Apparatus for beam combining on a quantum cascade laser chip and method of making the same

Abstract

The application relates to an on-chip light beam synthesis device for a quantum cascade laser and a preparation method thereof. Based on an integrated process of a selective area epitaxy method, a QCL pumping area and a low-loss passive waveguide area are integrated on a chip to realize on-chip light beam synthesis and high-power output of the QCL. According to the scheme of the application, firstly, the reasonable distribution of laser energy is realized by preparing a multi-channel active area array, and the problem of low-power output caused by uneven heat dissipation distribution of the laser is improved; secondly, a distributed feedback grating structure is prepared on the active area array to realize mode selection and single-mode light transmission; thirdly, when the multi-channel QCL active array with the grating and the low-loss passive light beam synthesis waveguide are integrated on the chip through butt coupling, the passive light beam synthesis avoids the problem of uneven heat dissipation caused by carrier absorption, realizes on-chip light beam synthesis and single-aperture high-power output of the QCL, and solves the problem of multi-peak interference of the light beam distribution caused by the array multi-aperture output.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of semiconductor lasers, and in particular to an on-chip beam combining device for quantum cascade lasers and a preparation method thereof. BACKGROUND

[0002] With the continuous development of integrated circuits towards photonic chips, photonic integrated chips have shown great application value in many research fields such as optical computing module integration, optical sensing and quantum communication. The development of photonic on-chip integrated devices has become a research direction with great practical significance in the development of frontier technology. Direct coupling of high-performance semiconductor lasers and low-loss passive waveguides is a crucial step to realize photonic integrated chips. Although near-infrared photonic integrated chips are already easily available, it still needs further efforts and exploration to achieve a similar level in the mid-infrared band. At present, quantum cascade lasers (QCL) are the only semiconductor coherent sources covering the entire mid-infrared spectrum in continuous wave (CW) operation at room temperature. After more than 20 years of continuous development, the pulse power of QCL can reach 200W, and the room temperature continuous power can reach 8.2W. Therefore, integrating QCL light sources with low-loss passive waveguides is a promising means to realize large-scale application of photonic integrated chips.

[0003] However, the inventors have found that there are mainly several problems in the current implementation of continuous wave high-performance laser lasing for on-chip integrated QCL. First, the power of a single-core QCL has approached the power bearing limit of the material itself, and the multi-peak interference beam distribution of the current array multi-aperture output means for improving power has affected the application range of such devices; second, the means of laser beam combining needs to be further optimized, on the one hand, the current external microlens light beam combining means has a quite complex design and preparation process; on the other hand, when light beam combining is performed in the QCL active region, laser light enters a single-channel output waveguide from an array with low light power density to a high light power density, which will excite more free carriers and increase the optical loss of the waveband, thereby worsening the heat dissipation problem of the laser and hindering the further improvement of the power of the laser. SUMMARY

[0004] Based on this, the present application provides an on-chip beam combining scheme for a high-power quantum cascade laser based on a selective area epitaxy technology, which integrates the QCL pumping region and the low-loss passive waveguide region on-chip based on the integration process of the selective area epitaxy method, to realize on-chip beam combining and single-aperture high-power output of the QCL.

[0005] According to one aspect of the present application, an on-chip beam combining device for quantum cascade lasers is provided, characterized in that it comprises:

[0006] a substrate;

[0007] a lower waveguide layer, located on the front side of the substrate, having a first part and a second part, the first part being located in the active region, the second part being located in the passive region;

[0008] an active layer, located on the first part of the lower waveguide layer, for generating light and amplifying the light;

[0009] a grating, located on the active layer, for realizing unidirectional transmission of light;

[0010] a passive material, located on the second part of the lower waveguide layer, forming an MMI type passive region and a light mode single-aperture output end, one end of the MMI type passive region being connected with the active layer, the other end being connected with the light mode single-aperture output end, the MMI type passive region being used for synthesizing light from the active region, and the light mode single-aperture output end being used for outputting the synthesized light beam;

[0011] an upper waveguide layer, having a first part and a second part, the first part of the upper waveguide layer being located in the active region and covering the active layer and the grating, the first part of the upper waveguide layer and the first part of the lower waveguide layer being used for guiding and confining the transmission of light, the second part of the upper waveguide layer covering the passive material, and an electrically isolating groove being formed on the upper waveguide layer for electrically isolating the active region and the passive region to prevent the diffusion of electric charges applied to the active region to the passive region.

[0012] According to another aspect of the present application, a preparation method of an on-chip light beam synthesis device for a quantum cascade laser is provided, characterized in that, comprising:

[0013] epitaxially generating an epitaxial wafer on a substrate, the epitaxial wafer comprising a lower waveguide layer, an active layer and an upper waveguide layer, the lower waveguide layer, the active layer and the upper waveguide layer each comprising a first part and a second part, the first part of the lower waveguide layer, the first part of the active layer and the first part of the upper waveguide layer being located in an active region, the second part of the lower waveguide layer and the second part of the upper waveguide layer being located in a passive region;

[0014] etching the first part of the upper waveguide layer to form a grating on the first part of the active layer;

[0015] growing a mask material layer on the second part of the upper waveguide layer, and forming a photoresist layer with an MMI type and a light mode single-aperture output end type by using photolithography;

[0016] etching the second part of the upper waveguide layer and the second part of the active layer until the lower waveguide layer;

[0017] forming an MMI type passive region and an optical mode single-aperture output end type region on the second part of the lower waveguide layer, and filling passive material in the MMI type passive region and the optical mode single-aperture output end type region, wherein the MMI type passive region is in butt-coupling with the first part of the active layer after filling;

[0018] re-epitaxially growing an upper waveguide layer;

[0019] lithographically forming a splitting groove of the beam combining device;

[0020] preparing an electrical isolation groove on the upper waveguide layer, the electrical isolation groove being used for electrically isolating the active region and the passive region, and preventing the diffusion of the electric charge applied to the active region to the passive region.

[0021] According to the on-chip beam combining device for quantum cascade laser and the preparation method thereof provided in the present application, firstly, the reasonable distribution of laser energy is achieved by preparing a multi-channel active region array, and the problem of low power output caused by uneven heat dissipation of the laser is improved; secondly, the mode selection is achieved by preparing a distributed feedback grating structure on the active region array, and single-mode optical transmission is realized; the passive optical beam combining single-aperture output waveguide prepared in the passive region has low light and heat loss; thirdly, when the multi-channel QCL active array with the grating and the low-loss passive optical beam combining waveguide are butt-coupled to realize single-aperture output on-chip integration, compared with the active optical beam combining design with serious heat dissipation problems, the passive optical beam combining avoids the problem of uneven heat dissipation caused by carrier absorption, thereby realizing the on-chip beam combining and single-aperture high-power output of the QCL, and solving the problem of multi-peak interference caused by the multi-aperture output of the array, and avoiding the limitation on the application range of the device; in addition, the low-loss passive waveguide is prepared by using the selective epitaxy technology, and the beam combining and transmission are performed in the passive waveguide region, thereby avoiding the use of the external microlens with complicated packaging process. Finally, the preparation method of the on-chip beam combining device for quantum cascade laser can be realized based on the existing preparation process, and is easy for the technicians to operate. The on-chip beam combining and single-aperture high-power output strategy of the QCL provided in the present application will greatly improve the performance of the laser and further promote the development of the fields of long-distance communication, infrared countermeasure, etc. BRIEF DESCRIPTION OF DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art based on these drawings, without exceeding the scope of the present application.

[0023] Figure 1is a sectional structure diagram of an on-chip beam combining device for a quantum cascade laser according to an embodiment of the present application.

[0024] Figure 2 is a top view structure diagram of an on-chip beam combining device for a quantum cascade laser according to an embodiment of the present application.

[0025] Figure 3 is a flow chart of a preparation method of an on-chip beam combining device for a quantum cascade laser according to an embodiment of the present application.

[0026] Figure 4 is a flow chart of a preparation method of an on-chip beam combining device for a quantum cascade laser according to another embodiment of the present application.

[0027] Figure 5 is a flow chart of a preparation method of an on-chip beam combining device for a quantum cascade laser according to still another embodiment of the present application.

[0028] Figure 6 is a flow chart of a preparation method of an on-chip beam combining device for a quantum cascade laser according to an embodiment of the present application.

[0029] Figure 7A 、 Figure 7B and Figure 7C are simulation result diagrams of beam combining area light coupling efficiency of a single-aperture output device of passive two-in-one, four-in-one and eight-in-one performed by an on-chip beam combining device for a quantum cascade laser according to an embodiment of the present application.

[0030] Figure 8 is a wafer bonding epitaxy SEM (Scanning electron microscope) diagram of an on-chip beam combining device for a quantum cascade laser according to an embodiment of the present application.

[0031] Figure 9A and Figure 9B are thermal simulation simulation diagrams of a high-power QCL on-chip light beam combining device.

[0032] Figure 10 is a room temperature pulse working current-light power, voltage curve diagram of a two-in-one, four-in-one and single-die (array part length is 4mm) of a high-power QCL on-chip light beam combining device.

[0033] Explanation of reference signs:

[0034] 1-Antireflective coating; 2-Active region; 3-Passive region; 4-Antireflective coating; 5-Substrate; 6-Lower waveguide layer; 7-Active layer; 8-Grating; 9-Upper waveguide layer; 10-Front-side metal layer; 11-Electrically isolated trench; 12, 13-Passive materials; 14-Back-side metal layer; 15-MMI-type passive region; 16-Single aperture output terminal for optical mode Detailed Implementation

[0035] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0036] The main objective of this application is to propose an on-chip beam combining scheme for high-power quantum cascade lasers based on selected area epitaxy technology, fabricating gratings, such as DFB (Distributed Feedback Laser) gratings, to form a stable optical feedback mechanism. A multi-channel active array is directly coupled to an MMI (Multi-Mode Inferometer) type passive waveguide to achieve a high-power single-aperture output quantum cascade laser and passive waveguide integrated device with low thermal effects.

[0037] Figure 1 This is a cross-sectional structural diagram of an on-chip beam combining device for a quantum cascade laser according to an embodiment of this application. Figure 2 This is a top view of an on-chip beam combining device for a quantum cascade laser according to an embodiment of this application.

[0038] like Figure 1 As shown, the on-chip beam combining device for quantum cascade lasers includes a substrate, a lower waveguide layer, an active layer, a grating, a passive material, and an upper waveguide layer. Figure 1 As shown, the lower waveguide layer is located on the front side of the substrate and has a first part and a second part (roughly corresponding to...) Figure 1 The upper waveguide layer has two parts (roughly corresponding to the left and right sides of the upper waveguide layer). The first part is located in the active region, and the second part is located in the passive region. The active layer is located above the first part of the lower waveguide layer and is used to generate light and amplify it. The grating is located above the active layer and is used to achieve unidirectional light transmission. The passive material is located above the second part of the lower waveguide layer, forming an MMI-type passive region and a single-aperture output terminal for optical mode. One end of the MMI-type passive region is connected to the active layer, and the other end is connected to the single-aperture output terminal for optical mode. The MMI-type passive region is used to synthesize light from the active region, and the single-aperture output terminal for optical mode is used to output the synthesized beam. The upper waveguide layer has a first part and a second part (roughly corresponding to the first part and the second part of the lower waveguide layer). Figure 1The first part of the upper waveguide layer is located in the active region and covers the active layer and the grating, the first part of the upper waveguide layer and the first part of the lower waveguide layer are used for guiding and confining the transmission of light, and the second part of the upper waveguide layer covers the passive material. In addition, an electrically isolated trench is formed on the upper waveguide layer for electrically isolating the active region and the passive region to prevent the diffusion of the electric charge applied to the active region to the passive region.

[0039] As shown in Figure 1 The on-chip beam combining device for the quantum cascade laser further includes a front metal layer and a back metal layer, the front metal layer covers the upper waveguide layer, and the back metal layer covers the back of the substrate.

[0040] According to some embodiments, the grating can be a DFB grating, more specifically, a first-order DFB grating. The quantum cascade laser utilizes the working mechanism of the grating to realize the unidirectional transmission of light, so that the multi-laser beam combining in the passive region part does not affect the laser working mode of the active region. In addition, the grating region can be independently adjusted and optimized in parameters, and a wavelength-tunable single-mode laser can be obtained. According to some embodiments, the grating can be prepared by using existing common mask manufacturing technology and etching technology, such as electron beam exposure and holographic exposure technology to prepare a mask, and combined with wet etching or dry etching technology to etch the grating.

[0041] According to some embodiments, the upper waveguide layer and the lower waveguide layer can include InP material for confining light in the active layer.

[0042] More specifically, the main functions of the upper and lower waveguide layers include: (1) optical waveguide guidance, the upper and lower waveguide layers are used to guide and confine the laser light wave. Waveguide is an optical structure that changes the way light propagates and confines the light beam in a small area. In a laser, this helps to concentrate the excitation and amplify the light signal, improving the efficiency of the laser. (2) Provide a reflective interface, the upper and lower waveguide layers form a reflective interface on both sides of the laser, which helps to build a laser resonant cavity. This reflective interface reflects part of the light wave back to the active layer, allowing the laser to repeatedly propagate in the resonant cavity, increasing the amplification effect, and ultimately forming a laser output. (3) Optical confinement, the design of the upper and lower waveguide layers can achieve optical confinement by changing the refractive index. This helps to ensure that the laser propagates in the active layer with proper optical confinement, thereby enhancing the amplification effect of the laser. (4) Current injection guidance, in a semiconductor laser, the upper and lower waveguide layers can also be used to guide the current. By applying current between the upper and lower waveguide layers, a current channel can be formed in the active layer, activating the semiconductor material and producing lasing. Overall, the upper and lower waveguide layers provide necessary conditions for the efficient operation and lasing of the laser through optical waveguide guidance, reflective interface provision, optical confinement, and other functions.

[0043] According to some embodiments, the active layer can be an InGaAs / InAlAs multi-quantum well structure for the realization of optical gain.

[0044] The active layer refers to the active layer in the laser, also known as the gain medium layer. This region has special properties in the structure of the laser, mainly serving to amplify the optical signal. The main functions and roles of the active layer are as follows: (1) amplifying optical signals: the active layer contains the amplification medium of the laser, usually a semiconductor material. When external energy (such as pump light or current injection) is input to the active layer, electrons and holes in the active layer are excited, causing them to recombine and release energy. This process leads to the amplification of photons, thereby amplifying the optical signal. (2) generating lasing: the main purpose of the active layer is to generate lasing through the process of stimulated emission. In this process, photons in the active layer interact with excited-state electrons, causing new photons to be released and in phase with existing photons, which leads to the amplification of the optical signal and ultimately forms lasing (laser). (3) constructing an optical resonant cavity: the active layer is generally located in the optical resonant cavity of the laser. The optical resonant cavity is a region sandwiched by two reflective interfaces (usually the upper and lower waveguide layers), with the active layer located therein. This structure helps to ensure that light repeatedly propagates in the active layer, enhancing the lasing effect. (4) wavelength selectivity: the material and design of the active layer can determine the wavelength of lasing. The laser can be designed to produce lasing at a specific wavelength range, which is crucial for different application scenarios. Overall, the active layer is the core part of the laser, which amplifies the optical signal and generates lasing, enabling the laser to achieve its specific functions.

[0045] According to some embodiments, the passive material filled to form the MMI type passive region and the optical mode single-aperture output end can include intrinsic multi-layer InP / InGaAs or InAlAs / InGaAs or Fe-doped multi-layer InP / InGaAs or InAlAs / InGaAs. By adjusting the thickness ratio of InP / InGaAs (or InAlAs / InGaAs), on the one hand, the effective refractive index matching the QCL active region can be obtained; and on the other hand, the energy density borne by the material can be reduced by expanding the optical mode area. By Fe-doping InP / InGaAs (or InAlAs / InGaAs), the passive waveguide loss can be reduced to 0.1 cm -1 The following.

[0046] According to some embodiments, the optical beam synthesis is performed in the MMI type passive region, and the number of optical beam synthesis can be set according to requirements, for example, 2, 3, 4, 5… and other multi-channel optical beam synthesis can be performed.

[0047] According to some embodiments, the single-aperture output terminal of the optical mode can adopt a tapered design. The tapered design of the single-aperture output terminal of the optical mode results in a wider aperture, a larger optical mode area, and a lower power density at the output surface, significantly reducing the probability of device failure. In addition, based on the wavelength of the synthesized beam, maximizing the area of ​​the single-aperture output terminal of the optical mode also reduces the probability of device failure.

[0048] According to some embodiments, such as Figure 1 As shown, the on-chip beam combining device for a quantum cascade laser may further include an anti-reflection coating and an anti-reflection coating. The anti-reflection coating is formed on the end face of the active region, and the anti-reflection coating is formed on the side of the synthesized light emission region of the passive region. The anti-reflection and anti-reflection coatings can be used to reflect light, allowing more light to enter the passive region.

[0049] According to some embodiments, the difference between the refractive index of the passive region material in the mid-to-long-wave infrared band and the refractive index of the active region material in the mid-to-long-wave infrared band does not exceed a first preset threshold, the Fresnel reflection loss at the interface between the passive and active regions is lower than a second preset threshold, and the ratio of the thickness of the MMI-type passive region to the thickness of the active layer is a set value. For example, the refractive index of the passive region material in the mid-to-long-wave infrared band is close to that of the active region material, at 3.3 and 3.2 respectively, the Fresnel reflection loss at the interface is less than 0.1%, and the thickness of the MMI-type passive region is close to 1.1 times the thickness of the active layer, further increasing the optical coupling efficiency between the active and passive regions.

[0050] Based on the on-chip beam combining device for quantum cascade lasers described above, according to another aspect of this application, a method for fabricating an on-chip beam combining device for quantum cascade lasers is provided, such as... Figure 3 As shown, the method includes the following steps.

[0051] Step S301: An epitaxial wafer is epitaxially generated on a substrate. The epitaxial wafer includes a lower waveguide layer, an active layer, and an upper waveguide layer. Each of the lower waveguide layer, the active layer, and the upper waveguide layer includes a first part and a second part. The first part of the lower waveguide layer, the first part of the active layer, and the first part of the upper waveguide layer are located in the active region, and the second part of the lower waveguide layer and the second part of the upper waveguide layer are located in the passive region.

[0052] According to some embodiments, the epitaxial wafer formed on the substrate includes a lower waveguide layer, an active layer, and an upper waveguide layer. The lower waveguide layer, the active layer, and the upper waveguide layer are respectively divided into a second part, roughly corresponding to... Figure 1The left and right sides are designated as the active and passive regions of the beam combining device, respectively. Therefore, the first part of the lower waveguide layer, the first part of the active layer, and the first part of the upper waveguide layer are located in the active region, while the second part of the lower waveguide layer and the second part of the upper waveguide layer are located in the passive region. According to some embodiments, the structurally complex QCL active layer can be grown on the substrate using molecular beam epitaxy (MBE) technology.

[0053] Step S302: Etch a first portion of the upper waveguide layer to form a grating on the first portion of the active layer.

[0054] According to some embodiments, a mask material can be deposited on the active layer by etching a first portion of the upper waveguide layer down to the active layer. The mask material layer with a patterned shape is used as a selected area mask. A grating is formed by combining holographic exposure with selective etching. After the grating is formed, the mask material layer is removed. According to one embodiment, the mask material may include SiO2. According to some embodiments, the grating can be fabricated using existing common mask fabrication and etching techniques, such as electron beam lithography and holographic exposure, and then etched using wet etching or dry etching techniques to form the grating.

[0055] According to some embodiments, the formed grating can be a DFB grating, and more specifically, a first-order DFB grating. Quantum cascade lasers utilize the grating's working mechanism to achieve unidirectional light transmission, enabling beam combining of multiple laser beams in the passive region without affecting the operating mode of the laser in the active region.

[0056] Step S303: A mask material layer is grown on the second part of the upper waveguide layer, and a photoresist layer with MMI type and single aperture output end with light mode is formed by photolithography.

[0057] Step S304: Etch the second portion of the upper waveguide layer and the second portion of the active layer down to the lower waveguide layer;

[0058] Step S305: An MMI-type passive region and an optical mode single aperture output end region are formed on the second part of the lower waveguide layer, and passive material is filled in the MMI-type passive region and the optical mode single aperture output end region. After the MMI-type passive region is filled, it is docked and coupled to the first part of the active layer.

[0059] According to some embodiments, a mask material layer is regrown on the second part of the upper waveguide layer, and a photoresist layer with MMI type and optical mode single aperture output terminal type is formed by photolithography; the mask material of MMI type and optical mode single aperture output terminal type is etched, and after removing the surface photoresist with an organic solvent, the MMI type and optical mode single aperture output terminal type region is etched with a selective etching solution until the lower waveguide layer is formed, and the MMI type passive region and optical mode single aperture output terminal type region are formed on the second part of the lower waveguide layer; then, passive material is grown in the MMI type passive region and optical mode single aperture output terminal type region where there is no mask material mask, so that the MMI type passive region is filled and coupled to the active region. This application employs selective area epitaxy (SIE) to fabricate an MMI-type passive region and an optical mode single-aperture output region (low-loss passive waveguide). Beam combining and transmission are performed within these two regions, avoiding the heat dissipation problems caused by carrier absorption in traditional active beam combining, thereby increasing laser power. Simultaneously, it eliminates the need for cumbersome external microlenses in the packaging process. This eliminates the need for any external beam combining optical components, achieving high integration and miniaturization, and improving the stability, reliability, and portability of the integrated device.

[0060] According to some embodiments, the passive material may include intrinsic multilayer InP / InGaAs or InAlAs / InGaAs, or Fe-doped multilayer InP / InGaAs or InAlAs / InGaAs. By adjusting the thickness ratio of InP / InGaAs (or InAlAs / InGaAs), an effective refractive index matching the active region of the QCL can be obtained; expanding the optical mode area can reduce the energy density carried by the material. By doping InP / InGaAs (or InAlAs / InGaAs), the passive waveguide loss can be reduced to 0.1 cm⁻¹. -1 the following.

[0061] Step S306: Re-epitaxially grow the upper waveguide layer.

[0062] According to some embodiments, after forming the grating, the MMI-type passive region, and the optical mode single aperture output end region, an upper waveguide layer is epitaxially grown again on the formed grating, MMI-type passive region, and optical mode single aperture output end region. According to one embodiment, the upper waveguide layer can be epitaxially grown using MOCVD (Metal-Organic Chemical Vapor Deposition).

[0063] Step S307: Photolithography is used to form the dissociation groove of the beam combining device.

[0064] According to some embodiments, forming the dissociation groove facilitates subsequent interception of the beam combining device.

[0065] Step S308: An electrically isolated trench is prepared on the upper waveguide layer. The electrically isolated trench is used to electrically isolate the active region and the passive region to prevent the charge applied to the active region from diffusing to the passive region.

[0066] According to some embodiments, a mask material layer is deposited on the upper waveguide layer, an electrically isolated trench is fabricated by photolithography, and the mask material is etched. The electrically isolated trench is used to electrically isolate the active and passive regions, preventing the diffusion of charge applied to the active region into the passive region.

[0067] Step 309: A front metal layer and a back metal layer are formed on the back side of the upper waveguide layer and the substrate, respectively.

[0068] According to some embodiments, a window is opened on the upper waveguide layer, and metal is evaporated by electron beam to form a front electrode, combined with electroplating to form a front metal layer; on the back side of the substrate, metal is evaporated by electron beam to form a front electrode, combined with electroplating to form a back metal layer. According to one embodiment, the substrate layer can be thinned and polished before evaporating the metal to form the front electrode, which can facilitate heat dissipation of the device.

[0069] Step S310: Cut the core according to the dissociation groove and sinter it.

[0070] According to some embodiments, after the die is cut and sintered according to the dissociation groove, an independent beam combining device is formed.

[0071] Figure 4 This is a flowchart illustrating a method for fabricating an on-chip beam combining device for a quantum cascade laser according to another embodiment of this application. Figure 3 compared to, Figure 4 Steps S401 to S410 and Figure 3 Steps S301 to S310 are the same, except that... Figure 4 Also includes:

[0072] Step S411: An anti-reflection film is formed by depositing a coating on the end face of the active region side; and

[0073] Step S412: An antireflection film is formed by depositing a coating on one side of the light emission region in the passive region.

[0074] According to some embodiments, after the die is cut and sintered according to the dissociation groove, an anti-reflection film can be formed by coating the end face on the active region side, and an anti-reflection film can be formed by coating the side of the light emission region in the passive region. The anti-reflection film and the anti-reflection film can be used to reflect light, so that more light can enter the passive region.

[0075] Figure 5This is a flowchart illustrating a method for fabricating an on-chip beam combining device for a quantum cascade laser according to yet another embodiment of this application. Figure 3 compared to, Figure 5 Steps S501 to S510 and Figure 3 Steps S301 to S310 are the same, except that... Figure 5 Also includes:

[0076] Step S511: Before the waveguide layer is re-epitaxially grown, a matching mark pattern is formed by photolithography.

[0077] Step S512: After the waveguide layer is re-epitaxically grown, the mask material left for the alignment mark is removed.

[0078] According to some embodiments, the alignment mark pattern can be located on the active region side. After the grating, MMI-type passive region, and optical mode single-aperture output end region are formed, and before the waveguide layer is re-epitaxetically grown, the alignment mark pattern is formed by photolithography. The mask material in the unprotected portion is removed, and after the waveguide layer is re-epitaxetically grown, the mask material remaining at the alignment mark location is washed away. The alignment mark pattern is used to identify the active or passive region of the beam combining device.

[0079] Figure 6 This is a flowchart illustrating a method for fabricating an on-chip beam combining device for a quantum cascade laser according to another embodiment of this application. Figure 3 compared to, Figure 6 Steps S601 to S610 and Figure 3 Steps S301 to S310 are the same, except that... Figure 6 Also includes:

[0080] Step S611: A double-groove ridge waveguide is formed on both sides of the beam combining device.

[0081] According to some embodiments, a mask material layer can be redeposited afterward, and a double-groove ridge waveguide can be formed by photolithography and etching on both sides of the beam combining device. The structure between the double-groove ridge waveguides can be called a ridge structure, which ensures mode matching between the active and passive regions.

[0082] According to one embodiment, the double-groove ridge waveguide is filled with a semi-insulating material, such as InP. Forming double-groove ridge waveguides on both sides of the beam combiner can facilitate heat dissipation of the beam combiner, thereby improving the power of the beam combiner.

[0083] It should be noted that, Figures 3 to 6 The epitaxial growth technology, photolithography technology, and etching technology involved in the preparation process can all adopt existing mature preparation processes.

[0084] Figure 7A , Figure 7B and Figure 7C The diagram shows the simulation results of the beam coupling efficiency of the on-chip beam combining device for quantum cascade lasers according to the embodiments of this application, performing passive two-in-one, four-in-one, and eight-in-one single-aperture output devices in the beam combining region. Figure 7A , Figure 7B and Figure 7C Simulation results of the optical coupling efficiency in the beam combining region of passive two-in-one, four-in-one, and eight-in-one beam combining devices for high-power quantum cascade lasers based on selected area epitaxy technology are shown, considering docking coupling and transmission loss respectively. The figures show that the docking coupling loss is 0.18 dB and the waveguide loss is 0.36 cm⁻¹. -1 .

[0085] Figure 8 This is a docking epitaxial SEM image of an on-chip beam combining device for a quantum cascade laser according to an embodiment of this application. Figure 8 In the image, the left side shows the SEM cross-sectional view before the selected area is extended; the right side shows the interface view after the selected area is extended. The light-colored area on the left represents the area filled by the passive material extension, and the dark-colored area on the right represents the area of ​​active material left after etching. Figure 8 It can be seen that the active and passive regions of the beam combining device prepared by this scheme have a very good docking effect.

[0086] Figure 9A and Figure 9B This is a thermal simulation diagram of a high-power QCL on-chip optical beam combiner, in which... Figure 9A Using an active waveguide structure, Figure 9B A passive waveguide structure is adopted. Figure 9A and Figure 9B Taking the four-in-one MMI coupler as an example, considering both active and passive waveguide structures, by comparing the thermal simulation results, it can be seen that when using the active-passive docking structure, the surface temperature of the waveguide part is around 295K, and the heat accumulation is significantly improved.

[0087] Figure 10 This is a graph showing the room temperature pulsed operating current-optical power and voltage curves for high-power QCL on-chip optical beam combiners in two-in-one, four-in-one, and single-chip configurations (array length is 4mm). Figure 10 The current-optical power curves of single-aperture output devices with different array numbers under room temperature pulse pumping are shown. By comparing the PIV curves of single-die and two-in-one and four-in-one devices, it can be seen that the multi-channel active array and low-loss passive optical beam combining waveguide integration method adopted has low transmission and docking coupling loss and high-efficiency optical power combining. That is, with a single-die output of 2W, the two-in-one and four-in-one devices can achieve single-aperture high-power output of 4W and 6.5W, respectively.

[0088] According to the on-chip beam combining device and its fabrication method for quantum cascaded lasers provided in this application, firstly, by fabricating a multi-channel active region array, the energy distribution of the laser is rationally allocated, improving the low-power output problem caused by uneven heat dissipation of the laser; secondly, by fabricating a distributed feedback grating structure on the active region array, mode selection is achieved, realizing single-mode optical transmission; the passive beam combining single-aperture output waveguide fabricated in the passive region has low optical and thermal losses; furthermore, the multi-channel QCL active array with grating is connected to the low-loss passive beam combining waveguide. When achieving on-chip integration via docking, compared to active beam combining designs with severe heat dissipation problems, passive beam combining with single-aperture output avoids the uneven heat dissipation issues caused by carrier absorption. This enables on-chip beam combining and high-power output with a single aperture in the QCL, and solves the beam distribution problem of multi-peak interference caused by array multi-aperture output, avoiding limitations on the device's application range. Furthermore, the use of selected area epitaxy to fabricate low-loss passive waveguides for beam combining and transmission within the passive waveguide region avoids the need for external microlenses with cumbersome packaging processes. Finally, the fabrication method for the on-chip beam combining device for quantum cascade lasers in this application can be implemented based on existing fabrication processes, making it easy for technicians to operate. The on-chip beam combining and high-power output strategy for QCLs provided in this application will significantly improve laser performance, thereby promoting further development in fields such as long-distance communication and infrared countermeasures.

[0089] The embodiments of this application have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the embodiments above are only for the purpose of helping to understand the method and core ideas of this application. Furthermore, any changes or modifications made by those skilled in the art based on the ideas of this application, and on the specific implementation methods and application scope of this application, are all within the scope of protection of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. An on-chip beam combining device for quantum cascade lasers, characterized in that, include: Substrate; The lower waveguide layer, located on the front side of the substrate, has a first part and a second part, the first part being located in the active region and the second part being located in the passive region; An active layer, located above the first part of the lower waveguide layer, is used to generate light and amplify it. A grating, located above the active layer, is used to enable unidirectional light transmission; A passive material is located on the second part of the lower waveguide layer to form an MMI-type passive region and an optical mode single aperture output terminal. One end of the MMI-type passive region is connected to the active layer, and the other end is connected to the optical mode single aperture output terminal. The MMI-type passive region is used to synthesize light from the active region, and the optical mode single aperture output terminal is used to output the synthesized light beam. The passive material includes intrinsic multilayer InP / InGaAs or InAlAs / InGaAs or Fe-doped multilayer InP / InGaAs or InAlAs / InGaAs. The upper waveguide layer has a first portion and a second portion. The first portion of the upper waveguide layer is located in the active region and covers the active layer and the grating. The first portion of the upper waveguide layer and the first portion of the lower waveguide layer are used to guide and constrain the transmission of light. The second portion of the upper waveguide layer covers the passive material. An electrically isolated trench is formed on the upper waveguide layer to electrically isolate the active region and the passive region to prevent the charge applied to the active region from diffusing to the passive region.

2. The apparatus as claimed in claim 1, characterized in that, Also includes: A front-side metal layer covers the upper waveguide layer; as well as A back metal layer covers the back side of the substrate.

3. The apparatus as described in claim 1, characterized in that, Also includes: An anti-reflection coating is deposited on the end face of the active region. as well as An antireflective coating is formed on one side of the passive region where the synthesized light is emitted.

4. The apparatus according to any one of claims 1 to 3, characterized in that, The grating includes a first-order DFB grating, the lower waveguide layer and the upper waveguide layer are made of InP material, and the active layer includes an InGaAs / InAlAs multi-quantum-well structure.

5. The apparatus according to any one of claims 1 to 3, characterized in that, The single-aperture output end of the optical mode is tapered.

6. The apparatus according to any one of claims 1 to 3, characterized in that, The difference between the refractive index of the material in the passive region in the mid-to-long-wave infrared band and the refractive index of the material in the active region in the mid-to-long-wave infrared band does not exceed a first preset threshold, the Fresnel reflection loss at the interface between the passive region and the active region is lower than a second preset threshold, and the ratio of the thickness of the MMI-type passive region to the thickness of the active layer is a set value.

7. A method for fabricating an on-chip beam combining device for a quantum cascade laser, characterized in that, include: An epitaxial wafer is epitaxially generated on a substrate. The epitaxial wafer includes a lower waveguide layer, an active layer, and an upper waveguide layer. Each of the lower waveguide layer, the active layer, and the upper waveguide layer includes a first part and a second part. The first part of the lower waveguide layer, the first part of the active layer, and the first part of the upper waveguide layer are located in the active region, and the second part of the lower waveguide layer and the second part of the upper waveguide layer are located in the passive region. The first portion of the upper waveguide layer is etched to form a grating on the first portion of the active layer; A mask material layer is grown on the second part of the upper waveguide layer, and a photoresist layer with MMI type and single aperture output end with light mode is formed by photolithography. Erosion of the second portion of the upper waveguide layer and the second portion of the active layer down to the lower waveguide layer; An MMI-type passive region and an optical mode single aperture output end region are formed on the second part of the lower waveguide layer, and passive material is filled in the MMI-type passive region and the optical mode single aperture output end region. After the MMI-type passive region is filled, it is docked and coupled to the first part of the active layer. The passive material includes intrinsic multilayer InP / InGaAs or InAlAs / InGaAs or Fe-doped multilayer InP / InGaAs or InAlAs / InGaAs. Re-epitaxially grow the upper waveguide layer; Photolithography forms the dissociation groove of the beam combining device; An electrically isolated trench is fabricated on the upper waveguide layer to electrically isolate the active region and the passive region, preventing the charge applied to the active region from diffusing into the passive region.

8. The method as described in claim 7, characterized in that, Also includes: A front metal layer and a back metal layer are formed on the back side of the upper waveguide layer and the substrate, respectively; as well as The core is cut and sintered according to the dissociation groove.

9. The method as described in claim 7, characterized in that, Also includes: An anti-reflection film is formed by coating the end face on one side of the active region; as well as An antireflection coating is formed by depositing a film on one side of the light emission region in the passive region.

10. The method according to any one of claims 7 to 9, characterized in that, Also includes: Before the waveguide layer is re-epitaxied, a alignment mark pattern is formed by photolithography; and After the waveguide layer is re-epitaxically grown, the mask material left for the alignment mark is removed.

11. The method according to any one of claims 7 to 9, characterized in that, Also includes: A double-groove ridge waveguide is formed on both sides of the beam combining device.

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