Laser based on double electrostatic field tfln grating and phase section external cavity enhancement

Abstract

The application relates to the technical field of semiconductor lasers, in particular to a laser based on a double-electrostatic-field TFLN grating and a phase-section external cavity enhancement, which comprises an InP-based gain chip and a monolithic thin-film lithium niobate (TFLN) passive optical waveguide chip; a high-reflection HR film is evaporated on the back light end surface of the InP-based gain chip, the reflectivity is 90%-99%, an ultra-low-reflection AR antireflection film is evaporated on the light-emitting end surface, and the reflectivity is 0.005%-1%; the monolithic TFLN passive optical waveguide chip is optically coupled and docked to the back light end surface of the InP-based gain chip; the monolithic TFLN passive optical waveguide chip is a continuous ridge back waveguide structure integrally etched and formed on the same chip, and a long Bragg grating ridge back waveguide section and a grating-free ridge are sequentially arranged along the light transmission direction. The application is different from the traditional single-grating electro-optic tuning mode, the two-section structure is independently modulated and works in series cooperation, and phase accurate compensation and wavelength accurate matching are respectively realized.

Description

Technical Field

[0001] This invention relates to the field of semiconductor laser technology, specifically to a laser based on a dual electrostatic field TFLN grating and phase segment external cavity enhancement. Background Technology

[0002] Ultra-narrow linewidth single-frequency lasers are the core light source for modern coherent detection and precision optical measurement systems. Currently, commercial and research-grade narrow linewidth light sources mainly fall into two mainstream technical routes, but both have inherent technical defects that cannot be avoided.

[0003] The first category consists of traditional silicon nitride and silicon dioxide passive waveguide external cavity lasers, which rely on thermo-optical effects to achieve wavelength matching and phase compensation modulation. Thermo-optical modulation depends on resistive Joule heating to change the effective refractive index of the waveguide, which has three major drawbacks: First, high static power consumption and severe heat accumulation during long-term operation induce thermal refraction noise and slow wavelength drift, significantly increasing low-frequency phase noise and making it difficult to maintain ultra-narrow linewidth output stably for a long time; second, limited by the thermal conduction rate, the tuning response speed is slow and cannot meet the application requirements of high-speed real-time frequency stabilization and fast linear frequency sweep; third, thermal crosstalk easily causes interference beat frequency in the composite cavity dual cavity, resulting in mode jitter, drop in spectral side-mode suppression ratio, frequent mode jumping, poor environmental disturbance resistance, and insufficient long-term operational stability.

[0004] The second type is the existing single-mode TFLN external cavity laser. Utilizing the excellent Pockels electro-optic effect of TFLN material, it can achieve low power consumption and high-speed tuning, completely avoiding the drawbacks of thermo-optic devices. However, the existing technology only sets a single electro-optic control electrode in the TFLN grating region, which can only achieve unidirectional wavelength tuning and has significant technical bottlenecks: limited by the thin film breakdown voltage and inherent electro-optic coefficient, the effective refractive index tuning range of a single grating segment is limited, and the wavelength matching window is narrow; at the same time, it cannot independently compensate for the phase drift of the composite cavity, and wavelength matching and phase stability cannot be decoupled and controlled. Small disturbances in temperature and driving current can cause mismatch between the gain chip resonance peak and the external cavity grating reflection peak, greatly limiting the narrow linewidth stable operating range.

[0005] In addition, the existing external cavity laser coupling architecture design is simple and fails to adapt to both industrial stable scenarios and scientific research extreme performance scenarios: DFB composite external cavity structure has good stability but lacks high-speed and high-precision phase compensation methods, SOA external cavity structure has great potential for extreme linewidth but is extremely prone to mode hopping due to loss of lock. The industry lacks a monolithic TFLN integrated architecture that can realize "wavelength coarse tuning + phase fine tuning" dual-degree-of-freedom electrostatic field decoupling control.

[0006] In summary, existing technologies suffer from multiple drawbacks, including high power consumption, slow response, and high noise in thermo-optical solutions; limited electro-optical tuning range of a single TFLN; inability to decouple and stabilize frequency; and poor architecture adaptability. Therefore, there is an urgent need for a novel dual electrostatic field decoupled control scheme for TFLN external cavity lasers. Summary of the Invention

[0007] To address the problems mentioned in the background section, the present invention provides the following technical solution:

[0008] Lasers based on dual electrostatic field TFLN gratings and phase segment external cavity enhancement include InP-based gain chips and monolithic thin-film lithium niobate (TFLN) passive optical waveguide chips.

[0009] The backlight end face of the InP-based gain chip is coated with a high-reflectivity (HR) film with a reflectivity of 90%-99%, and the light-emitting end face is coated with an ultra-low-reflectivity (AR) anti-reflection film with a reflectivity of 0.005%-1%. The monolithic TFLN passive waveguide chip is optically coupled to the backlight end face of the InP-based gain chip.

[0010] The monolithic TFLN passive optical waveguide chip is a continuous spine waveguide structure integrally etched on the same chip. A long Bragg grating spine waveguide section and a gratingless spine phase adjustment section are sequentially arranged along the optical transmission direction. The two waveguide sections are not cut or have discrete coupling interfaces, resulting in a continuous optical path with low loss.

[0011] The long Bragg grating back waveguide section is equipped with a first set of independent electro-optic driving electrodes, and the gratingless back phase adjustment section is equipped with a second set of independent electro-optic driving electrodes. The two sets of electrodes are mutually insulated and driven by independent electrostatic fields. The signal crosstalk between the electrodes is extremely low, and the crosstalk effect is negligible and will not interfere with the modulation accuracy.

[0012] Both waveguides rely on the electro-optic effect of Pockels electrostatic field of TFLN material to achieve effective refractive index modulation. No thermo-optic heating resistors or thermo-optic tuning electrodes are set. The entire process is carried out using a pure electro-optic tuning method.

[0013] The long Bragg grating back waveguide section is used to change the effective refractive index of the waveguide through electro-optic tuning to achieve coarse matching of the Bragg reflection center wavelength, so that the external cavity reflection peak is precisely aligned with the inherent resonant peak of the InP-based gain chip, thereby improving the external cavity self-injection feedback intensity.

[0014] The gratingless ridge phase adjustment section is used to precisely change the total optical path of the external cavity through electro-optic tuning, thereby achieving fine compensation of the round-trip phase of the composite cavity and suppressing the beat frequency noise of the dual-cavity interference.

[0015] The DFB chip integrates a distributed grating and an external long Bragg grating (TFLN) to construct a composite long resonant cavity structure, which extends the photon storage lifetime. It also compresses the intrinsic linewidth of the laser through a self-injection locking mechanism, and stably achieves ultra-narrow linewidth single-frequency laser output under normal constant temperature and vibration reduction conditions.

[0016] The InP-based gain chip is either an InP-based DFB gain chip or an InP-based SOA gain chip.

[0017] As a preferred embodiment of the above technical solution, the length of the gratingless spine phase adjustment section is in the range of hundreds of micrometers to millimeters, and the length of the long Bragg grating spine waveguide section is in the range of centimeters; the grating period of the long Bragg grating spine waveguide section is adapted to the 1550nm communication band, and the grating coupling coefficient is adapted to the narrowband frequency selection requirements.

[0018] As a preferred embodiment of the above technical solution, the first set of independent electro-optic driving electrodes and the second set of independent electro-optic driving electrodes are respectively applied with low-voltage electrostatic driving voltage. The electro-optic coefficient of TFLN material is used to achieve a small amount of effective refractive index modulation. The two modulation structures work in series and cooperate to greatly broaden the overall wavelength tunable range and make up for the deficiency of insufficient electro-optic tuning range of a single grating.

[0019] As a preferred embodiment of the above technical solution, the monolithic TFLN passive optical waveguide chip is a thin-film lithium niobate monolithic integrated waveguide bonded to a SiO2 / Si substrate, employing a conventional low-loss single-mode spine waveguide structure to meet the single-mode transmission requirements of the 1550nm band. The monolithic TFLN passive optical waveguide chip is configured with only two sets of independent electro-optic driving electrodes, without any thermo-optic heating resistors or thermo-optic tuning electrodes. The device achieves refractive index tuning and phase compensation entirely through the Pockels electro-optic effect.

[0020] The InP-based gain chip with TFLN dual electrostatic field external cavity coupled to the light-emitting end face is an alternative implementation structure; among them, the InP-based SOA gain chip with AR ultra-low reflection end face coupling can completely eliminate the chip parasitic short cavity and has a lower limiting intrinsic linewidth, which is only suitable for static scientific research scenarios with constant temperature and vibration reduction; the InP-based DFB gain chip with AR end face coupling is prone to forming dual cavity interference beat frequency, with poor mode stability, and is not used as an industrial implementation method.

[0021] As a preferred embodiment of the above technical solution, the ultra-narrow linewidth frequency stabilization method for a laser based on a dual electrostatic field TFLN grating and phase segment external cavity enhancement includes the following steps:

[0022] S1. Wavelength coarse matching: Apply a driving voltage to the electro-optic electrode of the long Bragg grating ridge waveguide section to change the effective refractive index of the grating waveguide, shift the center wavelength of the Bragg reflection, and make the external cavity reflection peak precisely coincide with the inherent resonance peak of the InP-based gain chip to maximize the self-injection feedback intensity.

[0023] S2. Phase fine compensation: Real-time acquisition of laser phase noise and wavelength drift signals, feedback adjustment of the electro-optic drive voltage of the gratingless ridge phase adjustment section, dynamic compensation of external cavity optical path phase drift caused by temperature and current disturbances, continuous maintenance of composite cavity phase matching conditions, and stable output of single-frequency ultra-narrow linewidth laser.

[0024] This invention provides a laser based on a dual electrostatic field TFLN grating and phase segment external cavity enhancement, which has the following significant advantages compared with the prior art:

[0025] 1. Dual electrostatic field series decoupling control, breaking through the bottleneck of single TFLN electro-optic tuning range.

[0026] This invention integrates two independent electrostatic field modulation structures—a long Bragg grating ridge waveguide segment and a gratingless ridge phase adjustment segment—on a single TFLN passive waveguide chip. Unlike traditional single-grating electro-optic tuning modes, these two segments are independently modulated and work in series to achieve precise phase compensation and wavelength matching, respectively. Within the safe breakdown voltage range of the thin film, this effectively widens the overall wavelength tunable window of the device, solving the technical pain points of limited refractive index modulation and narrow wavelength matching range of a single TFLN grating. This significantly improves the device's environmental disturbance immunity and mode-hopping-free operating range.

[0027] 2. Pure electro-optical modulation using a fully electrostatic field offers a performance advantage of orders of magnitude compared to thermo-optical architectures.

[0028] This invention completely abandons the thermo-optical tuning scheme of silicon nitride and silicon dioxide waveguides, eliminating any heating electrodes and heat consumption. It removes wavelength drift and phase noise induced by heat accumulation at the source, significantly improving laser frequency stability. Based on the TFLNPockels electro-optic effect, the tuning response is high-speed nanosecond-level, a significant improvement over traditional millisecond-level thermo-optical tuning. It enables high-speed real-time frequency stabilization and rapid linear frequency sweeping, making it suitable for high-end, high-speed coherent detection scenarios. Simultaneously, it features ultra-low drive power consumption, effectively reducing overall power consumption and thermal noise levels.

[0029] 3. Wavelength-phase dual-degree-of-freedom decoupling completely suppresses dual-cavity interference noise in the composite cavity.

[0030] This invention clearly defines the functional boundaries of the two electro-optic structures: the long Bragg grating back waveguide section is responsible for coarse wavelength alignment to ensure maximum resonant feedback intensity; the gratingless back phase adjustment section is responsible for fine-grained phase compensation of the composite cavity, correcting phase mismatch caused by environmental disturbances in real time. The two control mechanisms are decoupled and independent, and do not crosstalk each other, suppressing the dual-cavity beat noise of the DFB built-in short cavity and the TFLN external long cavity at the physical level, eliminating mode jump and spectral jitter problems, and stably maintaining ultra-narrow linewidth single-frequency output.

[0031] 4. Layered architecture design, balancing industrial mass production and research-driven performance limits.

[0032] This invention uses the DFB+HR backlight-coupled dual electrostatic field TFLN external cavity as the core industrialization solution, which has a stable structure, high coupling fault tolerance, and feasible process, making it suitable for industrial mass production and long-term continuous operation. The SOA gain chip and AR end-face coupling architecture are used as research extension solutions, which can achieve a lower limit intrinsic linewidth and are suitable for static precision measurement scenarios in the laboratory. One architecture covers the dual needs of commercialization and cutting-edge scientific research, and has a complete patent protection system.

[0033] 5. Monolithically integrated low-loss optical path improves feedback efficiency and output spectral purity.

[0034] The long Bragg grating back waveguide section and the gratingless back phase adjustment section are TFLN integral etched continuous waveguides with no discrete device end-face coupling insertion loss. The overall external cavity loss is low, the self-injection feedback efficiency is high, the output power is higher under the same operating conditions, the side-mode suppression ratio is high, and the spectral purity is excellent.

[0035] 6. Fully enclosed composite waveguide structure with extremely low grating radiation loss.

[0036] This invention employs a TFLN core layer combined with an upper and lower SiO2 fully encapsulated structure. After the grating is etched, the medium is fully covered and filled, completely eliminating vertical radiation loss and scattering loss caused by the high refractive index difference between the bare grating and air. The grating has high reflection efficiency and good parameter stability, ensuring long-term stable narrow linewidth operation of the external cavity. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the structure of Embodiment 1 of the present invention.

[0038] Figure 2 for Figure 1 Top view.

[0039] Figure 3 This is a schematic diagram of the structure of Embodiment 2 of the present invention.

[0040] Figure 4 This is a schematic diagram of the alternative optical path structure for the AR end face coupling of the TFLN external cavity of an InP-based gain chip.

[0041] Figure 5 The flowchart shows the frequency stabilization control method for decoupling dual electrostatic fields.

[0042] In the figure: 1. InP-based gain chip; 2. Monolithic TFLN passive waveguide chip; 21. Long Bragg grating ridge waveguide section; 211. First set of independent electro-optic driving electrodes; 22. Gratingless ridge phase adjustment section; 221. Second set of independent electro-optic driving electrodes. Detailed Implementation

[0043] The following will be based on embodiments of the present invention. Figures 1-5The technical solutions in the embodiments of the present invention will be clearly and completely described.

[0044] A laser based on a dual electrostatic field TFLN grating and a phase segment external cavity enhancement includes an InP-based gain chip 1 and a monolithic thin-film lithium niobate (TFLN) passive optical waveguide chip 2.

[0045] The backlight end face of the InP-based gain chip 1 is coated with a high-reflectivity HR film with a reflectivity of 90%-99%, and the light-emitting end face is coated with an ultra-low-reflectivity AR anti-reflection film with a reflectivity of 0.005%-1%. The monolithic TFLN passive waveguide chip is optically coupled to the backlight end face of the InP-based gain chip.

[0046] The monolithic TFLN passive optical waveguide chip 2 is a continuous spine waveguide structure integrally etched on the same chip. A long Bragg grating spine waveguide section 21 and a gratingless spine phase adjustment section 22 are sequentially arranged along the optical transmission direction. The two waveguide sections are not cut or have discrete coupling interfaces, and the optical path is continuous with low loss.

[0047] The long Bragg grating back waveguide section 21 is equipped with a first set of independent electro-optic driving electrodes 211, and the gratingless back phase adjustment section 22 is equipped with a second set of independent electro-optic driving electrodes 221. The two sets of electrodes are mutually insulated and driven by independent electrostatic fields. The signal crosstalk between the electrodes is extremely low, and the crosstalk effect is negligible and will not interfere with the modulation accuracy.

[0048] Both waveguides rely on the electro-optic effect of Pockels electrostatic field of TFLN material to achieve effective refractive index modulation. No thermo-optic heating resistors or thermo-optic tuning electrodes are set. The entire process is carried out using a pure electro-optic tuning method.

[0049] The long Bragg grating back waveguide section 21 is used to change the effective refractive index of the waveguide through electro-optic tuning to achieve coarse matching of the Bragg reflection center wavelength, so that the external cavity reflection peak is precisely aligned with the inherent resonant peak of the InP-based gain chip 1, thereby improving the external cavity self-injection feedback intensity.

[0050] The gratingless ridge phase adjustment section 22 is used to precisely change the total optical path of the external cavity through electro-optic tuning, so as to achieve fine compensation of the round-trip phase of the composite cavity and suppress the double cavity interference beat frequency noise.

[0051] The DFB chip integrates a distributed grating and an external long Bragg grating (TFLN) to construct a composite long resonant cavity structure, which extends the photon storage lifetime. It also compresses the intrinsic linewidth of the laser through a self-injection locking mechanism, and stably achieves ultra-narrow linewidth single-frequency laser output under normal constant temperature and vibration reduction conditions.

[0052] The InP-based gain chip 1 is either an InP-based DFB gain chip or an InP-based SOA gain chip.

[0053] As a preferred embodiment of the above technical solution, the length of the gratingless spine phase adjustment section 22 is in the range of hundreds of micrometers to millimeters, and the length of the long Bragg grating spine waveguide section 21 is in the range of centimeters; the grating period of the long Bragg grating spine waveguide section 21 is adapted to the 1550nm communication band, and the grating coupling coefficient is adapted to the narrowband frequency selection requirements.

[0054] As a preferred embodiment of the above technical solution, the first set of independent electro-optic driving electrodes 211 and the second set of independent electro-optic driving electrodes 221 are respectively independently applied with low-voltage electrostatic driving voltage. The electro-optic coefficient of TFLN material is used to achieve a small amount of effective refractive index modulation. The two modulation structures work in series and cooperate to greatly broaden the overall wavelength tunable range and make up for the deficiency of insufficient electro-optic tuning range of a single grating.

[0055] As a preferred embodiment of the above technical solution, the monolithic TFLN passive optical waveguide chip 2 is a thin-film lithium niobate monolithic integrated waveguide bonded to a SiO2 / Si substrate, employing a conventional low-loss single-mode spine waveguide structure to meet the single-mode transmission requirements of the 1550nm band. The monolithic TFLN passive optical waveguide chip 2 is configured with only two sets of independent electro-optic driving electrodes, without any thermo-optic heating resistors or thermo-optic tuning electrodes. The device achieves refractive index tuning and phase compensation entirely through the Pockels electrostatic field electro-optic effect.

[0056] The InP-based gain chip 1 with TFLN dual electrostatic field external cavity coupled to the light-emitting end face is an alternative implementation structure; among them, the InP-based SOA gain chip with AR ultra-low reflection end face coupling can completely eliminate the chip parasitic short cavity and has a lower limiting intrinsic linewidth, which is only suitable for static scientific research scenarios with constant temperature and vibration reduction; the InP-based DFB gain chip with AR end face coupling is prone to forming dual cavity interference beat frequency, and the mode stability is poor, so it is not used as an industrial implementation method.

[0057] As a preferred embodiment of the above technical solution, the ultra-narrow linewidth frequency stabilization method for a laser based on a dual electrostatic field TFLN grating and phase segment external cavity enhancement includes the following steps:

[0058] S1. Wavelength coarse matching: Apply a driving voltage to the electro-optic electrode of the long Bragg grating back waveguide section 21 to change the effective refractive index of the grating waveguide, shift the center wavelength of the Bragg reflection, and make the external cavity reflection peak precisely coincide with the inherent resonance peak of the InP-based gain chip 1 to maximize the self-injection feedback intensity.

[0059] S2, Phase Fine Compensation: Real-time acquisition of laser phase noise and wavelength drift signals, feedback adjustment of the electro-optic driving voltage of the gratingless ridge phase adjustment section 22, dynamic compensation of external cavity optical path phase drift caused by temperature and current disturbances, continuous maintenance of composite cavity phase matching conditions, and stable output of single-frequency ultra-narrow linewidth laser.

[0060] Example 1 (Core Industrialization Main Example: DFB+HR Backlight Dual Electrostatic Field TFLN External Cavity)

[0061] This embodiment represents the core optimal implementation architecture of the present invention. The optical path transmission sequence of the device is as follows: InP DFB gain chip → TFLN gratingless phase adjustment section → TFLN long Bragg grating section.

[0062] In this embodiment, the high-reflectivity film on the backlight end face and the anti-reflection film on the light-emitting end face of the DFB gain chip both adopt patented and compliant reflectivity ranges, balancing feedback intensity and output power. The TFLN chip adopts a low-loss single-mode spine waveguide structure adapted to the 1550nm band, and the phase adjustment section length is adapted to the phase compensation requirements under all operating conditions. The tuning range can be expanded through positive and negative bidirectional voltage scanning, and the operating point can be locked by closed-loop feedback to achieve stable phase compensation under all operating conditions. The long Bragg grating section adopts structural parameters adapted to the communication band and has excellent narrowband frequency selection characteristics.

[0063] The two sections are each equipped with independent electro-optic electrodes and employ a purely electro-optic driving mode without any thermo-optic heating structures. During operation, coarse wavelength matching is achieved through electro-optic tuning of the grating section, precisely aligning the external cavity reflection peak with the DFB resonant peak. This constructs a composite long cavity consisting of a DFB internal grating and a TFLN external long grating, extending photon storage lifetime and reducing intrinsic linewidth. The phase adjustment section dynamically compensates for the composite cavity phase drift in real time, suppressing dual-cavity interference noise. Under typical industrial constant temperature and vibration damping conditions, the device can stably achieve ultra-narrow linewidth single-frequency output without mode switching, demonstrating excellent long-term operational stability.

[0064] It should be noted that the present invention abandons the waveguide thermo-optical tuning electrode. The conventional temperature control system of the whole device is only used for stabilizing the ambient temperature and does not belong to the category of thermo-optical tuning. It does not affect the core advantage of the pure electro-optical control of the present invention.

[0065] Example 2 (Extended Example: SOA+HR Backlight Dual Electrostatic Field TFLN External Cavity)

[0066] In this embodiment, the DFB gain chip in Embodiment 1 is replaced with an InP SOA gain chip. The SOA chip has no built-in grating, high reflectivity at the backlight end face and ultra-low reflectivity at the light-emitting end face, and all resonant frequency selection and feedback locking rely on the TFLN dual electrostatic field external cavity.

[0067] This architecture relies on dual electrostatic field decoupling to broaden the tuning range and stabilize the resonant phase. However, due to the lack of a first-level mode lock with a DFB built-in grating, the mode-hopping working window is relatively narrow, making it more sensitive to environmental vibrations and temperature disturbances. It requires high-precision vibration reduction and ultra-precision temperature control. It is suitable for laboratory static precision spectral measurement and extreme low-noise scientific research experiments, but not for large-scale industrial mass production scenarios.

[0068] Example 3 (Alternative research example: AR end face coupled to TFLN external cavity)

[0069] 3-1 SOA+AR Coupling Example: The TFLN chip is coupled to the AR light-emitting end face of the SOA chip, while the HR backlight end face is exposed. Utilizing the ultra-low reflection characteristics of AR, the parasitic short cavity of the SOA chip is completely eliminated, retaining only the single-long external cavity resonance of the TFLN. There is no dual-cavity interference noise, and an even lower limiting intrinsic linewidth can be achieved under extremely static conditions. This is only suitable for cutting-edge scientific research experiments.

[0070] 3-2 DFB+AR Coupling Example: The TFLN chip is connected to the DFB light-emitting AR end face. The DFB's built-in grating short cavity and the TFLN's external long cavity form a strong and weak dual-cavity structure, which is prone to beat frequency noise and mode jitter, resulting in poor stability. This example is only used as a comparative example and is not intended as an industrial application solution of the present invention.

[0071] TFLN Back Grating Waveguide Manufacturing Process

[0072] I. Overview of the Plan

[0073] This manufacturing solution is compatible with the TFLN spine waveguide design of the monolithically integrated phase adjustment section + long Bragg grating section described in this patent. It meets the operating requirements of narrow-linewidth lasers in the 1550nm communication band. The process flow is compatible with semiconductor wafer mass production processes, enabling continuous etching of the two waveguide segments in one piece, with no splicing interface and low insertion loss. This solution adopts a composite waveguide structure with differentiated etching and full cladding coverage, completely eliminating air radiation loss from the bare grating. The process is stable and can be mass-produced.

[0074] II. Wafer Substrate Pretreatment

[0075] Lithium niobate thin film wafers were bonded using commercial SiO2 / Si substrates, with Z-cut TFLN material preferred to achieve optimal electro-optic modulation performance. The wafers underwent a standard wafer cleaning process to remove surface organic residues and particulate impurities, followed by drying and nitrogen purging before surface flatness testing to ensure a clean wafer surface and uniform thickness.

[0076] III. Hard Mask Deposition Process

[0077] A low-stress, dense SiO2 hard mask layer is deposited using the PECVD process, ensuring excellent mask layer adhesion and no pinhole defects, thus meeting the requirements for high-precision waveguide and grating pattern transfer.

[0078] IV. Integrated Patterning Lithography

[0079] Using high-precision photolithography, the integrated pattern of the gratingless phase segment and the long-period grating segment is fabricated in one step, ensuring that the grating period is regular, the pattern has no broken lines or adhesions, and the accuracy meets the working requirements of narrowband frequency selective devices.

[0080] V. Hard Mask Windowing and Graphic Transfer

[0081] ICP etching is used to open the hard mask, and the photolithographic pattern is completely transferred to the hard mask layer. Combined with oxygen plasma to thoroughly remove the resist, the mask edges are steep and the surface roughness is low.

[0082] VI. TFLN Differentiated Etching and Shaping (Core Process)

[0083] The waveguide is formed in segments using a mixed gas ICP dry etching process: full-domain etching forms a uniform ridge waveguide substrate, ensuring the continuity of the optical path between the phase segment and the grating segment; precise shallow etching is performed on the grating area to form a grating groove structure that meets the frequency selection requirements; the phase segment has no secondary etching, ensuring smooth sidewalls and extremely low transmission loss.

[0084] VII. Hard Mask Removal and Surface Cleaning

[0085] A specialized wet etching process is used to remove the SiO2 hard mask without damaging the TFLN thin film. Then, a standard cleaning process is used to remove etching residues and microparticles, ensuring an ultra-clean waveguide surface.

[0086] 8. Full coverage and leveling of the top SiO2 cladding layer

[0087] A dense SiO2 cladding is deposited on the etched waveguide and grating surfaces to completely fill the periodic grooves of the grating, forming a composite waveguide structure that is fully covered from top to bottom. This completely eliminates radiation and scattering losses caused by the air interface, improving device stability and optical performance.

[0088] IX. Fabrication process of dual independent electro-optic electrodes

[0089] Independent electro-optic electrodes for the phase segment and grating segment are fabricated through a two-stage precision photolithography, metal evaporation and lift-off process. The two sets of electrodes have excellent insulation and extremely low crosstalk, which can achieve stable independent electrostatic field driving and meet the requirements of two-degree-of-freedom decoupling modulation.

[0090] 10. End-face polishing and coating process

[0091] After wafer slicing, ultra-precision optical polishing is performed to ensure that the flatness of the end face meets the standards; then, compliant optical thin films are deposited to achieve high reflectivity and ultra-low reflectivity end face characteristics, respectively, to meet the requirements of laser resonance and output.

[0092] XI. Final Testing and Performance Screening

[0093] Batch screening is completed through morphology inspection, spectral testing, and electrical insulation testing to ensure that the devices have excellent consistency in waveguide loss, grating reflection characteristics, and electro-optic modulation performance, meeting the requirements of dual electrostatic field decoupling frequency stabilization and ultra-narrow linewidth output.

[0094] XII. Core Technological Advantages

[0095] 1. Integrated full-domain etching, seamless continuity between two waveguide sections, no interface insertion loss, and high external cavity feedback efficiency;

[0096] 2. Differentiated shallow groove grating etching, with controllable morphology and stable parameters, is suitable for narrowband frequency selective operation requirements;

[0097] 3. The fully encapsulated SiO2 composite waveguide completely eliminates the air radiation loss of the grating, resulting in extremely low optical loss and excellent long-term stability of the device.

[0098] 4. The dual-electrode independent insulation process eliminates voltage crosstalk, perfectly matching the core innovation of the dual electrostatic field decoupling control in this invention.

[0099] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A laser based on a dual electrostatic field TFLN grating and phase segment external cavity enhancement, characterized in that, Including an InP-based gain chip (1) and a monolithic TFLN passive waveguide chip (2); The backlight end face of the InP-based gain chip (1) is coated with a high-reflectivity HR film with a reflectivity of 90%-99%, and the light-emitting end face is coated with an ultra-low-reflectivity AR anti-reflection film with a reflectivity of 0.005%-1%; the monolithic TFLN passive waveguide chip is optically coupled to the backlight end face of the InP-based gain chip. The monolithic TFLN passive optical waveguide chip (2) is a continuous back waveguide structure integrally etched on the same chip, with a long Bragg grating back waveguide section (21) and a gratingless back phase adjustment section (22) arranged sequentially along the optical transmission direction. The long Bragg grating back waveguide section (21) is equipped with a first set of independent electro-optic driving electrodes (211), and the gratingless back phase adjustment section (22) is equipped with a second set of independent electro-optic driving electrodes (221). The InP-based gain chip (1) is an InP-based DFB gain chip or an InP-based SOA gain chip.

2. The laser based on a dual electrostatic field TFLN grating and phase segment external cavity enhancement according to claim 1, characterized in that: The length of the gratingless back phase adjustment section (22) is from hundreds of micrometers to millimeters, and the length of the long Bragg grating back waveguide section (21) is in the centimeter range; the grating period of the long Bragg grating back waveguide section (21) is adapted to the 1550nm communication band.

3. The laser based on a dual electrostatic field TFLN grating and phase segment external cavity enhancement according to claim 2, characterized in that: The first set of independent electro-optic driving electrodes (211) and the second set of independent electro-optic driving electrodes (221) are respectively independently subjected to low-voltage electrostatic driving voltage.

4. The laser based on a dual electrostatic field TFLN grating and phase segment external cavity enhancement according to claim 3, characterized in that: The monolithic TFLN passive optical waveguide chip (2) is a thin-film lithium niobate monolithic integrated waveguide bonded to a SiO2 / Si substrate. It adopts a conventional low-loss single-mode spine waveguide structure and is adapted to the single-mode transmission requirements of the 1550nm band.

5. The laser based on a dual electrostatic field TFLN grating and phase segment external cavity enhancement according to any one of claims 1-4, characterized in that, Its ultra-narrow linewidth frequency stabilization control method includes the following steps: S1. Wavelength coarse matching: Apply a driving voltage to the electro-optic electrode of the long Bragg grating back waveguide section (21) to change the effective refractive index of the grating waveguide, shift the center wavelength of the Bragg reflection, and make the external cavity reflection peak precisely coincide with the inherent resonance peak of the InP-based gain chip (1) to maximize the self-injection feedback intensity. S2, Phase Fine Compensation: Real-time acquisition of laser phase noise and wavelength drift signals, feedback adjustment of the electro-optic driving voltage of the gratingless spine phase adjustment section (22), dynamic compensation of external cavity optical path phase drift caused by temperature and current disturbance, continuous maintenance of composite cavity phase matching conditions, and stable output of single-frequency ultra-narrow linewidth laser.

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