Coiling implementation system and coiling method for tail fiber of hollow-core photonic crystal fiber loop

Abstract

The invention relates to a hollow-core photonic crystal fiber loop tail fiber coiling implementation system and a coiling method. The piezoelectric ceramic sleeve is used for winding two tail fibers of the optical fiber ring on the outer ring surface of the piezoelectric ceramic sleeve in parallel in the same direction; the wavelength tunable laser is used for generating corresponding required optical power in a specific wavelength range, light waves emitted by the wavelength tunable laser are coupled and input into a tail fiber at one end of the hollow-core photonic crystal fiber loop through the bare fiber adapter, and the light waves are transmitted for a circle in the hollow-core photonic crystal fiber loop and then are emitted from a tail fiber at the other end of the hollow-core photonic crystal fiber loop; the first lens, the polarizer and the second lens are sequentially arranged from front to back and are used for sequentially collimating, polarizing and focusing light waves emitted from the tail fiber at the other end; the near-infrared CCD camera is used for detecting and receiving the focused light waves and sending the light waves to the upper computer; and the upper computer changes the bending radius and the coiling tension of the tail fiber of the optical fiber ring through the expansion of the piezoelectric ceramic sleeve, and finally enables the hollow-core photonic crystal optical fiber ring 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 gyroscopes are high-precision sensors that use the Sagnac effect to measure the angular velocity of an object. Interferometric fiber optic gyroscopes increase measurement accuracy exponentially by winding multiple turns of optical fiber. However, the increase in fiber length also makes the system more susceptible to environmental influences such as temperature and magnetic fields, bringing more demanding engineering requirements such as symmetrical winding and more complex electromagnetic shielding. Whether it is possible to find a way to overcome environmental sensitivity from the optical fiber itself is a question that researchers in this field have always been concerned about.

[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. 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 from 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 optical transmission modes are also in the photon bandgap, they can all achieve low-loss transmission in the fiber core. It can be seen that the photon bandgap cannot distinguish the core mode. Therefore, the photon bandgap hollow-core photonic crystal fiber is essentially a multimode fiber. When multiple optical transmission modes coexist, the fundamental mode LP 01 Intermodal interference will occur between the higher-order modes, and the interference light intensity can be expressed by equation (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] In the formula, 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, and Δφ is the phase difference accumulated between the two modes during the optical fiber transmission process.

[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 shunt hole structure in the cladding on both sides of the core of the hollow-core photonic crystal fiber, the refractive index between the shunt 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 core will be resonantly coupled to the high-loss transmission in the shunt hole fundamental mode and eventually leaked out, thereby improving the transmission mode purity of the hollow-core photonic crystal fiber.

[0010] The shunt hole is set in the cladding of the hollow-core photonic crystal fiber, making the cladding structure more complicated. The size of the shunt hole is strongly related to the refractive index of the fundamental mode constructed by it, and then to the leakage efficiency of the high-order mode of the core. The complicated cladding structure increases the difficulty of fiber drawing, and the microstructure size accuracy is difficult to maintain over a long distance of the fiber, which brings uncontrollable factors to the mode purity noise suppression of the hollow-core photonic crystal fiber in the actual application of the gyroscope ring. 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 objects of the present invention is achieved by the following technical solution:

[0013] A hollow-core photonic crystal optical fiber loop pigtail winding implementation system, characterized in that it comprises 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 allowing two pigtails of the optical fiber ring to be coiled in parallel and in the same direction on its outer ring surface, and a UV-curing colloid is coated on the pigtails;

[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 ring through a bare fiber adapter. After the light wave is transmitted in the hollow-core photonic crystal fiber ring for one cycle, it is emitted from the pigtail at the other end of the fiber ring.

[0016] 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 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, so as to realize near-infrared CCD camera detection and reception under multiple wavelengths; and is used to perform data processing on the detection and reception signals of the multiple wavelength CCD camera based on the spatial and spectral resolution imaging method to obtain the light 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 light transmission mode field components, so as to realize the expansion of the piezoelectric ceramic sleeve, and to change the bending radius and winding tension of the optical fiber ring pigtail through the expansion of the piezoelectric ceramic sleeve, so as to finally make 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-level hollow-core photonic crystal fiber.

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

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

[0022] A winding method based on the hollow core photonic crystal fiber loop pigtail winding 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 shunt hole design and outputting the fibers in opposite directions, close them together, and coil them tightly, in parallel, and in the same direction on the outer surface of a piezoelectric ceramic sleeve, and coat the pigtails with a UV-curable colloid during the winding process;

[0024] Step 2: After the pigtail is coiled, a voltage is applied to the piezoelectric ceramic sleeve to control its expansion amount. During this period, 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 two pigtails of the hollow-core photonic crystal fiber ring on the piezoelectric ceramic sleeve to stimulate the refractive index tilt effect. Based on the detection result of the transmission mode component of the optical fiber ring, the expansion amount of the piezoelectric ceramic sleeve is controlled to optimize the refractive index matching efficiency between the core high-order mode and the shunt hole fundamental mode. The core high-order mode can be completely leaked. After the ring pigtail is solidified and the piezoelectric ceramic sleeve is withdrawn, the effect of improving the purity of the hollow-core photonic crystal fiber ring transmission mode can be obtained, which is beneficial to suppressing the mode purity-related noise in the interference type hollow-core microstructure optical fiber gyroscope;

[0028] 2. The present invention combines two pigtails of a hollow-core photonic crystal optical fiber ring and coils them tightly into a ring in the same direction and in parallel, without forming a Sagnac interference area. The pigtails are symmetrically located adjacent to each other along the midpoint of the ring, and the temperature performance of the Shupe effect of the ring is not affected under temperature changes. The 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 split hole design;

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

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

[0032] Figure 4 Schematic diagram of the hollow core photonic crystal optical 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 It is a transmission mode field component diagram of the hollow core photonic crystal optical fiber after the ring pigtail is coiled. DETAILED DESCRIPTION

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

[0037] Figure 1It is a schematic diagram of the end face of a hollow-core photonic crystal fiber with a shunt hole design. It is drawn from a single material of silica, and the cladding contains a periodic lattice structure with the characteristics of a two-dimensional photonic crystal structure. It 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 shunt holes (S1 and S2) are set on the left and right sides of the air core. The shunt holes also use the photonic bandgap effect constructed by the periodic lattice structure cladding to form a fundamental mode of light transmission. The refractive index of the fundamental mode transmission can be controlled by the size of the shunt 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 shunt hole fundamental mode is phase-matched with the core high-order mode, and the core high-order mode will be resonantly coupled to the shunt hole for leakage. Therefore, the purity of the core transmission mode 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 correlated with the refractive index of the fundamental mode it constructs, and thus is strongly correlated with 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, 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 improving the purity of the light transmission mode of the hollow-core photonic crystal fiber.

[0039] Figure 3 This is a schematic diagram of the refractive index tilt effect induced by random twisting and tightly coiling of hollow-core photonic crystal fibers. When hollow-core photonic crystal fibers are bent and coiled, the refractive index tilt will change on the fiber end face. The fiber twist angle, fiber bending radius and coiling tension determine the direction and degree of the refractive index tilt change on the fiber end face. In the loose state of hollow-core photonic crystal fibers with splitter holes, there is a refractive index mismatch problem between the splitter hole fundamental mode and the core high-order mode. When the fiber is randomly twisted and tightly coiled, the refractive index of the splitter hole fundamental mode and the core high-order mode changes to varying degrees. A large number of situations where the refractive index of the splitter hole fundamental mode matches the refractive index of the core high-order mode will be randomly and discretely generated along the fiber length. The refractive index tilt effect of the fiber surface caused by coiling can randomly and discretely change the phase matching relationship between the splitter hole fundamental mode and the core high-order mode. From the integral effect over the entire fiber length, it can ensure that the core high-order mode is completely resonantly coupled to the splitter hole for leakage treatment, which is beneficial to improve the light transmission mode purity of hollow-core photonic crystal fibers.

[0040] Figure 4The present invention is a schematic diagram of a hollow-core photonic crystal fiber loop pigtail winding system, wherein the method for winding using the winding system is as follows: two pigtails of a hollow-core photonic crystal fiber loop with a shunt hole design that output fibers in opposite directions are bundled together and tightly, parallelly and unidirectionally wound on a piezoelectric ceramic sleeve, a UV-curing colloid is coated on the pigtail during the winding process, a voltage is applied to the piezoelectric ceramic sleeve after the pigtail is wound to control its expansion, during which the optimal voltage control amount is selected by measuring the light transmission mode component of the loop so that the hollow-core photonic crystal fiber loop has a high mode purity transmission effect, in this state, the pigtail winding position of the loop is cured by UV irradiation and the piezoelectric ceramic sleeve is removed, the pigtail winding process of the loop is completed, and the obtained hollow-core fiber loop with high mode purity is beneficial to suppressing mode purity related noise in the hollow-core photonic crystal fiber gyroscope.

[0041] The winding system is mainly composed 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] 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 ring through a bare fiber adapter. The light wave is transmitted in the hollow-core photonic crystal fiber ring for one cycle and then emitted from the pigtail at the other end of the ring. The two pigtails 2 of the ring are coiled in parallel and in the same direction on the piezoelectric ceramic sleeve and coated with ultraviolet curing colloid. The light wave emitted from the pigtail of the ring passes through the first lens, the polarizer and the second lens in sequence, and the light wave is collimated, polarized and focused. The focused light wave is detected and received by the near-infrared CCD camera and sent to the host computer. The host computer controls the wavelength tunable laser to change the output wavelength to realize the detection and reception of the near-infrared CCD camera under multiple wavelengths. The host computer performs data processing on the detection and reception signal of the multi-wavelength CCD camera based on the spatial and spectral resolution imaging method to obtain the light transmission mode field component of the hollow-core photonic crystal fiber ring. The host computer controls the piezoelectric ceramic driver to change the control voltage of the piezoelectric ceramic sleeve, causing the piezoelectric ceramic sleeve to expand, and the bending radius and winding tension of the hollow-core photonic crystal fiber pigtail on the coil change, which can change the phase matching between the fundamental mode of the shunt hole in the pigtail and the high-order mode of the core, resulting in a change in the optical transmission mode field component of the hollow-core photonic crystal fiber ring. According to the optical transmission mode component of the ring, the optimal piezoelectric ceramic driver voltage control amount can be selected to enable the hollow-core photonic crystal fiber ring to have a high mode purity transmission effect. Under the high mode purity state of the ring, the coiling part of the pigtail is cured by ultraviolet irradiation and the piezoelectric ceramic sleeve is removed, so that a hollow-core photonic crystal fiber ring with high mode purity can be obtained.

[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 can realize the two-dimensional surface measurement of the light spot, which can improve the measurement speed of the pattern components;

[0045] The principle of the spatial and spectral resolved imaging method used to measure the optical fiber transmission mode components is based on the interference between the fundamental mode and the higher-order mode. If there are higher-order modes of light transmission in the optical fiber to be tested, there will be different group delays between the modes during the light 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 scanning the wavelength with a wavelength tunable laser, 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 tail fiber is not coiled, the fiber transmission in the hollow-core photonic crystal fiber ring includes the fundamental mode LP. 01 There are also higher-order modes, such as LP 11 LP 21 wait.

[0047] Figure 6 It 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, tightly and parallelly coiled in the same direction, and the pigtail coiling diameter and tension are fine-tuned through a 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 coiled in parallel on a piezoelectric ceramic sleeve. The pigtail is twisted and bent to produce a fiber refractive index tilt effect, which changes the refractive index matching between the core high-order mode and the diverter hole fundamental mode. 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 is cured by ultraviolet irradiation at the winding position 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 loop pigtail winding implementation system, characterized in that: 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 allowing two pigtails of the optical fiber ring to be coiled in parallel and in the same direction on its outer ring surface, and a UV-curing colloid is coated on the pigtails; 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 ring through a bare fiber adapter. After the light wave is transmitted in the hollow-core photonic crystal fiber ring for one cycle, it is emitted from the pigtail at the other end of the fiber ring. 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, so as to realize near-infrared CCD camera detection and reception under multiple wavelengths; and is used to perform data processing on the detection and reception signals of the multiple wavelength CCD camera based on the spatial and spectral resolution imaging method to obtain the light 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 light transmission mode field components, so as to realize the expansion of the piezoelectric ceramic sleeve, and to change the bending radius and winding tension of the optical fiber ring pigtail through the expansion of the piezoelectric ceramic sleeve, so as to finally make the hollow-core photonic crystal fiber ring have a high mode purity transmission effect.

2. The hollow core photonic crystal fiber loop 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-level hollow-core photonic crystal fiber.

3. The hollow core photonic crystal fiber loop 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 mode component.

4. A winding method based on the hollow core photonic crystal fiber loop pigtail winding implementation system 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 shunt hole design and outputting the fibers in opposite directions, close them together, and coil them tightly, in parallel, and in the same direction on the outer surface of a piezoelectric ceramic sleeve, and coat the pigtails with a UV-curable colloid during the winding process; Step 2: After the pigtail is coiled, a voltage is applied to the piezoelectric ceramic sleeve to control its expansion amount. During this period, 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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