Miniaturized adjustment-free ultra-narrow linewidth composite filtering external cavity semiconductor laser

Abstract

The invention discloses a miniaturized adjustment-free ultra-narrow linewidth composite filtering external cavity semiconductor laser, which belongs to the field of semiconductor lasers and is sequentially provided with a gain chip, an aspherical lens, a first FP etalon, a second FP etalon, an interference filter, a partial reflector, an optical isolator and a polarization maintaining optical fiber collimator. Wherein the first FP etalon and the second FP etalon are superposed in a non-coaxial mode to form a free spectral range difference, a longitudinal mode interval difference is generated through a Vernier effect, and a longitudinal mode interval generated by the Vernier effect is controlled by adjusting a dip angle difference between the first FP etalon and the second FP etalon. Through machining precision, optical coupling optimization and an automatic assembly technology, the problems of wide tuning bandwidth, ultra-narrow linewidth, multi-dimensional performance collaboration and environmental adaptability are synchronously solved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor lasers, and more particularly to a miniaturized, adjustment-free, ultra-narrow linewidth composite filter external cavity semiconductor laser. Background Technology

[0002] In existing technologies, conventional external cavity semiconductor lasers (ECDLs) generally employ a single Fabry-Pérot (FP) cavity structure, with a typical free spectral range (FSR) of 10-20 GHz and a reflectivity of approximately 95%. When the tuning range exceeds 3 nm, the mode-hopping frequency reaches 1.2 times / minute, and the side-mode rejection ratio is below 30 dB (test conditions: 10 Gbps transmission rate). The longitudinal mode spacing of this structure is only 1 / 10 of that of the conventional single FP structure, which cannot meet the requirements of spectral purity (>50 dB) and wavelength stability (±0.05 nm) for 10 Gbps high-speed transmission. Furthermore, the single FP cavity structure suffers from high mode-hopping frequencies and insufficient side-mode rejection ratios in multi-band applications, making it difficult to simultaneously meet the requirements of spectral purity and wavelength stability.

[0003] Grating-type external cavity lasers achieve wavelength selection through grating diffraction. Their linewidth is limited by the grating's dispersion characteristics (typically 12 kHz), and the tuning range is constrained by the grating period and incident angle (typically 2 nm). When the tuning range extends to 5 nm, the longitudinal mode spacing is 1 / 5 of that of a traditional single-FP structure, resulting in a spectral selection efficiency of only 72.4% at 0.1 nm resolution. The mode-hopping frequency increases significantly with the extension of the tuning range, while the linewidth remains at 12 kHz, failing to meet the requirements of high-precision spectral analysis where the linewidth is reduced to 1.2 kHz. Simultaneously, insufficient sparsity of the longitudinal mode spacing in the grating structure makes it difficult to simultaneously improve spectral selection efficiency and mode stability.

[0004] Existing temperature control systems employ TEC technology, achieving a temperature control accuracy of ±0.002℃. The heat conduction path relies on the AlN substrate (aluminum nitride substrate), reducing temperature drift from ±10MHz / ℃ to 0.45MHz / ℃. Vibration-resistant design optimizes the packaging structure through finite element analysis, controlling optical component displacement within 0.5μm, but it cannot effectively suppress mode stability fluctuations under 15g acceleration shocks. In existing technologies, a residual temperature drift error of 0.45MHz / ℃ still exists, and mode stability only reaches 85%, failing to meet the high environmental adaptability requirements of industrial testing scenarios.

[0005] Traditional debugging processes rely on manual adjustments, taking 2 hours per unit and yielding a yield rate of only 78%. The limited tuning range of single-FP cavity structures leads to high mode-hopping frequencies, while grating-type structures suffer from insufficient spectral selectivity; both struggle to achieve simultaneous optimization of wide tuning bandwidth and ultra-narrow linewidth. Existing technologies exhibit significant shortcomings in multi-dimensional performance optimization, environmental adaptability, and manufacturing efficiency, failing to meet the comprehensive requirements of fiber optic communication, spectral analysis, and industrial testing for spectral purity, wavelength stability, and production efficiency. Summary of the Invention

[0006] The present invention aims to provide a miniaturized, adjustment-free, ultra-narrow linewidth composite filter external cavity semiconductor laser to solve the technical defects of traditional external cavity semiconductor lasers in terms of wide tuning bandwidth and ultra-narrow linewidth synchronization limitations, multi-dimensional performance synergistic optimization, environmental adaptability and manufacturing process efficiency. It can achieve beneficial effects such as wide tuning range, ultra-narrow linewidth, high mode stability, adjustment-free assembly and high yield.

[0007] The objective of this invention is achieved through the following technical solution: a miniaturized, adjustable, ultra-narrow linewidth composite filter external cavity semiconductor laser, comprising, in sequence, a gain chip, an aspherical lens, a first FP etalon, a second FP etalon, an interference filter, a partial mirror, an optical isolator, and a polarization-maintaining fiber collimator; wherein, the first FP etalon and the second FP etalon are superimposed in a non-coaxial manner to form a difference in free spectral range, generating a difference in longitudinal mode spacing through the Vernier effect, and the longitudinal mode spacing generated by the Vernier effect is controlled by adjusting the tilt angle difference between the first FP etalon and the second FP etalon.

[0008] Furthermore, it also includes an AlN substrate and a packaging shell; The gain chip, aspherical lens, first FP etalon, second FP etalon, interference filter, partial reflector and optical isolator are all mounted on the AlN substrate. The AlN substrate is mounted on the bottom of the package. The polarization-maintaining fiber collimator extends from a pre-set hole on the side of the package and docks with the optical isolator.

[0009] Furthermore, the gain chip is soldered onto the AlN substrate; the aspherical lens, the first FP etalon, the second FP etalon, the interference filter, some mirrors, and the optical isolator are all fixed onto the AlN substrate using a UV adhesive curing process. The UV adhesive curing process includes: The curing equipment uses a servo motor-driven hydraulic loading system to apply pressure, and a pressure sensor monitors the stress distribution of the adhesive layer in real time. When the pressure reaches the set value, the curing timer is triggered. The curing time is adjusted by a dynamic compensation algorithm t=30+0.5×T_env-23+0.2×I_uv-300, where T_env is the ambient temperature and I_uv is the ultraviolet light intensity. When the environmental parameters are detected to deviate from the first preset threshold, the curing time is automatically adjusted to ensure that the shrinkage rate of the adhesive layer is less than or equal to the target value. The environmental parameters include ambient temperature and ultraviolet light intensity.

[0010] Furthermore, it also includes a temperature control system, which achieves temperature control through a thermoelectric cooler and a negative temperature coefficient thermistor; the thermoelectric cooler is installed on the bottom of the AlN substrate, and the negative temperature coefficient thermistor is arranged at the gain chip, forming a closed-loop temperature control circuit.

[0011] Furthermore, the aspherical lens is used to perform high-precision coupling and collimation of the broad spectrum generated by the gain chip, collimating the light emitted by the gain chip into a highly parallel beam, which is then coupled to the first FP etalon; the center wavelength of the interference filter is matched with the sparsification wavelength of the Vernier effect.

[0012] Furthermore, some of the reflectors are used to reflect the transmitted light from the interference filter back to the gain chip to form external cavity feedback.

[0013] Furthermore, the optical isolator suppresses the feedback of reverse-propagating laser light to the resonant cavity through its unidirectional light-guiding characteristics. The resonant cavity is jointly formed by the high-reflectivity end face of the gain chip and the reflective surface of part of the mirror. An aspherical lens, a first FP etalon, a second FP etalon, and an interference filter are sequentially arranged between the two to achieve mode selection and frequency stabilization.

[0014] Furthermore, the longitudinal mode spacing is determined by ΔνVernier=c / (2nL(cosθ2- cosθ1)), where ΔνVernier is the longitudinal mode spacing, c is the speed of light, n is the refractive index of the medium, θ1 and θ2 are the tilt angles of the first FP etalon and the second FP etalon, respectively, and the physical length of the first FP etalon and the second FP etalon is L.

[0015] Furthermore, the center wavelength of the interference filter deviates from the rarefaction wavelength of the Vernier effect by no more than 0.02 nm ± 0.005 nm.

[0016] Furthermore, the package is a multi-pin butterfly package.

[0017] The beneficial effects of this invention are as follows: It breaks through the bottleneck of traditional external cavity semiconductor lasers in spectral performance, which struggles to balance wide tuning bandwidth and ultra-narrow linewidth, achieving wide wavelength tuning while significantly compressing the output linewidth, improving spectral purity and selection efficiency, and meeting the needs of high-speed communication and high-precision spectral analysis; it significantly enhances mode stability, reduces mode jump frequency, controls micro-displacement of optical components, and ensures stable longitudinal mode spacing, superior to traditional structures; it significantly improves environmental adaptability, enabling stable operation over a wide temperature range and resistance to certain levels of impact, making it suitable for complex scenarios such as industrial inspection and outdoor sensing; it innovates manufacturing processes, shortening single-unit debugging time and improving batch production yield and consistency through adjustment-free assembly, high-precision machining, and intelligent control, breaking through mass production bottlenecks; and it strengthens long-term reliability, avoiding performance degradation caused by adhesive layer aging and component loosening, reducing long-term maintenance needs, and meeting the long lifespan and high reliability requirements of industrial equipment. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 A schematic diagram of the internal structure of a composite ECDL consisting of dual FP cavities and IF. Figure 2 A three-dimensional schematic diagram of ECDL with butterfly-shaped packaging and composite filtering; Figure 3 This is an ideal ECDL spectrum; Explanation of reference numerals in the attached figures: 1: Gain chip; 2: Aspherical lens; 3: First FP etalon; 4: Second FP etalon; 5: Interference filter; 6: Partial reflector; 7: Optical isolator; 8: Polarization-maintaining fiber collimator; 9: AlN substrate; 10: Package housing. Detailed Implementation

[0020] The present invention will now be described in detail with reference to the accompanying drawings. Unless otherwise specified, the features of the embodiments and implementations described below can be combined with each other. The terminology used in the implementation section of this application is only for explaining specific embodiments of this application and is not intended to limit this application.

[0021] This application discloses a miniaturized, adjustment-free, ultra-narrow linewidth composite filter external cavity semiconductor laser. See also... Figure 1 and Figure 2The device is configured with a gain chip 1, an aspherical lens 2, a first FP (Fabry-Pérot) etalon 3, a second FP etalon 4, an interference filter 5, a partial reflector 6, an optical isolator 7, and a polarization-maintaining fiber collimator 8. The first FP etalon 3 and the second FP etalon 4 are superimposed in a non-coaxial manner to form a difference in the free spectral range, which generates a difference in longitudinal mode spacing through the Vernier effect. The longitudinal mode spacing generated by the Vernier effect is controlled by adjusting the tilt angle difference between the first FP etalon 3 and the second FP etalon 4.

[0022] Specifically, it also includes an AlN substrate (9) and a package shell (10); the gain chip 1, aspherical lens 2, first FP etalon 3, second FP etalon 4, interference filter 5, partial reflector 6, and optical isolator 7 are all mounted on the AlN substrate 9 on the inner bottom plate of the package shell 10, and the polarization-maintaining fiber collimator 8 extends from a pre-set hole on the side of the butterfly-shaped package shell 10 and docks with the optical isolator 7. Preferably, the package shell 10 is a multi-pin butterfly-shaped package shell used to provide electrical connection lines, see [link to documentation]. Figure 2 An exemplary 14-pin butterfly package is provided.

[0023] In one embodiment, the gain chip 1, aspherical lens 2, first FP etalon 3, second FP etalon 4, interference filter 5, partial reflector 6, and optical isolator 7 are all mounted on an AlN substrate 9. The gain chip 1 is fixed to a copper-based heat sink structure with active temperature control using an AuSn eutectic bonding process. The surface of the heat sink is electroplated with nickel-gold to improve surface wettability and bonding reliability. During bonding, a thin layer of AuSn solder is pre-placed within a temperature range of 300°C to 320°C, and controlled reflow is performed under a nitrogen protective atmosphere to form a eutectic bonding layer with a thickness of 15–25 μm between the gain chip 1 and the heat sink surface. After bonding, the copper-based heat sink is fixed to the AlN substrate 9 with a layer of thermally conductive silver paste. The aspherical lens 2, first FP etalon 3, second FP etalon 4, interference filter 5, partial reflector 6, and optical isolator 7 are all fixed to the AlN substrate 9 using a UV adhesive curing process. The UV adhesive curing process includes: The curing equipment uses a servo motor-driven hydraulic loading system to apply pressure, and a pressure sensor monitors the stress distribution of the adhesive layer in real time. When the pressure reaches the set value, the curing timer is triggered. The curing time is adjusted by a dynamic compensation algorithm t=30+0.5×(T_env-23)+0.2×(I_uv-300), where T_env is the ambient temperature and I_uv is the ultraviolet light intensity. When the environmental parameters are detected to deviate from the first preset threshold, the curing time is automatically adjusted to ensure that the shrinkage rate of the adhesive layer is less than or equal to the target value.

[0024] This invention reduces debugging time from 2 hours / unit to 12 minutes / unit through an adjustment-free assembly process, and increases the yield rate from 78% to 92.6%. The Vernier effect design of the dual FP cavity expands the longitudinal mode spacing to 10 times that of the traditional structure. Combined with the narrow-band characteristics of the interference filter, it effectively suppresses mode jumps and achieves ultra-narrow linewidth and high stability.

[0025] In one embodiment, a temperature control system is also included, which achieves temperature control through a thermoelectric cooler and a negative temperature coefficient thermistor. The thermoelectric cooler is mounted on the bottom of the AlN substrate 9, and the negative temperature coefficient thermistor is arranged at the gain chip, forming a closed-loop temperature control circuit. The temperature control system, through the synergistic effect of the TEC and NTC, controls the temperature drift to 0.45 MHz / ℃, meeting the performance requirements of the operating temperature range of -20℃ to 60℃.

[0026] In one embodiment, this invention establishes an assembly and performance mapping system for external cavity semiconductor lasers based on a digital twin model, used to achieve real-time correlation and optimization of process parameters and performance parameters. Process parameters include optical alignment spacing and tilt angle, tilt angle difference and spacing between the first and second FP etalons, UV adhesive curing pressure and light intensity, heat sink temperature setpoint, and ambient temperature; performance parameters include output power, linewidth, side-mode rejection ratio (SMSR), tuning bandwidth, frequency stability, temperature drift, and packaging yield. The digital twin model collects sensor signals and performance detection data during the assembly process, and uses nonlinear regression and feedback learning algorithms to establish parameter mapping relationships, achieving dynamic correction and performance prediction of the assembly process. In batch verification, laser products assembled using this model achieved an average linewidth of approximately 320 Hz, a side-mode rejection ratio greater than 50 dB, a temperature drift of less than ±0.01 °C / 24 h, and a batch yield of 92.6%. This system achieves real-time bidirectional mapping and optimized control of process parameters and performance parameters, effectively improving assembly consistency and long-term stability of the light source.

[0027] In one embodiment, the centers of the aspherical lens 2, the first FP (Fabry-Pérot) etalon 3, the second FP etalon 4, the interference filter 5, the partial reflector 6, and the optical isolator 7 are all on the optical axis. For example, the optical axis alignment error is controlled within 0.05°±0.01° by a machine vision alignment system, and the glue volume control accuracy of the fully automatic dispensing equipment is ±0.05μL to ensure the consistency of curing quality.

[0028] Example 1: This example provides a miniaturized, adjustment-free, ultra-narrow linewidth composite filter external cavity semiconductor laser. An aspherical lens 2 precisely couples and collimates the broad spectrum generated by the gain chip 1. Leveraging the low aberration and high numerical aperture characteristics of the aspherical design, the light emitted by the gain chip 1 is collimated into a highly parallel beam, precisely coupled with the subsequent first FP etalon 3 (hereinafter referred to as FP1), increasing the coupling efficiency to 40%–70% and significantly reducing optical power loss. The tilt angle of FP1 is 6.5°±0.02°, and the tilt angle of the second FP etalon 4 (hereinafter referred to as FP2) is 1.1°±0.02°. The physical length of both FP etalons is 1.00±0.01 mm, and the reflectivity of their high-reflectivity films is 94%±1%. FP1 and FP2 are superimposed in a non-coaxial manner to form a free spectral range (FSR) difference, generating a longitudinal mode spacing difference through the Vernier effect. The transmission bandwidth of the interference filter 5 (IF) is 0.08 nm±0.01 nm. The center wavelength is precisely matched with the rarefaction wavelength of the Vernier effect, with a deviation of no more than 0.02 nm ± 0.005 nm. This filter suppresses multi-mode competition through its narrowband characteristics, improving the side-mode suppression ratio to 54 dB ± 2 dB. Partial reflector 6 is used to reflect the transmitted light of the IF back to the gain chip to form external cavity feedback, ensuring the stability of the laser mode. Optical isolator 7 suppresses the feedback of the reverse-propagating laser to the resonant cavity through its unidirectional light-guiding characteristics, avoiding mode jumps and power fluctuations. In the UV adhesive curing process, the curing time is 30 seconds ± 5 seconds, and the curing pressure is 0.2 MPa ± 0.02 MPa.

[0029] The 14-pin butterfly package provides mechanical protection and environmental isolation for all optical and electrical components. The 14 pins respectively power the gain chip, control the thermoelectric cooler (TEC), monitor the negative temperature coefficient thermistor (NTC) temperature, and output signals, ensuring the electrical connection and signal transmission of the laser. Simultaneously, the compact package structure achieves miniaturized integration. FP1 and FP2 are machined using a five-axis CNC machine tool, with a physical length deviation not exceeding ±0.01 mm and a tilt angle error not exceeding ±0.02°. During machining, an online laser interferometer is used to monitor the optical axis deviation in real time. When the measured path error is ≤0.05°±0.01°, the tilt angle difference is finely adjusted to 5.4°±0.03° using a rotation adjustment mechanism. The interference filter (IF) is immediately connected to the rear end of the dual FP etalon. Its transmission bandwidth is measured and calibrated using a Keysight 86142B spectrometer (0.01 nm resolution) to ensure bandwidth stability of 0.08 nm±0.01 nm within a 5 nm tuning range. The center wavelength of the IF (In-Frequency Interferometer) deviates from the Vernier wavelength of the dual FP (Frequency-Frequency) cavity by ≤0.02 nm ± 0.005 nm. The optical axis alignment error is controlled within 0.05° ± 0.01° using a machine vision alignment system. This ultimately improves the side-mode suppression ratio to ≥54 dB. (See [link to documentation]). Figure 3 The power difference between the main mode and the side modes and the stable longitudinal mode distribution are clearly presented. Part of the reflector 6 is cured onto the AlN substrate 9 with UV adhesive. The curing pressure is precisely controlled at 0.2 MPa ± 0.02 MPa by a servo motor-driven hydraulic loading system. The curing time is adjusted using a dynamic compensation algorithm (t = 30 + 0.5 × (T_env - 23) + 0.2 × (I_uv - 300)). The ambient temperature fluctuation range is 23 ± 1℃, and the UV light intensity fluctuation range is 300 mW / cm ± 10%. When the environmental parameters (ambient temperature and UV light intensity) deviate from the fluctuation range, the curing time is automatically adjusted to ensure that the adhesive layer shrinkage rate is less than or equal to 1.2%, and that the adhesive layer stress distribution is uniform, with optical element displacement ≤ 0.5 μm. The polarization-maintaining fiber collimator 8 extends from the side hole of the 14-pin butterfly package and precisely docks with the optical isolator 7, achieving efficient fiber output of the laser while maintaining its polarization state, with coupling loss ≤ 0.5 dB. Example 2: This embodiment provides a method for controlling the longitudinal mode spacing based on the Vernier effect, which controls the longitudinal mode spacing generated by the Vernier effect by adjusting the tilt angle difference between FP1 and FP2. The quantitative relationship between the two is derived by the following formula: the formula for the free spectral range (FSR) of the FP etalon as a function of tilt angle is FSR=c / (2nLcosθ), where c=3×108m / s is the speed of light in vacuum, n=1.458 is the refractive index of fused silica at 25℃, L is the physical length of FP, and θ is the tilt angle of FP. The longitudinal mode spacing ΔνVernier under the Vernier effect is determined by the difference in FSR between the two FPs, and the formula is ΔνVernier=FSR1×FSR2 / |FSR1−FSR2|. When the physical lengths of FP1 and FP2 are both L, substituting FSR1=c / (2nLcosθ1) and FSR2=c / (2nLcosθ2) (θ1 and θ2 are the tilt angles of FP1 and FP2, respectively), we can further obtain ΔνVernier=c / (2nL(cosθ2-cosθ1)). That is, the longitudinal mode spacing can be quantitatively controlled by adjusting the tilt angle difference Δθ=|θ1−θ2|. The tilt angle of FP1 is 6.5°±0.02°, the tilt angle of FP2 is 1.1°±0.02°, the physical length of the two FP etalons is 1.00±0.01 mm, and the reflectivity of the high-reflection film is 94%±1%. Machining using a five-axis CNC machine ensures a physical length deviation of ≤ ±0.01 mm and a tilt angle error of ≤ ±0.02°. The reflectivity consistency of the high-reflectivity film has a deviation of ≤ 0.5% under tilt conditions, ensuring stable optical performance. FP1 and FP2 are superimposed in a non-coaxial manner, forming a free spectral range (FSR) difference. The FSR of FP1 is 12.3 GHz ± 0.5 GHz, and the FSR of FP2 is 11.3 GHz ± 0.5 GHz, with a ΔFSR = 1.0 GHz. The longitudinal mode spacing is stabilized at 10 GHz ± 0.5 GHz through the Vernier effect to meet the application requirements of high-precision spectral analysis. Experimental data shows that when the tilt angle difference is set to 5.4° ± 0.03°, the longitudinal mode spacing fluctuation range is ≤ 10 GHz ± 5%, and the mode switching frequency is controlled at 0.3 times / hour ± 0.05 times / hour.

[0030] Interference filter 5 (IF) has a transmission bandwidth of 0.08 nm ± 0.01 nm, and its center wavelength precisely matches the rarefaction wavelength of the Vernier effect. Verification using a Keysight 86142B spectrometer showed that when the deviation between the IF center wavelength and the Vernier wavelength exceeds 0.02 nm ± 0.005 nm, the spectral selectivity decreases by 12% ± 2%, and the side-mode suppression ratio decreases by 8 dB ± 1 dB. The IF's mounting position is precisely adjusted using a machine vision alignment system to ensure an optical axis alignment error ≤ 0.05° ± 0.01°.

[0031] In the UV adhesive curing process, the curing pressure is 0.2 MPa ± 0.02 MPa, the curing time is 30 seconds ± 5 seconds, and the adhesive shrinkage rate is controlled within 1.0% ± 0.2%. Through finite element simulation optimization of stress distribution, the tilt angle difference stability of the dual FP etalons reaches 5.4° ± 0.03°, and the longitudinal die interval fluctuation value Δλ ≤ 0.01 nm. The curing equipment integrates a temperature-light intensity dual-parameter compensation module. When the ambient temperature deviates from 23 ± 1℃ or the UV light intensity fluctuation exceeds 300 mW / cm ± 10%, the curing time is dynamically adjusted using the formula t = 30 + 0.5 × (T_env - 23) + 0.2 × (I_uv - 300), compressing the curing time fluctuation range to ± 3 seconds.

[0032] Example 3: This embodiment provides a closed-loop control method for UV adhesive curing process, which includes a coordinated control process for curing time and curing pressure. Before curing, the Vernier effect of the dual FP etalon is pre-calibrated using a high-precision spectrometer (Keysight 86142B). When the longitudinal mode spacing is measured to be 10 GHz ± 0.5 GHz and the mode switching frequency is ≤ 0.3 times / hour, the curing program is started.

[0033] The curing equipment employs a servo motor-driven hydraulic loading system to apply a pressure of 0.2 MPa ± 0.02 MPa, with a pressure sensor monitoring the stress distribution of the adhesive layer in real time. When the pressure reaches the set value, a curing timer is triggered. The curing time is adjusted using a dynamic compensation algorithm (t = 30 + 0.5 × (T_env - 23) + 0.2 × (I_uv - 300)). The ambient temperature fluctuation range is 23 ± 1℃, and the ultraviolet light intensity fluctuation range is 300 mW / cm ± 10%. When environmental parameters deviate from the threshold (i.e., exceed the ambient temperature fluctuation range or the ultraviolet light intensity fluctuation range), the system automatically adjusts the curing time again using the dynamic compensation algorithm, typically within 35 seconds ± 5 seconds, ensuring that the adhesive layer shrinkage rate is ≤ 1.2% (standard deviation ± 0.3%).

[0034] The curing quality inspection adopts a segmented strategy: In the first stage, at the end of curing, the adhesive shrinkage rate is measured using a laser interferometer (Zygo GPI-XP). If the deviation exceeds 1.2%, a second curing procedure is initiated. In the second stage, after a 24-hour aging test, the interface flatness is inspected using an atomic force microscope (AFM), requiring ≤0.5 μm. In the third stage, during a 1000-hour continuous operation test, the mode jump frequency is monitored using a spectrometer, ensuring it remains stable at 0.28 times / hour ± 0.03 times / hour. All test data are uploaded to a digital twin model in real time, and the impact of process parameter fluctuations on performance is verified through Monte Carlo simulation. When the prediction error exceeds 2.3%, the curing time window is automatically optimized to the range of 25-35 seconds.

[0035] Example 4: This embodiment provides a closed-loop regulation method for a temperature control system, which uses a thermoelectric cooler (TEC), a negative temperature coefficient thermistor (NTC), and an embedded temperature control microcontroller (MCU) to form a complete closed-loop temperature control circuit, achieving a temperature control accuracy of ±0.002℃. The NTC, acting as a temperature sensing element, is precisely positioned near the gain chip 1. It collects real-time temperature data from the gain chip 1 and the surrounding AlN substrate 9, converting temperature changes into corresponding resistance signals, which are then synchronously transmitted to the MCU. The MCU, as the closed-loop control core, pre-stores the target operating temperature (22℃±0.002℃) of the core optical components. After receiving the feedback signal from the NTC, it converts it into an actual temperature value using a built-in algorithm, performing difference calculations and logical judgments with the target temperature. If the actual temperature is higher than 22.002℃ or lower than 21.998℃, it immediately generates and outputs a PWM (Pulse Width Modulation) control signal. The TEC, acting as an actuator, is mounted on the bottom of the AlN substrate. After receiving the control signal from the MCU, it precisely adjusts its cooling or heating power. Utilizing the high thermal conductivity of the AlN substrate, it quickly transmits the temperature regulation effect to all core optical components on the substrate, achieving dynamic overall temperature control. Simultaneously, the NTC continuously collects the adjusted temperature data and feeds it back to the MCU. The MCU dynamically corrects the control signal output to the TEC based on the real-time feedback, forming a "temperature sensing - signal processing - power adjustment -" process. The continuous closed-loop feedback ensures that the system temperature stability reaches 0.002℃±0.0005℃, providing a stable temperature control basis for subsequent temperature drift tests (wavelength drift ≤0.05 nm in the temperature range of -20℃ to 60℃).

[0036] Temperature drift testing was conducted in the range of -20°C to 60°C. A high-precision frequency meter (Rohde & Schwarz FSW-K10) was used to measure the output wavelength drift, which was ≤0.05 nm (corresponding to a frequency drift of 0.45 MHz / °C), representing an improvement of two orders of magnitude compared to traditional structures. This performance directly relies on the combined effects of optimized thermal conductivity of the AlN substrate (temperature drift of 0.45 MHz / °C) and the TEC temperature control system (temperature control accuracy ±0.002°C).

[0037] Environmental adaptability testing employed a standard vibration table (MIL-STD-810G Method 514.6) for 15g acceleration (10-2000Hz frequency band) shock tests. The mode stability remained at 99.2% (n=15 groups, standard deviation ±0.15%), a 12.5% ​​improvement over traditional structures. This result directly stems from the synergistic effect of the high-precision ceramic bearing structure of the optical bracket (long-term stability deviation ≤0.03° after tilt adjustment) and the UV adhesive curing process: precise control of the curing pressure (0.2 MPa ±0.02 MPa) ensured optical element displacement <0.5 μm. Simultaneously, the unidirectional light-guiding characteristics of the optical isolator 7 further suppressed reverse light interference caused by shock, and the side-insertion mounting of the polarization-maintaining fiber collimator 8 avoided additional stress on the internal encapsulation structure caused by vibration.

[0038] In summary, addressing the limitations of existing technologies such as limited tuning range, excessively wide linewidth, poor environmental adaptability, and complex manufacturing processes, an innovative structure based on the Vernier effect of dual Fabry-Pérot cavities is presented. By setting up non-coaxial dual Fabry-Pérot cavities (physical length 1.00±0.01mm, reflectivity 94%±1%) with a tilt angle difference of 5.4°±0.03°, and utilizing the difference in the free spectral range to generate a longitudinal mode spacing of 10GHz±0.5GHz, this design achieves dynamic control of the longitudinal mode distribution through periodic changes in the optical path difference, significantly improving the spectral selectivity resolution to 10 times that of traditional single Fabry-Pérot structures. Combined with an interference filter with a transmission bandwidth of 0.08nm±0.01nm to form a secondary screening, a spectral selectivity efficiency of 93.8% and a side-mode suppression ratio of 54dB are achieved within a 5nm tuning range. By employing a UV adhesive curing process and an intelligent pressure-time coupled control algorithm, the displacement of optical components is controlled within 0.12 μm, achieving a mode stability of 99.2%, reducing temperature drift to 0.45 MHz / ℃, shortening the debugging time to 12 minutes per unit, and increasing the yield rate to 92.6%. This design simultaneously solves the challenges of wide tuning bandwidth and ultra-narrow linewidth, multi-dimensional performance synergy, and environmental adaptability through machining precision, optical coupling optimization, and automated assembly processes.

[0039] The above embodiments are only used to illustrate the design concept and features of the present invention, and their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. The protection scope of the present invention is not limited to the above embodiments. Therefore, all equivalent changes or modifications made based on the principles and design ideas disclosed in the present invention are within the protection scope of the present invention.

Claims

1. A miniaturized, adjustment-free, ultra-narrow linewidth composite filtered external cavity semiconductor laser, characterized in that, The gain chip (1), the aspheric lens (2), the first FP etalon (3), the second FP etalon (4), the interference filter (5), the partial reflector (6), the optical isolator (7) and the polarization maintaining fiber collimator (8) are sequentially arranged; wherein the first FP etalon (3) and the second FP etalon (4) are superimposed in a non-coaxial manner to form a free spectral range difference, a longitudinal mode spacing difference is generated through the Vernier effect, and the longitudinal mode spacing difference generated by the Vernier effect is controlled by adjusting the inclination angle difference of the first FP etalon (3) and the second FP etalon (4).

2. The compact, adjustment-free, ultranarrow linewidth composite filtered external cavity semiconductor laser of claim 1, wherein, Further comprising an AlN substrate (9) and a packaging shell (10); The gain chip (1), the aspheric lens (2), the first FP etalon (3), the second FP etalon (4), the interference filter (5), the partial reflector (6) and the optical isolator (7) are all mounted on the AlN substrate (9), the AlN substrate (9) is mounted on the bottom of the packaging shell (10), and the polarization maintaining fiber collimator (8) extends into the preset hole of the side of the packaging shell (10) and is connected with the optical isolator (7).

3. The compact, adjustment-free, ultranarrow linewidth composite filtered external cavity semiconductor laser of claim 2, wherein, The gain chip (1) is welded on the AlN substrate (9); the aspheric lens (2), the first FP etalon (3), the second FP etalon (4), the interference filter (5), the partial reflector (6) and the optical isolator (7) are all fixed on the AlN substrate (9) through a UV glue curing process, and the UV glue curing process flow comprises: The curing equipment adopts a hydraulic loading system driven by a servo motor to apply pressure, and a pressure sensor monitors the stress distribution of the glue layer in real time; when the pressure reaches the set value, the curing timer is triggered, the curing time is adjusted through a dynamic compensation algorithm t=30+0.5×(T_env-23)+0.2×(I_uv-300), T_env is the environmental temperature, I_uv is the ultraviolet light intensity, when the environmental parameters deviate from the first preset threshold, the curing time is automatically adjusted to ensure that the shrinkage rate of the glue layer is less than or equal to the target value.

4. The compact, adjustment-free, ultranarrow linewidth composite filtered external cavity semiconductor laser of claim 1, wherein, Further comprising a temperature control system, which realizes temperature control through a thermoelectric cooler and a negative temperature coefficient thermistor; the thermoelectric cooler is installed at the bottom of the AlN substrate (9), and the negative temperature coefficient thermistor is arranged at the gain chip (1) to form a closed-loop temperature control loop.

5. The compact, adjustment-free, ultranarrow linewidth composite filtered external cavity semiconductor laser of claim 1, wherein, The aspheric lens (2) is used for high-precision coupling and collimation of the wide spectrum generated by the gain chip (1), and the light emitted by the gain chip (1) is collimated into a high-parallel light beam and coupled with the first FP etalon (3); the center wavelength of the interference filter (5) matches the sparsification wavelength of the Vernier effect.

6. The compact, adjustment-free, ultranarrow linewidth composite filtered external cavity semiconductor laser of claim 1, wherein, The partial reflector 6 is used for reflecting the transmitted light of the interference filter (5) back to the gain chip (1) to form an external cavity feedback.

7. The compact, adjustment-free, ultranarrow linewidth composite filtered external cavity semiconductor laser of claim 1, wherein, The optical isolator (7) suppresses the feedback of the reverse transmission laser to the resonant cavity through the one-way light guiding characteristic, and the resonant cavity is jointly formed by the high-reflective end face of the gain chip and the reflecting surface of the partial reflector.

8. The compact, adjustment-free, ultranarrow linewidth composite filtered external cavity semiconductor laser of claim 1, wherein, The longitudinal mode spacing is determined by Δν Vernier = c / (2nL(cosθ2- cosθ1)), where Δν Vernier is the longitudinal mode spacing, c is the speed of light, n is the refractive index of the medium, θ1 and θ2 are the tilt angles of the first and second FP cavities, respectively, and L is the physical length of the first and second FP cavities.

9. The compact, adjustment-free, ultranarrow linewidth composite filtered external cavity semiconductor laser of claim 1, wherein, The center wavelength of the interference filter (5) deviates from the sparsification wavelength of the Vernier effect by not more than 0.02 nm±0.005 nm.

10. The compact, adjustment-free, ultranarrow linewidth composite filtered external cavity semiconductor laser of claim 2, wherein, The package shell (10) is a multi-pin, butterfly-shaped package shell.

Images