Surface grating surface emitting laser

Abstract

The invention provides a surface grating surface emitting laser. The surface grating surface emitting laser comprises an N-face metal electrode layer; an N-face waveguide layer, an active layer, a P-face waveguide layer and a ridge waveguide layer are sequentially stacked on the N-face metal electrode layer, wherein the ridge waveguide layer comprises a gain region and a loss region; the P-surface metal electrode layer is arranged on the gain region of the ridge waveguide layer; and the P-surface silicon dioxide layer is arranged on the loss region of the ridge waveguide layer. According to the laser, through the characteristic that mode fields are distributed in a loss area and a gain area after PT symmetric breaking, a light field achieves surface light emitting through vertical diffraction coupling of surface gratings of the loss area, and the laser is different from a common laser structure in which gratings are completely etched in the longitudinal direction and electrodes are manufactured on the two sides. The mode gain difference is symmetrically manufactured through PT, double lobes are eliminated, a single mode is stabilized, lambda / 4 phase shift does not need to be introduced, and the process difficulty is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of semiconductor lasers, and in particular to a surface grating surface emitting laser. Background Art

[0002] Surface emitting lasers have become an important research direction in modern optoelectronic technology due to their unique structure, superior performance and broad application prospects. With the advancement of semiconductor material technology and the development of micro-nano processing technology, the performance of surface emitting lasers needs to be continuously improved. In the field of semiconductor lasers, surface emitting lasers can be divided into three types: vertical cavity surface emitting lasers (VCSEL), photonic crystal surface emitting lasers (PCSEL) and grating coupled surface emitting lasers (GCSEL). Among them, grating coupled surface emitting lasers are usually DFB lasers with m-order gratings (m is an integer between 2 and 20), which use the horizontal diffraction of the m-order grating for light feedback and realize surface emission through the vertical diffraction of the m-order grating. There are three main types of grating structures in grating coupled surface emitting lasers, namely buried gratings, metal gratings and surface gratings.

[0003] The buried grating needs to achieve flatness and high uniformity of the grating during the secondary epitaxial process to ensure effective integration with the subsequent layer structure. In addition, key parameters such as grating period, duty cycle and depth must be precisely controlled to achieve the desired optical feedback characteristics. This usually also requires high-quality epitaxial growth technology, and strict control of growth conditions is required to ensure the stability of the overall device performance. GCSELs with metal gratings provide optical feedback by introducing a metal grating structure on the surface of the semiconductor material. The metal grating is usually directly deposited or etched on the top layer of the laser active area and plays a strong reflective role in the grating structure. However, the light absorption of the metal grating will reduce the efficiency of the device, and the thermal effect of the metal will affect the long-term thermal stability of the device.

[0004] The surface grating can directly etch the grating on the surface of the finished epitaxial wafer, avoiding the epitaxial regrowth process required for the buried grating manufacturing process. Since the surface grating is far away from the waveguide, a larger grating height is usually required to increase the coupling strength between the laser mode and the grating. The use of the surface grating can not only improve the yield of the laser and reduce the production cost, but also increase the coupling coefficient of the grating to improve the single-mode characteristics of the laser. However, in the prior art, for GCSELs that emit light from the surface grating, the p-side electrode cannot be made on the grating, but is made by etching grooves or ridge waveguides and on both sides of the grating, with one electrode on each side, and carrier injection is performed by lateral diffusion. In addition, for the second-order grating, it is necessary to additionally introduce a λ / 4 phase shift to break the symmetrical mode gain, eliminate the far-field double lobe, and obtain a stable single mode. Summary of the invention

[0005] 1. Technical issues to be resolved

[0006] In view of the above shortcomings, the main purpose of the present invention is to provide a surface grating surface emitting laser, which is a surface grating surface emitting laser structure with periodic gain loss. The gain region is powered and injected with gain. After the PT symmetry is broken, the mode field is distributed in the loss region and the gain region respectively, so that the light field is coupled through the vertical diffraction of the surface grating in the loss region to realize the surface emission, which is different from the common laser structure in which the grating is completely etched longitudinally and electrodes are made on both sides. The mode gain difference is manufactured by PT symmetry, the double lobe is eliminated, the single mode is stabilized, and there is no need to introduce a λ / 4 phase shift, which reduces the process difficulty.

[0007] (II) Technical solution

[0008] In order to achieve the above-mentioned object, the present invention provides a surface grating surface emitting laser, comprising: an N-face metal electrode layer; an N-face waveguide layer, an active layer, a P-face waveguide layer and a ridge waveguide layer are sequentially stacked on the N-face metal electrode layer, wherein the ridge waveguide layer comprises a gain region and a loss region; the P-face metal electrode layer is arranged on the gain region of the ridge waveguide layer; and the P-face silicon dioxide layer is arranged on the loss region of the ridge waveguide layer.

[0009] In the above solution, the ridge waveguide layer includes a plurality of gain regions and loss regions, and the plurality of gain regions and loss regions are alternately arranged along the first direction.

[0010] In the above solution, along the first direction, the length of the loss region is the same as the length of the gain region; and / or the length of the loss region is different from the length of the gain region.

[0011] In the above solution, the loss region includes a surface grating, and the surface grating is a periodic groove structure arranged along a first direction in the loss region.

[0012] In the above scheme, the surface grating satisfies the Bragg condition, and the grating period Λ of the surface grating is obtained as follows:

[0013]

[0014] Where m is the grating order, is the Bragg wavelength, is the modal effective refractive index in the active layer.

[0015] In the above scheme, the P-plane metal electrode layer includes multiple P-plane metal electrodes for injecting current into the gain region; and the gain region with current injection and the loss region without current injection form a quasi-PT symmetric complex refractive index distribution along the first direction and realize surface emission through vertical diffraction of the surface grating.

[0016] In the above scheme, the laser is pumped by electrical injection to achieve the transition of the quasi-PT symmetric phase to the PT symmetry-broken phase of the laser longitudinal mode and obtain a single longitudinal mode output.

[0017] In the above solution, the cleavage surfaces on both sides of the laser along the first direction are coated with a high-reflection film.

[0018] In the above scheme, the structure of the active layer includes single quantum well, multiple quantum well, quantum dot and super lattice structure.

[0019] In the above solution, the first direction is parallel to the long side direction of the laser.

[0020] (III) Beneficial effects

[0021] The technical solution of the embodiment of the present invention has at least the following beneficial effects:

[0022] (1) The laser is a surface grating surface emitting laser structure with periodic gain loss. The gain region is powered and gain is injected. After the PT symmetry is broken, the mode field is distributed in the loss region and the gain region respectively. This allows the light field to be coupled through the vertical diffraction of the surface grating in the loss region to emit light on the surface. This is different from the common laser structure in which the grating is completely etched longitudinally and electrodes are made on both sides.

[0023] (2) The laser uses PT symmetry to create mode gain difference, eliminate double lobes, stabilize single mode, and eliminate the need to introduce λ / 4 phase shift, thus reducing the process difficulty.

[0024] (3) The laser does not require secondary epitaxial growth of materials, and the manufacturing process is simple, which reduces the manufacturing cost of the device and improves the reliability of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A schematic diagram of a three-dimensional structure of a surface grating surface emitting laser according to an embodiment of the present invention is shown;

[0026] Figure 2 A cross-sectional view of a second-order surface grating surface emitting laser according to an embodiment of the present invention is schematically shown;

[0027] Figure 3 A diagram schematically shows the relationship between the real part of the characteristic value of the second-order surface grating surface emitting laser according to an embodiment of the present invention and the imaginary part of the complex refractive index of the gain region material;

[0028] Figure 4 A diagram schematically shows the relationship between the imaginary part of the characteristic value of the second-order surface grating surface emitting laser and the imaginary part of the complex refractive index of the gain region material according to an embodiment of the present invention;

[0029] Figure 5aA mode field distribution diagram of a lasing mode of a second-order surface grating surface emitting laser according to an embodiment of the present invention when ni is 0 is schematically shown;

[0030] Figure 5b A mode field distribution diagram of a lasing mode of a second-order surface grating surface emitting laser according to an embodiment of the present invention when ni is 0.05 is schematically shown;

[0031] Figure 5c Schematically shows a mode field distribution diagram of a lasing mode of a second-order surface grating surface emitting laser according to an embodiment of the present invention when ni is 0.10;

[0032] Figure 5d A schematic diagram showing a mode field distribution diagram of a lasing mode of a second-order surface grating surface emitting laser according to an embodiment of the present invention when the electric field is emitted into a medium when ni is 0.10;

[0033] Figure 6a A mode field distribution diagram of a loss mode of a second-order surface grating surface emitting laser when ni is 0 according to an embodiment of the present invention is schematically shown;

[0034] Figure 6b A mode field distribution diagram of a loss mode of a second-order surface grating surface emitting laser according to an embodiment of the present invention when ni is 0.05 is schematically shown;

[0035] Figure 6c A mode field distribution diagram of a loss mode of a second-order surface grating surface emitting laser according to an embodiment of the present invention when ni is 0.10 is schematically shown;

[0036] Figure 6d Schematically shows a mode field distribution diagram of the loss mode of the second-order surface grating surface emitting laser according to an embodiment of the present invention when the electric field is emitted into the medium when ni is 0.10;

[0037] Figure 7 The surface emission power diagrams of the lasing mode and the loss mode of the second-order surface grating surface emitting laser at different gain levels ni according to an embodiment of the present invention are schematically shown. DETAILED DESCRIPTION

[0038] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

[0039] First, the technical terms described in this article are explained and described as follows.

[0040] PT symmetry, time reversal symmetry (T) and parity symmetry (P), are used to study the symmetry properties of a system and its influence on physical phenomena. In a PT-symmetric quantum system, there are real-valued eigenvalues, and the system is in a PT-symmetric phase. As specific non-Hermitian parameters in the system change, the system will spontaneously break PT symmetry and enter a PT-symmetry-breaking phase, and some of the eigenvalues ​​of the system will be transformed into pairs of conjugate complex numbers. The critical point between the PT-symmetric phase and the PT-symmetry-breaking phase of the system is the exceptional point (EP). At the EP, both the eigenvalues ​​and eigenwave functions of the system will be degenerate. In an optical system, the imaginary part of the eigenvalue corresponds to the gain and loss of the system.

[0041] Figure 1 The three-dimensional structure diagram of the surface grating surface emitting laser according to an embodiment of the present invention is schematically shown.

[0042] Please refer to Figure 1 and Figure 2 An embodiment of the present invention provides a surface grating surface emitting laser, comprising: an N-face metal electrode layer 1; an N-face waveguide layer 2, an active layer 3, a P-face waveguide layer 4 and a ridge waveguide layer 5 are sequentially stacked on the N-face metal electrode layer 1, wherein the ridge waveguide layer 5 includes a gain region and a loss region; a P-face metal electrode layer 6 is arranged on the gain region of the ridge waveguide layer 5; and a P-face silicon dioxide layer 7 is arranged on the loss region of the ridge waveguide layer 5.

[0043] Exemplarily, the cleavage surfaces on both sides of the laser along the first direction X1 may also be coated with a high-reflection film to increase the surface emission power of the laser.

[0044] Exemplarily, the structure of the active layer 3 may be one of four structures: a single quantum well, a multiple quantum well, a quantum dot, and a super lattice structure.

[0045] Exemplarily, the material of the N-type substrate layer in the N-side metal electrode layer 1 includes at least one of the following four materials: GaN, GaAs, InP and GaSb.

[0046] In the embodiment of the present invention, the ridge waveguide layer 5 includes a plurality of gain regions and loss regions, and the plurality of gain regions and loss regions are alternately arranged along the first direction X1. In the ridge waveguide layer 5, there are various situations such as the lengths of the gain region and the loss region are the same, and / or the lengths of the gain region and the loss region are different.

[0047] It should be noted that, in this embodiment, the first direction X1 is parallel to the long side direction of the laser.

[0048] like Figure 1As shown, the loss region includes a surface grating 51, and the surface grating 51 is a periodic groove structure arranged along a first direction X1 in the loss region.

[0049] Exemplarily, the surface grating 51 is of order m, for example, m is an integer between 2 and 20, the surface grating 51 satisfies the Bragg condition, and the grating period Λ of the surface grating 51 is obtained as follows:

[0050]

[0051] Where m is the grating order, is the Bragg wavelength, is the modal effective refractive index in the active layer 3.

[0052] Please continue reading Figure 1 For example, the P-side metal electrode layer 6 may include a plurality of P-side metal electrodes disposed on the gain region of the ridge waveguide layer 5 for injecting current into the gain region.

[0053] In an embodiment of the present invention, the pumping mode of the laser is electrical injection, so as to realize the transformation of the quasi-PT symmetric phase to the PT symmetry-broken phase of the longitudinal mode of the laser and obtain a single longitudinal mode output.

[0054] In an embodiment of the present invention, the entire ridge waveguide layer 5 is composed of a gain zone with current injection and a loss zone without current injection and etched with an m-order surface grating 51. At this time, the gain zone and the loss zone form a quasi-PT-symmetric complex refractive index distribution along the first direction X1 and realize surface emission through vertical diffraction of the surface grating 51.

[0055] Based on the above embodiment of the surface grating surface emitting laser, the central wavelength of the light wave emitted by the laser is located in both the infrared light band and the visible light band.

[0056] Through the embodiments of the present invention, the gain region is energized to inject gain, and due to the characteristics that the mode field is respectively distributed in the loss region and the gain region after the PT symmetry is broken, the light field is coupled through the vertical diffraction of the surface grating in the loss region to realize surface light emission, which is different from the common laser structure in which the grating is completely etched vertically and electrodes are made on both sides.

[0057] Based on the above description of the surface grating surface emitting laser, the present invention proposes a specific embodiment of a second-order surface grating surface emitting laser.

[0058] Figure 2 A cross-sectional view of a second-order surface grating surface emitting laser according to an embodiment of the present invention is schematically shown.

[0059] like Figure 2As shown, in the second-order surface grating surface emitting laser, the ridge waveguide layer 5 is composed of a gain zone with current injection and a loss zone without current injection etched with a second-order surface grating 51. At this time, the gain zone and the loss zone form a quasi-PT symmetrical complex refractive index distribution along the first direction X1 and realize single-frequency surface light emission through the first-order diffraction of the second-order surface grating 51.

[0060] Specifically, the gain region and the loss region of the ridge waveguide layer 5 in the second-order surface grating surface emitter are respectively etched to the same height as the P-plane waveguide layer 4, for example, both are 1.3μm, and the etched ridge waveguide is used to limit the lateral diffusion of current and realize single transverse mode lasing; and the second-order surface grating etching depth can be set to 1.5μm, for example, and the number of grating periods is 80.

[0061] It should be noted that the etching depth of the second-order grating should be greater than or equal to 1.3 μm, so that the grating can effectively control the light field extending into the waveguide layer.

[0062] The preset refractive indices of the upper cladding and lower cladding of the second-order surface grating surface emitting laser are 3.1529 and 3.1681 respectively. The refractive index of the active layer in the loss zone is set to 3.2827+i*0.001, and the refractive index of the active layer in the gain zone is set to 3.2827-i*ni, wherein i represents the sign of the imaginary part of the refractive index, a positive imaginary part of the refractive index corresponds to loss, a negative imaginary part corresponds to gain, and ni represents the gain applied in the gain zone.

[0063] Figure 3 The diagram schematically shows the relationship between the real part of the characteristic value of the second-order surface grating surface emitting laser according to an embodiment of the present invention and the imaginary part of the complex refractive index of the gain region material. Figure 4 The diagram schematically shows the relationship between the imaginary part of the eigenvalue of the second-order surface grating surface emitting laser according to an embodiment of the present invention and the imaginary part of the complex refractive index of the gain region material.

[0064] In the embodiment of the present invention, the finite element method is used to solve the relationship between the real part and the imaginary part of the eigenvalue of the second-order surface grating surface emitting laser and the gain ni, and the simulation results are as follows: Figure 3 and Figure 4 shown.

[0065] It can be seen that when the gain is small, the laser is in the PT symmetry stage, the real parts of the lasing mode and the loss mode diverge and the imaginary parts are degenerate, and both modes can be lasered at this time; PT symmetry breaking occurs at ni=0.05, and this point is the phase transition point; after ni exceeds 0.05, the imaginary parts of the lasing mode and the loss mode diverge, and the real parts are not completely degenerate, indicating that this is a quasi-PT symmetry stage, and the absolute value of the imaginary part of the characteristic frequency of the lasing mode increases with the increase of the gain ni, indicating that the lasing mode can always obtain gain and laser, while the imaginary part of the characteristic frequency of the loss mode remains at a fixed value. In actual devices, it cannot be lasered due to factors such as internal loss coupling loss.

[0066] According to the embodiments of the present invention, the laser is a surface grating surface emitting laser structure with periodic gain loss. The laser selects the mode by introducing PT symmetry, creates the mode gain difference, eliminates the double lobes, and realizes the stable single-mode output of the PT symmetry breaking phase. There is no need to introduce λ / 4 phase shift, thereby reducing the process difficulty.

[0067] Figure 5a The mode field distribution diagram of the lasing mode of the second-order surface grating surface emitting laser according to an embodiment of the present invention when ni is 0 is schematically shown. Figure 5b The mode field distribution diagram of the lasing mode of the second-order surface grating surface emitting laser according to an embodiment of the present invention is schematically shown when ni is 0.05. Figure 5c The mode field distribution diagram of the lasing mode of the second-order surface grating surface emitting laser according to an embodiment of the present invention is schematically shown when ni is 0.10. Figure 5d The mode field distribution diagram of the lasing mode of the second-order surface grating surface emitting laser according to an embodiment of the present invention when the electric field is emitted into the medium when ni is 0.10 is schematically shown.

[0068] Figure 6a The mode field distribution diagram of the loss mode of the second-order surface grating surface emitting laser according to an embodiment of the present invention when ni is 0 is schematically shown. Figure 6b The mode field distribution diagram of the loss mode of the second-order surface grating surface emitting laser according to an embodiment of the present invention is schematically shown when ni is 0.05. Figure 6c The mode field distribution diagram of the loss mode of the second-order surface grating surface emitting laser according to an embodiment of the present invention is schematically shown when ni is 0.10. Figure 6d The mode field distribution diagram of the loss mode of the second-order surface grating surface emitting laser according to an embodiment of the present invention when the electric field is emitted into the medium when ni is 0.10 is schematically shown.

[0069] like Figure 5a-5d as well as Figure 6a-6dAs shown, the medium is air, with a refractive index of n=1. In the PT symmetry stage, the lasing mode and loss mode fields are relatively symmetrically distributed in the gain region and the loss region. When the PT symmetry is broken, that is, ni is greater than 0.05, the mode field of the intrinsic mode will be localized: the lasing mode is mainly localized in the gain region, while the loss mode is mainly localized in the loss region. Figure 5d It can be seen that the lasing mode expands the light field to the loss region and couples out the light using the grating.

[0070] Through the embodiments of the present invention, the light field is modulated by regulating the gain and loss of the device, and the PT symmetry characteristics of the system are utilized to expand the light field to the loss region and realize surface light emission.

[0071] Figure 7 The surface emission power diagrams of the lasing mode and the loss mode of the second-order surface grating surface emitting laser at different gain levels ni according to an embodiment of the present invention are schematically shown.

[0072] like Figure 7 As shown, in the PT symmetry stage, the mode fields of the lasing mode and the loss mode are similar, so the surface emission powers are close, and the surface emission power decreases when the gain ni increases; after the PT symmetry is broken, the mode field becomes localized, the lasing mode energy increases, and the loss mode energy decreases.

[0073] Through the embodiments of the present invention, a method for preparing a laser with periodic gain loss is proposed, in which a second-order surface grating is etched on a ridge waveguide as a loss region and a light-emitting region, and an electrode is made on the remaining ridge waveguide where the grating is not etched as a gain region. The method modulates the light field by regulating the gain loss of the device, and uses the PT symmetry characteristics of the system to extend the light field to the loss region and realize surface light emission; single longitudinal mode output can be obtained without introducing a λ / 4 phase shift, simplifying the process steps; at the same time, the use of a surface grating does not require secondary epitaxy, reducing the process difficulty and reducing the production cost.

[0074] The surface grating surface emitting laser based on the above-mentioned embodiment of the present invention is not only highly integrated, but also does not require external light feedback and external light injection, thereby avoiding the weak periodicity caused by light feedback. Single longitudinal mode output is achieved through the surface grating, and the transverse mode distribution in the cavity is regulated by adjusting the waveguide size and spacing. The nonlinear state optical signal of the actual output is controlled by different injected currents.

[0075] The above specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A surface grating surface emitting laser, characterized in that: include: N-side metal electrode layer (1); An N-side waveguide layer (2), an active layer (3), a P-side waveguide layer (4) and a ridge waveguide layer (5) are sequentially stacked on the N-side metal electrode layer (1), wherein the ridge waveguide layer (5) comprises a gain region and a loss region; A P-surface metal electrode layer (6) arranged on the gain region of the ridge waveguide layer (5); A P-face silicon dioxide layer (7) is arranged on the loss region of the ridge waveguide layer (5).

2. The surface grating surface emitting laser according to claim 1, characterized in that: The ridge waveguide layer (5) comprises a plurality of gain regions and loss regions, and the plurality of gain regions and loss regions are alternately arranged along a first direction.

3. The surface grating surface emitting laser according to claim 1 or 2, characterized in that: In the first direction, the length of the loss region is the same as the length of the gain region; and / or The length of the loss region is different from the length of the gain region.

4. The surface grating surface emitting laser according to claim 3, characterized in that: The loss region comprises a surface grating (51), and the surface grating (51) is a periodic groove structure arranged along the first direction in the loss region.

5. The surface grating surface emitting laser according to claim 4, characterized in that: The surface grating (51) satisfies the Bragg condition, and the grating period Λ of the surface grating (51) is obtained as follows: Where m is the grating order, is the Bragg wavelength, is the effective refractive index of the mode in the active layer (3).

6. The surface grating surface emitting laser according to claim 1 or 2, characterized in that: The P-side metal electrode layer (6) comprises a plurality of P-side metal electrodes for injecting current into the gain region; as well as The gain region with current injection and the loss region without current injection form a quasi-PT symmetric complex refractive index distribution along the first direction and realize surface emission through vertical diffraction of the surface grating (51).

7. The surface grating surface emitting laser according to claim 6, characterized in that: The pumping mode of the laser is electric injection, so as to realize the transformation of the quasi-PT symmetric phase to the PT symmetry breaking phase of the longitudinal mode of the laser and obtain the single longitudinal mode output.

8. The surface grating surface emitting laser according to claim 6, characterized in that: The cleavage surfaces on both sides of the laser along the first direction are plated with high reflection films.

9. The surface grating surface emitting laser according to claim 1, characterized in that: The structure of the active layer (3) includes a single quantum well, a multiple quantum well, a quantum dot and a super lattice structure.

10. The surface grating surface emitting laser according to claim 6, characterized in that: The first direction is parallel to the long side direction of the laser.

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