Phase-locked quantum cascade laser array based on evanescent wave coupling and preparation method

Abstract

The invention provides a phase-locked quantum cascade laser array based on evanescent wave coupling and a preparation method, and relates to the technical field of infrared semiconductor photoelectric devices. The quantum cascade laser array comprises a back metal electrode, a substrate, a buffer layer, a coupling layer, a lower waveguide layer, a lower limiting layer, an active region layer, an upper limiting layer, an upper waveguide layer and an upper cover layer which are sequentially stacked from bottom to top, the surface of the upper cover layer is provided with a plurality of pairs of etching grooves extending downwards into the lower waveguide layer, and the etching grooves are filled with an iron-doped indium phosphide material. An electrode injection window is formed in the surface of the upper cover layer between each pair of etching grooves, and the area, except the electrode injection window, on the surface of the upper cover layer is covered with an insulating layer; the upper surface of the insulating layer and the interior of the electrode injection window are both covered with front metal electrodes.

Description

Technical Field

[0001] This application relates to the field of infrared semiconductor optoelectronic device technology, and in particular to a phase-locked quantum cascade laser array based on evanescent wave coupling and its fabrication method. Background Technology

[0002] Quantum cascade lasers (QCLs) are monopolar devices based on inter-subband electronic transitions, with emission wavelengths covering the mid-far-infrared to terahertz range. Due to their ability to precisely control the emission wavelength through bandgap design, and their miniaturization, high power, and tunable wavelength, QCLs have shown broad application prospects in fields such as atmospheric pollution monitoring, trace gas detection, space optical communication, and medical diagnostics.

[0003] While progress has been made in active layer bandgap design and waveguide optimization, further increases in the power of single-tube QCLs are limited by heat dissipation and mode control. Simply increasing the ridge width to increase the active layer area often leads to increased thermal resistance and excitation of higher-order modes, resulting in decreased beam quality or even device failure. Therefore, single-tube structures are unlikely to overcome existing power bottlenecks. To achieve higher power output, phase-locked array (PLA) technology has become an effective approach. This method integrates multiple narrow-ridge QCL units on a chip and achieves phase locking, enabling coherent superposition of the output light fields, thereby obtaining higher output power and improving far-field beam quality. Currently, existing PLA arrays have made some progress in achieving high power and narrow far-field output, but they generally suffer from the following shortcomings: excessively small array spacing leads to heat dissipation difficulties, limiting continuous wave operation; competition between in-phase and out-of-phase modes affects phase-locking stability, making it difficult to guarantee far-field beam quality; complex structures or excessively high process precision requirements reduce the feasibility of large-scale fabrication.

[0004] Therefore, how to achieve stable optical field phase locking between array units while maintaining good heat dissipation, and further improve the output power and far-field beam quality of the device, has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] In view of this, this application proposes a phase-locked quantum cascade laser array based on evanescent wave coupling and its fabrication method. By setting an InGaAs coupling layer below the active region layer, the phase locking between array units is achieved by utilizing the evanescent light field partially leaking into the layer. This not only effectively reduces the adverse effect of array spacing on heat dissipation, but also ensures that the array obtains high power output and high-quality far-field beam under continuous wave conditions.

[0006] The first aspect of this application provides a phase-locked quantum cascade laser array based on evanescent wave coupling, comprising: a back metal electrode 14, a substrate 1, a buffer layer 2, a coupling layer 3, a lower waveguide layer 4, a lower confinement layer 5, an active region layer 6, an upper confinement layer 7, an upper waveguide layer 8, and an upper capping layer 9 stacked sequentially from bottom to top; the upper capping layer 9 has multiple pairs of etched trenches 11 extending downward into the lower waveguide layer 4, and the etched trenches 11 are filled with iron-doped indium phosphide material; an electrode injection window is formed between each pair of etched trenches 11 on the surface of the upper capping layer 9, and the area on the surface of the upper capping layer 9 other than the electrode injection window is covered with an insulating layer 12; the upper surface of the insulating layer 12 and the area inside the electrode injection window are both covered with a front metal electrode 13.

[0007] Furthermore, both substrate 1 and buffer layer 2 are made of n-type doped InP.

[0008] Furthermore, the coupling layer 3, the upper confinement layer 7, and the lower confinement layer 5 are all made of n-type doped InGaAs.

[0009] Furthermore, the materials of the lower waveguide layer 4, the upper waveguide layer 8, and the upper cover layer 9 are all n-type doped InP.

[0010] Furthermore, the active region layer 6 consists of multiple periodic InGaAs / InAlAs quantum well / barrier pairs.

[0011] Furthermore, the front metal electrode 13 is made of Ti / Au electrode material; the back metal electrode 14 is made of Au / Ge / Ni / Au electrode material.

[0012] Furthermore, the laser array has a lasing band in the mid-to-far infrared band of 3μm to 14μm.

[0013] The second aspect of this application provides a method for fabricating a phase-locked quantum cascade laser array based on evanescent wave coupling, comprising: step S1, growing a buffer layer 2, a coupling layer 3, a lower waveguide layer 4, a lower confinement layer 5, an active region layer 6, an upper confinement layer 7, an upper waveguide layer 8, and an upper capping layer 9 sequentially from bottom to top on a substrate 1; step S2, using photolithography and etching processes, etching from the upper capping layer 9 to the interior of the lower waveguide layer 4 to form multiple pairs of etching trenches 11 perpendicular to the upper capping layer 9, and forming a ridge structure between each pair of etching trenches 11; step S3, utilizing metal-organic chemical vapor deposition... In step S4, an insulating layer 12 is deposited on the upper surface of the capping layer 9 and the upper surface of the etched trench 11. The insulating layer 12 at the top of the ridge structure is removed by photolithography and etching processes to form an electrode injection window. In step S5, a front metal electrode 13 is deposited on the upper surface of the insulating layer 12 and at the electrode injection window by electron beam evaporation, and the surface of the front metal electrode 13 is gold-plated to form a low-resistance ohmic contact. In step S6, the substrate 1 is thinned and polished, and a back metal electrode 14 is formed by evaporation under the substrate 1.

[0014] Furthermore, the substrate 1 is grown sequentially from bottom to top by metal-organic chemical vapor deposition or molecular beam epitaxy.

[0015] Furthermore, for the laser array made in step S6, the front metal electrode (13) is sintered with the upper surface of the diamond heat sink using indium solder, and the lower surface of the diamond heat sink is bonded to the copper heat sink using a sintering process.

[0016] By adopting the above technical solution, this application proposes a phase-locked quantum cascade laser array based on evanescent wave coupling and its fabrication method, which has the following beneficial effects:

[0017] (1) This application introduces an InGaAs coupling layer below the active region layer and uses the evanescent optical field leaking from the active region layer to this layer as a coherent coupling channel to effectively achieve phase synchronization between array units. By obtaining a stable in-phase working state in this way, the coherence and directionality of the far-field beam are significantly improved, the beam quality is greatly improved, and the requirements of high-precision applications are met.

[0018] (2) The output power of this application is significantly improved. By integrating multiple array units on the same chip, the output power can be flexibly multiplied and amplified, breaking through the bottleneck of single-transistor QCL power limitation. This structure avoids the high-order mode competition problem caused by ridge width expansion and can achieve power expansion while maintaining single-mode output, which is particularly suitable for high-power application scenarios.

[0019] (3) The process flow of this application is simple and does not require complex large-size structures such as gratings, MMIs or Talbot cavities. In addition, the structure has high repeatability, is suitable for large-scale preparation and application, and has significant engineering application value.

[0020] (4) The laser array units of this application maintain a relatively wide array spacing, which effectively reduces the heat accumulation problem during array operation and avoids performance degradation and device failure caused by overheating. As a result, this invention can support stable operation of the device under continuous wave conditions, significantly improving power carrying capacity and service life. Attached Figure Description

[0021] The embodiments of this application are described below with reference to the accompanying drawings, in which:

[0022] Figure 1 The diagram schematically illustrates the structure of a phase-locked quantum cascade laser array based on evanescent wave coupling according to an embodiment of this application;

[0023] Figure 2 A flowchart illustrating a method for fabricating a phase-locked quantum cascade laser array based on evanescent wave coupling according to an embodiment of this application is shown.

[0024] Figure 3A A simulation diagram of the in-phase mode according to an embodiment of this application is shown schematically;

[0025] Figure 3B A schematic diagram illustrating a simulation of the electric field distribution according to an embodiment of this application is shown.

[0026] Figure 3C A schematic diagram illustrating a near-field light intensity distribution according to an embodiment of this application is shown.

[0027] Figure 3D A simulation diagram illustrating the light intensity distribution in an InGaAs intercalation layer according to an embodiment of this application is shown schematically.

[0028] Figure 3E A simulation diagram illustrating the vertical light intensity distribution according to an embodiment of this application is shown schematically.

[0029] Figure 4 The diagram schematically illustrates the flip-chip bonding structure of a method for fabricating a phase-locked quantum cascade laser array based on evanescent wave coupling according to an embodiment of this application.

[0030] Figure 5A The diagram schematically illustrates a thermal field simulation of a phase-locked quantum cascade laser array based on evanescent wave coupling according to an embodiment of this application.

[0031] Figure 5BThe diagram schematically illustrates the lateral temperature simulation of the active region of a phase-locked quantum cascade laser array based on evanescent wave coupling according to an embodiment of this application.

[0032] Figure 6 The diagram schematically illustrates the far-field light intensity distribution of a phase-locked quantum cascade laser array based on evanescent wave coupling according to an embodiment of this application.

[0033] Figure 7 The diagram schematically illustrates the near-field spot of a phase-locked quantum cascade laser array based on evanescent wave coupling according to an embodiment of this application.

[0034] Explanation of reference numerals in the attached figures:

[0035] 1-Substrate; 2-Buffer layer; 3-Coupled layer; 4-Lower waveguide layer; 5-Lower confinement layer; 6-Active region layer; 7-Upper confinement layer; 8-Upper waveguide layer; 9-Upper capping layer; 11-Etched trench; 12-Insulating layer; 13-Front metal electrode; 14-Back metal electrode; 15-Copper secondary heat sink; 16-Diamond heat sink. Detailed Implementation

[0036] The embodiments of this application will now be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of this application. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of this application for ease of explanation. However, it will be apparent that one or more embodiments may be implemented without these specific details. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concepts of this application.

[0037] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of this application. The terms “comprising,” “including,” etc., as used herein indicate the presence of features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0038] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein are to be interpreted in a manner consistent with the context of this specification, and not in an idealized or overly rigid way.

[0039] Secondly, this application provides a detailed description in conjunction with schematic diagrams. When detailing the embodiments of this application, for ease of explanation, the cross-sectional views illustrating the device structure may be partially enlarged, not adhering to the usual scale. Furthermore, the schematic diagrams are merely examples and should not limit the scope of protection of this application. In addition, actual fabrication should include three-dimensional spatial dimensions of length, width, and depth.

[0040] Figure 1 A schematic diagram of a phase-locked quantum cascade laser array based on evanescent wave coupling according to an embodiment of this application is shown.

[0041] like Figure 1 As shown, this application provides a phase-locked quantum cascade laser array based on evanescent wave coupling, comprising: a back metal electrode 14, a substrate 1, a buffer layer 2, a coupling layer 3, a lower waveguide layer 4, a lower confinement layer 5, an active region layer 6, an upper confinement layer 7, an upper waveguide layer 8, and an upper capping layer 9 stacked sequentially from bottom to top; the upper capping layer 9 has multiple pairs of etched trenches 11 extending downward into the lower waveguide layer 4, and the etched trenches 11 are filled with iron-doped indium phosphide material; an electrode injection window is formed between each pair of etched trenches 11 on the surface of the upper capping layer 9, and the area on the surface of the upper capping layer 9 other than the electrode injection window is covered with an insulating layer 12; the upper surface of the insulating layer 12 and the area inside the electrode injection window are covered with a front metal electrode 13.

[0042] In this embodiment, a ridge structure is formed between each pair of etched trenches 11, and the ridge structure is a single array unit. The coupling layer 3 provides an evanescent wave coupling channel between the array units. Part of the optical field generated by the active region layer 6 leaks to the coupling layer 3. Adjacent array units achieve energy exchange and phase synchronization through the evanescent optical field, avoiding mode competition and ensuring stable in-phase phase-locked loop.

[0043] In this embodiment, the iron-doped indium phosphide material within the etched trench 11 enhances lateral heat dissipation. Combined with the flip-chip heat sink design, this effectively reduces the temperature of the active region layer 6, supporting continuous wave high-power output. Simultaneously, the depth design of the etched trench 11 (extending to the lower waveguide layer 4) avoids damage to the active region layer 6, ensuring laser emission efficiency.

[0044] Meanwhile, the electrode injection window ensures that current is precisely injected into the active region layer 6 only through the injection window, reducing current leakage and lowering additional power consumption; the insulating layer 12 also protects the device surface and avoids environmental factors from interfering with performance.

[0045] In this embodiment, both the substrate 1 and the buffer layer 2 are made of n-type doped InP.

[0046] Specifically, n-type doping gives InP high electronic conductivity, and the substrate 1 and the buffer layer 2 form a continuous high conductivity channel. Current can be transmitted vertically and with low loss from the back metal electrode 14 to the active region layer 6, avoiding the problem of excessive series resistance caused by the undoped substrate, reducing Joule heat generation, and relieving heat dissipation pressure.

[0047] In this embodiment, the coupling layer 3, the upper confinement layer 7, and the lower confinement layer 5 are all made of n-type doped InGaAs.

[0048] Specifically, n-type doping gives the InGaAs layer moderate conductivity, which ensures that the current can be efficiently transmitted to the active region layer 6 after being injected from the electrode, while avoiding the increase in free carrier absorption (FCA) loss due to excessive doping concentration. At the same time, the high refractive index of InGaAs concentrates the light field more in the vicinity of the coupling layer and the active region layer 6, reducing the leakage of the light field to the substrate or air.

[0049] In this embodiment, the materials of the lower waveguide layer 4, the upper waveguide layer 8, and the upper cover layer 9 are all n-type doped InP.

[0050] Specifically, n-type doping gives the InP layer high electronic conductivity. The lower waveguide layer 4, the upper waveguide layer 8, and the upper cover layer 9 form a continuous conductive channel. That is, after the current is injected from the front metal electrode 13, it is transmitted to the active region layer 6 through the upper cover layer 9 and the upper waveguide layer 8, and then to the back metal electrode 14 through the lower waveguide layer 4, the coupling layer 3, and the buffer layer 2. The resistance is low throughout the process, and the Joule heat generation is small, which alleviates the heat dissipation pressure.

[0051] In this embodiment, the active region layer 6 is composed of multiple periodic InGaAs / InAlAs quantum well / barrier pairs.

[0052] In this embodiment, the front metal electrode 13 is made of Ti / Au electrode; the back metal electrode 14 is made of Au / Ge / Ni / Au electrode.

[0053] In this embodiment, the lasing band of the laser array is the mid-far infrared band.

[0054] Based on the above-described phase-locked quantum cascade laser array based on evanescent wave coupling, this embodiment provides a method for fabricating a phase-locked quantum cascade laser array based on evanescent wave coupling.

[0055] Figure 2 A flowchart illustrating a method for fabricating a phase-locked quantum cascade laser array based on evanescent wave coupling according to an embodiment of this application is shown.

[0056] like Figure 2 As shown in the flowchart, the fabrication method of phase-locked quantum cascade laser array based on evanescent wave coupling provided in this application includes steps S1 to S6.

[0057] Step S1: Buffer layer 2, coupling layer 3, lower waveguide layer 4, lower confinement layer 5, active region layer 6, upper confinement layer 7, upper waveguide layer 8 and upper cover layer 9 are grown sequentially from bottom to top on substrate 1.

[0058] In this embodiment, an indium phosphide (InP) substrate that matches the lattice of the subsequent materials is typically selected for substrate 1 to ensure the quality of the epitaxial layer. Metal-organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE) techniques are used to deposit the epitaxial layer sequentially from bottom to top on substrate 1.

[0059] In step S2, photolithography and etching processes are used to etch from the upper cover layer 9 to the interior of the lower waveguide layer 4 to form multiple pairs of etching trenches 11 perpendicular to the upper cover layer 9, and a ridge structure is formed between each pair of etching trenches 11.

[0060] Specifically, photolithography and wet etching processes are used, with photoresist as a mask, to etch downwards from the upper cover layer 9 until the lower waveguide layer 4 is etched (without penetrating the lower waveguide layer). Finally, multiple pairs of etching trenches 11 perpendicular to the surface of the upper cover layer 9 are formed on the multilayer epitaxial structure, and the unetched area between each pair of etching trenches 11 forms a ridge structure, which is the core structure of a single laser unit (each ridge structure corresponds to a laser unit, and multiple sets of ridge structures constitute a laser array).

[0061] Step S3: Fill the etched trench 11 with iron-doped indium phosphide material using metal-organic chemical vapor deposition (MOCVD).

[0062] Specifically, using metal-organic chemical vapor deposition (MOCVD) technology, iron-doped indium phosphide (Fe:InP) material is filled into the etched trench 11 formed in step 2 until the trench is completely filled and the surface of the filling layer is flush with the surface of the capping layer 9.

[0063] Step S4: An insulating layer 12 is deposited on the upper surface of the cover layer 9 and the etched trench 11. The insulating layer 12 on the top of the ridge structure is removed by photolithography and etching processes to form an electrode injection window.

[0064] Specifically, plasma-enhanced chemical vapor deposition (PECVD) is used to uniformly deposit an insulating layer 12 (usually silicon dioxide) on the upper surface of the capping layer 9 and the upper surface of the etched trench 11 (i.e., the Fe:InP filling layer surface), with a thickness of several hundred nanometers.

[0065] Then, photoresist is coated on the surface of insulating layer 12, and the pattern of electrode injection window is defined by photolithography (the window position corresponds to the top area of ​​the ridge structure). Then, wet etching or dry etching is used to remove the insulating layer 12 in the top area of ​​the ridge structure, while retaining the insulating layer in the remaining areas, thus forming the electrode injection window, which is the contact area between the subsequent front electrode and the top cover layer.

[0066] Step S5: A front metal electrode 13 is deposited on the upper surface of the insulating layer 12 and at the electrode injection window by electron beam evaporation, and gold is plated on the surface of the front metal electrode 13 to form a low-resistance ohmic contact.

[0067] Specifically, using electron beam evaporation technology, a front metal electrode 13 is deposited on the upper surface of the insulating layer 12 formed in step S4 and at the electrode injection window (i.e., the exposed surface of the upper cover layer 9). The metal material is usually a multilayer metal structure.

[0068] Step S6: Thin and polish the substrate 1, and evaporate the back metal electrode 14 under the substrate 1.

[0069] Specifically, the back side of substrate 1 is mechanically thinned (e.g., polished) to reduce the substrate thickness from the initial hundreds of micrometers to tens of micrometers. Electron beam evaporation is then used to evaporate and fabricate the back metal electrode 14 onto the lower surface of the thinned and polished substrate 1.

[0070] The back metal electrode 14 serves as the negative electrode of the device (the front electrode is the positive electrode), forming a current loop with the front electrode. Current is injected from the front electrode, flows out from the back electrode after passing through the active region layer 6, and is an important component of the complete current path. At the same time, the back electrode is in direct contact with the heat sink and is also a key interface for heat transfer from the substrate to the heat sink.

[0071] In this embodiment, for the laser array made in step S6, the front metal electrode (13) is sintered with the upper surface of the diamond heat sink using indium solder, and the lower surface of the diamond heat sink is bonded to the copper heat sink using a sintering process.

[0072] Specifically, for the laser array made in step S6, the front metal electrode 13 is bonded to the upper surface of the diamond heat sink through an indium solder sintering process; then the lower surface of the diamond heat sink is bonded to the copper heat sink through a sintering process, forming a three-level thermal management structure of device-diamond heat sink-copper heat sink.

[0073] This application relates to a semiconductor laser array structure based on evanescent wave coupling, the core of which lies in achieving coherent phase-locking of the array units by introducing a specific coupling layer. To verify and optimize this design, we first established a physical model of the array structure based on COMSOL Multiphysics simulation software and conducted a series of simulation analyses.

[0074] Figure 3A A simulation diagram of the in-phase mode according to an embodiment of this application is shown schematically.

[0075] like Figure 3A As shown in the figure, this application provides a simulation result diagram of the transverse optical mode of a quantum cascade laser array. It can be observed that the optical field mode morphology of each unit is consistent and the phase is synchronized. The array units are in the same-direction mode state, with no obvious mode differences or disorder.

[0076] Simulation results show that the array structure designed in this invention can effectively excite and stabilize the in-phase supermode operating in the base transverse mode. This mode dominates the entire array, thus effectively suppressing phase-locked instability caused by mode competition. This provides a mode basis for subsequent overall phase-locked operation via evanescent wave coupling and also verifies the effectiveness of the structural design in mode control.

[0077] Figure 3B A schematic diagram illustrating the electric field distribution simulation according to an embodiment of this application is shown.

[0078] like Figure 3B As shown in the figure, this application provides a simulation diagram of the electric field line distribution between units of a quantum cascade laser array, clearly presenting the distribution of the electric field in the active region layer 6, the coupling layer, and between adjacent units. It can be clearly observed from the figure that the electric field generated by the active region layer 6 is not completely confined within the active region layer 6; part of the electric field leaks into the underlying InGaAs coupling layer in the form of evanescent waves. These leaked evanescent waves extend within the coupling layer and overlap with the evanescent waves leaked from adjacent units, forming cross-unit electric field coupling channels.

[0079] The coupling layer was confirmed to effectively receive and transmit evanescent light fields, providing a practical physical channel for phase synchronization between array units. Compared to traditional coupling methods, this evanescent wave-based coupling does not require reducing the unit spacing or setting up complex cavity structures, thus solving the problems of difficult heat dissipation and complex structure of traditional phase-locked arrays from a mechanistic perspective. This is the key simulation evidence for the core innovation of this invention.

[0080] Figure 3C A schematic diagram illustrating a near-field light intensity distribution according to an embodiment of this application is shown.

[0081] like Figure 3C As shown in the figure, this application embodiment provides a simulation diagram of the light intensity distribution in the near-field region (near the output end face of the active layer 6) of a quantum cascade laser array. The horizontal axis represents the lateral distance, and the vertical axis represents the relative light intensity. The figure shows multiple distinct light intensity peaks, and the peak positions correspond one-to-one with the positions of each laser unit in the array. The peak intensities are relatively uniform, with no obvious differences in strength.

[0082] The uniform peak distribution confirms that the working state of each unit in the array structure of the present invention is consistent, and there is effective optical field interaction between the units. This further provides near-field evidence for the effectiveness of the evanescent wave coupling mechanism, and also shows that the structural design can ensure that each unit works in a balanced manner, avoiding phase-locking failure or output power fluctuation caused by differences in unit performance.

[0083] Figure 3D A simulation diagram illustrating the light intensity distribution in an InGaAs intercalation layer according to an embodiment of this application is shown.

[0084] like Figure 3D As shown in the figure, this application provides a simulation diagram of the light intensity distribution in an InGaAs intercalation layer of a quantum cascade laser array. The horizontal axis represents the lateral distance, and the vertical axis represents the relative light intensity. It can be observed that the light intensity extends laterally within the coupling layer, covering not only the area directly below each laser unit but also forming a continuous light intensity distribution in the coupling layer region between adjacent units. There is no obvious interruption in light intensity, and the light intensity value does not drastically decrease between adjacent units, maintaining a certain intensity level.

[0085] This application Figure 3D This study confirms that the evanescent wave leaking from layer 6 in the active region exhibits excellent lateral propagation characteristics within the InGaAs coupling layer, effectively covering the coupling layer region between adjacent cells, and with sufficient light intensity to support energy exchange between cells. This result further verifies the feasibility of the evanescent wave coupling mechanism from the perspective of optical field transmission within the coupling layer, demonstrating that the selection of the coupling layer material (InGaAs) and the design of parameters such as thickness and doping are reasonable, providing sufficient coupling conditions for array phase-locked loops.

[0086] Figure 3E A simulation diagram illustrating the vertical light intensity distribution according to an embodiment of this application is shown.

[0087] like Figure 3E As shown in the figure, this application provides a simulation diagram of the vertical light intensity distribution of a quantum cascade laser array. This diagram is a simulation curve of the light intensity distribution along the vertical direction of the device (z-direction, i.e., from the substrate to the top capping layer). The horizontal axis represents the relative light intensity, and the vertical axis represents the vertical distance. The curve shows a clear region of concentrated light intensity, corresponding to the active layer 6. At the same time, there is an extension of light intensity below the active layer 6 (coupling layer region), that is, the light intensity is not completely confined to the active layer 6, but leaks towards the coupling layer, forming a detectable light intensity distribution.

[0088] The concentrated distribution of light intensity in the active region layer 6 in the figure indicates that the structural design of the lower waveguide layer, upper waveguide layer and confinement layer is effective, which can confine most of the light field in the active region layer 6, ensuring that the energy generated by electron transition is efficiently converted into laser energy and reducing light field loss. The light intensity extending into the coupling layer confirms the existence of evanescent waves, that is, the light field can break through the confinement of the active region layer 6 and enter the coupling layer to participate in the coupling between units.

[0089] Figure 4 The diagram schematically illustrates the flip-chip bonding structure of a method for fabricating a phase-locked quantum cascade laser array based on evanescent wave coupling according to an embodiment of this application.

[0090] like Figure 4As shown in the figure, this application provides a structural diagram of a quantum cascade laser array fabrication method with flip-chip bonding to a heat sink. The connection method and hierarchical relationship between the device and the heat sink are clearly illustrated. The figure includes the laser array (labeled with a dashed box), a copper secondary heat sink 15, and a diamond heat sink 16. The front electrode of the laser array faces downwards and is sintered to the upper surface of the diamond heat sink 16 via an indium solder layer; the lower surface of the diamond heat sink 16 is sintered to the upper surface of the copper secondary heat sink 15, forming a stepped heat dissipation structure. This constructs an efficient vertical heat dissipation path, which can quickly remove the heat generated by the active region layer 6, reduce thermal crosstalk, and provide heat dissipation assurance for stable operation of the device under high power and continuous wave conditions. This is a crucial packaging step for achieving high device performance.

[0091] Figure 5A The diagram schematically illustrates a thermal field simulation of a phase-locked quantum cascade laser array based on evanescent wave coupling according to an embodiment of this application.

[0092] like Figure 5A As shown in the figure, this application provides a thermal simulation diagram of a quantum cascade laser array. The temperature distribution of each region of the device is displayed in the form of a color gradient (e.g., from blue to red, corresponding to temperatures from low to high). It can be observed in the figure that the highest temperature region is concentrated near the active layer 6, with the highest temperature value marked as 361K (approximately 88°C). The temperature gradually decreases from the active layer 6 to the surrounding areas (e.g., the coupling layer, buffer layer, and heat sink direction). The temperature of the diamond heat sink and copper heat sink regions is significantly lower than that of the active layer 6, and the temperature distribution is uniform with no obvious local high-temperature accumulation points.

[0093] The highest temperature of active layer 6 is a key indicator for evaluating laser performance and reliability. Excessive temperature can lead to decreased gain, increased threshold current, reduced output power, and even device failure. In this figure, the highest temperature of active layer 6 at 361K is within the reasonable temperature range for continuous wave operation of mid-to-far-infrared quantum cascade lasers, indicating that the diamond-copper composite heat sink design effectively controls the temperature of active layer 6 and avoids overheating. Furthermore, the uniform overall thermal distribution, without any localized high-temperature dead zones, further confirms the effectiveness of the heat dissipation structure and provides thermal assurance for the long-term stable operation of the device.

[0094] Figure 5B The diagram schematically illustrates the lateral temperature simulation of the active region of a phase-locked quantum cascade laser array based on evanescent wave coupling according to an embodiment of this application.

[0095] like Figure 5BAs shown in the figure, this application provides a simulation diagram of the temperature distribution along the lateral direction (unit arrangement direction) of the active layer 6 of a quantum cascade laser array. The horizontal axis represents the lateral distance (corresponding to each active layer unit and the region between units), and the vertical axis represents the temperature value (unit K). The figure shows that the temperature values ​​of each active layer unit are relatively close, with no significant temperature differences, and the temperature transition between units is smooth, without any sudden local temperature rise due to thermal crosstalk. For example, the temperature of each unit in the figure fluctuates around 361K, with a small temperature gradient between units and uniform heat distribution.

[0096] The uniform lateral temperature distribution of the active layer 6 confirms that the present invention effectively suppresses thermal crosstalk between adjacent units through a wide-spacing array design (dividing the active layer 6 into equally spaced units) and a lateral heat dissipation structure using iron-doped indium phosphide (Fe:InP) material. Simultaneously, the suppression of thermal crosstalk further reduces the overall thermal load of the active layer 6. Combined with the longitudinal heat dissipation of the composite heat sink, this achieves highly efficient heat dissipation of the device, providing crucial thermal assurance for stable phase-locking of the array and improved output power.

[0097] Figure 6 The diagram schematically illustrates the far-field light intensity distribution of a phase-locked quantum cascade laser array based on evanescent wave coupling according to an embodiment of this application.

[0098] like Figure 6 As shown in the figure, this application provides a measured far-field light intensity distribution curve of a quantum cascade laser array under pulsed operation with a duty cycle of 2%. The horizontal axis represents the far-field angle, and the vertical axis represents the relative light intensity. The figure shows a typical interference fringe distribution, i.e., multiple alternating bright and dark light intensity peaks. The peak intensity varies regularly with the angle, and the spacing between adjacent peaks (interference peaks) is uniform. The figure also shows the comparison between the measured interference peak spacing and the theoretical calculated value (e.g., actual Δθ≈1.20°, theoretical Δθ≈1.26°), and the two are in high agreement.

[0099] According to coherent array theory, the angular spacing Δθ of the far-field interference peaks satisfies the formula Δθ≈sinθ. -1 (λ / d) (where λ is the peak wavelength of the laser and d is the center-to-center distance of the array units). In this invention, the measured peak wavelength of the laser is λ=7.7μm and the center-to-center distance of the units is d=350μm. Substituting these values ​​into the formula, the theoretical interference peak spacing Δθ≈1.26° is calculated, while the measured interference peak spacing is ≈1.20°. The deviation is within the allowable range of instrument measurement error and process tolerance.

[0100] The regular interference fringes in the figure closely match the measured-theoretical interference peak spacing, directly confirming that the laser array has successfully achieved phase locking and verifying the effectiveness of the phase-locked loop scheme based on evanescent wave coupling in this invention. Simultaneously, the concentrated peaks in the far-field intensity distribution, without obvious sidelobes or clutter, indicate good far-field beam quality, meeting the requirements of high-precision applications for beam directionality and coherence. This also proves that the device has not sacrificed beam quality while increasing output power.

[0101] Figure 7 The diagram schematically illustrates the near-field spot of a phase-locked quantum cascade laser array based on evanescent wave coupling according to an embodiment of this application.

[0102] like Figure 7 As shown in the figure, this application provides a measured image of the near-field light spot of a quantum cascade laser array. The actual distribution of the near-field light field is illustrated in the intuitive light spot morphology. Multiple independent and clear light spots can be observed in the figure, each corresponding to the output of a laser unit. The light spot morphology is regular (e.g., close to rectangular or circular, without obvious distortion), the size is uniform, and there is a slight light field superposition region between adjacent light spots, without obvious light spot defects or sudden drops in intensity.

[0103] The experimental results of the near-field light spot in this figure verify the reliability of the device fabrication process from an experimental perspective. This demonstrates that key processes such as photolithography, etching, and epitaxial growth can precisely control structural parameters, ensuring consistent performance across all units. Furthermore, the regular distribution and superposition of the light spots corroborate the simulation results, confirming the rationality of the array structure design and contributing to the far-field phase-locked loop effect (e.g., ...). Figure 6 This provides experimental support at the near-field level and demonstrates that the device can stably output high-quality near-field optical fields in actual operation, laying the foundation for subsequent optical field transmission and applications.

[0104] Those skilled in the art will understand that the features described in the various embodiments of this disclosure can be combined and / or combined in various ways, even if such combinations or combinations are not explicitly described in this disclosure. In particular, the features described in the various embodiments of this disclosure can be combined and / or combined in various ways without departing from the spirit and teachings of this disclosure. All such combinations and / or combinations fall within the scope of this disclosure.

[0105] The embodiments of this disclosure have been described above. However, these embodiments are for illustrative purposes only and are not intended to limit the scope of this disclosure. Although various embodiments have been described above, this does not mean that the measures in the various embodiments cannot be used advantageously in combination. Various substitutions and modifications can be made by those skilled in the art without departing from the scope of this disclosure, and all such substitutions and modifications should fall within the scope of this disclosure.

Claims

1. A phase-locked quantum cascade laser array based on evanescent wave coupling, characterized in that, include: The following layers are stacked sequentially from bottom to top: back metal electrode (14), substrate (1), buffer layer (2), coupling layer (3), lower waveguide layer (4), lower confinement layer (5), active region layer (6), upper confinement layer (7), upper waveguide layer (8), and upper cover layer (9). The surface of the upper cover layer (9) has multiple pairs of etched trenches (11) extending downward into the interior of the lower waveguide layer (4), and the interior of the etched trenches (11) is filled with iron-doped indium phosphide material. An electrode injection window is provided between each pair of the etched trenches (11) on the surface of the upper cover layer (9), and the area on the surface of the upper cover layer (9) other than the electrode injection window is covered with an insulating layer (12). The upper surface of the insulating layer (12) and the electrode injection window are both covered with a front metal electrode (13).

2. The phase-locked quantum cascade laser array based on evanescent wave coupling according to claim 1, characterized in that, The substrate (1) and the buffer layer (2) are both made of n-type doped InP.

3. The phase-locked quantum cascade laser array based on evanescent wave coupling according to claim 1, characterized in that, The coupling layer (3), upper confinement layer (7) and lower confinement layer (5) are all made of n-type doped InGaAs.

4. The phase-locked quantum cascade laser array based on evanescent wave coupling according to claim 1, characterized in that, The materials of the lower waveguide layer (4), upper waveguide layer (8) and upper cover layer (9) are all n-type doped InP.

5. The phase-locked quantum cascade laser array based on evanescent wave coupling according to claim 1, characterized in that, The active region layer (6) is composed of multiple periodic InGaAs / InAlAs quantum well / barrier pairs.

6. The phase-locked quantum cascade laser array based on evanescent wave coupling according to claim 1, characterized in that, The front metal electrode (13) is made of Ti / Au electrode material; The back metal electrode (14) is made of Au / Ge / Ni / Au electrode material.

7. The phase-locked quantum cascade laser array based on evanescent wave coupling according to any one of claims 1 to 6, characterized in that, The laser array emits light in the mid- to far-infrared band.

8. A method for fabricating a phase-locked quantum cascade laser array based on evanescent wave coupling, characterized in that, The method includes: Step S1: A buffer layer (2), a coupling layer (3), a lower waveguide layer (4), a lower confinement layer (5), an active region layer (6), an upper confinement layer (7), an upper waveguide layer (8), and an upper cover layer (9) are grown sequentially from bottom to top on the substrate (1). Step S2: Using photolithography and etching processes, etching is performed from the upper cover layer (9) to the interior of the lower waveguide layer (4) to form multiple pairs of etching trenches (11) perpendicular to the upper cover layer (9), and a ridge structure is formed between each pair of etching trenches (11); Step S3: Fill the etched trench (11) with iron-doped indium phosphide material using metal-organic chemical vapor deposition (MOCVD). Step S4: An insulating layer (12) is deposited on the upper surface of the cover layer (9) and the etched trench (11). The insulating layer (12) at the top of the ridge structure is removed by photolithography and etching processes to form an electrode injection window. Step S5: A front metal electrode (13) is deposited on the upper surface of the insulating layer (12) and at the electrode injection window by electron beam evaporation, and the surface of the front metal electrode (13) is gold-plated to form a low-resistance ohmic contact. Step S6: Thinning and polishing the substrate (1), and evaporating to form a back metal electrode (14) under the substrate (1).

9. The method according to claim 8, characterized in that, The method further includes: The substrate (1) is grown sequentially from bottom to top by metal-organic chemical vapor deposition or molecular beam epitaxy.

10. The method according to claim 8, characterized in that, The method further includes: For the laser array made in step S6, the front metal electrode (13) is sintered with the upper surface of the diamond heat sink using indium solder, and the lower surface of the diamond heat sink is bonded to the copper heat sink using a sintering process.

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