Narrow linewidth semiconductor laser

Abstract

The utility model provides a narrow-linewidth semiconductor laser. The narrow-linewidth semiconductor laser comprises a photoelectric detector, a gain chip, a first collimating lens, a narrow-band filter, a reflector, a polarizer and an isolator which are sequentially arranged along the light path direction of emitted light, one side of the first converging lens is arranged outside the isolator; an output end assembly is arranged on the other side of the first converging lens; incident light generates gain through the gain chip, and light beams after gain generation pass through the first collimating lens, the narrow-band filter and the reflector, then coincide with the polarization direction of the polarizer, converge to the first convergent lens and reach the output end assembly, so that intracavity oscillation in the outer cavity structure is achieved, and the light beams are output through the output end assembly. The piezoelectric ceramic is arranged below the reflecting mirror and is used for providing a voltage value and high and low level directions so as to realize bidirectional position scanning and tune the cavity length of the outer cavity; therefore, the integrated narrow-linewidth semiconductor laser which has the advantages of wide output power modulation, high polarization extinction ratio, ultra-narrow linewidth and small-range rapid wavelength scanning is provided.

Description

Technical Field

[0001] This utility model relates to the field of laser technology, specifically to a narrow linewidth semiconductor laser. Background Technology

[0002] Narrow-linewidth semiconductor lasers have very narrow linewidths and good directionality, and are relatively inexpensive, making them widely used in fields such as LiDAR, fiber optic sensing, and quantum communication.

[0003] Existing polarization-modulated semiconductor lasers, ring-cavity ultra-narrow linewidth semiconductor lasers, and high-feedback-power tunable semiconductor lasers cannot simultaneously meet the requirements of stable output power, extremely narrow linewidth (1 kHz and below), high environmental stability, high polarization suppression ratio (above 20 dB), and fast scanning wavelength range. External-cavity narrow-linewidth semiconductor lasers, in principle, add a wavelength-selective feedback circuit outside the gain region to narrow the spontaneous emission (ASE) lines fed back to the gain region. Simultaneously, they reduce losses, increase cavity length, improve photon lifetime, and perform phase matching during the round trip. The final result can be single-mode lasing, or noise suppression can be achieved by increasing the side-mode suppression ratio (SMSR), maximizing the difference between the main peak and side peak optical resonant frequencies, and using polarization separation of the reflection spectrum.

[0004] In addition to common issues such as the need for alignment between the laser output port and the fiber during fiber coupling, most existing external cavity devices do not directly couple with the fiber for output. Direct coupling would significantly affect the wavelength. Furthermore, some devices cannot provide feedback through high-speed electrical parameters, thus hindering rapid control of optical parameters such as scanning wavelength, scanning range, and suppression ratio. Moreover, existing external cavity narrow-linewidth semiconductor lasers and optical amplifiers are often separate components, resulting in excessively large sizes.

[0005] Based on this, this utility model proposes an integrated narrow-linewidth semiconductor laser with wide-range modulated output power, high polarization extinction ratio, ultra-narrow linewidth, and fast scanning wavelength over a small range. Utility Model Content

[0006] Based on the above description, this utility model provides an integrated narrow-linewidth semiconductor laser with wide-range modulated output power, high polarization extinction ratio, ultra-narrow linewidth, and fast scanning wavelength over a small range.

[0007] The technical solution of this utility model to solve the above-mentioned technical problems is as follows:

[0008] This utility model provides a narrow linewidth semiconductor laser, comprising: a photodetector, a gain chip, a first collimating lens, a narrowband filter, a mirror, a polarizer, a piezoelectric ceramic, an isolator, a first converging lens, an output terminal assembly, and a thermistor.

[0009] The photodetector, the gain chip, the first collimating lens, the narrowband filter, the reflector, and the isolator are arranged sequentially along the optical path of the emitted light to form an external cavity structure; one side of the first converging lens is located outside the isolator; the other side of the first converging lens is provided with the output terminal assembly;

[0010] The incident light is amplified by the gain chip. After the amplified light passes through the first collimating lens, the narrowband filter and the mirror, the beam is aligned with the polarization direction of the polarizer and converges to the first converging lens, reaching the output component to achieve intracavity oscillation within the external cavity structure and output through the output component.

[0011] The piezoelectric ceramic is located below the reflector and is used to provide voltage values ​​and high / low level directions to achieve bidirectional position scanning and tune the cavity length of the outer cavity; the thermistor is located inside the outer cavity structure and is used to adjust the internal temperature of the outer cavity structure.

[0012] Based on the above technical solution, the present invention can be further improved as follows.

[0013] Furthermore, the output component includes an optical amplifier, a second collimating lens, a second converging lens, and a polarization-maintaining fiber ferrule arranged sequentially along the optical path direction;

[0014] When the gain chip and the optical amplifier are powered on simultaneously, the first converging lens is inserted between the input terminal of the optical amplifier and the isolator, and the position of the converging lens can be adjusted according to the power output by the output terminal component.

[0015] Furthermore, the isolator is a two-stage isolator.

[0016] Furthermore, the polarization incident direction of the dual-stage isolator is set to coincide with the linear polarization direction of the formed laser cavity.

[0017] Furthermore, the narrowband filter includes an etalon and a bandpass filter;

[0018] The etalon and the bandpass filter are arranged side by side;

[0019] The etalon is used to form transmission peaks with fixed channel spacing from the ASE beam of the gain chip; the bandpass filter is used to provide a selective channel to the beam for filtering.

[0020] Furthermore, the gain chip is aligned with the polarization direction of the polarizer.

[0021] Furthermore, the polarizer's polarizer is tilted at a certain angle in the horizontal direction, and the power is defined as P1; when the power P1 is at its maximum, the gain chip and the polarizer are aligned in polarization direction.

[0022] Furthermore, the narrow linewidth semiconductor laser also includes a ceramic substrate;

[0023] The gain chip is packaged on the ceramic substrate.

[0024] Furthermore, the working distance between the first collimating lens and the gain chip is set to 14~16mm.

[0025] Furthermore, the working distance between the first collimating lens and the gain chip is set to 15mm.

[0026] Compared with the prior art, the technical solution of this application has the following beneficial technical effects:

[0027] The narrow-linewidth semiconductor laser provided by this invention includes a photodetector, a gain chip, a first collimating lens, a narrowband filter, a mirror, a polarizer, a piezoelectric ceramic, an isolator, a first converging lens, an output assembly, and a thermistor. Incident light gains gain after passing through the gain chip. The gained beam then passes through the first collimating lens, the narrowband filter, and the mirror, and its polarization direction coincides with that of the polarizer before converging to the first converging lens. This convergence then reaches the output assembly, enabling intracavity oscillation within the external cavity structure, and is output through the output assembly. The piezoelectric ceramic is located below the mirror and provides voltage and high / low level directions to achieve bidirectional position scanning and tuning of the external cavity length.

[0028] Compared with the prior art, this utility model co-packages two discrete components, the semiconductor laser and the amplifier, through core optical co-packaging to obtain the final output laser, which can reduce the size by half and achieve integration. Moreover, with the help of core optical devices such as piezoelectric ceramics, polarizers, output end components, and external cavities, a semiconductor laser with wide-range modulated output power, high polarization extinction ratio, ultra-narrow linewidth, and fast scanning wavelength in a small range is realized. Attached Figure Description

[0029] Figure 1 A schematic diagram of the structure of a narrow linewidth semiconductor laser provided in an embodiment of this utility model;

[0030] Figure 2 A schematic diagram of the narrowband spectrum formed by the combination of a standard etalon and a bandpass filter in a narrow-linewidth semiconductor laser provided for an embodiment of this utility model;

[0031] The attached diagram lists the components represented by each number as follows:

[0032] 1. Photodetector;

[0033] 2. Gain chip;

[0034] 3. First collimating lens;

[0035] 4. Narrowband filter; 41. Ether; 42. Bandpass filter;

[0036] 5. Reflector;

[0037] 6. Polarizer;

[0038] 7. Piezoelectric ceramics;

[0039] 8. Isolator;

[0040] 9. First converging lens;

[0041] 10. Output assembly; 101. Optical amplifier; 102. Second collimating lens; 103. Second converging lens; 104. Polarization-maintaining fiber optic ferrule;

[0042] 11. Thermistor;

[0043] 12. External cavity structure;

[0044] 13. Ceramic substrate. Detailed Implementation

[0045] In the description of this utility model, it should be noted that, unless otherwise explicitly specified and limited, the terms "provided with" and "connected," etc., should be interpreted broadly. For example, "connected" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can also refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model according to the specific circumstances.

[0046] To make the objectives, technical solutions, and advantages of this utility model clearer, the technical solutions of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this utility model, not all embodiments. Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this utility model.

[0047] In existing technologies, common semiconductor lasers include the following three types:

[0048] The first method involves fabricating a planar Bragg waveguide reflection grating (PBG) using photolithography, and then coupling it to the end face of a gain chip using mode field matching. This method is described in detail in patents US8358889 and US8295320 from RIO Corporation. The disadvantages of this method are:

[0049] 1. There is a significant difference between the intrinsic waveguide mode fields of PBG and Gain chip. Even if the end-face mode fields of the two are processed separately, the coupling tolerance is too small, the process requirements are very high, and it is difficult to ensure that the mode fields are perfectly matched. As a result, the laser formed in this way cannot achieve a narrower linewidth and lower phase noise, and the power is often lower.

[0050] 2. PBG itself has multiple sidelobes and adopts straight end-to-end contact, so the reflection problem between the two end faces cannot be completely solved. The straight waveguide design of the gain chip inevitably has FP effect. Although the high frequency band is smooth, the overall amplitude is high, and the side modes formed at the sidelobes will limit the laser's subsequent multi-wavelength and EDFA amplification related applications.

[0051] 3. It is precisely because of the compensation of the positive and negative thermo-optic coefficients of PBG material that the product is not sensitive to temperature, which limits the wavelength temperature tuning range of the product. Often, Δλ < 30pm, and it is difficult to maintain the consistency of the phase state during the wavelength tuning process, resulting in large fluctuations in power and linewidth.

[0052] The second method uses two or more etalons as wavelength selection elements, such as Intel's 2003 invention patent ZL 02809947.8. This patent focuses on a wavelength selection feedback method. This patent partially references this method in the external cavity laser forming section, but makes improvements and innovations for specific applications. The differences between the utility model embodiments protected by this patent are as follows:

[0053] 1. The external cavity and SOA core optics are co-packaged to form the final laser.

[0054] 2. Adjustable external cavity: Existing technologies are limited by the use of Mems, temperature, etc., and the linewidth can only be guaranteed to be <100kHz. This application emphasizes that piezoelectric ceramic (PZT) combined with thermistor can maintain the narrow linewidth characteristic, with a linewidth <1kHz.

[0055] 3. Single polarization feedback: This technology does not exist in the prior art. The polarizer set in this application can play the role of single polarization feedback.

[0056] The third approach integrates at least two ring resonators and an asymmetric MZI loop phase shifter into the external cavity of the gain chip within a Si-based waveguide, as exemplified by Neophotonics' patent CN113557643A. This method is based on the double-ring vernier effect, which can satisfy wide-range wavelength tuning and SOA integration. It can also introduce TE / TM waveguide loss differences into the external cavity. However, its drawbacks include the presence of side modes in the vernier effect, and the coupling coefficient between the ring waveguide and the straight waveguide significantly affects the linewidth. Small-range wavelength scanning relies on thermal tuning, resulting in slow speeds. This approach differs significantly from the method described in this paper.

[0057] Based on the aforementioned technical problems and background, this utility model provides a narrow linewidth semiconductor laser.

[0058] The following is in conjunction with the appendix Figures 1 to 2 The embodiments and examples will be described in further detail below. The following embodiments are used to illustrate the present invention, but should not be used to limit the scope of the present invention.

[0059] like Figure 1 As shown, the narrow linewidth semiconductor laser provided in this embodiment of the present invention specifically includes: a photodetector 1, a gain chip 2, a first collimating lens 3, a narrowband filter 4, a reflector 5, a polarizer 6, a piezoelectric ceramic 7, an isolator 8, a first converging lens 9, an output terminal assembly 10, and a thermistor 11.

[0060] The photodetector 1, gain chip 2, first collimating lens 3, narrowband filter 4, reflector 5 and bipolar isolator 8 are arranged sequentially along the optical path of the emitted light to form an external cavity structure 12; one side of the first converging lens 9 is located outside the isolator 8; the other side of the first converging lens 9 is provided with an output terminal assembly 10.

[0061] The aforementioned output assembly 10 includes an optical amplifier 101, a second collimating lens 102, a second converging lens 103, and a polarization-maintaining fiber ferrule 104 arranged sequentially along the optical path.

[0062] When the gain chip 2 and the optical amplifier 101 are powered on at the same time, the first converging lens 9 is inserted between the input terminal of the optical amplifier 101 and the isolator 8. The position of the converging lens can be adjusted according to the power output by the output terminal component 10.

[0063] Specifically, the incident light is amplified by the gain chip 2. After amplification, the beam passes through the first collimating lens 3, the narrowband filter 4, and the reflector 5. The beam then converges with the polarizer 6 and is focused by the first converging lens 9, reaching the output assembly 10 to achieve intracavity oscillation within the external cavity structure 12. The beam is then output through the output assembly 10.

[0064] Among them, the piezoelectric ceramic 7 is located below the reflector 5 and is used to provide voltage value and high and low level direction to realize bidirectional position scanning and tune the cavity length of the outer cavity; the thermistor 11 is located inside the outer cavity structure 12 and is used to adjust the internal temperature of the outer cavity structure 12.

[0065] Specifically, by adjusting the reflector 5, the initial oscillation spectrum obtained from the narrowband spectrum formed by the combination of the etalon 41 and the bandpass filter 42 is returned to the inside of the gain chip 2 along the original path to form stimulated emission. The power is adjusted to the maximum by fixing the current, and the position of the reflector 5 is determined. The part between the rear end face of the gain chip 2 and the front end face of the reflector 5 forms the FP laser cavity. According to the voltage value and high and low level direction of the externally supplied piezoelectric ceramic 7, bidirectional position scanning can be realized, thereby tuning the cavity length of the outer cavity to achieve the purpose of rapid small-range scanning.

[0066] After the isolator 8 and the optical amplifier 101 are mounted on the reflector 5, the relative positions of the two waveguides of the optical amplifier 101 and the gain chip 2 need to be carefully calculated because the isolator 8 has an angle. In this embodiment, the gain chip 2 is selected to be polarization-independent to avoid excessive polarization rotation.

[0067] In one specific embodiment, preferably, the isolator 8 is a two-stage isolator 8. The polarization incident direction of the two-stage isolator 8 coincides with the linear polarization direction of the formed laser cavity to avoid reflected light from the optical amplifier 101.

[0068] In an optional embodiment, the narrowband filter 4 includes an etalon 41 and a bandpass filter 42.

[0069] The etalon 41 and the bandpass filter 42 are arranged side by side; the etalon 41 is used to form the ASE beam of the gain chip 2 into a transmission peak with a fixed channel spacing; the bandpass filter 42 is used to provide a selection channel to the beam for filtering.

[0070] Specifically, a narrowband filter 4 is formed by combining a standard etalon 41 and a bandpass filter 42. The narrowband spectrum formed by the combination of the two is as follows: Figure 2 As shown; the pink line is formed by superimposing the spectrum of the gain chip ASE and the transmission spectrum of the standard etalon 41. This spectrum has sharp peaks and a periodic distribution; the green line is the spectrum of the bandpass filter 42. This spectrum should be as flat as possible; the yellow line is the spectrum formed by superimposing the above two parts again, which serves as the initial oscillation spectrum fed back to the gain chip 2.

[0071] It should be noted that if the polarization directions of the gain chip 2 and the polarizer 6 in the external cavity are not highly aligned, even if the polarization extinction ratio fed back to the gain chip 2 is improved, a large amount of round-trip loss is introduced, affecting the output power and linewidth. In this embodiment, the polarization directions of the gain chip 2 and the polarizer 6 are aligned.

[0072] Specifically, the power of the collimated gain chip 2 is tested and recorded as P0; the polarizer 6 is tilted at a certain angle in the horizontal direction, and its power is defined as P1; when the power P1 is at its maximum, the polarization directions of the gain chip 2 and the polarizer 6 are aligned. Since the main polarization direction of the gain chip 2 is parallel to the slow axis, the polarization direction of the polarizer must also be marked for easy adjustment.

[0073] In particular, in fields such as laser gyroscopes and frequency doubling crystals, the frequency, phase, and polarization of the laser are required to be used as references or determinants. This necessitates that the laser has narrow linewidth and high polarization extinction ratio. Therefore, it is crucial to align the ASE polarization of the gain chip 2 with the polarizer's polarization direction to form single polarization feedback.

[0074] The ASE polarization of gain chip 2 can only achieve a linearly polarized output with an extinction ratio ≥17dB, while the polarization extinction ratio of polarizer 6 can reach ≥40dB. The ASE polarization degree of gain chip 2 is determined by the chip waveguide fabrication. Even after stimulated emission, it often only achieves a stable extinction ratio of around 23dB. Moreover, the higher the power, the more significant the thermal effect and the greater the polarization jitter. Polarizer 6 utilizes Malus's law and can be applied in passive devices. For example, by inserting polarizer 6 with a polarization angle equal to the crystal polarization rotation angle on both sides of a Faraday crystal, a free-space optical isolator 8 can be fabricated using the non-reciprocity of Faraday crystals. There are almost no reports in existing patent technologies of inserting polarizer 6 into the external cavity feedback section to further improve the final output laser polarization extinction ratio, which is one of the inventive points of this application.

[0075] Furthermore, the narrow linewidth semiconductor laser also includes a ceramic substrate 13; the gain chip 2 is packaged on the ceramic substrate 13.

[0076] In an optional embodiment, the working distance between the first collimating lens 3 and the gain chip 2 is set to 14~16mm.

[0077] Preferably, the working distance between the first collimating lens 3 and the gain chip 2 is set to 15mm. That is, at a working distance of 15mm, the divergence angle of the output light spot is minimized, and the off-axis is within 0.2°.

[0078] In summary, compared with the prior art, the narrow linewidth semiconductor laser provided by this utility model embodiment co-packages the semiconductor laser and the amplifier, two discrete components, to obtain the final output laser, thereby reducing the size by half and achieving integration. Furthermore, with the help of core optical devices such as piezoelectric ceramics, polarizers, output components, and external cavities, a semiconductor laser with wide-range modulated output power, high polarization extinction ratio, ultra-narrow linewidth, and fast scanning wavelength in a small range is achieved.

[0079] In the description of this specification, references to terms such as "specific example" or "some examples" refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example that are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example.

[0080] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this utility model, and not to limit it. Although this utility model has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this utility model.

Claims

1. A narrow linewidth semiconductor laser, characterized in that, include: Photodetector, gain chip, first collimating lens, narrowband filter, reflector, polarizer, piezoelectric ceramic, isolator, first converging lens, output terminal assembly and thermistor; The photodetector, the gain chip, the first collimating lens, the narrowband filter, the reflector, and the isolator are arranged sequentially along the optical path of the emitted light and formed within the external cavity structure; one side of the first converging lens is located outside the isolator; the other side of the first converging lens is provided with the output terminal assembly; The incident light is amplified by the gain chip. After the amplified light passes through the first collimating lens, the narrowband filter and the mirror, the beam is aligned with the polarization direction of the polarizer and converges to the first converging lens, reaching the output component to achieve intracavity oscillation within the external cavity structure and output through the output component. The piezoelectric ceramic is located below the reflector and is used to provide voltage values ​​and high / low level directions to achieve bidirectional position scanning and tune the cavity length of the outer cavity; the thermistor is located inside the outer cavity structure and is used to adjust the internal temperature of the outer cavity structure.

2. The narrow linewidth semiconductor laser according to claim 1, characterized in that, The output component includes an optical amplifier, a second collimating lens, a second converging lens, and a polarization-maintaining fiber ferrule arranged sequentially along the optical path. When the gain chip and the optical amplifier are powered on simultaneously, the first converging lens is inserted between the input terminal of the optical amplifier and the isolator, and the position of the converging lens can be adjusted according to the power output by the output terminal component.

3. The narrow linewidth semiconductor laser according to claim 1, characterized in that, The isolator is a two-stage isolator.

4. The narrow linewidth semiconductor laser according to claim 3, characterized in that, The polarization incident direction of the two-stage isolator is set to coincide with the linear polarization direction of the formed laser cavity.

5. The narrow linewidth semiconductor laser according to claim 1, characterized in that, The narrowband filter includes an etalon and a bandpass filter; The etalon and the bandpass filter are arranged side by side; The etalon is used to form transmission peaks with fixed channel spacing from the ASE beam of the gain chip; the bandpass filter is used to provide a selective channel to the beam for filtering.

6. The narrow linewidth semiconductor laser according to claim 1, characterized in that, The gain chip is aligned with the polarizer in polarization direction.

7. The narrow linewidth semiconductor laser according to claim 6, characterized in that, The polarizer's polarizer is tilted at a certain angle in the horizontal direction, and its power is defined as P1. When the power P1 is at its maximum, the gain chip and the polarizer are aligned in polarization direction.

8. The narrow linewidth semiconductor laser according to claim 1, characterized in that, The narrow linewidth semiconductor laser also includes a ceramic substrate; The gain chip is packaged on the ceramic substrate.

9. The narrow linewidth semiconductor laser according to claim 8, characterized in that, The working distance between the first collimating lens and the gain chip is set to 14~16mm.

10. The narrow linewidth semiconductor laser according to claim 9, characterized in that, The working distance between the first collimating lens and the gain chip is set to 15mm.

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