阅读说明：本技术 线偏振窄线宽外腔型半导体激光器 (Linear polarization narrow linewidth external cavity type semiconductor laser ) 是由 陈超 罗曦晨 宁永强 张星 秦莉 王立军 于 2021-09-06 设计创作，主要内容包括：本发明提供一种线偏振窄线宽外腔型半导体激光器,包括增益芯片和外腔选频器件,外腔选频器件的基本结构为硅基波导布拉格光栅,基于硅基波导布拉格光栅的双折射效应,使得外腔选频器件反射的TE模式和TM模式分裂,当TE模式和TM模式反射回增益芯片并注入到增益芯片的ASE谱上时,TE模式与TM模式之间形成增益差,并且TM模式和TM模式的增益受到抑制,使线偏振窄线宽外腔型半导体激光器以线偏振模式输出。本发明无需偏振控制器就可以输出线偏振的激光,从而简化外腔半导体激光器的结构并降低外腔半导体激光器中各元器件之间的损耗。(The invention provides a linear polarization narrow linewidth external cavity type semiconductor laser, which comprises a gain chip and an external cavity frequency selection device, wherein the basic structure of the external cavity frequency selection device is a silicon-based waveguide Bragg grating, and the TE mode and the TM mode reflected by the external cavity frequency selection device are split based on the birefringence effect of the silicon-based waveguide Bragg grating. The invention can output the linearly polarized laser without a polarization controller, thereby simplifying the structure of the external cavity semiconductor laser and reducing the loss among all components in the external cavity semiconductor laser.)

1. The external cavity type semiconductor laser with the linear polarization narrow linewidth is characterized by comprising a gain chip and an external cavity frequency selection device, wherein the external cavity frequency selection device is in a silicon-based waveguide Bragg grating structure, a TE mode and a TM mode reflected by the external cavity frequency selection device are split based on the birefringence effect of the silicon-based waveguide Bragg grating, when the TE mode and the TM mode are reflected back to the gain chip and injected onto an ASE spectrum of the gain chip, a gain difference is formed between the TE mode and the TM mode, the gains of the TM mode and the TM mode are restrained, and the external cavity type semiconductor laser with the linear polarization narrow linewidth is enabled to output in a linear polarization mode.

2. The linearly polarized narrow linewidth external cavity semiconductor laser as claimed in claim 1, wherein an F-P cavity is formed between the external cavity frequency selective device and the gain chip, and a longitudinal mode is selected from a reflection band gap of the silica-based waveguide bragg grating and a resonance spectrum of the F-P cavity and injected into a gain peak spectrum of the linearly polarized narrow linewidth external cavity semiconductor laser to realize single longitudinal mode lasing of the linearly polarized narrow linewidth external cavity semiconductor laser.

3. The linearly polarized narrow linewidth external cavity semiconductor laser of claim 1 further comprising a coupling lens between the external cavity frequency selective device and the gain chip for matching the mode fields of the gain chip and the external cavity frequency selective device.

4. The linearly polarized narrow linewidth external cavity semiconductor laser as claimed in claim 1 wherein an inverted cone shaped spot size converter is integrated on said external cavity frequency selective device for matching the mode fields of said gain chip and said external cavity frequency selective device.

5. The linearly polarized narrow linewidth external cavity semiconductor laser according to claim 3 or 4, wherein the gain chip is used as a high-inversion end of the linearly polarized narrow linewidth external cavity semiconductor laser, and the external cavity frequency-selecting device is used as an exit end of the linearly polarized narrow linewidth external cavity semiconductor laser; a high reflection film is plated at one end of the gain chip, which is far away from the external cavity frequency selection device, and an antireflection film is plated at one end of the gain chip, which is towards the external cavity frequency selection device; and two ends of the external cavity frequency selection device are respectively plated with antireflection films.

6. The linearly polarized narrow linewidth external cavity semiconductor laser as claimed in claim 5 wherein an anti-reflection coating plated on said gain chip forms a predetermined reflection angle with a vertical plane.

7. The linearly polarized narrow linewidth external cavity semiconductor laser as claimed in claim 1 wherein said gain chip is used as an exit end of said linearly polarized narrow linewidth external cavity semiconductor laser and said external cavity frequency selective device is used as a high reflection end of said linearly polarized narrow linewidth external cavity semiconductor laser; and one end of the gain chip facing the external cavity frequency selection device is plated with an antireflection film, and the other end of the gain chip is plated with a low reflection film.

8. The linearly polarized narrow linewidth external cavity semiconductor laser as claimed in claim 6 or 7 wherein both ends of said external cavity frequency selective device form an inclined plane at a predetermined angle to a vertical plane.

9. The linearly polarized narrow linewidth external cavity semiconductor laser as claimed in claim 8 further comprising a lens group disposed in an output direction of an exit end of the linearly polarized narrow linewidth external cavity semiconductor laser, the lens group comprising an isolator for reducing external feedback and a collimating lens for collimating laser light output from the exit end of the linearly polarized narrow linewidth external cavity semiconductor laser.

10. The linearly polarized narrow linewidth external cavity semiconductor laser as claimed in claim 8, further comprising a lens group and a polarization maintaining fiber sequentially arranged along an output direction of the exit end of the linearly polarized narrow linewidth external cavity semiconductor laser, wherein the lens group comprises an isolator and two collimating lenses, the isolator is located between the two collimating lenses, the isolator is used for reducing external feedback, and the two collimating lenses are used for focusing and coupling laser light output by the exit end of the linearly polarized narrow linewidth external cavity semiconductor laser into the polarization maintaining fiber.

Technical Field

The invention relates to the technical field of photoelectronic devices, in particular to a linearly polarized narrow linewidth external cavity type semiconductor laser.

Background

The narrow linewidth semiconductor laser has the characteristics of narrow spectral linewidth, good coherence, low phase frequency noise and low Relative Intensity Noise (RIN), is widely applied to the fields of coherent optical communication, optical sensing, high-resolution spectral measurement, laser radar and the like, and generally requires that the linewidth level of the laser can reach the kHz level. Currently, a commonly used narrow linewidth semiconductor laser usually adopts a monolithic integrated Distributed Bragg Reflector (DBR) laser and a Distributed Bragg feedback (DFB) laser, the cavity lengths of the two lasers are usually short, the photon life is determined to be short, the linewidth performance is limited, the linewidths of the two lasers are generally at the MHz level, and the requirements of high-coherence optical communication and low-bit-error-rate signal transmission are difficult to meet; in addition, the preparation of the DFB/DBR laser generally needs secondary epitaxy, the process is complex, the requirement on production equipment is high, and the cost and the difficulty of commercialization are greatly improved.

An External cavity semiconductor laser (ECL) is a narrow linewidth semiconductor laser solution having the most potential at present, and a gain chip and an External cavity frequency selection device are coupled and integrated together, for example, the External cavity frequency selection device selects a Fabry-perot (F-P) External cavity frequency selection device, a fiber bragg grating, a waveguide bragg grating, a micro-ring resonator, and the like. Based on the optical injection locking effect, the external cavity frequency selection devices can select a single longitudinal mode with a specific wavelength to be injected into the gain chip, so that lasing is formed in a laser cavity, the linewidth output of dozens of kHz magnitude is easily realized, and if the structure and the performance of the external cavity laser are optimized, the linewidth of hundreds of Hz or even Hz level can be realized, such as the Q value of the frequency selection device is improved, the laser is packaged, and the like.

The conventional external cavity semiconductor laser is based on a silicon-based planar waveguide as an external cavity frequency selection device, a quasi-on-chip integrated laser is easily realized by a hybrid integration method, the structure is simple, the compactness is high, and the line width performance is excellent, but the linear polarization characteristic of the laser is often ignored in the current research, and the output of the linear polarization laser can be realized only by adding a polarization control device or a polarization selection device at the rear end of the laser, so that the structure of the external cavity semiconductor laser is complicated, the internal loss of the external cavity semiconductor laser is increased, and the application of the external cavity semiconductor laser in a polarization-related optical system is limited.

Disclosure of Invention

The invention aims to provide a linearly polarized narrow linewidth external cavity type semiconductor laser to solve the problem that the linearly polarized narrow linewidth external cavity type semiconductor laser in the prior art can output linearly polarized laser only by additionally adding a polarization controller.

In order to achieve the purpose, the invention adopts the following specific technical scheme:

the invention provides a linear polarization narrow linewidth external cavity type semiconductor laser, which comprises a gain chip and an external cavity frequency selection device, wherein the basic structure of the external cavity frequency selection device is a silicon-based waveguide Bragg grating, and the TE mode and the TM mode reflected by the external cavity frequency selection device are split based on the birefringence effect of the silicon-based waveguide Bragg grating.

Preferably, an F-P resonant cavity is formed between the external cavity frequency selection device and the gain chip, a longitudinal mode is selected by the reflection band gap of the silicon-based waveguide Bragg grating and the resonance spectrum of the F-P resonant cavity together, and is injected onto the gain peak spectrum of the linearly polarized narrow linewidth external cavity type semiconductor laser, so that single longitudinal mode lasing of the linearly polarized narrow linewidth external cavity type semiconductor laser is realized.

Preferably, the linearly polarized narrow linewidth external cavity type semiconductor laser further comprises a coupling lens located between the external cavity frequency selective device and the gain chip for matching mode fields of the gain chip and the external cavity frequency selective device.

Preferably, an inverted cone-shaped mode spot converter is integrated on the external cavity frequency selection device and used for matching mode fields of the gain chip and the external cavity frequency selection device.

Preferably, the gain chip is used as a high reflection end of the linearly polarized narrow linewidth external cavity type semiconductor laser, and the external cavity frequency selection device is used as an emergent end of the linearly polarized narrow linewidth external cavity type semiconductor laser; a high reflection film is plated at one end of the gain chip, which is far away from the external cavity frequency selection device, and an anti-reflection film is plated at one end of the gain chip, which faces the external cavity frequency selection device; and two ends of the external cavity frequency selection device are respectively plated with antireflection films.

Preferably, the antireflection film plated on the gain chip forms a preset reflection angle with the vertical plane.

Preferably, the gain chip is used as an emitting end of the linearly polarized narrow linewidth external cavity type semiconductor laser, and the external cavity frequency selecting device is used as a high reflecting end of the linearly polarized narrow linewidth external cavity type semiconductor laser; and one end of the gain chip facing the external cavity frequency selection device is plated with an antireflection film, and the other end of the gain chip is plated with a low reflection film.

Preferably, two ends of the external cavity frequency-selecting device form an inclined plane which forms a preset angle with a vertical plane.

Preferably, the linearly polarized narrow linewidth external cavity semiconductor laser further includes a lens group arranged in an output direction of an exit end of the linearly polarized narrow linewidth external cavity semiconductor laser, the lens group includes an isolator and a collimating lens, the isolator is used for reducing external feedback, and the collimating lens is used for collimating laser output by the exit end of the linearly polarized narrow linewidth external cavity semiconductor laser.

Preferably, the linearly polarized narrow linewidth external cavity semiconductor laser further comprises a lens group and a polarization maintaining optical fiber which are sequentially arranged in the output direction of the exit end of the linearly polarized narrow linewidth external cavity semiconductor laser, the lens group comprises an isolator and two collimating lenses, the isolator is located between the two collimating lenses, the isolator is used for reducing external feedback, and the two collimating lenses are used for focusing laser output by the exit end of the linearly polarized narrow linewidth external cavity semiconductor laser and then coupling the laser into the polarization maintaining optical fiber.

Compared with the existing external cavity semiconductor laser, the external cavity frequency selection device with the polarization mode selection function is integrated with the gain chip, an F-P resonant cavity is formed between the external cavity frequency selection device and the gain chip, the basic structure of the external cavity frequency selection device is a silicon-based waveguide Bragg grating, the mode injected into the gain chip has obvious linear polarization characteristics by utilizing the polarization mode selection function of the silicon-based waveguide Bragg grating, and meanwhile, the F-P resonant cavity has the polarization mode selection function, so that the polarized laser can be output without a polarization controller, the structure of the external cavity semiconductor laser is simplified, and the loss among all components in the external cavity semiconductor laser is reduced.

Drawings

Fig. 1 is a schematic diagram of a linearly polarized narrow linewidth external cavity semiconductor laser provided in accordance with an embodiment of the present invention;

fig. 2 is a schematic diagram of a Matlab simulation result of a linearly polarized narrow linewidth external cavity semiconductor laser according to an embodiment of the present invention;

fig. 3 is a lasing spectrum of a linearly polarized narrow linewidth external cavity semiconductor laser provided in accordance with an embodiment of the present invention;

FIG. 4 is a graphical illustration of normalized power versus angle provided in accordance with an embodiment of the present invention;

fig. 5 is a schematic diagram of noise power spectral density and frequency stable allen variance of a linearly polarized narrow linewidth external cavity semiconductor laser provided in accordance with an embodiment of the present invention;

fig. 6 is a schematic diagram of relative intensity noise spectra of a linearly polarized narrow linewidth external cavity semiconductor laser provided in accordance with an embodiment of the present invention at different currents;

fig. 7 is a schematic structural view of a linearly polarized narrow linewidth external cavity semiconductor laser provided in embodiment 1 of the present invention;

fig. 8 is a schematic structural view of a linearly polarized narrow linewidth external cavity semiconductor laser provided in embodiment 2 of the present invention;

fig. 9 is a schematic structural view of a linearly polarized narrow linewidth external cavity semiconductor laser provided in embodiment 3 of the present invention.

The reference numerals of embodiment 1 include: a gain chip 101, an external cavity frequency-selecting device 102, a coupling lens 103, a lens group 104, an L-shaped bracket 105, a polarization maintaining fiber 106, a metal bracket 107 and a substrate 108;

the reference numerals of embodiment 2 include: a gain chip 201, an external cavity frequency-selecting device 202, a lens group 203, an L-shaped bracket 204, a polarization-maintaining fiber 205, a metal bracket 206 and a substrate 207;

the reference numerals of embodiment 3 include: a gain chip 301, an external cavity frequency-selecting device 302, a spot size converter 303, a lens group 304, an L-shaped bracket 305, a polarization maintaining fiber 306, a metal bracket 307 and a substrate 308.

Detailed Description

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, the same reference numerals are used for the same blocks. In the case of the same reference numerals, their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not to be construed as limiting the invention.

The invention provides a linear polarization narrow linewidth external cavity type semiconductor laser, which comprises a gain chip and an external cavity frequency-selecting device, wherein the gain chip comprises a gain chip and a plurality of gain chips, and the external cavity frequency-selecting device comprises a gain chip, an external cavity frequency-selecting device and a frequency-selecting device, wherein the gain chip comprises a gain chip, a frequency-selecting device and a frequency-selecting device, wherein the gain chip comprises a gain chip, a narrow linewidth, and a narrow linewidth, and a narrow linewidth, and a narrow linewidth, and a narrow width, a narrow linewidth, a narrow width, and a narrow:

1. gain chip

The invention selects a gain chip with high gain and low line width broadening factors, which can be a quantum well structure or a quantum dot structure. The gain chip has the output of an Amplified Spontaneous Emission (ASE) spectrum, and is used as an active region of a linearly polarized narrow-linewidth external cavity type semiconductor laser and provides an active part with low noise, high gain and low linewidth broadening factors. One end of the gain chip is plated with an antireflection film to reduce extra F-P resonance effect caused by unnecessary cavity surface reflection, and further, the end can be plated with an antireflection film forming a preset reflection angle with a vertical plane or a bent waveguide structure/inclined waveguide structure to further eliminate the F-P resonance effect; and a high-reflection film is plated at the other end of the gain chip to form an equivalent F-P resonant cavity with the external cavity frequency-selecting device.

2. External cavity frequency-selecting device

The external cavity frequency-selecting device in the invention selects a narrow-band external cavity frequency-selecting device with a polarization mode selection function, and the basic structure of the external cavity frequency-selecting device is a Waveguide Bragg Grating (WBG) with high birefringence effect. The waveguide Bragg grating with the high birefringence effect is a typical three-layer slab waveguide structure, the material of the waveguide Bragg grating is a silica-based silicon dioxide structure doped in a core layer, the stress birefringence effect is further improved by doping the core layer, the surface of the core layer is engraved with the grating, and the grating brings an additional shape birefringence effect by changing the shape of the core layer. The high birefringence effect can split the narrow-bandwidth TE (Transverse Electric field) mode and TM (Transverse Electric field) mode reflected by the narrow-band external cavity frequency-selecting device, so that when the TE mode and TM (Transverse Magnetic field) mode are reflected back to the gain chip and injected and locked to the ASE spectrum of the gain chip, an additional gain difference is brought between the TE mode and the TM mode due to mode splitting, and after a series of nonlinear processes, the gains of the TM mode and the TM mode are more strongly suppressed, so that the output of the linearly-polarized narrow-linewidth external cavity semiconductor laser is output in a high-linear polarization mode, that is, in the TE mode.

The gain chip and the narrow-band external cavity frequency selection device are integrated together through end face coupling or element coupling, so that the waveguide Bragg grating can provide mode feedback with linear polarization characteristics, is injected and locked into the gain chip, forms an equivalent F-P resonant cavity with the gain chip, and jointly selects a longitudinal mode with a high Q value factor by the reflection band gap of the waveguide Bragg grating and the resonance spectrum of the F-P resonant cavity, is injected and locked into a gain peak spectrum of the linear polarization narrow-linewidth external cavity type semiconductor laser to realize single longitudinal mode lasing, and realizes linewidth narrowing of the linear polarization narrow-linewidth external cavity type semiconductor laser and output of the narrow-linewidth laser by utilizing a negative feedback effect brought by an adiabatic chirp theory.

The linear polarization narrow linewidth external cavity type semiconductor laser provided by the invention is based on the combination of a high birefringent external cavity frequency-selecting device and a gain chip, utilizes the splitting characteristics of a TE mode and a TM mode, and realizes the output of linear polarization and narrow linewidth laser through the narrow-band polarization mode selection characteristic and the polarization mode gain control characteristic, and the principle is shown in figure 1:

two modes of Amplified Spontaneous Emission (ASE) of the gain chip are TE-ASE and TM-ASE respectively, and the gain chip is characterized in that: (1) TE polarization is dominant, i.e., the TE-ASE gain is greater than the TM-ASE gain; (2) the peak of the TM-ASE spectrum is far away from the peak of the TE-SAE spectrum towards the short wave side. As shown in fig. 1 (a), for a planar external cavity frequency-selective device without birefringence, the TE mode and TM mode whose reflection is injected into the gain chip are overlapped; for the external cavity frequency-selective device with the polarization mode selection function in the invention, the TE mode and the TM mode which are injected into the gain chip in a reflection mode are split, and the resonance peak of the TM mode is far away from the resonance peak of the TE mode towards the long wavelength side. If the chips are the same gain chip, mode splitting further brings extra gain difference to the TE mode and the TM mode on the basis that the gain of the TE mode is dominant, after a series of nonlinear effects, the gain of the TM mode is remarkably inhibited, and the linearly polarized narrow-linewidth external cavity type semiconductor laser can realize the output of laser with high linear polarization characteristic without a polarization controller, so that the polarization extinction ratio of the laser output is improved. Furthermore, narrow-bandwidth polarization mode injection locking is adopted, narrowing of the laser line width is achieved, and therefore output of narrow-line-width laser is obtained.

The invention simulates and calculates the narrow linewidth of waveguide grating based on the adiabatic chirp theory, and can simplify the equivalent F-P laser cavity of a double reflector and a back reflector r for an external cavity feedback system of a gain chip₁Set to 1, and the reflectivity of the output end is equivalently replaced by a complex reflectivity r related to the wavelength_eff：

Wherein phi is₁Is the constant phase of the laser cavity; r is₀Is the front end reflectivity of the gain chip due to the presence of the anti-reflection film₀Can be set to 0; r is_extIs the optical feedback reflected by the waveguide bragg grating into the gain chip, and is expressed as:

r_ext＝r_g*C_e (2)

C_eis the coupling efficiency between the waveguide bragg grating and the gain chip; r is_gIs the complex field reflectivity, r, of the external cavity part in relation to the wavelength_gIs defined as:

μ＝(κ²+(iΔω/v_g-α₁/2)²)^1/2 (4)

wherein κ is a coupling coefficient of the waveguide bragg grating; v. of_gIs the group velocity of the optical mode; alpha is alpha₁Is the loss of the waveguide; ω is the angular frequency; Δ ω is the angular frequency detuning amount of the optical field; i is an imaginary number; m is a quantity related to the propagation constant and the coupling coefficient; the adiabatic chirp factor can be defined as:

F＝1+A+B (5)

f is the adiabatic chirp factor, from_effIt is determined that the corresponding lorentz line width Δ ν is narrowed as:

wherein alpha is_HIs a line width broadening factor; Δ ν₀The intrinsic lorentz line width of the gain chip is set to be 4; tau is_GCIs the single loop time, τ, of the optical mode inside the gain chip_GC＝2n_effL_a/c；n_effIs the mode effective index in the gain chip, which is set to 3.2 for an InP-based gain chip; l is_aAnd c represents the length of the gain chip and the speed of light, respectively, and the calculated corresponding loop time is 21.3 ps.

The parameter a represents the effect of reducing the longitudinal mode confinement on the suppressed linewidth, usually expressed as the ratio of the external effective length to the active region length. The parameter B represents the influence of its partial variation, which varies with the variation of the optical field frequency, and its negative feedback effect is often expressed as: the laser wavelength is detuned to the short (or long) side to make r_effAn increase (or decrease) in amplitude; the optical field reflected by the polarization mode external cavity frequency selective device increases (or decreases), and thus the photon density in the cavity increases (or decreases), while the carrier density decreases (or increases) due to the enhancement of spontaneous emission, resulting in a shift of the wavelength to the long (or short) wavelength side due to the plasmon effect of the carriers. The parameter B generally has a larger value at a position away from the F-P cavity where the loss is smallest, i.e. where the transmission is relatively high.

Fig. 2 shows the results of calculations for Matlab simulations with a detuned range of 1.6nm (200 Ghz). For the frequency selective device with narrow-band external cavity, 1.6nm is many times larger than the bandwidth, so there are many side lobe peaks in this range as shown in (a) of fig. 2. F in the stop band is low because the reflectivity is highest, which means that the strongest optical confinement (smaller a value) and the smallest optical loss/transmission (smaller B value) are produced. Around the energy gap, F is significantly enhanced. Only wavelengths near the center of the bragg resonance are considered because lasing is difficult to occur elsewhere. Fig. 2 (b) shows the simulation result corresponding to the long wavelength side in the 0.08nm wavelength detuning range. The maximum F value appears on the long wavelength side from the center of the wavelength, the maximum line width decreases by about 2000, and the predicted output is about 2kHz at 9dBm (8 mW). Therefore, the waveguide bragg grating of the present invention is designed for high reflectivity, and the laser wavelength occurs on the longer side of the peak, far from the band gap of the waveguide bragg grating, as shown by the spectrum, i.e., the region where F is greatly enhanced, so that the line width can be remarkably suppressed.

The advantages of the invention will be illustrated below in connection with the test results:

as shown in fig. 3, the side mode suppression ratio reached 50.2dB, and the operation was performed in a good single longitudinal mode state.

As shown in FIG. 4, the normalized power variation with angle is obtained by the polarization extinction ratio test platform, and the polarization extinction ratio greater than 39.6dB can be calculated. This shows that the linearly polarized narrow linewidth external cavity semiconductor laser operates in the TE mode, and the TM mode is highly suppressed and is in a good linearly polarized state.

As shown in fig. 5, gray points in (a) and (a) in fig. 5 are integral line widths calculated according to a beta isolation line method, the minimum integral line width reaches 4.15kHz, the line width is greatly narrowed, and good narrow line width output is realized; referring to (b) and (b) in FIG. 5, the gray points are calculated frequency-stable Allan variances, and the minimum Allan variance reaches 4.41 × 10^-11The reason is that the narrow-band external cavity frequency-selecting device brings negative feedback effect, so that the linear polarization narrow-linewidth external cavity type semiconductor laser works under a highly frequency stable state.

As shown in FIG. 6, the RIN power density spectra at 400mA current were measured to have a lowest RIN of-155 dBc/Hz or less at 400mA, with very low relative intensity noise.

Example 1

The linearly polarized narrow linewidth external cavity semiconductor laser provided in embodiment 1 of the present invention includes a gain chip 101, an external cavity frequency selective device 102, a coupling lens 103, a lens group 104, an L-shaped support 105, a polarization maintaining fiber 106, a metal support 107, and a substrate 108, where the substrate 108 is a metal substrate, and the gain chip 101, the external cavity frequency selective device 102, the coupling lens 103, the lens group 104, the L-shaped support 105, the polarization maintaining fiber 106, and the metal support 107 are respectively disposed on the substrate 108.

An F-P resonant cavity is formed between the gain chip 101 and the external cavity frequency-selecting device 102, and the coupling lens 103 is located between the gain chip 101 and the external cavity frequency-selecting device 102, and is used for matching the mode fields of the gain chip and the external cavity frequency-selecting device, so as to improve the coupling efficiency between the gain chip 101 and the external cavity frequency-selecting device 102, and thus improve the final output power of the linearly polarized narrow linewidth external cavity semiconductor laser. The gain chip 101 and the external cavity frequency-selecting device 102 are coupled by a lens.

The gain chip 101 is used as an active medium of a wide ASE spectrum of the linearly polarized narrow linewidth external cavity semiconductor laser, the gain chip 101 is used as a high-reflection end of the linearly polarized narrow linewidth external cavity semiconductor laser, and the external cavity frequency selector 102 is used as an emitting end of the linearly polarized narrow linewidth external cavity semiconductor laser.

A high-reflection film is plated on the high-reflection end (i.e. the end away from the coupling lens 103) of the gain chip 101 to form an equivalent F-P resonant cavity with the external cavity frequency-selecting device 102; an antireflection film is plated at the coupling end (i.e., the end facing the coupling lens 103) of the gain chip 101 to reduce the unwanted cavity surface reflection and bring about an additional F-P effect, and the antireflection film may also have a certain reflection angle, or a curved waveguide or an inclined waveguide with a certain angle is used to further suppress the F-P cavity effect of the gain chip itself.

Antireflection films are respectively plated on two end faces of the external cavity frequency-selecting device 102, the external cavity frequency-selecting device 102 has a high birefringence effect, can provide a narrow-bandwidth polarization mode, and reflects and injects the polarization mode into an ASE spectrum of the gain chip 101 to form stable lasing. The two ends of the external cavity frequency-selecting device 102 are polished to present an inclined plane with a predetermined angle with the vertical plane, for example, the inclined plane is 8 ° with the vertical plane, so as to reduce unnecessary reflection at the two end faces of the external cavity frequency-selecting device 102.

The lens group 104 and the polarization maintaining fiber 106 are sequentially arranged along the output direction of the exit end of the external cavity type semiconductor laser with narrow line width of linear polarization. The lens assembly 104 is fixed on the substrate 108 through two L-shaped brackets 105, and the lens assembly 104 is used for coupling laser light emitted from an emitting end of the linearly polarized narrow linewidth external cavity semiconductor laser into the polarization maintaining fiber 106 and outputting the laser light through the polarization maintaining fiber 106.

The polarization maintaining fiber 106 is a partially metalized polarization maintaining fiber and is fixed on the substrate 108 through a metal bracket 107, the metal bracket 107 is a semicircular metal bracket, and the metalized part of the polarization maintaining fiber 106 is fixed on the substrate 108 through laser welding. When the polarization maintaining optical fiber 106 is coupled, it is necessary to adjust the polarization extinction ratio to the maximum position and then fix it by the metal bracket 107.

The lens group 104 comprises an isolator and two collimating lenses, the isolator is positioned between the two collimating lenses and is used for reducing external feedback, improving the stability of the linearly polarized narrow linewidth external cavity type semiconductor laser and reducing the noise of the linearly polarized narrow linewidth external cavity type semiconductor laser; the two collimating lenses are used for collimating and focusing laser output by the exit end of the linearly polarized narrow linewidth external cavity type semiconductor laser and then coupling the laser into the polarization maintaining optical fiber 106, so that the coupling efficiency of the external cavity frequency selection device 102 and the polarization maintaining optical fiber 106 is improved, and the output power of the on-fiber is finally improved.

It should be noted that, if the application of the linearly polarized narrow linewidth external cavity semiconductor laser does not need to output laser light through the polarization maintaining fiber 106, the lens assembly 104 may also use only one collimating lens to achieve laser light output.

The substrate 108 is preferably a copper substrate, the rear end of the substrate controls the temperature of the line-polarized narrow-linewidth external cavity semiconductor laser through a thermoelectric controller and a thermistor, and simultaneously the gain chip 101, the external cavity frequency selection device 102, the coupling lens 103, the lens group 104 and the polarization maintaining fiber 106 are respectively fixed on the copper substrate after finding the optimal coupling position, so that the stability of the whole line-polarized narrow-linewidth external cavity semiconductor laser is improved.

Example 2

Example 2 differs from example 1 in that: the coupling mode of the gain chip 201 and the external cavity frequency selection device 202 is changed from lens coupling to end face coupling. More specifically, the positions of the gain chip 201 and the external cavity frequency selection device 202 are exchanged with the positions of the gain chip 101 and the external cavity frequency selection device 102 in embodiment 1, the gain chip 201 is used as the emitting end of the linearly polarized narrow-linewidth external cavity semiconductor laser, the external cavity frequency selection device 202 is used as the high-reflection end of the linearly polarized narrow-linewidth external cavity semiconductor laser, and the gain chip 201 and the external cavity frequency selection device 202 are directly integrated together through end-face coupling.

An anti-reflection film is plated on the end face of the gain chip 201 coupled with the external cavity frequency-selecting device 202, and a low-reflection film is plated on the other end of the gain chip 201, and the end is used as the emergent end face of the linear polarization narrow-linewidth external cavity semiconductor laser.

The structures and positions of the lens group 203, the L-shaped bracket 204, the polarization maintaining fiber 205, the metal bracket 206 and the substrate 207 in the embodiment 2 are the same as those of the lens group 104, the L-shaped bracket 105, the polarization maintaining fiber 106, the metal bracket 107 and the substrate 108 in the embodiment 1.

Example 3

Example 3 differs from example 1 in that: the coupling lens 103 in embodiment 1 is replaced by a spot size converter 303, the spot size converter 303 is integrated at the front end of the external cavity frequency selecting device 302, and the spot size converter 303 has an inverted cone-shaped structure, is on the same layer as the waveguide, and has the same thickness as the waveguide. The function of the spot size converter 303 is the same as that of the coupling lens 103 in embodiment 1, and is used for matching the mode field between the gain chip 301 and the external cavity frequency-selecting device 302, so as to improve the coupling efficiency between the gain chip 301 and the external cavity frequency-selecting device 302.

The lens group 304, the L-shaped holder 305, the polarization maintaining fiber 306, the metal holder 307, and the substrate 308 in example 3 have the same structures and positions as those of the lens group 104, the L-shaped holder 105, the polarization maintaining fiber 106, the metal holder 107, and the substrate 108 in example 1.

In the description herein, references to the description of the term "one embodiment," "some embodiments," "one example," "another example" or "a specific example" or the like are intended to mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.

Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.

The above embodiments of the present invention should not be construed as limiting the scope of the present invention. Any other corresponding changes and modifications made according to the technical idea of the present invention should be included in the protection scope of the claims of the present invention.