Narrow-linewidth single-longitudinal-mode seed laser system and generation method

Abstract

The invention discloses a narrow-linewidth single-longitudinal-mode seed laser system and a generation method. The narrow-linewidth single-longitudinal-mode seed laser system comprises a VCSEL laser, a polarization-maintaining beam splitter, a reflector and a half-wave plate. A light beam emitted by a VCSEL laser is firstly divided into a TM mode light beam and a TE mode light beam through a polarization-maintaining beam splitter. A plurality of reflectors are arranged on the propagation path of the TM mode light beam and the TE mode light beam, and the design of the reflectors enables the light beams of the two modes to form an annular loop. And a half-wave plate is arranged on the annular loop so as to regulate and control the polarization state of the light beam. Through the arrangement of the system, narrow-linewidth (about 1MHZ) single-longitudinal-mode seed laser can be generated, and a high-quality light source is provided for the fields of optical communication, spectral analysis and the like; meanwhile, the structure is simple, implementation is easy, and implementation complexity and cost of the narrow-linewidth single-longitudinal-mode seed laser are reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of lasers and relates to a narrow-linewidth single longitudinal mode seed laser system and a generation method thereof. Background Art

[0002] As a high-efficiency light source device, the core function of laser is to convert electrical energy into monochromatic, coherent and high-energy light beams. This feature makes lasers have broad application prospects in many fields such as optical communications, medical treatment, and material processing. With the continuous advancement of science and technology, the performance requirements for lasers are also increasing, especially in terms of line width and longitudinal mode characteristics.

[0003] A narrow linewidth laser means that the light it outputs has a very narrow spectrum width, that is, the frequency of the light wave is very concentrated. This feature is particularly important in many application scenarios. For example, in the field of laser communications, narrow linewidth lasers can achieve higher information transmission rates and longer transmission distances, thereby significantly improving the performance of communication systems. In addition, in scientific research, narrow linewidth lasers are also widely used in fields such as high-precision measurement and frequency stability experiments, providing more accurate tools for scientific research.

[0004] A single longitudinal mode laser refers to a laser that contains only one frequency and spatial mode in its beam. The beam generated by this laser is very spatially concentrated and can form a very fine light spot. This feature is particularly important in fields such as optical sensing and laser medicine. For example, in optical sensing, a single longitudinal mode laser can provide a more stable and accurate sensing signal; in laser medicine, a single longitudinal mode laser can achieve more precise and safe medical operations.

[0005] However, it is not easy to achieve a narrow-linewidth single-longitudinal-mode seed laser. Since the inherent gain linewidth of the laser working material is usually wide, traditional oscillators can hardly directly output narrow-linewidth lasers. In order to overcome this technical difficulty, researchers usually need to adopt a series of complex technical means. Among them, using filters, gratings and other devices to limit or select the number of longitudinal modes in the gain spectrum is a common method. However, these methods often also need to be combined with technical means such as temperature stabilization and optical feedback control to achieve more stable and precise laser output.

[0006] Although these methods can achieve the output of narrow-linewidth single-longitudinal-mode lasers to a certain extent, their complexity and cost are still high. Therefore, how to further simplify the technical means, reduce costs and improve the performance of narrow-linewidth single-longitudinal-mode lasers is still an important issue that needs to be solved in the current field of laser technology. Summary of the invention

[0007] The purpose of the present invention is to solve the technical problems of complexity and high cost in the prior art in achieving the output of narrow-linewidth single-longitudinal-mode lasers, and to provide a narrow-linewidth single-longitudinal-mode seed laser system and a generation method.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions: A first aspect of the present invention provides a narrow linewidth single longitudinal mode seed laser system, comprising a VCSEL laser, a polarization-maintaining beam splitter, a reflector and a half-wave plate; The light beam emitted by the VCSEL laser is divided into a TM mode light beam and a TE mode light beam by a polarization-maintaining beam splitter; a plurality of reflectors are arranged on the propagation paths of the TM mode light beam and the TE mode light beam, so that the TM mode light beam and the TE mode light beam form a ring loop on the optical path; a half-wave plate is arranged on the ring loop.

[0009] Furthermore, the annular loop is a square loop with four vertical corners.

[0010] Furthermore, a beam splitter is provided between the VCSEL laser and the polarization-maintaining beam splitter.

[0011] Furthermore, a collimating lens is arranged between the beam splitter and the VCSEL laser.

[0012] Furthermore, after the light beam emitted by the VCSEL laser is split by a beam splitter, one beam enters a photodetector, and the other beam passes through a polarization-maintaining beam splitter.

[0013] Furthermore, an optical isolator and a collimating lens are arranged between the photoelectric detector and the beam splitter; after the light beam is split by the beam splitter, it passes through the optical isolator and the collimating lens in sequence and then enters the photoelectric detector.

[0014] A second aspect of the present invention provides a method for generating a narrow linewidth single longitudinal mode seed laser, comprising the following steps: S1, splitting the light beam emitted by the VCSEL laser to obtain a first light beam and a second light beam; S2, performing polarization splitting on the second light beam to obtain a TM mode light beam and a TE mode light beam; S3, propagating the TM mode beam and the TE mode beam in opposite directions along the external ring cavity respectively, and during the propagation process, the TM mode beam and the TE mode beam pass through the same half-wave plate respectively; S4, the TM mode beam and the TE mode beam pass through the circular loop and then propagate back along the original path to the VCSEL laser, completing a polarization rotation; S5, after the TM mode light beam and the TE mode light beam are reflected by the VCSEL laser, a secondary polarization rotation is performed; the secondary polarization rotation is performed in the same manner as the primary polarization rotation; S6, the VCSEL laser couples the TM mode beam and TE mode beam after secondary polarization rotation into the resonant cavity to achieve narrow linewidth single longitudinal mode seed laser output.

[0015] Furthermore, the angle of the half-wave plate can be adjusted as needed.

[0016] Furthermore, the VCSEL laser couples the TM mode beam and the TE mode beam after secondary polarization rotation into the resonant cavity to achieve narrow linewidth single longitudinal mode seed laser output, specifically: Under the relaxation oscillation frequency of the TE mode beam and the eigenmode resonance conditions of the external ring cavity, the component ratio and phase of the TE mode beam and the TM mode beam are adjusted by adjusting the angle of the half-wave plate until the beat frequency condition is achieved, forming a narrow linewidth single longitudinal mode seed laser output.

[0017] Furthermore, the relaxation oscillation frequency of the TE mode beam and the eigenmode of the external ring cavity are resonated by adjusting the pump current of the VCSEL laser.

[0018] Compared with the prior art, the present invention has the following beneficial effects: The present invention discloses a narrow linewidth single longitudinal mode seed laser system. By utilizing the characteristics of a polarization-maintaining beam splitter, the present invention successfully separates the light beam emitted by a VCSEL laser into two independent beams of light, a TM mode and a TE mode. This design not only ensures the purity of the two mode beams, but also provides a basis for subsequent regulation; a stable ring loop is formed by setting a number of reflectors on the propagation paths of the TM mode beam and the TE mode beam. This structure helps the light beam to reflect multiple times in the cavity, increases the interaction time between the light beam and the gain medium, and thus improves the stability and output efficiency of the laser; the half-wave plate set on the ring loop can accurately control the phase relationship between the TM mode and the TE mode beam by rotating the half-wave plate, and realizes the output of narrow linewidth (about 1 MHz) and single longitudinal mode laser; the laser system of the present invention has a compact structure, and the connection between the components is simple and clear, and it is easy to integrate with other optical elements or systems. This design not only improves the flexibility of the system, but also provides convenience for subsequent expansion and upgrading; compared with traditional narrow linewidth single longitudinal mode lasers, the components used in the present invention are relatively simple and low in cost, thereby achieving higher cost-effectiveness. The present invention provides a narrow line width single longitudinal mode seed laser generation method, which efficiently separates the light beam emitted by the VCSEL laser into two independent light beams of TM mode and TE mode through beam splitting and polarization beam splitting steps. This polarization separation not only ensures the purity of the two mode beams, but also provides a basis for subsequent polarization control; by propagating the TM mode beam and the TE mode beam in opposite directions along the external ring cavity respectively, the beam is reflected multiple times in the cavity, which increases the interaction time between the beam and the gain medium, thereby improving the stability and output efficiency of the laser. At the same time, the design of the external ring cavity also helps to suppress the noise and fluctuation of the laser; during the propagation of the TM mode beam and the TE mode beam, they pass through the same half-wave plate respectively. By rotating the half-wave plate, the polarization state of the two mode beams can be dynamically adjusted, thereby realizing fine control of the laser output; after completing a polarization rotation, the TM mode beam and the TE mode beam are reflected by the VCSEL laser and undergo a secondary polarization rotation. This multiple polarization rotation design helps to enhance the selectivity of a specific mode (such as a single longitudinal mode), thereby suppressing other unnecessary modes; the components used in this method are relatively simple and easy to integrate, which provides a guarantee for the flexibility and scalability of the system. By adjusting the parameters of the external ring cavity, the rotation angle of the half-wave plate, etc., the laser output can be further regulated and optimized. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0020] Figure 1 This is a structural diagram of a narrow linewidth single longitudinal mode seed laser system according to an embodiment of the present invention; Figure 2 1 is the input-output curve of two linear polarization modes of the laser according to the embodiment of the present invention; Figure 3 is the time domain light output of the TE mode under the beat frequency condition of the embodiment of the present invention; Figure 4 The spectrum measured by the time-domain optical signal of the embodiment of the present invention; Figure 5 This is a block diagram of a method for generating a narrow-linewidth single longitudinal mode seed laser according to an embodiment of the present invention. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. The components of the embodiments of the present invention described and marked in the drawings here can be arranged and designed in various different configurations.

[0022] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0024] In the description of the embodiments of the present invention, it should be noted that if the terms "upper", "lower", "horizontal", "inner", etc. indicate an orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product of the invention is usually placed when in use, it is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first", "second", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0025] In addition, if the term "horizontal" appears, it does not mean that the component must be absolutely horizontal, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", which does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0026] In the description of the embodiments of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it 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 it can be indirectly connected through an intermediate medium, or it can be the internal connection of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0027] The present invention is further described in detail below in conjunction with the accompanying drawings: See also Figure 1The present invention provides a narrow line width single longitudinal mode seed laser system, comprising a VCSEL laser, wherein the light source emitted by the VCSEL laser passes through a collimating lens L and is then split by a beam splitter BS, wherein the beam splitter in this embodiment adopts a 50:50 ratio; wherein one beam passes through an optical isolator ISO and enters a fast photodetector PD, and then a signal is collected by an oscilloscope Scope; the other beam passes through a polarization-maintaining beam splitter prism PBS and enters an external annular cavity, wherein the length of the external annular cavity is 1.35 m, and the polarization-maintaining beam splitter prism PBS splits the beam into a TE mode beam and a TM mode beam; then the TE mode beam and the TM mode beam propagate in clockwise and counterclockwise directions respectively, and pass through a half-wave plate during the propagation process, at which time, the TE mode beam and the TM mode beam are respectively rotated by 90 degrees, namely, the TE mode becomes the TM mode, and the TM mode becomes the TE mode; the TE mode beam and the TM mode beam are reflected back when they first reach the VCSEL laser after passing through the external annular cavity, and then propagate to the VCSEL laser after undergoing a polarization rotation, and the VCSEL laser couples them into a resonant cavity.

[0028] The external annular cavity is realized by arranging several reflectors on the propagation paths of the TM mode beam and the TE mode beam, so that the TM mode beam and the TE mode beam form an annular loop; a half-wave plate is arranged on the annular loop; the annular loop can be a square loop with four vertical corners. A collimating lens L is arranged between the beam splitter BS and the VCSEL laser. An optical isolator ISO and a collimating lens L are arranged between the photodetector PD and the beam splitter BS; after the beam is split by the beam splitter BS, the beam passes through the optical isolator ISO and the collimating lens L in sequence and then enters the photodetector PD.

[0029] like Figure 5 As shown, the present invention provides a method for generating a narrow linewidth single longitudinal mode seed laser, comprising the following steps: S1, splitting the light beam emitted by the VCSEL laser to obtain a first light beam and a second light beam; S2, performing polarization splitting on the second light beam to obtain a TM mode light beam and a TE mode light beam; S3, propagating the TM mode beam and the TE mode beam in opposite directions along the external ring cavity respectively, and during the propagation process, the TM mode beam and the TE mode beam pass through the same half-wave plate respectively; S4, the TM mode beam and the TE mode beam pass through the circular loop and then propagate back along the original path to the VCSEL laser, completing a polarization rotation; S5, after the TM mode light beam and the TE mode light beam are reflected by the VCSEL laser, a secondary polarization rotation is performed; the secondary polarization rotation is performed in the same manner as the primary polarization rotation; S6, the VCSEL laser couples the TM mode beam and TE mode beam after secondary polarization rotation into the resonant cavity to achieve narrow linewidth single longitudinal mode seed laser output.

[0030] An embodiment of the present invention provides a method for generating a narrow linewidth single longitudinal mode seed laser, comprising: S1, the light source is provided by a VCSEL laser, which has a good temperature control and power control system, so the laser output has good stability; the light beam emitted by the VCSEL laser passes through a collimating lens L to obtain a collimated laser.

[0031] S2, the collimated laser is first split by a beam splitter. In this embodiment, a beam splitting prism is used, and the beam ratio of the beam splitting prism is set to 50:50; one path of light passes through an optical isolator and enters a fast photodetector with a bandwidth of 10 GHz, and then the signal is collected by an oscilloscope. Since the optical isolator selects the TE mode, the measured time domain signal represents the time domain dynamic behavior of the TE mode.

[0032] S3, another light path passes through the polarization-maintaining beam splitter prism and enters the external ring cavity. The length of the external ring cavity is 1.35m. After passing through the polarization-maintaining beam splitter prism, the TE and TM polarization modes of the laser are separated to obtain a TE mode beam and a TM mode beam. Then, the two polarization modes propagate in the external ring cavity in the clockwise and counterclockwise directions respectively. The external ring cavity is provided with a half-wave plate.

[0033] S4, the TE mode beam and the TM mode beam realize polarization rotation when passing through the half-wave plate for the first time, and then propagate to the VCSEL laser and be reflected back, and realize the second polarization rotation after passing through the half-wave plate again, and then propagate to the VCSEL laser. The VCSEL laser couples the TE mode beam and the TM mode beam into the resonant cavity of the VCSEL laser.

[0034] S5, by adjusting the pump current of the VCSEL laser, the relaxation oscillation frequency of the TE mode beam and the eigenmode of the external ring cavity are resonated; S6, under the resonant condition, by rotating the half-wave plate, the component ratio and phase of the TE mode beam and the TM mode beam in the optical path are adjusted until the beat frequency condition is achieved, thereby realizing narrow linewidth single longitudinal mode seed laser output.

[0035] The beat frequency signal achieved in this embodiment is at 7.6 GHz, with a line width of only 10 MHz, and can be continuously adjusted within a certain range. This greatly enhances the application range of seed lasers and provides a reliable, efficient and feasible implementation method for the practical application of narrow line width seed lasers. In addition, this method is expected to be extended to lasers in other frequency bands and has a certain degree of universality.

[0036] The invention discloses a method for generating a narrow linewidth single longitudinal mode seed laser. The method utilizes the characteristics of two linear polarization modes (TE and TM modes) of a semiconductor vertical cavity surface emitting laser (VCSEL), especially the advantage of a lower threshold of the TE mode, and realizes effective modulation of the laser gain through an external time-delay feedback mechanism. This design not only improves the efficiency of the laser, but also realizes the selective enhancement of a specific mode (such as the TE mode), thereby suppressing other unnecessary modes. Through the external ring cavity structure, combined with the adjustment of the half-wave plate, the ratio and phase relationship of the TE and TM modes can be accurately controlled. Under resonant conditions, the TE and TM modes produce a beat frequency effect. This interaction causes the laser output to exhibit the characteristics of narrow linewidth and single longitudinal mode, which can significantly improve the resolution and accuracy of the system. By adjusting the laser pump current, the tunability of the relaxation oscillation frequency of the TE mode is realized. This means that users can flexibly adjust the output frequency of the laser according to actual needs, thereby meeting the needs of different application scenarios. The external time-delay feedback and ring cavity design are adopted, which has good stability and reliability. At the same time, the external time-delay feedback can suppress the noise and fluctuation of the laser, while the ring cavity structure helps to maintain the continuity and stability of the laser output. Furthermore, the laser system of the present invention has a compact structure, is easy to integrate, and can be conveniently connected and expanded with other optical elements or systems, which facilitates its application in complex optical systems.

[0037] In order to demonstrate the superiority of the present invention, the performance of the laser is comprehensively evaluated by analyzing in detail the input and output characteristics, time domain dynamic behavior, and frequency domain characteristics of different polarization modes (TE and TM modes).

[0038] The embodiment of the present invention uses an oscilloscope to monitor and collect time domain signals, and sets the data monitoring window to 20 μs. The time domain signals are subjected to Fourier transformation to perform frequency domain characterization.

[0039] See also Figure 2 , Figure 2 It is a characterization of the input-output curve of the two linear polarization modes of the laser. It can be seen from the figure that the threshold of the TE mode is much smaller than that of the TM mode; this shows that under the same input power, the TE mode is easier to reach and maintain laser output, which illustrates that the present invention has higher efficiency and lower energy consumption in the TE mode.

[0040] See also Figure 3 It is the time domain light output of the TE mode under the beat frequency condition. It can be seen that under the beat frequency condition, the time domain light output of the TE mode shows a rapid relaxation oscillation phenomenon. Relaxation oscillation is a dynamic process before the laser runs stably. Its rapidity indicates that the present invention has a faster response speed and better stability.

[0041] See also Figure 4 This is the spectrum measured for the corresponding time domain optical signal. It can be seen from the figure that the main peak position is 7.6 GHz, and there is a small peak with weaker intensity at 15.2 GHz. The inset is an enlarged view of the main peak mode. It can be seen from the figure that the line width of this mode is only 1 MHz. The stability of the main peak position and the narrow line width (1 MHz) indicate that the laser system of the present invention has excellent monochromaticity and coherence in the frequency domain, and has high frequency stability.

[0042] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A narrow linewidth single longitudinal mode seed laser system, characterized in that: Includes VCSEL laser, polarization-maintaining beam splitter, reflector and half-wave plate; The light beam emitted by the VCSEL laser is divided into a TM mode light beam and a TE mode light beam by a polarization-maintaining beam splitter; a plurality of reflectors are arranged on the propagation paths of the TM mode light beam and the TE mode light beam, so that the TM mode light beam and the TE mode light beam form a ring loop on the optical path; a half-wave plate is arranged on the ring loop.

2. The narrow linewidth single longitudinal mode seed laser system according to claim 1, characterized in that: The annular loop is a square loop with four vertical corners.

3. The narrow linewidth single longitudinal mode seed laser system according to claim 1, characterized in that: A beam splitter is arranged between the VCSEL laser and the polarization-maintaining beam splitter.

4. The narrow linewidth single longitudinal mode seed laser system according to claim 3, characterized in that: A collimating lens is arranged between the beam splitter and the VCSEL laser.

5. The narrow linewidth single longitudinal mode seed laser system according to claim 3, characterized in that: After the light beam emitted by the VCSEL laser is split by the beam splitter, one beam enters the photodetector and the other beam passes through the polarization-maintaining beam splitter.

6. The narrow linewidth single longitudinal mode seed laser system according to claim 5, characterized in that: An optical isolator and a collimating lens are arranged between the photoelectric detector and the beam splitter; after the light beam is split by the beam splitter, it passes through the optical isolator and the collimating lens in sequence and then enters the photoelectric detector.

7. A method for generating a narrow linewidth single longitudinal mode seed laser, characterized in that: The following steps are involved: S1, splitting the light beam emitted by the VCSEL laser to obtain a first light beam and a second light beam; S2, performing polarization splitting on the second light beam to obtain a TM mode light beam and a TE mode light beam; S3, propagating the TM mode beam and the TE mode beam in opposite directions along the external ring cavity respectively, and during the propagation process, the TM mode beam and the TE mode beam pass through the same half-wave plate respectively; S4, the TM mode beam and the TE mode beam pass through the circular loop and then propagate back along the original path to the VCSEL laser, completing a polarization rotation; S5, after the TM mode light beam and the TE mode light beam are reflected by the VCSEL laser, a secondary polarization rotation is performed; the secondary polarization rotation is performed in the same manner as the primary polarization rotation; S6, the VCSEL laser couples the TM mode beam and TE mode beam after secondary polarization rotation into the resonant cavity to achieve narrow linewidth single longitudinal mode seed laser output.

8. The method for generating a narrow linewidth single longitudinal mode seed laser according to claim 7, characterized in that: The angle of the half-wave plate can be adjusted as required.

9. The method for generating a narrow linewidth single longitudinal mode seed laser according to claim 7, characterized in that: The VCSEL laser couples the TM mode beam and TE mode beam after secondary polarization rotation into the resonant cavity to achieve narrow linewidth single longitudinal mode seed laser output, specifically: Under the relaxation oscillation frequency of the TE mode beam and the eigenmode resonance conditions of the external ring cavity, the component ratio and phase of the TE mode beam and the TM mode beam are adjusted by adjusting the angle of the half-wave plate until the beat frequency condition is achieved, forming a narrow linewidth single longitudinal mode seed laser output.

10. The method for generating a narrow linewidth single longitudinal mode seed laser according to claim 9, characterized in that: By adjusting the pump current of the VCSEL laser, the relaxation oscillation frequency of the TE mode beam and the eigenmode of the external ring cavity are resonated.

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