Middle and far infrared low-noise ultra-wideband spectrum generating device

Abstract

The invention discloses a middle and far infrared low-noise ultra-wideband spectrum generating device, which comprises a femtosecond fiber laser, a single-mode ZBLAN fiber, a single-mode InF3 fiber, a first mode field adapter, a hollow-core anti-resonance fiber, a second mode field adapter, a full-positive dispersion chalcogenide fiber and an air chamber which are sequentially arranged along a laser path, and is characterized in that the femtosecond fiber laser is used for outputting laser pulses; the wavelength of laser pulses is larger than or equal to 2.1 micrometers, the pulse width is smaller than or equal to 30 fs, and the average power is larger than or equal to 2 W. A tail fiber of the femtosecond fiber laser, the single-mode ZBLAN fiber and the single-mode InF3 fiber are sequentially welded, and the single-mode InF3 fiber is in mode field adaptive connection with the hollow-core anti-resonance fiber through a first mode field adapter. The hollow-core anti-resonance optical fiber is in mode field adaptive connection with the full-positive-dispersion chalcogenide optical fiber through a second mode field adapter, the single-mode ZBLAN optical fiber and the single-mode InF3 optical fiber are packaged in a gas chamber, and the gas chamber is filled with protective gas. The device disclosed by the invention realizes all-fiber, and can generate an ultra-wideband spectrum which covers a wave band of 3-8 microns and has a low-noise characteristic.

Description

Technical Field

[0001] This invention belongs to the field of nonlinear optics technology, specifically relating to a mid- and far-infrared low-noise ultrawideband spectral generator. Background Technology

[0002] The 3–8 μm wavelength band covers multiple atmospheric windows and numerous characteristic absorption peaks of atoms and molecules, serving as a crucial "fingerprint" region for detection instruments and corresponding to the optical spectrum of blackbody radiation from objects at room temperature or high temperatures. In the mid-infrared region of the spectrum, ultra-wideband spectroscopy in this 3–8 μm band has wide applications in optical coherence tomography (OCT), multispectral diagnosis of cancerous tissue cells, molecular fingerprinting, high-precision optical measurement, environmental trace gas monitoring, and military infrared countermeasures. However, the main challenge currently limiting the application of this technology lies in simultaneously meeting three core requirements: ultra-wideband spectral coverage, low noise characteristics, and ease of integration.

[0003] The main methods for achieving mid- and far-infrared ultra-wideband spectroscopy can be summarized into the following four categories: 1) Solid-state optical parametric laser (OPO) pumped chalcogenide fiber: The high peak intensity and wide frequency modulation characteristics of this laser can generate mid- and far-infrared ultra-wideband spectra in chalcogenide fiber. However, it is limited by high cost, large size, low power and difficult maintenance, which makes it difficult to meet the practical needs. 2) Nanosecond supercontinuum laser cascade-pumped chalcogenide fiber: This fiber can achieve watt-level all-fiber broadband spectrum by cascading pumping different fiber materials through multi-stage amplified distributed feedback (DFB) electrically modulated pulses. However, since the seed laser is an incoherent source, and the pulse splitting and Raman effect dominate the spectral broadening process in the fiber, the resulting ultra-wideband spectrum has significant amplitude noise and intensity fluctuations, which cannot meet the application scenarios such as fiber coherent tomography that have strict requirements for the phase stability of the light source. 3) Cascaded mid-infrared crystal difference frequency generation of high coherence broadband light source: Its outstanding advantages are low noise and high spectral coherence, but it is limited by the limited phase matching bandwidth of nonlinear crystals. A single difference frequency process is difficult to cover the entire 3~8 μm band, and the space optical structure has temperature drift sensitivity problem, which restricts the long-term stability of the system. 4) Mid-infrared fiber-pumped chalcogenide fiber by ultrashort pulse laser: This fiber shows great potential for achieving all-fiber, high-power, low-noise ultrawideband spectra. Specifically, it can be divided into two types. One is pumping the chalcogenide fiber with a mode-locked fiber laser, which can achieve high-power spectral broadening. However, due to limitations of the gain medium, the initial pump wavelength is difficult to break through the 3.5 μm bottleneck, resulting in the ultrawideband spectrum generated by pumping having a long wavelength that cannot exceed 6 μm. The other is using mid-infrared Raman solitons to pump the fully positive dispersive chalcogenide fiber. In this case, the spectral broadening mechanism is mainly self-phase modulation and wave breaking. These two nonlinear effects can effectively avoid the noise-sensitive dynamic soliton process, thus obtaining a low-noise ultrawideband spectrum. However, this method excites multiple solitons during the cascading process. The interaction between these solitons in the short-wavelength region is extremely sensitive to small fluctuations in the pump light, leading to large power fluctuations in the final ultrawideband spectrum in the short-wavelength band and resulting in high noise. In addition, multiple solitons can also excite dispersive waves at different positions, causing multiple peaks and dips in the spectrum. In previous studies, spatial filtering structures were typically introduced to filter out unwanted short-wavelength solitons. However, the core drawback of spatial filtering structures is their poor system stability and low integration. They rely on discrete optical components to construct precise optical paths in free space, making the entire system highly sensitive to mechanical vibration, temperature drift, and air disturbances, requiring frequent calibration. At the same time, their large size, complex assembly process, and susceptibility to dust contamination also limit their application in scenarios requiring high reliability, compact structure, and strong environmental adaptability. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a mid- and far-infrared low-noise ultra-wideband spectrum generator that addresses the shortcomings of the prior art. This device is fully fiber-optic and can generate ultra-wideband spectra with low noise characteristics covering the 3-8 μm band.

[0005] The technical solution adopted by this invention to solve the above-mentioned technical problems is as follows: a mid-far-infrared low-noise ultra-wideband spectral generator, comprising a femtosecond fiber laser, a single-mode ZBLAN fiber, a single-mode InF3 fiber, a first mode field adapter, a hollow anti-resonant fiber, a second mode field adapter, a fully positive dispersion chalcogenide fiber, and a gas chamber arranged sequentially along the laser optical path. The femtosecond fiber laser is used to output laser pulses, the wavelength of which is ≥2.1 μm, the pulse width is ≤30 fs, and the average power is ≥2W. The pigtail of the femtosecond fiber laser, the single-mode ZBLAN fiber, and the single-mode InF3 fiber are sequentially fused together. The single-mode InF3 fiber is connected to the hollow anti-resonant fiber through the first mode field adapter for mode field adaptation. The hollow anti-resonant fiber is connected to the fully positive dispersion chalcogenide fiber through the second mode field adapter for mode field adaptation. The single-mode ZBLAN fiber and the single-mode InF3 fiber are encapsulated in the gas chamber, which is filled with a protective gas.

[0006] In this invention, the device comprises a five-stage fiber cascade structure consisting of a femtosecond fiber laser pigtail, a single-mode ZBLAN fiber, a single-mode InF3 fiber, a hollow-core antiresonant fiber, and a fully positive dispersion chalcogenide fiber. The hollow-core antiresonant fiber effectively filters stray light outside the 4-5 μm band and transmits femtosecond soliton laser light in the 4-5 μm band with extremely low loss. The fully positive dispersion chalcogenide fiber exhibits low-loss transmission characteristics in the 3-8 μm band. Furthermore, thanks to its fully positive dispersion characteristics, when a 4-5 μm laser pulse propagates in the fiber, it is mainly affected by two nonlinear effects: self-phase modulation and light wave breaking, while the effects of modulation instability and soliton effects are relatively small. This avoids noise amplification during transmission, resulting in a superior low-noise performance for the final ultra-wideband light source. In addition, since both the single-mode InF3 fiber and the fully positive dispersion chalcogenide fiber can be connected to the hollow-core antiresonant fiber with low loss via a mode field adapter (MFA), this invention enables an all-fiber system, thus avoiding environmental influences on the optical path and further improving system stability and low-noise performance.

[0007] Preferably, the pigtail of the femtosecond fiber laser is a single-mode silica fiber with a core diameter ≤9 μm and a cladding diameter ≤125 μm. The pigtail, serving as the first-stage cascaded fiber, primarily transmits the femtosecond laser output. The use of a shorter single-mode silica fiber is mainly due to the significantly increased infrared absorption loss and strong dispersion and nonlinear effects inherent in silica fiber at this wavelength. On one hand, the shorter fiber minimizes transmission loss, preventing excessive broadening of the ultrashort pulse due to dispersion, thus maintaining the femtosecond characteristics of the laser. On the other hand, the shorter fiber effectively suppresses harmful nonlinear effects (such as spectral distortion and pulse degradation) caused by high peak power, preventing damage to the laser's stability and ensuring the output beam quality, spectral purity, and timing shape.

[0008] Preferably, the core diameter of the single-mode ZBLAN fiber is ≤8 μm, and the cladding diameter is ≤150 μm. As the second-stage cascaded fiber, the single-mode ZBLAN fiber primarily achieves a crucial spectral shift through the soliton self-frequency shift (SSFS) effect. The specific process is as follows: First, the pigtail of the femtosecond fiber laser is connected to the single-mode ZBLAN fiber via fusion splicing, coupling the femtosecond laser into the single-mode ZBLAN fiber. Since the 2.1 μm band is located in the anomalous dispersion region of the single-mode ZBLAN fiber, group velocity dispersion (GVD) causes pulse broadening, while the nonlinear effect of self-phase modulation (SPM) (refractive index changes with light intensity) produces the opposite compression effect. When the spectral broadening caused by SPM and the pulse compression effect caused by GVD reach equilibrium, a fundamental optical soliton with a center wavelength of 3 μm is formed within the fiber.

[0009] Preferably, the core diameter of the single-mode InF3 fiber is ≤9.5 μm, and the cladding diameter is ≤125 μm. As the third-stage cascaded fiber, the main function of the single-mode InF3 fiber is to further enhance the soliton frequency shift efficiency and spectral broadening capability. This is due to its three key characteristics in the mid-infrared band: anomalous dispersion, high nonlinear coefficient, and wide transparency window. Specifically: First, the single-mode InF3 fiber is located in the anomalous dispersion region in the mid-infrared band, enabling efficient spectral redshift through the soliton self-frequency shift (SSFS) effect. Second, the mode field area of ​​the single-mode InF3 fiber is smaller than that of the single-mode ZBLAN fiber, resulting in a higher nonlinear coefficient, which helps to increase the peak power of the soliton, thereby more effectively driving the nonlinear frequency shift process. Finally, the single-mode InF3 fiber has a wide mid-infrared transparency window covering ~5 μm, and its loss in the 4~5 μm band is significantly lower than that of the single-mode ZBLAN fiber, ensuring no significant material absorption loss during soliton frequency shift, thus achieving efficient soliton laser transmission. In summary, single-mode InF3 fiber provides an ideal nonlinear environment for solitons, which can significantly enhance the energy proportion in the long-wavelength direction, laying the foundation for the subsequent fiber extension to longer wavelength bands.

[0010] Preferably, the hollow-core antiresonant fiber is a silica fiber or a fluoride fiber. The hollow-core antiresonant fiber is a fourth-stage cascaded fiber, its main function being to achieve all-fiber spectral filtering. Its filtering function is based on the antiresonant reflection waveguide mechanism: when light propagates within the hollow core, the periodically arranged thin-walled capillary structure of the cladding forms an optical barrier. When light of a specific wavelength (λ) satisfies the antiresonance condition (optical path difference satisfies a π-phase jump), it is reflected from the inner wall of the capillary, and its leakage field is strongly suppressed at the interface due to destructive interference. Conversely, light deviating from the resonant wavelength is rapidly lost due to not satisfying the phase-matching condition. Ultimately, only light outside the resonant bandpass is efficiently confined within the hollow core, forming a wavelength selectivity similar to band-stop filtering, thus achieving the filtering function. By designing specific core diameters, capillary diameters, and wall thicknesses, different filtering bands can be achieved. In this device, the soliton energy output from the single-mode InF3 fiber is mainly distributed at 2.1 μm, 3 μm, and 4.5 μm. To achieve the final low-noise ultrawideband spectrum, the energy at 2.1 μm and 3 μm needs to be filtered out using the filtering effect of a hollow-core anti-resonant fiber. Furthermore, this fiber can achieve efficient mode field matching with single-mode InF3 fiber and fully positive dispersion single-mode chalcogenide fiber through a mode field adapter, further improving the coupling efficiency of different fiber types. It also enables an all-fiber structure, avoiding disturbances from the external space environment and improving the system's stability and noise immunity.

[0011] Preferably, the fully positive dispersive chalcogenide fiber has a zero-dispersion wavelength ≥ 8 μm, and its dispersion characteristics are fully positive on the shorter wavelength side of the zero-dispersion wavelength. As the fifth-stage cascaded fiber, the fully positive dispersive chalcogenide fiber's main function is to generate an ultra-wideband spectrum covering 3–8 μm. Thanks to its fully positive dispersion characteristics, when a 4–5 μm laser pulse propagates within it, the spectral broadening process is mainly dominated by self-phase modulation and light wave breaking, while modulation instability and soliton effects are significantly suppressed. This mechanism ensures that noise during transmission is not amplified, thus the resulting ultra-wideband light source possesses both good low-noise performance and high coherence.

[0012] As a further preferred embodiment, the fully positive dispersive chalcogenide fiber is a Ge-As-Se-Te chalcogenide fiber. Ge-As-Se-Te chalcogenide fibers offer significant performance advantages in generating ultra-wideband spectra: First, they possess an ultra-wideband infrared transmission range, typically exceeding 1–12 μm, covering the mid-infrared spectral band and extending into the far-infrared band. Within this transmission range, they exhibit extremely low loss, with the lowest recorded loss below 0.1 dB / m. Second, the nonlinear refractive index of Ge-As-Se-Te chalcogenide fibers is typically 100–1000 higher than that of silica fibers. This allows for the generation of extremely strong nonlinear effects with shorter fiber lengths or lower incident pump power, ultimately resulting in an ultra-wideband spectrum with extremely large bandwidth (up to several octaves). Finally, Ge-As-Se-Te chalcogenide fibers offer flexible dispersion design advantages. By changing the fiber composition, core diameter, and structural design (such as microstructured fibers), the dispersion characteristics of chalcogenide fibers can be precisely controlled over a wide wavelength range, shifting the zero-dispersion point to fully utilize the fiber's nonlinear effects for efficient spectral broadening. This design flexibility allows chalcogenide fibers to be optimized for pump lasers of different wavelengths. As a further preferred embodiment, the fully positive dispersion chalcogenide fiber is a double-clad Ge... 15 As 25 Se 40 Te 20 Chalcogenide optical fiber.

[0013] Compared with existing technologies, the present invention has the following advantages: The device of the present invention achieves all-fiber cascading, and can generate an ultra-wideband spectrum covering the 3-8 μm band with low noise characteristics. In the device of the present invention, the pigtail of the femtosecond fiber laser, single-mode ZBLAN fiber, single-mode InF3 fiber, hollow-core antiresonant fiber, and fully positive dispersion chalcogenide fiber constitute a five-stage fiber cascade structure. Among them, the hollow-core antiresonant fiber can effectively filter out stray light outside the 4-5 μm band and transmit femtosecond soliton laser in the 4-5 μm band with extremely low loss; the fully positive dispersion chalcogenide fiber has low-loss transmission characteristics in the 3-8 μm band. At the same time, thanks to its fully positive dispersion characteristics, when the 4-5 μm laser pulse is transmitted in the fiber, it is mainly affected by two nonlinear effects: self-phase modulation and light wave breaking, while the effects of modulation instability and soliton effect are relatively small, thereby avoiding noise amplification during transmission. Therefore, the final ultra-wideband light source exhibits good low-noise performance. Furthermore, since both single-mode InF3 fiber and fully positive dispersion chalcogenide fiber can be connected to hollow anti-resonant fiber with low loss via mode field adapter (MFA), the device of this invention can achieve all-fiber operation, thereby avoiding the influence of the environment on the optical path and further improving the stability and low-noise performance of the system. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the overall structure of the mid- and far-infrared low-noise ultrawideband spectrum generator in the embodiment. Figure 2 A schematic diagram of the soliton spectrum generated in a single-mode ZBLAN fiber; Figure 3 A schematic diagram of the soliton spectrum generated in a single-mode InF3 fiber; Figure 4 This is a schematic diagram of the structure of a hollow anti-resonant optical fiber. Figure 5 The simulated loss curves for hollow-core anti-resonant optical fiber are shown. Figure 6 This is a schematic spectrum after filtering through a hollow anti-resonant fiber optic cable. Figure 7 The dispersion curve of a fully positive dispersion chalcogenide optical fiber; Figure 8 A schematic diagram of the ultrawideband spectrum output from a fully positive dispersive chalcogenide optical fiber; Figure 9 The output ultrawideband spectrum contains coherence characteristic curves. Figure 1 The specific reference numerals in the attached figures are as follows: 1- Femtosecond fiber laser, 2- Single-mode ZBLAN fiber, 3- Single-mode InF3 fiber, 4- First mode field adapter, 5- Hollow-core anti-resonant fiber, 6- Second mode field adapter, 7- Fully positive dispersive chalcogenide fiber, 8- Gas cell. Detailed Implementation

[0015] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0016] The mid- and far-infrared low-noise ultrawideband spectral generator of the embodiment, such as Figure 1 As shown, the system includes a femtosecond fiber laser 1, a single-mode ZBLAN fiber 2, a single-mode InF3 fiber 3, a first mode field adapter 4, a hollow-core anti-resonant fiber 5, a second mode field adapter 6, a fully positive dispersive chalcogenide fiber 7, and a gas cell 8, arranged sequentially along the laser optical path. The femtosecond fiber laser 1 is used to output a pulse with a repetition frequency of 50 MHz, a pulse width of 30 fs, and an average power of 2 W. A laser pulse with a wavelength of μm is used. The pigtail of the femtosecond fiber laser 1, the single-mode ZBLAN fiber 2, and the single-mode InF3 fiber 3 are sequentially fused together. The single-mode InF3 fiber 3 is connected to the hollow anti-resonant fiber 5 through the first mode field adapter 4. The hollow anti-resonant fiber 5 is connected to the fully positive dispersion chalcogenide fiber 7 through the second mode field adapter 6. The single-mode ZBLAN fiber 2 and the single-mode InF3 fiber 3 are encapsulated in a gas chamber 8 to prevent moisture from entering and causing deliquescence and damage. The gas chamber 8 is filled with high-purity nitrogen gas with a purity of 99.999% and a temperature of 15°C as a protective gas for dehumidification and heat dissipation.

[0017] The pigtail of the femtosecond fiber laser 1 serves as the first-stage cascaded fiber. This pigtail is a single-mode silica fiber, model SMF-28e, with a core diameter of 8.2 μm, a cladding diameter of 125 μm, a numerical aperture of 0.14, and a fiber length of 0.2m.

[0018] Single-mode ZBLAN fiber 2, used as the second-stage cascaded fiber, has the following parameters: core diameter of 7.5 μm, cladding diameter of 148 μm, numerical aperture of 0.23, zero-dispersion wavelength of 1.65 μm, and effective mode area A. eff 106 μm 2 Nonlinear refractive index n 2 2.55×10 -20 m 2 / W, using an 8 m long optical fiber. Part of the energy of the femtosecond pulse generated by the femtosecond laser is shifted from 2.1 μm to 3 μm in this cascaded optical fiber through the Raman soliton self-frequency shift effect. Figure 2 This is a schematic diagram of the soliton spectrum generated in a single-mode ZBLAN fiber. Figure 2 It can be seen that most of the energy in the spectrum shifts to 3 μm, while a small portion of the energy remains at 2.1 μm.

[0019] The single-mode InF3 fiber 3, used as the third-stage cascaded fiber, has the following parameters: core diameter of 9.5 μm, cladding diameter of 125 μm, numerical aperture of 0.3, zero-dispersion wavelength of 1.70 μm, and effective mode area A. eff 77 μm 2 The nonlinear refractive index n2 is 3.5 × 10⁻⁶. -20 m 2 / W, using an optical fiber length of 7 m. In this cascaded fiber, the Raman soliton self-frequency shift effect spectrum is further frequency shifted to 4.5 μm. Figure 3 This is a schematic diagram of the soliton spectrum generated in a single-mode InF3 fiber. Figure 3 As can be seen, a 4.5 μm soliton pulse is generated in single-mode InF3 fiber 3. Compared with single-mode ZBLAN fiber 2, single-mode InF3 fiber 3 has a higher nonlinear coefficient and lower loss in the 4~5 μm band, ensuring the energy transfer efficiency of soliton frequency shift.

[0020] Hollow-core anti-resonant fiber 5 serves as the fourth cascaded fiber, and its material is either quartz fiber or fluoride fiber. Its structural schematic diagram is shown below. Figure 4 As shown. Its parameters are: core diameter a is 128 μm, cladding consists of seven capillaries with an average wall thickness b of 0.68 μm, capillary diameter c is 65 μm, the fiber length used is 4 m, and the total diameter is 400 μm. Figure 5 To simulate the loss curve of the hollow-core antiresonant fiber considering only the limited loss, the loss of the hollow-core antiresonant fiber 5 is 3.5 dB / m at 2.1 μm, 7.8 dB / m at 3 μm, and 0.03 dB / m at 4.5 μm, which fully meets the conditions for filtering out the residual energy at 2.1 μm and 3 μm and efficiently transmitting the soliton pulse at 4.5 μm. Figure 6 The image shows a schematic spectrum after filtering through a hollow anti-resonant fiber. After passing through a 4 m hollow anti-resonant fiber 5, the energy at 2.1 μm and 3 μm is filtered out, and only the pulse at 4.5 μm continues to propagate along the fiber.

[0021] All-positive dispersion chalcogenide fiber 7 is used as the fifth cascaded fiber in this embodiment, and double-clad Ge is employed. 15 As 25 Se 40 Te 20 Chalcogenide optical fiber, its parameters are: core material is Ge 15 As 25 Se 40 Te 20 Chalcogenide glass, the inner cladding and outer cladding are made of Ge. 15 As 25 Se 45 Te15 Glass and Ge 15 As 25 Se 50 Te 10 The fiber is a chalcogenide glass fiber with a core diameter of 30 μm, an inner cladding diameter of 90 μm, and an outer cladding diameter of 270 μm. The fiber length is 10 cm. Compared to traditional single-clad fibers, double-clad fibers exhibit superior mechanical strength during practical operation. The dispersion curve of the fully positive dispersion chalcogenide fiber 7 in this embodiment is shown below. Figure 7 As shown, its zero-dispersion wavelength is 8.6 μm, exhibiting all-positive dispersion characteristics in the 3–8 μm band. In this all-positive dispersion chalcogenide fiber 7, self-phase modulation and the light wave breaking effect induced by self-steepening and third-order dispersion jointly dominate the nonlinear broadening process of the pulse, thereby generating a low-noise ultra-wideband spectrum. A schematic diagram of its output ultra-wideband spectrum is shown below. Figure 8 .

[0022] To verify the noise characteristics of the ultra-wideband spectrum generated by the mid-to-far-infrared low-noise ultra-wideband spectrometer in the above embodiment, we calculated the coherence of the generated ultra-wideband spectrum. In the simulation, we considered the effect of fiber loss and statistically evaluated the stability of the output spectrum by introducing multiple sets of pulses with different random noises (including incident pulse random noise and spontaneous Raman noise). The calculation results of the coherence of the output ultra-wideband spectrum are as follows: Figure 9 The coherence characteristic curve is shown below. From Figure 9 It can be seen that in the 2–8 μm band, the value of the first-order coherence factor is approximately 1, and the coherence curve does not show a significant dip, indicating that the output light source has excellent temporal coherence. This ultra-wideband spectrum remains in the fully positive dispersion region throughout the broadening process. Thanks to the effective suppression of modulation instability and soliton effects, the nonlinear dynamics are dominated only by non-noise amplification mechanisms such as self-phase modulation and light wave breaking. Therefore, this ultra-wideband spectrum exhibits good low-noise performance.

Claims

1. A mid-to-far-infrared low-noise ultrawideband spectral generator, characterized in that, The device comprises a femtosecond fiber laser, a single-mode ZBLAN fiber, a single-mode InF3 fiber, a first mode field adapter, a hollow anti-resonant fiber, a second mode field adapter, a fully positive dispersion chalcogenide fiber, and a gas chamber arranged sequentially along the laser optical path. The femtosecond fiber laser is used to output laser pulses with a wavelength ≥2.1 μm, a pulse width ≤30 fs, and an average power ≥2 W. The pigtail of the femtosecond fiber laser, the single-mode ZBLAN fiber, and the single-mode InF3 fiber are sequentially fused together. The single-mode InF3 fiber is connected to the hollow anti-resonant fiber via the first mode field adapter for mode field adaptation. The hollow anti-resonant fiber is connected to the fully positive dispersion chalcogenide fiber via the second mode field adapter for mode field adaptation. The single-mode ZBLAN fiber and the single-mode InF3 fiber are encapsulated in the gas chamber, which is filled with a protective gas.

2. The mid-far-infrared low-noise ultra-wideband spectral generator according to claim 1, characterized in that, The pigtail of the femtosecond fiber laser is a single-mode silica fiber, with a core diameter ≤9 μm and a cladding diameter ≤125 μm.

3. The mid-far-infrared low-noise ultra-wideband spectral generator according to claim 1, characterized in that, The single-mode ZBLAN fiber has a core diameter ≤8 μm and a cladding diameter ≤150 μm.

4. The mid-far-infrared low-noise ultra-wideband spectral generator according to claim 1, characterized in that, The single-mode InF3 optical fiber has a core diameter ≤9.5 μm and a cladding diameter ≤125 μm.

5. The mid- and far-infrared low-noise ultra-wideband spectral generator according to claim 1, characterized in that, The hollow anti-resonant optical fiber is a quartz optical fiber or a fluoride optical fiber.

6. The mid-far-infrared low-noise ultra-wideband spectral generator according to claim 1, characterized in that, The fully positive dispersion chalcogenide optical fiber has a zero dispersion wavelength ≥ 8 μm, and its dispersion characteristics on the short wavelength side of the zero dispersion wavelength are fully positive dispersion.

7. The mid-far-infrared low-noise ultra-wideband spectral generator according to claim 6, characterized in that, The fully positive dispersion chalcogenide optical fiber is a Ge-As-Se-Te chalcogenide optical fiber.

8. The mid-far-infrared low-noise ultra-wideband spectral generator according to claim 7, characterized in that, The totally positive dispersion chalcogenide optical fiber is a double-clad Ge fiber. 15 As 25 Se 40 Te 20 Chalcogenide optical fiber.

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