is a cross-sectional view of the surface emitting laser elements 102 and 103 which are the main parts of the surface emitting laser array element 100 shown in FIG. As shown in FIG. 2, the surface emitting laser element 101 includes a lower DBR mirror 1 that is a lower multilayer reflector, an active layer 2 having a multiple quantum well structure, a p-type spacer layer 3 on a substrate S, The p ⁺ type contact layer 4 has a stacked structure. In the p-type spacer layer 3, a current confinement layer 5 having a circular current injection portion 5a at the center is disposed. The active layer 2 to the p ⁺ -type contact layer 4 constitute a cylindrical mesa post.

A semi-annular n-side electrode 6 is formed on the surface of the lower DBR mirror 1 around the mesa post. A p-side annular electrode 7 is formed on the p ⁺ -type contact layer 4. In the opening of the p-side annular electrode 7, a temperature compensation layer 8a and an upper DBR mirror 9 that is an upper multilayer film reflecting mirror are sequentially formed. The temperature compensation layer 8a has a temperature compensation function to be described later, and is disposed between the lower DBR mirror 1 and the upper DBR mirror 9 constituting the optical resonator, thereby adjusting the optical length of the optical resonator. Thus, it also has a function as a phase adjustment layer that makes the positions of the nodes and antinodes of the standing wave of light appropriate.

On the other hand, the surface-emitting laser element 103 has the same structure as the surface-emitting laser element 101 and has a lower DBR mirror 1, an active layer 2, a p-type spacer layer 3, and a p ⁺ -type contact layer 4 on a substrate S. A current confinement layer 5 having a current injection portion 5a, a semi-annular n-side electrode 6, and a p-side annular electrode 7. A temperature compensation layer 8b and an upper DBR mirror 9 are sequentially formed in the opening of the p-side annular electrode 7. Similar to the temperature compensation layer 8a of the surface emitting laser element 101, the temperature compensation layer 8b has a temperature compensation function and a function as a phase adjustment layer, but is thicker than the temperature compensation layer 8a. Is set.

  The surface emitting laser element 102 also has the same structure as the surface emitting laser elements 101 and 103, but the layer thickness of the temperature compensation layer is thicker than the temperature compensation layer 8a of the surface emitting laser element 101, and the surface emitting laser element 102 has the same structure. It is set thinner than the temperature compensation layer 8b of the element 103.

The substrate S is made of undoped GaAs, for example. The lower DBR mirror 1 is composed of, for example, 34 pairs of GaAs / Al _0.9 Ga _0.1 As layers, and at least the uppermost portion is formed with n-type GaAs serving as a contact layer for the n-side electrode 6. The active layer 2 has a structure in which an InGaAs well layer having 3 layers and a GaAs barrier layer having 4 layers are alternately stacked for use in, for example, a 1100 nm band laser beam. The layer also functions as an n-type cladding layer. The p-type spacer layer 3 and the p ⁺ -type contact layer 4 are made of, for example, p-type and p ⁺ -type GaAs doped with carbon. As for the current confinement layer 5, for example, the current injection portion 5a is made of AlAs having a diameter of about 10 μm, and the circumferentially changing portion is made of Al ₂ O ₃ . The acceptor or donor concentration of each p-type or n-type layer is, for example, about 1 × 10 ¹⁸ cm ⁻³ , and the acceptor concentration of the p ⁺ -type layer is, for example, 1 × 10 ¹⁹ cm ⁻³ or more. Also, a lower graded composition layer and an upper graded composition layer, which are made of AlGaAs, for example, above and below the current confinement layer 5 and whose Al composition increases stepwise as the current confinement layer 5 is approached in the thickness direction. May be provided.

  The p-side annular electrode 7 is made of, for example, Pt / Ti, has an outer diameter of 30 μm that coincides with the outer periphery of the mesa post, and an inner diameter of the opening is, for example, 11 to 16 μm. The n-side electrode 6 is made of, for example, AuGeNi / Au, and has an outer diameter of 80 μm and an inner diameter of 40 μm.

The temperature compensation layers 8a and 8b are made of, for example, silicon nitride (SiN _x ) that is a dielectric. The upper DBR mirror 9 is composed of, for example, 10-12 pairs of SiN _x / SiO ₂ , and an α-Si / SiO ₂ or α-Si / Al ₂ O ₃ pair is selected depending on the refractive index of the material. The number of pairs may be such that an appropriate reflectivity of about 99% can be obtained.

  Further, the n-side electrode 6 of each of the surface emitting laser elements 101 to 103 is connected to the p-side annular electrode 7 of another surface emitting laser element adjacent thereto via an extraction electrode made of Au. As a result, the surface emitting laser elements 101 to 103 are connected in series. Each of the surface emitting laser elements 101 to 103 according to the first embodiment has a double intracavity structure so that current injection from the n-side electrode 6 and the p-side annular electrode 7 is performed without passing through the DBR mirrors 1 and 9. Therefore, since the wiring area for electrical connection between the surface emitting laser elements 101 to 103 may be small, the surface emitting laser elements 101 to 103 can be integrated with high density.

  Next, the operation of the surface emitting laser array element 100 will be described. When current is injected from the n-side electrode 6 and the p-side annular electrode 7 of each of the surface emitting laser elements 101 to 103, the current is confined in the current injection portion 5a by the current confinement layer 5, and the active layer 2 has a high current density. To be supplied. As a result, the active layer 2 is injected with carriers and emits spontaneous emission light. Of the spontaneous emission light, light in the 1100 nm band that is the laser oscillation wavelength forms a standing wave between the lower DBR mirror 1 and the upper DBR mirror 9 and is amplified by the active layer 2. When the injection current becomes equal to or greater than the threshold value, the light that forms the standing wave oscillates, and the upper DBR mirror 9 outputs laser beams L1 and L2 in the 1100 nm band.

  Here, each of the surface-emitting laser elements 101 to 103 generates heat during operation. In particular, the surface-emitting laser element 101 arranged in the central region A1 has a large number of other surface-emitting laser elements adjacent to each other. Is big. On the other hand, the surface emitting laser element 102 has a smaller temperature rise because the number of other adjacent surface emitting laser elements is smaller than that of the surface emitting laser element 101. Further, in the case of the surface emitting laser element 103, the number of other adjacent surface emitting laser elements is further smaller, and therefore the temperature rise is further reduced. As described above, the surface emitting laser elements 101 to 103 have a temperature difference depending on the region where they are arranged.

  However, in the surface emitting laser array element 100, the surface emitting laser elements 101 to 103 are compensated for the difference in laser oscillation wavelength due to the temperature difference among the central region A1, the intermediate region A2, and the peripheral region A3. The thickness of the temperature compensation layer is set. As a result, the laser oscillation wavelength, that is, the wavelengths of the laser beams L1 and L2 become uniform regardless of the temperature difference between the surface emitting laser elements 101 to 103.

  In addition, by compensating for the difference in laser oscillation wavelength by the layer thickness of the temperature compensation layer in this way, the configurations of the surface emitting laser elements 101 to 103 may be almost the same except for the layer thickness of the temperature compensation layer. The design and configuration of the laser array element 100 are simple. Further, even if the surface emitting laser elements 101 to 103 are arranged at a high density, the laser oscillation wavelength can be made uniform, so that the degree of integration can be increased. As a result, the surface emitting laser array element 100 has a higher output. In particular, the surface emitting laser array element 100 is more preferable in terms of higher integration and higher output because each of the surface emitting laser elements 101 to 103 has a double intracavity structure.

(Setting the thickness of the temperature compensation layer)
Next, setting of the thickness of the temperature compensation layer will be described. In the case of the surface-emitting laser array element 100 in which the surface-emitting laser elements 101 to 103 are arranged in a triangular lattice pattern as shown in FIG. 1, the surface-emitting laser elements 101 arranged in the central region A1 are nearest to each other. The surface emitting laser elements are six surface emitting laser elements 102, and the secondary surface emitting laser elements are six surface emitting laser elements 103 indicated by hatched circles. In addition, regarding the surface emitting laser element 103 indicated by a white circle arranged in the peripheral region A3, the closest surface emitting laser elements are two surface emitting laser elements 103 indicated by hatched circles and one surface emitting laser element. The number of the surface emitting laser elements is three in total with the laser elements 102, and the two surface emitting laser elements 102 adjacent to each other are the two surface emitting laser elements 102. As a result, assuming that the amount of heat generated by each of the surface emitting laser elements 101 to 103 is equal, the temperature rise due to the inflow of heat from the periphery of the surface emitting laser element 103 indicated by a white circle is about the temperature rise of the surface emitting laser element 101. It is about half or less.

  FIG. 3 is a diagram showing an example of the relationship between the center-to-center distance of the surface emitting laser elements and the temperature rise in the central region in the surface emitting laser array element in which the surface emitting laser elements are arranged as shown in FIG. In FIG. 3, the diameter of the current injection portion 5a of the current confinement layer is 10 μm, and the injection current is 15 mA. The temperature rise is based on the case where this surface emitting laser element is present alone. As shown in FIG. 3, the amount of temperature increase increases rapidly as the distance between the centers decreases. For example, when the distance between the centers is 35 μm, a temperature difference of 20 ° C. occurs between the central region A1 and the peripheral region A3. When the active layer is made of InGaAs, which is a semiconductor material for laser light in the 1100 nm band, the temperature coefficient of the laser oscillation wavelength is 0.067 nm / ° C. Therefore, in the central region A1 and the peripheral region A3, the surface emitting laser element is used. A difference in lasing wavelength of about 1.34 nm can occur.

  According to the experiments by the present inventors, when the temperature compensation layer is made of silicon nitride, if the temperature compensation layer is thickened by about 2.7 nm in the 1100 nm band, the laser oscillation wavelength becomes longer by 1.34 nm. Therefore, by making the layer thickness of the temperature compensation layer 8b in the surface emitting laser element 103 in the peripheral region A3 about 2.7 nm thicker than the layer thickness of the temperature compensation layer 8a in the surface emitting laser element 101 in the central region A1, The 1.34 nm difference can be compensated almost completely. However, if the layer thickness of each of the surface emitting laser elements 101 to 103 is set so that the difference becomes small without completely compensating for the difference in laser oscillation wavelength in this way, the difference in laser oscillation wavelength is compensated. effective.

By the way, changing the layer thickness of the temperature compensation layer for each region can be easily performed as follows, for example. FIG. 4 is a diagram for explaining an example of a method for changing the layer thickness of the temperature compensation layer for each region. First, the lower DBR mirror 1, the active layer 2, the p-type spacer layer 3, and the p ⁺ -type contact layer 4 are sequentially formed on the substrate S by an epitaxial growth method such as MOCVD. In forming the p-type spacer layer 3 is formed so that the AlAs layer (not shown) to be the current constricting layer 5 containing Al ₂ O ₃ is interposed therein. Further, a temperature compensation layer 8 made of silicon nitride is formed on the p ⁺ type contact layer 4 by the CVD method. The temperature compensation layer 8 has the same thickness as the temperature compensation layer 8b of the surface emitting laser element 103.

  Thereafter, an annular mask M is formed in the peripheral region A3 by photolithography, and the temperature compensation layer 8 is thinned by etching the central region A1 and the intermediate region A2 by dry etching. Thereafter, after removing the mask M, another mask is formed in the intermediate region A2 and the peripheral region A3, and the central region A1 is etched by dry etching to make the temperature compensation layer 8 thinner. Thereby, a temperature compensation layer having a different layer thickness for each region can be easily formed.

  In the above embodiment, the material of the substrate, each semiconductor layer, the electrode, or the like or the composition thereof can be appropriately selected according to the desired laser oscillation wavelength. The lower side of the active layer is an n-type semiconductor and the upper side is a p-type semiconductor, but this may be reversed. Further, the arrangement of the surface emitting laser elements is not limited to a triangular lattice shape, but may be a square lattice shape, a circular shape, or the like. Further, the structure of the surface emitting laser element is not limited to the double intracavity structure, and various structures can be employed. For example, in the structure of the embodiment, a single intracavity structure in which the upper DBR mirror is formed of a p-type semiconductor and the p-side electrode is disposed on the upper side to inject current may be used between the surface emitting laser elements. Since the wiring area for this electrical connection may be small, the surface emitting laser elements can be integrated with high density.

DESCRIPTION OF SYMBOLS 1 Lower DBR mirror 2 Active layer 3 p-type spacer layer 4 p ⁺ type contact layer 5 Current confinement layer 5a Current injection part 6 N side electrode 7 P side annular electrode 8, 8a, 8b Temperature compensation layer 9 Upper DBR mirror 100 surface Light emitting laser array element 101-103 Each surface emitting laser element A1 Central region A2 Intermediate region A3 Peripheral region L1, L2 Laser light M Mask S Substrate

Claims (4)

A surface-emitting laser array element in which a plurality of surface-emitting laser elements are two-dimensionally arranged,
Each surface emitting laser element has a temperature compensation layer in which the layer thickness is set so that the difference in laser oscillation wavelength due to the temperature difference between the first region where many other surface emitting laser elements are adjacent and the second region where there are few is small. In a surface-emitting laser array element.   The surface emitting laser element according to claim 1, wherein the surface emitting laser element has an intracavity structure.   The surface emitting laser array element according to claim 1, wherein the temperature compensation layer functions as a phase adjustment layer.   The temperature compensation layer of the surface emitting laser element disposed in the second region is thicker than the temperature compensation layer of the surface emitting laser element disposed in the first region. The surface emitting laser array element according to any one of the above.

Images