A polarization state controller of optical fiber and a manufacturing method of photonic crystal fiber

Abstract

The application belongs to the technical field of astronomical photonics, and particularly relates to a kind of optical fiber polarization state controller, including support table;High-precision rotary table, assembly is in support table side wall;First piezoelectric glass and second piezoelectric glass, first piezoelectric glass and second piezoelectric glass are arranged in high-precision rotary table one side;Liquid crystal filled photonic crystal fiber, liquid crystal filled photonic crystal fiber is sequentially penetrated from left to right support table, high-precision rotary table, first piezoelectric glass and second piezoelectric glass;High-precision rotary table load first piezoelectric glass, second piezoelectric glass is compared with liquid crystal filled photonic crystal fiber rotation, applies rotating electric field, for controlling the director of liquid crystal;Controllable voltage source, the positive and negative electrode of controllable voltage source is connected with wire.The application constructs a rotating electric field to the director of liquid crystal in photonic crystal fiber, so as to realize the polarization state of the light wave through photonic crystal fiber.

Description

Technical Field

[0001] This invention belongs to the field of astronomical photonics technology, specifically relating to an optical fiber polarization state controller and a method for fabricating photonic crystal fibers. Background Technology

[0002] A stellar interferometer is a cross-correlation device based on spatial coherence analysis used to measure interference signals between stars. This instrument requires multiple telescopes to collect optical signals to preserve their optical field coherence characteristics. However, factors such as optical signal loss, polarization, dispersion, and energy fluctuations can corrupt fringe visibility information, thus affecting the accuracy of interferometric measurements. Unlike light wave propagation in space, light waves are easily affected by polarization states when propagating in optical fibers, leading to unstable interference signals and reduced fringe visibility. Therefore, the polarization problem of light is particularly important in stellar interferometry. To overcome the polarization effects in all-waveguide stellar interferometry systems, the key technologies are polarization control and polarization compensation, the core of which lies in adjusting and controlling the polarization state.

[0003] The instability of the polarization state of light in optical fibers stems from both intrinsic fiber factors and environmental factors, including fiber inhomogeneities, asymmetries, residual stress, temperature, stress, and vibration. These factors lead to polarization effects such as birefringence, polarization-dependent loss, and polarization mode dispersion, which in turn destabilize the polarization state of the optical signal. In single-mode fibers, the polarization state of light changes with time and location, introducing significant noise and disturbances. This results in unstable and unpredictable optical signals transmitted through the fiber, thereby reducing the accuracy of stellar interferometry. Summary of the Invention

[0004] The purpose of this invention is to provide an optical fiber polarization state controller and a method for fabricating photonic crystal fibers. By constructing a rotatable electric field, the polarization state of light waves passing through the photonic crystal fiber can be controlled by directing the liquid crystal in the fiber to the direction of the polarization.

[0005] The specific technical solution adopted by this invention is as follows: A fiber optic polarization state controller includes a support platform; A high-precision rotary table (10) is mounted on the side wall of the support table (2); The first piezoelectric glass (3) and the second piezoelectric glass (4) are disposed on one side of the high-precision rotary table (10); Liquid crystal-filled photonic crystal fiber (6) passes through the support stage (2), high-precision rotating stage (10), first piezoelectric glass (3) and second piezoelectric glass (4) from left to right. The liquid crystal-filled photonic crystal fiber (6) is coaxial with the rotation center of the high-precision rotating stage (10). The first piezoelectric glass (3), the second piezoelectric glass (4) and the liquid crystal-filled photonic crystal fiber (6) are parallel to each other. The high-precision rotating stage (10) loads the first piezoelectric glass (3) and the second piezoelectric glass (4) to rotate relative to the liquid crystal-filled photonic crystal fiber (6), and applies a rotating electric field to control the pointing vector of the liquid crystal. A controllable voltage source (1) has wires connected to its positive and negative terminals, and the wires on the positive and negative terminals are electrically connected to the first piezoelectric glass (3) and the second piezoelectric glass (4), respectively. The liquid crystal-filled photonic crystal fiber (6) is fixed on a high-precision rotary table (10) by a first clamp (7) and a second clamp (8), and is located on a straight line coaxial with the rotation center.

[0006] The first and second piezoelectric glass end faces are respectively fixedly installed with brushes, and each brush is connected to a ring armature. The wires on the positive and negative poles are connected to the ring armature.

[0007] The corresponding sidewalls of the first and second piezoelectric glass are coated with an indium tin oxide semiconductor transparent conductive oxide film.

[0008] The aperture of the liquid crystal-filled photonic crystal fiber is arranged in a hexagonal pattern along the radial direction of the fiber, and the outer diameter is 125 μm. The liquid crystal-filled photonic crystal fiber (6) is filled with nematic liquid crystal.

[0009] The step angle of the high-precision rotary table is less than 1.8°.

[0010] In this invention, the polarization state of light transmitted in an optical fiber is directly controlled by nematic liquid crystal filling the photonic crystal fiber. Liquid crystal is a material with adjustable refractive index and polarization characteristics. By filling the air channels of the photonic crystal fiber with liquid crystal, its refractive index and polarization characteristics can be changed by adjusting the electric field of the liquid crystal, thereby achieving polarization state control of the optical signal. After the nematic liquid crystal is filled into the air channels of the photonic crystal fiber, the long axis of the nematic liquid crystal molecules is aligned along the axial direction of the fiber. For selectively filled photonic crystals, the nematic liquid crystal waveguide is close to the fiber core, and the mode in the fiber core will leak into the liquid crystal waveguide, causing a shift in the interference wavelength in the transmission spectrum. The liquid crystal molecules will deflect with changes in voltage, causing a change in the effective refractive index of the liquid crystal. When the applied voltage is greater than the threshold voltage of the nematic liquid crystal, the liquid crystal molecules will deflect, and the relationship between the deflection angle and the voltage is: ; in, For the threshold voltage, E For the applied voltage, This represents the deflection angle of the liquid crystal molecules.

[0011] With respect to the optical axis of the liquid crystal When incident light at an angle undergoes birefringence due to the anisotropy of the liquid crystal, the refractive index along its two optical axes can be expressed as: ; Where, n e and n o and represent the refractive indices of the material for e-ray and o-ray, respectively, where n ⊥ and n ∥ Let be the refractive index along the optic axis and the refractive index perpendicular to the optic axis, respectively. Therefore, the change in birefringence of a crystal can be expressed as:

[0012] From the two formulas above, it is clear that the refractive index of the liquid crystal can be modulated by controlling the direction of the voltage. When light propagates in the liquid crystal, its phase delay is:

[0013] Therefore, the phase and polarization state of light waves passing through the liquid crystal can be precisely controlled by controlling the intensity or direction of the electric field applied to the liquid crystal, thus making the control of the polarization state of the light waves equivalent to the control of the electric field.

[0014] A method for fabricating a photonic crystal fiber, the method comprising the following steps: S1: Take a section of porous photonic crystal fiber, use a fiber taper with a tip diameter close to that of the photonic crystal pore to dip a small amount of UV-curable adhesive, apply it to one of the pores of the photonic crystal fiber, and then irradiate with a UV lamp to seal the pore. S2: Repeat S1 above to seal all pores except those to be filled; S3: After the S2 operation is completed, the obtained photonic crystal fiber is inserted into the nematic liquid crystal. Utilizing the capillary effect, the unblocked pores in the photonic crystal fiber are filled by the liquid crystal. S4: Remove the portion of the photonic crystal fiber obtained in S3 that was sealed with UV glue; S5: Repeat S1-S3 above to fill all the pores in a specified area of ​​the photonic crystal fiber with nematic liquid crystal.

[0015] The technical effects achieved by this invention are as follows: This invention discloses a fiber polarization state controller and a method for fabricating photonic crystal fibers. By constructing a precision electric field rotation mechanism and designing and fabricating a liquid crystal-filled photonic crystal fiber, the electric field rotation mechanism is used to control the liquid crystal filling in the photonic crystal, thereby achieving precise control of the polarization state of light passing through the photonic crystal fiber. Nematic liquid crystal is selectively filled into the pores of the photonic crystal fiber through capillary effect. The liquid crystal's director changes under different electric field directions, altering the polarization state of the light wave transmitted through the liquid crystal. Therefore, by controlling the direction of the precision electric field rotation system via computer, precise control of the polarization state of the light wave is achieved.

[0016] In the fiber polarization state controller and the method for fabricating photonic crystal fiber of the present invention, liquid crystal not only has the optical properties of crystal, but also the fluidity of liquid. Liquid crystal can be arranged according to certain rules within a certain temperature range. When liquid crystal is filled into photonic crystal fiber to form liquid crystal filled photonic crystal fiber, the liquid crystal can cause phase delay in the light passing through the liquid crystal filled photonic crystal fiber. The electric field can cause the directionality of the liquid crystal to be deflected. The magnitude of the polarization angle is related to the magnitude of the electric field. Therefore, the polarization control purpose can be achieved by changing the magnitude of the electric field. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the high-precision rotary table structure required for polarization control in an embodiment of the present invention; Figure 2 This is a flowchart illustrating the selective filling of photonic crystal pores with liquid crystal according to an embodiment of the present invention.

[0018] The attached diagram lists the components represented by each number as follows: 1. Controllable voltage source; 2. Support platform; 3. First piezoelectric glass; 4. Second piezoelectric glass; 5. Brush; 6. Liquid crystal filled photonic crystal fiber; 7. First clamp; 8. Second clamp; 9. Ring armature; 10. High-precision rotary table. Detailed Implementation

[0019] To make the objectives and advantages of this invention clearer, the invention will be specifically described below with reference to embodiments. It should be understood that the following text is merely used to describe one or more specific embodiments of the invention and does not strictly limit the scope of protection specifically claimed by the invention.

[0020] Example 1:

[0021] like Figures 1-2 As shown, a fiber polarization state controller includes a support platform 2; A high-precision rotary table 10 is mounted on the side wall of the support table 2; The first piezoelectric glass 3 and the second piezoelectric glass 4 are disposed on one side of the high-precision rotary table 10. The liquid crystal-filled photonic crystal fiber 6 passes through the support stage 2, the high-precision rotating stage 10, the first piezoelectric glass 3 and the second piezoelectric glass 4 from left to right. The liquid crystal-filled photonic crystal fiber 6 is coaxial with the rotation center of the high-precision rotating stage 10. The first piezoelectric glass 3, the second piezoelectric glass 4 and the liquid crystal-filled photonic crystal fiber 6 are parallel to each other. The high-precision rotating stage 10 drives the first piezoelectric glass 3 and the second piezoelectric glass 4 to rotate relative to the liquid crystal-filled photonic crystal fiber 6, so as to apply a rotating electric field to control the pointing vector of the liquid crystal. A controllable voltage source 1, wherein wires are connected to the positive and negative terminals of the controllable voltage source 1, and the wires on the positive and negative terminals are electrically connected to the first piezoelectric glass 3 and the second piezoelectric glass 4, respectively; The liquid crystal-filled photonic crystal fiber 6 is fixed on the high-precision rotary table 10 by the first clamp 7 and the second clamp 8, and is located on a straight line coaxial with the rotation center.

[0022] Polarization control and polarization compensation are crucial approaches to addressing the effects of polarization in fiber optic systems. The core technology lies in adjusting and controlling the polarization state of optical signals. Polarization control technology is a vital prerequisite for the development of polarization-dependent applications such as fiber optic communication, fiber optic measurement, and fiber optic sensing. It can effectively compensate for various polarization-dependent signal fading phenomena in fiber optic systems, significantly improving system performance.

[0023] To achieve precise control over the polarization state of light waves transmitted in optical fibers, this invention proposes a simple and highly controllable fiber polarization controller. The technical solution adopted in this invention is to construct a rotatable electric field to influence the director of the liquid crystal in the photonic crystal fiber, thereby controlling the polarization state of the light waves passing through the photonic crystal fiber.

[0024] Brushes 5 are fixedly installed on the end faces of the first piezoelectric glass 3 and the second piezoelectric glass 4 respectively. A ring armature 9 is connected to each brush 5, and the wires are connected to the ring armature 9.

[0025] The corresponding sidewalls of the first piezoelectric glass 3 and the second piezoelectric glass 4 are both coated with an indium tin oxide semiconductor transparent conductive oxide film.

[0026] The aperture of the liquid crystal-filled photonic crystal fiber 6 is arranged in a hexagonal pattern along the radial direction of the fiber, and the outer diameter is 125 μm. The liquid crystal-filled photonic crystal fiber 6 is filled with nematic liquid crystal.

[0027] The high-precision rotary table has a step angle of less than 1.8°.

[0028] Long-baseline stellar interferometry is the only way to achieve the angular resolution of diffraction-limited telescopes with apertures of several hundred meters. Fiber optic technology provides a new technological approach for the miniaturization and integration of stellar interferometers, improving observational capabilities and reducing costs. With the development of fiber optic technology, second-generation interferometers use single-mode fiber to replace classical optical systems, directionally transmitting the beam from the telescope focal point to the beam combiner. Fiber optic devices, such as fiber couplers, fiber grating filters, and fiber delay lines, are widely used in all-waveguide stellar interferometers. However, fiber optics are susceptible to environmental interference, such as temperature, stress, and vibration, all of which can alter fiber birefringence, leading to instability in the polarization state of the light signal. In single-mode fiber, the polarization state of the transmitted light changes continuously along the fiber, and the polarization state at each point in the fiber also changes over time. This complex change introduces a large amount of noise or disturbance, resulting in unstable and unpredictable light signals transmitted in the fiber, reducing the accuracy of stellar interferometry measurements. A crucial approach to overcoming the environmental influence on the polarization of fiber optic systems is polarization control and polarization compensation, the core technology of which is the adjustment and control of the polarization state. Polarization control technology can compensate for various polarization-dependent signal fading in fiber optic systems, significantly improving system performance. This invention aims to achieve precise control and compensation of fiber polarization states, providing a precise polarization state control and compensation system for fiber optic stellar interferometry systems and fiber optic communication systems, enabling high-fidelity and highly stable transmission of optical signals in fiber optic links.

[0029] When the applied voltage exceeds the threshold voltage of the nematic liquid crystal, the liquid crystal molecules will deflect. The relationship between the deflection angle and the voltage is as follows: ; in, For the threshold voltage, E For the applied voltage, This represents the deflection angle of the liquid crystal molecules. It is perpendicular to the optical axis of the liquid crystal. When incident light at an angle undergoes birefringence due to the anisotropy of the liquid crystal, the refractive index along its two optical axes can be expressed as: ; Where, n e and n o and represent the refractive indices of the material for e-ray and o-ray, respectively, where n ⊥ and n ∥ Let be the refractive index along the optic axis and the refractive index perpendicular to the optic axis, respectively. Therefore, the change in birefringence of a crystal can be expressed as:

[0030] From the two formulas above, it is clear that the refractive index of the liquid crystal can be modulated by controlling the direction of the voltage. When light propagates in the liquid crystal, its phase delay is:

[0031] Therefore, the phase and polarization state of light waves passing through the liquid crystal can be precisely controlled by controlling the intensity or direction of the electric field applied to the liquid crystal, thus making the control of the polarization state of the light waves equivalent to the control of the electric field.

[0032] Example 2:

[0033] like Figure 2 As shown, a method for fabricating a photonic crystal fiber, specifically a liquid crystal selective filling method for photonic crystal pores, is as follows: A fine fiber taper with a diameter close to the diameter of the photonic crystal fiber pores is dipped in UV-curable adhesive and applied to all pores except the first one to be filled. The adhesive is then cured by UV curing. The end face is then inserted into a nematic liquid crystal solution, where the liquid crystal automatically enters the pores through capillary action. The end face is then cut off, and the above steps are repeated until the liquid crystal fills all the pores. Finally, the photonic crystal fiber is fused with a single-mode fiber to obtain a fiber polarization control unit that can be controlled by an electric field.

[0034] Example 3:

[0035] like Figure 2 As shown, a method for fabricating a photonic crystal fiber is described. The method for fabricating a liquid crystal-filled photonic crystal is as follows: A section of porous photonic crystal fiber with a flat cross-section is cut using a fiber cleaver. A small amount of UV-curable adhesive is applied to one of the pores of the photonic crystal fiber using a fiber taper with a tip diameter close to that of the pore. The pore is then sealed by UV irradiation. The above steps are repeated until all pores except the one to be filled are sealed. Then, the end face is cut off, and the above steps are repeated to fill all the pores in the specified shape area of ​​the photonic crystal fiber with nematic liquid crystal. Finally, the two ends of the liquid crystal-filled photonic crystal fiber are fused to a single-mode fiber using a fiber fusion splicer.

[0036] A liquid crystal-filled photonic crystal fiber is placed on the central axis of a high-precision electric field rotation device using a fixture. The angle and direction of the electric field rotation are controlled by a computer, and the polarization state of the light transmitted in the fiber is controlled experimentally.

[0037] Working principle: First, a high-precision rotary stage 10 required for polarization control is built. The positive and negative terminals of the controllable voltage source 1 are connected to two annular armatures 9 through wires. The first piezoelectric glass 3 and the second piezoelectric glass 4, which are coated with a semiconductor transparent conductive oxide film, are respectively connected to the two annular armatures 9 through brushes 5. When the voltage of the adjustable voltage source 1 is controlled, an approximately uniform electric field perpendicular to the two conductive glasses is generated between the first piezoelectric glass 3 and the second piezoelectric glass 4. The uniformity of the electric field can reach 99.98% in the middle position. The first piezoelectric glass 3 and the second piezoelectric glass 4 are both fixed on the same high-precision rotary stage, which can rotate at any angle between 0° and 720°. The precision can be controlled by a stepper motor driver, with a minimum step angle of 0.15°, which can realize arbitrary changes in the direction of the electric field. The entire rotating component is fixed on the support platform 2. The liquid crystal-filled photonic crystal fiber 6 with specific air holes is fixed on a straight line coaxial with the high-precision rotating platform 10 by the first clamp 7 and the second clamp 8. When controlling the polarization state of the light wave transmitted in the fiber, the fiber coupler couples the linearly polarized light into the fiber input end. The light intensity at the fiber output end is detected by the light intensity detector. When a periodic electric field is applied, the detected light intensity at the output end changes significantly periodically. It can be concluded that the polarization state of the fiber can be controlled by the applied voltage. When the direction of the electric field rotates with the high-precision rotating platform 10, the light intensity at the fiber output end changes periodically with the rotation of the hollow rotating platform.

[0038] The above description is merely a preferred embodiment of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention. Structures, devices, and operating methods not specifically described or explained in this invention are implemented according to conventional methods in the art unless otherwise specified or limited.

Claims

1. A fiber optic polarization state controller, characterized in that: Including the support platform (2); A high-precision rotary table (10) is mounted on the side wall of the support table (2); The first piezoelectric glass (3) and the second piezoelectric glass (4) are disposed on one side of the high-precision rotary table (10); Liquid crystal-filled photonic crystal fiber (6) passes through the support stage (2), high-precision rotating stage (10), first piezoelectric glass (3) and second piezoelectric glass (4) from left to right. The liquid crystal-filled photonic crystal fiber (6) is coaxial with the rotation center of the high-precision rotating stage (10). The first piezoelectric glass (3), the second piezoelectric glass (4) and the liquid crystal-filled photonic crystal fiber (6) are parallel to each other. The high-precision rotary stage (10) drives the first piezoelectric glass (3) and the second piezoelectric glass (4) to rotate relative to the liquid crystal-filled photonic crystal fiber (6) to apply a rotating electric field to control the pointing vector of the liquid crystal. A controllable voltage source (1) has wires connected to its positive and negative terminals, and the wires on the positive and negative terminals are electrically connected to the first piezoelectric glass (3) and the second piezoelectric glass (4), respectively.

2. The fiber polarization state controller according to claim 1, characterized in that: The first piezoelectric glass (3) and the second piezoelectric glass (4) are respectively fixedly installed with brushes (5), and each brush (5) is connected to a ring armature (9), and the wires on the positive and negative poles are connected to the ring armature (9).

3. The fiber polarization state controller according to claim 1, characterized in that: The corresponding sidewalls of the first piezoelectric glass (3) and the second piezoelectric glass (4) are coated with an indium tin oxide semiconductor transparent conductive oxide film.

4. The fiber polarization state controller according to claim 1, characterized in that: The aperture of the liquid crystal filled photonic crystal fiber (6) is arranged in a hexagonal pattern along the radial direction of the fiber, and the outer diameter is 125 μm.

5. A fiber optic polarization state controller according to claim 1, characterized in that: The liquid crystal-filled photonic crystal fiber (6) is filled with nematic liquid crystal.

6. The fiber polarization state controller according to claim 1, characterized in that: The step angle of the high-precision rotary table (10) is less than 1.8°.

7. The fiber polarization state controller according to claim 1, characterized in that: The liquid crystal-filled photonic crystal fiber (6) is fixed on the high-precision rotary table (10) by the first clamp (7) and the second clamp (8), and is located on a straight line coaxial with the rotation center.

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