A hollow-core photonic crystal fiber loop pigtail winding implementation system and winding method

Abstract

The invention relates to a hollow-core photonic crystal optical fiber loop pigtail winding implementation system and winding method. The system comprises: a piezoelectric ceramic sleeve for allowing two pigtails of the optical fiber loop to be coiled in parallel and in the same direction on its outer ring surface; a wavelength tunable laser for generating corresponding required optical power within a specific wavelength range, wherein the emitted light wave is coupled and input into the pigtail at one end of the hollow-core photonic crystal optical fiber loop through a bare optical fiber adapter, and the light wave is transmitted in the hollow-core photonic crystal optical fiber loop for one cycle and then emitted from the pigtail at the other end; a first lens, a polarizer, and a second lens arranged in sequence, for sequentially collimating, polarizing, and focusing the light wave emitted from the pigtail at the other end; a near-infrared CCD camera for detecting and receiving the focused light wave and transmitting it to a host computer; and the host computer for changing the bending radius and the coiling tension of the optical fiber loop pigtail by expanding the piezoelectric ceramic sleeve, thereby ultimately enabling the hollow-core photonic crystal optical fiber loop to have a high-mode-purity transmission effect.

Description

Technical Field

[0001] The invention belongs to the technical field of optical fiber gyroscopes, and in particular relates to a hollow-core photonic crystal optical fiber loop pigtail winding implementation system and a winding method. Background Art

[0002] Fiber optic gyros (FOGs) are high-precision sensors that utilize the Sagnac effect to measure the angular velocity of an object. Interferometric FOGs utilize multiple turns of optical fiber to exponentially improve measurement accuracy. However, this increased fiber length also makes the system more susceptible to environmental influences such as temperature and magnetic fields, necessitating more stringent engineering requirements such as symmetrical windings and more complex electromagnetic shielding. Whether methods can be found within the optical fiber itself to overcome this environmental sensitivity has long been a concern for researchers in this field.

[0003] Hollow-core photonic crystal fiber uses a periodic lattice cladding structure to form a photonic bandgap effect, which confines light waves to propagate in the air core and uses air as the transmission medium. The light waves are no longer sensitive to the influence of heat, magnetism, and radiation in the environment, and ideal high-stability optical transmission can be achieved. It is expected to solve the problem of further improving the environmental adaptability of high-precision fiber-optic gyroscopes at the optical fiber material level.

[0004] In hollow core photonic crystal fiber, in addition to the fundamental mode LP 01 In addition, if the refractive index curves of other high-order light transmission modes are also in the photonic bandgap, they can all achieve low-loss transmission in the fiber core. The visible photonic bandgap cannot distinguish the core mode. Therefore, the photonic bandgap hollow-core photonic crystal fiber is essentially a multimode fiber. When multiple light transmission modes coexist, the fundamental mode LP 01 Intermodal interference occurs between the high-order modes, and the interference light intensity can be expressed by formula (1). However, the Sagnac effect in the fiber optic gyroscope is ideally based on the fundamental mode LP. 01 The inter-mode interference caused by the bidirectional transmission will form a multipath interference effect in the optical path of the fiber ring, which, combined with the Sagnac effect, will seriously affect the stability of the gyroscope output.

[0005]

[0006] Where η1 and η2 are the excitation energy distribution ratios of the fundamental mode and a certain higher-order mode, r is the radial coordinate of the optical fiber, e1(r) and e2(r) are the electric field distributions of the two modes, respectively. and Δφ is the phase difference accumulated between the two modes during optical fiber transmission.

[0007]

[0008] Where n eff1 and n eff2are the effective refractive indices of the fundamental mode and a certain higher-order mode, respectively; λ is the light transmission wavelength; and L is the length of the hollow-core photonic crystal fiber.

[0009] By introducing a diverter hole structure in the cladding on both sides of the core of the hollow-core photonic crystal fiber, the refractive index between the diverter hole fundamental mode and the high-order mode of the fiber core is matched, thereby achieving a phase matching effect. The high-order mode of the fiber core will be resonantly coupled to the high-loss transmission in the diverter hole fundamental mode and eventually leaked out, thereby improving the transmission mode purity of the hollow-core photonic crystal fiber.

[0010] The inclusion of diverter holes in the cladding of hollow-core photonic crystal fibers complicates the cladding structure. The size of the diverter holes is strongly correlated with the refractive index of the fundamental mode they construct, and thus with the leakage efficiency of the core's higher-order modes. This complex cladding structure complicates fiber drawing, making it difficult to maintain microstructure dimensional accuracy over long fiber lengths. This creates uncontrollable factors in suppressing mode purity noise in practical applications of hollow-core photonic crystal fibers in gyroscope loops. Summary of the Invention

[0011] In view of the deficiencies in the prior art, the present invention provides a hollow-core photonic crystal optical fiber loop pigtail winding system and a winding method.

[0012] One of the above-mentioned purposes of the present invention is achieved by the following technical solutions:

[0013] A hollow-core photonic crystal fiber loop pigtail winding implementation system, characterized by comprising: a wavelength tunable laser, a piezoelectric ceramic sleeve, a first lens, a polarizer, a second lens, a near-infrared CCD camera, a host computer, and a piezoelectric ceramic driver; the wavelength tunable laser, the first lens, the polarizer, the second lens, and the near-infrared CCD camera constitute a detection unit; the piezoelectric ceramic sleeve and the piezoelectric ceramic driver constitute a pigtail winding deformation action unit;

[0014] The piezoelectric ceramic sleeve is used for the two pigtails of the optical fiber ring to be coiled in parallel and in the same direction on its outer ring surface, and the pigtails are coated with ultraviolet curing colloid;

[0015] The wavelength tunable laser is used to generate the required optical power within a specific wavelength range. The light wave emitted by the laser is coupled into the pigtail at one end of the hollow-core photonic crystal fiber loop through a bare fiber adapter. After transmitting one cycle in the hollow-core photonic crystal fiber loop, the light wave is emitted from the pigtail at the other end of the fiber loop.

[0016] The first lens, the polarizer and the second lens are arranged in sequence in front and behind, and are used to collimate, polarize and focus the light waves emitted from the other pigtail of the optical fiber loop in sequence;

[0017] The near-infrared CCD camera is used to detect and receive the focused light waves and send them to the host computer;

[0018] The host computer is used to control the wavelength tunable laser to change the output wavelength, thereby realizing near-infrared CCD camera detection and reception at multiple wavelengths; and is used to perform data processing on the multi-wavelength CCD camera detection and reception signals based on the spatial and spectral resolution imaging method to obtain the optical transmission mode field components of the hollow-core photonic crystal fiber ring, and to control the piezoelectric ceramic driver to change the control voltage of the piezoelectric ceramic sleeve according to the optical transmission mode field components to realize the expansion of the piezoelectric ceramic sleeve. The expansion of the piezoelectric ceramic sleeve changes the bending radius and winding tension of the optical fiber ring pigtail, ultimately making the hollow-core photonic crystal fiber ring have a high mode purity transmission effect.

[0019] Moreover, the wavelength tunable laser used is used to achieve ultra-narrow linewidth laser output, which can support the measurement of ring mode components of kilometer-long hollow-core photonic crystal fiber.

[0020] Furthermore, the near-infrared CCD camera is used to realize two-dimensional surface measurement of the light spot, so as to improve the measurement speed of the pattern component.

[0021] The second object of the present invention is achieved by the following technical solutions:

[0022] A coiling method based on the hollow-core photonic crystal fiber loop pigtail coiling implementation system is characterized by comprising the following steps:

[0023] Step 1: Bundle two pigtails of a hollow-core photonic crystal fiber ring with a diverter hole design that output fibers in opposite directions together, tightly and parallelly coil them on the outer surface of a piezoelectric ceramic sleeve in the same direction, and coat the pigtails with a UV-curable colloid during the coiling process;

[0024] Step 2: After the pigtail is coiled, a voltage is applied to the piezoelectric ceramic sleeve to control its expansion. During this process, the optimal voltage control amount is selected by measuring the light transmission mode component of the ring, so that the hollow-core photonic crystal fiber ring has a high mode purity transmission effect;

[0025] Step 3: When the hollow-core photonic crystal fiber ring has a high mode purity transmission effect, the ring pigtail is cured by ultraviolet irradiation and the piezoelectric ceramic sleeve is removed. The ring pigtail winding process is completed to obtain a high mode purity hollow-core fiber ring.

[0026] The present invention has the following advantages and positive effects:

[0027] 1. The present invention tightly spirally coils the two pigtails of a hollow-core photonic crystal fiber loop around a piezoelectric ceramic sleeve to stimulate a refractive index tilting effect. Controlling the expansion of the piezoelectric ceramic sleeve based on the detection results of the transmission mode components of the fiber loop optimizes the refractive index matching efficiency between the core high-order mode and the diverter hole fundamental mode. The core high-order mode can be completely leaked. After the pigtails of the loop are cured and the piezoelectric ceramic sleeve is removed, the purity of the transmission mode of the hollow-core photonic crystal fiber loop can be improved, which is beneficial for suppressing mode purity-related noise in the interferometric hollow-core microstructure fiber gyroscope.

[0028] 2. The present invention combines the two pigtails of the hollow-core photonic crystal fiber ring and tightly coils them into a ring in the same direction and in parallel, without forming a Sagnac interference area. The pigtails are positioned adjacent to each other symmetrically along the midpoint of the ring, and the temperature performance of the ring's Shupe effect is not affected by temperature changes. This pigtail coiling processing method does not introduce negative noise. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a schematic diagram of the end face of a hollow-core photonic crystal fiber with a diverter hole design;

[0030] Figure 2 This is a schematic diagram of the refractive index mismatch between the fundamental mode of the split hole and the high-order mode of the fiber core in the loose state of the optical fiber;

[0031] Figure 3 This is a diagram of the refractive index tilt effect induced by random twisting and tight coiling of optical fiber;

[0032] Figure 4 Schematic diagram of the hollow-core photonic crystal fiber loop pigtail winding system of the present invention;

[0033] In the figure: 1. Wavelength tunable laser; 2. Hollow-core photonic crystal fiber loop pigtail; 3. Piezoelectric ceramic sleeve; 4. Hollow-core photonic crystal fiber loop; 5. First lens; 6. Polarizer; 7. Second lens; 8. Near-infrared CCD camera; 9. Host computer; 10. Piezoelectric ceramic driver.

[0034] Figure 5 This is the original transmission mode field component diagram of the hollow-core photonic crystal fiber ring;

[0035] Figure 6 This is a transmission mode field component diagram of the hollow-core photonic crystal optical fiber after the pigtail is coiled. DETAILED DESCRIPTION

[0036] The structure of the present invention will be further described below with reference to the accompanying drawings and through examples. It should be noted that the present examples are descriptive rather than restrictive.

[0037] Figure 1This is a schematic diagram of the end face of a hollow-core photonic crystal fiber with a diverter hole design. It is drawn from a single material of silica, and the cladding contains a periodic lattice structure. It has the characteristics of a two-dimensional photonic crystal structure, which can form a photonic bandgap effect to confine light to the air core at the center of the optical fiber for transmission. In addition, two diverter holes (S1 and S2) are set on the left and right sides of the air core. The diverter holes also use the photonic bandgap effect constructed by the periodic lattice structure cladding to form the light transmission fundamental mode. The transmission refractive index of the fundamental mode can be controlled by the size of the diverter hole structure to make it equal to the refractive index of the core high-order mode at the center of the optical fiber. At this time, the diverter hole fundamental mode is phase-matched with the core high-order mode, and the core high-order mode will be resonantly coupled into the diverter hole for leakage. Therefore, the core transmission mode purity of the hollow-core photonic crystal fiber is improved.

[0038] Figure 2 This is a schematic diagram of the refractive index mismatch between the fundamental mode of the diverter hole and the high-order mode of the core in the loose state of the hollow-core photonic crystal fiber. The introduction of the diverter hole design in the cladding of the hollow-core photonic crystal fiber increases the complexity of the cladding structure. The size of the diverter hole is strongly related to the refractive index of the fundamental mode it constructs, and thus is strongly related to the leakage efficiency of the high-order mode of the core. The complex cladding structure is bound to increase the difficulty of drawing the optical fiber, and the dimensional accuracy and consistency of the diverter hole microstructure cannot be well maintained over long optical fiber distances. The dimensional accuracy of the diverter hole is difficult to guarantee under realistic conditions, resulting in unequal refractive indices between the fundamental mode of the diverter hole and the high-order mode of the core. The refractive index of the internal mode in the loose state of the optical fiber is as follows. Figure 2 As shown in the figure, the failure of phase matching causes the high-order modes of the core to be unable to leak out of the core and dissipate, and thus there are uncontrollable factors in the effect of improving the purity of the light transmission mode of the hollow-core photonic crystal fiber.

[0039] Figure 3 This diagram illustrates the refractive index tilt effect induced by randomly twisting and tightly coiling a hollow-core photonic crystal fiber. When bent and coiled, a hollow-core photonic crystal fiber induces a refractive index tilt on the fiber end face. The direction and extent of this refractive index tilt change are determined by the fiber twist angle, bend radius, and coiling tension. In a loosely coiled hollow-core photonic crystal fiber with a splitter hole design, there is a refractive index mismatch between the splitter hole fundamental mode and the core's higher-order modes. When the fiber is randomly twisted and tightly coiled, the refractive indices of both the splitter hole fundamental mode and the core's higher-order modes change to varying degrees, resulting in a large number of random, discrete instances of refractive index matching between the splitter hole fundamental mode and the core's higher-order modes along the fiber's length. This twist-induced refractive index tilt on the fiber surface randomly and discretely alters the phase matching relationship between the splitter hole fundamental mode and the core's higher-order modes. The integrated effect over the entire fiber length ensures that the core's higher-order modes are fully resonantly coupled into the splitter hole for leakage control, thereby improving the optical transmission mode purity of the hollow-core photonic crystal fiber.

[0040] Figure 4This is a schematic diagram of the hollow-core photonic crystal fiber loop pigtail winding system of the present invention. The winding method using the winding system is: the two pigtails of the hollow-core photonic crystal fiber loop with a diversion hole design that output the fiber in opposite directions are bundled together and wound tightly, in parallel and in the same direction on a piezoelectric ceramic sleeve. During the winding process, the pigtails are coated with ultraviolet-curing colloid. After the pigtails are wound, voltage is applied to the piezoelectric ceramic sleeve to control their expansion. During this period, the optimal voltage control amount is selected by measuring the light transmission mode component of the loop to ensure that the hollow-core photonic crystal fiber loop has a high-mode purity transmission effect. In this state, the winding position of the loop pigtail is cured by ultraviolet irradiation and the piezoelectric ceramic sleeve is removed. The loop pigtail winding process is completed, and the obtained high-mode-purity hollow-core fiber loop is beneficial to suppressing mode purity-related noise in the hollow-core photonic crystal fiber gyroscope.

[0041] The winding system mainly consists of a wavelength tunable laser 1, a piezoelectric ceramic sleeve 3, a first lens 5, a polarizer 6, a second lens 7, a near-infrared CCD camera 8, a host computer 9 and a piezoelectric ceramic driver 10.

[0042] A wavelength-tunable laser is used to generate the required optical power within a specific wavelength range. The emitted lightwave is coupled into a pigtail at one end of a hollow-core photonic crystal fiber loop through a bare fiber adapter. After transmitting one cycle within the hollow-core photonic crystal fiber loop, the lightwave exits the pigtail at the other end of the loop. The two pigtails (2) in the loop are coiled in parallel and in the same direction around a piezoelectric ceramic sleeve and coated with a UV-curable colloid. The lightwaves emitted from the pigtails pass sequentially through a first lens, a polarizer, and a second lens for collimation, polarization, and focusing. The focused lightwaves are detected and received by a near-infrared CCD camera and transmitted to a host computer. The host computer controls the wavelength-tunable laser to change its output wavelength, enabling near-infrared CCD camera detection and reception at multiple wavelengths. The host computer processes the multi-wavelength CCD camera detection and reception signals based on spatially and spectrally resolved imaging methods to obtain the optical transmission mode field components of the hollow-core photonic crystal fiber loop. The host computer controls the piezoelectric ceramic driver to vary the control voltage of the piezoelectric ceramic sleeve, causing the piezoelectric ceramic sleeve to expand. This changes the bending radius and winding tension of the hollow-core photonic crystal fiber (HCPF) pigtail coiled above it. This, in turn, alters the phase matching between the fundamental mode of the bypass hole within the pigtail and the higher-order modes of the fiber core, resulting in changes in the optical transmission mode field composition of the HCPF ring. Based on the optical transmission mode composition of the ring, the optimal piezoelectric ceramic driver voltage control value is selected to achieve high-mode-purity transmission of the HCPF ring. Under high-mode-purity conditions, the coiled area of ​​the pigtail is cured by ultraviolet irradiation and the piezoelectric ceramic sleeve is removed, resulting in a high-mode-purity HCPF ring.

[0043] Among them, the wavelength tunable laser used achieves ultra-narrow linewidth laser output, which can support the measurement of ring mode components of kilometer-level hollow-core photonic crystal fiber.

[0044] The near-infrared CCD camera used realizes two-dimensional surface measurement of the light spot, which can improve the speed of pattern component measurement;

[0045] The principle of the spatial and spectral resolved imaging method used to measure the transmission mode components of optical fibers is based on the interference between the fundamental mode and the higher-order modes. If there are higher-order modes of optical transmission in the optical fiber to be tested, there will be different group delays between the modes during the optical transmission process. Any two modes in the hollow-core photonic crystal fiber ring to be tested will form a spatial superposition on the photosensitive surface of the near-infrared CCD camera and produce a two-dimensional plane interference image. By using a wavelength tunable laser to perform wavelength scanning, the inter-mode spectral interference signals at different wavelengths can be recorded. By performing Fourier transform spectrum analysis on the two-dimensional plane spectral interference signal, different mode beats can be obtained at different relative group delay positions, thereby imaging the optical fiber transmission mode components.

[0046] Figure 5 This is a schematic diagram of the original transmission mode field components of the hollow-core photonic crystal fiber ring. When the pigtail is not coiled, the fiber transmission inside the hollow-core photonic crystal fiber ring is 01 There are also higher-order modes, such as LP 11 LP 21 wait.

[0047] Figure 6 This is a schematic diagram of the transmission mode field components after the hollow-core photonic crystal fiber ring pigtail coiling process. The two pigtails of the hollow-core photonic crystal fiber ring with a diverter hole design are bundled together and coiled tightly and in parallel in the same direction. The pigtail coiling diameter and tension are fine-tuned by the piezoelectric ceramic sleeve to obtain ideal hollow-core photonic crystal fiber ring fundamental mode transmission, thereby improving the purity of the optical fiber transmission mode.

[0048] In summary, the present invention proposes a hollow-core photonic crystal fiber loop pigtail winding implementation system and winding method based on the refractive index tilt effect, specifically: after the hollow-core photonic crystal fiber with a diverter hole design is wound into a ring, the two loop pigtails with opposite fiber output directions are bundled together, and then coated with ultraviolet glue and tightly wound on a piezoelectric ceramic sleeve in parallel. The pigtail is twisted and bent to produce a fiber refractive index tilt effect, which changes the refractive index matching between the high-order mode of the fiber core and the fundamental mode of the diverter hole. The refractive index matching efficiency can be actively adjusted by applying voltage control to the piezoelectric ceramic sleeve. The optical fiber loop transmission mode detection unit equipped in the implementation system can be used to obtain the optimal piezoelectric ceramic sleeve voltage control amount, so as to obtain a hollow-core photonic crystal fiber loop with high mode purity transmission effect. In this state, the loop pigtail winding position is cured by ultraviolet irradiation and the piezoelectric ceramic sleeve is removed. The high-mode purity hollow-core fiber loop is beneficial to suppressing mode purity related noise in the hollow-core photonic crystal fiber gyroscope.

Claims

1. A hollow core photonic crystal fiber pigtail winding implementation system, characterized by: It includes a wavelength tunable laser, a piezoelectric ceramic sleeve, a first lens, a polarizer, a second lens, a near-infrared CCD camera, a host computer and a piezoelectric ceramic driver; the wavelength tunable laser, the first lens, the polarizer, the second lens and the near-infrared CCD camera constitute a detection unit; the piezoelectric ceramic sleeve and the piezoelectric ceramic driver constitute a pigtail coiling deformation action unit; The piezoelectric ceramic sleeve is used for the two pigtails of the optical fiber ring to be coiled in parallel and in the same direction on its outer ring surface, and the pigtails are coated with ultraviolet curing colloid; The wavelength tunable laser is used to generate the required optical power within a specific wavelength range. The light wave emitted by the laser is coupled into the pigtail at one end of the hollow-core photonic crystal fiber loop through a bare fiber adapter. After transmitting one cycle in the hollow-core photonic crystal fiber loop, the light wave is emitted from the pigtail at the other end of the fiber loop. The first lens, the polarizer and the second lens are arranged in sequence in front and back, and are used to collimate, polarize and focus the light waves emitted from the pigtail at the other end of the optical fiber loop in sequence; The near-infrared CCD camera is used to detect and receive the focused light waves and send them to the host computer; The host computer is used to control the wavelength tunable laser to change the output wavelength, thereby realizing near-infrared CCD camera detection and reception at multiple wavelengths; and is used to perform data processing on the multi-wavelength CCD camera detection and reception signals based on the spatial and spectral resolution imaging method to obtain the optical transmission mode field components of the hollow-core photonic crystal fiber ring, and to control the piezoelectric ceramic driver to change the control voltage of the piezoelectric ceramic sleeve according to the optical transmission mode field components to realize the expansion of the piezoelectric ceramic sleeve. The expansion of the piezoelectric ceramic sleeve changes the bending radius and winding tension of the optical fiber ring pigtail, ultimately making the hollow-core photonic crystal fiber ring have a high mode purity transmission effect.

2. The hollow core photonic crystal fiber pigtail winding implementation system according to claim 1, characterized in that: The wavelength tunable laser used is used to achieve ultra-narrow linewidth laser output, which can support the measurement of ring mode components of kilometer-long hollow-core photonic crystal fiber.

3. The hollow core photonic crystal fiber pigtail winding implementation system according to claim 1, characterized in that: The near-infrared CCD camera is used to realize two-dimensional surface measurement of the light spot to improve the measurement speed of the pattern component.

4. A method for winding a hollow-core photonic crystal fiber loop pigtail according to any one of claims 1 to 3, characterized in that: The steps include: Step 1: Bundle two pigtails of a hollow-core photonic crystal fiber ring with a diverter hole design that output fibers in opposite directions together, tightly and parallelly coil them on the outer surface of a piezoelectric ceramic sleeve in the same direction, and coat the pigtails with a UV-curable colloid during the coiling process; Step 2: After the pigtail is coiled, a voltage is applied to the piezoelectric ceramic sleeve to control its expansion. During this process, the optimal voltage control amount is selected by measuring the light transmission mode component of the ring, so that the hollow-core photonic crystal fiber ring has a high mode purity transmission effect; Step 3: When the hollow-core photonic crystal fiber ring has a high mode purity transmission effect, the ring pigtail is cured by ultraviolet irradiation and the piezoelectric ceramic sleeve is removed. The ring pigtail winding process is completed to obtain a high mode purity hollow-core fiber ring.

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