JP5799623B2 - Laser element - Google Patents

Description

  The present invention relates to a laser element used in, for example, industrial equipment.

  Patent Document 1 discloses a laser element having a ridge waveguide structure.

Japanese Patent Laid-Open No. 02-162786

  In a laser element, it is desirable to reduce the loss of light inside the laser element in order to improve the light emission efficiency. However, the laser element disclosed in Patent Document 1 cannot sufficiently reduce light loss.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a laser element with low loss.

The laser device according to the present invention includes a substrate, a lower cladding layer formed on the substrate, an active layer formed on the lower cladding layer, and an upper cladding layer formed on the active layer. And a second-order light formed in the upper layer of the active layer in a period in which light generated in the active layer and having a wavelength longer than that of light having the highest gain is diffracted above the upper cladding layer. A diffraction grating, a first reflective film that is formed on a first end face of a resonator having the lower clad layer, the active layer, and the upper clad layer and reflects light generated in the active layer, and the resonator A second reflection film that is formed on a second end surface that is opposite to the first end surface of the first reflective surface and reflects light generated by the active layer, and a ridge stripe . The length in the longitudinal direction of the resonator is equal to the length in the lateral direction of the resonator, and the secondary diffraction grating , Characterized in that it is formed only on the ridge stripe.

  According to the present invention, a laser element with a small loss can be manufactured.

It is a top view of the laser element which concerns on Embodiment 1 of this invention. It is sectional drawing in the 2-2 broken line of FIG. It is sectional drawing which shows the light emission direction of the laser element which concerns on Embodiment 1 of this invention. It is a figure which shows the light which a secondary diffraction grating diffracts. It is a top view which shows the modification of the laser element which concerns on Embodiment 1 of this invention. It is a figure which shows the wavelength of the light diffracted by a secondary diffraction grating and a 2nd diffraction grating. It is sectional drawing of the laser element which concerns on Embodiment 2 of this invention. It is sectional drawing of the laser element which concerns on Embodiment 3 of this invention. It is sectional drawing of the laser element which concerns on Embodiment 4 of this invention. It is sectional drawing of the laser element which concerns on Embodiment 5 of this invention. It is sectional drawing which shows the modification of the laser element which concerns on Embodiment 5 of this invention. It is sectional drawing of the laser element which concerns on Embodiment 6 of this invention. It is sectional drawing of the laser element which concerns on Embodiment 7 of this invention. It is sectional drawing which shows reflection of the downward laser beam based on Embodiment 7 of this invention. It is sectional drawing which shows that the light reflection layer was formed in the lower clad layer. It is sectional drawing which shows that light reflection occurs in a reflection layer.

Embodiment 1 FIG.
FIG. 1 is a plan view of a laser element according to Embodiment 1 of the present invention. A ridge stripe 12 is formed in the laser element 10 according to the first embodiment of the present invention. A secondary diffraction grating 14 is formed in the middle portion of the ridge stripe 12. Portions other than the secondary diffraction grating 14 are covered with an electrode 16. As the end face coating of the laser element 10, a first reflective film 20 and a second reflective film 22 are formed.

  2 is a cross-sectional view taken along a broken line 2-2 in FIG. The laser element 10 includes a substrate 30. A lower cladding layer 32 is formed on the substrate 30. An active layer 34 is formed on the lower cladding layer 32. An upper clad layer 36 is formed on the active layer 34. The lower cladding layer 32, the active layer 34, and the upper cladding layer 36 form a resonator. The resonator is made of a GaN-based material (GaN, InGaN, InAlGaN, etc.).

  In the upper clad layer 36, the second-order diffraction grating 14 is formed with a period for diffracting the light generated in the active layer 34 and having a wavelength longer than that of the light having the highest gain above the upper clad layer 36. ing. Specifically, the secondary diffraction grating 14 is formed with a period for diffracting a pure blue light wavelength. The length of the secondary diffraction grating 14 in the longitudinal direction of the resonator (L in FIG. 1) is about 3 μm, and the length in the lateral direction of the resonator (W in FIG. 1) is also about 3 μm. The length of the secondary diffraction grating 14 in the longitudinal direction of the resonator is equal to the length in the lateral direction of the resonator. The reason why the width of the ridge stripe 12 is thus narrowed is to reduce the threshold current of the laser element 10 and improve the current efficiency.

  Note that the length of the secondary diffraction grating 14 in the longitudinal direction of the resonator (L in FIG. 1) and the length in the lateral direction of the resonator (W in FIG. 1) define the light emission region and are desired. It is good also as arbitrary values in order to obtain a light emission angle and a spot. Further, the length of the secondary diffraction grating 14 in the longitudinal direction of the resonator and the length in the lateral direction of the resonator may not be equal.

  As shown in FIG. 2, a first end face 19 formed by cleavage or the like and a second end face 21 that is an end face opposite to the first end face 19 are formed at the resonator end. A first reflective film 20 that reflects light generated in the active layer 34 is formed on the first end face 19. A second reflective film 22 that reflects light generated in the active layer 34 is formed on the second end face 21. The first reflective film 20 and the second reflective film 22 reflect 100% of the light generated in the active layer 34.

  A contact layer 38 is formed on the upper cladding layer 36. An electrode 16 is formed on the contact layer 38. An electrode 40 is formed on the back surface of the substrate 30.

  FIG. 3 is a cross-sectional view showing the light emitting direction of the laser element 10 according to Embodiment 1 of the present invention. Laser light is emitted in a direction perpendicular to the crystal plane of the resonator by the secondary diffraction grating 14 of the laser element 10. The emission direction of the laser beam is indicated by an arrow in FIG.

  FIG. 4 is a diagram showing light diffracted by the second-order diffraction grating 14. As shown in FIG. 4A, the wavelength of light generated in the active layer 34 has a certain width (spread) with the center wavelength (λ1) as the center. Here, the second-order diffraction grating 14 is formed with a period for diffracting light (pure blue light λ2) having a wavelength longer than that of light (λ1) having the highest gain generated in the active layer 34. Yes. The light of λ2 has a smaller band gap energy than the light of λ1. The wavelength of light diffracted by the second-order diffraction grating 14 is shown in FIG. When the light of λ2 is oscillated in the resonator, the optical loss in the active layer 34 can be reduced as compared with the case where the light of λ1 is oscillated by the resonator. Therefore, according to the laser element 10 according to the first embodiment of the present invention, the loss of the laser element can be reduced.

  In the laser element 10 according to the first embodiment of the present invention, the first reflection film 20 and the second reflection film 22 prevent light from being emitted from the cavity end face. Therefore, loss due to light leaking from the resonator end face can be prevented.

  FIG. 5 is a plan view showing a modification of the laser device according to Embodiment 1 of the present invention. Only differences from the laser element 10 will be described. In the laser element 41, secondary diffraction gratings 14 and 52 are formed so as to diffract light generated in the active layer above the upper cladding layer. The secondary diffraction grating 52 is formed in the upper cladding layer at a different period from the secondary diffraction grating 14. The secondary diffraction grating 52 is referred to as a second diffraction grating.

  FIG. 6 is a diagram showing the wavelength of light diffracted by the secondary diffraction grating 14 and the secondary diffraction grating 52 (second diffraction grating). The wavelength of the light diffracted by the second-order diffraction grating 14 is λ2 as described above. The wavelength of light diffracted by the second diffraction grating is λ3 that is larger than λ1 and smaller than λ2. As described above, when two diffraction gratings having different periods are formed at two locations on the ridge stripe 12, light emission of two wavelengths is possible.

  In the laser device 10 according to the first embodiment of the present invention, the resonator is formed of a GaN-based material, but the present invention is not limited to this as long as the characteristics of the present invention are not lost. The diffraction grating 14 may be formed over the entire resonator length. In order to reduce the loss of the laser element, the first reflective film 20 and the second reflective film 22 desirably reflect 100% of the light generated in the active layer 34. However, the present invention is not limited to this as long as the loss of light at the resonator end face can be reduced. The second-order diffraction grating 14 and the second diffraction grating may be formed on the layer above the active layer 34 and is not particularly limited to the upper cladding layer 36.

Embodiment 2. FIG.
FIG. 7 is a sectional view of a laser device according to the second embodiment of the present invention. Only differences from the laser element 10 will be described. The upper cladding layer 37 is formed thicker than the upper cladding layer 36 of the laser element 10. Specifically, a part of the thick upper clad layer 37 is etched, and the second-order diffraction grating 14 is formed in the bottom portion exposed by the etching. The resonator is made of a GaAs-based material such as an AlGaInP-based or AlGaAs-based material. The contact layer 38 is made of GaAs. According to the laser device according to the second embodiment of the present invention, the light absorption in the contact layer 38 can be reduced by forming the upper cladding layer 37 thick.

Embodiment 3 FIG.
FIG. 8 is a cross-sectional view of a laser device according to Embodiment 3 of the present invention. Only differences from the laser element 10 will be described. The laser device according to the third embodiment of the present invention includes an upper clad layer 37 formed thicker than the upper clad layer 36 of the laser device 10. An etching stopper layer 39 for forming the secondary diffraction grating 14 is also provided. The upper cladding layer 37 is formed so as to sandwich the etching stopper layer 39. After the formation up to the contact layer 38, the portion where the secondary diffraction grating 14 is to be formed is etched up to the etching stopper layer 39, and the secondary diffraction grating 14 is formed there. Therefore, the secondary diffraction grating 14 can be easily formed. Further, since the upper clad layer 37 can be thickened, the light absorption of the contact layer can be reduced as in the second embodiment.

Embodiment 4 FIG.
FIG. 9 is a cross-sectional view of a laser device according to Embodiment 4 of the present invention. Only differences from the laser element 10 will be described. In the laser element according to Embodiment 4 of the present invention, the secondary diffraction grating 14 is covered with a contact layer 38. The contact layer 38 is made of GaN. The resonator is made of a GaN-based material. By forming the contact layer 38 from GaN, light absorption by the contact layer 38 can be eliminated, and the second-order diffraction grating 14 can be embedded in the contact layer 38. Such a laser element is formed by forming the contact layer 38 after forming the upper cladding layer 36 and the secondary diffraction grating 14. The material of the contact layer 38 is not limited to GaN, but may be a crystal having a band gap larger than the oscillation light of the laser element.

Embodiment 5 FIG.
FIG. 10 is a sectional view of a laser device according to the fifth embodiment of the present invention. Only differences from the laser element 10 will be described. In the laser device according to the fifth embodiment of the present invention, the diffraction grating layer 43 is formed on the upper cladding layer 41. The diffraction grating layer 43 is made of InGaN. A secondary diffraction grating 14 is formed in the diffraction grating layer 43. Thus, even if the secondary diffraction grating 14 is formed in a layer other than the upper clad layer 41, the effect of the present invention can be obtained.

  FIG. 11 is a cross-sectional view showing a modification of the laser device according to the fifth embodiment of the present invention. In this laser element, the secondary diffraction grating 14 formed in the diffraction grating layer 43 is embedded with a contact layer 38. The contact layer 38 is made of GaN. By forming the second-order diffraction grating 14 and the contact layer 38 with different materials, the second-order diffraction grating 14 can be embedded with the contact layer 38.

Embodiment 6 FIG.
FIG. 12 is a sectional view of a laser device according to the sixth embodiment of the present invention. Hereinafter, only differences from the first embodiment will be described. On the second end face 21 of the laser device according to the sixth embodiment of the present invention, a half mirror coat 42 is formed that reflects light generated by the active layer 34 and transmits light from the outside.

  The external laser element 44 is used for the use of the laser element according to Embodiment 6 of the present invention. Light generated in the active layer 46 of the external laser element 44 enters the laser element via the half mirror coat 42 and excites light in the active layer 34. The light excited by the active layer 34 is diffracted above the upper cladding layer 36 by the secondary diffraction grating 14. As described above, when the external laser element 44 is used, light can be efficiently excited.

  The grating period of the secondary diffraction grating 14 according to Embodiment 6 of the present invention is not particularly limited. However, as in the first embodiment of the present invention, the second-order diffraction grating is formed at a period in which light generated in the active layer and having a wavelength longer than that of light having the highest gain is diffracted above the upper cladding layer. It may be formed. Further, the laser element according to the sixth embodiment of the present invention can be modified at least as much as the laser element according to the first embodiment. Similarly, the features described in any of Embodiments 2 to 5 of the present invention may be incorporated into the laser element according to Embodiment 6 of the present invention.

Embodiment 7 FIG.
FIG. 13 is a cross-sectional view of a laser device according to Embodiment 7 of the present invention. Hereinafter, only differences from the first embodiment will be described. A light reflecting layer 62 is formed on the back surface of the substrate 60. The light reflecting layer 62 is formed by gold plating. The substrate 60 is made of a material having a band gap larger than that of the active layer 34.

  By the way, the diffraction grating 14 diffracts light not only in the resonator upper surface direction but also in the resonator lower surface direction. The light in the upper surface direction of the resonator is referred to as upward laser light, and the light in the lower surface direction of the resonator is referred to as downward laser light. The downward laser light is lost, for example, by being absorbed by the substrate. However, this loss can be suppressed by the laser device according to the seventh embodiment of the present invention. FIG. 14 is a cross-sectional view showing the reflection of the downward laser beam according to the seventh embodiment of the present invention. In FIG. 14, the downward laser beam is indicated by a broken line. According to the laser element according to the seventh embodiment of the present invention, since the downward laser light is reflected by the light reflection layer 62, the downward laser light can contribute to the upward laser light. Further, since the band gap of the substrate 60 is larger than the band gap of the active layer 34, it is possible to suppress the downward laser light from being absorbed by the substrate 60.

  The light reflection layer 62 is not limited to gold plating, and may be formed of a reflection film or a reflection coating. The main effect of the present invention can be obtained by converting the downward laser beam into the upward laser beam. Therefore, for example, a light reflection layer may be formed in the lower cladding layer. FIG. 15 is a cross-sectional view showing that the light reflecting layer 70 is formed in the lower cladding layer. The light reflecting layer 70 is a multilayer film in which crystals having different refractive indexes are alternately formed. FIG. 16 is a cross-sectional view showing that light reflection occurs in the reflective layer.

  The grating period of the secondary diffraction grating 14 according to Embodiment 7 of the present invention is not particularly limited. However, as in the first embodiment of the present invention, the second-order diffraction grating is formed at a period in which light generated in the active layer and having a wavelength longer than that of light having the highest gain is diffracted above the upper cladding layer. It may be formed. The laser element according to the seventh embodiment of the present invention can be modified at least as much as the laser element according to the first embodiment. The features described in any of Embodiments 2 to 5 of the present invention may be incorporated into the laser device according to Embodiment 7 of the present invention.

  In the above description, in order to explain the invention in an easy-to-understand manner, a fine epi structure such as an active layer structure was not described. However, the structure of the active layer is SQW (single quantum well) or MQW (multiquantum well) of a quantum well structure. ) Structure is also acceptable. Further, a structure having a band discontinuous relaxation layer for relaxing the band gap between the cladding layer and the contact layer may be used.

  DESCRIPTION OF SYMBOLS 10 Laser element, 12 Ridge stripe, 14 Secondary diffraction grating, 16 Electrode, 20 1st reflection film, 22 2nd reflection film, 30 Substrate, 32 Lower clad layer, 34 Active layer, 36 Upper clad layer, 38 Contact layer , 40 electrodes, 42 half mirror coat, 52 second diffraction grating 60 substrate, 62, 70 light reflection layer

Claims (6)

A substrate,
A lower cladding layer formed on the substrate;
An active layer formed on the lower cladding layer;
An upper cladding layer formed on the active layer;
A second-order diffraction grating formed in a layer above the active layer with a period for diffracting the light generated in the active layer and having a wavelength longer than that of the light having the highest gain above the upper cladding layer When,
A first reflective film for reflecting light generated in the active layer, formed on a first end face of a resonator having the lower clad layer, the active layer, and the upper clad layer;
A second reflective film for reflecting light generated in the active layer, formed on a second end surface that is an end surface opposite to the first end surface of the resonator;
With ridge stripes ,
The length in the resonator longitudinal direction of the secondary diffraction grating is equal to the length in the resonator short direction,
The laser element , wherein the secondary diffraction grating is formed only in the ridge stripe .   2. The laser device according to claim 1, wherein the first reflective film and the second reflective film are formed so as to reflect 100% of light generated in the active layer.   3. The laser device according to claim 1, wherein the second-order diffraction grating is formed in an intermediate portion of the ridge stripe. The resonator is formed of GaN;
4. The laser device according to claim 1, wherein the secondary diffraction grating is formed with a period for diffracting a pure blue light wavelength. 5. A second-order diffraction grating formed in a layer above the active layer at a different period from the second-order diffraction grating so as to diffract light generated in the active layer above the upper cladding layer. With two diffraction gratings ,
5. The laser device according to claim 1 , wherein the second diffraction grating is formed only in the ridge stripe . 6. A substrate,
A lower cladding layer formed on the substrate;
An active layer formed on the lower cladding layer;
An upper cladding layer formed on the active layer;
A second-order diffraction grating formed in a layer above the active layer so as to diffract the light generated in the active layer above the upper cladding layer;
Light generated in the active layer formed on one of the first end face and the second end face opposite to the first end face of the resonator having the lower clad layer, the active layer, and the upper clad layer A reflective film that reflects
A half mirror coat that is formed on the other of the first end surface and the second end surface and reflects light generated by the active layer while transmitting light from the outside;
A laser device comprising:

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