A photonic crystal laser based on topological edge states

Abstract

The application provides a photonic crystal laser based on a topological boundary state, and relates to the technical field of semiconductor optoelectronic devices, and comprises a substrate, a buffer layer, a lower-layer superlattice photonic crystal, an active region, an upper-layer superlattice photonic crystal, a cover layer and a contact layer, wherein the lower-layer superlattice is formed by alternately growing two semiconductor materials with a certain size, and contains a two-layer structure in a period unit; the upper-layer superlattice is formed by alternately growing two or three semiconductor materials with a certain size, and contains a three-layer structure in a period unit. By changing the thickness proportion of each material in the period unit and the topological properties of the photonic energy band, the superlattice photonic crystals corresponding to different topological property energy bands are combined, a specific photonic interface state can be generated, the quality factor is increased, the mode volume of the optical field is reduced, the energy is concentrated, the gain of the optical field is better realized, and then the subsequent modulation of light in the optoelectronic integrated device is better realized.

Description

Technical Field

[0001] This application relates to the field of semiconductor optoelectronic device technology, and more specifically, to a photonic crystal laser based on topological boundary states. Background Technology

[0002] Semiconductor lasers, such as vertical-cavity surface-emitting lasers (VCSELs), have wide applications in sensing, communication, and medical fields. High-output-power semiconductor CCSELs are important in many applications, such as pumping solid-state lasers and materials processing, but their output beam power is inferior to that of gas and solid-state lasers. The demands for high power and high energy efficiency place higher requirements on the limiting capabilities and gain of semiconductor CCSELs, as well as on improving their quality factor and mode volume. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this application provides a photonic crystal laser based on topological boundary states, comprising:

[0004] Substrate;

[0005] A buffer layer is disposed on the substrate;

[0006] A lower-layer superlattice photonic crystal is disposed on the buffer layer;

[0007] The active region is disposed on the superlattice photonic crystal of the lower region.

[0008] An upper-layer superlattice photonic crystal is disposed on the active region;

[0009] A capping layer is disposed on the superlattice photonic crystal in the upper region;

[0010] A contact layer is disposed on the cover layer.

[0011] Optionally, the lower-layer superlattice photonic crystal comprises multiple layers of lower-layer photonic crystal periodic units, and each lower-layer photonic crystal periodic unit comprises:

[0012] The lower region is a high-refractive-index layer; and

[0013] A low-refractive-index layer is disposed on the high-refractive-index layer in the lower region, and multiple lower-layer photonic crystal periodic units are repeatedly arranged.

[0014] Optionally, the upper-layer superlattice photonic crystal includes multiple upper-layer photonic crystal periodic units, and each upper-layer photonic crystal periodic unit includes:

[0015] Upper region low refractive index layer one; and

[0016] A high-refractive-index layer is disposed on the low-refractive-index layer in the upper region; and

[0017] The second low-refractive-index layer is disposed on the high-refractive-index layer of the upper region, and multiple upper photonic crystal periodic units are repeatedly arranged.

[0018] Optionally, the refractive index of the lower low-refractive-index layer is lower than that of the lower high-refractive-index layer, and the thickness of the lower low-refractive-index layer is greater than that of the lower high-refractive-index layer.

[0019] Optionally, the refractive index of the active region should be between that of the lower low-refractive-index layer and the lower high-refractive-index layer, and its thickness should be greater than that of the upper high-refractive-index layer.

[0020] Optionally, it should also include: an N-type electrode layer disposed on the lower part of the substrate; and a P-type electrode layer disposed on the upper surface of the contact layer.

[0021] Optionally, at least one layer of at least one periodic unit in the lower superlattice photonic crystal and / or the upper superlattice photonic crystal contains a phase change material, the phase state of which can be changed in response to external excitation, thereby tunable photonic band topological properties of the topological boundary state photonic crystal laser structure.

[0022] Optionally, it may also include a control structure coupled to the phase change material and configured to apply electrical or optical excitation to the phase change material to controllably induce at least one phase transition between an amorphous and a crystalline state.

[0023] Optionally, the phase change material is divided into multiple independently addressable units, and the control structure further includes a processing unit configured to: in response to input of a target optical function, determine, based on a sparse reconstruction algorithm, a combination of the minimum number of independently addressable units that require a change in the phase state to achieve the target optical function; and generate and output a control signal to drive the control structure to apply excitation only to the units in the combination.

[0024] Optionally, the sparse reconstruction algorithm includes:

[0025] The difference between the target optical function and the current optical function, which consists of all independently addressable units, is initialized as a residual signal, and the candidate unit set is initialized to empty.

[0026] Calculate the response contribution of each independently addressable cell that has not yet been selected into the candidate cell set to the residual signal when the phase state changes, and identify and select the cell that produces the largest response contribution from all the independently addressable cells that have not yet been selected, and add it to the candidate cell set.

[0027] Based on all units in the current candidate unit set, a temporary combined optical function is calculated, and the target optical function is subtracted from the temporary combined optical function to update the residual signal;

[0028] Repeat the above steps until the amplitude of the residual signal is lower than a preset threshold.

[0029] The final set of candidate units is determined as the combination of the minimum number of units required to change the phase state.

[0030] Compared with the prior art, this application changes the topological properties of the photonic band by altering the thickness ratio of each material in the periodic unit. By combining superlattice photonic crystals corresponding to bands with different topological properties, specific photonic interface states can be generated, thereby increasing the quality factor and reducing the mode volume of the light field, achieving energy concentration, better realizing the gain of the light field, and thus better realizing subsequent modulation of light in optoelectronic integrated devices. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of a topological boundary state photonic crystal laser structure implemented according to this application;

[0032] Figure 2 yes Figure 1 A schematic diagram of a superlattice photonic crystal in the middle and lower layers;

[0033] Figure 3 yes Figure 1 A schematic diagram of a superlattice photonic crystal in the upper-middle region;

[0034] Figure 4 yes Figure 2 Band diagram of a superlattice photonic crystal in the middle and lower layers;

[0035] Figure 5 yes Figure 3 Band diagram of a superlattice photonic crystal in the upper-middle region;

[0036] Figure 6 yes Figure 4 The dashed and ellipsis lines represent the optical field pattern distribution of the band at the center of the Brillouin zone, and the solid and dashed lines represent the optical field pattern distribution of the band at the boundary of the Brillouin zone.

[0037] Figure 7 yes Figure 5 The dashed and ellipsis lines represent the optical field pattern distribution of the band at the center of the Brillouin zone, and the solid and dashed lines represent the optical field pattern distribution of the band at the boundary of the Brillouin zone.

[0038] Figure 8yes Figure 1 Light field distribution diagrams after simulation of the superlattice photonic crystal in the middle and lower regions, the active region, and the upper region;

[0039] Figure 9 The diagram shows the PI curve of the topological boundary state photonic crystal laser structure provided in this application. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with specific embodiments and accompanying drawings. However, it should be understood that the described embodiments are only some, not all, of the embodiments of this application. In the following detailed description, many specific details are set forth to provide a comprehensive understanding of the embodiments of this application for ease of explanation. However, it is apparent that one or more embodiments may be implemented without these specific details.

[0041] 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 the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0042] When using expressions such as "at least one of A, B, and C," the expression should generally be interpreted in accordance with the meaning commonly understood by a person skilled in the art (e.g., "a system having at least one of A, B, and C" should include, but is not limited to, systems having A alone, having B alone, having C alone, having A and B, having A and C, having B and C, and / or having A, B, and C, etc.). When using expressions such as "at least one of A, B, or C," the expression should generally be interpreted in accordance with the meaning commonly understood by a person skilled in the art (e.g., "a system having at least one of A, B, or C" should include, but is not limited to, systems having A alone, having B alone, having C alone, having A and B, having A and C, having B and C, and / or having A, B, and C, etc.).

[0043] Traditional semiconductor lasers have inferior beam quality compared to gas and solid-state lasers. In distributed Bragg reflector semiconductor lasers used in electro-absorption modulated high-speed lasers, a portion of the emitted laser beam is difficult to effectively focus on the quantum well portion of the electro-absorption modulator. While the introduction of traditional photonic crystal structures can improve beam quality, it affects the device's power output. Furthermore, laser output in the upper layer requires misalignment with the modulator's quantum well, making the manufacturing process relatively difficult.

[0044] To at least partially solve the technical problems existing in the related technologies, according to the general concept of one aspect of this application, a topological boundary state photonic crystal laser structure is provided. By changing the thickness ratio of each material in the periodic unit, the topological properties of the photonic band are changed, and superlattice photonic crystals corresponding to different topological property bands are combined to generate specific photonic interface states, thereby reducing the mode volume of the light field to achieve energy concentration, better confine the light field, and thus better achieve light modulation in optoelectronic devices that simultaneously integrate lasers and modulators.

[0045] Figure 1 A schematic diagram of the topological boundary state photonic crystal laser structure according to an embodiment of this application is shown.

[0046] According to embodiments of this application, such as Figure 1 As shown, the electroabsorption modulated laser structure includes: a substrate 1; a buffer layer 2; a lower region superlattice photonic crystal 3; an active region 4; an upper region superlattice photonic crystal 5; a capping layer 6; and a contact layer 7.

[0047] Figure 2 An enlarged schematic diagram of the lower region superlattice photonic crystal 3 of the electroabsorption modulated laser structure provided in this application is shown. Figure 3 This is an enlarged schematic diagram of the upper region superlattice photonic crystal 5 of the electroabsorption modulated laser structure provided in this application.

[0048] According to embodiments of this application, such as Figure 2 As shown, the lower region superlattice photonic crystal 3 includes multiple lower region photonic crystal periodic units. Each lower region photonic crystal periodic unit includes: a lower region high refractive index layer 8; and a lower region low refractive index layer 9, which is disposed on the lower region high refractive index layer 8. Multiple lower region photonic crystal periodic units are repeatedly arranged.

[0049] According to an embodiment of this application, the refractive index of the lower region low-refractive-index layer 9 is lower than the refractive index of the lower region high-refractive-index layer 8; the refractive index of the lower region low-refractive-index layer 9 is between 2.1 and 3.1, and the refractive index of the lower region high-refractive-index layer 8 is between 2.5 and 3.5; the materials of the lower region low-refractive-index layer 9 and the high-refractive-index layer 8 include, but are not limited to, InGaAlAs, wherein the refractive index of the materials can be achieved by adjusting the flow rate of the In, Ga, and Al growth sources during the epitaxial growth process.

[0050] In addition, the range can be expanded according to the actual situation. For example, the refractive index of the low refractive index layer 9 in the lower region is between 2.1 and 3.3, and the refractive index of the high refractive index layer 8 in the lower region is between 2.5 and 3.7.

[0051] According to an embodiment of this application, the total optical path length of the lower region high refractive index layer 8 and the lower region low refractive index layer 9 is half the wavelength of light. When a photon traverses a lower layer of photonic crystal periodic unit, the cumulative phase shift is π. The thickness of the lower region low refractive index layer 9 is greater than that of the lower region high refractive index layer 8 in order to form a specific photonic crystal band. The thickness of the lower region low refractive index layer 9 is 105 to 125 nm, and the thickness of the lower region high refractive index layer 8 is 80 to 100 nm.

[0052] According to embodiments of this application, such as Figure 3 As shown, the upper superlattice photonic crystal 5 includes multiple upper photonic crystal periodic units. Each upper photonic crystal periodic unit includes: an upper region low refractive index layer 10; an upper region high refractive index layer 11 disposed on the upper region low refractive index layer 10; and an upper region low refractive index layer 12 disposed on the upper region high refractive index layer. Multiple upper photonic crystal periodic units are arranged repeatedly.

[0053] According to an embodiment of this application, in order to obtain photonic boundary states, the proportions of high refractive index layer and low refractive index layer in the upper and lower superlattice photonic crystals are different; the total optical path length of the upper region high refractive index layer 11, the upper region low refractive index layer 10, and the upper region low refractive index layer 12 is half the wavelength of light, and when a photon traverses a periodic unit of an upper photonic crystal, the cumulative phase shift is π.

[0054] For example, the refractive index of the upper low-refractive-index layer 10 is between 2.1 and 3.3, and the thickness is between 40 and 65 nm; the refractive index of the upper high-refractive-index layer 11 is between 2.5 and 3.7, and the thickness is between 80 and 125 nm; and the refractive index of the upper low-refractive-index layer 12 is between 2.1 and 3.3, and the thickness is between 40 and 65 nm. The materials of the upper low-refractive-index layer 10, the upper high-refractive-index layer 11, and the upper low-refractive-index layer 12 include, but are not limited to, InGaAlAs. The refractive index of the materials can be achieved by adjusting the flow rate of the In, Ga, and Al growth sources during the epitaxial growth process. The active region thickness is between 80 and 125 nm.

[0055] Figure 4 The diagram illustrates the photonic band structure of the lower region superlattice photonic crystal 3 of the electroabsorption modulated laser structure provided in this application.

[0056] According to embodiments of this application, such as Figure 4 As shown, the horizontal axis represents the location of the Brillouin zone. The energy band indicated by the dash in the middle has a high density of states in the range of 217 to 236 THz, corresponding to wavelengths of 1380 to 1270 nm. The energy band indicated by the ellipsis above has a high density of states in the range of 452 to 453 THz, corresponding to wavelengths of 663 to 661 nm.

[0057] For example, the refractive index of the lower low-refractive-index layer 9 is 3.0, and the refractive index of the lower high-refractive-index layer 8 is 3.4; the thickness of the lower low-refractive-index layer 9 is 111 nm, and the thickness of the lower high-refractive-index layer 8 is 97 nm.

[0058] Figure 5 The diagram illustrates the photonic band structure of the upper region superlattice photonic crystal 5 of the electroabsorption modulated laser structure provided in this application.

[0059] According to embodiments of this application, such as Figure 5 As shown, the horizontal axis represents the location of the Brillouin zone. The middle short line indicates that the energy band has a high density of states in the range of 217 to 235 THz, corresponding to wavelengths of 1380 to 1275 nm. The ellipsis line above indicates that the energy band has a high density of states in the range of 448 to 457 THz, corresponding to wavelengths of 669 to 656 nm.

[0060] For example, the upper region low refractive index layer 10 has a refractive index of 3.0 and a thickness of 47 nm; and the upper region high refractive index layer has a refractive index of 3.4 and a thickness of 113 nm, disposed on the upper region low refractive index layer 10; and the upper region low refractive index layer 2 has a refractive index of 3.0 and a thickness of 46 nm.

[0061] Figure 6 Schematic illustration Figure 4 The dashed and ellipsis lines represent the light field pattern distribution of the energy band at the center of the Brillouin zone, while the solid and dashed lines represent the light field pattern distribution of the energy band at the boundary of the Brillouin zone.

[0062] According to embodiments of this application, such as Figure 6 As shown, Figure 4 The solid line indicates that the optical field vibration mode corresponding to the energy band at the Brillouin zone boundary is antisymmetric with the peak at the bottom and the trough at the top; the dash line indicates that the optical field vibration mode corresponding to the energy band at the Brillouin zone boundary is antisymmetric with the peak at the top and the trough at the bottom; the dash line indicates that the optical field vibration mode corresponding to the energy band at the center of the Brillouin zone is symmetric with the peak at the center; the ellipsis line indicates that the optical field vibration mode corresponding to the energy band at the center of the Brillouin zone is symmetric with the trough at the center.

[0063] Figure 7 Schematic illustration Figure 5 The dashed and ellipsis lines represent the light field pattern distribution of the energy band at the center of the Brillouin zone, while the solid and dashed lines represent the light field pattern distribution of the energy band at the boundary of the Brillouin zone.

[0064] According to embodiments of this application, such as Figure 7 As shown, Figure 5The solid line indicates that the optical field vibration mode corresponding to the band at the Brillouin zone boundary is antisymmetric with the peak at the bottom and the trough at the top; the dash line indicates that the optical field vibration mode corresponding to the band at the Brillouin zone boundary is antisymmetric with the peak at the top and the trough at the bottom; the dash line indicates that the optical field vibration mode corresponding to the band at the center of the Brillouin zone is symmetric with the center being a trough; the ellipsis line indicates that the optical field vibration mode corresponding to the band at the center of the Brillouin zone is symmetric with the center being a peak.

[0065] Different mode symmetries in the band structure represent different topological properties, which makes it possible to generate photonic interface states.

[0066] According to an embodiment of this application, the refractive index of the active region 4 should be between the low refractive index layer 9 and the high refractive index layer 8 in the lower region, and its thickness should be greater than that of the high refractive index layer in the upper region, so that the optical path of light passing through the active region is between the high refractive index layer of the photonic crystal in the upper region and the high refractive index layer of the photonic crystal in the lower region.

[0067] According to an embodiment of this application, the structure of the active region 4 includes: a quantum well or a quantum dot; the active region 4 is used to provide optical gain, with the peak wavelength of the gain spectrum ranging from 1270 nm to 1380 nm, or from 656 nm to 669 nm; the material of the active region 4 may include, but is not limited to, InGaAlAs and InGaAlP.

[0068] For example, the active region 4 can be composed of an InGaAs / AlGaAs quantum well with a refractive index of 3.23 and a gain wavelength of approximately 1.28 micrometers.

[0069] Figure 8 yes Figure 1 The simulated light field distribution diagrams of the superlattice photonic crystal 3 in the middle and lower regions, the active region 4, and the superlattice photonic crystal 5 in the upper region.

[0070] According to embodiments of this application, such as Figure 8 As shown, a distinct photonic mode is generated between the lower superlattice photonic crystal 3 and the upper superlattice photonic crystal 5, which is characterized by the strongest laser light being concentrated at the central interface and effectively confined.

[0071] Figure 9 The schematic diagram shows the PI curve of the topological boundary state photonic crystal laser structure provided in this application.

[0072] According to embodiments of this application, such as Figure 9 As shown, as the injected current increases, the laser generates lasing, and subsequently the optical power increases with the increase of the current.

[0073] According to an embodiment of this application, it should further include: an N-type electrode layer disposed on the lower part of the substrate 1; and a P-type electrode layer disposed on the upper surface of the contact layer 7.

[0074] For example, the lower region low-refractive-index layer 9 has a refractive index of 3.23 and a thickness of 115 nm; the lower region high-refractive-index layer 8 has a refractive index of 3.54 and a thickness of 90 nm. The upper region low-refractive-index layer 10 has a refractive index of 3.23 and a thickness of 57.5 nm; the upper region high-refractive-index layer has a refractive index of 3.54 and a thickness of 90 nm; the upper region low-refractive-index layer 12 has a refractive index of 3.23 and a thickness of 57.5 nm.

[0075] In another embodiment of this application, in order to overcome the performance deviation of static devices caused by manufacturing process errors and to endow the devices with dynamic reconfigurability, a phase change material can be introduced into the laser structure. A phase change material is a type of material whose phase state can undergo a reversible change through external excitation, accompanied by a significant change in its optical properties (especially refractive index).

[0076] According to embodiments of this application, in the lower superlattice photonic crystal 3 and / or the upper superlattice photonic crystal 5, at least one layer within at least one periodic unit may contain a phase change material.

[0077] For example, a portion or all of the high-refractive-index layer 8 in the lower region can be replaced with a phase change material layer, or a phase change material film can be deposited on it. The phase change material may include, but is not limited to, chalcogenides such as Ge₂Sb₂Te₅ (GST), Sb₂S₃, or Sb₂Se₃. These materials are capable of reversible transformation between amorphous and crystalline states. In the amorphous state, their refractive index is low; in the crystalline state, their refractive index increases significantly.

[0078] The phase state of the phase change material can change in response to external stimuli. This phase change leads to a change in its refractive index, which in turn alters the effective optical parameters of the periodic unit cell of the photonic crystal in which it resides. Since the band structure of a photonic crystal is extremely sensitive to the refractive index distribution of its constituent materials, by changing the phase state of the phase change material, the band structure of the superlattice photonic crystal in which it resides can be actively and reversibly altered, thereby tunable photonic band topological properties of the topological boundary state photonic crystal laser structure.

[0079] For example, the resonant frequency of the topological boundary states can be changed to tune the output wavelength of a laser; or the characteristics of the topological bandgap can be changed to turn the topological boundary states on or off, thus serving as an optical switch or optical modulator. Since the state of a phase change material is non-volatile, meaning it retains its phase state after the external excitation is removed, this tuning or switching function has the advantage of low power consumption.

[0080] According to embodiments of this application, to achieve control over the phase state of the phase change material, the laser structure may further include a control structure. The control structure is coupled to the phase change material, meaning it is positioned at a location capable of effectively transferring energy to the phase change material. The control structure is configured to apply external excitation to the phase change material.

[0081] In one embodiment, the external excitation is an electrical excitation. The control structure may include one or more micro-electric heaters, such as a transparent conductive layer made of indium tin oxide (ITO) or a heavily doped semiconductor, disposed adjacent to the phase change material layer. By applying specific electrical pulses to the heaters, the temperature of the phase change material can be precisely controlled using the Joule heating effect to controllably induce at least one phase transition between an amorphous and crystalline state.

[0082] Typically, an electrical pulse with a low amplitude and a long duration, such as hundreds of nanoseconds, can crystallize it; while an electrical pulse with a high amplitude and an extremely short duration, such as tens of nanoseconds, can rapidly melt it and then quench it, thus transforming it into an amorphous state.

[0083] In another embodiment, the external excitation is optical excitation. The control structure may include an external light source, such as a focused laser pulse. By irradiating the phase change material region with this laser pulse, precise control over its phase state can also be achieved using the photothermal effect.

[0084] In another embodiment of this application, to achieve efficient and intelligent programming of the device's optical functions, the phase change material can be divided into multiple independently addressable units. This can be achieved by patterning the control structure, such as a micro-electric heater array, so that each heater unit corresponds to one phase change material unit. The control structure may also include a processing unit, such as a microprocessor (MCU), a digital signal processor (DSP), or a field-programmable gate array (FPGA).

[0085] The processing unit is configured to execute a control method based on a sparse reconstruction algorithm. Upon receiving input of a target optical function, such as a desired laser emission wavelength or a specific filtered spectral shape, the processing unit first executes the sparse reconstruction algorithm.

[0086] The purpose of this algorithm is to identify the fewest possible combination of target units that need to change the phase state among all independently addressable units. By changing the state of this sparsest combination of units, the target optical function can be achieved as close as possible while meeting the accuracy requirements.

[0087] The advantage of this method is that it avoids the need to adjust the state of all units, thereby significantly reducing energy consumption and data processing complexity in the control process. After determining the combination, the processing unit then generates and outputs corresponding control signals, such as a series of electrical pulses with specific parameters, to drive the control structure to apply excitation only to specific units in the combination, thereby reconstructing the optical function of the device.

[0088] According to embodiments of this application, the sparse reconstruction algorithm may specifically include:

[0089] First, initialization is performed. The input target optical function is compared with the initial optical function of the device, which is currently determined by the phase states of all independently addressable cells. The difference between the two is defined as a residual signal. Simultaneously, a candidate cell set for storing the selected cell is initialized, making it an empty set.

[0090] Next, iterative selection is performed. In each iteration, for each independently addressable cell not yet selected into the candidate cell set, its response contribution to the current residual signal when the phase state changes (e.g., from amorphous to crystalline) is calculated. This response contribution can be quantified by correlating the cell's predicted optical response with the residual signal. Then, from all the cells not yet selected, the cell that produces the largest response contribution is identified and added to the candidate cell set.

[0091] Next, residual updates are performed. Based on all cells included in the current candidate cell set, a temporary combined optical function is calculated using the least squares method or other optimization methods. Subsequently, this temporary combined optical function is subtracted from the initial target optical function to update the residual signal.

[0092] Next, the iterative selection and residual update steps are repeated. This repetitive process continues until the amplitude of the residual signal, for example, its L2 norm, decreases below a preset threshold, or the number of iterations reaches a preset maximum value.

[0093] Finally, the determination is completed. When the repetition process terminates, all the units ultimately included in the candidate unit set are determined as the combination of the minimum number of units that need to change the phase state.

[0094] For example, in the upper region superlattice photonic crystal 5 of the topological boundary state photonic crystal laser structure, 100 independently addressable phase change material units are integrated. In the initial state, all units are amorphous, and the initial lasing wavelength of the device is 1550.0 nm. At this time, an external system issues a command to precisely tune the lasing wavelength to 1551.5 nm, which is the "target optical function".

[0095] Upon receiving the instruction, the processing unit executes the sparse reconstruction algorithm, the specific steps of which are as follows:

[0096] First, initialization occurs. The processing unit compares the target wavelength of 1551.5nm with the initial wavelength of 1550.0nm, determining that the required wavelength offset is +1.5nm. This +1.5nm offset constitutes the initial "residual signal." Simultaneously, the "candidate unit set" within the processing unit is cleared.

[0097] Further, in the first iteration of selection and update, the processing unit accesses a pre-stored database that records the offset to the lasing wavelength caused by switching any one of the 100 units individually from an amorphous state to a crystalline state. The processing unit calculates the "response contribution" of each unit's change to reducing the +1.5nm residual.

[0098] For example, calculations revealed that changing the state of cell 52 resulted in the largest blue shift in wavelength, at +0.4 nm. Therefore, the processing unit selected cell 52 and added it to the "candidate cell set." Subsequently, the processing unit updated the "residual signal," and the new target offset became 1.5 nm - 0.4 nm = +1.1 nm.

[0099] The next step is a second iteration of selection and update. The processing unit repeats the above calculation process among the remaining 99 units, searching for the unit that can make the largest contribution to the response of the current +1.1nm residual signal. Suppose that it is found at this time that changing unit number 48 can produce a wavelength shift of +0.38nm. Therefore, unit number 48 is selected into the "candidate unit set". The processing unit then updates the "residual signal" again based on the total shift generated by the combined effect of units number 52 and 48, for example, +0.78nm. The new target shift becomes 1.5nm - 0.78nm = +0.72nm.

[0100] Furthermore, there is repetition and termination. The processing unit continuously repeats the above iterative process, greedily selecting the unit that is most effective in reducing the current residual in each round and adding it to the set, and continuously updating the residual.

[0101] For example, after several iterations, the "candidate unit set" contains four units {52, 48, 55, 45}, whose combined effect results in a total wavelength shift of +1.48 nm. At this point, the updated residual signal is only 1.5 nm - 1.48 nm = +0.02 nm. The processing unit compares the amplitude of this residual (0.02 nm) with a preset precision threshold, such as 0.05 nm. Since 0.02 nm is lower than 0.05 nm, the algorithm's repeated execution terminates.

[0102] Ultimately, the processing unit identifies the four cells {52, 48, 55, 45} from the "candidate cell set" as the combination of the minimum number of cells whose states need to be changed to achieve the target optical function. Subsequently, the processing unit generates and outputs a series of precise electrical or optical excitation signals, which, through a control structure, drive only these four selected cells to undergo a phase transition, while the remaining 96 cells remain unchanged.

[0103] In this way, instead of traversing or calculating all 100 units, a highly efficient iterative optimization process is used to achieve high-precision tuning of the laser wavelength with only 4 unit state changes, thereby greatly saving energy consumption and control time.

[0104] In practical implementation, the selection of integration parameters for phase change materials (PCMs) is closely related to the target operating wavelength and performance requirements of the device.

[0105] For example, in communication bands, such as applications near 1550 nm, low-loss phase change materials such as Sb₂Se₃ or Sb₂S₃ are preferred to reduce the impact on the laser's quality factor. The thickness of the phase change material layer is a critical parameter, typically designed between 20 nm and 60 nm. This thickness requires a trade-off between two aspects: on the one hand, the thickness needs to be sufficient to induce a significant effective refractive index change during the phase transition, thereby providing a sufficiently large tuning range; on the other hand, the thickness should not be too large to avoid introducing excessive optical absorption losses and to ensure that the heat generated by control structures, such as microheaters, can penetrate the entire PCM layer quickly and uniformly.

[0106] For example, the generation of the "predictive optical response" database upon which the sparse reconstruction algorithm relies can be achieved through one or a combination of the following two methods.

[0107] The first approach is based on numerical simulation. During the device design phase, an accurate physical model of the device is established using electromagnetic field simulation software, such as the finite-difference time-domain method or the finite element method. By changing the phase state of each independently addressable unit in the model and calculating its impact on the device's optical functions, such as the resonant wavelength, a complete response matrix or lookup table is generated.

[0108] The second approach is based on experimental calibration. After device fabrication, an automated testing system applies an individual stimulus to each independently addressable cell to induce a phase transition, and equipment such as a spectrometer is used to measure changes in the device's optical function in real time. The database generated by this method automatically incorporates the effects of manufacturing errors, thus providing greater accuracy.

[0109] In practice, the determination of the "preset threshold" in the sparse reconstruction algorithm is determined by the specific application scenario and system performance indicators.

[0110] For example, in dense wavelength division multiplexing (WDM) optical communication applications, the channel spacing might be 100 GHz (approximately 0.8 nm). To avoid inter-channel crosstalk, extremely high precision is required for wavelength tuning. In this case, the threshold can be set to a small fraction of the channel spacing, such as one-tenth, or 0.08 nm.

[0111] In other applications where high precision is not required, this threshold can also be set according to the resolution of the measurement system. If the minimum resolution of the spectrometer used to monitor the wavelength is 0.1 nm, then setting the threshold at a level far below this value is meaningless.

[0112] For example, a control system architecture for a reconfigurable topological boundary state photonic crystal laser may include core components such as a processing unit, a storage unit, a control interface and drive circuitry, a row / column addressing decoder, and a microheater array tightly coupled to multiple independently addressable phase change material (PCM) units. These components work together to form a complete closed-loop control system.

[0113] The processing unit can be a microcontroller (MCU), a digital signal processor (DSP), or a field-programmable gate array (FPGA).

[0114] In a preferred embodiment, an MCU is selected, such as an ARM Cortex-M series microcontroller. The MCU integrates a central processing unit (CPU), flash memory, static random access memory (SRAM), and peripheral interfaces such as SPI, I2C, GPIO, and DAC. The CPU is responsible for executing the firmware program stored in the flash memory, which implements the sparse reconstruction algorithm described above.

[0115] In another embodiment, an FPGA can be used. The advantage of an FPGA lies in its high parallel processing capability. When the number of independently addressable units is very large, for example, thousands or more, an FPGA can compute the response contribution of each unit in parallel, thereby greatly reducing the execution time of the algorithm.

[0116] The storage unit stores a database or response matrix of "predicted optical responses" upon which the sparse reconstruction algorithm relies. This database records the specific impact of each independently addressable unit on the laser's optical characteristics (such as the lasing wavelength) during a phase transition. The storage unit can be integrated within the processing unit, such as the on-chip flash memory of an MCU, or it can be an external non-volatile memory, such as a Flash chip, connected to the processing unit via an SPI or I2C bus.

[0117] The control interface and drive circuitry are responsible for converting the digital logic signals emitted by the processing unit into precise analog electrical pulses capable of driving the microheater to generate the required heat. This circuitry may include:

[0118] Digital-to-analog converter (DAC): Receives digital instructions from the processing unit to precisely set the voltage amplitude of the output pulse.

[0119] Pulse shaping and power amplification circuit: Based on the amplitude set by the DAC and the timing control signal of the processing unit (which determines the pulse width), it generates current pulses with specific shapes, such as low-amplitude, long-duration pulses for crystallization, or high-amplitude, short-duration pulses for amorphization, and sufficient driving capability.

[0120] Regarding the microheater array and addressing mechanism, the phase change material is divided into multiple independently addressable units. This is achieved by fabricating a two-dimensional microheater array near the phase change material layer during the manufacturing process using semiconductor processes such as photolithography and etching. Each microheater, for example, a miniature resistor made of ITO or TiN material, physically corresponds one-to-one with a PCM unit.

[0121] To independently control any one of the heaters in the array, this embodiment employs a matrix addressing mechanism. The micro-heater array is arranged as an M-row, N-column matrix. One end of each heater is connected to its row and the other end is connected to its column.

[0122] For a row / column addressing decoder, the decoder receives an address signal from the processing unit and selects specific row and column lines based on that address. For example, when the processing unit needs to excite the PCM cell located in the i-th row and j-th column, it outputs the address (i, j) to the decoder. The decoder then connects the i-th row line to the output of the drive circuit and grounds the j-th column line (or connects it to another potential), thus forming a complete current loop. The current flows through the micro-heater located at (i, j), generating Joule heating, precisely heating the corresponding PCM cell, and inducing a phase transition.

[0123] For example, the processing unit receives an input for a “target optical function” via an external interface, such as UART or USB, for example, “tuning the laser wavelength to 1551.5nm”.

[0124] The processing unit retrieves the predicted response matrix from the storage unit and executes a sparse reconstruction algorithm. After calculation, the algorithm determines the minimum number of target unit combinations that need to change the phase state and outputs the coordinates of these units in the microheater array, for example, a list: {(i1, j1), (i2, j2), ..., (ik, jk)}.

[0125] The processing unit iterates through the list of coordinates. For each coordinate (i, j), it performs the following operations a~c:

[0126] a. Output address: Send the address (i, j) to the row / column addressing decoder.

[0127] b. Set pulse parameters: Depending on the phase transition type to be achieved (crystallization or amorphization), the system outputs precise digital amplitude and timing control signals to the control interface and drive circuit through its internal timer and DAC peripheral.

[0128] c. Triggering excitation: Send a trigger signal to cause the drive circuit to generate and apply an electrical pulse with preset parameters to the micro heater selected by the decoder.

[0129] After the processing unit sequentially excites all the units in the list, the optical function of the laser is reconstructed to a state that most closely approximates the target function. The entire process is efficient and energy-saving because only a minimal number of units are excited.

[0130] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed in this application can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

Claims

1. A photonic crystal laser based on topological boundary states, characterized in that, include: Substrate; A buffer layer is disposed on the substrate; A lower-layer superlattice photonic crystal is disposed on the buffer layer; The active region is disposed on the superlattice photonic crystal of the lower region. An upper-layer superlattice photonic crystal is disposed on the active region; A capping layer is disposed on the superlattice photonic crystal in the upper region; A contact layer is disposed on the cover layer; The lower-layer superlattice photonic crystal comprises multiple lower-layer photonic crystal periodic units, each of which includes: a lower-layer high-refractive-index layer; and A low-refractive-index layer is disposed on the high-refractive-index layer in the lower region, and multiple lower-layer photonic crystal periodic units are repeatedly arranged. The upper-layer superlattice photonic crystal comprises multiple upper-layer photonic crystal periodic units, and each upper-layer photonic crystal periodic unit includes: Upper region low refractive index layer one; and A high-refractive-index layer is disposed on the low-refractive-index layer in the upper region; and The second low-refractive-index layer in the upper region is disposed on the high-refractive-index layer in the upper region, and multiple periodic units of the upper photonic crystal are repeatedly arranged. At least one layer of at least one periodic unit in the lower region superlattice photonic crystal and / or the upper region superlattice photonic crystal contains a phase change material, the phase state of which can be changed in response to external excitation, thereby tunable photonic band topological properties of the topological boundary state photonic crystal laser structure. The aforementioned photonic crystal laser based on topological boundary states further includes a control structure coupled to the phase change material and configured to apply electrical or optical excitation to the phase change material to controllably induce at least one phase transition between an amorphous state and a crystalline state. The phase change material is divided into multiple independently addressable units, and the control structure further includes a processing unit configured to: in response to input of a target optical function, determine, based on a sparse reconstruction algorithm, a combination of the minimum number of independently addressable units that require a change in the phase state to achieve the target optical function; and generate and output a control signal to drive the control structure to apply excitation only to the units in the combination.

2. The photonic crystal laser based on topological boundary states according to claim 1, characterized in that, The refractive index of the lower low-refractive-index layer is lower than that of the lower high-refractive-index layer, and the thickness of the lower low-refractive-index layer is greater than that of the lower high-refractive-index layer.

3. A photonic crystal laser based on topological boundary states according to claim 1, characterized in that, The refractive index of the active region should be between that of the low-refractive-index layer in the lower region and the high-refractive-index layer in the lower region, and its thickness should be greater than that of the high-refractive-index layer in the upper region.

4. A photonic crystal laser based on topological boundary states according to claim 1, characterized in that, It should also include: An N-type electrode layer is disposed on the lower part of the substrate; and a P-type electrode layer is disposed on the upper surface of the contact layer.

5. A photonic crystal laser based on topological boundary states according to claim 1, characterized in that, The sparse reconstruction algorithm includes the following steps: The difference between the target optical function and the current optical function, which consists of all independently addressable units, is initialized as a residual signal, and the candidate unit set is initialized to empty. Calculate the response contribution of each independently addressable cell that has not yet been selected into the candidate cell set to the residual signal when the phase state changes, and identify and select the cell that produces the largest response contribution from all the independently addressable cells that have not yet been selected, and add it to the candidate cell set. Based on all units in the current candidate unit set, a temporary combined optical function is calculated, and the target optical function is subtracted from the temporary combined optical function to update the residual signal; Repeat the above steps until the amplitude of the residual signal is lower than a preset threshold. The final set of candidate units is determined as the combination of the minimum number of units required to change the phase state.

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