A littman narrow linewidth laser for semiconductor metrology

Abstract

The application provides a Littman narrow linewidth laser for semiconductor measurement, and relates to the technical field of narrow linewidth semiconductor lasers.The Littman narrow linewidth laser comprises a semiconductor gain chip, an optical shaping module, an external cavity tuning module, an output collimation module and an output monitoring module.The output monitoring module, the output collimation module, the semiconductor gain chip and the optical shaping module are located on the same optical axis, and the two ends of the semiconductor gain chip are used as the feedback end and the output end of the resonant cavity respectively.The optical shaping module receives a first light beam emitted from the feedback end, shapes and adjusts the polarization state of the first light beam to form a second light beam.The external cavity tuning module adjusts the equivalent optical path of the external cavity and selects the frequency of the second light beam.The output collimation module collimates the third light beam emitted from the output end in the fast axis and the slow axis directions, and outputs a fourth light beam obtained after collimation to the output monitoring module.The output monitoring module splits the fourth light beam at a preset ratio.

Description

Technical Field

[0001] This invention relates to the field of narrow linewidth semiconductor laser technology, and more particularly to a Littman narrow linewidth laser for semiconductor measurement. Background Technology

[0002] The core structure of a Littman laser is based on a traditional semiconductor laser, incorporating a diffraction grating and an independently tuned mirror to form an external cavity resonant system. Its basic working principle is as follows: the laser emitted from the semiconductor laser diode is collimated by a collimating lens and then incident on the diffraction grating. The grating splits and diffracts the laser beam. The first-order diffracted beam is directed towards the tuned mirror, reflected, and then incident again on the diffraction grating. The second-order diffracted beam is fed back to the active region of the semiconductor laser, forming a resonant amplification. The zero-order diffracted beam of the grating serves as the laser output, enabling the laser to be emitted. Compared to the mainstream Littrow external cavity structure, the Littman laser achieves wavelength tuning by rotating the tuned mirror instead of the grating. This keeps the output beam direction fixed as the wavelength changes, effectively solving the drawbacks of the Littrow structure where the output beam changes direction with wavelength tuning and requires frequent calibration, significantly improving the device's practicality.

[0003] Chinese patent CN110112652A discloses an external cavity tunable laser and a wavelength tuning method, belonging to the field of laser technology. The external cavity tunable laser includes: a semiconductor gain chip, a first collimating lens, a blazed grating, and a mirror opposite the blazed grating; the semiconductor gain chip, the first collimating lens, and the blazed grating are located on the same optical axis, and the grating plane of the blazed grating has an angle greater than 0 with the optical axis; wherein, the semiconductor gain chip, from left to right, includes a sampling grating region, a phase-tuning region, a gain region, and a first electrode, a second electrode, and a third electrode respectively covering the sampling grating region, the phase-tuning region, and the gain region; the blazed grating and the mirror are both fixed on an electrically or manually controlled mechanical structure. However, the above scheme only uses a single collimating lens to shape the laser at the output end and lacks a real-time closed-loop monitoring mechanism for output power and wavelength, resulting in large ellipticity of the output beam, low coupling efficiency, and the inability to automatically compensate for output power drift caused by environmental disturbances. Therefore, it is essential to provide a Littman narrow-linewidth laser for semiconductor measurement to improve the beam quality and transmission characteristics of the output beam. Summary of the Invention

[0004] In view of this, the present invention proposes a Littman narrow linewidth laser for semiconductor measurement, which helps to improve the beam quality and transmission characteristics of the output beam.

[0005] This invention provides a Littman narrow linewidth laser for semiconductor measurement. The Littman narrow linewidth laser includes a semiconductor gain chip, an optical shaping module, an external cavity tuning module, an output collimation module, and an output monitoring module. The output monitoring module, the output collimation module, the semiconductor gain chip, and the optical shaping module are located on the same optical axis. The end of the semiconductor gain chip closer to the external cavity tuning module serves as the feedback end of the resonant cavity, and the end of the semiconductor gain chip farther from the external cavity tuning module serves as the output end of the resonant cavity. The optical shaping module receives the first beam emitted from the semiconductor gain chip, shapes and adjusts the polarization state of the first beam to form a second beam, so that the polarization mode of the second beam incident on the external cavity tuning module matches the polarization mode requirement of the external cavity tuning module. The external cavity tuning module adjusts the equivalent optical path of the external cavity and selects the frequency of the second beam, and returns the frequency-selected third beam to the semiconductor gain chip; The output collimation module collimates the third beam emitted from the semiconductor gain chip in the fast axis and slow axis directions respectively, and outputs the collimated fourth beam to the output monitoring module. The output monitoring module splits the fourth beam at a preset ratio, wherein a portion of the fourth beam is used to monitor the output power of the Littman narrow linewidth laser, and the other portion of the fourth beam serves as the working light source of the semiconductor measurement system.

[0006] Based on the above technical solutions, preferably, the optical shaping module includes an aspherical lens and a half-wave plate located on the same optical axis. The aspherical lens is disposed on the side close to the semiconductor gain chip, and the half-wave plate is disposed on the side close to the external cavity tuning module. The focal length of the aspherical lens is 3mm, the numerical aperture of the focal length of the aspherical lens is 0.5, and the operating wavelength of the half-wave plate is 600~700nm.

[0007] Based on the above technical solutions, preferably, the external cavity tuning module includes a blazed metal grating, a mirror, a piezoelectric tuning component, and a piezoelectric driving unit. The blazed metal grating is used to diffract the second beam and select the -1st order diffracted light as the external cavity feedback light. The mirror is used to perform total internal reflection of the -1st order diffracted light and cause the -1st order diffracted light to return to the semiconductor gain chip after secondary diffraction by the blazed metal grating. The piezoelectric tuning component is connected to the mirror and, driven by the piezoelectric driving unit, causes the mirror to deflect at an angle to change the equivalent optical path of the external cavity.

[0008] More preferably, the scintillation density of the scintillation metal grating is 1200~2400 lines / mm, the scintillation angle of the scintillation metal grating is 21.8°, and the incident angle between the second beam and the scintillation metal grating in the external cavity tuning module is 5°~15°.

[0009] More preferably, the polarization direction of the semiconductor gain chip is parallel to the scribed line direction of the blazed metal grating.

[0010] More preferably, the extension lines of the semiconductor gain chip, the blazed metal grating, and the reflector intersect at a virtual rotation center, and the reflector deflects at an angle around the virtual rotation center.

[0011] More preferably, the output collimation module includes a fast-axis collimating lens and a slow-axis collimating lens located on the same optical axis. The fast-axis collimating lens is disposed on the side closer to the semiconductor gain chip, and the slow-axis collimating lens is disposed on the side closer to the output monitoring module.

[0012] More preferably, the beam output by the semiconductor gain chip has a divergence angle of 30° in the fast axis direction and a divergence angle of 8° in the slow axis direction, the focal length of the fast axis collimating lens is 1.5 mm, the numerical aperture of the fast axis collimating lens is 0.6, and the focal length of the slow axis collimating lens is 8 mm.

[0013] More preferably, the output monitoring module includes a beam splitter, an isolator, an optical fiber collimator, and a photodetector. The beam splitter, the isolator, and the optical fiber collimator are located on the same optical axis. The beam splitter is used to split the fourth beam from the output collimation module into a first output beam and a second output beam according to a preset ratio. The first output beam is used to monitor the output power of the Littman narrow linewidth laser, and the second output beam serves as the working light source of the semiconductor measurement system. The beam splitting ratio between the first output beam and the second output beam is 1:99 to 1:20.

[0014] More preferably, the isolator is an optical fiber isolator or a free space optical isolator, the isolator has an isolation greater than 40dB, and the isolator has an insertion loss less than 0.5dB.

[0015] The Littman narrow-linewidth laser for semiconductor measurement provided by this invention has the following advantages over the prior art: (1) The external cavity equivalent optical path is adjusted and the frequency is selected by the external cavity tuning module. The frequency-selected third beam is fed back to the semiconductor gain chip to form a highly selective external cavity resonance, realize narrow linewidth output and reduce mode jump, and meet the requirements of semiconductor measurement for high coherence and high frequency stability. The optical shaping module shapes and adjusts the polarization state of the feedback beam so that the second beam is precisely matched with the polarization requirements of the external cavity tuning module in terms of polarization mode, improves the working efficiency of the external cavity frequency selection element, reduces loss and parasitic modes, thereby improving the stability and repeatability of the laser output. In addition, the output collimation module collimates the third beam emitted from the output end in the fast axis and slow axis directions respectively to obtain The fourth beam, which is approximately circularly symmetrical and has a small divergence angle, can significantly improve beam quality and transmission characteristics. The output monitoring module splits the fourth beam according to a preset ratio. One beam is used to monitor the laser output power in real time, and the other beam serves as the working light source of the semiconductor measurement system. This enables power drift detection and closed-loop control, thereby ensuring the long-term stability of the working light source power and improving the accuracy and repeatability of measurement results. The output monitoring module, output collimation module, semiconductor gain chip, and optical shaping module are located on the same optical axis, simplifying the optical path design and assembly process, reducing the system alignment difficulty and environmental disturbance sensitivity, which is conducive to miniaturization and integrated packaging, and improving the reliability of engineering applications.

[0016] (2) By using a blazed metal grating to diffract the second beam and selecting the -1st order diffracted light as the external cavity feedback light, the external cavity feedback is mainly concentrated on the high-efficiency working order of the grating. The blazed metal grating has high diffraction efficiency and obvious wavelength selectivity in the target band. Combined with the structure of the -1st order diffracted light returning to the semiconductor gain chip after secondary diffraction, a highly spectral selectivity external cavity feedback channel can be formed, thereby effectively suppressing the undesired longitudinal mode, realizing narrow linewidth output and improving the purity of the laser spectrum. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art 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.

[0018] Figure 1 A schematic diagram of the structure of a Littman narrow linewidth laser for semiconductor measurement provided by the present invention; Figure 2 This is a schematic diagram of the structure of the optical shaping module provided by the present invention; Figure 3 This is a schematic diagram of the reflector rotating around a virtual rotation center provided by the present invention.

[0019] Explanation of reference numerals in the attached figures: 1. Semiconductor gain chip; 2. Optical shaping module; 21. Aspherical lens; 22. Half-wave plate; 23. Coaxial lens barrel; 3. External cavity tuning module; 31. Blazed metal grating; 32. Mirror; 33. Piezoelectric tuning assembly; 34. Piezoelectric drive unit; 4. Output collimation module; 41. Fast axis collimating lens; 42. Slow axis collimating lens; 5. Output monitoring module; 51. Beam splitter prism; 52. Photodetector; 53. Isolator; 54. Fiber optic collimator. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0021] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Similarly, the terms "an" or "a" and similar terms do not indicate a quantity limitation, but rather indicate the presence of at least one. The terms "connected" or "linked" and similar terms are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. "Up," "down," "left," "right," etc., are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship also changes accordingly.

[0022] refer to Figure 1 This invention provides a Littman narrow linewidth laser comprising a semiconductor gain chip 1, an optical shaping module 2, an external cavity tuning module 3, an output collimation module 4, and an output monitoring module 5, wherein... The output monitoring module 5, the output collimation module 4, the semiconductor gain chip 1, and the optical shaping module 2 are located on the same optical axis. The end of the semiconductor gain chip 1 closest to the external cavity tuning module 3 serves as the feedback end of the resonant cavity, and the end of the semiconductor gain chip 1 furthest from the external cavity tuning module 3 serves as the output end of the resonant cavity.

[0023] Semiconductor gain chip 1 serves as a laser radiation source, providing optical gain. The semiconductor laser gain chip covers commonly used semiconductor measurement wavelengths such as 633nm, 785nm, and 1064nm. The polarization of semiconductor gain chip 1 is in conventional TE mode, with the polarization direction parallel to the scribe lines of the blazed metal grating 31. The beam output from semiconductor gain chip 1 has a divergence angle of 30° along the fast axis and 8° along the slow axis.

[0024] The optical shaping module 2 receives the first beam emitted from the semiconductor gain chip 1, shapes and adjusts the polarization state of the first beam to form a second beam, so that the second beam incident on the external cavity tuning module 3 matches the polarization mode requirement of the external cavity tuning module 3.

[0025] Specifically, the optical shaping module 2 includes an aspherical lens 21 and a half-wave plate 22 located on the same optical axis. The aspherical lens 21 is disposed on the side close to the semiconductor gain chip 1, and the half-wave plate 22 is disposed on the side close to the external cavity tuning module 3. The focal length of the aspherical lens 21 is 3mm, the numerical aperture of the focal length of the aspherical lens 21 is 0.5, the operating wavelength of the half-wave plate 22 is 600~700nm, and the phase delay accuracy is λ / 300.

[0026] In one example, the optical shaping module 2 also includes a coaxial lens barrel 23, in which the aspherical lens 21 and the half-wave plate 22 are fixed. The optical shaping module 2 collimates and shapes the light beam emitted from the feedback end of the semiconductor gain chip 1 through the aspherical lens 21. The collimated laser beam undergoes polarization rotation through the half-wave plate 22 to match the polarization mode of the diffraction grating. Figure 2 As shown, the aspherical lens 21 and the half-wave plate 22 are fixed to the coaxial lens barrel 23 with glue.

[0027] In this embodiment, an aspherical lens 21 with a focal length of 3mm and a numerical aperture of 0.5 is provided on the side close to the semiconductor gain chip 1. This lens can fully converge the high numerical aperture divergent light output by the semiconductor gain chip 1, effectively reduce aberrations such as spherical aberration, and improve the beam shaping quality. This optimizes the spatial mode and divergence angle of the first beam, providing a high-quality incident light field for subsequent external cavity frequency selection, thereby improving the efficiency and stability of the external cavity operation.

[0028] A half-wave plate 22 with a working wavelength of 600~700nm and a phase delay accuracy of λ / 300 is set on the side near the external cavity tuning module 3. It can finely adjust the polarization state of the second beam throughout the entire working wavelength range, ensuring high precision and high stability of the output polarization angle. This ensures that the polarization mode of the second beam incident on the external cavity tuning module 3 is highly matched with the polarization requirements of the external cavity tuning module 3, thereby improving the working efficiency of the polarization-related frequency selection element.

[0029] By combining beam shaping and polarization matching, the second beam entering the external cavity tuning module 3 meets the optimal operating conditions of the external cavity in both spatial and polarization modes. This can significantly reduce insertion loss caused by mode mismatch, suppress oscillations of undesired polarization states and higher-order transverse modes, reduce parasitic modes and mode competition in the external cavity, thereby improving frequency selection and enhancing the linewidth characteristics and frequency stability of the laser.

[0030] The half-wave plate 22 operates in the 600-700nm band and has high phase delay accuracy, ensuring stable and repeatable polarization state control within the laser's operating wavelength tuning range. This avoids fluctuations in external cavity frequency selection performance caused by significant changes in polarization state at different wavelengths, further ensuring the continuity and consistency of the output characteristics of the narrow-linewidth laser across a wide band.

[0031] The external cavity tuning module 3 adjusts the equivalent optical path of the external cavity and selects the frequency of the second beam, and then returns the frequency-selected third beam to the semiconductor gain chip 1.

[0032] Specifically, the external cavity tuning module 3 includes a blazed metal grating 31, a mirror 32, a piezoelectric tuning component 33, and a piezoelectric driving unit 34. The blazed metal grating 31 is used to diffract the second beam and select the -1st order diffracted light as the external cavity feedback light. The mirror 32 is used to perform total internal reflection of the -1st order diffracted light and make the -1st order diffracted light return to the semiconductor gain chip 1 after secondary diffraction by the blazed metal grating 31. The piezoelectric tuning component 33 is connected to the mirror 32 and drives the mirror 32 to deflect at an angle under the drive of the piezoelectric driving unit 34, so as to change the equivalent optical path of the external cavity.

[0033] A blazed metal grating 31 is used to diffract the second beam, and the -1st order diffracted light is selected as the external cavity feedback light, so that the external cavity feedback is mainly concentrated on the high-efficiency operating order of the grating. The blazed metal grating 31 has high diffraction efficiency and obvious wavelength selectivity in the target wavelength band. Combined with the structure where the -1st order diffracted light returns to the semiconductor gain chip 1 after secondary diffraction, a highly spectrally selective external cavity feedback channel can be formed, thereby effectively suppressing undesired longitudinal modes, achieving narrow linewidth output, and improving laser spectral purity. The mirror 32 performs total internal reflection on the -1st order diffracted light and causes it to re-enter the blazed metal grating 31, returning to the semiconductor gain chip 1 after secondary diffraction. Through the two diffraction effects of the grating, the overall wavelength selectivity of the external cavity is significantly enhanced, and the suppression of non-resonant wavelengths and undesired modes is more effective. This is beneficial for increasing the single longitudinal mode operating probability, reducing mode jumps, and improving the frequency stability and output consistency of the laser.

[0034] The reflector 32 is mounted on the piezoelectric tuning assembly 33 and driven by the piezoelectric driving unit 34, causing the reflector 32 to deflect at a fine angle, thereby changing the equivalent optical path of the external cavity and the center wavelength of the feedback light. The piezoelectric tuning method offers fast response and high resolution, exhibiting smaller mechanical backlash and better repeatability compared to large-stroke mechanical rotation or translation mechanisms. It enables high-precision, continuous tuning of the external cavity wavelength, which is beneficial for obtaining continuously adjustable laser output with narrow linewidth and low drift.

[0035] During external cavity tuning, only a small angle adjustment is required for the reflector 32 mounted on the piezoelectric tuning assembly 33, while other optical components such as the blazed metal grating 31 remain fixed, reducing the number and range of motion of moving elements within the external cavity. This structure helps reduce the impact of environmental factors such as vibration and temperature changes on optical path alignment and frequency selection performance, improving the overall stability and long-term reliability of the external cavity structure.

[0036] In one example, the external cavity tuning module 3 is used to achieve laser external cavity locking and precise tuning. The blazed metal grating 31 is used to diffract the laser collimated at the feedback end. Light of a specific wavelength with a diffraction order of -1 is selected and incident on the reflector 32. The reflector 32 is used for total internal reflection grating to diffract the perpendicularly incident laser. The light returns along the original path, is diffracted by the blazed metal grating 31, and then returns to the laser gain chip to form external cavity resonance. The piezoelectric tuning component 33 is rigidly connected to the reflector 32. The piezoelectric control system drives the piezoelectric tuning component 33, which drives the reflector 32 to perform high-speed, high-precision angle deflection through the piezoelectric effect, thereby changing the equivalent optical path of the external cavity and achieving tuning of the output wavelength. The reflector 32 is located between the blazed metal grating 31 and the piezoelectric tuning component 33.

[0037] The piezoelectric tuning component 33 adopts a multi-layer piezoelectric ceramic stacked structure. The telescopic end of the piezoelectric tuning component 33 is rigidly connected to the cantilever end of the reflector 32. The piezoelectric ceramic extends and retracts tangentially parallel to the rotation axis of the reflector 32, driving the reflector 32 to perform high-precision angle deflection around the virtual rotation center. The response time is less than or equal to 50μs, and the maximum deflection angle is greater than or equal to ±1.5°. Preferably, the driving voltage of the piezoelectric tuning component 33 is 0~150V, the response time is 30μs, and the maximum deflection angle is ±2°.

[0038] The blazed metal grating 31 has a line density of 1200~2400 lines / mm, a blaze angle of 21.8°, and an incident angle of 5°~15° between the second beam and the blazed metal grating 31 in the external cavity tuning module 3. Furthermore, the polarization direction of the semiconductor gain chip 1 is parallel to the line direction of the blazed metal grating 31.

[0039] In this embodiment, the piezoelectric tuning component 33 adopts a multilayer piezoelectric ceramic stacked structure. Its telescopic end is rigidly connected to the cantilever end of the reflector 32. The piezoelectric ceramic extends and retracts along a tangential direction parallel to the rotation axis of the reflector 32, driving the reflector 32 to deflect at an angle around a virtual rotation center. This structure highly couples the angle tuning of the reflector 32 with the linear extension and retraction of the piezoelectric ceramic, resulting in high angular resolution, low hysteresis, and a response time of less than or equal to 50 μs, preferably 30 μs. This enables high-speed and precise tuning of the external cavity equivalent optical path, meeting the application requirements of narrow-linewidth lasers such as rapid scanning and frequency locking.

[0040] The multilayer piezoelectric ceramic stack structure provides a large stroke, with a maximum deflection angle greater than or equal to ±1.5°, preferably ±2° under a driving voltage of 0~150V. This allows the incident angle of the external cavity feedback light to change continuously within a certain range, thereby achieving continuous adjustment of the laser output wavelength within a predetermined range, taking into account both high-resolution tuning and a large wavelength scanning range.

[0041] The blazed metal grating 31 has a line density of 1200~2400 lines / mm. Combined with a blaze angle of 21.8° and a second beam incident angle of 5°~15°, the -1st order diffracted light achieves high diffraction efficiency and large angular dispersion within the target operating wavelength range. This significantly improves the external cavity's wavelength resolution, which is beneficial for obtaining laser output with narrow linewidth and high spectral purity. At the same time, it matches the blaze direction with the diffraction direction corresponding to the operating wavelength, thereby achieving near-optimal blaze efficiency near the target operating wavelength range. This reduces the power loss of the external cavity feedback link, increases the feedback light power and external cavity quality factor, and improves the laser's start-up conditions and output stability.

[0042] The polarization direction of the semiconductor gain chip 1 is designed to be parallel to the scribed direction of the blazed metal grating 31, so that the polarization state incident on the grating matches the diffraction efficiency characteristics of the grating in that polarization direction, thereby improving the effective utilization of the -1st order diffracted light and further reducing the external cavity insertion loss. At the same time, the uniformity of the polarization state helps to suppress the oscillation of unwanted polarization modes, and together with the frequency selection function of the external cavity, improves the stability of single-polarization, single-longitudinal-mode output.

[0043] In one example, such as Figure 3 As shown, the extended lines of the semiconductor gain chip 1, the blazed metal grating 31, and the reflector 32 intersect at the virtual rotation center, and the reflector 32 deflects at an angle around the virtual rotation center.

[0044] Specifically, the reflector 32 is fixed on the piezoelectric tuning assembly 33, which is driven by the piezoelectric driving unit 34. When the piezoelectric driving unit 34 applies a control voltage, the piezoelectric tuning assembly 33 undergoes a slight stretching and contraction deformation, causing the reflector 32 to deflect at a small angle around a predetermined virtual rotation center. Figure 3 In the diagram, the extensions of the three optical paths, indicated by dashed lines, intersect at a single point, which is the virtual rotation center. This structural arrangement ensures that during tuning, the angle change of the reflector 32 is equivalent to rotation around the virtual rotation center. This allows for changing the equivalent optical path of the external cavity and achieving continuous adjustment of the laser output wavelength while maintaining the spatial direction of the output beam. The introduction of a piezoelectric angle tuning mechanism constrained by the virtual rotation center enables rapid and precise electronic tuning of the laser's center wavelength while maintaining a stable output beam direction.

[0045] The output collimation module 4 collimates the third beam emitted from the semiconductor gain chip 1 in the fast axis and slow axis directions respectively, and outputs the collimated fourth beam to the output monitoring module 5.

[0046] Specifically, the output collimation module 4 includes a fast-axis collimating lens 41 and a slow-axis collimating lens 42 located on the same optical axis. The fast-axis collimating lens 41 is disposed on the side closer to the semiconductor gain chip 1, and the slow-axis collimating lens 42 is disposed on the side closer to the output monitoring module 5. The fast-axis collimating lens 41 has a focal length of 1.5 mm and a numerical aperture of 0.6, while the slow-axis collimating lens 42 has a focal length of 8 mm.

[0047] The output monitoring module 5 splits the fourth beam at a preset ratio. One part of the fourth beam is used to monitor the output power of the Littman narrow linewidth laser, and the other part of the fourth beam serves as the working light source for the semiconductor measurement system.

[0048] Specifically, the output monitoring module 5 includes a beam splitter 51, an isolator 53, an optical fiber collimator 54, and a photodetector 52. The beam splitter 51, the isolator 53, and the optical fiber collimator 54 are located on the same optical axis. The beam splitter 51 is used to split the fourth beam from the output collimation module 4 into a first output beam and a second output beam according to a preset ratio. The first output beam is used to monitor the output power of the Littman narrow linewidth laser, and the second output beam serves as the working light source of the semiconductor measurement system. The beam splitting ratio of the first output beam to the second output beam is 1:99 to 1:20.

[0049] The output monitoring module 5 is used to proportionally split the beam emitted from the output collimating module 4 by the beam splitter prism 51. The majority of the beam passes through the isolator 53 and then enters the fiber optic collimator 54 for output. A small portion of the beam is input to the detector for power monitoring. The isolator 53 is either a fiber optic isolator or a free-space isolator, with an isolation greater than 40 dB and an insertion loss less than 0.5 dB.

[0050] During operation, the first beam emitted from the semiconductor gain chip 1 towards the feedback end first enters the optical shaping module 2. The optical shaping module 2 collimates and shapes the first beam using an aspherical lens 21 and rotates its polarization state using a half-wave plate 22. This ensures that the shaped second beam matches the operating mode of the blazed metal grating 31 in the external cavity tuning module 3 in both beam shape and polarization state, thereby achieving narrow linewidth and high side-mode suppression ratio without sacrificing diffraction efficiency. By changing the position of the optical shaping module 2 along the optical axis, the incident angle of the second beam onto the blazed metal grating 31 can be adjusted, achieving coarse tuning of the laser's center wavelength. Furthermore, since the output optical path is separated from the feedback optical path, the coarse tuning process does not cause a change in the output beam direction.

[0051] The second beam, shaped by the optical shaping module 2, is incident on the blazed metal grating 31 in the external cavity tuning module 3. The blazed metal grating 31 diffracts the incident light and selects the -1st order diffracted light that satisfies the grating equation as the external cavity feedback light. This -1st order diffracted light is then incident on the mirror 32 in the external cavity tuning module 3 at a predetermined angle. The mirror 32 performs total internal reflection on the incident diffracted light, causing it to be incident on the blazed metal grating 31 again. The feedback light after the second diffraction returns along the original optical path and is injected into the active region from the feedback end of the semiconductor gain chip 1, coupling with the longitudinal mode inside the chip to form an external cavity resonance. The piezoelectric tuning component 33 in the external cavity tuning module 3 is rigidly connected to the reflector 32. Under the action of the piezoelectric driving signal, the reflector 32 is driven to deflect at a small angle around the virtual rotation center, thereby changing the equivalent optical path and frequency selection conditions of the external cavity, realizing continuous fine tuning of the output wavelength, and keeping the output beam direction basically unchanged throughout the entire tuning range, thus obtaining a wide range of mode-free narrow linewidth tunable laser output.

[0052] Simultaneously, the laser beam emitted from the output end of the semiconductor gain chip 1 is collimated and shaped along the fast and slow axes by the fast-axis collimating lens 41 and slow-axis collimating lens 42 of the output collimation module 4, respectively, forming a fourth beam that is approximately parallel and has good spot quality. After entering the output monitoring module 5, the fourth beam is split by a non-polarizing beam splitter according to a preset ratio. A small portion of the optical power is guided to a detector for real-time monitoring of the laser's output power, achieving closed-loop stable control. The remaining majority of the optical power is output through the isolator 53 and fiber collimator 54, serving as the working light source for the semiconductor measurement system. The isolator 53 is used to suppress external reflected light from returning to the laser, thereby improving the overall system stability and reliability.

[0053] In this embodiment, the external cavity tuning module 3 adjusts the equivalent optical path and selects the frequency of the external cavity, feeding the frequency-selected third beam back to the semiconductor gain chip 1 to form a highly selective external cavity resonance. This achieves narrow linewidth output and reduces mode hopping, meeting the requirements of semiconductor measurement for high coherence and high frequency stability. The optical shaping module 2 shapes and adjusts the polarization state of the feedback beam, ensuring that the second beam's polarization mode precisely matches the polarization requirements of the external cavity tuning module 3. This improves the efficiency of the external cavity frequency selection element, reduces losses and parasitic modes, thereby enhancing the stability and repeatability of the laser output. Furthermore, the output collimation module 4 collimates the third beam emitted from the output end in the fast and slow axis directions, respectively. The system obtains a fourth beam with near-circular symmetry and a small divergence angle, which can significantly improve beam quality and transmission characteristics. The output monitoring module 5 splits the fourth beam according to a preset ratio. One beam is used to monitor the laser output power in real time, and the other beam serves as the working light source of the semiconductor measurement system. It can realize power drift detection and closed-loop control to ensure the long-term stability of the working light source power, thereby improving the accuracy and repeatability of measurement results. The output monitoring module 5, output collimation module 4, semiconductor gain chip 1 and optical shaping module 2 are located on the same optical axis, which simplifies the optical path design and assembly process, reduces the system alignment difficulty and environmental disturbance sensitivity, and is conducive to miniaturization and integrated packaging, thereby improving the reliability of engineering applications.

[0054] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A Littman narrow-linewidth laser for semiconductor measurement, characterized in that, The Littman narrow linewidth laser includes a semiconductor gain chip (1), an optical shaping module (2), an external cavity tuning module (3), an output collimation module (4), and an output monitoring module (5), wherein, The output monitoring module (5), the output collimation module (4), the semiconductor gain chip (1) and the optical shaping module (2) are located on the same optical axis. The end of the semiconductor gain chip (1) closer to the external cavity tuning module (3) serves as the feedback end of the resonant cavity, and the end of the semiconductor gain chip (1) further away from the external cavity tuning module (3) serves as the output end of the resonant cavity. The optical shaping module (2) receives the first beam emitted from the semiconductor gain chip (1), shapes and adjusts the polarization state of the first beam to form a second beam, so that the second beam incident on the external cavity tuning module (3) matches the polarization mode requirement of the external cavity tuning module (3) in terms of polarization mode. The external cavity tuning module (3) adjusts the external cavity equivalent optical path and selects the frequency of the second beam, and returns the frequency-selected third beam to the semiconductor gain chip (1); The output collimation module (4) collimates the third beam emitted from the semiconductor gain chip (1) in the fast axis and slow axis directions respectively, and outputs the collimated fourth beam to the output monitoring module (5); The output monitoring module (5) splits the fourth beam at a preset ratio, wherein a portion of the fourth beam is used to monitor the output power of the Littman narrow linewidth laser, and the other portion of the fourth beam serves as the working light source of the semiconductor measurement system.

2. A Littman narrow-linewidth laser for semiconductor measurement as described in claim 1, characterized in that, The optical shaping module (2) includes an aspherical lens (21) and a half-wave plate (22) located on the same optical axis. The aspherical lens (21) is disposed on the side close to the semiconductor gain chip (1), and the half-wave plate (22) is disposed on the side close to the external cavity tuning module (3). The focal length of the aspherical lens (21) is 3 mm, the numerical aperture of the focal length of the aspherical lens (21) is 0.5, and the operating wavelength of the half-wave plate (22) is 600~700 nm.

3. A Littman narrow-linewidth laser for semiconductor measurement as described in claim 1, characterized in that, The external cavity tuning module (3) includes a blazed metal grating (31), a mirror (32), a piezoelectric tuning component (33), and a piezoelectric driving unit (34). The blazed metal grating (31) is used to diffract the second beam and select the -1st order diffracted light as the external cavity feedback light. The mirror (32) is used to perform total internal reflection on the -1st order diffracted light and make the -1st order diffracted light return to the semiconductor gain chip (1) after secondary diffraction by the blazed metal grating (31). The piezoelectric tuning component (33) is connected to the mirror (32) and drives the mirror (32) to deflect at an angle under the drive of the piezoelectric driving unit (34) to change the equivalent optical path of the external cavity.

4. A Littman narrow-linewidth laser for semiconductor measurement as described in claim 3, characterized in that, The scintillation density of the scintillation grating (31) is 1200~2400 lines / mm, the scintillation angle of the scintillation grating (31) is 21.8°, and the incident angle between the second beam and the scintillation grating (31) in the external cavity tuning module (3) is 5°~15°.

5. A Littman narrow-linewidth laser for semiconductor measurement as described in claim 3, characterized in that, The polarization direction of the semiconductor gain chip (1) is parallel to the scribed line direction of the blazed metal grating (31).

6. A Littman narrow-linewidth laser for semiconductor measurement as described in claim 3, characterized in that, The extension lines of the semiconductor gain chip (1), the blazed metal grating (31), and the reflector (32) intersect at a virtual rotation center, and the reflector (32) deflects at an angle around the virtual rotation center.

7. A Littman narrow-linewidth laser for semiconductor measurement as described in claim 1, characterized in that, The output collimation module (4) includes a fast-axis collimating lens (41) and a slow-axis collimating lens (42) located on the same optical axis. The fast-axis collimating lens (41) is disposed on the side close to the semiconductor gain chip (1), and the slow-axis collimating lens (42) is disposed on the side close to the output monitoring module (5).

8. A Littman narrow-linewidth laser for semiconductor measurement as described in claim 7, characterized in that, The beam output by the semiconductor gain chip (1) has a divergence angle of 30° in the fast axis direction and 8° in the slow axis direction. The focal length of the fast axis collimating lens (41) is 1.5 mm, the numerical aperture of the fast axis collimating lens (41) is 0.6, and the focal length of the slow axis collimating lens (42) is 8 mm.

9. A Littman narrow-linewidth laser for semiconductor measurement as described in claim 1, characterized in that, The output monitoring module (5) includes a beam splitter (51), an isolator (53), an optical fiber collimator (54), and a photodetector (52). The beam splitter (51), the isolator (53), and the optical fiber collimator (54) are located on the same optical axis. The beam splitter (51) is used to split the fourth beam from the output collimation module (4) into a first output beam and a second output beam according to a preset ratio. The first output beam is used to monitor the output power of the Littman narrow linewidth laser, and the second output beam is used as the working light source of the semiconductor measurement system. The beam splitting ratio of the first output beam and the second output beam is 1:99 to 1:

20.

10. A Littman narrow-linewidth laser for semiconductor measurement as described in claim 9, characterized in that, The isolator (53) is an optical fiber isolator (53) or a free space optical isolator (53), the isolation of the isolator (53) is greater than 40dB, and the insertion loss of the isolator (53) is less than 0.5dB.

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