A wide-tuning long-wavelength Littman-type external cavity laser

Abstract

The present application belongs to the technical field of semiconductor laser, and provides a wide-tuning long-wavelength Littman type external cavity laser, which comprises a wide-gain-bandwidth laser source module, an incident angle regulation unit, a diffraction angle regulation unit, a high-diffraction-efficiency grating module, a synchronous closed-loop control unit and an output unit. The present application synchronously adjusts the incident angle and the diffraction angle of the light beam by linking the incident angle regulation unit and the diffraction angle regulation unit through the synchronous closed-loop control unit, and realizes the super-wide tuning of the long-wavelength band by combining the long-wavelength adapted high-diffraction-efficiency grating and relying on the stable structure of the Littman type external cavity, thereby solving the technical problems of the narrow tuning range of the existing Littman type laser, the low diffraction efficiency of the grating at the long wavelength and the unstable laser mode. The tuning range of the laser can cover 1510-1530 nm, the 3dB bandwidth is narrow, the central frequency is stable and the out-of-band rejection ratio is high, and the laser can be adapted to application scenarios such as infrared spectrum detection and biological tissue deep imaging.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor laser technology, and particularly relates to a wide-tunable long-wavelength Littman type external cavity laser based on synchronous control of incident angle and diffraction angle, which is suitable for long-wavelength application scenarios such as infrared spectroscopy detection, deep imaging of biological tissues, and wavelength multiplexing in fiber optic communication. Background Technology

[0002] Littman-type external cavity lasers are widely used in wide-range scanning applications due to their structural advantages of fixed gratings and stable beam position. Their core principle is wavelength tuning achieved by adjusting the beam angle in conjunction with grating diffraction. However, existing technologies face two major bottlenecks:

[0003] (a) Limited tuning range

[0004] Traditional solutions only adjust the incident angle (such as lens displacement) or diffraction angle (such as galvanometer angle) separately. They are constrained by the single variable sinθ+sinΦ in the grating equation, and the tuning range is usually ≤10nm, which cannot cover the wide gain bandwidth requirements of long wavelength bands (such as 1.3-1.6μm).

[0005] To address the aforementioned issues, Chinese patent CN121748923A proposes a wide-tunable external cavity semiconductor laser based on dual-pivot linkage. This laser uses a dual-pivot linkage mechanism to drive the diffraction grating to synchronously translate and rotate, achieving a longitudinal mode number N=H. OB / d remains constant. CN101604818B proposes setting the rotation axis of the diffraction grating on the back of the grating, and keeping the longitudinal mode modulus of the resonant cavity constant by pre-selecting the position of the rotation axis, thereby achieving mode-skipping-free tuning. However, the above schemes are essentially open-loop passive mechanical designs, which have extremely high requirements for processing accuracy, assembly accuracy and long-term stability. Factors such as mechanical wear and temperature drift can cause the tuning relationship to deviate from the design value, and there is a lack of real-time compensation methods.

[0006] (ii) Long-wavelength mode instability

[0007] In long-wavelength scenarios (such as 1.5μm), the grating diffraction efficiency decreases significantly with increasing angle (diffraction efficiency <25% when incident angle >60°), and the external cavity feedback light intensity is insufficient, resulting in laser mode jumps and large power fluctuations, which makes it difficult to meet the high stability requirements of applications such as deep imaging of biological tissues and infrared spectroscopy detection.

[0008] Chinese patent CN115021076A discloses a 1550nm wavelength grating external cavity tunable semiconductor laser device, which uses a 600 lines / mm diffraction grating to achieve a 100nm tuning range. However, it does not optimize the grating blaze angle for long wavelength bands, nor does it address the synchronous control of the incident angle and diffraction angle. CN107611777A proposes using a fixed grating filter combined with a Littrow-type reflection grating to form an ultra-narrow filter, achieving flexible wavelength output by adjusting the incident angle of each filter. However, it belongs to the Littrow structure, and the output light direction changes with tuning. Furthermore, the problem of insufficient diffraction efficiency at long wavelengths remains unresolved.

[0009] Furthermore, US7230960B2 proposes using two actuators to control the rotation and translation of the rearward mirror, or the gain medium or grating, to suppress mode hopping. However, in this scheme, wavelength selection and cavity length adjustment are performed by two independent actuators, and the control logic is independent rather than synchronous, making it difficult to achieve precise coordinated changes in the incident angle and diffraction angle. Moreover, it does not address the optimization of the diffraction efficiency of long-wavelength gratings.

[0010] Although there are various Littman laser solutions available, none have solved the problem of combining long wavelength, wide tuning, and high stability, thus failing to meet the long wavelength and wide tuning requirements in fields such as high-purity spectrum microwave signal generation and high-resolution sensing. Summary of the Invention

[0011] Existing Littman-type external cavity lasers suffer from narrow tuning ranges (≤10nm), low diffraction efficiency at long wavelengths (<25%), and mode instability, making it impossible to achieve wide-range stable tuning in the long wavelength band (1.3-1.6μm), which is insufficient to meet the application requirements of infrared spectroscopy detection, deep imaging of biological tissues, and other applications. This disclosure provides a wide-tunable long-wavelength Littman-type external cavity laser, aiming to at least partially solve the above-mentioned technical problems.

[0012] To achieve the above objectives, embodiments of this disclosure provide a wide-tuning, long-wavelength Littman-type external cavity laser.

[0013] A first aspect of the present invention is to provide a wide-tunable, long-wavelength Littman-type external cavity laser, comprising:

[0014] Wide gain bandwidth laser source module, used to generate laser with center wavelength in the 1.3-1.6μm band;

[0015] An incident angle adjustment unit is disposed on the output optical path of the wide gain bandwidth laser source module, and is used to collimate the laser into parallel light and adjust the incident angle θ of the parallel light onto the high diffraction efficiency grating module.

[0016] A high diffraction efficiency grating module is disposed in the output optical path of the incident angle control unit. It is used to filter the wavelength of the beam after the angle is adjusted. Its first-order diffracted light is output to the diffraction angle control unit, and its zero-order diffracted light is output to the output unit.

[0017] The diffraction angle control unit is set on the first-stage diffraction optical path of the high diffraction efficiency grating module. It is used to control the diffraction angle Φ of the first-stage diffraction light and make the first-stage diffraction light return to the wide gain bandwidth laser source module along the original path to form a stable external cavity feedback.

[0018] The synchronous closed-loop control unit is electrically connected to the incident angle control unit, the diffraction angle control unit, and the high diffraction efficiency grating module, respectively. It is used to receive the target wavelength command, link the incident angle control unit to adjust the incident angle θ, and link the diffraction angle control unit to synchronously adjust the diffraction angle Φ, so that the sum of sinθ + sinΦ ≥ 1.7, which satisfies the long wavelength resonance condition of the grating equation mλ = d(sinθ + sinΦ).

[0019] The output unit is located on the zero-order diffraction path of the high diffraction efficiency grating module and is used to collimate and output the zero-order diffraction light after it has been locked by external cavity feedback.

[0020] Furthermore, the synchronous closed-loop control unit includes a controller, a light intensity detector, a displacement sensor, and an angle sensor;

[0021] The light intensity detector is used to monitor the feedback light intensity, the displacement sensor is used to detect the position of the incident angle control unit, and the angle sensor is used to detect the angle of the diffraction angle control unit.

[0022] The controller receives feedback signals from the displacement sensor, the angle sensor, and the light intensity detector, performs closed-loop calibration on the adjustment of the incident angle and the diffraction angle to ensure that the synchronization error between the two is ≤0.01°, and dynamically compensates for diffraction efficiency fluctuations based on the feedback light intensity.

[0023] Furthermore, the feature is that the wide gain-bandwidth laser source module is an InP-based multi-quantum-well diode laser, encapsulated with an integrated graphene heat dissipation layer, with a center wavelength of 1.55 μm, a gain-bandwidth ≥ 40 nm, and a heat dissipation efficiency ≥ 15 W / (cm²). 2 ·K).

[0024] Furthermore, the incident angle adjustment unit includes an electromagnetically driven apochromatic collimating lens, a nano-displacement platform, and a displacement sensor. The nano-displacement platform is used to drive the collimating lens to make a lateral micro-displacement to adjust the incident angle θ, with a displacement accuracy of ±0.05μm. The focal length of the collimating lens is 6-10mm.

[0025] Furthermore, the diffraction angle control unit is a biaxial piezoelectric-electromagnetic composite galvanometer with an angular resolution of 3×10⁻⁶. -4 Radius, response speed ≤0.8ms, angular travel ±15°.

[0026] Furthermore, the high diffraction efficiency grating module is a 1200 lines / mm holographic grating with optimized blaze angle and a blaze angle of 55°, achieving a first-order diffraction efficiency of ≥60% in the 1.5μm band.

[0027] Furthermore, the output unit includes an output beam collimator and a photodetector;

[0028] The output beam collimator is used to collimate the zero-order diffracted light twice and then output it stably, and the photodetector is used to monitor the laser output power in real time.

[0029] Furthermore, the external cavity laser has a tuning range of 1510-1530nm, an output power of ≥200mW, a power fluctuation of ≤0.015 for 1 hour, and a spot position fluctuation of <0.2μm.

[0030] A second aspect of the present invention provides a method for synchronously controlling a wide-tunable, long-wavelength Littman-type external cavity laser, comprising the following steps:

[0031] A wide-gain, wide-bandwidth laser source module generates laser light with a center wavelength in the 1.3-1.6 μm band;

[0032] The laser is collimated into parallel light by the incident angle adjustment unit, and the incident angle θ of the parallel light is adjusted to be incident on the high diffraction efficiency grating module.

[0033] The synchronous closed-loop control unit receives the target wavelength command, and the incident angle adjustment unit adjusts the incident angle θ in conjunction with the incident angle adjustment unit. The diffraction angle adjustment unit adjusts the diffraction angle Φ in conjunction with the incident angle adjustment unit, so that the sum of sinθ + sinΦ is ≥ 1.7, which satisfies the long wavelength resonance condition of the grating equation mλ = d(sinθ + sinΦ).

[0034] The high diffraction efficiency grating module filters the wavelength of the beam after the angle is adjusted, and the first-order diffracted light is reflected by the diffraction angle control unit and returned to the wide gain bandwidth laser source module along the original path to form a stable external cavity feedback.

[0035] The synchronous closed-loop control unit calibrates the synchronization between the incident angle and the diffraction angle in real time and dynamically compensates for fluctuations in diffraction efficiency to ensure the stability of the laser mode.

[0036] The zero-order diffracted light, after being locked by feedback from the external cavity, is collimated by the output unit and then output.

[0037] Furthermore, the synchronous closed-loop control unit receives real-time feedback signals from the displacement sensor, angle sensor, and light intensity detector through its controller, performs closed-loop calibration on the adjustment of the incident angle and diffraction angle, so that the synchronization error between the two is ≤0.01°, and dynamically compensates for diffraction efficiency fluctuations based on the feedback light intensity.

[0038] The working principle of this laser:

[0039] The InP-based multi-quantum-well diode laser in the wide-gain-bandwidth laser source module generates a laser with a center wavelength of 1.55 μm. After thermal drift is suppressed by the graphene heat dissipation layer, the laser is input to the incident angle control unit.

[0040] The electromagnetically driven apochromatic collimating lens in the incident angle control unit collimates the diverging laser into parallel light. Under the control of the synchronous closed-loop control unit, the nano-displacement platform drives the lens to make a lateral micro-displacement, precisely adjusting the incident angle θ of the beam incident on the high diffraction efficiency grating module. The displacement sensor monitors the lens displacement in real time to ensure the adjustment accuracy (referencing the high-precision displacement control technology of electromagnetically driven lenses, the displacement resolution can reach ±0.05μm).

[0041] The high diffraction efficiency grating module uses a 1200-line / mm holographic grating with a blaze angle of 55° to precisely select the wavelength of the incident parallel light. The first-order diffracted light is directed to the diffraction angle control unit, and the zero-order diffracted light is used as the candidate output light of the laser. Through blaze angle optimization, the first-order diffraction efficiency of the grating in the 1.5μm band is increased to ≥60%, which solves the problem of insufficient diffraction efficiency at long wavelengths and large angles.

[0042] Under the control of the synchronous closed-loop control unit, the biaxial piezoelectric-electromagnetic composite galvanometer in the diffraction angle control unit achieves synchronous angle adjustment with the incident angle, precisely controlling the diffraction angle Φ, so that the first-order diffracted light returns to the active region of the wide-gain bandwidth laser source module along the original path, resonating with the intracavity optical signal, and achieving stable external cavity feedback locking; the angle sensor calibrates the galvanometer angle in real time to ensure the accuracy of diffraction angle adjustment;

[0043] The FPGA controller of the synchronous closed-loop control unit receives real-time signals from the displacement sensor and the angle sensor, and performs closed-loop calibration on the adjustment of the incident angle and the diffraction angle to ensure that the synchronization error between the two is <0.01°; the light intensity detector monitors the feedback light intensity of the external cavity in real time. When the diffraction efficiency of the grating fluctuates and causes the feedback light intensity to change, the controller dynamically fine-tunes the incident angle and the diffraction angle to compensate for the light intensity loss.

[0044] The zero-order diffracted light, locked by external cavity feedback, is then collimated a second time by the output beam collimator of the output unit before being stably output. A photodetector monitors the output power in real time to ensure power stability. Key design features:

[0045] Synchronous adjustment of incident angle and diffraction angle: By linking the nano-displacement platform and the piezoelectric-electromagnetic composite galvanometer with the FPGA controller, the incident angle θ and diffraction angle Φ can be adjusted synchronously and precisely, so that the sum of sinθ + sinΦ is extended from 1.2 in the traditional scheme to 1.8, breaking through the angle constraint of the grating equation on wavelength tuning, and extending the tuning range from the traditional ≤45nm to 50nm, which greatly improves the tuning range;

[0046] Long-wavelength adapted high diffraction efficiency grating: The blaze angle of the holographic grating is optimized to 55° for the 1.5μm long-wavelength band, and a high grating density design of 1200 lines / mm is adopted to make the first-order diffraction efficiency ≥60% in the 1.5μm band (unlike the low diffraction efficiency of short-wavelength holographic gratings, such as the first-order diffraction efficiency of 455nm holographic gratings which is only 8.3%), solving the problem of low grating diffraction efficiency at long wavelengths and large angles, and ensuring the intensity of external cavity feedback light;

[0047] High-efficiency heat dissipation and end-to-end closed-loop stability: The laser source module is packaged with an integrated graphene heat dissipation layer, achieving a heat dissipation efficiency of ≥15W / (cm²). 2 •K), effectively suppressing thermal drift during high-power operation; introducing triple sensing feedback of displacement, angle, and light intensity to construct full-link synchronous closed-loop control, realizing synchronous calibration of incident angle and diffraction angle, and dynamic compensation of feedback light intensity, ensuring stable laser mode without jumps.

[0048] Advantages and beneficial effects of the present invention:

[0049] 1. The tuning range of this invention is significantly expanded. By synchronously controlling the incident angle and diffraction angle, the tuning range covers 1510-1530nm (30nm bandwidth), which is 3 times that of the traditional solution, achieving wide range coverage in long wavelength bands;

[0050] 2. This invention exhibits stable long-wavelength performance, employs a blaze angle optimized grating, achieves a diffraction efficiency ≥60% in the 1.5μm band, output power ≥200mW, power fluctuation ≤0.015 over 1 hour, and exhibits no mode jump.

[0051] 3. The center frequency of this invention is adjustable and stable. By adjusting the synchronous combination of the incident angle and the diffraction angle, the center frequency can be flexibly adjusted. It is less affected by the environment, and the spot position fluctuation is <0.2μm.

[0052] 4. This invention has strong adaptability and its structure is compatible with various long-wavelength application scenarios such as infrared spectroscopy detection, deep imaging of biological tissues, and fiber optic communication. It can be adapted to different needs without major modifications. Attached Figure Description

[0053] Figure 1 This is a flowchart illustrating the operation of the wide-tunable long-wavelength Littman type external cavity laser of this invention.

[0054] Figure 2 The simulation curves show the wavelength tuning characteristics under the condition of synchronous adjustment of the incident angle and diffraction angle of the present invention.

[0055] Figure 3 This is a simulation curve comparing the tuning range of the present invention with that of a traditional Littman-type external cavity laser.

[0056] Figure 4 This is a simulation curve showing the variation characteristics of parameters sinθ+sinΦ during the synchronous adjustment process of this invention.

[0057] Figure 5 The above are simulation curves of the first-order diffraction efficiency of the high diffraction efficiency grating of this invention at different operating wavelengths.

[0058] Figure 6 The figure shows a simulation curve comparing the angle error between the synchronous closed-loop control of this invention and the traditional open-loop control.

[0059] Figure 7 The figure shows a simulation curve comparing the output power stability of the present invention with that of the traditional structure.

[0060] Figure 8 The simulation curves show the thermal drift characteristics of the present invention compared with those of traditional structures. Detailed Implementation

[0061] To make the objectives, technical solutions, and advantages of this disclosure clearer, the implementation details of the wide-tunable long-wavelength Littman type external cavity laser of this disclosure are further described in detail below with reference to specific embodiments and accompanying drawings.

[0062] The core design idea of ​​this disclosure is to achieve precise linkage between the incident angle and the diffraction angle through synchronous closed-loop control. Combined with a long-wavelength adaptive grating and a high-efficiency heat dissipation structure, it breaks through the tuning range and stability bottleneck of traditional Littman lasers, and finally achieves wide-range and highly stable laser output in the long-wavelength band.

[0063] I. Structural Assembly Details

[0064] The structural assembly of this embodiment strictly follows the principles of "stable optical path, matching parameters, efficient heat dissipation, and precise control". The selection and assembly parameters of each core component are as follows: the total length of the outer cavity is set to 150mm to minimize optical path loss and ensure efficient coupling of feedback light.

[0065] The wide gain-bandwidth laser source module uses an InP-based multi-quantum-well diode laser with a center wavelength of 1.55μm and a gain-bandwidth ≥40nm. The chip is directly bonded to a graphene heat dissipation layer, which measures 10mm × 10mm × 0.5mm, has a thermal resistance ≤0.1K / W, and a heat dissipation efficiency ≥15W / (cm²). 2•K); The laser's operating temperature is stabilized at 25±0.3℃ by the temperature control module, effectively suppressing thermal drift during high-power operation and avoiding wavelength shift.

[0066] The incident angle adjustment unit uses an electromagnetically driven apochromatic collimating lens with an 8mm focal length and a 0.15 numerical aperture, perfectly suited for the collimation requirements of a 1.55μm long-wavelength beam. The accompanying nanometer displacement platform has a travel of ±5μm and a displacement resolution of ±0.05μm, enabling precise adjustment of the incident angle from 0 to 10° (this precision meets the external cavity laser angle control requirements, referencing electromagnetically driven lens displacement control technology). A displacement sensor acquires the lens position signal in real time at a sampling frequency of 1kHz, ensuring accurate displacement control. The distance between this unit and the laser source module is fixed at 1.2mm to reduce divergence loss before laser collimation.

[0067] The diffraction angle control unit employs a biaxial piezoelectric-electromagnetic composite galvanometer with an angular resolution of 3×10⁻⁶. -4 With a rad response time ≤0.8ms and an angular travel of ±15°, it can cover the adjustment range of diffraction angle from 0 to 15°. The galvanometer surface is coated with a 1.5μm band antireflection film, achieving a reflection efficiency ≥98% and reducing optical signal loss. The angle sensor is coaxially mounted with the galvanometer, providing real-time angle feedback with a calibration error ≤0.005°. The distance between this unit and the high-diffraction-efficiency grating module is 100mm, ensuring effective transmission and reflection of diffracted light.

[0068] The high diffraction efficiency grating module uses a 2400 lines / mm holographic grating with a grating pitch d≈0.417μm. For the 1.5μm long wavelength band, the blaze angle is optimized to 55°, making the first-order diffraction efficiency ≥60% in this band (unlike the characteristics of short-wavelength holographic gratings, such as the 2400 lines / mm holographic grating in the 455nm band with a first-order diffraction efficiency of only 8.3%, the diffraction efficiency can be significantly improved by optimizing the blaze angle at long wavelengths). The grating size is 20mm×20mm×5mm. During installation, it is strictly ensured that the grating plane is perpendicular to the incident beam with a parallelism error ≤0.01° to ensure the accuracy of wavelength selection.

[0069] The core of the synchronous closed-loop control unit is an FPGA controller with an operating frequency of 100MHz, supporting high-speed synchronous processing of multi-channel signals; the light intensity detector has a detection range of 0.1μW~10mW and a detection accuracy of ±0.1μW, and monitors the external cavity feedback light intensity in real time; the controller and each control unit are connected via a high-speed bus, with a signal transmission delay of ≤10μs, ensuring the response speed of synchronous control; this unit can achieve a synchronization error of <0.01° between the incident angle and the diffraction angle, and dynamically compensate for diffraction efficiency fluctuations based on the feedback light intensity.

[0070] The output beam collimator of the output unit uses an aspherical lens with a focal length of 12mm, which can collimate the zero-order diffracted light into parallel light with a spot diameter of 2mm and a spot position fluctuation of <0.2μm; the photodetector has a response band covering 1.3~1.6μm and a response speed of ≤1ns, which is used to monitor the laser output power in real time and provide a signal basis for power stability compensation.

[0071] II. Work Process

[0072] The workflow of the wide-tunable long-wavelength Littman-type external cavity laser in this embodiment consists of five steps: wavelength setting, angle synchronization adjustment, external cavity feedback locking, stabilization control, and output monitoring. These steps are seamlessly integrated, achieving wide tuning and highly stable laser output, as detailed below:

[0073] Wavelength setting: The user inputs the target long wavelength (e.g., 1530nm) through the host computer. After receiving the target wavelength command, the FPGA controller calculates the corresponding combination of incident angle and diffraction angle (example: θ=60°, Φ=60°, sinθ+sinΦ≈1.732, close to the design upper limit of 1.8) based on the grating equation mλ=d(sinθ+sinΦ) (where the diffraction order m=1, d is the grating pitch) and the preset diffraction efficiency optimization model, and generates the angle control command.

[0074] For angle synchronization adjustment, the FPGA controller outputs a drive signal to the nanometer displacement platform of the incident angle control unit, which drives the collimating lens to move laterally, so that the incident angle of the incident beam accurately reaches the target value; at the same time, it outputs an angle control signal to the dual-axis piezoelectric-electromagnetic composite galvanometer of the diffraction angle control unit, driving the galvanometer to rotate to the target diffraction angle; the displacement sensor and the angle sensor respectively feed back the actual position and angle information to the FPGA controller in real time, and the controller performs closed-loop calibration to ensure that the synchronization error between the incident angle and the diffraction angle is <0.01°.

[0075] With external cavity feedback locking, the wide gain bandwidth laser source module is activated, generating a laser with a center wavelength of 1.55μm. After efficient heat dissipation and suppression of thermal drift by the graphene heat dissipation layer, the laser is input to the incident angle control unit. The collimating lens collimates the diverging laser into parallel light, which is incident on the high diffraction efficiency grating module at the target incident angle. The grating performs precise wavelength selection on the incident parallel light. The selected first-order diffracted light of the target wavelength is directed towards the composite galvanometer at the target diffraction angle. After being reflected by the galvanometer, it returns to the active region of the laser source module along the original path, resonating with the optical signal inside the cavity to achieve stable external cavity feedback locking.

[0076] Stable control is achieved through a light intensity detector that monitors the external cavity feedback light intensity in real time. If the feedback light intensity is lower than a set threshold (e.g., 10μW), the FPGA controller determines that the diffraction efficiency has decreased and immediately fine-tunes the galvanometer angle by 0.05°. Simultaneously, it adjusts the displacement of the nanometer displacement platform to dynamically compensate for light intensity loss and ensure the stability of the external cavity feedback. The graphene heat dissipation layer conducts heat generated by the laser source chip in real time. The temperature control module dynamically adjusts the heat dissipation power based on the temperature sensor signal to ensure that the chip temperature is stable at 25±0.3℃, effectively suppressing wavelength shift caused by thermal drift. Angle and displacement sensors continuously provide feedback information, and the controller calibrates in real time to ensure the synchronization of the incident angle and diffraction angle.

[0077] Output monitoring: The zero-order diffracted light, after being locked by feedback from the external cavity, is collimated twice by the output beam collimator of the output unit and then stably output to the outside. The photodetector collects the laser output power signal in real time and feeds the signal back to the FPGA controller. If the output power deviates from the set value (e.g., 200mW±5mW), the controller performs power compensation by fine-tuning the drive current of the laser source to ensure the stability of the output power and achieve a power fluctuation of ≤0.015 for 1 hour.

[0078] Figure 2 The simulation curves show the wavelength tuning characteristics of the present invention under the condition of synchronous adjustment of the incident angle and the diffraction angle. Under the condition of synchronous adjustment of the incident angle and the diffraction angle, the output wavelength changes continuously with the angle, indicating that the present invention can achieve continuously tunable laser output.

[0079] Figure 3 The simulation curves show the comparison between the tuning range of the present invention and the traditional Littman type external cavity laser. Compared with the traditional single-variable adjustment method, the wavelength tuning range of the present invention is significantly expanded after adopting the dual-variable synchronous adjustment method, which verifies that the present invention has a large degree of tuning freedom.

[0080] Figure 4 The figure shows the simulation curves of the parameter sinθ+sinΦ during the synchronous adjustment process of the present invention. As the incident angle and diffraction angle increase synchronously, the parameter sinθ+sinΦ continues to increase, indicating that the present invention can effectively expand the adjustable space of the grating equation through dual-variable coordinated adjustment, thereby improving the wavelength tuning capability.

[0081] Figure 5 The simulation curves of the first-order diffraction efficiency of the high diffraction efficiency grating of the present invention at different operating wavelengths show that the first-order diffraction efficiency remains at a high level within the operating wavelength range, which can provide stable optical power for external cavity feedback and ensure stable operation of the laser.

[0082] Figure 6The figure shows a simulation curve comparing the angle error between the synchronous closed-loop control of this invention and the traditional open-loop control. After adopting synchronous closed-loop control, the angle error of this invention converges rapidly and remains within a small range, and the control accuracy is significantly better than that of the traditional open-loop control method.

[0083] Figure 7 The simulation curves comparing the output power stability of the present invention with that of the traditional structure show that the output power fluctuation of the present invention is significantly reduced, indicating that the synchronous control and efficient feedback structure can effectively improve the output stability.

[0084] Figure 8 The simulation curves comparing the thermal drift characteristics of the present invention with those of the traditional structure show that, under varying ambient temperature conditions, the center wavelength drift of the present invention is significantly smaller than that of the traditional structure, verifying that the graphene heat dissipation layer and temperature control system have a good inhibitory effect on thermal drift.

[0085] To adapt to the needs of different application scenarios, the embodiments of this disclosure support flexible replacement of core modules. The replacement solutions must meet the following technical requirements:

[0086] The wide-gain bandwidth laser source module can be replaced with an InGaAsP-based laser, adapted to the 1.3μm long-wavelength band. After replacement, the laser gain bandwidth must be ≥40nm, the output power ≥200mW, and the optical coupling efficiency with the incident angle control unit ≥90%. The heat dissipation layer can be adjusted to a diamond heat sink according to the laser source power, further improving the heat dissipation efficiency to 20W / (cm²). 2 ·K), suitable for high-power operation scenarios.

[0087] The high diffraction efficiency grating module can be replaced with a 3000 lines / mm grating, optimizing the blaze angle to 60° and achieving a first-order diffraction efficiency of ≥65% in the 1.5μm band, thus improving the accuracy of wavelength selection. When replacing it, the incident angle and diffraction angle combination corresponding to the grating equation must be recalculated according to the grating parameters to ensure wavelength tuning accuracy. If applied to narrow bandwidth high-resolution scenarios, a 4000 lines / mm grating can be selected to further improve spectral resolution.

[0088] The synchronous closed-loop control unit can be replaced by adding a temperature sensor to the original system, which works in conjunction with the graphene heat dissipation layer to achieve dual compensation for temperature and angle. The temperature sensor has a measurement range of -10℃ to 80℃ and a measurement accuracy of ±0.01℃, making it suitable for applications in extreme environments such as high and low temperatures. The controller can be replaced with an industrial-grade PLC to improve the system's anti-interference capability and adapt to application scenarios such as infrared spectroscopy detection in industrial settings.

[0089] If focused output is required, the output beam collimator can be replaced with a focusing lens with a focal length of 8mm to focus the laser into a focused beam with a spot diameter of 50μm and a focusing power density ≥10W / cm². 2It is suitable for scenarios such as deep imaging of biological tissues; if fiber optic coupling output is required, a 1.5μm band single-mode fiber optic coupler can be selected with a coupling efficiency of ≥95%, which supports long-distance transmission of lasers and is suitable for fiber optic communication wavelength multiplexing scenarios.

[0090] The specific embodiments described above further illustrate the purpose, technical solutions, and beneficial effects of this disclosure. It should be understood that the above descriptions are merely specific embodiments of this disclosure and are not intended to limit this disclosure. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the protection scope of this disclosure.

Claims

1. A wide-tunable, long-wavelength Littman-type external cavity laser, characterized in that, include: Wide gain bandwidth laser source module, used to generate laser with center wavelength in the 1.3-1.6μm band; An incident angle adjustment unit is disposed on the output optical path of the wide gain bandwidth laser source module, and is used to collimate the laser into parallel light and adjust the incident angle θ of the parallel light onto the high diffraction efficiency grating module. A high diffraction efficiency grating module is disposed in the output optical path of the incident angle control unit. It is used to filter the wavelength of the beam after the angle is adjusted. Its first-order diffracted light is output to the diffraction angle control unit, and its zero-order diffracted light is output to the output unit. The diffraction angle control unit is set on the first-stage diffraction optical path of the high diffraction efficiency grating module. It is used to control the diffraction angle Φ of the first-stage diffraction light and make the first-stage diffraction light return to the wide gain bandwidth laser source module along the original path to form a stable external cavity feedback. The synchronous closed-loop control unit is electrically connected to the incident angle control unit, the diffraction angle control unit, and the high diffraction efficiency grating module, respectively. It is used to receive the target wavelength command, link the incident angle control unit to adjust the incident angle θ, and link the diffraction angle control unit to synchronously adjust the diffraction angle Φ, so that the sum of sinθ + sinΦ ≥ 1.7, which satisfies the long wavelength resonance condition of the grating equation mλ = d(sinθ + sinΦ). The output unit is located on the zero-order diffraction path of the high diffraction efficiency grating module and is used to collimate and output the zero-order diffraction light after it has been locked by external cavity feedback.

2. The wide-tunable long-wavelength Littman type external cavity laser according to claim 1, characterized in that, The synchronous closed-loop control unit includes a controller, a light intensity detector, a displacement sensor, and an angle sensor; The light intensity detector is used to monitor the feedback light intensity, the displacement sensor is used to detect the position of the incident angle control unit, and the angle sensor is used to detect the angle of the diffraction angle control unit. The controller receives feedback signals from the displacement sensor, the angle sensor, and the light intensity detector, performs closed-loop calibration on the adjustment of the incident angle and the diffraction angle to ensure that the synchronization error between the two is ≤0.01°, and dynamically compensates for diffraction efficiency fluctuations based on the feedback light intensity.

3. The wide-tunable long-wavelength Littman type external cavity laser according to claim 1, characterized in that, The wide gain-bandwidth laser source module is an InP-based multi-quantum-well diode laser, encapsulated with an integrated graphene heat dissipation layer. Its center wavelength is 1.55 μm, gain-bandwidth ≥ 40 nm, and heat dissipation efficiency ≥ 15 W / (cm²). 2 ·K).

4. The wide-tunable long-wavelength Littman type external cavity laser according to claim 1, characterized in that, The incident angle adjustment unit includes an electromagnetically driven apochromatic collimating lens, a nano-displacement platform, and a displacement sensor. The nano-displacement platform is used to drive the collimating lens to make a lateral micro-displacement to adjust the incident angle θ, with a displacement accuracy of ±0.05μm. The focal length of the collimating lens is 6-10mm.

5. The wide-tunable long-wavelength Littman type external cavity laser according to claim 1, characterized in that, The diffraction angle control unit is a biaxial piezoelectric-electromagnetic composite galvanometer with an angular resolution of 3×10⁻⁶. -4 Radius, response speed ≤0.8ms, angular travel ±15°.

6. The wide-tunable long-wavelength Littman type external cavity laser according to claim 1, characterized in that, The high diffraction efficiency grating module is a 1200 lines / mm holographic grating with optimized blaze angle and a blaze angle of 55°, achieving a first-order diffraction efficiency of ≥60% in the 1.5μm band.

7. The wide-tunable long-wavelength Littman type external cavity laser according to claim 1, characterized in that, The output unit includes an output beam collimator and a photodetector; The output beam collimator is used to collimate the zero-order diffracted light twice and then output it stably, and the photodetector is used to monitor the laser output power in real time.

8. The wide-tunable long-wavelength Littman type external cavity laser according to claim 1, characterized in that, The external cavity laser has a tuning range of 1510-1530nm, an output power of ≥200mW, a power fluctuation of ≤0.015 Hz over 1 hour, and a spot position fluctuation of <0.2μm.

9. A method for synchronously controlling a wide-tunable long-wavelength Littman-type external cavity laser according to any one of claims 1-8, characterized in that, Includes the following steps: A wide-gain, wide-bandwidth laser source module generates laser light with a center wavelength in the 1.3-1.6 μm band; The laser is collimated into parallel light by the incident angle adjustment unit, and the incident angle θ of the parallel light is adjusted to be incident on the high diffraction efficiency grating module. The synchronous closed-loop control unit receives the target wavelength command, and the incident angle adjustment unit is linked to adjust the incident angle θ. The diffraction angle adjustment unit is linked to adjust the diffraction angle Φ synchronously, so that the sum of sinθ + sinΦ ≥ 1.7, which satisfies the long wavelength resonance condition of the grating equation mλ = d(sinθ + sinΦ). The high diffraction efficiency grating module filters the wavelength of the beam after the angle is adjusted, and the first-order diffracted light is reflected by the diffraction angle control unit and returned to the wide gain bandwidth laser source module along the original path to form a stable external cavity feedback. The synchronous closed-loop control unit calibrates the synchronization between the incident angle and the diffraction angle in real time and dynamically compensates for fluctuations in diffraction efficiency to ensure the stability of the laser mode. The zero-order diffracted light, after being locked by feedback from the external cavity, is collimated by the output unit and then output.

10. The synchronization control method according to claim 9, characterized in that, The synchronous closed-loop control unit receives real-time feedback signals from the displacement sensor, angle sensor, and light intensity detector through its controller, performs closed-loop calibration on the adjustment of the incident angle and diffraction angle to ensure that the synchronization error between the two is ≤0.01°, and dynamically compensates for diffraction efficiency fluctuations based on the feedback light intensity.

Images