Quasi-aerospace time symmetric quantum cascade laser and preparation method thereof

Abstract

The invention provides a quasi-space time symmetric quantum cascade laser and a preparation method thereof, and relates to the technical field of semiconductor lasers. The laser comprises a single gain waveguide and a plurality of loss waveguides, the loss waveguides are sequentially arranged on the two sides of the gain waveguide, isolation trenches are engraved between the waveguides, the gain waveguide is wide in ridge width and injects current through an upper electrode to generate high power, the loss waveguides are narrow in ridge width, and the tops of the loss waveguides are completely covered by an insulating layer without current injection. High-order modes detrimental to beam quality are filtered out by resonant coupling between a fundamental mode in the loss waveguide and a high-order mode in the gain waveguide. According to the quantum cascade laser, the space-time symmetry concept is introduced into the quantum cascade laser for the first time, high output power and good light beam quality can be achieved through a traditional technology, and single longitudinal mode output is expected to be obtained.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor lasers, and more particularly to a parity-time (PT) symmetric quantum cascade laser and a preparation method thereof. BACKGROUND

[0002] As a high-performance light source in the mid-infrared waveband, the quantum cascade laser (QCL) has the characteristics of wavelength tunable and high output power, and since its advent, it has been widely used in gas detection, spectral analysis, medical examination, infrared countermeasure and other fields. For an ideal quantum cascade laser, it is desired to maintain the energy of the optical field concentrated in the symmetry center, i.e., the fundamental transverse mode lasing, while obtaining high output power. By controlling the etching depth of the ridge waveguide, the cutoff width of the high-order mode can be affected. Therefore, using a narrow ridge waveguide is the simplest method to achieve good beam quality.

[0003] For a mid-infrared QCL, if the fundamental transverse mode lasing is to be ensured in a large dynamic range, the width of the ridge waveguide usually needs to be limited to about 7-9 µm. However, a narrow ridge waveguide not only limits the power improvement of the device, but also causes a large far-field divergence angle.

[0004] Traditional quantum cascade lasers use many schemes such as tapered waveguides, coupled ridge waveguides, photonic crystal structures, etc. to balance high output power and good beam quality. These traditional spatial mode control methods mainly optimize the device geometry, and the core is the control of the real part of the refractive index. Moreover, these traditional methods often have a complicated fabrication process.

[0005] In summary, it is still a problem to be solved to obtain high output power and good beam quality while maintaining a simple process. SUMMARY

[0006] Therefore, the present application provides a parity-time symmetric quantum cascade laser and a preparation method thereof. The single longitudinal mode output of the laser is achieved, and the laser has good beam quality and high power.

[0007] A first aspect of the present application provides a parity-time symmetric quantum cascade laser, characterized in that it comprises: an upper waveguide 5; a gain waveguide 1 arranged on the upper surface of the upper waveguide 5; a plurality of loss waveguides 2 distributed on both sides of the gain waveguide 1 and arranged on the upper surface of the upper waveguide 5, wherein an isolation groove is etched between any two adjacent waveguides in the gain waveguide 1 and the plurality of loss waveguides 2; the plurality of loss waveguides 2, the isolation groove and part of the surface of the gain waveguide 1 are covered with an insulating layer 4, and the surface of the gain waveguide 1 not covered with the insulating layer 4 and the surface of the insulating layer 4 are further covered with an upper electrode 3, and the gain waveguide 1 injects current through the upper electrode 3.

[0008] Further, the quantum cascade laser has, from top to bottom, an upper confinement layer 6, a multi-period gain active region 7, a lower confinement layer 8, a lower waveguide 9, a substrate 10, and a lower electrode 11.

[0009] Further, the depth of the isolation grooves is less than the thickness of the upper waveguide 5, other optical material layers are connected through, and the widths of the plurality of isolation grooves are different.

[0010] Further, there is resonant coupling between the fundamental mode of the plurality of loss waveguides 2 and the high-order modes of the gain waveguide 1, so that the high-order modes of the gain waveguide 1 are in a quasi-time-symmetric state, while the fundamental mode of the gain waveguide 1 is not affected, and finally single-mode lasing is achieved.

[0011] Further, the ridge width of the gain waveguide 1 is greater than the ridge width of each loss waveguide 2, and the ridge widths of the plurality of loss waveguides 2 are different.

[0012] Further, the ridge width of the gain waveguide 1 depends on the center wavelength of the material and the cutoff width of the mode in the waveguide. The longer the wavelength, the more high-order modes, and the larger the corresponding ridge width.

[0013] Further, the loss waveguide 2 is a plurality of loss waveguides corresponding to different high-order modes.

[0014] Further, the gain waveguide 1 and each loss waveguide 2 are single-ridge waveguide structures.

[0015] Further, the material of the upper electrode 3 is Ti / Au; the insulating layer 4 is a SiO2 layer; the upper waveguide 5 is a Si-doped graded-doped InP layer; the upper confinement layer 6 and the lower confinement layer 8 are Si-doped matching InGaAs layers; the multi-period gain active region 7 is an X-period stacked InGaAs / InAlAs quantum cascade laser functional superlattice, 20≤X≤50; the lower waveguide 9 is a Si-doped InP layer; the substrate 10 is an N-type doped InP; and the material of the lower electrode 11 is Ge / Au / Ni / Au.

[0016] The second aspect of the present application provides a preparation method of a quasi-time-symmetric quantum cascade laser, comprising the following steps:

[0017] S1, epitaxially growing, on the surface of the substrate 10, the lower waveguide 9, the lower confinement layer 8, the multi-period gain active region 7, the upper confinement layer 6, and the upper waveguide 5 in sequence;

[0018] S2, spin-coating photoresist on the surface of the upper waveguide 10, obtaining a mask for a double-groove pattern in a silicon oxide process through photolithography, and etching the upper waveguide 5, the upper confinement layer 6, and the multi-period gain active region 7 according to the pattern mask, and the etching depth exceeds the active region 7;

[0019] S3, removing photoresist, growing a layer of SiO2 on the surface of the upper waveguide 5, and again spin-coating photoresist, and then removing the photoresist on the top of the isolation groove through photolithography to form a mask of the SiO2 layer;

[0020] S4, removing the exposed SiO2 layer through reactive ion etching, and then removing the photoresist to form a mask of the gain waveguide 1 and the loss waveguide 2;

[0021] S5, etching the upper waveguide 5 through dry etching, and the etching depth is less than the thickness of the upper waveguide 5;

[0022] S6, removing the SiO2 layer on the surface through wet etching, and then growing a layer of SiO2 through plasma-enhanced chemical vapor deposition to form the insulating layer 4;

[0023] S7, forming an electrical injection window on the top of the gain waveguide 1 through photolithography, forming a Ti / Au layer on the surface through electron beam evaporation, and then thickening the Ti / Au layer through electroplating to form the upper electrode 3;

[0024] S8, thinning the back surface of the substrate 10, forming a Ge / Au / Ni / Au layer on the surface of the substrate 10, annealing to form the lower electrode 11, and cleaving to obtain the quantum cascade laser, wherein the lower electrode 11 also needs to be welded on a copper heat sink plated with indium on the surface.

[0025] According to the quasi-time-reversal-symmetry quantum cascade laser and the preparation method thereof provided in the application, the following beneficial effects can be achieved:

[0026] (1) The ridge width of the gain waveguide can be several times larger than that of a conventional single-transverse-mode QCL, so that a larger gain area is obtained, and high-power output is achieved.

[0027] (2) Through the coupling between the fundamental mode in the loss waveguide and the high-order mode in the gain waveguide, the high-order mode can be suppressed, so that single-transverse-mode output is achieved, and good beam quality is obtained.

[0028] (3) The time-reversal symmetry is a regulation of the imaginary part of the refractive index, and a complex geometric structure does not need to be designed to change the real part of the refractive index as in the traditional method, so that the manufacturing process is compatible with the process of the traditional straight-bar laser.

[0029] (4) Due to the large threshold difference of lasing gain between longitudinal modes, the mode in the time-reversal-symmetry-breaking phase is preferentially lased, and the remaining longitudinal modes are suppressed, so that single-longitudinal-mode output can be achieved. BRIEF DESCRIPTION OF DRAWINGS

[0030] The above and other objects, features and advantages of the present application will become more apparent from the following description of embodiments of the present application with reference to the accompanying drawings, in which:

[0031] Figure 1 A structure diagram of a cross section of a quasi-time-reversal symmetric quantum cascade laser according to an embodiment of the present application is schematically shown.

[0032] Figure 2 A three-dimensional structure diagram of a quasi-time-reversal symmetric quantum cascade laser according to an embodiment of the present application is schematically shown.

[0033] Figure 3 A schematic diagram of a quasi-time-reversal symmetric quantum cascade laser according to an embodiment of the present application is schematically shown.

[0034] Figure 4 A flow chart of a method of fabricating a quasi-time-reversal symmetric quantum cascade laser according to an embodiment of the present application is schematically shown. DETAILED DESCRIPTION

[0035] Hereinafter, embodiments of the present application will be described with reference to the accompanying drawings. It should be understood, however, that the description which follows is merely illustrative and is not intended to limit the scope of the present application. In the following detailed description of embodiments of the present application, numerous specific details are set forth in order to provide a thorough understanding of the present application. However, it will be apparent to one skilled in the art that one or more embodiments of the present application can be practiced without these specific details. In other instances, well-known structures and functions have not been described in detail in order to avoid obscuring aspects of the present application.

[0036] The terms used herein are merely used to describe specific embodiments and are not intended to limit the present application. The terms "include" and "have" and the like used herein indicate the presence of the features, steps, operations and / or components, but do not exclude the presence or addition of one or more other features, steps, operations or components.

[0037] All terms used herein, including technical and scientific terms, have the same meanings as those generally understood by those skilled in the art unless otherwise defined. It should be noted that the terms used herein should be interpreted as having meanings consistent with the context of the present description, and should not be interpreted in an idealized or overly formal way.

[0038] In view of the problems related to the foregoing background art, in implementing the inventive concept of the present application, the applicant has found that:

[0039] The parity-time (PT) symmetry theory in non-Hermite system of quantum physics is introduced into optical system. The gain and loss are regulated by designing the imaginary part of refractive index, which provides a new idea for the problem. The method does not need to introduce new process flow, but only needs to use the traditional process of bar laser to change the coupling strength between modes by designing the etching depth and ridge width, so that different modes are in parity-time symmetry phase and parity-time symmetry breaking phase, thereby realizing the regulation of laser modes. In addition, the gain spectrum of the laser is specific, and the gain obtained by different longitudinal modes is different, so the mode with larger gain will enter the parity-time symmetry breaking phase first, thereby increasing the difference of lasing gain threshold between longitudinal modes, and suppressing the lasing of other longitudinal modes to realize single longitudinal mode output.

[0040] Therefore, the application provides a quasi-parity-time-symmetry quantum cascade laser and a preparation method thereof, which can realize single longitudinal mode output of the laser and have good beam quality and high power.

[0041] Figure 1 A cross-sectional view of a quasi-parity-time-symmetry quantum cascade laser according to an embodiment of the application is schematically shown.

[0042] As shown in Figure 1 According to the embodiment, the quasi-parity-time-symmetry quantum cascade laser can include:

[0043] The upper waveguide 5; the gain waveguide 1 arranged on the upper surface of the upper waveguide 5; a plurality of loss waveguides 2 distributed on both sides of the gain waveguide 1 and arranged on the upper surface of the upper waveguide 5, wherein an isolation groove is engraved between any two adjacent waveguides in the gain waveguide 1 and the plurality of loss waveguides 2; the plurality of loss waveguides 2, the isolation groove and part of the surface of the gain waveguide 1 are covered with an insulating layer 4, and the surface of the gain waveguide 1 not covered with the insulating layer 4 and the surface of the insulating layer 4 are further covered with an upper electrode 3, and the gain waveguide 1 injects current through the upper electrode 3.

[0044] The quantum cascade laser has an upper limiting layer 6, a multi-period gain active region 7, a lower limiting layer 8, a lower waveguide 9, a substrate 10 and a lower electrode 11 stacked in sequence from the upper waveguide 5.

[0045] According to the embodiment of the application, the gain waveguide 1 and the loss waveguide 2 of the quasi-parity-time-symmetry quantum cascade laser are single-ridge waveguide structures.

[0046] In detail, the gain waveguide 1 and the loss waveguide 2 of the quasi-parity-time-symmetry quantum cascade laser are arranged in sequence and have an isolation groove engraved therebetween, the depth of the isolation groove is less than the thickness of the upper waveguide, the depth does not reach the active region, and other optical material layers are connected in penetration. For example, the width of the isolation groove can be 2 µm and 4.5 µm respectively, so as to achieve appropriate coupling strength.

[0047] The application has resonant coupling between the fundamental mode of the lossy waveguide 2 and the high-order mode of the gain waveguide 1, so that the high-order mode is in the parity-time symmetric state and is suppressed, while the fundamental mode of the gain waveguide 1 is not affected, and finally single-mode lasing is achieved.

[0048] According to the embodiment of the application, the ridge width of the gain waveguide 1 of the quasi-parity-time symmetric quantum cascade laser is wide, which can achieve a large gain area to obtain high output power, and the ridge width of the lossy waveguide 2 is narrow, so as to regulate the propagation constant of the fundamental mode in the lossy waveguide 2 to match the propagation constant of the high-order mode in the gain waveguide 1, and the ridge widths of each lossy waveguide 2 are different from each other and correspond to different high-order modes.

[0049] Specifically, the ridge width of the waveguide of the quasi-parity-time symmetric quantum cascade laser is the width of the single tube of the laser in the transverse direction, which depends on the center wavelength of the material and the cutoff width of the mode in the waveguide.

[0050] Specifically, the ridge width of the gain waveguide 1 is greater than the cutoff width of the first-order mode, and there are a fundamental mode and a high-order mode in the waveguide, and the maximum width depends on the number of the lossy waveguides 2 on both sides, the more the lossy waveguides 2, the more the high-order modes can be suppressed, and the ridge width can be larger.

[0051] Meanwhile, the ridge width of the lossy waveguide 2 must be less than the cutoff width of the first-order mode of the center wavelength and greater than the cutoff width of the fundamental mode, so as to ensure that only the fundamental mode propagates in the lossy waveguide 2.

[0052] According to the embodiment of the application, all the waveguides of the quasi-parity-time symmetric quantum cascade laser are deposited with an insulating SiO2 layer on both sides and the top, wherein the gain waveguide 2 has an electric injection window on the top, and the top of the rest of the waveguides is completely covered by the SiO2 layer.

[0053] According to the embodiment of the application, the material of the upper electrode 3 of the quasi-parity-time symmetric quantum cascade laser is Ti / Au; the insulating layer 4 is a SiO2 layer; the upper waveguide 5 is a Si-doped graded-doped InP layer; the upper confinement layer 6 and the lower confinement layer 8 are Si-doped matching InGaAs layers; the multi-period gain active region 7 is an X-period stacked InGaAs / InAlAs quantum cascade laser functional superlattice, 20≤X≤50; the lower waveguide 9 is a Si-doped InP layer; the substrate 10 is an N-type doped InP; and the material of the lower electrode 11 can be Ge / Au / Ni / Au.

[0054] Further, the upper electrode 3 of the quasi-parity-time symmetric quantum cascade laser is a separate electrode corresponding to the top of each gain waveguide 1, and the lower electrode 11 is a coplanar electrode prepared on the back of the substrate 10.

[0055] Figure 2 A three-dimensional structure diagram of the quasi-nearly time symmetric quantum cascade laser is shown schematically.

[0056] As shown in Figure 2 , the embodiment of the present application provides a three-dimensional structure diagram of the quasi-nearly time symmetric quantum cascade laser, which mainly includes a gain waveguide 1, M loss waveguides 2 distributed on both sides of the gain waveguide 1, and M≥1 in the structure transversely.

[0057] In the embodiment of the present application, the value of M is 2.

[0058] On the other hand, the structure includes an upper electrode 3, an insulating layer 4, an upper waveguide 5, an upper confinement layer 6, a multi-period gain active region 7, a lower confinement layer 8, a lower waveguide 9, a substrate 10, and a lower electrode 11 in the longitudinal direction.

[0059] It should be noted that the "longitudinal direction" in the embodiment of the present application is the direction perpendicular to the surface of the substrate, corresponding to the thickness or height of the device; on the contrary, the "transverse direction" in the embodiment of the present application refers to the direction parallel to the surface of the substrate (such as the upper surface of a silicon wafer).

[0060] Figure 3 A schematic diagram of the principle of the quasi-nearly time symmetric quantum cascade laser is shown.

[0061] As shown in Figure 3 , a loss waveguide 2 with a narrow ridge width is designed on both sides of the gain waveguide 1 with a wide gain area, there are a fundamental mode and a high-order mode in the wide gain waveguide 1, and only the fundamental mode exists in the narrow loss waveguide 2, the modes between the two waveguides will resonate and couple, and the complex propagation constant of the coupled supermode can be analyzed by the coupled mode method, and the complex propagation constant and the gain or loss of the material are obtained:

[0062] ,

[0063] wherein, is the real part of the complex propagation constant of the coupled mode, is the coupling constant in the waveguide unit, when , the imaginary parts of the two coupled modes are degenerate, the coupled mode is in the nearly time symmetric phase, the two modes have two different real frequency solutions, at this time the imaginary part of the coupled mode is zero, neither gain nor loss;

[0064] when The real part of the coupling mode is degenerate, and there are two solutions for the imaginary part. The system is in a parity-time symmetry breaking phase, and the imaginary part of the coupling mode with a positive value generates gain and concentrates in the gain waveguide, while the other part concentrates in the loss waveguide and does not lase.

[0065] Further, the resonant coupling between the fundamental mode of the loss waveguide 2 of the quasi-parity-time-symmetric quantum cascade laser and the high-order mode of the gain waveguide 1 causes the high-order mode to be in a parity-time symmetric state and thus to be suppressed, while the fundamental mode in the gain waveguide 1 is not affected, and finally single transverse mode lasing is achieved.

[0066] In the formula, the ridge width of the waveguide of the quasi-parity-time-symmetric quantum cascade laser is the width of the single tube of the laser in the transverse direction, which depends on the center wavelength of the material and the cutoff width of the mode in the waveguide.

[0067] In detail, the ridge width of the gain waveguide 1 is wide, which can achieve a large gain area to obtain high output power. The ridge width needs to be greater than the cutoff width of the first-order mode, and there are a fundamental mode and high-order modes in the waveguide. The maximum width depends on the number of loss waveguides 2 on both sides. The more the number of loss waveguides 2, the more high-order modes can be suppressed, and the ridge width can be made larger. In the embodiment of the present application, the center wavelength of the material is 8.2 µm, and the ridge width of the gain waveguide 1 is 20 µm.

[0068] In detail, the ridge width of the loss waveguide 2 is narrow, which is used to regulate the propagation constant of the fundamental mode in the loss waveguide 2 to match the propagation constant of the high-order mode in the gain waveguide 1. The ridge width needs to be less than the cutoff width of the first-order mode of the center wavelength and greater than the cutoff width of the fundamental mode, so as to ensure that only the fundamental mode propagates in the loss waveguide 2. The ridge width of each loss waveguide 2 is different, corresponding to different high-order modes. In the embodiment of the present application, the widths are 9 µm and 4.5 µm, respectively, and the corresponding fundamental modes correspond to TM1 and TM2 order modes in the gain waveguide 1.

[0069] Further, all the waveguides of the quasi-parity-time-symmetric quantum cascade laser are deposited with an insulating SiO2 layer on both sides and the top. The gain waveguide 2 has an electric injection window on the top, and the top of the rest of the waveguides is completely covered by the SiO2 layer.

[0070] According to the embodiment of the present application, the material of the upper electrode 3 of the quasi-parity-time-symmetric quantum cascade laser is Ti / Au; the insulating layer 4 is a SiO2 layer; the upper waveguide 5 is a Si-doped graded-doped InP layer; the upper confinement layer 6 and the lower confinement layer 8 are Si-doped matching InGaAs layers; the multi-period gain active region 7 is an X-period stacked InGaAs / InAlAs superlattice, 20≤X≤50; the lower waveguide 9 is a Si-doped InP layer; the substrate 10 is an N-type doped InP; and the material of the lower electrode 11 can be Ge / Au / Ni / Au.

[0071] The upper electrode 3 of the quasi-time-nearly symmetric quantum cascade laser is a single electrode corresponding to the top of each gain waveguide 1, and the lower electrode 11 is a coplanar electrode prepared on the back of the substrate 10. In summary, the quasi-time-nearly symmetric quantum cascade laser provided by the embodiments of the present application can obtain a larger gain area, realize high-power single-transverse-mode output, and obtain good beam quality. Based on the quasi-time-nearly symmetric quantum cascade laser disclosed in the above embodiments, the present application further provides a preparation method of a quasi-time-nearly symmetric quantum cascade laser, which will be described below in combination with Figure 4 The method will be described in detail.

[0072] Figure 4 A flowchart of the preparation method of the quasi-time-nearly symmetric quantum cascade laser according to the embodiments of the present application is schematically shown.

[0073] As Figure 4 shown, the preparation method of the quasi-time-nearly symmetric quantum cascade laser according to the embodiments of the present application is as follows:

[0074] First, the lower waveguide 9, the lower confinement layer 8, the multi-period gain active region 7, the upper confinement layer 6, and the upper waveguide 5 are sequentially epitaxially grown on the surface of the substrate 10 by a metal compound vapor deposition system.

[0075] The substrate 10 is n-doped InP with a doping concentration of 5x10 18 cm -3 , the lower waveguide layer 9 is n-doped InP with a doping concentration of 3x10 16 cm -3 , and a thickness of 3.5 µm; the lower confinement layer 8 is n-doped In 0.53 Ga 0.47 As with a doping concentration of 3x10 16 cm -3 , and a thickness of 200 nm; the multi-period gain active region 7 is an X-period stack of n-doped InGaAs / InAlAs superlattices, 20≤X≤50, with a doping concentration of 1.5x10 17 cm -3 , and a corresponding center emission wavelength of 8.2 µm; the upper confinement layer 6 is n-doped In 0.53 Ga 0.47 As with a doping concentration of 3x10 16 cm -3 , and a thickness of 200 nm; and the upper waveguide 5 is n-doped InP with a thickness of 4 µm, wherein the doping concentration in the 3 µm close to the upper confinement layer 6 is 3x10 16 cm -3, the 500 nm near the top is a high-doped layer with a doping concentration of 5 x 1018cm-3 18 cm -3 , the 500 nm in the middle is a transition-doped layer with a doping concentration linearly changing from 3 x 1018cm-3 16 cm -3 to 5 x 1018cm-3 18 cm -3 .

[0076] Secondly, photoresist is spin-coated on the surface of the epitaxial wafer, and then a mask for the double-groove pattern in the silicon oxide process is obtained through photolithography. The upper waveguide 5, the upper confinement layer 6, and the multi-period gain active region 7 are etched by using an InP etching solution, so as to form the double groove in the silicon oxide process. The etching depth needs to exceed the active region 7, and the depth needs to be relatively deep to form a relatively straight sidewall.

[0077] Further, the photoresist is removed, and a layer of SiO2 is grown on the surface through plasma-enhanced chemical vapor deposition. The thickness of the layer of SiO2 needs to consider the selectivity ratio when dry etching the body and cannot exceed the critical thickness. In the embodiment of the present application, the thickness is about 1 µm. Then, photoresist is spin-coated on the surface, and the photoresist on the top of the isolation groove is removed through photolithography.

[0078] Further, the exposed SiO2 layer is removed through reactive ion etching, and then the photoresist is removed, to form a mask layer when dry etching the body.

[0079] Further, the upper waveguide 5 is etched through dry etching, and the body at the isolation groove is etched to form the gain waveguide 1 and the loss waveguide 2. The etching depth should be less than the thickness of the upper waveguide 5. Since the coupling strength between the modes is also related to the etching depth, the specific etching depth needs to be simulated and calculated. The target depth in the embodiment of the present application is about 2.8 µm.

[0080] Further, the SiO2 layer on the surface is completely removed by using wet etching, and then a layer of SiO2 is grown to form the insulating layer 4 through plasma-enhanced chemical vapor deposition. The growth thickness is 450 nm.

[0081] Further, photoresist is spin-coated on the surface, and the photoresist on the top of the electrical injection window of the gain waveguide 1 is removed through photolithography. Then, the exposed SiO2 is etched through wet etching, and then all the photoresist is removed. A Ti / Au layer is formed on the surface through electron beam evaporation, and then the Au layer is thickened through electroplating to form the upper electrode 3. The thickness of the electroplated Au layer is about 1 µm.

[0082] Further, the back surface of the substrate 10 is thinned and polished, and the total thickness of the chip is about 150 µm. Then, a Ge / Au / Ni / Au layer is formed on the back surface of the substrate by electron beam evaporation, and annealing is performed to form the lower electrode 11. Finally, the device is cleaved to obtain the final device.

[0083] In the quasi-time-reversal symmetric quantum cascade laser, the lower electrode 11 is also welded on the copper heat sink plated with indium on the surface.

[0084] In summary, the preparation method of the quasi-time-reversal symmetric quantum cascade laser provided by the embodiments of the present application is highly compatible with the existing quantum cascade laser (QCL) process, reduces the technical iteration threshold, and reduces the energy loss of invalid modes through mode suppression. The quasi-time-reversal symmetric quantum cascade laser has higher fault tolerance for the preparation process, can improve the yield and reduce the production cost.

[0085] On the other hand, the structural parameters (such as ridge width and coupling distance) of the quasi-time-reversal symmetric quantum cascade laser can be flexibly adjusted according to the target wavelength and application scenarios to adapt to different scene requirements.

[0086] The embodiments of the present application have been described above. However, these embodiments are only for illustrative purposes, and are not intended to limit the scope of the present application. Although each embodiment is described above separately, this does not mean that the measures in each embodiment cannot be used advantageously in combination. Those skilled in the art can make various substitutions and modifications without departing from the scope of the present application, and these substitutions and modifications should all fall within the scope of the present application.

Claims

1. A quasi-parity-time symmetric quantum cascade laser, characterized in that: include: Upper waveguide (5); A gain waveguide (1) is arranged on the upper surface of the upper waveguide (5); A plurality of loss waveguides (2) are distributed on both sides of the gain waveguide (1) and are arranged on the upper surface of the upper waveguide (5), wherein an isolation groove is engraved between the gain waveguide (1) and any two adjacent waveguides in the plurality of loss waveguides (2); The surfaces of the plurality of loss waveguides (2), the isolation grooves and part of the gain waveguide (1) are covered with an insulating layer (4); the surface of the gain waveguide (1) not covered with the insulating layer (4) and the surface of the insulating layer (4) are also covered with an upper electrode (3); and the gain waveguide (1) is injected with current through the upper electrode (3).

2. The quasi-parity-time-symmetric quantum cascade laser according to claim 1, characterized in that: The quantum cascade laser comprises an upper confinement layer (6), a multi-cycle gain active region (7), a lower confinement layer (8), a lower waveguide (9), a substrate (10), and a lower electrode (11) stacked in sequence from an upper waveguide (5) downward.

3. The quasi-parity-time-symmetric quantum cascade laser according to claim 1, characterized in that: The depth of the isolation groove is less than the thickness of the upper waveguide (5); Other optical material layers are connected through the layers, and the widths of the plurality of isolation grooves are different.

4. The quasi-parity-time symmetric quantum cascade laser according to claim 1, characterized in that There is resonant coupling between the fundamental modes of the multiple loss waveguides (2) and the high-order modes of the gain waveguide (1), so that the high-order modes of the gain waveguide (1) are in a quasi-parity-time symmetric state, while the fundamental mode of the gain waveguide (1) is not affected, and single-mode lasing is ultimately achieved.

5. The quasi-parity-time-symmetric quantum cascade laser according to claim 1, characterized in that: The ridge width of the gain waveguide (1) is greater than the ridge width of each of the loss waveguides (2); The ridge widths of the multiple lossy waveguides (2) are different from each other.

6. The quasi-parity-time-symmetric quantum cascade laser according to claim 5, characterized in that: The ridge width of the gain waveguide (1) depends on the central wavelength of the material and the cutoff width of the mode in the waveguide. The longer the wavelength and the more high-order modes there are, the larger the corresponding ridge width.

7. The quasi-parity-time-symmetric quantum cascade laser according to claim 1, characterized in that: There are multiple lossy waveguides (2), corresponding to different high-order modes.

8. The quasi-parity-time symmetric quantum cascade laser according to claim 1, characterized in that: The gain waveguide (1) and each loss waveguide (2) are single-ridge waveguide structures.

9. The quasi-parity-time symmetric quantum cascade laser according to claim 1 or 2, characterized in that: The material of the upper electrode (3) is Ti / Au; The insulating layer (4) is a SiO2 layer; The upper waveguide (5) is a Si-doped gradient doped InP layer; The upper confinement layer (6) and the lower confinement layer (8) are Si-doped matching InGaAs layers; The multi-period gain active region (7) is an InGaAs / InAlAs quantum cascade laser functional superlattice stacked with X periods, 20≤X≤50; The lower waveguide (9) is a Si-doped InP layer; The substrate (10) is N-type doped InP; The material of the lower electrode (11) is Ge / Au / Ni / Au.

10. A method for preparing a quasi-parity-time symmetric quantum cascade laser, characterized in that: The following steps are involved: S1, epitaxially growing a lower waveguide (9), a lower confinement layer (8), a multi-period gain active region (7), an upper confinement layer (6), and an upper waveguide (5) on the surface of a substrate (10); S2, spin-coating photoresist on the surface of the upper waveguide (10), obtaining a mask of a double-groove pattern in a silicon oxide process by photolithography, and etching the upper waveguide (5), the upper confinement layer (6), and the multi-period gain active region (7) according to the pattern mask, with the etching depth exceeding the active region (7); S3, removing the photoresist, growing a layer of SiO2 on the surface of the upper waveguide (5), and spin-coating the photoresist again, and then removing the photoresist on the top of the isolation groove by photolithography to form a mask of the SiO2 layer; S4, removing the exposed SiO2 layer by reactive ion etching, and then removing the photoresist to form masks for the gain waveguide (1) and the loss waveguide (2); S5, etching the upper waveguide (5) by dry etching, wherein the etching depth is less than the thickness of the upper waveguide (5); S6, using wet etching to completely remove the surface SiO2 layer, and then growing a layer of SiO2 by plasma enhanced chemical vapor deposition to form an insulating layer (4); S7, forming an electric injection window on the top of the gain waveguide (1) by photolithography, forming a Ti / Au layer on the surface by electron beam evaporation, and then thickening the Ti / Au layer by electroplating to form an upper electrode (3); S8, thinning the back side of the substrate (10), forming a Ge / Au / Ni / Au layer on the surface of the substrate (10), annealing to form a lower electrode (11), and cleaving to obtain a quantum cascade laser, wherein the lower electrode (11) also needs to be welded to a copper heat sink with an indium-plated surface.

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