A High-Efficiency Nonlinear Optical Frequency Converter Based on High-Power Continuous Optical Transmission in Quartz Micro-Nano Fibers

Abstract

This invention discloses a high-efficiency nonlinear optical frequency converter based on high-power continuous optical transmission using quartz micro / nano fiber, comprising a wavelength-tunable laser, an optical fiber amplifier, a quartz micro / nano fiber, a sealed cavity, and an optical fiber low-pass filter; the quartz micro / nano fiber includes a first untapered portion, a second untapered portion, a first tapered transition region, a second tapered transition region, and a waist region, transmitting an optical field TE. 01 The mode cutoff method precisely controls the waist diameter of micro / nano fiber and accurately tunes the input light wavelength. The nonlinear light frequency conversion process excited by high-power continuous light transmitted in quartz micro / nano fiber satisfies perfect phase matching. The fundamental mode of the input light and the higher-order mode fields of the harmonic signal light have high overlap in the waveguide mode, which can efficiently generate continuous second and third harmonic signal light. The device has high stability, high efficiency, and low cost, and can be applied in fiber lasers, all-optical signal processing, fiber optic sensing and other fields.

Description

Technical Field

[0001] This invention belongs to the field of nonlinear optics, specifically, it is a high-efficiency nonlinear optical frequency converter based on high-power continuous optical transmission of quartz micro-nano optical fibers. Background Technology

[0002] Quartz micro / nano fiber is a miniaturized optical waveguide device with advantages such as a large evanescent field, strong optical confinement capability, flexible and controllable dispersion, and perfect compatibility with standard optical fibers. In recent years, it has been widely researched and applied in nonlinear optics, fiber optic sensing, atomic optics, fiber lasers, and optomechanics. Compared with other typical micro / nano optical waveguides, quartz micro / nano fiber has extremely low optical absorption, minimal surface roughness, and the lowest optical transmission loss. Therefore, quartz micro / nano fiber is a highly promising micro / nano optical waveguide for transmitting high-power continuous light. Because micro / nano fiber also possesses strong optical field confinement capability during light transmission, it greatly increases the power density of the transmission mode field, which can be used to enhance the intensity of nonlinear optical interactions. A micro / nano fiber nonlinear optical frequency converter is an optical device that utilizes nonlinear optical effects to generate new laser wavelengths. As an all-fiber structure device, it has advantages over commonly used nonlinear crystal frequency converters, such as high device stability, low cost, ease of use, and ease of integration. Currently, micro / nano fiber nonlinear optical frequency converters typically use high-peak-power pulsed light as input light to excite the nonlinear effects of the micro / nano fiber to generate pulsed harmonic signal light.

[0003] However, continuous light has a wider range of applications in scientific research and practical use. Micro / nano fiber continuous-mode frequency converters are often limited by factors such as low input power, phase mismatch, or low overlap between the fundamental mode and higher-order mode fields of the input light in the guided wave mode, making it difficult to achieve efficient harmonic signal output. Therefore, it is necessary to further increase the transmission power of continuous light in quartz micro / nano fibers and achieve perfect phase matching and maintain high mode overlap during nonlinear optical frequency conversion, thereby improving the conversion efficiency of micro / nano fiber nonlinear optical frequency converters and obtaining higher-power continuous harmonic signal output. Summary of the Invention

[0004] The purpose of this invention is to provide a high-efficiency nonlinear optical frequency converter based on high-power continuous optical transmission of quartz micro-nano optical fiber, which overcomes the low efficiency of existing quartz fiber micro-nano optical fiber nonlinear optical frequency converters and improves the optical power of continuous harmonic signals.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] This invention discloses a high-efficiency nonlinear optical frequency converter based on high-power continuous optical transmission of quartz micro-nano fiber, comprising a wavelength-tunable laser, an optical fiber amplifier, a quartz micro-nano fiber, and an optical fiber low-pass filter connected sequentially by optical fibers. The quartz micro-nano fiber portion is located within a sealed cavity. The quartz micro-nano fiber is a whole formed by sequentially connecting a first untapered portion, a first tapered transition region, a waist region, a second tapered transition region, and a second untapered portion. The front and rear ends of the quartz micro-nano fiber are located outside the sealed cavity, while the rest are stored within the sealed cavity.

[0007] As a further improvement, the output end of the wavelength-tunable laser of the present invention is connected to the input end of the fiber amplifier, the output end of the fiber amplifier is connected to one end of the first untapered portion of the quartz micro-nano fiber, the other end of the first untapered portion is connected to one end of the first tapered transition region, the other end of the first tapered transition region is connected to one end of the waist region, the other end of the waist region is connected to one end of the second tapered transition region, the other end of the second tapered transition region is connected to one end of the second untapered portion, and the other end of the second untapered portion is connected to the input end of the fiber low-pass filter.

[0008] As a further improvement, the output light of the wavelength-tunable laser described in this invention is used as a seed light source. After being amplified by an optical fiber amplifier, it generates high-power continuous light. This light then passes sequentially through the first untapered section, the first tapered transition region, the waist region, the second tapered transition region, and the second untapered section of a quartz micro-nano optical fiber, generating second and third harmonic signal light. After being input into an optical fiber low-pass filter, the high-power continuous light is filtered out, thereby realizing the output of second and third harmonic signal light.

[0009] As a further improvement, the first untapered portion and the second untapered portion of the quartz micro-nano optical fiber of the present invention are respectively fixed on both sides of the sealed chamber. Both the first untapered portion and the second untapered portion are partially located in the sealed chamber, which is filled with high-purity gas for sealed preservation.

[0010] As a further improvement, one end of the first untapered portion of the quartz micro-nano optical fiber described in this invention is connected to the output end of the optical fiber amplifier by optical fiber fusion splicing, and one end of the second untapered portion is connected to the input end of the optical fiber low-pass filter by optical fiber fusion splicing, with an insertion loss of less than 0.05dB.

[0011] As a further improvement, the quartz micro / nano fiber described in this invention is prepared by mechanically stretching a standard single-mode quartz fiber. The first tapered transition region and the second tapered transition region have an adiabatic tapered structure, realizing near-lossless optical coupling of the transmitted optical field from the standard fiber to the micro / nano fiber.

[0012] As a further improvement, the waist region of the quartz micro / nano fiber described in this invention transmits the optical field TE.01 The mode cutoff method enables precise diameter control, ensuring perfect phase matching in the nonlinear optical frequency conversion process. In the waveguide mode, the fundamental mode of the input light and the higher-order modes of the harmonic signal light have high mode field overlap.

[0013] As a further improvement, the fiber optic low-pass filter of the present invention is made by winding a standard single-mode fiber along the outer ring of a metal rod, which is in a filtering state for high-power continuous light and in a conducting state for second and third harmonic signal light.

[0014] This invention discloses a high-efficiency nonlinear optical frequency converter based on high-power continuous optical transmission using quartz micro / nano fiber, comprising a wavelength-tunable laser, an optical fiber amplifier, a quartz micro / nano fiber, a sealed cavity, and an optical fiber low-pass filter; the quartz micro / nano fiber includes a first untapered portion, a second untapered portion, a first tapered transition region, a second tapered transition region, and a waist region. The quartz micro / nano fiber of this invention can transmit continuous light in the communication band exceeding 10W with an insertion loss of less than 0.23dB. Through the transmission of the optical field TE... 01 The mode cutoff method precisely controls the waist diameter of the micro / nano fiber and accurately tunes the input light wavelength. The nonlinear optical frequency conversion process excited by high-power continuous light transmitted through quartz micro / nano fibers satisfies perfect phase matching. In the waveguide mode, the fundamental mode of the input light and the higher-order mode fields of the harmonic signal light have high overlap, enabling efficient generation of continuous second and third harmonic signal light. The nonlinear optical frequency converter of this invention adopts an all-fiber structure, is perfectly compatible with standard fiber optic systems, and features high device stability, high efficiency, and low cost. It can be applied in fields such as fiber lasers, all-optical signal processing, and fiber optic sensing.

[0015] Compared with the prior art, the beneficial effects of the present invention are:

[0016] (1) Existing quartz micro-nano optical fibers are limited by structural precision, packaging, and the cleanliness of the testing environment. During the transmission of high-power laser light fields, issues such as excessive concentration of local surface field strength and thermal effects caused by optical absorption due to adsorption on the fiber surface can occur, leading to optical damage to the micro-nano optical fibers. The quartz micro-nano optical fiber of the present invention has an adiabatic tapered transition region, perfect structural symmetry, and a uniform waist diameter. When stored in a well-sealed chamber with good airtightness and filled with high-purity gas for protection, it can avoid the thermal effects caused by optical absorption due to adsorption of contaminants on the surface of the micro-nano optical fiber, making it suitable for high-power continuous optical transmission.

[0017] (2) The highest optical power of continuous optical transmission in the prior art of quartz micro-nano fiber is 0.4W. The quartz micro-nano fiber of the present invention can transmit more than 10W of continuous light in the communication band with a loss of less than 0.23dB.

[0018] (3) Existing quartz micro / nano fiber optic frequency converters suffer from poor diameter uniformity due to the difficulty in precisely controlling the waist region diameter. This makes it difficult to achieve phase matching during nonlinear optical frequency conversion, and the overlap between the fundamental mode and higher-order mode fields of the input light and the harmonic signal light in the guided wave mode is low. Therefore, the device efficiency is relatively low, and high-peak-power pulsed light is typically used as the input light to generate pulsed harmonic signal light. This invention utilizes TE... 01 The mode cutoff method precisely controls the waist diameter of micro / nano fiber, enabling perfect phase matching and high mode overlap nonlinear optical frequency conversion, generating continuous harmonic signal light, and resulting in high device efficiency.

[0019] (4) The optical frequency converter of the present invention adopts an all-fiber structure, which is perfectly compatible with standard optical fiber systems and can efficiently generate continuous nonlinear harmonic signal light, including second harmonic and third harmonic signal light. It has great application value in the fields of fiber lasers, all-optical signal processing, and fiber optic sensing. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the structure of the high-efficiency nonlinear optical frequency converter based on high-power continuous optical transmission of quartz micro-nano optical fiber according to the present invention.

[0021] In the figure, 1-wavelength tunable laser, 2-fiber amplifier, 3-1-first untapered section, 3-2-second untapered section, 4-1-first tapered transition region, 4-2-second tapered transition region, 5-waist region, 6-sealed cavity, 7-fiber low-pass filter;

[0022] Figure 2 This is a graph showing the optical transmittance of 1552nm continuous light transmitted through quartz micro-nano optical fibers, with the transmitted optical power ranging from 0W to 13W.

[0023] Figure 3 The input optical fundamental mode HE of a quartz micro / nano fiber with a waist diameter of 779 nm during the third harmonic generation process. 11 (ω1) and the higher-order mode HE of the third harmonic signal light 12 The cross-sectional field strength distribution diagram of (3ω1), with an angular frequency ω1 = 190.8 THz;

[0024] Figure 4 This is a normalized optical transmittance curve at a wavelength of 1055nm during the fiber taper process.

[0025] Figure 5 This is a diagram showing the waist diameter distribution of micro / nano optical fibers drawn using the higher-order mode cutoff method.

[0026] Figure 6 The input optical fundamental mode HE in a quartz micro / nano fiber with a waist diameter of 779 nm 11 (ω1), HE11 (ω2) Higher-order mode of harmonic signal light HE 12 (3ω1), HE 21 The effective refractive index curve of (2ω2) is shown, with angular frequencies ω1 = 190.8 THz and ω2 = 192.5 THz.

[0027] Figure 7 This invention relates to the nonlinear optical frequency converter and its third harmonic signal spectrum and output light spot diagram when the input optical power is 5W.

[0028] Figure 8 This invention relates to the nonlinear optical frequency converter, showing the second harmonic signal spectrum and output light spot diagram when the input optical power is 5W.

[0029] Figure 9 This is a graph showing the change in harmonic signal power generated by the nonlinear optical frequency converter of the present invention as a function of input optical power. Detailed Implementation

[0030] To make the technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the described examples are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0031] This invention discloses a high-efficiency nonlinear optical frequency converter based on high-power continuous optical transmission using quartz micro / nano optical fibers, such as... Figure 1 As shown, the specific implementation includes a wavelength-tunable laser 1, an optical fiber amplifier 2, a quartz micro-nano fiber, and an optical fiber low-pass filter 7 connected sequentially by optical fibers; the quartz micro-nano fiber is located inside the sealed cavity 6; the quartz micro-nano fiber is a whole formed by sequentially connecting the first untapered portion 3-1, the first tapered transition region 4-1, the waist region 5, the second tapered transition region 4-2, and the second untapered portion 3-2, with the front and rear ends of the quartz micro-nano fiber located outside the sealed cavity 6, and the rest stored inside the sealed cavity 6. The output end of the wavelength-tunable laser 1 is connected to the input end of the fiber amplifier 2. The output end of the fiber amplifier 2 is connected to one end of the first untapered portion 3-1 of the quartz micro-nano fiber. The other end of the first untapered portion 3-1 is connected to one end of the first tapered transition region 4-1. The other end of the first tapered transition region 4-1 is connected to one end of the waist region 5. The other end of the waist region 5 is connected to one end of the second tapered transition region 4-2. The other end of the second tapered transition region 4-2 is connected to one end of the second untapered portion 3-2. The other end of the second untapered portion 3-2 is connected to the input end of the fiber low-pass filter 7.

[0032] The output light of the wavelength-tunable laser 1 serves as a seed light source. After being amplified by the fiber amplifier 2, it generates high-power continuous light. This light then passes sequentially through the first untapered section 3-1, the first tapered transition region 4-1, the waist region 5, the second tapered transition region 4-2, and the second untapered section 3-2 of the quartz micro-nano fiber, generating second and third harmonic signal light. This high-power continuous light is then filtered out by the fiber low-pass filter 7, thereby achieving the output of second and third harmonic signal light.

[0033] The first untapered portion 3-1 and the second untapered portion 3-2 of the quartz micro-nano optical fiber are fixed on both sides of the sealed chamber 6, respectively. Both the first untapered portion 3-1 and the second untapered portion 3-2 are partially located inside the sealed chamber 6, while the front end of the first untapered portion 3-1 and the rear end of the second untapered portion 3-2 are located outside the sealed chamber 6. The sealed chamber 6 is filled with high-purity gas for sealed preservation.

[0034] One end of the first untapered section 3-1 of the quartz micro-nano fiber is connected to the output end of the fiber amplifier 2 by fiber fusion splicing, and one end of the second untapered section 3-2 is connected to the input end of the fiber low-pass filter 7 by fiber fusion splicing, with an insertion loss of less than 0.05dB.

[0035] Quartz micro-nano optical fibers are prepared by mechanically stretching standard single-mode quartz optical fibers. The first tapered transition region 4-1 and the second tapered transition region 4-2 have an adiabatic tapered structure, which can realize near-lossless optical coupling of the transmitted optical field from standard optical fiber to micro-nano optical fiber.

[0036] Quartz micro-nano fiber waist region 5 transmits optical field TE 01 The mode cutoff method enables precise diameter control, ensuring perfect phase matching in the nonlinear optical frequency conversion process. In the waveguide mode, the fundamental mode of the input light and the higher-order modes of the harmonic signal light have high mode field overlap.

[0037] The fiber optic low-pass filter 7 is made by winding a standard single-mode fiber along the outer ring of a metal rod. It is in a filtering state for high-power continuous light and in a conducting state for second and third harmonic signal light.

[0038] The following example illustrates this. In this example, wavelength-tunable laser 1 is used to output single-frequency continuous light with a wavelength range of 1480nm-1640nm and an output power of 10mW. Fiber amplifier 2 is an erbium-doped fiber amplifier with a maximum gain of 41.5dB, meaning a maximum output optical power of 14W. The quartz micro / nano fiber is stored in a sealed chamber 6 filled with high-purity nitrogen. The optical transmission characteristics of the quartz micro / nano fiber during high-power continuous light transmission are as follows: Figure 2As shown, during the process of increasing the input optical power from 0W to 13W and decreasing it back to 0W, the output optical power of the quartz micro-nano fiber changes linearly with the input power, and the optical transmittance remains above 95%, i.e., the insertion loss is less than 0.23dB. This indicates that the quartz micro-nano fiber can transmit high-power continuous light above 10W. At an input optical power of 13W, the maximum power density of the transmitted optical field in the quartz micro-nano fiber reaches as high as 23W / μm. 2 They exhibit strong nonlinear interactions.

[0039] To achieve efficient nonlinear optical frequency conversion, it is first necessary to maximize the mode field overlap between the fundamental mode of the input light and the higher-order modes of the harmonic signal light. Generally, the mode field overlap integral is used to quantitatively characterize this overlap. Taking third-harmonic generation as an example, the formula for calculating the mode field overlap integral between the fundamental mode of the input light and the higher-order modes of the third-harmonic signal light is as follows:

[0040]

[0041] In formula (1), F1 and F3 represent the transverse electric fields of the fundamental mode of the input light and the higher-order modes of the third harmonic signal light, respectively, and S is the cross-section of the micro / nano fiber. By calculating the transverse electric fields of the fundamental mode of the input light and the higher-order modes of the third harmonic signal light, the mode field overlap integral can be calculated using formula (1). Figure 3 As shown, for third harmonic generation, the fundamental mode HE of the input light in a 779nm diameter micro / nano fiber at the communication band is... 11 (ω1) and the higher-order mode HE of the third harmonic signal light 12 The mode field overlap integral of (3ω1) is the largest, at 0.31 μm. -2 To obtain micro / nano optical fibers with a diameter of 779 nm, this example involves monitoring the TE wavelength at a specific wavelength. 01 The cutoff pattern is used to achieve precise control of the waist region 5 diameter, for the target waist region 5 cutoff diameter D. co The corresponding TE 01 Mode cutoff wavelength λ co for:

[0042]

[0043] In formula (2), V is the normalized frequency (V = 2.405), n2 is the refractive index of air (n2 = 1), and n1 is the refractive index of quartz, which can be expressed as:

[0044]

[0045] In formula (3), the unit of λ is μm. A target diameter is set as TE according to formula (1). 01 By determining the cutoff diameter of the mode and calculating the corresponding cutoff wavelength, the TE at that cutoff wavelength can be monitored in real time.01 The mode cutoff signal is used to achieve precise control of the waist region 5 diameter. In this example, the target diameter of the waist region 5 of the micro-nano fiber is 779 nm, and the cutoff wavelength is calculated to be 1055 nm according to formula (2). Figure 4 As shown, there are five sudden drops in transmittance intensity in the optical transmission spectrum at a wavelength of 1055 nm, representing EH respectively. 21 ,EH 11 HE 12 HE 21 and TE 01 Mode cutoff. When the fiber diameter decreases to 779 nm, TE begins to appear. 01 Upon mode termination, the fiber pulling process immediately ceases. For example... Figure 5 As shown, the deviation between the diameter of the waist region 5 of the micro / nano fiber prepared based on this high-order mode cutoff method and the target diameter is as low as ±2nm, which also indicates that the diameter uniformity of the waist region 5 is very high.

[0046] For quartz micro / nano fiber optics, to achieve perfect phase matching in the nonlinear optical frequency conversion process, the refractive indices of the fundamental mode of the input light and the higher-order modes of the harmonic signal light need to be precisely matched, i.e., intermodal phase matching. The mode refractive index curves of the input light and harmonic signal light in a quartz micro / nano fiber nonlinear optical frequency converter are shown in the figure below. Figure 6 As shown, for a micro / nano fiber with a diameter of 779 nm in the waist region 5, the phase-matching modes generated by the third harmonic are respectively the HE modes of the input light. 11 (ω1) mode and third harmonic signal light HE 12 The (3ω1) mode, ω1 = 190.8 THz is the angular frequency of the perfectly phase-matched light wave, and the corresponding wavelength λ1 = 1572.5 nm; the phase-matching modes generated by the second harmonic are respectively the HE of the input light. 11 (ω2) mode and second harmonic signal light HE 21 The (2ω²) mode, where ω² = 192.5 THz is the angular frequency of the perfectly phase-matched light wave, corresponds to a wavelength λ² = 1558.2 nm. Perfect phase matching in the nonlinear optical frequency conversion process can be achieved by precisely adjusting the input light wavelength using a wavelength-tunable laser.

[0047] like Figure 7 and Figure 8 As shown, compared to other wavelengths, the third harmonic signal is strongest at the perfectly phase-matched wavelength λ1 = 1572.5 nm, with a wavelength of 524.5 nm; the second harmonic signal is strongest at the perfectly phase-matched wavelength λ2 = 1558.2 nm, with a wavelength of 779.1 nm. At the output of the fiber optic low-pass filter, the output optical field modes of the third and second harmonic signals correspond to the linear offset mode LP in the phase-matched mode, respectively.02 and LP 11 .

[0048] Based on achieving perfect phase matching and maintaining high mode field overlap in the phase-matched mode, the nonlinear optical frequency converter in this example, using high-power continuous optical transmission in quartz micro / nano fiber, achieves efficient continuous optical output of third and second harmonic signals. Figure 9 As shown, when the input optical power is 11W, the third harmonic signal optical power reaches as high as 55μW, and the conversion efficiency reaches as high as 4.9×10⁻⁶. -6 The second harmonic signal optical power reaches 0.92μW, and the conversion efficiency reaches 8.2×10⁻⁶. -8 Through fitting, the output third harmonic signal power of the nonlinear optical frequency converter exhibits a cubic exponential growth relationship with the input optical power, while the output second harmonic signal power exhibits a quadratic exponential growth relationship with the input optical power. Since the optical damage threshold of the quartz micro / nano fiber in this example is higher than 11W, increasing the input optical power of the nonlinear optical frequency converter can further improve the nonlinear optical frequency conversion efficiency of the device, thereby obtaining higher power harmonic signal light.

[0049] It will be understood by those skilled in the art that the above are merely individual examples of the invention and are not intended to limit the invention. Although the invention has been described in detail with reference to the foregoing examples, those skilled in the art can still modify the technical solutions described in the foregoing examples or make equivalent substitutions for some of the technical features. All modifications and equivalent substitutions made within the spirit and principles of the invention should be included within the scope of protection of the invention.

Claims

1. A high-efficiency nonlinear optical frequency converter based on high-power continuous optical transmission using quartz micro / nano optical fibers, characterized by: The system includes a wavelength-tunable laser (1), an optical fiber amplifier (2), a quartz micro / nano fiber, and an optical fiber low-pass filter (7) connected sequentially via optical fibers. The quartz micro / nano fiber portion is located within a sealed cavity (6). The quartz micro / nano fiber is a whole consisting of a first untapered portion (3-1), a first tapered transition region (4-1), a waist region (5), a second tapered transition region (4-2), and a second untapered portion (3-2) connected sequentially. The front and rear ends of the quartz micro / nano fiber are located outside the sealed cavity (6), while the rest are stored within the sealed cavity (6). The waist region (5) of the quartz micro / nano fiber transmits the optical field TE. 01 The mode cutoff method performs precise diameter control, so that the nonlinear optical frequency conversion process satisfies perfect phase matching, and the fundamental mode of the input light and the higher-order modes of the harmonic signal light in the waveguide mode have high mode field overlap; the fiber low-pass filter (7) is made by winding a standard single-mode fiber along the outer ring of a metal rod, which is in a filtering state for high-power continuous light and in a conducting state for second and third harmonic signal light.

2. The high-efficiency nonlinear optical frequency converter based on high-power continuous optical transmission of quartz micro-nano optical fiber according to claim 1, characterized in that: The output end of the wavelength-tunable laser (1) is connected to the input end of the fiber amplifier (2). The output end of the fiber amplifier (2) is connected to one end of the first untapered portion (3-1) of the quartz micro-nano fiber. The other end of the first untapered portion (3-1) is connected to one end of the first tapered transition region (4-1). The other end of the first tapered transition region (4-1) is connected to one end of the waist region (5). The other end of the waist region (5) is connected to one end of the second tapered transition region (4-2). The other end of the second tapered transition region (4-2) is connected to one end of the second untapered portion (3-2). The other end of the second untapered portion (3-2) is connected to the input end of the fiber low-pass filter (7).

3. The high-efficiency nonlinear optical frequency converter based on high-power continuous optical transmission of quartz micro-nano optical fiber according to claim 1 or 2, characterized in that: The output light of the wavelength-tunable laser (1) serves as a seed light source. After being amplified by the fiber amplifier (2), it generates high-power continuous light. The light passes through the first untapered section (3-1), the first tapered transition region (4-1), the waist region (5), the second tapered transition region (4-2), and the second untapered section (3-2) of the quartz micro-nano fiber in sequence, generating second and third harmonic signal light. After being input into the fiber low-pass filter (7), the high-power continuous light is filtered out, thereby realizing the output of second and third harmonic signal light.

4. The high-efficiency nonlinear optical frequency converter based on high-power continuous optical transmission of quartz micro-nano optical fiber according to claim 3, characterized in that: The first untapered portion (3-1) and the second untapered portion (3-2) of the quartz micro-nano optical fiber are fixed on both sides of the sealed chamber (6). The first untapered portion (3-1) and the second untapered portion (3-2) are both partially located inside the sealed chamber (6). The sealed chamber (6) is filled with high-purity gas for sealed preservation.

5. The high-efficiency nonlinear optical frequency converter based on high-power continuous optical transmission of quartz micro-nano optical fiber according to claim 4, characterized in that: One end of the first untapered portion (3-1) of the quartz micro-nano fiber is connected to the output end of the fiber amplifier (2) by fiber fusion splicing, and one end of the second untapered portion (3-2) is connected to the input end of the fiber low-pass filter (7) by fiber fusion splicing, with an insertion loss of less than 0.05dB.

6. The high-efficiency nonlinear optical frequency converter based on high-power continuous optical transmission of quartz micro-nano optical fiber according to claim 1, 2, 4, or 5, characterized in that: The quartz micro / nano fiber is prepared by mechanically stretching a standard single-mode quartz fiber. The first tapered transition region (4-1) and the second tapered transition region (4-2) have an adiabatic tapered structure, realizing near-lossless optical coupling of the transmitted optical field from the standard fiber to the micro / nano fiber.

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