阅读说明：本技术 一种集成化外腔式单频线偏振半导体激光器 (Integrated external cavity type single-frequency linearly polarized semiconductor laser ) 是由 胡阿健 廖明龙 武春风 李强 姜永亮 刘厚康 宋祥 戴玉芬 王光斗 王天晗 于 2020-11-02 设计创作，主要内容包括：本发明的一种集成化外腔式单频线偏振半导体激光器,包括InGaAs半导体芯片、LiNbO-3晶体衬底、LiNbO-3波导结构、LiNbO-3波导光栅和热电制冷器TEC；LiNbO-3波导结构、LiNbO-3波导光栅制作于LiNbO3晶体衬底上；LiNbO-3波导光栅是所述LiNbO-3波导结构的一部分刻蚀周期性结构而形成；LiNbO-3波导光栅的周期性结构包括一半低折射率长度部分和一半高折射率长度部分,共同构成一个周期长度L。本发明将InGaAs多量子阱材料作为激光的增益介质,输出波长范围可覆盖1000nm到1100nm,实现了InGaAs半导体芯片高TE模式占比激发,提高输出激光的消光比；采用短直线型谐振腔结构,通过InGaAs半导体芯片与LiNbO3波导光栅直接键合集成方式,提升了对准精度,增加了激光耦合效率,改善光束质量,降低耦合损耗,提高了激光器单纵模稳定性。(The invention discloses an integrated external cavity type single-frequency linear polarization semiconductor laser, which comprises an InGaAs semiconductor chip and LiNbO 3 Crystal substrate and LiNbO 3 Waveguide structure and LiNbO 3 Waveguide grating and thermoelectric cooler TEC; LiNbO 3 Waveguide structure and LiNbO 3 The waveguide grating is manufactured on the LiNbO3 crystal substrate; LiNbO 3 The waveguide grating is said LiNbO 3 Etching a part of the waveguide structure to form a periodic structure; LiNbO 3 The periodic structure of the waveguide grating comprises a half low refractive index length portion and a half high refractive index length portion, which together form a period length L. The invention takes InGaAs multi-quantum well material as gain medium of laser and outputThe wavelength range can cover 1000nm to 1100nm, high TE mode proportion excitation of the InGaAs semiconductor chip is realized, and the extinction ratio of output laser is improved; by adopting a short linear resonant cavity structure and a direct bonding integration mode of an InGaAs semiconductor chip and LiNbO3 waveguide grating, the alignment precision is improved, the laser coupling efficiency is increased, the beam quality is improved, the coupling loss is reduced, and the single longitudinal mode stability of the laser is improved.)

1. An integrated external cavity single-frequency linearly polarized semiconductor laser is characterized by comprising an InGaAs semiconductor chip and LiNbO₃Crystal substrate and LiNbO₃Waveguide structure and LiNbO₃Waveguide grating and thermoelectric cooler TEC;

the LiNbO₃Waveguide structure and LiNbO₃The waveguide grating is manufactured on the LiNbO3 crystal substrate; the LiNbO₃The waveguide grating is said LiNbO₃Etching a part of the waveguide structure to form a periodic structure; the LiNbO₃The periodic structure of the waveguide grating comprises a half low-refractive-index length part and a half high-refractive-index length part which jointly form a period length L;

the InGaAs semiconductor chip is directly bonded and integrated with the LiNbO3 waveguide, and the InGaAs semiconductor chip and the LiNbO are directly bonded and integrated₃LiNbO of periodic structure formed by etching part of waveguide structure₃The waveguide grating forms a short linear resonant cavity structure; laser emitted by the InGaAs semiconductor chip is incident to the LiNbO3 waveguide structure and then is incident to the LiNbO₃Waveguide grating, and incident on LiNbO₃Outputting single-frequency linearly polarized laser after waveguide structure, LiNbO₃The waveguide grating is positioned at the front part and the rear part of the waveguide grating₃The middle of the waveguide structure;

the InGaAs semiconductor chip and LiNbO₃Crystal substrate and LiNbO₃Waveguide structure and LiNbO₃Waveguide lightThe grid is installed on the thermoelectric cooler TEC.

2. An integrated external cavity single frequency linearly polarized semiconductor laser as claimed in claim 1 wherein: the InGaAs semiconductor chip adopts a multi-quantum well epitaxial structure and a narrow spine gain structure, one end face of the InGaAs semiconductor chip is plated with an antireflection film of 1000nm-1100nm, and the end face and LiNbO₃The waveguide is directly bonded, and the other end surface is plated with a high-reflection film of 1000nm-1100 nm.

3. An integrated external cavity single frequency linearly polarized semiconductor laser as claimed in claim 1 or 2 wherein: the LiNbO₃In the periodic structure of the waveguide grating, the low refractive index of a half low refractive index length part is 1.3-1.4, the high refractive index of a half high refractive index length part is 1.5-1.8, and the period length L of the periodic structure is 100-200 μm.

4. An integrated external cavity single frequency linearly polarized semiconductor laser as claimed in claim 3 wherein: the LiNbO₃The two end surfaces of the crystal substrate are coated with light absorbing materials to cover the LiNbO₃An end face other than the waveguide.

5. An integrated external cavity single frequency linearly polarized semiconductor laser as claimed in claim 1 wherein: the LiNbO₃The waveguide structure is a straight waveguide structure or a Y-shaped waveguide structure containing the straight waveguide structure.

6. An integrated external cavity single frequency linearly polarized semiconductor laser as claimed in claim 5 wherein: the LiNbO₃The waveguide structure is manufactured by adopting an annealing proton exchange process, and particularly, benzoic acid is selected as a proton source, and LiNbO is used₃The crystal is immersed in a benzoic acid solution at the temperature of 120-₊To H₊Exchange, forming H on the crystal surface_xLi_1-xNbO₃High foldA refractive index layer, further LiNbO₃A straight waveguide structure or a Y-shaped waveguide structure containing the straight waveguide structure is formed on the substrate.

7. An integrated external cavity single frequency linearly polarized semiconductor laser as claimed in claim 1 wherein: the optical fiber further comprises a focusing lens and a polarization maintaining optical fiber, and the LiNbO₃The waveguide structure, the focusing lens and the polarization maintaining fiber are connected in sequence through an optical path, and one end of the polarization maintaining fiber close to the focusing lens is polished and then plated with an anti-reflection film with a wave band of 1000nm-1100 nm.

8. An integrated external cavity single frequency linearly polarized semiconductor laser as claimed in claim 1 wherein: the polarization maintaining optical fiber is welded on the LiNbO₃An output end face of the waveguide structure.

9. An integrated external cavity single frequency linearly polarized semiconductor laser as claimed in claim 7 or 8 wherein: the LiNbO₃An electrode is also added on the crystal substrate, and LiNbO is added on the crystal substrate₃LiNbO behind waveguide grating₃The waveguide structure carries out phase modulation on the output laser loading microwave signal, and the line width of the output light beam is adjustable.

10. An integrated external cavity single frequency linearly polarized semiconductor laser as claimed in claim 1 wherein: the LiNbO₃The crystal substrate is X-Y cut LiNbO₃And the direction of the X is the light emergent direction of the crystal, and the direction of the Y is determined by a right-hand rule.

Technical Field

The invention relates to the field of linearly polarized single-frequency lasers, in particular to an integrated external cavity type single-frequency linearly polarized semiconductor laser.

Background

The single-frequency semiconductor laser is an important branch of laser development, has the advantages of small volume, light weight, high efficiency, long service life, direct current drive, narrow spectral line width, good coherence and the like, and is an ideal light source for applications such as narrow-line-width optical fiber lasers, all-solid-state laser radars, coherent optical communication and the like. A single-frequency semiconductor laser usually integrates a frequency selection structure in a resonant cavity or is coupled with a mode selection device outside a laser cavity, thereby controlling gain loss of different wavelengths to achieve the purpose of compressing the spectral line width thereof. Methods for narrowing the line width of a semiconductor laser are mainly classified into two types: the first is an intracavity Feedback method, which is typically represented by a Distributed Feedback semiconductor laser (DFB); the other is an external cavity optical feedback method, which mainly includes a Volume Holographic Grating (VHG), a Fiber Bragg Grating (FBG) semiconductor laser, and the like. The method has the advantages that high requirements are provided for extremely narrow spectral linewidth, linear polarization operation and high reliability of the laser in the application fields of narrow linewidth optical fiber lasers, laser radars, nonlinear frequency conversion and the like, the output line width of the external cavity type single-frequency semiconductor laser is narrower (smaller by 2-3 orders of magnitude) than the linewidth of the DFB semiconductor laser, and the application advantages are obvious.

The external cavity single-frequency semiconductor laser reported in the current research generally adopts fiber grating, bulk grating and the like as wavelength selection devices. Because the output resonant cavity is long and the longitudinal mode interval of the laser is small, single longitudinal mode output is easy to realize, the output power is easy to reach dozens of mW magnitude, and the line width can be below 10 kHz. However, due to the resonant cavity structure of the spatial structure, spatial coupling causes poor single-mode stability, linear polarization characteristic (about 15dB), and noise characteristic of the laser, and the application of the extremely narrow single-frequency semiconductor laser is severely limited. Therefore, it is urgently needed to develop an integrated semiconductor laser with extremely narrow line width and linearly polarized output, and to realize stable output of single-frequency linearly polarized laser with the line width of 10kHz and the extinction ratio of more than 50 dB.

Disclosure of Invention

The invention aims to overcome the defects of the traditional external cavity type semiconductor laser and provides a laser based on LiNbO₃A single-frequency linear polarization laser with integrated crystal. Is adopted in LiNbO₃The crystal is used as a substrate, a straight waveguide structure is formed by photoetching (adopting an annealing proton exchange process), a waveguide grating integrated external cavity type wavelength selective device is formed, and LiNbO is fully utilized₃The crystal has good double refraction characteristic, and the single-frequency laser polarization extinction ratio is improved; aligned bonding with the semiconductor laser chip to realize single-frequency laser chip and LiNbO₃The crystal waveguide grating is highly coupled, the single longitudinal mode stability of the single-frequency laser is improved, the noise is reduced, and the stable output of the single-frequency linear polarization laser with the line width of 10kHz and the extinction ratio exceeding 50dB is finally realized.

In order to achieve the purpose, the technical scheme provided by the invention is as follows:

an integrated external cavity single-frequency linearly polarized semiconductor laser is characterized byComprises InGaAs semiconductor chip and LiNbO₃Crystal substrate and LiNbO₃Waveguide structure and LiNbO₃Waveguide grating and thermoelectric cooler TEC;

the LiNbO₃Waveguide structure and LiNbO₃The waveguide grating is manufactured on the LiNbO3 crystal substrate; the LiNbO₃The waveguide grating is said LiNbO₃Etching a part of the waveguide structure to form a periodic structure;

the LiNbO₃The periodic structure of the waveguide grating comprises a half low-refractive-index length part and a half high-refractive-index length part which jointly form a period length L;

the InGaAs semiconductor chip and the LiNbO₃Direct bonding integration of waveguide, the InGaAs semiconductor chip and the LiNbO₃LiNbO of periodic structure formed by etching part of waveguide structure₃The waveguide grating forms a short linear resonant cavity structure; laser emitted by the InGaAs semiconductor chip is incident to the LiNbO3 waveguide structure and then is incident to the LiNbO₃Waveguide grating, and incident on LiNbO₃Outputting single-frequency linearly polarized laser after waveguide structure, LiNbO₃The waveguide grating is positioned at the front part and the rear part of the waveguide grating₃The middle of the waveguide structure;

or the InGaAs semiconductor chip and the LiNbO₃The waveguide grating is directly bonded and integrated, and the InGaAs semiconductor chip is connected with LiNbO₃The waveguide grating forms a short linear resonant cavity structure; laser emitted by the InGaAs semiconductor chip is incident to LiNbO₃Waveguide grating, and incident on LiNbO₃Outputting single-frequency linearly polarized laser after the waveguide structure;

the laser emitted by the InGaAs semiconductor chip is TE mode high-specific-ratio laser and enters the LiNbO₃Waveguide grating by said LiNbO₃The waveguide grating compresses the spectral line width and outputs narrow-line-width laser;

the InGaAs semiconductor chip and LiNbO₃Crystal substrate and LiNbO₃Waveguide structure and LiNbO₃The waveguide grating is arranged on the thermoelectric refrigerator TEC.

Furthermore, the InGaAs semiconductor chip adopts a multi-quantum well epitaxial structure and a narrow spine gain structure, one end face of the InGaAs semiconductor chip is plated with an antireflection film of 1000nm-1100nm, and the end face and LiNbO₃The waveguide is directly bonded, and the other end surface is plated with a high-reflection film of 1000nm-1100 nm.

Further, the LiNbO₃In the periodic structure of the waveguide grating, the low refractive index of a half low refractive index length part is 1.3-1.4, the high refractive index of a half high refractive index length part is 1.5-1.8, and the period length L of the periodic structure is 100-200 μm.

Further, the LiNbO₃The two end surfaces of the crystal substrate are coated with light absorbing materials to cover the LiNbO₃An end face other than the waveguide. To try to absorb the radiated light outside the waveguide.

Specifically, the LiNbO₃The waveguide structure is a straight waveguide structure or a Y-shaped waveguide structure containing the straight waveguide structure.

Specifically, the LiNbO₃The waveguide structure is made by annealing proton exchange process, specifically benzoic acid (C)₆H₅COOH) as a proton source, LiNbO₃The crystal is immersed in a benzoic acid solution at the temperature of 120-₊To H₊Exchange, forming H on the crystal surface_xLi_1-xNbO₃High refractive index layer, and further LiNbO₃A straight waveguide structure or a Y-shaped waveguide structure containing the straight waveguide structure is formed on the substrate.

Preferably, the optical fiber further comprises a focusing lens and a polarization-maintaining optical fiber, and the LiNbO₃The waveguide structure, the focusing lens and the polarization maintaining fiber are connected in sequence through an optical path, and one end of the polarization maintaining fiber close to the focusing lens is polished and then plated with an anti-reflection film with a wave band of 1000nm-1100 nm. The LiNbO₃TE mode laser in the waveguide structure is coupled into the PM980 polarization-maintaining optical fiber through the focusing lens, and the polarization extinction ratio of the output laser is improved.

Optionally, the polarization maintaining fiber is welded on the LiNbO₃An output end face of the waveguide structure. The LiNbO₃TE mode laser direct coupling in waveguide structureAnd the optical fiber is combined into a PM980 polarization-maintaining optical fiber, so that the laser coupling efficiency is increased, and the coupling loss is reduced.

Preferably, the LiNbO₃An electrode is also added on the crystal substrate, and LiNbO is added on the crystal substrate₃LiNbO behind waveguide grating₃The waveguide structure carries out phase modulation on the output laser loading microwave signal, and the line width of the output light beam is adjustable.

Specifically, the LiNbO₃The crystal substrate is X-Y cut LiNbO₃And the direction of the X is the light emergent direction of the crystal, namely the emergent direction of the laser, and the direction of the Y is determined by a right-hand rule.

Preferably, one end of the polarization maintaining optical fiber is polished and then plated with an antireflection film with a wave band of 1000nm-1100nm, so that the coupling efficiency is improved.

Preferably, the integrated external cavity type single-frequency linear polarization semiconductor laser is packaged through a standard 14-pin butterfly packaging process, and stable and reliable single-frequency semiconductor laser output can be obtained.

Specifically, the LiNbO₃Part of the waveguide structure is formed by etching a periodic structure, and particularly, a femtosecond laser direct writing or focused ion beam etching mode is adopted to form LiNbO₃And a waveguide grating for forming oscillation and lasing of the linearly polarized laser TE.

Compared with the prior art, the invention has the following beneficial effects:

1. the InGaAs multi-quantum well material is used as a gain medium of laser, the output wavelength range can cover 1000nm to 1100nm, high TE mode proportion excitation of an InGaAs semiconductor chip is achieved, and the extinction ratio of the output laser can be improved due to the high TE mode proportion;

2. adopts a short linear resonant cavity structure and passes through an InGaAs semiconductor chip and LiNbO₃The waveguide grating direct bonding integration mode improves the alignment precision, increases the laser coupling efficiency, improves the beam quality, reduces the coupling loss, improves the single longitudinal mode stability of the laser and reduces the noise of the laser caused by coupling;

3. using LiNbO₃The crystal has excellent birefringence property, and LiNbO is cut in X-Y₃CrystalForming a straight waveguide structure on the substrate by adopting an annealing proton exchange mode, and forming LiNbO by adopting a femtosecond laser direct writing or focused ion beam etching periodic structure mode₃A waveguide grating for forming oscillation and lasing of the linearly polarized laser TE;

4. by reaction on LiNbO₃And the mode of plating light absorption materials on two end faces of the crystal substrate absorbs the TM mode laser radiated outside the waveguide, further ensures the high occupancy rate of the TE mode laser in the output laser, and finally realizes the stable output of the single-frequency linear polarization laser with the line width of kHz magnitude and the extinction ratio exceeding 50 dB.

Drawings

Fig. 1 is a schematic diagram of the principle of an integrated external cavity single-frequency linearly polarized semiconductor laser according to embodiment 1 of the present invention.

FIG. 2 is LiNbO₃Waveguide polarization extinction diagram.

FIG. 3 is LiNbO₃Schematic view of the coating of crystalline end face light absorbing material.

FIG. 4 is LiNbO₃The structure diagram of the periodic distribution of the refractive index on the crystal.

Fig. 5 is a schematic diagram of the principle of an integrated external cavity single-frequency linearly polarized semiconductor laser according to embodiment 2 of the present invention.

Wherein: 1-InGaAs semiconductor chip, 2-light absorbing material film (same as 7-light absorbing material film), 3-LiNbO₃Crystal waveguide (with 6-LiNbO)₃Compared with a crystal waveguide, the 4-LiNbO has the same structure except that the crystal waveguide is positioned at different spatial positions and different lengths), and the 4-LiNbO has the same structure₃Crystalline substrate, 5-LiNbO₃Waveguide grating, 6-LiNbO₃Crystal waveguide (with 3-LiNbO)₃Compared with the crystal waveguide, the crystal waveguide is the same except that the crystal waveguide is located at different spatial positions and different lengths), a 7-light absorption material film (the same as a 2-light absorption material film), an 8-focusing lens, a 9-polarization maintaining fiber, 10-extraordinary light and 11-heat sink.

In fig. 4: n is₁-low refractive index, value 1.3-1.4; n is₂-high refractive index, with a value of 1.5-1.8; l is a period length of 100 μm to 200 μm; starting point of the length of the periodic structure from refractive index n₁Starting from a portion of refractive index n₂All of the above are possible.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Example 1

An integrated external cavity single-frequency linearly polarized semiconductor laser comprises an InGaAs semiconductor chip and LiNbO₃Crystal substrate and LiNbO₃Waveguide structure and LiNbO₃Waveguide grating and thermoelectric cooler TEC;

the LiNbO₃Waveguide structure and LiNbO₃The waveguide grating is manufactured on the LiNbO3 crystal substrate; the LiNbO₃The waveguide grating is said LiNbO₃Etching a part of the waveguide structure to form a periodic structure;

the LiNbO₃The periodic structure of the waveguide grating comprises a half low-refractive-index length part and a half high-refractive-index length part which jointly form a period length L;

the LiNbO₃Low refractive index n of half of the low refractive index length portion in the periodic structure of the waveguide grating₁Specifically 1.3 to 1.4, high refractive index n of half the length of the high refractive index₂Specifically 1.5-1.8, wherein the period length of the periodic structure is 100-200 μm; in this example n₁Is 1.35, n₂Is 1.7; in another embodiment is n₁Is 1.3, n₂Is 1.5; in yet another embodiment is n₁Is 1.4, n₂Is 1.8;

one period length of the periodic structure is 100-200 μm, and one period length is 150 μm in this embodiment. 100 μm in another embodiment; 200 μm in yet another embodiment;

the InGaAs semiconductor chip and the LiNbO₃Direct bonding integration of waveguides, said InGaAs semiconductorBulk chip and LiNbO₃LiNbO of periodic structure formed by etching part of waveguide structure₃The waveguide grating forms a short linear resonant cavity structure;

laser emitted by the InGaAs semiconductor chip is incident to the LiNbO3 waveguide structure and then is incident to the LiNbO₃Waveguide grating, and incident on LiNbO₃Outputting single-frequency linearly polarized laser after waveguide structure, LiNbO₃The waveguide grating is positioned at the front part and the rear part of the waveguide grating₃The middle of the waveguide structure;

the laser emitted by the InGaAs semiconductor chip is TE mode high-specific-ratio laser and enters the LiNbO₃Waveguide grating by said LiNbO₃The waveguide grating compresses the spectral line width and outputs narrow-line-width laser;

the InGaAs semiconductor chip and LiNbO₃Crystal substrate and LiNbO₃Waveguide structure and LiNbO₃The waveguide grating is arranged on the thermoelectric refrigerator TEC.

The InGaAs semiconductor chip adopts a multi-quantum well epitaxial structure and a narrow spine gain structure, one end face of the InGaAs semiconductor chip is plated with an antireflection film of 1000nm-1100nm, and the end face and LiNbO₃The waveguide is directly bonded, and the other end surface is plated with a high-reflection film of 1000nm-1100 nm; epitaxially growing an ultra-low defect density epitaxial material by a metal organic vapor deposition technology, adjusting various components and material structures, adjusting a light limiting factor, improving output power, and adjusting a spontaneous reflection spectrum to enable the excitation wavelength of the chip to cover 1000nm to 1100 nm; laser emitted by the InGaAs semiconductor chip is incident to LiNbO₃A waveguide structure through which LiNbO is passed₃Selecting a waveguide structure, and outputting TE mode laser corresponding to extraordinary light;

the TE mode laser is incident on the LiNbO₃Waveguide grating by said LiNbO₃The waveguide grating compresses the spectral line width and outputs narrow-line-width laser;

the LiNbO3 crystal substrate adopts X-Y cut LiNbO₃The direction of the X is the light emergent direction of the crystal, namely the emergent direction of the laser, and the direction of the Y is determined by the right-hand rule(ii) a The LiNbO₃The waveguide structure is manufactured on the LiNbO3 crystal substrate to prepare LiNbO₃The waveguide structure is prepared by annealing proton exchange process, specifically selecting benzoic acid (C)₆H₅COOH) as a proton source, LiNbO₃The crystal is immersed in a benzoic acid solution at the temperature of 120-₊To H₊Exchange, forming H on the crystal surface_xLi_1-xNbO₃High refractive index layer, and further LiNbO₃A straight waveguide structure or a Y-shaped waveguide structure containing the straight waveguide structure is formed on a substrate, and the proton exchange process can be described by using an equilibrium equation:

LiNbO₃+(C₆H₅OOH)_x＝Li_1-xH_xNbO₃+(C₆H₅OOLi)_x

after proton exchange, a straight waveguide structure with the refractive index difference delta n of approximately equal to 0.15 is formed to meet the requirements of a semiconductor chip output beam mode field and LiNbO₃Waveguide mode field matching, adopting annealing process to change refractive index distribution, adjust waveguide depth, reduce transmission loss, and simultaneously adjust beam mode field and LiNbO₃Waveguide mode field matching is achieved, and coupling efficiency is improved. In this embodiment, the LiNbO manufactured by the annealing autonomous exchange process condition is used₃The waveguide structure only transmits TE mode laser corresponding to extraordinary ray, and TM mode laser corresponding to ordinary ray can be radiated into the LiNbO₃Crystal substrate, as shown in FIG. 2, i.e. the LiNbO₃The waveguide can perform the functions of polarization extinction and single-polarization transmission.

LiNbO to be polished in this example₃The crystal end faces are selectively coated with aluminum, titanium or other light absorbing material to cover most of the end faces except the waveguide to absorb TM mode laser radiation outside the waveguide as much as possible, the coating shape being shown in fig. 3.

In this example, the InGaAs semiconductor chip and the LiNbO₃LiNbO of periodic structure formed by etching part of waveguide structure₃The waveguide grating forms a short linear resonant cavity structure, and an external cavity LiNbO is used₃The waveguide grating forms external cavity optical feedback, and the modified Schawlow-Townes lineBroad formula:

wherein is v₁Group velocity of the semiconductor chip region is the optical confinement factor of the gamma semiconductor chip, g_thIs the threshold gain, N is the intracavity photon density, V is the photon cavity product, N_spIs a particle flip factor, alpha is a laser linewidth broadening factor, n₁And L₁Is the refractive index and cavity length of the semiconductor chip region, n₂And L₂Is LiNbO₃The waveguide grating region refractive index and the cavity length. Through the corrected line width formula, simulation analysis of LiNbO can be performed by using COMSOL multi-physical field simulation software and FDTD finite element analysis software₃The influences of waveguide refractive index, cavity length, grating characteristics and the like on laser line width and noise can be optimized according to the influences₃Parameters of the waveguide grating.

The LiNbO₃The waveguide grating is formed on LiNbO in a femtosecond laser direct writing or focused ion beam etching mode₃Etching periodic structure on the straight waveguide, and locating in the LiNbO₃The middle of the waveguide structure; the length and refractive index distribution of the periodic structure on the waveguide grating are controlled to be compressed to 10kHz, and the periodic structure plays a role in compressing the laser line width to 10KHZ level.

Example 2

The present embodiment is different from embodiment 1 in that:

the LiNbO₃The other end of the crystal is selectively coated by aluminum, titanium or other light absorption materials to cover most end faces except the waveguide, TE mode laser in the waveguide is placed as much as possible and coupled into the PM980 polarization-maintaining optical fiber through a focusing lens, and the polarization extinction ratio of output laser is improved.

Also comprises a focusing lens and a polarization-maintaining optical fiber, and the LiNbO₃The waveguide structure, the focusing lens and the polarization maintaining fiber are connected in sequence through an optical path, the polarization maintaining fiber is a PM980 polarization maintaining gain fiber, and the LiNbO₃TE mode laser pass in waveguide structureThe over-focusing lens is coupled to the PM980 polarization-maintaining gain fiber, so that the polarization extinction ratio of the output laser is improved and can reach 50 dB.

One end of the polarization maintaining optical fiber, which is close to the focusing lens, is polished and then is plated with a 1000nm-1100nm wave band antireflection film, so that the coupling efficiency of laser coupled into the PM980 polarization maintaining optical fiber through the focusing lens can be improved.

The LiNbO₃An electrode is added on the crystal substrate, and LiNbO can be added on the crystal substrate₃LiNbO behind waveguide grating₃The waveguide structure carries out phase modulation on the output laser loading microwave signal, and the line width of the output light beam is adjustable.

The rest is the same as in example 1.

Example 3

The present embodiment is different from embodiment 1 in that:

the LiNbO₃The two end faces of the crystal substrate are coated with titanium to cover the end faces except the waveguide to absorb the radiation light outside the waveguide as much as possible.

The polarization maintaining fiber is a PM980 polarization maintaining gain fiber, and after polishing, the PM980 polarization maintaining gain fiber adopts CO₂The fusion splicer directly fuses the PM980 polarization-maintaining gain fiber to the LiNbO₃The end face of the waveguide structure is coupled and output, so that the laser coupling efficiency is increased, and the coupling loss is reduced.

The integrated external cavity type single-frequency linear polarization semiconductor laser in the embodiment can obtain stable and reliable single-frequency semiconductor laser output through a standard 14-pin butterfly-shaped packaging process.

In the embodiment, the whole optical path and optical devices of all the optical paths are fixed in a heat sink made of metal materials, so that the heat dissipation performance of the semiconductor laser is improved.

The rest is the same as in example 1.

Example 4

The present embodiment is different from embodiment 1 in that:

the InGaAs semiconductor chip and the LiNbO₃The waveguide grating is directly bonded and integrated, and the InGaAs semiconductor chip is connected with LiNbO₃Waveguide grating formationA short linear resonant cavity structure; laser emitted by the InGaAs semiconductor chip is incident to LiNbO₃Waveguide grating, and incident on LiNbO₃The single-frequency linearly polarized laser is output after the waveguide structure.

The rest is the same as in example 1.

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