Time delay-frequency high-linearity optical fiber and preparation method and application thereof

Abstract

The invention belongs to the technical field of special optical fibers, and discloses a time delay-frequency high-linearity optical fiber and a preparation method and application thereof. The time delay-frequency high-linearity optical fiber provided by the invention comprises a fiber core, and a first cladding, a second cladding, a third cladding and a fourth cladding which are sequentially coated outside the fiber core, the relative refractive index range and the radius range of each layer are set, and in the set range, in a target working bandwidth, the relative refractive index range of each layer and the radius range of each layer are set, so that the time delay-frequency high-linearity optical fiber is obtained. The change value of the dispersion coefficient of the optical fiber is smaller than the first parameter, and the linear fitting correlation between the time delays of different wavelengths and the wavelengths is superior to the second parameter, and determining the structure parameters of the relative refractive index and radius of each layer in the optical fiber. The optical fiber provided by the invention has high time delay-frequency linearity, and can ensure that the pulse is not distorted when the optical fiber is used for pulse compression or broadening.

Description

Technical Field

[0001] This invention belongs to the field of special optical fiber technology, and more specifically, relates to a time-delay-frequency high linearity optical fiber, its preparation method, and its application. Background Technology

[0002] In the field of ultrafast optics, the manipulation of ultrashort pulses (on the order of femtoseconds or picoseconds) is one of the core technologies. Among them, chirped pulse amplification and supercontinuum generation are two crucial processes, both of which rely heavily on precise control of the pulse in the time domain.

[0003] The essence of chirped pulse amplification (CPA) lies in "broadening first, then compressing." First, a high-power, fragile ultrashort pulse is broadened in the time domain into a low-power, wide pulse (introducing "chirp"). Then, it is safely amplified. Finally, the amplified pulse is compressed back to its original ultrashort pulse width. The success of this process hinges on the complete reversibility and distortion-free nature of the broadening and compression. This means that the time difference between the propagation of different frequency light components in the optical fiber must be strictly constant. Only under these conditions can a compressor (such as a grating pair) resynchronize all frequency components, perfectly reproducing the transform-limited short pulse.

[0004] Supercontinuum generation (SC) aims to convert narrowband pulses into extremely wide supercontinuums using nonlinear effects. A high-quality supercontinuum generation source requires not only a flat spectrum but also good temporal coherence, meaning the generated white light has a definite phase relationship. The core challenge of supercontinuum generation is that its generation strongly depends on the dispersion characteristics of the pulse propagating in a nonlinear medium. If the time-delay-frequency relationship of the medium is nonlinear (i.e., significant higher-order dispersion exists), the nonlinear interactions of different frequency components (such as four-wave mixing, soliton self-frequency shift, etc.) become chaotic and disordered. This leads to huge spectral fluctuations and complex distortions and noise in the time domain, severely compromising its coherence and practicality.

[0005] To achieve high dispersion, traditional high-dispersion fiber designs often focus on obtaining high negative dispersion values ​​(D). However, the dispersion value D itself varies with wavelength, exhibiting a rate of change characteristic of third-order dispersion. When such fibers are used for pulse broadening or as supercontinuum generation media, third-order and higher-order dispersion introduces nonlinear time-delay-frequency relationships. In chirped pulse amplification, this leads to distortion of the broadened pulse shape, resulting in "picosecond bases" or "pre-pulses." After amplification, the compressor cannot perfectly compensate for this distortion, resulting in increased pulse width, sidelobes, and decreased peak power in the compressed pulse, severely limiting the final achievable pulse intensity. In supercontinuum generation, this nonlinear time-delay relationship disrupts the phase-matching conditions between different frequency components, reducing and unpredicting nonlinear energy transfer efficiency, ultimately producing supercontinuums with poor spectral flatness, low coherence, and poor stability. In other words, when high dispersion coefficient (i.e., high absolute value of dispersion coefficient) fiber is used for pulse broadening or pulse compression in applications related to supercontinuum generation or chirped pulse amplification, the nonlinear time delay introduced by higher-order dispersion will cause distortion of the pulse distribution in the time domain (such as asymmetric broadening, substrate or subpulse). This will seriously degrade the final compression effect of the chirped pulse amplification system and the coherence and flatness of the supercontinuum light source. Summary of the Invention

[0006] This invention provides a time-delay-frequency high linearity optical fiber, its fabrication method, and its application, solving the problem in the prior art where the distribution of pulses in the time domain is distorted due to the nonlinear time delay introduced by high-dispersion optical fibers when used for pulse compression or broadening.

[0007] In a first aspect, the present invention provides a high-delay-frequency linearity optical fiber, comprising: a fiber core, and a first cladding, a second cladding, a third cladding, and a fourth cladding sequentially covering the fiber core; The relative refractive index of the fiber core ranges from 1.2% to 2.0%, and the radius ranges from 1 μm to 1.5 μm. The first cladding layer has a relative refractive index ranging from -0.7% to -0.3% and a radius ranging from 1.5 μm to 6 μm. The second cladding has a relative refractive index ranging from 0.2% to 1.0% and a radius ranging from 6 μm to 9 μm. The third cladding has a relative refractive index ranging from -0.6% to -0.09% and a radius ranging from 9 μm to 15 μm. The fourth cladding layer is a pure quartz layer with a radius ranging from 50 μm to 60 μm. Within the aforementioned parameter range, the structural parameters of the relative refractive index and radius of each layer in the optical fiber are determined with the optimization objective being that the change in the dispersion coefficient of the optical fiber is less than the first parameter within the target working bandwidth, and the correlation between the time delay and the wavelength linear fitting is better than the second parameter. Preferably, the target operating bandwidth belongs to the O-band, E-band, C-band or L-band; the first parameter is 0 ps / km·nm to 4 ps / km·nm, the second parameter is 99.999% to 99.9999%; and the dispersion coefficient of the time-delay-frequency high linearity optical fiber is -100 ps / nm·km to -300 ps / nm·km.

[0008] Preferably, within the target operating bandwidth, the dispersion curve of the delay-frequency high linearity optical fiber forms at least one flat region, in which the dispersion slope is close to zero.

[0009] Preferably, within the target operating bandwidth, the attenuation of the delay-frequency high linearity optical fiber is less than 0.6 dB / km.

[0010] Secondly, the present invention provides a method for fabricating a time-delay-frequency high linearity optical fiber, comprising the following steps: Hollow quartz tubes with a target refractive index profile were prepared by MCVD or PCVD. The hollow quartz tube is melted and shrunk to obtain a solid doped glass core rod; The doped glass core rod is assembled with a pure quartz sleeve and then melted and shrunk to obtain a solid quartz rod. The solid quartz rod is drawn into a fiber to obtain a high time-delay-frequency linearity optical fiber; The high-delay-frequency linearity optical fiber includes a core and a first cladding, a second cladding, a third cladding, and a fourth cladding sequentially covering the core. The relative refractive index of the core ranges from 1.2% to 2.0%, and the radius ranges from 1 μm to 1.5 μm. The relative refractive index of the first cladding ranges from -0.7% to -0.3%, and the radius ranges from 1.5 μm to 6 μm. The relative refractive index of the second cladding ranges from 0.2% to 1.0%, and the radius ranges from 6 μm to 9 μm. The relative refractive index of the third cladding ranges from -0.6% to -0.09%, and the radius ranges from 9 μm to 15 μm. The fourth cladding is a pure silica layer with a radius ranging from 50 μm to 60 μm. The optimization objective is to ensure that the change in the dispersion coefficient of the optical fiber is less than the first parameter within the target operating bandwidth, and that the linear correlation between the delay and wavelength at different wavelengths is better than the second parameter. Within the above parameter range, the structural parameters of the relative refractive index and radius of each layer in the optical fiber are determined. Preferably, the target operating bandwidth belongs to the O-band, E-band, C-band or L-band; the first parameter is 0 ps / km·nm to 4 ps / km·nm, the second parameter is 99.999% to 99.9999%; and the dispersion coefficient of the time-delay-frequency high linearity optical fiber is -100 ps / nm·km to -300 ps / nm·km.

[0011] Preferably, within the target operating bandwidth, the dispersion curve of the delay-frequency high linearity optical fiber forms at least one flat region, in which the dispersion slope is close to zero.

[0012] Preferably, when drawing the solid quartz rod, the dispersion curve of the optical fiber is finely adjusted at the nanometer level by adjusting the drawing tension and the drawing diameter.

[0013] Preferably, the fiber core is co-doped with germanium, fluorine, and chlorine, or co-doped with germanium and fluorine; the first cladding is co-doped with fluorine and chlorine; the second cladding is co-doped with germanium, fluorine, and chlorine, or co-doped with germanium and fluorine; the third cladding is co-doped with germanium, fluorine, and chlorine, or co-doped with germanium and fluorine; by controlling the doping ratio of germanium and fluorine, the attenuation of the high-delay-frequency linearity optical fiber within the target operating bandwidth is less than 0.6 dB / km.

[0014] Thirdly, the present invention provides an application of the time-delay-frequency high linearity optical fiber as provided in the first aspect of the present invention, applying the time-delay-frequency high linearity optical fiber to supercontinuum generation or chirped pulse amplification.

[0015] One or more technical solutions provided in this invention have at least the following technical effects or advantages: The time-delay-frequency high linearity optical fiber provided by this invention includes a fiber core and four cladding layers sequentially covering the fiber core. This invention sets the relative refractive index range and radius range for each layer, and within these ranges, optimizes the fiber's dispersion coefficient variation to be less than a first parameter within the target operating bandwidth, and ensures that the linear correlation between the time delay and wavelength for different wavelengths is better than a second parameter. The structural parameters of the relative refractive index and radius of each layer in the optical fiber are determined accordingly. Specifically, this invention aims to ensure that the optical fiber does not distort when used for pulse compression or broadening. By optimizing the fiber's profile design and synergistically adjusting the structure of each layer within the parameter range disclosed in this invention, a time-delay-frequency high linearity optical fiber can be obtained. The optical fiber provided by this invention maintains a essentially constant time delay difference between different wavelengths within the operating range of a broadband light source, thereby ensuring uniform optical power distribution. This invention provides a highly customized, high-performance key photonic device for various ultrafast optical systems and broadband light source applications requiring distortion-free pulse operation. Attached Figure Description

[0016] Figure 1 A relative refractive index profile structure distribution diagram of a time-delay-frequency high linearity optical fiber provided in an embodiment of the present invention; Figure 2 A schematic diagram of a flat region formed by the dispersion curve of a high-delay-frequency linearity optical fiber, provided in an embodiment of the present invention; Figure 3 A process flow diagram corresponding to a method for fabricating a time-delay-frequency high linearity optical fiber provided in an embodiment of the present invention; Figure 4 This is a linear fitting diagram of time delay versus wavelength for a high-delay-frequency linearity optical fiber provided in an embodiment of the present invention. Detailed Implementation

[0017] To better understand the above technical solutions, the following will provide a detailed explanation of the technical solutions in conjunction with the accompanying drawings and specific implementation methods.

[0018] In a first aspect, the present invention provides a high-delay-frequency linearity optical fiber.

[0019] The present invention aims to ensure that the pulse is not distorted when using optical fiber for pulse compression or broadening, and optimizes the cross-sectional design of the optical fiber, including the relative refractive index and radius of each layer.

[0020] For details, see Figure 1 The present invention provides a high-delay-frequency linearity optical fiber comprising: a fiber core (i.e., Figure 1 The core), and the first cladding layer that sequentially covers the core (i.e. Figure 1 clad1), the second clad (i.e. Figure 1 clad2 in the middle), the third clad (i.e. Figure 1 clad3) and the fourth cladding (i.e. Figure 1 (clad4 in the middle).

[0021] The relative refractive index of the fiber core (i.e. Figure 1 The Δn1 in the first cladding layer ranges from 1.2% to 2.0%, and the radius ranges from 1 μm to 1.5 μm; the relative refractive index of the first cladding layer (i.e., Figure 1 The Δn2 in the second cladding ranges from -0.7% to -0.3%, and the radius ranges from 1.5 μm to 6 μm; the relative refractive index of the second cladding (i.e., Figure 1 The Δn3 in the third cladding has a range of 0.2% to 1.0% and a radius range of 6 μm to 9 μm; the relative refractive index of the third cladding (i.e., Figure 1 The Δn4 in the figure ranges from -0.6% to -0.09%, and the radius ranges from 9 μm to 15 μm; the fourth cladding layer is a pure quartz layer (i.e., Figure 1Δn5 (where Δn5 is 0) has a radius ranging from 50um to 60um.

[0022] The fiber core may be co-doped with germanium, fluorine, and chlorine (Ge / F / Cl) or co-doped with germanium and fluorine (Ge / F); the first cladding may be co-doped with fluorine and chlorine; the second cladding may be co-doped with germanium, fluorine, and chlorine or co-doped with germanium and fluorine; and the third cladding may be co-doped with germanium, fluorine, and chlorine or co-doped with germanium and fluorine.

[0023] The present invention can be further optimized and limited based on the above range, and the preferred range is as follows: the relative refractive index of the fiber core is in the range of 1.8% to 2.0%, and the radius is in the range of 1.1 μm to 1.3 μm; the relative refractive index of the first cladding layer is in the range of -0.5% to -0.4%, and the radius is in the range of 4 μm to 4.5 μm; the relative refractive index of the second cladding layer is in the range of 0.5% to 0.6%, and the radius is in the range of 6 μm to 7 μm; the relative refractive index of the third cladding layer is in the range of -0.2% to 0%, and the radius is in the range of 9 μm to 12 μm; the fourth cladding layer is a pure quartz layer with a radius in the range of 55 μm to 58 μm.

[0024] In addition to the fiber glass portion, the high-delay-frequency linearity optical fiber may also include a coating layer, which may be acrylate, modified acrylic resin, polyimide, etc., and the diameter of the coating layer is 165 μm or 245 μm.

[0025] This invention provides highly customized, high-performance key photonic devices for various ultrafast optical systems and broadband light source applications requiring distortion-free pulse operation. In specific applications, the structural parameters of the relative refractive index and radius of each layer in the time-delay-frequency high-linearity fiber provided by this invention are determined according to customized requirements in the following manner: Within the range of the above parameters, the optimization objective is to ensure that the dispersion coefficient variation of the time-delay-frequency high-linearity fiber is less than a set first parameter within a set target operating bandwidth, and that the linear correlation between the time delay and wavelength for different wavelengths is better than a set second parameter.

[0026] The first parameter can be set from 0 ps / km·nm to 4 ps / km·nm, and the second parameter can be set from 99.999% to 99.9999%.

[0027] For further optimization, see [link / reference]. Figure 2 Within the target operating bandwidth, the dispersion curve of the delay-frequency high linearity optical fiber provided by the present invention forms at least one flat region, and the dispersion slope within the flat region is close to zero.

[0028] The four-cladding structure of the optical fiber provided by this invention essentially constructs a precise "waveguide dispersion engineering" system. By using specific refractive index differences and radius combinations between the fiber core and multiple cladding layers, the dispersion curve (D-λ curve) of the optical fiber can be precisely shaped.

[0029] This invention achieves precise control over the shape of the fiber dispersion curve through an adjustable, multi-layered waveguide structure design, thereby creating a "plateau region" with a near-zero dispersion slope within the target operating wavelength. By synergistically adjusting the structure layers within the parameter range disclosed in this invention, this high-linearity plateau can be flexibly set in different target wavelengths, thus providing highly customized, high-performance key photonic devices for various ultrafast optical systems and broadband light source applications requiring distortion-free pulse operation.

[0030] The optimization design goal of this invention is not simply to pursue a high dispersion value, but rather to achieve a nearly flat "plateau" or "valley" in the dispersion curve within the target operating bandwidth. This "plateau" corresponds to the wavelength region where the dispersion slope (i.e., third-order dispersion) is close to zero. The dispersion curve can be imagined as a "valley." Traditional dispersion-shifting fibers may only move the zero-dispersion point (the lowest point of the valley) to a specific wavelength, while the design goal of this invention is to create a flat valley floor. Within this flat valley floor range, the dispersion coefficient (D) changes very little with wavelength (i.e., dispersion slope S≈0), thus ensuring a very high linear relationship between the time delay τ and the frequency ν (or wavelength λ) (because τ∝D, and if D is constant, τ is linear with λ).

[0031] The relative refractive index and radius of each layer in the optical fiber provided by this invention jointly determine the center wavelength, flatness (linearity), and width of the aforementioned "dispersion plateau." Therefore, by coordinating adjustments within the parameter range defined by this invention, a high-linearity operating window can be precisely set in different target wavelength bands.

[0032] The target operating bandwidth in this invention can be O-band (1260nm to 1360nm), E-band (1360nm to 1460nm), C-band (1530nm to 1565nm), or L-band (1565nm to 1625nm). For example, the target operating bandwidth can be set to a 20nm bandwidth range in the C-band. Further, the target operating bandwidth can be selected from 1540nm to 1560nm, or the target operating bandwidth can be selected from 1530nm to 1550nm.

[0033] For example, if the target operating bandwidth is selected as 1540nm to 1560nm, the first parameter is set to 3ps / km·nm, and the second parameter is set to 99.9999%, then the optimization objective is to ensure that the dispersion coefficient of the delay-frequency high linearity fiber is less than 3ps / km·nm within the range of 1540nm to 1560nm, and that the linear fitting correlation between the delay and wavelength at different wavelengths is better than 99.9999%. Within the aforementioned range, specific fiber parameters are further determined.

[0034] In addition to the C-band, the present invention can also move to shorter wavelengths (such as the O-band or E-band) or to longer wavelengths (such as the L-band).

[0035] When moving to shorter wavelengths (such as the O-band or E-band), the core radius can be appropriately reduced, and the relative refractive index of the second cladding can be fine-tuned to the upper limit of the range (e.g., close to 1.0%). This adjustment enhances waveguide dispersion, causing an overall "blue shift" in the dispersion profile, thereby moving the flat "dispersion plateau" to shorter wavelengths (e.g., around 1310 nm or below 1530 nm). Such fibers can be used in systems requiring distortion-free pulse processing in this band, such as pre-chirp management in certain biomedical imaging or short-range communications.

[0036] When moving towards longer wavelengths (such as the L-band), the radius of the third cladding can be appropriately increased to the upper limit of the range (e.g., close to 15 μm), and the absolute value of its negative refractive index can be reduced (e.g., close to -0.09%). This adjustment changes the cladding's ability to confine longer wavelengths, causing a "redshift" in the dispersion curve and extending the high linearity window to above 1565 nm. This type of fiber is suitable for dispersion compensation in high-power fiber amplifiers in the L-band, or for producing a flatter supercontinuum in this band.

[0037] Furthermore, the present invention can also take the dispersion coefficient and attenuation conditions that the time-delay-frequency high linearity optical fiber need to meet as additional optimization targets, and combine the dispersion coefficient variation value and the linear fitting correlation between the time delay and wavelength of different wavelengths to jointly determine the structural parameters of the relative refractive index and radius of each layer in the time-delay-frequency high linearity optical fiber.

[0038] For example, within the target operating bandwidth, the dispersion coefficient of the delay-frequency high linearity optical fiber is -100ps / nm·km to -300ps / nm·km, and the attenuation of the delay-frequency high linearity optical fiber is less than 0.6dB / km.

[0039] By optimizing parameters, optical fibers can achieve better performance. For example, by optimizing parameters, the final optical fiber can have a dispersion coefficient of -180 ps / nm·km to -220 ps / nm·km in the 20nm bandwidth range of the C-band, with a dispersion coefficient variation of less than 2 ps / nm·km in the 20nm bandwidth range, and an attenuation of less than 0.4dB / km in the range; at the same time, within the 20nm bandwidth range, the correlation between the delay and the wavelength is better than 99.9999%.

[0040] Furthermore, by controlling the doping ratio, losses can be further reduced, for example, to achieve an attenuation of less than 0.4 dB / km within a certain range. Specifically, in highly doped fibers, attenuation mainly originates from the intrinsic absorption of doping elements, microscopic defects in the silicate structure, scattering losses between the core and cladding interfaces, losses caused by stress at the core-cladding interface, and Rayleigh scattering introduced by fluctuations in the total material density during the fiber drawing process. Ge (Ge) in the doping system increases the refractive index and affects the viscosity of silicate materials, lowering their softening temperature. F (F) in the doping system decreases the refractive index and also alters the viscosity, lowering the softening point. Additionally, F can reduce silicon-oxygen bond breakage in silicate materials, reducing attenuation in specific wavelength bands or increasing hydrogen loss. Cl (Cl) has a significant impact on viscosity and also increases the refractive index in the doping system. Therefore, when using Ge and F co-doping in the fiber core, the content of hydroxyl groups can be reduced by F, decreasing the additional absorption generated by hydroxyl groups. However, excessive F can lead to an increase in Ge content at the same refractive index, resulting in greater intrinsic losses in Ge. Therefore, comprehensive control is necessary. Similarly, the core composition can be adjusted by combining F, Ge, and Cl to achieve a certain level of intrinsic absorption loss. Given a fixed core composition, if the core viscosity differs significantly from the cladding viscosity, it will introduce substantial interfacial stress and interfacial scattering loss during fiber drawing. Correspondingly, the F and Ge content of the cladding needs to be adjusted to bring the core viscosity closer to the cladding viscosity, thereby reducing loss.

[0041] The high-delay-frequency linearity optical fiber provided by this invention can achieve high linearity between delay and frequency, and has low attenuation performance, under the premise of a large absolute value of dispersion coefficient (i.e., high negative dispersion coefficient).

[0042] Secondly, the present invention provides a method for fabricating a time-delay-frequency high linearity optical fiber, comprising the following steps: Hollow quartz tubes with a target refractive index profile were prepared by MCVD or PCVD. The hollow quartz tube is melted and shrunk to obtain a solid doped glass core rod; The doped glass core rod is assembled with a pure quartz sleeve and then melted and shrunk to obtain a solid quartz rod. The solid quartz rod is drawn into a fiber to obtain a high time-delay-frequency linearity optical fiber; The high-delay-frequency linearity optical fiber includes a core and a first cladding, a second cladding, a third cladding, and a fourth cladding sequentially covering the core. The relative refractive index of the core ranges from 1.2% to 2.0%, and the radius ranges from 1 μm to 1.5 μm. The relative refractive index of the first cladding ranges from -0.7% to -0.3%, and the radius ranges from 1.5 μm to 6 μm. The relative refractive index of the second cladding ranges from 0.2% to 1.0%, and the radius ranges from 6 μm to 9 μm. The relative refractive index of the third cladding ranges from -0.6% to -0.09%, and the radius ranges from 9 μm to 15 μm. The fourth cladding is a pure silica layer with a radius ranging from 50 μm to 60 μm. The optimization objective is to ensure that the change in the dispersion coefficient of the optical fiber is less than the first parameter within the target operating bandwidth, and that the linear correlation between the delay and wavelength at different wavelengths is better than the second parameter. Within the above parameter range, the structural parameters of the relative refractive index and radius of each layer in the optical fiber are determined.

[0043] Wherein, the first parameter is 0 ps / km·nm to 4 ps / km·nm, and the second parameter is 99.999% to 99.9999%.

[0044] The target operating bandwidth can be O-band, E-band, C-band, or L-band. For example, the target operating bandwidth is a 20nm bandwidth range in the C-band, the target operating bandwidth is selected from 1540nm to 1560nm, or the target operating bandwidth is selected from 1530nm to 1550nm.

[0045] The dispersion coefficient of the time-delay-frequency high linearity optical fiber is -100ps / nm·km to -300ps / nm·km.

[0046] For example, by controlling the fabrication process, the correlation between the delay and wavelength in the high-delay-frequency linearity optical fiber within the target operating bandwidth can be better than 99.99995%, achieving high wavelength-delay linearity and ensuring a dispersion coefficient of less than -200 ps / km·nm.

[0047] In a further optimized scheme, within the target operating bandwidth, the dispersion curve of the time-delay-frequency high linearity optical fiber prepared by the present invention forms at least one flat region, and the dispersion slope within the flat region is close to zero.

[0048] When drawing the solid quartz rod, the dispersion curve of the optical fiber can be finely adjusted at the nanometer level by adjusting the drawing tension and the drawing diameter. Specifically, the drawing parameters include furnace temperature, drawing speed, and furnace gas flow rate; the control of the fabrication process mainly includes adjusting two online testing parameters: drawing tension and drawing diameter. By controlling these two parameters, the dispersion curve can be finely adjusted. High linearity is achieved by designing the profile so that the wavelength with a dispersion slope of 0 is controlled near the working wavelength, and then fine-tuning the drawing parameters to an accuracy of 1 nm. The above combined design enables the present invention to fabricate low-attenuation optical fibers with high negative dispersion coefficients and high time-delay-frequency linearity. That is, in the drawing step, the dispersion curve of the final optical fiber can be finely adjusted at the nanometer level by adjusting the drawing tension and the drawing diameter. This step is crucial for ensuring that the "dispersion platform" is accurately aligned with the target working wavelength (such as accurately aligned with 1540-1560 nm or 1530-1550 nm). This allows even different batches of optical fibers drawn from the same preform to have their performance peak locked within the precise wavelength range specified by the customer through adjustments to process parameters.

[0049] During the preparation process, the diameter of the solid doped glass core rod ranges from 20 mm to 50 mm, and the outer diameter of the solid quartz rod ranges from 80 mm to 200 mm.

[0050] See Figure 3 , Figure 3 The process flow diagram corresponding to the fabrication method of the time-delay-frequency high linearity optical fiber provided by the present invention is shown below. As described above, during the fabrication process, when the solid quartz rod is drawn into fibers, the dispersion curve of the optical fiber is finely adjusted at the nanometer level by regulating the drawing tension and drawing diameter. The process flow includes a fifth step: online monitoring of the optical fiber dispersion parameters, and a sixth step: testing all parameters of the optical fiber before warehousing. This invention achieves real-time feedback through online monitoring of the optical fiber dispersion coefficient, thereby enabling real-time control of the drawing parameters. Furthermore, the core rod design and deposition can be improved based on this real-time feedback. Based on the above process, dispersion parameter drift caused by preform fluctuations can be compensated for by adjusting the drawing parameters, resulting in an optical fiber with the target performance.

[0051] The fiber core can be co-doped with germanium, fluorine, and chlorine, or co-doped with germanium and fluorine; the first cladding can be co-doped with fluorine and chlorine; the second cladding can be co-doped with germanium, fluorine, and chlorine, or co-doped with germanium and fluorine; the third cladding can be co-doped with germanium, fluorine, and chlorine, or co-doped with germanium and fluorine; by controlling the doping ratio of germanium and fluorine, the attenuation of the high-delay-frequency linearity optical fiber is less than 0.6 dB / km within the operating bandwidth range.

[0052] The method for fabricating a high-delay-frequency linear optical fiber provided in the second aspect of the present invention corresponds to the method scheme for fabricating a high-delay-frequency linear optical fiber provided in the first aspect of the present invention. Therefore, the description of the first aspect of the present invention can also be used to understand the fabrication method provided in the second aspect of the present invention.

[0053] Thirdly, the present invention provides an application of the time-delay-frequency high linearity optical fiber as provided in the first aspect of the present invention, applying the time-delay-frequency high linearity optical fiber to supercontinuum generation or chirped pulse amplification.

[0054] By utilizing the linear time delay characteristics of the high time delay-frequency linearity optical fiber provided by this invention, it can be used as a dispersion management element or nonlinear medium in optical systems to optimize the pulse fidelity in chirped pulse amplification systems or improve the spectral flatness and coherence in the supercontinuum generation process.

[0055] Specifically, the high-delay-frequency linearity optical fiber provided by this invention can be applied to the following scenarios: (1) As a dispersion compensation element in a chirped pulse amplification system, it is used to broaden or compress chirped pulses with low distortion. That is, it can be applied to chirped pulse amplification systems in different bands: for example, to provide customized “distortion-free” broadened optical fibers that match the wavelength of ultrafast lasers operating at different center wavelengths such as 1μm, 1.5μm, and 2μm.

[0056] (2) As a nonlinear medium for supercontinuum generation, its linear time delay characteristics are used to obtain supercontinuum output with high flatness and high coherence. That is, it can be applied to the generation of high-quality supercontinuum in multiple bands: through customization, supercontinuum light sources with high flatness and high coherence can be manufactured in different target bands from visible light to mid-infrared, meeting different needs in fields such as optical coherence tomography and spectroscopy.

[0057] Furthermore, this invention can also be applied to dispersion management in high-speed optical communication systems. Although this invention focuses on nonlinear applications, its linear delay characteristics are also suitable for precise dispersion compensation of specific channels, reducing signal distortion.

[0058] This invention addresses the linear frequency broadening of pulses by developing a novel special optical fiber with high time-delay-frequency linearity. This fiber can linearly chirp ultrashort pulse signals, resulting in broadened pulse signals with no significant distortion and no significant shift in the center wavelength in the frequency domain. It also exhibits low tailing effect caused by third-order dispersion. Furthermore, based on the description of the fabrication method of the high-delay-frequency linearity optical fiber in the second aspect of this invention, the adjustable design flexibility of this invention greatly expands the application range of the optical fiber, no longer limited to a specific C-band sub-range, but also applicable to multiple bands such as O-band, E-band, and L-band. Any scenario requiring distortion-free pulse broadening / compression or highly coherent nonlinear spectral broadening within a specific band can be achieved by customizing the structural parameters of this optical fiber.

[0059] The invention will be further explained below using four embodiments, taking its application in C-band and O-band as examples.

[0060] Example 1: Example 1 provides a high-delay-frequency linearity optical fiber, the fabrication method of which includes: fabricating a core rod using PCVD process; depositing a certain doping design of quartz glass on the inner wall of a quartz-based hollow liner tube, achieving different refractive index structures through co-doping with germanium, fluorine, or chlorine; then melting and shrinking the deposited hollow quartz tube, controlling the melting and shrinking process of the core rod by controlling the temperature, speed, and internal pressure of the heating furnace, finally melting and shrinking it into a solid doped glass core rod with a diameter of approximately 22 mm; next, assembling the core rod with a pure quartz liner and melting and shrinking it to prepare a solid quartz rod with an outer diameter of 80 mm; finally, drawing it through a drawing tower to form an optical fiber with a high negative dispersion coefficient and high time-delay-frequency linearity with an outer diameter of 110 μm.

[0061] The structural parameters of the high-delay-frequency linearity optical fiber provided in Example 1 are shown in Table 1.

[0062] Table 1. Structural parameters of the high-delay-frequency linearity optical fiber provided in Example 1

[0063] This profile design enables the achievement of a high negative dispersion coefficient. This process route reduces defects at the junction of the core rod and the sleeve in the preform, as well as on the surface of the preform, thus reducing weak points in strength during the fiber drawing process. By changing the drawing parameters (mainly drawing tension and drawing diameter), the drawing diameter is controlled at around 108 μm, and the tension is controlled at around 450 g. Based on online dispersion testing / offline rapid testing, the fiber diameter and drawing tension are quickly corrected, avoiding the influence of geometric fluctuations / doping inhomogeneities of the fiber preform on the dispersion flat region. This corrects the dispersion coefficient curve of the fiber, achieving a dispersion coefficient of -205 ps / km·nm and a time-delay-frequency linearity of 99.99995%.

[0064] The attenuation and dispersion coefficient test data of the optical fiber provided in Example 1 correspond to sample number 1 in Tables 4 and 5, respectively. The dispersion curve varies by less than 1.2 ps / km·nm in the range of 1540nm to 1560nm. The time delay and wavelength in the range of 1540nm to 1560nm were linearly fitted, and the correlation was 99.99996%.

[0065] Example 2: Example 2 provides a high-delay-frequency linearity optical fiber. The difference between Example 2 and Example 1 is that: (1) the diameter of the preform after melting and shrinking (i.e. the diameter of the solid doped glass core rod) is 23 mm; (2) the structural parameters of the high-delay-frequency linearity optical fiber provided in Example 2 are shown in Table 2.

[0066] Table 2 Structural parameters of the high-delay-frequency linearity optical fiber provided in Example 2

[0067] Example 2 modifies the fiber drawing parameters (mainly drawing tension and drawing diameter) to control the drawing diameter at approximately 112 μm and the tension at approximately 380 g. Based on online dispersion testing / offline rapid testing, the fiber diameter and drawing tension are quickly corrected to avoid the influence of geometric fluctuations / doping inhomogeneities of the fiber preform on the dispersion flat region. This corrects the fiber's dispersion coefficient curve, resulting in a fiber with a time-delay-frequency linearity of 99.99995% in the 1540 nm to 1560 nm range. The dispersion curve changes by less than 1.1 ps / km·nm in the 1540 nm to 1560 nm range. The attenuation test data and dispersion coefficient test data of the fiber provided in Example 2 correspond to sample number 2 in Tables 4 and 5, respectively.

[0068] Example 3: Example 3 provides a high-delay-frequency linearity optical fiber. The difference between Example 3 and Example 1 is that: (1) the diameter of the preform after fusion shrinkage is 21mm; (2) the structural parameters of the high-delay-frequency linearity optical fiber provided in Example 3 are shown in Table 3.

[0069] Table 3. Structural parameters of the high-delay-frequency linearity optical fiber provided in Example 3.

[0070] The attenuation test data and dispersion coefficient test data of the optical fiber provided in Example 3 correspond to sample number 3 in Tables 4 and 5, respectively.

[0071] This profile design achieves a high negative dispersion coefficient and high linearity by shifting the window to 1530nm to 1550nm. By modifying the drawing parameters (primarily drawing tension and diameter), the drawing diameter is controlled at approximately 105µm, and the tension at approximately 450g. Based on online dispersion testing and rapid offline testing, the fiber diameter and drawing tension are quickly corrected, avoiding the influence of geometric fluctuations / doping inhomogeneities of the fiber preform on the dispersion flat region. This corrects the fiber's dispersion coefficient curve, resulting in an fiber with a 1540nm dispersion coefficient of -270ps / km·nm and a time-delay-frequency linearity of 99.9998%. Testing showed that the dispersion coefficient variation is less than 3ps / km·nm in the 1530nm to 1560nm range, and the time-delay-frequency linear fit is better than 99.999% in the 1530nm to 1550nm range.

[0072] The attenuation test results and dispersion coefficient test results of Examples 1 to 3 are shown in Table 4 and Table 5, respectively.

[0073] Table 4. Attenuation test results of the sample optical fibers corresponding to the three embodiments.

[0074] Table 5. Dispersion coefficient test results of the sample optical fibers corresponding to the three embodiments.

[0075] In summary, the optical fibers corresponding to Examples 1 to 3 all exhibit dispersion coefficient variations of less than 3 ps / km·nm within the target operating bandwidth, with high absolute dispersion coefficient values ​​(greater than 200 ps / km·nm) and attenuation values ​​of less than 0.6 dB / km within the range. Furthermore, within the target operating bandwidth, the correlation between time delay and wavelength is better than 99.999%. Figure 4 As shown, it should be noted that Figure 4 China has uniformly reduced the benchmark by 4,928,000 ps / km, that is Figure 4 This is a schematic diagram of the frequency-time delay relationship (relative time delay). This invention can provide low-attenuation optical fibers with high negative dispersion coefficients and high time-delay-frequency linearity.

[0076] Example 4: Example 4 aims to achieve a time-delay-wavelength high linear fiber with a negative dispersion coefficient by setting the high linearity platform in the O-band (1260nm to 1360nm) through a blue-shift strategy.

[0077] Design adjustment rationale: To shift the dispersion plateau towards shorter wavelengths (blue shift), it is necessary to appropriately reduce the core radius and fine-tune the relative refractive index of the second cladding to the upper limit of the range (e.g., close to 1.0%). This adjustment can enhance the waveguide dispersion effect.

[0078] Table 6 Structural parameters of the high-delay-frequency linearity optical fiber provided in Example 4

[0079] Example 4 sets the optimization objective as having a dispersion coefficient variation of less than 3 ps / km·nm in the range of 1300nm to 1320nm and a linear fitting correlation better than 99.9999%.

[0080] Table 7 Test performance results of the high delay-frequency linearity optical fiber provided in Example 4

[0081] The above embodiments provide structural parameters and test performance results of high delay-frequency linearity optical fibers with target operating bandwidth in C-band and O-band. The target operating bandwidth of the present invention can also be in E-band or L-band, and the target performance can still be achieved.

[0082] In summary, the optical fiber provided by this invention exhibits high time-delay-frequency linearity, ensuring pulse distortion-free operation during pulse compression or broadening. This invention provides highly customized, high-performance key photonic devices for various ultrafast optical systems and broadband light source applications requiring distortion-free pulse operation.

[0083] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A time-delay-frequency high linearity optical fiber, characterized in that, include: The fiber core, and a first cladding, a second cladding, a third cladding, and a fourth cladding sequentially covering the fiber core; The relative refractive index of the fiber core ranges from 1.2% to 2.0%, and the radius ranges from 1 μm to 1.5 μm. The first cladding layer has a relative refractive index ranging from -0.7% to -0.3% and a radius ranging from 1.5 μm to 6 μm. The second cladding has a relative refractive index ranging from 0.2% to 1.0% and a radius ranging from 6 μm to 9 μm. The third cladding has a relative refractive index ranging from -0.6% to -0.09% and a radius ranging from 9 μm to 15 μm. The fourth cladding layer is a pure quartz layer with a radius ranging from 50 μm to 60 μm. Within the aforementioned parameter range, the structural parameters of the relative refractive index and radius of each layer in the optical fiber are determined with the optimization objective being that the change in the dispersion coefficient of the optical fiber is less than the first parameter within the target working bandwidth, and the correlation between the time delay and the wavelength linear fitting is better than the second parameter.

2. The high-delay-frequency linearity optical fiber according to claim 1, characterized in that, The target operating bandwidth belongs to the O-band, E-band, C-band, or L-band; the first parameter is 0 ps / km·nm to 4 ps / km·nm, and the second parameter is 99.999% to 99.9999%; the dispersion coefficient of the time-delay-frequency high linearity optical fiber is -100 ps / nm·km to -300 ps / nm·km.

3. The high-delay-frequency linearity optical fiber according to claim 1, characterized in that, Within the target operating bandwidth, the dispersion curve of the delay-frequency high linearity optical fiber forms at least one flat region, in which the dispersion slope is close to zero.

4. The high-delay-frequency linearity optical fiber according to claim 1, characterized in that, Within the target operating bandwidth, the attenuation of the high-delay-frequency linearity optical fiber is less than 0.6 dB / km.

5. A method for fabricating a time-delay-frequency high linearity optical fiber, characterized in that, Includes the following steps: Hollow quartz tubes with target refractive index profiles were prepared using MCVD or PCVD. The hollow quartz tube is melted and shrunk to obtain a solid doped glass core rod; The doped glass core rod is assembled with a pure quartz sleeve and then melted down to obtain a solid quartz rod. The solid quartz rod is drawn into a fiber to obtain a high time-delay-frequency linearity optical fiber; The high-delay-frequency linearity optical fiber includes a core and a first cladding, a second cladding, a third cladding, and a fourth cladding sequentially covering the core. The relative refractive index of the core ranges from 1.2% to 2.0%, and the radius ranges from 1 μm to 1.5 μm. The relative refractive index of the first cladding ranges from -0.7% to -0.3%, and the radius ranges from 1.5 μm to 6 μm. The relative refractive index of the second cladding ranges from 0.2% to 1.0%, and the radius ranges from 6 μm to 9 μm. The relative refractive index of the third cladding ranges from -0.6% to -0.09%, and the radius ranges from 9 μm to 15 μm. The fourth cladding is a pure silica layer with a radius ranging from 50 μm to 60 μm. The optimization objective is to ensure that the change in the dispersion coefficient of the optical fiber is less than the first parameter within the target operating bandwidth, and that the linear correlation between the delay and wavelength at different wavelengths is better than the second parameter. Within the above parameter range, the structural parameters of the relative refractive index and radius of each layer in the optical fiber are determined.

6. The method for fabricating a high-delay-frequency linearity optical fiber according to claim 5, characterized in that, The target operating bandwidth belongs to the O-band, E-band, C-band, or L-band; the first parameter is 0 ps / km·nm to 4 ps / km·nm, and the second parameter is 99.999% to 99.9999%; the dispersion coefficient of the time-delay-frequency high linearity optical fiber is -100 ps / nm·km to -300 ps / nm·km.

7. The method for fabricating a high-delay-frequency linearity optical fiber according to claim 5, characterized in that, Within the target operating bandwidth, the dispersion curve of the delay-frequency high linearity optical fiber forms at least one flat region, in which the dispersion slope is close to zero.

8. The method for fabricating a high-delay-frequency linearity optical fiber according to claim 5, characterized in that, When drawing the solid quartz rod, the dispersion curve of the optical fiber is finely adjusted at the nanometer level by adjusting the drawing tension and the drawing diameter.

9. The method for fabricating a high-delay-frequency linearity optical fiber according to claim 5, characterized in that, The fiber core is co-doped with germanium, fluorine, and chlorine, or co-doped with germanium and fluorine; the first cladding is co-doped with fluorine and chlorine; the second cladding is co-doped with germanium, fluorine, and chlorine, or co-doped with germanium and fluorine; the third cladding is co-doped with germanium, fluorine, and chlorine, or co-doped with germanium and fluorine; by controlling the doping ratio of germanium and fluorine, the attenuation of the high-delay-frequency linearity optical fiber within the target operating bandwidth is less than 0.6 dB / km.

10. An application of a time-delay-frequency high linearity optical fiber as described in any one of claims 1 to 4, characterized in that, High-delay-frequency linearity optical fibers can be used for supercontinuum generation or chirped pulse amplification.

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