JP5205705B2 - Surface emitting laser device, array light source, phase-locked light source - Google Patents

Description

  The present invention relates to a surface emitting laser device, an array light source in which a plurality of the surface emitting laser devices are integrated, and a phase-locked light source.

  As a semiconductor laser device, there is a so-called end surface type light emitting laser device. The apparatus is configured to emit output light in a direction parallel to the substrate surface. The end face type light emitting laser device is easy to increase the output, but there is a problem that the end face is destroyed when the light intensity is increased.

  On the other hand, a surface emitting semiconductor laser device that emits laser light from the surface side of a semiconductor substrate is known. This type of laser device has higher coupling efficiency with an optical fiber and can be easily integrated two-dimensionally than an edge-emitting laser device that emits laser light from the end surface of a semiconductor substrate. It has the advantages such as. As an example of such a laser apparatus, a feedback distribution type laser apparatus having a diffraction grating in an optical waveguide of the laser apparatus is known (for example, see Patent Document 1).

  The laser device includes a lower cladding layer, an active layer stacked on the lower cladding layer, and an upper cladding layer stacked on the active layer. That is, it has a laminated structure in which an active layer is formed between a pair of clad layers. A diffraction grating is formed between the active layer and the upper cladding layer, and the diffraction grating is formed in a plane parallel to the active layer. This laminated structure functions as a resonator.

Since the diffraction grating group is formed point-symmetric with a common center, there is no anisotropy of the gain region in the plane where the diffraction grating is formed. Therefore, there is a problem that the polarization direction of the emitted laser beam is not determined. If the polarization direction is not determined, it is often impossible to obtain laser light with good beam quality.
JP-A-10-209554

  The present invention aims to solve the above problems. That is, an object of the present invention is to provide a surface emitting laser device that has good beam quality and does not cause problems such as end face destruction, an array light source and a phase-locked light source in which a plurality of these are integrated.

  As a result of intensive studies to solve the above problems, the present inventors have conceived the following present invention and found that the problems can be solved.

That is, the present invention has a stacked structure having a photoactive layer between a P-type semiconductor and an N-type semiconductor on a substrate, and is provided on the stacked structure, and current is supplied in the stacking direction of the stacked structure. injected have a current injection mechanism gain is obtained in a cross shape, between the substrate and the current injection mechanism in the stacking direction of the laminated structure, direction parallel to the lamination plane of the substrate, and the substrate a surface emitting laser device which is characterized in that have a plurality of secondary diffraction grating inclined direction with respect to the end face.

A secondary diffraction grating of the specific structure, before Symbol by having the injected current injection mechanism that gain is obtained in a cross shape a current in the central portion of the substrate, it is possible to make the beam quality favorable . Further, since the present invention is a surface emitting laser device, the problem of end face destruction does not occur.

  The surface emitting laser device of the present invention preferably includes at least one of the following first to third aspects.

(1) A 1st aspect is an aspect with a diffraction grating defect in the area | region in which the said some 2nd-order diffraction grating was formed. Due to the presence of diffraction grating defects, the light intensity profile can be adjusted. Especially when the defect has a size of λ / 4, the beam profile is unimodal, and the laser beam quality (beam quality) is improved. It can be.

(2) The second mode is a mode in which a reflective film is further provided on the current injection mechanism or between the current injection mechanism and the second-order diffraction grating in the stacking direction of the stacked structure . Since the light extraction efficiency is improved by providing the reflective film, high-quality laser light can be efficiently obtained.

(3) A 3rd aspect is an aspect which has a quantum well transparent with respect to a light beam in a part of active layer . Since it is transparent, the absorption of light by the quantum well can be greatly reduced, so that high-quality laser light can be obtained efficiently.

  Further, the present invention is an array light source in which a plurality of the surface emitting laser devices of the present invention described above are integrated. Furthermore, the present invention is a phase-locked light source in which a plurality of the surface emitting laser devices of the present invention described above are integrated. Since these are provided with a plurality of the surface emitting laser devices of the present invention, the beam quality is good, and the effect that the problem of end face destruction does not occur is exhibited.

  According to the present invention, it is possible to provide a surface emitting laser device that has good beam quality and does not cause problems such as end face destruction, an array light source and a phase-locked light source in which a plurality of these are integrated.

  The surface-emitting laser device of the present invention will be described with reference to the drawings. In the following description of the drawings, the description of the reference numerals once described may be omitted in the following drawings.

  As illustrated in FIG. 1, the surface-emitting laser device of the present invention has an N-type clad layer 12, a guide layer 14, an active layer 16, a guide layer 18, and a P-type as an N-type semiconductor on one surface side of a substrate 10. The clad layer 20 has a P-type contact layer 22 as a P-type semiconductor, and further has a P-type electrode 26 as a current injection mechanism thereon. Further, an N-type electrode is provided on the other surface side of the substrate 10 (not shown). A plurality of second-order diffraction gratings 24 are provided below the P-type electrode 26 in a direction parallel to the laminated surface of the substrate 10 and in an inclined direction with respect to the end surface of the substrate 10. A current injection mechanism is provided in which the gain passes in a cross shape in the vertical direction of the substrate 10.

  The N-type electrode is made of Ti / Au or the like. The substrate 10 (for example, an N-type substrate) and the N-type clad layer 12 are made of InP doped with sulfur. The guide layers 14 and 18 are made of InGaAsP or the like, and the active layer 16 is made of InGaAsP / InGaAsP or the like. The P-type cladding layer 20 is made of InP or InGaAs doped with Zn. The P-type contact layer 22 is made of InP doped with Zn at a high concentration. The P-type electrode 26 is made of Pt / Ti / Au or the like.

  Further, a reflective film 28 is provided on the P-type electrode 26. The reflective film 28 is made of TiO / SiO or the like.

  Each layer of the surface emitting laser device can be formed by a known MOCVD method. The second-order diffraction grating 24 first forms a resist periodic structure by coating a resist on a semiconductor substrate, exposing and developing it with an electron beam drawing apparatus or the like. After that, etching is performed using phosphoric acid, hydrogen peroxide solution, a mixed solution of water or the like using the resist as a mask, and the pattern is transferred onto the semiconductor substrate.

The inclination angle of the second-order diffraction grating 24 is preferably 42 to 48 °, and more preferably 45 °. The interval between the second-order diffraction gratings 24 (“Λ” in FIG. 2) is Λ = mλ / (2n _r sin θ) [λ is the oscillation wavelength, n _r is the refractive index, θ is the tilt angle, and m is a positive integer. ], Λ = 1550, n _r = 3.3, θ = 45 °, and m = 2, it is preferable that the distance is about 664 nm, and the depth is preferably about 150 nm.

  In the surface emitting laser device of the present invention, first, as shown in FIG. 2, when light rays are obliquely incident on the diffraction grating 24 at equal intervals, diffracted light appears strongly in the same direction as the incident angle. Here, as shown in FIG. 3, when the P-type electrode 26 is installed so that the four corners approach the center of the end face of the substrate, the light beam that has passed through the diffraction grating 24 goes straight and undergoes diffraction as shown in FIG. The light beam bends at a right angle. Since these light rays are reflected at the end face of the substrate and are again reflected by the diffraction grating at a right angle with the same passage, the resonance mode is excited in a cross shape. In the portion where no current is injected, the active layer acts as an optical loss. Therefore, as shown in FIG. 5, the light beam that has passed through the portion of the diffracted light where no current is injected is lost and attenuated. Furthermore, if the light does not enter the end face at a right angle, the reflectivity is significantly reduced, so there is no such optical mode. For the reasons described above, a single mode laser in which only the cross-shaped resonance mode as shown in FIG. 3 is excited is obtained.

  Next, as shown in FIG. 6, when the quality of the beam is improved by intentionally providing a diffraction grating defect (also simply referred to as “grating defect”) 23 in a region where the secondary diffraction grating 24 is formed on a diagonal line, There is. This is considered because the intentional boundary condition is given to the diffraction grating due to the defect, and a reproducible light intensity distribution is obtained. For example, when the lattice defect 23 is ¼ Λ shift, the light intensity distribution becomes unimodal with the light intensity at the center being high, as shown in FIG. As an aspect of the grating defect 23, in the case of the first-order diffraction grating, the length of 1/4 of the wavelength, and in the case of the m-order diffraction grating, the length of m / 4 of the wavelength (considering the refractive index n, mλ / (4 n sin θ ): Λ is preferably an oscillation wavelength, m is an integer, and θ is an inclination angle.

  If the second-order diffraction grating 24 is used, the laser beam can be taken out perpendicular to the substrate as shown in FIG. Alternatively, the second-order diffraction grating 24 may be provided around the grating defect 23, and the first-order diffraction grating 25 may be provided around the second-order diffraction grating 24. The first-order diffraction grating is effective for changing the orientation in the plane, and good operability can be obtained.

  FIG. 9 shows a mode in which a hole (for example, φ several μm to several hundred μm) is formed in the center of the P-type electrode 26 and light is extracted from the P-type electrode 26 side using this hole as a light window. This facilitates the manufacturing process. On the other hand, FIG. 10 shows a mode in which holes (for example, φ several μm to several hundred μm) are formed in the N-type electrode on the back surface of the substrate 10 and light rays are extracted from the back surface of the substrate 10. In this case, since the light distribution is close to Gaussian, the beam quality can be improved despite the large surface emitting laser.

  As shown in FIG. 11, the efficiency can be improved by forming the reflective film 28 under the P-type electrode 26. Light rays are radiated on both sides of the second-order diffraction grating. However, as shown in FIG. 12, the surface of the P-type electrode 26 acts as a scattering surface, and emits light in an undesirable direction. On the other hand, as shown in FIGS. 11 and 13, the light extraction efficiency can be improved by forming the reflective film 28 at an appropriate position. The “appropriate position” is preferably a location such as between the semiconductor and the electrode. As shown in FIG. 13, if the light absorptance is reduced by making a part of the active layer 16 16A transparent by quantum well disordering or the like, a higher output can be obtained.

  As shown in FIGS. 14 to 16, the shape of the P-type electrode 26 has various modifications. In the present invention, as shown in FIG. 14A, it is important that a cross-shaped light path (resonance mode) can be formed. Therefore, the shape of the P-type electrode 26 is not necessarily a rhombus as shown in FIG. May be. As shown in FIG. 14 (B), the shape of the rhombus may overlap with the end face by a certain distance, or as shown in FIG. 14 (C), it may have a cross shape. Further, in the case where the element is rectangular as shown in FIG. 15A, as shown in FIG. Furthermore, as shown in FIG. 16, the center of the cross-shaped resonance mode may not be the center of the element as shown in FIG. In this case, the shape of the P-type electrode 26 can also be a shape corresponding to the shape (such as the diamond shape in FIG. 16B). The edge of the electrode may be a curve instead of a straight line.

  In the surface emitting laser device of the present invention, as shown in FIG. 17, the second-order diffraction grating 24 may be formed by embedded growth. By adopting such a configuration, it is possible to prevent the efficiency of the P-type electrode 26 and the second-order diffraction grating 24 from being alloyed to reduce the efficiency.

  As shown in FIG. 18, a plurality of the surface-emitting laser devices of the present invention are integrated in a planar manner as shown in FIG. 18 so that phase synchronization is possible, and it can be applied to an array light source or a phase-synchronized light source.

  It is preferable that the array light source has a configuration in which the element interval is sufficiently large so that the array light source operates independently of the adjacent elements, or the arrangement is devised so that the cross paths do not overlap. In addition, the phase-synchronized light source is preferably arranged so as to be nKL (n is a positive number) in the coupling constant K and the element center distance L.

It is a perspective view which shows the layer structure of the surface emitting laser apparatus of this invention. It is explanatory drawing for demonstrating the diffraction of light with a secondary diffraction grating. It is explanatory drawing for demonstrating the resonance mode of the surface emitting laser apparatus of this invention. It is explanatory drawing for demonstrating the resonance mode of the surface emitting laser apparatus of this invention. It is explanatory drawing for demonstrating the resonance mode of the surface emitting laser apparatus of this invention. It is a schematic diagram which shows the state by which the diffraction grating defect was provided in the area | region in which the 2nd-order diffraction grating was formed. It is explanatory drawing for demonstrating the resonance mode in the state in which the diffraction grating defect was provided in the area | region in which the secondary diffraction grating was formed. It is a schematic diagram which shows the state in which the 1st diffraction grating, the 2nd diffraction grating, and the diffraction grating defect were provided. It is explanatory drawing for demonstrating the phenomenon of top surface radiation. It is explanatory drawing for demonstrating the phenomenon of bottom emission. It is a perspective view which shows the layer structure of the surface emitting laser apparatus of this invention which provided the reflecting film. It is sectional drawing which shows the layer structure of the surface emitting laser apparatus of this invention. It is sectional drawing which shows the layer structure of the surface emitting laser apparatus of this invention which provided the reflecting film. It is explanatory drawing for demonstrating a resonance mode, and the top view which illustrates the shape of a P-type electrode. It is explanatory drawing for demonstrating a resonance mode, and the top view which illustrates the shape of a P-type electrode. It is explanatory drawing for demonstrating a resonance mode, and the top view which illustrates the shape of a P-type electrode. It is a perspective view which shows the layer structure of the surface emitting laser apparatus of this invention which provided the 2nd-order diffraction grating in the inner layer side. It is a perspective view which illustrates an array light source.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Substrate 12 ... N-type clad layer 14 ... Guide layer 16 ... Active layer 18 ... Guide layer 20 ... P-type clad layer 22 ... P-type contact layer 24 ... Second-order diffraction grating 26 P-type electrode 28 Reflective film

Claims (6)

On the substrate, it has a laminated structure having a photoactive layer between a P-type semiconductor and an N-type semiconductor,
Wherein provided on the stacked structure, it possesses the current injection mechanism gain current is injected in a cross shape in the laminating direction of the multilayer structure is obtained,
Between the substrate and the current injection mechanism in the stacking direction of the laminated structure, direction parallel to the lamination plane of the substrate, and to have a plurality of secondary diffraction grating inclination direction with respect to the end face of the substrate A surface-emitting laser device.   2. The surface emitting laser device according to claim 1, wherein there is a diffraction grating defect in a region where the plurality of secondary diffraction gratings are formed. The surface light emission according to claim 1 or 2, further comprising a reflective film on the current injection mechanism or between the current injection mechanism and the second-order diffraction grating in the stacking direction of the stacked structure. Laser device.   The surface emitting laser device according to claim 1, wherein a part of the active layer has a quantum well that is transparent to light.   An array light source in which a plurality of surface emitting laser devices are integrated, wherein the surface emitting laser device is the surface emitting laser device according to any one of claims 1 to 4.   A phase-locked light source in which a plurality of surface-emitting laser devices are integrated, wherein the surface-emitting laser device is the surface-emitting laser device according to any one of claims 1 to 4. .

Images