Surface grating face emitting laser

Abstract

The application 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; a P-face metal electrode layer is arranged on the gain region of the ridge waveguide layer; and a P-face silicon dioxide layer is arranged on the loss region of the ridge waveguide layer. The laser is characterized in that the mode field is distributed in the loss region and the gain region after the PT symmetry is broken, so that the light field is realized to be emitted on the surface through the vertical diffraction coupling of the surface grating of the loss region, which is different from the common laser structure that all grating is etched in the longitudinal direction and electrodes are made on both sides. Through the PT symmetry manufacturing mode gain difference, the double lobes are eliminated, the single mode is stabilized, the λ / 4 phase shift is not needed to be introduced, and the process difficulty is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor lasers, and particularly relates to a surface grating surface emitting laser. BACKGROUND

[0002] Surface emitting lasers have become an important research direction in modern optoelectronic technology due to their unique structure, superior performance and wide application prospects. With the progress 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, the grating coupled surface emitting laser is usually a DFB laser with an m-order grating (m is an integer between 2 and 20), which uses the horizontal diffraction of the m-order grating for optical feedback and realizes surface emission through the vertical diffraction of the m-order grating. The grating structure in the grating coupled surface emitting laser mainly includes three types: buried grating, metal grating and surface grating.

[0003] The buried grating needs to realize the planarization and high uniformity of the grating in the secondary epitaxy process to ensure the effective combination with the subsequent layer structure. In addition, the key parameters such as grating period, duty cycle and depth must be precisely controlled to achieve the required optical feedback characteristics. This usually involves high-quality epitaxial growth technology and requires strict control of growth conditions to ensure stable overall device performance. The GCSEL with a metal grating provides optical feedback by introducing a metal grating structure on the surface of the semiconductor material. The metal grating is usually deposited or etched directly on the top layer of the laser active region and plays a role of strong reflection in the grating structure. However, the light absorption of the metal grating reduces the device efficiency, and the thermal effect of the metal affects the long-term thermal stability of the device.

[0004] The surface grating can be etched directly on the surface of the finished epitaxial wafer, avoiding the epitaxial regrowth process required in the manufacturing process of the buried grating. 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 surface grating not only improves the yield of the laser and reduces the manufacturing cost, but also increases the coupling coefficient of the grating and improves the single-mode characteristics of the laser. However, in the prior art, the p-face electrode of the GCSEL with surface grating cannot be made on the grating, but is etched into a groove or ridge waveguide and made on both sides of the grating, with one electrode on each side, and the carrier injection is realized by lateral diffusion. In addition, for the second-order grating, a λ / 4 phase shift needs to be introduced to break the symmetrical mode gain and eliminate the far-field double lobes to obtain stable single mode. SUMMARY

[0005] (1) Technical problems to be solved

[0006] In view of the above problems, the main purpose of the present application is to provide a surface grating surface emitting laser, which is a surface grating surface emitting laser structure with periodic gain and loss. The gain region is injected with gain, and the mode field is distributed in the loss region and the gain region after the PT symmetry is broken. The vertical diffraction coupling of the light field through the surface grating of the loss region realizes the surface light emission, which is different from the common longitudinal all-grating laser structure and the laser structure with electrodes on both sides. The PT symmetry manufacturing mode gain difference eliminates the double lobes, stabilizes the single mode, and does not need to introduce λ / 4 phase shift, which reduces the process difficulty.

[0007] (2) Technical solutions

[0008] In order to achieve the above purpose, the present application provides a surface grating surface emitting laser, comprising: an N-face metal electrode layer; N-face waveguide layers, 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; a P-face metal electrode layer is arranged on the gain region of the ridge waveguide layer; a P-face silicon dioxide layer is arranged on the loss region of the ridge waveguide layer.

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

[0010] In the above scheme, 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 not the same as the length of the gain region.

[0011] In the above scheme, the loss region comprises a surface grating, and the surface grating is a periodic groove structure arranged along the 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 derived as follows:

[0013]

[0014] Wherein, m is the grating order, is the Bragg wavelength, is the effective refractive index of the mode in the active layer.

[0015] In the above scheme, the P-face metal electrode layer comprises a plurality of P-face metal electrodes for injecting current to the gain region; and the current-injected gain region and the current-uninjected loss region form a quasi-PT symmetric complex refractive index distribution along the first direction and realize surface emission through the vertical diffraction of the surface grating.

[0016] In the scheme, the laser is pumped by electric injection to realize the transition of the quasi-PT symmetric phase of the longitudinal mode of the laser to the PT symmetric breaking phase and obtain single longitudinal mode output.

[0017] In the scheme, the two cleavage surfaces on the two sides of the laser along the first direction are plated with high reflection films.

[0018] In the scheme, the structure of the active layer includes a single quantum well, a multiple quantum well, a quantum dot and a superlattice structure.

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

[0020] (Three) beneficial effects

[0021] The technical scheme of the embodiment of the application has at least the following beneficial effects:

[0022] (1) The laser is a surface grating surface emitting laser structure with periodic gain and loss. The gain region is electrically injected to gain. Through the characteristics that the mode field is distributed in the loss region and the gain region after the PT symmetry breaking, the light field is vertically diffracted and coupled to realize surface light emission through the surface grating of the loss region. It is different from the common laser structure of longitudinal etching grating and electrode on both sides.

[0023] (2) The laser eliminates the double lobes by the PT symmetric manufacturing mode gain difference, stabilizes the single mode, and does not need to introduce a lambda / 4 phase shift, thereby reducing the process difficulty.

[0024] (3) The laser does not need secondary epitaxial growth of the material, the manufacturing process is simple, the manufacturing cost of the device is reduced, and the reliability of the device is improved. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 The three-dimensional structure of the surface grating surface emitting laser according to the embodiment of the application is schematically shown;

[0026] Figure 2 The cross-sectional view of the second-order surface grating surface emitting laser according to the embodiment of the application is schematically shown;

[0027] Figure 3 The characteristic value real part of the second-order surface grating surface emitting laser according to the embodiment of the application is schematically shown. The change relationship diagram of the gain region material complex refractive index imaginary part size;

[0028] Figure 4 The characteristic value imaginary part of the second-order surface grating surface emitting laser according to the embodiment of the application is schematically shown. The change relationship diagram of the gain region material complex refractive index imaginary part size;

[0029] Figure 5aFig. 6 schematically shows the mode field distribution of the lasing mode of the second-order surface grating face-emitting laser of the embodiment of the present application when ni is 0.10;

[0030] Figure 5b Fig. 7 schematically shows the mode field distribution of the lasing mode of the second-order surface grating face-emitting laser of the embodiment of the present application when ni is 0.05;

[0031] Figure 5c Fig. 8 schematically shows the mode field distribution of the lasing mode of the second-order surface grating face-emitting laser of the embodiment of the present application when ni is 0.10;

[0032] Figure 5d Fig. 9 schematically shows the mode field distribution of the lasing mode of the second-order surface grating face-emitting laser of the embodiment of the present application when ni is 0.10, with the electric field exiting into the medium;

[0033] Figure 6a Fig. 10 schematically shows the mode field distribution of the loss mode of the second-order surface grating face-emitting laser of the embodiment of the present application when ni is 0;

[0034] Figure 6b Fig. 11 schematically shows the mode field distribution of the loss mode of the second-order surface grating face-emitting laser of the embodiment of the present application when ni is 0.05;

[0035] Figure 6c Fig. 12 schematically shows the mode field distribution of the loss mode of the second-order surface grating face-emitting laser of the embodiment of the present application when ni is 0.10;

[0036] Figure 6d Fig. 13 schematically shows the mode field distribution of the loss mode of the second-order surface grating face-emitting laser of the embodiment of the present application when ni is 0.10, with the electric field exiting into the medium;

[0037] Figure 7 Fig. 14 schematically shows the face-emitting power of the lasing mode and the loss mode of the second-order surface grating face-emitting laser of the embodiment of the present application at different gain levels ni, respectively. DETAILED DESCRIPTION

[0038] In order to make the objectives, technical solutions, and advantages of the present application clearer, the present application will be further described in detail below with reference to specific embodiments and with reference to the accompanying drawings.

[0039] First, the technical terms described in this document 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 the influence on physical phenomena. In a PT symmetric quantum system, there are real eigenvalues, and the system is in a PT symmetric phase. With the change of a specific non-Hermitian parameter in the system, the system will spontaneously break the PT symmetry, enter a PT symmetric broken phase, and some eigenvalues of the system will change into a pair of complex conjugate numbers. The critical point between the PT symmetric phase and the PT symmetric broken phase is an exceptional point (EP). At the EP, the eigenvalues and eigenfunctions of the system are degenerate. In an optical system, the imaginary part of the eigenvalue corresponds to the gain and loss of the system.

[0041] Figure 1 A perspective view of a surface grating face-emitting laser according to an embodiment of the present application is schematically shown.

[0042] For a more complete understanding of the present application, reference is made to Figure 1 and Figure 2 An embodiment of the present application provides a surface grating face-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 comprises 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] Illustratively, the cleavage surfaces on both sides of the laser along the first direction X1 can also be coated with a high reflection film to improve the face-emitting power of the laser.

[0044] Illustratively, the structure of the active layer 3 may, for example, be one of the following four structures: single quantum well, multiple quantum well, quantum dot and superlattice structure.

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

[0046] In an embodiment of the present application, the ridge waveguide layer 5 comprises a plurality of gain regions and loss regions, and the plurality of gain regions and loss regions are arranged alternately along the first direction X1. Wherein, there are multiple cases that the length of the gain region and the length of the loss region in the ridge waveguide layer 5 are the same, and / or the length of the gain region and the length of the loss region are not the same.

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

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

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

[0050]

[0051] where m is the grating order, is the Bragg wavelength, is the effective refractive index of the mode in the active layer 3.

[0052] For further details, please refer to Figure 1 For example, the P-face metal electrode layer 6 can comprise a plurality of P-face metal electrodes arranged on the gain region of the ridge waveguide layer 5 for injecting current to the gain region.

[0053] In the embodiment of the present application, the pump mode of the laser is electrical injection, so as to realize the transition of the longitudinal mode of the laser from the quasi-PT symmetric phase to the PT symmetric breaking phase and obtain single longitudinal mode output.

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

[0055] Based on the above-described 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 wave band and the visible light wave band.

[0056] Through the embodiment of the present application, the gain region is added with electrical injection gain, and the characteristics of the mode field distribution in the loss region and the gain region after PT symmetric breaking make the light field realize surface light emission through the vertical diffraction coupling of the surface grating of the loss region, which is different from the common laser structure of etching grating longitudinally and making electrodes on both sides.

[0057] Based on the above-described description of the surface grating surface-emitting laser, the present application 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 application is schematically shown.

[0059] As Figure 2As shown, in the second-order surface grating face-emitting laser, the ridge waveguide layer 5 is composed of a current-injected gain region and a current-non-injected loss region etched with a second-order surface grating 51, at this time, the gain region and the loss region form a quasi-PT symmetric complex refractive index distribution along the first direction X1 and realize single-frequency face-emitting by first-order diffraction of the second-order surface grating 51.

[0060] Specifically, in the second-order surface grating face-emitting laser, the gain region and the loss region of the ridge waveguide layer 5 are etched to the same height of the P-plane waveguide layer 4, for example, both are 1.3 μm, the ridge waveguide obtained by etching is used to limit the lateral diffusion of current and realize single transverse mode lasing; and the etching depth of the second-order surface grating can be set to 1.5 μm, and the grating period number 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 regulate the light field expanded into the waveguide layer.

[0062] The second-order surface grating face-emitting laser is preset with upper cladding layer and lower cladding layer refractive indexes of 3.1529 and 3.1681 respectively, then the loss region active layer refractive index is set to 3.2827+i*0.001, and the gain region active layer refractive index is set to 3.2827-i*ni, wherein i represents the imaginary part symbol of the refractive index, the positive imaginary part corresponds to loss, and the negative imaginary part corresponds to gain, and ni represents the gain size applied to the gain region.

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

[0064] In the embodiment of the present application, by using the finite element method to solve the relationship between the real part and the imaginary part of the eigenvalue of the second-order surface grating face-emitting laser and the gain ni, the simulation results obtained are as shown in Figure 3 and Figure 4

[0065] ​It can be seen that when the gain is small, the laser is in a PT symmetric phase, the real and imaginary parts of the lasing mode and the loss mode are degenerate, at this time both modes can lase; the PT symmetry is broken at ni=0.05, which is the phase transition point; after ni exceeds 0.05, the imaginary parts of the lasing mode and the loss mode are divergent, and the real parts are not completely degenerate, which represents a quasi-PT symmetric phase, 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 lase, while the imaginary part of the characteristic frequency of the loss mode remains at a fixed value, and in actual devices, the lasing cannot be achieved due to factors such as internal loss and coupling loss.

[0066] Through the embodiment of the present application, the laser is a surface grating face-emitting laser structure with periodic gain and loss, the laser selects modes by introducing PT symmetry, makes the mode gain difference, eliminates the double lobes, realizes the stable single-mode output of the PT symmetry breaking phase, does not need to introduce a lambda / 4 phase shift, and reduces the process difficulty.

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

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

[0069] As Figures 5a-5d and Figures 6a-6dAs shown, the medium is air with a refractive index n=1. During the PT symmetry phase, the lasing mode and loss mode modes are relatively symmetrically distributed in the gain and loss regions, respectively. When PT symmetry breaking occurs, i.e., ni is greater than 0.05, the mode fields of the intrinsic modes become localized: the lasing mode is mainly localized in the gain region, while the loss mode is mainly localized in the loss region. From... Figure 5d It can be seen that the lasing mode extends the light field to the loss region and uses a grating to couple out the light.

[0070] Through the embodiments of the present invention, the optical field is modulated by adjusting the gain and loss of the control device, and the optical field is extended to the loss region by utilizing the PT symmetry characteristics of the system to achieve surface light emission.

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

[0072] like Figure 7 As shown, during the PT symmetry stage, the lasing mode and the loss mode have similar mode fields, so their surface emission powers are close. As the gain ni increases, the surface emission power decreases. After PT symmetry breaking occurs, the lasing mode energy increases and the loss mode energy decreases due to the localization of the mode field.

[0073] This invention proposes a method for fabricating a periodically gain-loss laser by etching a second-order surface grating on a ridge waveguide as both the loss and output regions, and fabricating electrodes on the remaining unetched ridge waveguide as the gain region. This method modulates the optical field by adjusting the gain loss of the device, utilizing the PT symmetry of the system to extend the optical field to the loss region and achieve surface-level light output. Single-mode output can be obtained without introducing a λ / 4 phase shift, simplifying the fabrication process. Furthermore, the use of a surface grating eliminates the need for secondary epitaxy, reducing fabrication complexity and costs.

[0074] Based on the surface grating surface-emitting laser of the present invention described above, the laser is not only highly integrated, but also does not require external optical feedback and external optical injection, thus avoiding the weak periodicity caused by optical feedback. It achieves single longitudinal mode output through surface grating, regulates the transverse mode distribution in the cavity by adjusting the waveguide size and spacing, and controls the nonlinear state optical signal of the actual output by different injection currents.

[0075] The above specific embodiments further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above are merely 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 within the protection scope of the present invention.

Claims

1. A surface grating face emitting laser, characterized by, Comprise: 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) comprises 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); A P-face silicon dioxide layer (7) is arranged on the loss region of the ridge waveguide layer (5); The ridge waveguide layer (5) comprises a plurality of gain regions and loss regions, and the plurality of gain regions and loss regions are arranged alternately along a first direction; In the first direction, the length of the loss region is the same as the length of the gain region; 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; The P-face metal electrode layer (6) comprises a plurality of P-face 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 (51).

2. The surface grating face emitting laser of claim 1, wherein, The surface grating (51) satisfies the Bragg condition, and the grating period Λ of the surface grating (51) is derived 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).

3. The surface grating face emitting laser of claim 1, wherein, The pumping mode of the laser is electrical injection to realize the transition of the laser longitudinal mode from quasi-PT symmetric phase to PT symmetry breaking phase and obtain single longitudinal mode output.

4. The surface grating face emitting laser of claim 1, wherein, The two sides of the laser along the first direction are coated with high reflection film.

5. The surface grating face emitting laser of claim 1, wherein, The structure of the active layer (3) comprises one of single quantum well, multiple quantum well, quantum dot and superlattice structure.

6. The surface grating face emitting laser of claim 1, wherein, The first direction is parallel to the long side direction of the laser.

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