GaSb-based 2.3 m single-frequency semiconductor laser and working method thereof

Abstract

The invention relates to a GaSb-based 2.3 m single-frequency semiconductor laser and a working method thereof, and belongs to the technical field of semiconductors. The GaSb-based 2.3 m single-frequency semiconductor laser comprises a GaSb-based semiconductor laser and an external cavity structure; the GaSb-based semiconductor laser is provided with a main waveguide, the end face away from the outer cavity is provided with a high-reflection layer, and the end face close to the outer cavity is provided with a partial-reflection layer. The outer cavity structure is provided with a micro-ring resonant cavity, the micro-ring resonant cavity is coupled and connected to the main waveguide through a lateral evanescent field, and the high reflection layers and the partial reflection layers on the two sides and the micro-ring resonant cavity form a composite resonant system. The micro-ring resonant cavity and the coating reflection structure are integrated in the GaSb-based semiconductor laser, continuous oscillation of light between the reflection layers at the two ends is achieved, and stable single-frequency 2.3 m laser output is finally obtained by means of the resonance mode selection effect of the micro-ring resonant cavity.

Description

Technical Field

[0001] This invention relates to a GaSb-based 2.3µm single-frequency semiconductor laser and its operating method. Specifically, the semiconductor laser based on the GaSb material system achieves stable single-frequency laser output at a wavelength of 2.3µm, belonging to the field of semiconductor technology. Background Technology

[0002] Gallium antimonide (GaSb) and related material systems (such as AlGaAsSb and InGaAsSb) possess excellent band structure and good lattice matching in the mid-infrared band (2~5µm), making them important material systems for fabricating mid-infrared semiconductor lasers. GaSb-based lasers, due to their high quantum efficiency, room-temperature continuous-wave operation, and strong wavelength designability, have been widely used in gas detection, infrared countermeasures, environmental monitoring, and medical diagnostics.

[0003] Current GaSb-based semiconductor lasers still face numerous technical challenges in achieving stable single-frequency output at the 2.3 µm wavelength. GaSb has low thermal conductivity, leading to heat accumulation during operation. This heat causes changes in cavity length and refractive index, resulting in laser wavelength drift and mode hopping, severely impacting the long-term stability of single-frequency lasers. Furthermore, the gain spectrum of GaSb-based materials deviates from traditional distributed feedback grating designs, resulting in low output power, high threshold current, and short single-frequency hold time, making it difficult to achieve stable single-frequency laser output at 2.3 µm. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention proposes a GaSb-based 2.3µm single-frequency semiconductor laser and its operating method. By integrating a microring resonant cavity and a coated reflective structure into a GaSb-based epitaxial structure, continuous oscillation of light between the two reflective layers is achieved. Furthermore, by utilizing the resonant mode selection effect of the microring cavity, a stable single-frequency 2.3µm laser output is finally obtained.

[0005] The present invention adopts the following technical solution:

[0006] A GaSb-based 2.3µm single-frequency semiconductor laser includes a GaSb-based semiconductor laser and an external cavity structure disposed at the output end of the GaSb-based semiconductor laser. The epitaxial structure of the GaSb-based semiconductor laser includes, from top to bottom, an anode, a contact layer, an upper confinement layer, an active region, a lower confinement layer, and a substrate, and a cathode electrode is formed at the bottom of the substrate.

[0007] The GaSb-based semiconductor laser has a main waveguide, a high-reflectivity layer on the end face away from the external cavity structure, and a partial-reflectivity layer on the end face closer to the external cavity structure. A micro-ring resonator is provided on the external cavity structure, and the micro-ring resonator is connected to the main waveguide through lateral evanescent field coupling to provide narrowband feedback and mode selection for the external cavity structure. The high-reflectivity layer, the partial-reflectivity layer, and the micro-ring resonator on both sides form a composite resonant system. The light oscillates continuously between the high-reflectivity layer and the partial-reflectivity layer, and with the help of the resonant mode selection effect of the micro-ring resonator, a stable single-frequency 2.3 µm laser output is finally obtained.

[0008] In this invention, the micro-ring resonator is arranged as an external cavity structure independent of the main cavity (GaSb-based semiconductor laser) at the laser's side emission port. It is connected to the main waveguide through lateral evanescent field coupling, forming an external cavity feedback device based on on-chip integrated optics, achieving high Q mode selection and narrow linewidth output.

[0009] By adjusting the radius and equivalent refractive index, the resonant wavelength of the microring can be precisely adjusted to achieve accurate matching with the longitudinal modes allowed by the main cavity, thus realizing single-frequency output.

[0010] Preferably, the active region of the GaSb-based semiconductor laser adopts a multi-quantum-well structure, which includes multiple quantum well units. The multi-quantum-well (MQW) structure is a semiconductor structure formed by the alternating superposition of multiple thin quantum well layers and barrier layers.

[0011] Each quantum well unit comprises a quantum well layer and a barrier layer. The quantum well layer is made of GaInAsSb, and the barrier layer is made of AlGaAsSb. The quantum well layer serves as the light-emitting layer; this structure helps to balance the injection efficiency of electrons and holes and is a key technology for reducing the threshold current. The barrier layer provides a barrier to confine charge carriers and is also the core layer of the optical waveguide.

[0012] The quantum well layer and the barrier layer together form a quantum well unit. In lasers, the number of quantum wells should not be too many or too few. Therefore, in this invention, the laser uses five quantum wells to achieve a good balance between obtaining sufficient optical gain and maintaining uniform carrier injection. By designing and matching the GaSb-based multiple quantum well (MQW) active layer, the gain peak of the GaInAsSb / AlGaAsSb multiple quantum well (MQW) structure can be precisely located in the 2.3 μm band through band engineering design.

[0013] The bandgap of the quantum well layer material GaInAsSb is continuously adjustable by the ratio of In and Sb components. As the In and Sb contents increase, the bandgap decreases, and the emission wavelength shifts towards longer wavelengths. This invention, by precisely controlling the In / Sb content, ensures that the gain peak corresponding to the quantum well layer bandgap falls precisely in the 2.3 μm band.

[0014] The barrier layer employs the high-bandgap material AlGaAsSb. By adjusting its Al content, the barrier height is optimized, thereby stabilizing the carrier distribution and suppressing peak drift caused by temperature changes. Simultaneously, this invention achieves minute compressive and tensile strains through synergistic material composition design and layer thickness control. Specifically, in the quantum well layer, by appropriately increasing the In and Sb composition ratio, the lattice constant of the GaInAsSb quantum well material is made slightly larger than that of the GaSb substrate, thus introducing minute compressive strain into the quantum well layer. Correspondingly, in the barrier layer, by increasing the Al content and adjusting the As / Sb ratio, the lattice constant of the AlGaAsSb barrier layer is made slightly smaller than that of the GaSb substrate, thus introducing minute tensile strain into the barrier layer. During epitaxial growth, the quantum well layer and barrier layer grow alternately and periodically, with compressive and tensile strains canceling each other out within one cycle, achieving strain compensation and balance in the overall structure.

[0015] This invention employs a strain compensation design, which introduces a small compressive strain in the quantum well and a corresponding tensile strain in the potential barrier to achieve overall strain balance, improve the stability of the band structure, and avoid the shift in the position of the gain peak caused by strain relaxation. This ensures that the gain peak is precisely located in the 2.3µm band and can match the wavelength of the micro-ring resonator, thereby guaranteeing the conditions for single-frequency oscillation.

[0016] Preferably, the material of the quantum well layer is Ga. x In 1-x As y Sb 1-y The value of x ranges from 0.7 to 0.9, and the value of y ranges from 0.01 to 0.2.

[0017] Preferably, the microring resonator is made of Ta2O5, SiC or Si3N4 material. By designing the refractive index, waveguide width and radius of the microring resonator material, the wavelength of its main resonant mode coincides with the 2.3 μm gain peak of the active region.

[0018] Preferably, the laser's two ends are coated as reflective layers. The high-reflectivity layer is made of a material selected from Ta2O5, Nb2O5, Si, and ZnS, with a reflectivity ≥ 95%. The partial-reflectivity layer is made of a material selected from SiO2 and Al2O3, with a reflectivity of 20–40%. The coatings on both sides and the microring resonant cavity form a composite resonant system. The light oscillates between the two reflective films and is coupled with the microring, ultimately achieving mode suppression and frequency stabilization. This improves the laser's output power and spectral purity, thereby significantly enhancing the device's performance.

[0019] Preferably, the substrate is an n-type GaSb single crystal substrate, and the contact layer is located on the top layer, using highly doped p-GaSb, to form a good ohmic contact with the anode;

[0020] The upper confinement layer is p-type doped, and the lower confinement layer is n-type doped. Both the lower and upper confinement layers are made of Al. 0.5 Ga 0.5 As 0.04 Sb 0.96 .

[0021] Preferably, the active region is grown using molecular beam epitaxy (MBE) technology, and the growth temperature needs to be strictly controlled between 490-520℃, with a V / III ratio of approximately 5:1.

[0022] Preferably, the outer cavity structure is made of SiO2 or silicon carbide material, and the micro-ring resonator is composed of a micro-ring and a straight waveguide.

[0023] This invention introduces a microring resonant cavity structure into a GaSb-based semiconductor laser and combines it with a double-ended coated reflective cavity surface to form a composite resonant system. This allows light to oscillate and reflect multiple times within the cavity, achieving high selective feedback and single-frequency locking. The GaSb-based multiple quantum well (MQW) active layer of this invention achieves high-gain emission at a wavelength of 2.3 µm through bandgap design and strain compensation of the GaInAsSb / AlGaAsSb heterostructure, precisely matching the mode resonance conditions with the microring resonant cavity. By meticulously designing the refractive index, waveguide width, and radius of the microring material, the wavelength of its main resonant mode coincides with the 2.3 μm gain peak of the MQW active region, ensuring higher feedback of the longitudinal mode corresponding to this wavelength in the external cavity, thereby guaranteeing stable single-frequency laser output in this wavelength band.

[0024] A method for operating the aforementioned GaSb-based 2.3µm single-frequency semiconductor laser involves first injecting an external driving current from the anode, which then passes through the upper confinement layer into the active region. Electrons and holes undergo radiative recombination in the quantum well, generating spontaneous emission light. When the intracavity optical gain reaches the intracavity loss, the GaSb-based semiconductor laser enters a stimulated emission state and forms a stable oscillation, generating laser output in the 2.3 μm band.

[0025] A portion of the light output from the GaSb-based semiconductor laser (main cavity) enters the external cavity structure through the side emitter and couples with the evanescent field of the microring resonator located near the output. When the wavelength of the incident light satisfies the standing wave resonance condition with the microring resonator, the light will undergo cyclic amplification inside the microring. Light that does not meet the resonance condition will rapidly attenuate because it cannot form a stable standing wave in the microring. The microring resonator only provides narrowband enhancement feedback for light that matches its resonance wavelength. This feedback signal is then injected into the GaSb-based semiconductor laser, enabling this specific longitudinal mode to obtain a higher net gain than other longitudinal modes.

[0026] Under repeated cycles, the coupling between the GaSb-based semiconductor laser and the microring resonator selectively amplifies the longitudinal modes that match the microring resonant mode, while the mismatched longitudinal modes are gradually suppressed due to insufficient gain. Through this co-selection mechanism of the main cavity and the external cavity, the laser ultimately retains only a single longitudinal mode oscillation, achieving a narrow linewidth and high stability 2.3μm single-frequency output.

[0027] Furthermore, the microring resonator possesses a high Q value, which significantly increases the residence time of light in the external cavity, thereby further narrowing the spectral linewidth and reducing frequency noise. If the output wavelength needs to be adjusted, the effective refractive index can be changed by applying a control voltage to the microring heating electrode, thus fine-tuning the microring resonant wavelength to achieve precise control of the laser output frequency.

[0028] In summary, the working method of this invention combines the main cavity gain mechanism, cavity surface reflection feedback, and the narrow-band mode selection effect of the micro-ring resonant external cavity, enabling the laser to achieve high-purity, narrow-linewidth single-frequency laser output in the 2.3 μm band, with excellent frequency stability and anti-mode hopping capability.

[0029] For any details not covered in this invention, please refer to the prior art.

[0030] The beneficial effects of this invention are as follows:

[0031] 1. This invention introduces a micro-ring resonant cavity structure. The micro-ring resonant cavity is fabricated using dielectric materials with extremely low intrinsic absorption, such as Si3N4, which significantly reduces the absorption loss of light propagating in the waveguide compared to semiconductor materials, thereby effectively preserving the optical energy within the cavity. Since the micro-ring itself forms a closed ring optical path, light can repeatedly circulate within it, resulting in a longer residence time for the optical field within the cavity. Energy is continuously accumulated during this circulation, ultimately forming a highly selective and stable resonant mode. The micro-ring resonant cavity of this invention enables the optical field within the resonant cavity to satisfy the high Q-value resonance condition, allowing for precise selection of a single longitudinal mode from a broad material gain spectrum, achieving high-purity single-frequency laser output.

[0032] 2. This invention forms a composite feedback system of "reflective layer + micro-ring resonator", which improves output stability. By coating reflective films at both ends of the laser, which work together with the micro-ring resonator, the energy coupling and standing wave stability of the optical field within the cavity are enhanced, effectively suppressing mode hopping and resulting in a more stable output spectrum.

[0033] 3. The multi-quantum well structure of the present invention has uniform thickness and is a periodic structure. By precisely controlling the In / Sb content, the gain peak corresponding to the bandgap of the quantum well layer falls precisely in the 2.3 μm band, which can match the wavelength of the micro-ring resonator, thereby ensuring the conditions for single-frequency oscillation and significantly improving the probability of stimulated emission. Furthermore, by optimizing the epitaxial layer structure and heat dissipation design, the heat accumulation in the cavity is reduced, the influence of temperature changes on the cavity length and refractive index is suppressed, and wavelength drift and mode hopping phenomena are reduced. Attached Figure Description

[0034] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments of this application and their descriptions are used to explain this application and do not constitute an undue limitation of this application.

[0035] Figure 1 This is a schematic cross-sectional view of the epitaxial structure of the GaSb-based semiconductor laser of the present invention;

[0036] Figure 2 This is a schematic diagram of the overall structure of the GaSb-based 2.3µm single-frequency semiconductor laser of the present invention. Detailed Implementation

[0037] To enable those skilled in the art to better understand the technical solutions in this specification, the technical solutions in the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. However, this is not the only description; all aspects not described in detail herein are based on conventional techniques in the art.

[0038] Semiconductor lasers are devices that use semiconductor materials as the gain medium and achieve optical amplification through stimulated emission. Due to their advantages such as compact structure, fast response speed, high conversion efficiency, and ease of integration, they have been widely used in various fields including optical communication, spectral detection, ranging, medical diagnostics, and environmental monitoring. However, traditional semiconductor lasers also have some limitations during operation, such as significant thermal effects, strong temperature sensitivity, severe multimode competition, and unstable output wavelength. These factors cause the device's performance to degrade during continuous operation, especially in the mid-infrared band.

[0039] In the field of mid-infrared (approximately 2–3 micrometers or even longer) optoelectronic devices, gallium antimonide (GaSb)-based materials are an important area of ​​current research and application. GaSb is a direct bandgap semiconductor with a large lattice constant, enabling excellent lattice matching with various antimony-containing quaternary alloys such as GaInAsSb and AlGaAsSb. This characteristic makes it an ideal substrate material for the epitaxial growth of mid-infrared lasers. Compared to gallium arsenide (GaAs) or indium phosphide (InP) systems, GaSb-based materials exhibit lower nonradiative recombination rates and better carrier confinement capabilities in the mid-infrared band, thus possessing unique advantages in realizing high-efficiency, low-threshold mid-infrared lasers.

[0040] This invention, based on this material system, proposes a structurally optimized GaSb-based semiconductor laser and its operating method. This laser achieves single-frequency continuous-wave output in the 2.3-micron wavelength band by introducing a multiple quantum well (MQW) structure in the active region and combining it with a highly selective optical feedback mechanism of a microring resonator. It not only exhibits excellent performance in terms of output power, spectral stability, and linewidth control, but also significantly improves upon the problems of strong thermal effects and mode instability inherent in traditional mid-infrared lasers.

[0041] Example 1

[0042] A GaSb-based 2.3µm single-frequency semiconductor laser, such as Figure 2 As shown, the diagram includes a GaSb-based semiconductor laser and an external cavity structure disposed at the output end of the GaSb-based semiconductor laser. The epitaxial structure of the GaSb-based semiconductor laser, from top to bottom, includes an anode, a contact layer, an upper confinement layer, an active region, a lower confinement layer, and a substrate. A cathode electrode is formed at the bottom of the substrate. Figure 1 As shown;

[0043] The GaSb-based semiconductor laser has a main waveguide. A high-reflectivity layer is located on the end face of the GaSb-based semiconductor laser away from the external cavity structure, and a partial-reflectivity layer is located on the end face of the GaSb-based semiconductor laser closer to the external cavity structure. A micro-ring resonator is located on the external cavity structure and is connected to the main waveguide through lateral evanescent field coupling to provide narrowband feedback and mode selection for the external cavity structure. The high-reflectivity layer, the partial-reflectivity layer, and the micro-ring resonator form a composite resonant system. The light oscillates continuously between the high-reflectivity layer and the partial-reflectivity layer, and with the help of the resonant mode selection effect of the micro-ring resonator, a stable single-frequency 2.3 µm laser output is finally obtained. The overall structure is compact, clearly hierarchical, and combines electrical conductivity and optical confinement.

[0044] In this invention, the micro-ring resonator is arranged as an external cavity structure independent of the main cavity (GaSb-based semiconductor laser) at the laser's side emission port. It is connected to the main waveguide through lateral evanescent field coupling, forming an external cavity feedback device based on on-chip integrated optics, achieving high Q mode selection and narrow linewidth output.

[0045] By adjusting the radius and equivalent refractive index, the resonant wavelength of the microring can be precisely adjusted to achieve accurate matching with the longitudinal modes allowed by the main cavity, thus realizing single-frequency output.

[0046] Example 2

[0047] A GaSb-based 2.3µm single-frequency semiconductor laser, as described in Example 3, differs in that the active region of the GaSb-based semiconductor laser adopts a multi-quantum well structure, including multiple quantum well units. The multi-quantum well (MQW) structure is a semiconductor structure formed by the alternating superposition of multiple thin quantum well layers and barrier layers.

[0048] Each quantum well unit comprises a quantum well layer and a barrier layer. The quantum well layer is made of GaInAsSb, and the barrier layer is made of AlGaAsSb. The quantum well layer serves as the light-emitting layer; this structure helps to balance the injection efficiency of electrons and holes and is a key technology for reducing the threshold current. The barrier layer provides a barrier to confine charge carriers and is also the core layer of the optical waveguide.

[0049] The quantum well layer and the barrier layer together form a quantum well unit. In lasers, the number of quantum wells should not be too many or too few. Therefore, in this invention, the laser uses five quantum wells to achieve a good balance between obtaining sufficient optical gain and maintaining uniform carrier injection. By designing and matching the GaSb-based multiple quantum well (MQW) active layer, the gain peak of the GaInAsSb / AlGaAsSb multiple quantum well (MQW) structure can be precisely located in the 2.3 μm band through band engineering design.

[0050] The bandgap of the quantum well layer material GaInAsSb is continuously adjustable by the ratio of In and Sb components. As the In and Sb contents increase, the bandgap decreases, and the emission wavelength shifts towards longer wavelengths. This invention, by precisely controlling the In / Sb content, ensures that the gain peak corresponding to the quantum well layer bandgap falls precisely in the 2.3 μm band.

[0051] The barrier layer employs the high-bandgap material AlGaAsSb. By adjusting its Al content, the barrier height is optimized, thereby stabilizing the carrier distribution and suppressing peak drift caused by temperature changes. Simultaneously, this invention achieves minute compressive and tensile strains through synergistic material composition design and layer thickness control. Specifically, in the quantum well layer, by appropriately increasing the In and Sb composition ratio, the lattice constant of the GaInAsSb quantum well material is made slightly larger than that of the GaSb substrate, thus introducing minute compressive strain into the quantum well layer. Correspondingly, in the barrier layer, by increasing the Al content and adjusting the As / Sb ratio, the lattice constant of the AlGaAsSb barrier layer is made slightly smaller than that of the GaSb substrate, thus introducing minute tensile strain into the barrier layer. During epitaxial growth, the quantum well layer and barrier layer grow alternately and periodically, with compressive and tensile strains canceling each other out within one cycle, achieving strain compensation and balance in the overall structure.

[0052] This invention employs a strain compensation design, introducing minute compressive strain in the quantum well and corresponding tensile strain in the potential barrier to achieve overall strain balance, thereby improving the stability of the band structure and avoiding gain peak position shift caused by strain relaxation. This ensures the gain peak is precisely located in the 2.3µm band and can match the wavelength of the microring resonator, thus guaranteeing single-frequency oscillation.

[0053] The active region employs a multi-quantum-well structure, which consists of multiple alternating quantum well layers and barrier layers. The design philosophy of the multi-quantum-well system is to enhance carrier recombination efficiency through spatial confinement effects. Each quantum well acts like a tiny "energy trap," confining injected electrons and holes to a lower-energy well, making them less likely to escape. This significantly increases the probability of carrier recombination, thereby increasing the number of photons generated. By periodically arranging multiple such wells, a highly efficient gain region is formed, enabling the laser to achieve threshold lasing at relatively low currents. The quantum well layers are made of Ga, a material with a small bandgap. x In 1-x As y Sb 1-yThe values ​​of x and y range from 0.7 to 0.9, and y range from 0.01 to 0.2, respectively. The y layer is primarily used as the light-emitting layer and serves as the main gain source. The barrier layer is made of AlGaSb, a material with a large bandgap, and its main function is to confine charge carriers and prevent their leakage. These two materials have very similar lattice constants, allowing for smooth growth on the GaSb substrate without significant lattice mismatch. Although the lattice constants of the different materials are similar, subtle differences still exist. To avoid lattice defects caused by strain accumulation, this invention employs a strain compensation design. The quantum well layer has a small compressive strain, while the barrier layer has a tensile strain in the opposite direction. The alternating superposition of these two strains leads to an overall strain equilibrium. This design ensures a smooth interface and a complete lattice while preventing dislocation propagation, thus maintaining good thermal stability during continuous operation. The active region is mainly grown using molecular beam epitaxy (MBE) technology, with the growth temperature strictly controlled between 490-520℃ and a V / III ratio of approximately 5:1. During the growth process, RHEED (Reflected High Energy Electron Diffraction) is used to monitor surface reconstruction in real time to ensure layer thickness accuracy and interface smoothness. Alternating growth of quantum well layers and barrier layers is performed according to the design, which also effectively improves the temperature characteristics of the laser. Due to the presence of the barrier layer, electrons and holes are less likely to escape from the luminescent region when the temperature rises, thus maintaining high luminous efficiency. Compared with traditional single-layer active structures, the multi-quantum well design of this invention enables the laser to maintain stable output over a wider temperature range, improving the temperature stability and lifetime of the laser during continuous wave (CW) operation.

[0054] Example 3

[0055] A GaSb-based 2.3µm single-frequency semiconductor laser, as described in Example 2, differs in that the micro-ring resonator is one of the key innovations of this invention. It achieves frequency selection through the cyclic resonance of light in a ring waveguide, thereby ensuring that the laser outputs light of a single wavelength. Its fabrication method includes three steps: photolithography, etching, and cladding deposition. First, photoresist is spin-coated onto the sample surface, and a mask is used to define the micro-ring and main waveguide pattern. Then, reactive ion etching (ICP-RIE) technology is used to transfer the pattern to the semiconductor layer, with the etching depth controlled within the thickness range of the optical waveguide to form lateral optical confinement. The micro-ring resonator can be made of at least one material selected from Ta2O5, SiC, and Si3N4; in specific embodiments, one of these materials is preferred as the core material of the micro-ring waveguide, combined with cladding materials such as SiO2 to reduce scattering loss and improve thermal stability and long-term reliability. These materials not only enable the micro-ring to be smaller and more integrated, but also further improve the selectivity of filtering, provide higher external cavity feedback quality, and improve thermal stability. To further reduce scattering loss on the waveguide sidewalls and protect the device structure, a layer of silicon dioxide is typically grown as the top cladding using chemical vapor deposition (CVD). This cladding more tightly confines the optical field within the waveguide and protects the microring from environmental dust and moisture, thus ensuring its long-term stability and reliability. By precisely controlling the microring radius and refractive index, the quality factor of the microring can be further improved, resulting in a narrower output linewidth and better coherence. The microring radius is typically on the order of tens of micrometers; by adjusting the radius and waveguide width, the resonant mode spacing can be precisely controlled. A very small gap is maintained between the microring and the main waveguide, utilizing evanescent fields to achieve energy coupling. When the frequency of the light wave in the main waveguide matches the resonant frequency of the microring, the light energy forms a strong cyclic resonance within the microring, while mismatched wavelengths are naturally suppressed. This optical feedback mechanism is equivalent to embedding a frequency selector in the main resonant cavity, thereby achieving single-frequency output.

[0056] Example 4

[0057] A GaSb-based 2.3µm single-frequency semiconductor laser, as described in Example 3, differs in that reflective layers are formed at both ends of the laser using dielectric coating technology. The high-reflectivity layer is made of a material selected from Ta2O5, Nb2O5, Si, and ZnS, with a reflectivity ≥ 95%, used to reflect most of the light back into the cavity to maintain the optical feedback required for stimulated emission. The partial-reflectivity layer is made of a material selected from SiO2 and Al2O3, with a reflectivity of 20–40%, used for outputting the laser signal. The coatings on both sides and the microring resonant cavity form a composite resonant system. The light oscillates between the two reflective films and is simultaneously coupled with the microring, ultimately achieving mode suppression and frequency stabilization. This improves the laser's output power and spectral purity, thereby significantly enhancing the device's performance.

[0058] In this embodiment, by adjusting the thickness and refractive index of the reflective layer, an optimal balance between reflectivity and transmittance can be achieved. This combination of a "high-reflectivity end + output end" constitutes the main resonant cavity of the laser, forming a composite feedback structure together with the micro-ring resonant cavity. This design makes the laser more mode-selective, and the output light frequency more singular and stable. The synergistic effect of the two cavities effectively suppresses multimode competition, resulting in an extremely narrow output spectral linewidth and extremely high frequency stability.

[0059] Example 5

[0060] A GaSb-based 2.3µm single-frequency semiconductor laser, as described in Example 4, differs in that the substrate is an n-type GaSb single-crystal substrate. This substrate possesses excellent lattice matching and flatness, which is a crucial foundation for subsequent epitaxial growth. Before growth, the substrate undergoes rigorous cleaning and degassing to remove surface contaminants and oxide layers, ensuring the quality of the epitaxial layers. Subsequently, the substrate is placed in a molecular beam epitaxy system, and each layer of semiconductor material is sequentially grown under ultra-high vacuum conditions.

[0061] The contact layer, located on the top layer, is made of highly doped p-GaSb to form a good ohmic contact with the anode, thereby achieving stable current injection. The design of the top and bottom electrodes is equally important in lasers: it must ensure low contact resistance while preventing excessive absorption of emitted light.

[0062] The main function of the lower and upper confinement layers is to confine charge carriers (electrons and holes) and the optical field within the active region. The upper and lower confinement layers are grown using an MBE device. The upper confinement layer is p-type doped, and the lower confinement layer is n-type doped. Both layers are made of Al. 0.5 Ga 0.5 As 0.04 Sb 0.96 During the growth process, attention should be paid to the cleaning of the substrate and the growth temperature and V / III beam ratio should be precisely controlled to ensure that epitaxial materials with steep interfaces, low defect density and precise composition can be grown.

[0063] During device fabrication, all semiconductor layers are grown using molecular beam epitaxy. This method allows for atomic-level control of growth thickness and material composition, ensuring smooth interfaces and accurate thickness at each layer.

[0064] Example 6

[0065] A GaSb-based 2.3µm single-frequency semiconductor laser, as described in Example 5, differs in that the external cavity structure is made of SiO2 or silicon carbide material, and the micro-ring resonant cavity is composed of a micro-ring and a straight waveguide.

[0066] Example 7

[0067] A method for operating a GaSb-based 2.3µm single-frequency semiconductor laser is described. In operation, the laser is driven by a constant current source. First, an external driving current is injected from the anode, passes through the upper confinement layer, and enters the active region. Electrons and holes undergo radiative recombination in the quantum well, generating spontaneous emission light. When the intracavity optical gain reaches the intracavity loss, the GaSb-based semiconductor laser enters a stimulated emission state and forms a stable oscillation, generating laser output in the 2.3 μm band.

[0068] A portion of the light output from the GaSb-based semiconductor laser (main cavity) enters the external cavity structure through the side emitter and couples with the evanescent field of the microring resonator located near the output. When the wavelength of the incident light satisfies the standing wave resonance condition with the microring resonator, the light will undergo cyclic amplification inside the microring. Light that does not meet the resonance condition will rapidly attenuate because it cannot form a stable standing wave in the microring. The microring resonator only provides narrowband enhancement feedback for light that matches its resonance wavelength. This feedback signal is then injected into the GaSb-based semiconductor laser, enabling this specific longitudinal mode to obtain a higher net gain than other longitudinal modes.

[0069] Under repeated cycles, the coupling between the GaSb-based semiconductor laser and the microring resonator selectively amplifies the longitudinal modes that match the microring resonant mode, while the mismatched longitudinal modes are gradually suppressed due to insufficient gain. Through this co-selection mechanism of the main cavity and the external cavity, the laser ultimately retains only a single longitudinal mode oscillation, achieving a narrow linewidth and high stability 2.3μm single-frequency output.

[0070] In this embodiment, during operation, the laser is driven by a constant current source, with current injected from the p-type electrode, passing through the active region to the n-type layer. Electrons and holes meet and recombine in the quantum well, releasing photons. These photons are reflected back and forth within the cavity, receiving further amplification each time they pass through the active region. When the optical gain reaches the cavity loss, the system enters stimulated emission, generating laser output. Simultaneously, the micro-ring resonator selectively selects the frequency of the light, allowing only specific wavelengths to form stable standing waves within the cavity, while suppressing other wavelengths. Furthermore, the presence of the micro-ring resonator significantly reduces the cavity linewidth. The light circulates multiple times within the micro-ring, effectively "extending" the path length and increasing the equivalent cavity length, thereby reducing the mode spacing and narrowing the spectral linewidth. Combined with a high-reflectivity coating and optical cladding design, the optical loss of the entire system is minimized, the quality factor of the resonator is improved, and the coherence of the output light is significantly enhanced. Thus, the laser output spectrum contains only a single frequency of light, achieving single-frequency lasing.

[0071] Compared to traditional lasers, this invention significantly improves mode selectivity by introducing a microring resonant cavity, avoiding multimode competition. Simultaneously, the multi-quantum-well active region structure enhances carrier recombination efficiency, resulting in a lower threshold current and higher output efficiency. To further reduce heat accumulation, the thicknesses of the active region and confinement layer are optimized to achieve uniform current distribution and moderate power density. The microring cladding material possesses excellent thermal conductivity, further facilitating heat diffusion and dissipation. Through these combined measures, the laser maintains stable operating temperature and output power during continuous operation. Due to the precise matching between the active region's band structure and the resonant cavity modes, the output wavelength is stable and has an extremely narrow linewidth, preventing significant wavelength drift.

[0072] The GaSb-based semiconductor laser of this invention possesses advantages such as high spectral purity, excellent temperature characteristics, and stable single-frequency output, making it particularly suitable for applications such as mid-infrared gas absorption spectroscopy detection, high-precision optical ranging, infrared communication, and optical radar. By adjusting the material composition of the quantum well and the size of the microrings, the emission wavelength can be extended to the 2–4 μm range to meet different application requirements.

[0073] From a manufacturing perspective, all key processes in this invention are based on standard semiconductor processing equipment, enabling high consistency and large-scale production. Its low power consumption, high reliability, and long lifespan make it widely applicable in industrial, scientific research, and defense fields.

[0074] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A GaSb-based 2.3µm single-frequency semiconductor laser, characterized in that, The invention includes a GaSb-based semiconductor laser and an external cavity structure disposed at the output end of the GaSb-based semiconductor laser. The epitaxial structure of the GaSb-based semiconductor laser, from top to bottom, includes an anode, a contact layer, an upper confinement layer, an active region, a lower confinement layer, and a substrate, and a cathode electrode is formed at the bottom of the substrate. The GaSb-based semiconductor laser has a main waveguide, a high-reflectivity layer on the end face away from the external cavity structure, and a partial-reflectivity layer on the end face closer to the external cavity structure. A micro-ring resonator is provided on the external cavity structure, and the micro-ring resonator is connected to the main waveguide through lateral evanescent field coupling to provide narrowband feedback and mode selection for the external cavity structure. The high-reflectivity layer, the partial-reflectivity layer, and the micro-ring resonator on both sides form a composite resonant system. The light oscillates continuously between the high-reflectivity layer and the partial-reflectivity layer, and with the help of the resonant mode selection effect of the micro-ring resonator, a stable single-frequency 2.3 µm laser output is finally obtained.

2. The GaSb-based 2.3µm single-frequency semiconductor laser according to claim 2, characterized in that, The active region of the GaSb-based semiconductor laser adopts a multi-quantum-well structure, including multiple quantum well units. Each quantum well unit includes a quantum well layer and a barrier layer. The quantum well layer is made of GaInAsSb, and the barrier layer is made of AlGaAsSb.

3. The GaSb-based 2.3µm single-frequency semiconductor laser according to claim 2, characterized in that, The number of quantum well units is 5. The band gap of the quantum well layer material GaInAsSb is continuously adjustable by the composition ratio of In and Sb. By precisely controlling the In / Sb content, the gain peak corresponding to the quantum well layer band gap falls precisely in the 2.3 μm band and can match the wavelength of the micro-ring resonator, thus ensuring the conditions for single-frequency oscillation. The barrier layer optimizes the barrier height by adjusting the Al content, thereby stabilizing the carrier distribution and suppressing peak drift caused by temperature changes.

4. The GaSb-based 2.3µm single-frequency semiconductor laser according to claim 3, characterized in that, The quantum well layer is made of Ga x In 1-x As y Sb 1-y The value of x ranges from 0.7 to 0.9, and the value of y ranges from 0.01 to 0.

2.

5. The GaSb-based 2.3µm single-frequency semiconductor laser according to claim 4, characterized in that, The microring resonator is made of Ta2O5, SiC or Si3N4 material. By designing the refractive index, waveguide width and radius of the microring resonator material, the wavelength of its main resonant mode coincides with the 2.3 μm gain peak of the active region.

6. The GaSb-based 2.3µm single-frequency semiconductor laser according to claim 5, characterized in that, The material of the high-reflectivity layer is selected from one of Ta2O5, Nb2O5, Si, and ZnS, with a reflectivity ≥ 95%. The material of the partial-reflectivity layer is selected from one of SiO2 and Al2O3, with a reflectivity of 20–40%.

7. The GaSb-based 2.3µm single-frequency semiconductor laser according to claim 6, characterized in that, The substrate is an n-type GaSb single crystal substrate, and the contact layer is located on the top layer. It uses highly doped p-GaSb to form a good ohmic contact with the anode. The upper confinement layer is p-type doped, and the lower confinement layer is n-type doped. Both the lower and upper confinement layers are made of Al. 0.5 Ga 0.5 As 0.04 Sb 0.96 .

8. The GaSb-based 2.3µm single-frequency semiconductor laser according to claim 7, characterized in that, The active region is grown using molecular beam epitaxy, with the growth temperature controlled at 490-520℃ and the V / III ratio at 5:

1.

9. The GaSb-based 2.3µm single-frequency semiconductor laser according to claim 8, characterized in that, The external cavity structure is made of SiO2 or silicon carbide material, and the micro-ring resonant cavity is composed of a micro-ring and a straight waveguide.

10. A method for operating the GaSb-based 2.3µm single-frequency semiconductor laser according to any one of claims 1-9, characterized in that, First, an external driving current is injected from the anode, passes through the upper confinement layer and enters the active region. Electrons and holes undergo radiative recombination in the quantum well, generating spontaneous emission light. When the intracavity optical gain reaches the intracavity loss, the GaSb-based semiconductor laser enters the stimulated emission state and forms a stable oscillation, generating laser output in the 2.3 μm band. A portion of the light output from the GaSb-based semiconductor laser enters the external cavity structure through the side emitter and couples with the evanescent field of the microring resonator located near the output. When the wavelength of the incident light satisfies the standing wave resonance condition of the microring resonator, the light will undergo cyclic amplification inside the microring. Light that does not meet the resonance condition will rapidly attenuate because it cannot form a stable standing wave in the microring. The microring resonator only provides narrowband enhancement feedback for light that matches its resonance wavelength, and this feedback signal is then injected into the GaSb-based semiconductor laser. Under repeated cycles, the coupling between the GaSb-based semiconductor laser and the microring resonator selectively amplifies the longitudinal mode that matches the microring resonant mode, while the mismatched longitudinal modes are gradually suppressed due to insufficient gain. Ultimately, the laser retains only a single longitudinal mode oscillation, achieving a narrow linewidth and high stability 2.3μm single-frequency output.

Images