Dual-wavelength laser synchronous frequency doubling system

Abstract

The invention discloses a dual-wavelength laser synchronous frequency doubling system, and relates to the technical field of optical fibers and laser. Comprising a high-power dual-wavelength fundamental frequency light source, a diffraction grating, a first half-wave plate, a first lens, a first periodic lithium niobate crystal, a first temperature control system, a first dichroscope, a second half-wave plate, a second lens, a second periodic lithium niobate crystal, a second temperature control system, a third lens, a third periodic lithium niobate crystal, a third temperature control system and a second dichroscope. The invention provides an effective solution aiming at the problems of low efficiency and poor stability in the synchronous generation process of the dual-wavelength frequency doubling laser. The problem of spatial separation of laser beams with different wavelengths in the propagation process is mainly solved, and efficient frequency doubling conversion and high signal-to-noise ratio output of dual-wavelength laser are achieved. The device has the advantages of reasonable structure and stable performance, and is widely applied to the fields of precision optical measurement, medical treatment, industrial processing and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical fiber and laser technology, in particular to a dual-wavelength laser synchronous frequency doubling system. BACKGROUND

[0002] Dual-wavelength laser systems have important application value in the fields of spectral analysis, biomedical imaging, material processing, etc. By frequency doubling technology, infrared laser can be converted into visible light or ultraviolet light, which can expand the application range of laser. However, the research on existing dual-wavelength frequency doubling laser systems is still relatively limited. Traditional schemes usually rely on two independent lasers to generate different wavelengths required, which not only leads to complex system structure and large volume, but also has great challenges in optical path matching, synchronous control and stability, and is difficult to meet the actual demand for compactness and high performance of the system. Therefore, designing and implementing a dual-wavelength laser synchronous frequency doubling system with compact structure, simple adjustment, high output stability and high frequency doubling conversion efficiency has important engineering significance and research value for improving the overall performance of the laser system and promoting its application in many fields. SUMMARY

[0003] In order to solve the above problems, the present application provides a dual-wavelength laser synchronous oscillation system, which realizes efficient synchronous frequency doubling output of dual-wavelength laser by efficient splitting of dual-wavelength fundamental light, independent frequency doubling path design and precise temperature control.

[0004] To achieve the above purpose, the technical scheme adopted by the present application is:

[0005] A dual-wavelength laser synchronous frequency doubling system, comprising a high-power dual-wavelength fundamental light source, a diffraction grating, a first half-wave plate, a first lens, a first periodic lithium niobate crystal, a first temperature control system, a first dichroic mirror, a second half-wave plate, a second lens, a second periodic lithium niobate crystal, a second temperature control system, a third lens, a third periodic lithium niobate crystal, a third temperature control system, and a second dichroic mirror, wherein,

[0006] The double-wavelength fundamental light beams output by the high-power double-wavelength fundamental light source first enter the diffraction grating, and the diffraction grating separates the fundamental light beams of different wavelengths in space to form two independent light beams. One of the fundamental light beams enters the first periodical lithium niobate crystal after being adjusted in polarization state by the first half-wave plate and being focused by the first lens, and quasi-phase matching frequency doubling is realized under the temperature control of the first temperature control system, and the first frequency-doubled wavelength signal is output by the first dichroic mirror. The other fundamental light beam enters the second periodical lithium niobate crystal for the first frequency doubling conversion after being adjusted by the second half-wave plate and the second lens, and then enters the third periodical lithium niobate crystal for cascade frequency doubling conversion after being focused by the third lens, and the second frequency-doubled wavelength signal is output by the second dichroic mirror; wherein the second temperature control system and the third temperature control system control the temperature of the second periodical lithium niobate crystal and the third periodical lithium niobate crystal respectively to realize stable quasi-phase matching condition.

[0007] The present application has the beneficial effects of:

[0008] The present application efficiently separates the double-wavelength fundamental light by the diffraction grating, and solves the path length matching problem of light beams of different wavelengths by independent light path design, ensuring the space-time separation characteristics of the two laser beams in the frequency doubling process. After polarization optimization by the half-wave plate, the light beams of different wavelengths are focused by the lens into the corresponding periodical lithium niobate crystal for efficient frequency doubling conversion, and the temperature control system accurately controls the crystal temperature to maintain the quasi-phase matching condition, and finally realizes the efficient output of the frequency-doubled laser by the dichroic mirror.

[0009] The present system has significant flexibility in the design of the frequency doubling structure: for the first wavelength laser, a single periodical lithium niobate crystal is used for frequency doubling, which is suitable for medium and low power laser output requirements; and for the second wavelength laser, a cascade frequency doubling structure composed of two periodical lithium niobate crystals in series is constructed to meet the frequency doubling requirements of high-power lasers. This design not only optimizes the system performance, but also improves the adaptability of different power levels of laser output and the universality of the overall system. BRIEF DESCRIPTION OF DRAWINGS

[0010] Figure 1 Figure 1 is a schematic diagram of the structure of the double-wavelength laser synchronous frequency doubling system of the present application;

[0011] Figure 2 Figure 3 is a schematic diagram of the relationship between the input beam wavelength and the diffraction angle of the diffraction grating of the present application;

[0012] Figure 3 Figure 5 is a schematic diagram of the relationship between the frequency doubling efficiency and the temperature of the frequency doubling crystal of the present application;

[0013] REFERENCE SIGNS:

[0014] 1. High-power dual-wavelength fundamental frequency light source; 2. Diffraction grating; 3. First half-wave plate; 4. First lens; 5. First periodic lithium niobate crystal; 6. First temperature control system; 7. First dichroic mirror; 8. Second half-wave plate; 9. Second lens; 10. Second periodic lithium niobate crystal; 11. Second temperature control system; 12. Third lens; 13. Third periodic lithium niobate crystal; 14. Third temperature control system; 15. Second dichroic mirror. Detailed Implementation

[0015] To make the objectives and technical solutions of this application clearer, the present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention, but should not be used to limit the scope of protection of the present invention.

[0016] In the description of this invention, the use of terms such as "first," "second," and "third" is merely for distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of technical features or the order of the technical features.

[0017] like Figure 1 As shown, the present invention provides a dual-wavelength laser synchronous frequency doubling system, which includes the following components: a high-power dual-wavelength fundamental frequency light source 1, a diffraction grating 2, a first half-wave plate 3, a first lens 4, a first periodic lithium niobate crystal 5, a first temperature control system 6, a first dichroic mirror 7, a second half-wave plate 8, a second lens 9, a second periodic lithium niobate crystal 10, a second temperature control system 11, a third lens 12, a third periodic lithium niobate crystal 13, a third temperature control system 14, and a second dichroic mirror 15.

[0018] The connections between the various components are as follows:

[0019] The dual-wavelength laser output from the high-power dual-wavelength fundamental frequency light source 1 is first incident on the diffraction grating 2. The diffraction grating 2 spatially separates the fundamental frequency beams of different wavelengths, forming two independent beams. One fundamental frequency beam passes sequentially through the first half-wave plate 3 to adjust its polarization state, and is focused by the first lens 4 before entering the first periodic lithium niobate crystal 5. Under the temperature control of the first temperature control system 6, quasi-phase-matched frequency doubling is achieved, and the first frequency-doubled wavelength signal is output by the first dichroic mirror 7. The other fundamental frequency beam passes sequentially through the second half-wave plate 8 and the second lens 9, and enters the second periodic lithium niobate crystal 10 for the first frequency doubling conversion. Then, after being focused by the third lens 12, it enters the third periodic lithium niobate crystal 13 for cascaded frequency doubling conversion, and the second frequency-doubled wavelength signal is output by the second dichroic mirror 15. The second temperature control system 11 and the third temperature control system 14 respectively control the temperature of the second periodic lithium niobate crystal 10 and the third periodic lithium niobate crystal 13 to achieve stable quasi-phase-matched conditions.

[0020] In an embodiment, the high-power dual-wavelength fundamental light source 1, the diffraction grating 2, the first half-wave plate 3, the first lens 4, the first periodical lithium niobate crystal 5, the first dichroic mirror 7, the second half-wave plate 8, the second lens 9, the second periodical lithium niobate crystal 10, the third lens 12, the third periodical lithium niobate crystal 13, and the second dichroic mirror 15 together constitute the optical path structure of the dual-wavelength laser oscillator.

[0021] The high-power dual-wavelength fundamental light source 1 can be an erbium-doped fiber laser or a solid-state laser, with an output wavelength range of 1500-1600 nm, typically set to two wavelengths of 1540 nm and 1590 nm, and good wavelength stability and optical power stability.

[0022] The diffraction grating 2 is a transmission grating with a diffraction efficiency of not less than 90% and a tolerance power of up to 20 W.

[0023] The first half-wave plate 3 and the second half-wave plate 8 are high-precision rotating wave plates with adjustable angles, used to optimize the polarization state of the laser of different wavelengths to match the polarization direction of the nonlinear crystal, with an adjustment accuracy of better than 0.1°, which is beneficial to achieving efficient phase matching.

[0024] The first lens 4 is used to adjust the spot size and spot position of one of the two fundamental light beams incident on the first periodical lithium niobate crystal 5, to improve the spatial position matching efficiency of the first wavelength corresponding to the one of the two fundamental light beams, the second lens 9 is used to adjust the spot size and spot position of the other of the two fundamental light beams incident on the second periodical lithium niobate crystal 10, and the third lens 12 is used to adjust the spot size and spot position of the fundamental light incident on the third periodical lithium niobate crystal 13. The efficiency of frequency doubling is improved by selecting the focal length of the first half-wave plate 3 and the second half-wave plate 8 and adjusting their positions.

[0025] The first periodical lithium niobate crystal 5, the second periodical lithium niobate crystal 10, and the third periodical lithium niobate crystal 13 are quasi-phase-matched nonlinear frequency-doubling crystals used to convert the fundamental frequency laser into a frequency-doubled laser.

[0026] The first dichroic mirror 7 and the second dichroic mirror 15 are used to extract the first and second frequency-doubled laser outputs, respectively, with a reflectivity of not less than 96% in the fundamental frequency wavelength range (1500-1600 nm) and a transmittance of not less than 98% in the frequency-doubled wavelength range (750-800 nm), to achieve efficient frequency conversion and beam separation.

[0027] The first wavelength frequency multiplication light path is composed of the first half-wave plate 3, the first lens 4, the first periodical lithium niobate crystal 5 and the first dichroic mirror 7, and is suitable for frequency multiplication output of low-power 1540nm signals; the second wavelength frequency multiplication light path is composed of the second half-wave plate 8, the second lens 9, the second periodical lithium niobate crystal 10, the third lens 12, the third periodical lithium niobate crystal 13 and the second dichroic mirror 15, and is suitable for cascade frequency multiplication output of high-power 1590nm signals.

[0028] The first temperature control system 6, the second temperature control system 11 and the third temperature control system 14 include thermoelectric refrigeration components and corresponding temperature control control circuits, and are used for accurately controlling the temperatures of the first periodical lithium niobate crystal 5, the second periodical lithium niobate crystal 10 and the third periodical lithium niobate crystal 13 respectively, the temperature control accuracy is preferably up to ±0.01℃, and the temperature adjustment range is 20℃ to 230℃, so as to ensure high phase matching conditions of the laser frequency multiplication process.

[0029] Through the design of the light path structure, the application realizes the synchronous frequency multiplication output of the dual-wavelength laser, the interval between the frequency multiplication wavelengths reaches 50nm, the application demand of multi-band laser is met, and a new solution is provided for the high-performance laser light source system.

[0030] In summary, the core target of the application is to realize high-efficiency dual-wavelength frequency multiplication laser output by diffracting, independently frequency multiplying and converting and wavelength-selective output of high-power dual-wavelength base frequency laser. First, the system realizes spatial separation of dual-wavelength base frequency light by using the wavelength-angle dependent characteristics of the diffraction grating.

[0031] ,

[0032] Among them, is the grating period, is the incident angle, is the diffraction angle, is the diffraction order (usually ). Assuming that the light beam is vertically incident, the incident angle is 90°, and the relationship between the simulation light beam wavelength and the diffraction angle is as shown in Figure 2 . Since the diffraction angle changes with the wavelength, the incident dual-wavelength laser is separated into independent transmission light paths after passing through the transmission grating. The grating has a splitting efficiency of ≥90% and a high-power tolerance of 20W, ensuring the efficiency and stability of the splitting process.

[0033] In the frequency multiplication conversion part, the two light paths are adjusted by the half-wave plates to align the polarization state with the quasi-phase matching direction of the periodical lithium niobate crystal, and then focused by the lens to improve the power density. Since the frequency multiplication efficiency and the crystal temperature have a close relationship in the frequency multiplication process, reference Figure 3Here, a high-precision temperature control system (±0.01℃) is adopted, the temperature is tuned periodically to the polarization period, the phase matching condition of different wavelengths is met, and thus the optimal conversion efficiency is realized. In order to further improve the frequency doubling efficiency of the first wavelength, a cascade frequency doubling optical path structure is also adopted, and the frequency doubling optical power of the first wavelength is further improved.

[0034] Therefore, the innovation of the present application lies in the design idea of spatial light splitting and independent optimization, physical isolation is realized through a diffraction grating, and the two frequency doubling lights do not interfere with each other; in combination with a temperature control tuned frequency doubling crystal and an optimized dichroic mirror, the system stability is improved while the conversion efficiency is ensured. In addition, the cascade frequency doubling architecture provides flexibility for wavelength expansion.

[0035] The contents not described in detail in the present application belong to the prior art known to those skilled in the art.

[0036] The above embodiments are provided only for the purpose of describing the present application, and are not intended to limit the scope of the present application. The scope of the present application is defined by the appended claims. Various equivalent replacements and modifications made without departing from the spirit and principles of the present application should be covered within the scope of the present application.

Claims

1. A dual-wavelength laser synchronous frequency doubling system, characterized in that, The high-power dual-wavelength fundamental light source (1), the diffraction grating (2), the first half-wave plate (3), the first lens (4), the first periodical lithium niobate crystal (5), the first dichroic mirror (7), the second half-wave plate (8), the second lens (9), the second periodical lithium niobate crystal (10), the third lens (12), the third periodical lithium niobate crystal (13), and the second dichroic mirror (15) are connected in sequence according to the order of light propagation. The specific connection relationship is as follows: The high-power dual-wavelength fundamental light source (1) outputs a dual-wavelength fundamental light beam, which is incident on the diffraction grating (2). The diffraction grating (2) spatially separates the dual-wavelength fundamental light beam into two independent light beams. One of the two independent light beams is incident on the first periodical lithium niobate crystal (5) after being focused by the first lens (4) and being adjusted in polarization state by the first half-wave plate (3), and the first frequency-doubled wavelength signal is output by the first dichroic mirror (7). The other of the two independent light beams is incident on the second periodical lithium niobate crystal (10) after being focused by the second lens (9) and being adjusted by the second half-wave plate (8), and the second frequency-doubled wavelength signal is output by the second dichroic mirror (15) after the third periodical lithium niobate crystal (13) is cascaded for frequency-doubled conversion.

2. The dual-wavelength laser synchronous frequency doubling system according to claim 1, characterized in that, The first temperature control system (6), the second temperature control system (11), and the third temperature control system (14) are further included, wherein the first temperature control system (6), the second temperature control system (11), and the third temperature control system (14) are respectively used for temperature control of the first periodical lithium niobate crystal (5), the second periodical lithium niobate crystal (10), and the third periodical lithium niobate crystal (13) to achieve stable quasi-phase matching conditions.

3. The dual-wavelength laser synchronous frequency doubling system according to claim 1, wherein, The high-power dual-wavelength fundamental light source (1) is a fiber laser or a solid-state laser, and outputs a dual-wavelength range of 1500-1600 nm.

4. The dual-wavelength laser synchronous frequency doubling system according to claim 1, characterized in that, The diffraction grating (2) is a transmission grating, and the diffraction efficiency thereof is not less than 90%, and the tolerance power reaches 20 W.

5. The dual-wavelength laser synchronous frequency doubling system according to claim 1, wherein, The rotation angles of the first half-wave plate (3) and the second half-wave plate (8) are adjustable, and the adjustment accuracy is better than 0.1 degree.

6. The dual-wavelength laser synchronous frequency doubling system according to claim 1, wherein, The first periodical lithium niobate crystal (5), the second periodical lithium niobate crystal (10), and the third periodical lithium niobate crystal (13) are quasi-phase matching nonlinear frequency-doubled crystals, which are used for converting the fundamental frequency laser into a frequency-doubled laser.

7. The dual-wavelength laser synchronous frequency doubling system according to claim 1, wherein, The temperature control accuracy of the first temperature control system (6), the second temperature control system (11), and the third temperature control system (14) is ±0.01℃, and the temperature adjustment range is 20℃ to 230℃.

8. The dual-wavelength laser synchronous frequency doubling system according to claim 1, wherein, The reflectivity of the first dichroic mirror (7) and the second dichroic mirror (15) in the wavelength range of 1500 nm to 1600 nm is not less than 96%, and the transmittance in the wavelength range of 750 nm to 800 nm is not less than 98%.

9. The dual-wavelength laser synchronous frequency doubling system according to claim 1, wherein, The first lens (4), the second lens (9), and the third lens (12) are respectively used for adjusting the spot size and the spot position of the fundamental frequency light incident on the first periodical lithium niobate crystal (5), the second periodical lithium niobate crystal (10), and the third periodical lithium niobate crystal (13).

10. The dual-wavelength laser synchronous frequency doubling system of claim 1, wherein, The system synchronizes the wavelength interval of the double-wavelength laser with the frequency multiplication output to reach 50 nm.

Images