Edge-emitting laser capable of simultaneously selecting longitudinal mode and transverse mode and preparation method of edge-emitting laser

Abstract

The invention relates to the technical field of lasers, and discloses an edge-emitting laser with a longitudinal mode and transverse mode selection function and a preparation method of the edge-emitting laser. The edge-emitting laser comprises a chip element, a mode modulation structure and an insulating layer, a ridge waveguide structure is arranged at the top of the chip element, and the mode modulation structure is located on one side of the ridge waveguide structure at the top of the chip element; the mode modulation structure comprises an annular cavity and an annular cavity electrode layer, and the annular cavity and the annular cavity electrode layer are spaced by an insulating layer; a P-type contact metal layer is arranged on the top of the chip element and located on the outer side of the ridge waveguide structure. According to the edge-emitting laser capable of selecting the longitudinal mode and the transverse mode at the same time, the mode modulation structure is arranged on the main ridge-shaped edge of laser feedback in the edge-emitting laser, flexible regulation and control of output of the longitudinal mode and the transverse mode in the ridge-shaped edge-emitting laser are achieved through the mode coupling principle, and external optical assemblies do not need to be added; the integration level and the compactness are good, and the technology is compatible with an existing laser.

Description

Technical Field

[0001] The present invention relates to the technical field of lasers, and specifically provides an edge-emitting laser with longitudinal and transverse mode selection and a preparation method thereof. The flexible regulation of longitudinal and transverse mode outputs in a ridge-type edge-emitting laser is realized by using the principle of mode coupling. Without adding external optical components, the integration and compactness are relatively good. Moreover, the process is compatible with existing lasers. Background Art

[0002] Gallium nitride (GaN) lasers adopt a P-N junction structure. Electrons and holes are injected through N-type and P-type electrodes, and these carriers are confined in the active region to recombine and emit light, thereby realizing the confinement of the optical field. The confinement of the optical field in the horizontal direction is achieved through a ridge structure, while the confinement of the optical field in the vertical direction is realized by using the refractive index difference between the waveguide layer and the confinement layer.

[0003] The mode of the laser light wave can be divided into transverse mode and longitudinal mode. The transverse mode intensity distribution in the cross-section perpendicular to the optical axis is determined by the waveguide structure of the edge-emitting laser with both longitudinal and transverse mode selection. If the transverse mode is complex and unstable, the coherence of the output light is poor. The longitudinal mode is a standing wave distribution in the propagation direction of the resonant cavity. If many longitudinal modes lase simultaneously or there are inter-mode variations, high temporal coherence cannot be obtained, it is difficult to modulate the transverse and longitudinal modes, and the far-field image FFP quality is poor.

[0004] In order to adapt to the requirements in different scenarios, it is necessary to modulate the transverse and longitudinal modes of the laser light wave. In some scenarios, single transverse and single longitudinal modes are required. For example, when shooting starry sky or a single line, a single transverse mode is needed; in communication, a single longitudinal mode is required.

[0005] In the prior art, for single longitudinal mode, gratings are added on the top or inside of the ridge, and an external resonant optical path is used. However, these methods are first relatively complex, and second, there is no adjustability. Once the grating is made, the wavelength is fixed and mode selection cannot be performed. For single transverse mode, methods such as reducing the ridge width, using a wedge-shaped or trumpet-shaped ridge, and adding loss structures at the edge of the ridge are adopted. By using the spatial distribution of loss generated in a certain section of the ridge, some high-order transverse modes are filtered out. These solutions may lead to excessive loss and reduce the luminous power. At the same time, they also have the disadvantage of lacking adjustability. Summary of the Invention

[0006] (1) Technical Problems to be Solved

[0007] Aiming at the deficiencies of the prior art, the present invention provides an edge-emitting laser with both longitudinal and transverse mode selection, which has the advantages of modulating both transverse and longitudinal modes, etc., and solves the problems of difficult modulation of transverse and longitudinal modes and poor far-field image FFP quality.

[0008] (2) Technical Solutions

[0009] An annular resonator is arranged at the main ridge edge of laser feedback in an edge-emitting laser. The annular resonator is spaced within 100 - 200 nm from the main ridge. During operation, the longitudinal and transverse modes inside the annular resonator are coupled with the modes inside the main ridge, and the formed supermode is redistributed inside the ridge. At the same time, a forward bias can be added at both ends of the annular resonator, and the electro-optic effect is used to adjust the effective refractive index of the annular resonator, thereby regulating the coupling.

[0010] The implementation principle is as follows:

[0011] Electro-optic effect: [n = n0 + aE + bE 2 , where: n is the refractive index after applying an external electric field; n0 is the refractive index without applying an external electric field; a and b are constants; E is the external electric field strength. By changing the external electric field strength, the electric dipole moment in the material is changed, thereby changing the dielectric constant of the material, and further causing a change in the refractive index.

[0012] Optical Vernier effect: The optical Vernier effect utilizes two resonators with slightly different cavity lengths. When the two resonators are coupled, longitudinal modes with periodic oscillations are formed inside each of them, and the mode periods are slightly different. The coupled modes form a larger beat period, thereby increasing the longitudinal mode spacing. If there is only one mode in the gain spectrum, a single longitudinal mode will be formed. In addition, controlling the effective perimeter of the ring cavity can directly control the mode spacing. The formula for the longitudinal mode spacing is as follows:

[0013]

[0014] Φ1 = 2πn1l1 / λ

[0015] Φ2 = 2πn2l2 / λ

[0016]

[0017] Among them, I represents the light intensity or light intensity distribution, A represents the amplitude or light intensity parameter related to the first resonator, B represents the amplitude or light intensity parameter related to the second resonator, R1 represents the reflectivity of the first resonator, R2 represents the reflectivity of the second resonator, R3 represents the reflectivity of the third resonator, Φ1 represents the phase related to the first resonator, Φ2 represents the phase related to the second resonator, λ represents the wavelength of light, g1 represents the gain of the first resonator, g2 represents the gain of the second resonator, Δ represents the optical path difference between the two resonators, n1, n2 represent the refractive indices of the two resonators, and l1, l2 represent the lengths of the two resonators.

[0018] Supersymmetric SUSY waveguide effect: When two waveguides are very close to each other, the transverse modes inside will couple to form a supermode. By designing appropriate waveguide width parameters, aligning the propagation constant of the high-order mode in the main ridge with the propagation constant of the fundamental mode in the ring cavity, efficient mode conversion can be achieved. Convert the high-order mode in the main ridge into the low-order mode in the ring cavity. Since there is no gain medium inside the ring cavity and the absorption coefficient here is large, the loss of the high-order mode in the main ridge increases, and good high-order mode filtering can be achieved to realize single transverse mode output. At the same time, the electro-optic effect can adjust the refractive index in the ring cavity, thereby adjusting the phase difference between the ring cavity and the main ridge modes, and ultimately affecting the coupling strength between the two.

[0019] An edge-emitting laser with both longitudinal and transverse mode selection, comprising a chip element, a mode modulation structure, and an insulating layer. A ridge waveguide structure is provided on the top of the chip element, and the mode modulation structure is located on one side of the ridge waveguide structure on the top of the chip element;

[0020] The mode modulation structure includes a ring cavity and a ring cavity electrode layer, and there is an insulating layer interval between the ring cavity and the ring cavity electrode layer;

[0021] A P-type contact metal layer is provided on the top of the chip element and outside the ridge waveguide structure.

[0022] Furthermore, the ring cavity is located on one side of the middle of the ridge waveguide structure, and the ring cavity is formed by directly etching the chip element or depositing after etching.

[0023] Furthermore, the outer diameter of the ring cavity is 100 - 200 μm, the wall thickness of the ring cavity is 1 - 2 μm, and the distance a between the ring cavity and the ridge waveguide structure is 100 - 200 nm.

[0024] Furthermore, the ring cavity material is lithium niobate, lithium tantalate, lead zirconate titanate ceramics, gallium nitride, gallium arsenide, etc.

[0025] Furthermore, there is a gap between the outside of the ring cavity electrode layer and the P-type contact metal layer.

[0026] A preparation method for an edge-emitting laser with both longitudinal and transverse mode selection, comprising the following steps:

[0027] 1) Prepare a wafer with an epitaxially grown laser structure completed;

[0028] 2) Prepare a ridge waveguide structure and a ring cavity on the P side of the wafer;

[0029] 3) Prepare an insulating layer on the outside of the ridge waveguide structure and the ring cavity;

[0030] 4) Prepare a P-type contact metal layer and a ring cavity electrode layer on the top of the insulating layer.

[0031] Furthermore, the ridge waveguide structure is formed by etching, and the ring cavity is formed by etching or etching followed by re-deposition.

[0032] Furthermore, the outer diameter of the ring cavity is 100 - 200 μm, the wall thickness of the ring cavity is 1 - 2 μm, and the distance between the ring cavity and the ridge waveguide structure is 100 - 200 nm.

[0033] Furthermore, the P-type contact metal layer is electrically connected to the ridge waveguide structure by opening a current injection window in the insulating layer on the top of the ridge waveguide structure. The ring cavity electrode layer is not electrically connected to the ring cavity, that is, a window is opened in the insulating layer at the top of the ridge, and no window is opened in the insulating layer at the top of the ring cavity. Electrodes are provided on the tops of both the ridge waveguide structure and the ring cavity, serving as the current injection area of the ridge waveguide structure and the voltage application area of the ring cavity respectively.

[0034] Furthermore, the ring cavity electrode layer is not electrically connected to the P-type contact metal layer, which helps to not affect the normal current and voltage of the laser when adjusting the applied voltage of the ring cavity electrode layer.

[0035] (III) Beneficial Effects

[0036] Compared with the prior art, the present invention provides an edge-emitting laser that simultaneously has longitudinal mode and transverse mode selection, and has the following

[0037] beneficial effects:

[0038] 1. The edge-emitting laser that simultaneously has longitudinal mode and transverse mode selection does not need to be connected to an external cavity structure, and a single chip can simultaneously achieve the simultaneous regulation of longitudinal mode and transverse mode, with higher integration and compactness.

[0039] 2. The edge-emitting laser that simultaneously has longitudinal mode and transverse mode selection has a certain degree of flexibility. Different from the grating in DFB lasers that cannot be adjusted, this scheme uses the electro-optic effect to not only accurately regulate the coupling strength of the mode, but also has good stability.

[0040] 3. The edge-emitting laser that simultaneously has longitudinal mode and transverse mode selection takes into account the regulation of both longitudinal mode and transverse mode, and can efficiently and simply simultaneously achieve single longitudinal mode and single transverse mode output by using the width and perimeter dimensions of the ring cavity. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 is a schematic structural diagram of an edge-emitting laser that simultaneously has longitudinal mode and transverse mode selection according to the present invention;

[0042] Figure 2 is a schematic diagram of the process preparation of an edge-emitting laser that simultaneously has longitudinal mode and transverse mode selection according to the present invention;

[0043] Figure 3The top view of the ridge waveguide structure and the mode modulation structure of an edge-emitting laser with longitudinal mode and transverse mode selection according to the present invention;

[0044] Figure 4 The top view of an edge-emitting laser with longitudinal mode and transverse mode selection according to the present invention.

[0045] In the figure: 1-chip element, 11-ridge waveguide structure, 12-P-type contact metal layer, 2-mode modulation structure, 21-ring cavity, 22-ring cavity electrode layer, 3-insulating layer. Specific embodiments

[0046] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0047] Embodiment 1:

[0048] Please refer to Figures 1-4 , an edge-emitting laser with longitudinal mode and transverse mode selection, including a chip element 1, a mode modulation structure 2 and an insulating layer 3. A ridge waveguide structure 11 is provided on the top of the chip element 1, and the mode modulation structure 2 is located on one side of the ridge waveguide structure 11 on the top of the chip element 1;

[0049] The mode modulation structure 2 includes a ring cavity 21 and a ring cavity electrode layer 22, and there is an insulating layer 3 separating the ring cavity 21 and the ring cavity electrode layer 22;

[0050] A P-type contact metal layer 12 is provided on the top of the chip element 1 and outside the ridge waveguide structure 11.

[0051] In this embodiment, the ring cavity 21 is located on one side of the middle of the ridge waveguide structure 11, and the ring cavity 21 is formed by directly etching the chip element 1 or depositing after etching. Forming the ring cavity 21 by deposition can change the material of the ring cavity 21 and regulate the refractive index.

[0052] In this embodiment, the outer diameter of the ring cavity 21 is 102 μm, the wall thickness of the ring cavity 21 is 2 μm, and the distance a between the ring cavity 21 and the ridge waveguide structure 11 is 100 nm.

[0053] In this embodiment, the material of the ring cavity 21 is gallium nitride.

[0054] In this embodiment, the distance (i.e., a) between the outside of the ring cavity electrode layer 22 and the P-type contact metal layer 12 is 100 nm.

[0055] Embodiment 2:

[0056] A preparation method of an edge-emitting laser with both longitudinal mode and transverse mode selection is as follows Figure 2 shown, including the following steps:

[0057] 1) Use MOCVD to epitaxially grow a wafer with a standard gallium nitride-based 450nm blue laser structure;

[0058] 2) Use ICP etching on the P side of the wafer to prepare a ridge waveguide structure 11 and a ring cavity 21. The width of the ridge waveguide structure 11 is 5μm, the length is 600μm, the inner diameter of the ring cavity 21 is 100μm, the outer diameter is 102μm, and the spacing a between the ridge waveguide structure 11 and the ring cavity 21 is 100nm;

[0059] 3) Use PECVD to deposit a 200nm thick SiO2 insulating layer 3 on the outside of the ridge waveguide structure 11 and the ring cavity 21 at 300°C;

[0060] 4) Use RIE to etch a 4μm wide current injection window on the top of the ridge waveguide structure 11, and prepare a photoresist mask on the outside of the ring cavity electrode layer 22. Then deposit 10nm / 500nm of Ni / Au on the top of the insulating layer 3. After deposition, remove the photoresist mask to complete the preparation of the P-type contact metal layer 12 and the ring cavity electrode layer 22.

[0061] When in use, connect the ring cavity electrode layer 22 to the third pin of the socket, and then connect it to an external voltage regulating source meter. By adjusting the voltage, use the electro-optic effect to adjust the effective refractive index of the ring cavity 21, and then regulate the coupling, that is, regulate the coupling between the longitudinal and transverse modes inside the ring cavity and the modes inside the ridge waveguide structure.

[0062] This edge-emitting laser with both longitudinal mode and transverse mode selection does not need to access an external cavity structure, and a single chip can simultaneously realize the simultaneous regulation of longitudinal mode and transverse mode, with higher integration and compactness.

[0063] This edge-emitting laser with both longitudinal mode and transverse mode selection has a certain degree of flexibility. Different from the grating in the DFB laser that cannot be adjusted, this scheme uses the electro-optic effect to not only accurately regulate the coupling strength of the mode, but also has good stability.

[0064] This edge-emitting laser with both longitudinal mode and transverse mode selection takes into account the regulation of longitudinal mode and transverse mode. By using the width and perimeter dimensions of the ring cavity, single longitudinal mode and single transverse mode output can be efficiently and simply realized simultaneously.

[0065] For the cleavage process of the epitaxial wafer, the cavity surface film process, etc., it belongs to the recognized field for those of ordinary skill in the art, and will not be elaborated too much in this article.

[0066] Although embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. An edge-emitting laser with both longitudinal mode and transverse mode selection, comprising a chip element (1), a mode modulation structure (2) and an insulating layer (3), characterized in that: A ridge waveguide structure (11) is provided on the top of the chip element (1), and the mode modulation structure (2) is located on one side of the ridge waveguide structure (11) on the top of the chip element (1). The mode modulation structure (2) includes an annular cavity (21) and an annular cavity electrode layer (22), and there is an insulating layer (3) separating between the annular cavity (21) and the annular cavity electrode layer (22). A P-type contact metal layer (12) is provided on the top of the chip element (1) and outside the ridge waveguide structure (11).

2. The edge-emitting laser with longitudinal mode and transverse mode selection according to claim 1, characterized in that: The annular cavity (21) is located on one side of the middle of the ridge waveguide structure (11), and the annular cavity (21) is formed by directly etching the chip element (1) or depositing after etching.

3. The edge-emitting laser with longitudinal mode and transverse mode selection according to claim 1, characterized in that: The outer diameter of the annular cavity (21) is 100 - 200 μm, the wall thickness of the annular cavity (21) is 1 - 2 μm, and the distance between the annular cavity (21) and the ridge waveguide structure (11) is 100 - 200 nm.

4. The edge-emitting laser with longitudinal mode and transverse mode selection according to claim 1, characterized in that: The material of the annular cavity (21) is lithium niobate, lithium tantalate, lead zirconate titanate ceramics, gallium nitride, gallium arsenide, etc.

5. The edge-emitting laser with both longitudinal mode and transverse mode selection according to claim 1, characterized in that: There is a gap between the outer side of the annular cavity electrode layer (22) and the P-type contact metal layer (12).

6. A preparation method of an edge-emitting laser simultaneously having longitudinal mode and transverse mode selection, comprising the following steps: 1) Prepare a wafer with an epitaxially grown laser structure completed. 2) Prepare a ridge waveguide structure (11) and an annular cavity (21) on the P side of the wafer. 3) Prepare an insulating layer (3) outside the ridge waveguide structure (11) and the annular cavity (21). 4) Prepare a P-type contact metal layer (12) and an annular cavity electrode layer (22) on the top of the insulating layer (3).

7. The preparation method according to claim 6, characterized in that: The ridge waveguide structure (11) is formed by etching, and the annular cavity (21) is formed by etching or depositing after etching.

8. The preparation method according to claim 6, characterized in that: The outer diameter of the annular cavity (21) is 100 - 200 μm, the wall thickness of the annular cavity (21) is 1 - 2 μm, and the distance between the annular cavity (21) and the ridge waveguide structure (11) is 100 - 200 nm.

9. The preparation method according to claim 6, wherein: The P-type contact metal layer (12) is electrically connected to the ridge waveguide structure (11) through a current injection window opened in the insulating layer (3) located on the top of the ridge waveguide structure (11), and the annular cavity electrode layer (22) has no electrical connection with the annular cavity (21).

10. The edge-emitting laser with both longitudinal mode and transverse mode selection according to claim 6, wherein: The annular cavity electrode layer (22) has no electrical connection with the P-type contact metal layer (12).

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