Optically integrated fiber-optic current transformer

Abstract

The application discloses an optical integrated fiber current transformer, and belongs to the technical field of optical fiber sensing. The fiber current transformer comprises an integrated optical chip, a lambda / 4 wave plate, a sensing optical fiber ring, a reflector and a signal processing system. In the integrated optical chip, the light beam emitted by the super-radiation light source is filtered in mode through a first beam splitting / combining waveguide and a polarization waveguide, is split through a second beam splitting / combining waveguide, is modulated through a phase modulator in two paths, one of the two paths is converted in mode through a mode conversion waveguide after modulation, and then is combined through a polarization beam combining / splitting waveguide and enters an optical fiber through a fiber waveguide coupler. The light is reflected by the reflector after passing through the lambda / 4 wave plate and the sensing optical fiber ring in the optical fiber, and returns along the original path. The two light beams are combined into a photoelectric detector to form a photoelectric current signal after interference in the integrated optical chip, and the photoelectric current signal is input into the signal processing system for demodulation. The fiber current transformer is miniaturized and integrated.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of optical fiber sensing, and more particularly relates to an optical integrated fiber current transformer. BACKGROUND

[0002] In recent years, with the increase of electrical equipment and power consumption worldwide, all-fiber current transformers have gradually become the focus of researchers. Compared with the traditional active electronic current transformer represented by the air core coil, the optical fiber current transformer has the advantages of anti-electromagnetic interference, large dynamic range, small size, light weight, high precision, etc., making it a valuable asset for the new generation of smart grid.

[0003] However, as more and more all-fiber current transformers are being used in engineering applications in recent years, they are working in complex environments such as vibration, high and low temperature for a long time. These factors will cause the output signal of the transformer to contain environmental vibration interference, greatly reducing the measurement accuracy of the system, and in severe cases, the current transformer will malfunction. The optical fiber current transformers reported so far use discrete components, which cannot fully reflect the advantages of small size and light weight of fiber current transformers, and the connection and fixation between discrete components to some extent affect the long-term stability and anti-interference ability of the system. With the continuous development and improvement of micro-nano scale manufacturing technology, the integration and miniaturization of various optoelectronic devices and systems have become an inevitable trend.

[0004] Therefore, it has high research value and practical application significance to study an integrated fiber current transformer. SUMMARY

[0005] In view of the defects of the related art, the purpose of the present application is to provide an optical integrated fiber current transformer, which aims to solve the problem of large size, poor stability and poor anti-interference ability of fiber current transformer caused by discrete components.

[0006] To achieve the above-mentioned purpose, the present application provides an optical integrated fiber current transformer, comprising: an integrated optical chip, a lambda / 4 wave plate, a sensing optical fiber ring, a mirror and a signal processing system.

[0007] One end of the integrated optical chip is connected to the lambda / 4 wave plate and the sensing optical fiber ring in turn through a polarization maintaining optical fiber, the end of the sensing optical fiber ring is provided with the mirror, and the other end of the integrated optical chip is connected to the signal processing system.

[0008] The integrated optical chip integrates a superluminescent light source, a first beam splitting / combining waveguide, a polarization / polarization waveguide, a first phase modulator, a mode conversion waveguide, a polarization beam combining / splitting waveguide, a fiber waveguide coupler, a second beam splitting / combining waveguide and a second phase modulator.

[0009] The incident light beam emitted by the superluminescent light source passes through the first beam splitting / coupling waveguide, then passes through the polarization waveguide for mode filtering, and then passes through the second beam splitting / coupling waveguide to obtain a first light beam and a second light beam; the first light beam passes through the first phase modulator for modulation, and the second light beam passes through the second phase modulator for modulation; after the phase modulation, the polarization mode of the first light beam after passing through the mode conversion waveguide is orthogonal to the polarization mode of the second light beam; after the mode conversion, the first light beam and the second light beam pass through the polarization beam coupling / dividing waveguide and then pass through the fiber waveguide coupler to enter the polarization maintaining optical fiber, pass through the λ / 4 wave plate and the sensing fiber ring, and are reflected by the mirror and return along the original path; after the interference of the two beams at the second beam splitting / coupling waveguide, the beams are split by the first beam splitting / coupling waveguide, and one of the beams enters the photodetector to form a photocurrent signal, and the photocurrent signal is input into the signal processing system for demodulation.

[0010] Optionally, the first phase modulator and the second phase modulator are thin-film LiNbO3 modulators or silicon-based phase modulators; the first phase modulator and the second phase modulator introduce phase shifts of equal size and opposite signs.

[0011] Optionally, the λ / 4 wave plate is an optical fiber λ / 4 wave plate or a birefringent crystal.

[0012] Optionally, the optical fiber λ / 4 wave plate is a truncated optical fiber λ / 4 wave plate or a full-optical-fiber integrated λ / 4 wave plate.

[0013] The truncated optical fiber λ / 4 wave plate is a panda-type polarization maintaining optical fiber and an elliptical core optical fiber that are axially fused at 45°, and the elliptical core polarization maintaining optical fiber is truncated at a quarter of the beat length.

[0014] The full-optical-fiber integrated λ / 4 wave plate is a panda-type polarization maintaining optical fiber that is rotated at different speeds in one direction in a molten state.

[0015] Optionally, the thickness of the birefringent crystal is The optical axis is parallel to the surface of the integrated optical chip, wherein λ is the wavelength of the incident light beam, Δn=n o -n e , n o is the fast-axis refractive index, and n e is the slow-axis refractive index, which is polished and attached to the integrated optical chip to be coupled with the optical fiber.

[0016] Optionally, the polarization waveguide is a straight-through waveguide or an S-bend waveguide.

[0017] The polarization waveguide is used for mode filtering of the incident light beam to obtain a TE mode light beam.

[0018] Optionally, the mode conversion waveguide is an etching waveguide or a subwavelength grating waveguide.

[0019] The mode conversion waveguide is used to convert the first light beam after phase modulation from a TE mode to a TM mode.

[0020] Optionally, the first beam splitting / coupling waveguide and the second beam splitting / coupling waveguide are one of a Y-branch waveguide, a multimode interference waveguide, an adiabatic coupling waveguide and a directional coupling waveguide.

[0021] Optionally, the polarization beam splitting / coupling waveguide is one of a multimode interference waveguide, a directional coupling waveguide, a photonic crystal waveguide and a Mach-Zehnder interference waveguide.

[0022] Optionally, the fiber waveguide coupler is a fiber waveguide end face coupler or a grating coupler.

[0023] Compared with the prior art, the above technical scheme of the present application can achieve the following beneficial effects:

[0024] 1. The present application provides an optical integrated fiber current transformer. On the basis of an all-fiber current transformer, all components except a sensing optical fiber are integrated on an optical chip. The present application can be mass-produced by using current micro-nano processing technology. Compared with the original system, the present application has no discrete components, no spatial optical path, simple structure and is more compact. Through certain packaging technology, the present application can make the whole system more stable and reliable, and reduce the packaging and installation cost of the equipment. Meanwhile, the present application adopts a reflection type structure and a phase generation carrier demodulation scheme, which can improve the sensitivity, and has high demodulation precision and anti-interference ability.

[0025] 2. The present application provides an optical integrated fiber current transformer. Since the on-chip device has strong polarization correlation, the TM mode loss is large. In the present application, the second beam splitting / coupling waveguide is used for beam splitting in the integrated optical chip. The TE mode is used for processing first, and then the phase modulation is performed in two ways. The mode conversion waveguide is used to convert the light after modulation from a TE mode to a TM mode. The polarization beam splitting / coupling waveguide is used to combine and output the two-way light, thereby reducing the loss.

[0026] 3. The present application provides an optical integrated fiber current transformer. Multiple systems can be made on the same chip to form redundancy and improve reliability. DETAILED DESCRIPTION

[0027] Figure 1 is a schematic diagram of an optical integrated fiber current transformer provided by the present application;

[0028] Figure 2 is a schematic diagram of another optical integrated fiber current transformer provided by the present application;

[0029] Figure 3 This is a schematic diagram of the internal structure of the integrated optical chip provided by the present invention;

[0030] Figure 4 This is a schematic diagram of the truncated fiber λ / 4 waveplate provided by the present invention;

[0031] Figure 5 This is a schematic diagram of the birefringent crystal provided by the present invention.

[0032] In the figures, the same reference numerals have the same meaning: 1—integrated optical chip, 2—λ / 4 waveplate, 3—current-carrying wire, 4—sensing fiber ring, 5—mirror, 6—signal processing system, 61—lock-in amplifier, 62—signal processing device, 8—light source, 9—photodetector, 10—first beam splitter / combiner waveguide, 11—polarization waveguide, 12—first phase modulator, 13—mode conversion waveguide, 14—polarization beam splitter / combiner waveguide, 15—fiber waveguide coupler, 16—second beam splitter / combiner waveguide, 17—second phase modulator. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0034] The following description, in conjunction with a preferred embodiment, illustrates the content involved in the above embodiments.

[0035] like Figures 1 to 3 As shown, an optically integrated fiber optic current transformer includes: an integrated optical chip 1, a λ / 4 waveplate 2, a sensing fiber optic ring 4, a reflector 5, and a signal processing system 6.

[0036] One end of the integrated optical chip 1 is connected to the λ / 4 waveplate 2 and the sensing fiber ring 4 in sequence via a polarization-maintaining fiber. The end of the sensing fiber ring 4 is provided with the reflector 5. The other end of the integrated optical chip 1 is connected to the signal processing system 6.

[0037] The integrated optical chip integrates a superluminescent light source 8, a first beam splitter / combiner waveguide 10, a polarization waveguide 11, a first phase modulator 12, a mode conversion waveguide 13, a polarization combiner / splitter waveguide 14, an optical fiber waveguide coupler 15, a second beam splitter / combiner waveguide 16, and a second phase modulator 17.

[0038] The incident light beam emitted by the superluminescent light source 8 passes through the first beam splitting / coupling waveguide 10, then passes through the polarization waveguide 11 for mode filtering, and then passes through the second beam splitting / coupling waveguide 16 for beam splitting to obtain a first light beam and a second light beam; the first light beam passes through the first phase modulator 12 for modulation, and the second light beam passes through the second phase modulator 17 for modulation; the first light beam after phase modulation passes through the mode conversion waveguide 13, and the polarization mode of the first light beam is orthogonal to the polarization mode of the second light beam; the first light beam after mode conversion and the second light beam pass through the polarization beam coupling / splitting waveguide 14 for beam coupling, then pass through the fiber waveguide coupler 15 to enter the polarization maintaining fiber, are reflected by the mirror 5 after passing through the λ / 4 wave plate 2 and the sensing fiber ring 4, and return along the original path; the two light beams interfere at the second beam splitting / coupling waveguide 16, and then are split by the first beam splitting / coupling waveguide 10, wherein one of the light beams enters the photodetector 9 to form a photocurrent signal, and the photocurrent signal is input into the signal processing system 6 for demodulation.

[0039] Inside the integrated optical chip 1, the waveguide connecting between devices is a nanowire waveguide, the superluminescent light source 8 emits a wide-spectrum continuous light, which is coupled to the nanowire waveguide, and after mode filtering by the polarization waveguide 11, only the TE mode light is left.

[0040] The center wavelength of the incident light beam emitted by the superluminescent light source 8 is 850 nm, 1310 nm or 1550 nm.

[0041] The first phase modulator 12 and the second phase modulator 17 are thin-film LiNbO3 modulators or silicon-based phase modulators; the first phase modulator 12 and the second phase modulator 17 introduce phase shifts of equal size and opposite signs, so that a larger phase difference is introduced between the two signals, and the required modulation voltage is reduced.

[0042] The mode conversion waveguide 13 is used to convert the first light beam after phase modulation from the TE mode to the TM mode. Since the on-chip device has strong polarization dependence, the TM mode loss will be large, and the light after modulation is converted from the TE mode to the TM mode to reduce the loss.

[0043] The first light beam in the TM mode and the second light beam in the TE mode are coupled into the polarization maintaining fiber through the polarization beam splitting / coupling waveguide 14 and the fiber waveguide coupler 15, and the polarization maintaining fiber is used to keep the two linearly polarized lights from interfering with each other during transmission, wherein the TE mode and the TM mode are converted into x and y linearly polarized lights in the fiber, respectively.

[0044] Subsequently, the light beam is output from the integrated optical chip 1 through the polarization-maintaining fiber and enters the fiber λ / 4 waveplate 2. The two x and y linearly polarized beams become left-handed and right-handed circularly polarized beams, respectively, and enter the sensing fiber loop 4 surrounding the current conductor 3. Due to the Faraday effect caused by the magnetic field generated by the current transmitted through the current conductor 3, the two circularly polarized beams with opposite polarization directions propagate at different speeds, resulting in a phase difference between the two beams that is related to the magnitude of the current. After being reflected by the mirror, the polarization modes of the two beams are interchanged (left-handed becomes right-handed, and right-handed becomes left-handed). During their return journey, they pass through the sensing fiber loop 4 surrounding the current conductor 3, where they are again affected by the Faraday effect. Due to the non-reciprocity of the Faraday effect, the phase difference between the two beams caused by the magnetic field is doubled. After passing through the λ / 4 waveplate 2, the two circularly polarized beams with opposite polarization directions become orthogonally linearly polarized beams with interchanged modes: specifically, the x-axis linearly polarized beam is converted to the y-axis, and the y-axis linearly polarized beam is converted to the x-axis. Among them, the sensing fiber ring 4 is a spiral high birefringence fiber.

[0045] The two beams of light are coupled into the integrated optical chip 1 again through the fiber optic waveguide coupler 15. After passing through the fiber optic waveguide coupler 15, they are converted back to TE mode and TM mode, respectively. After being split by the polarization beam splitter / combiner waveguide 14, the TM mode is converted into TE mode by the mode conversion waveguide 13. The two beams are then modulated again by the first phase modulator 12 and the second phase modulator 17, and interfere at the second beam splitter / combiner waveguide 16. The interference signal enters the first beam splitter / combiner waveguide 10 through the polarization waveguide 11. In the first beam splitter / combiner waveguide 10, one beam enters the photodetector 9, which converts it into a photocurrent signal. The photocurrent signal is input to the signal processing system 6 for demodulation after passing through the photodetector 9.

[0046] Among them, such as Figure 1 and 2 As shown, the signal processing system 6 includes a lock-in amplifier 61 and a signal processing device 62. The signal processing system 6 acquires current signals and performs subsequent data processing to obtain the magnitude information of the current to be measured in the current conductor 3. During the experiment, the modulation frequencies of the first phase modulator 12 and the second phase modulator 17 are consistent with the local reference signal frequency of the lock-in amplifier 61, thereby allowing the extraction of the first harmonic component of the signal.

[0047] The signal processing system 6 is used for signal display, data storage and processing; the light intensity signal received by the detector is as follows:

[0048]

[0049] In the formula, K is the responsivity of the photodetector, and I0 is the initial light intensity of the light source. The modulation phase introduced for the phase modulator, a phase difference of the current.

[0050] The output light intensity is expanded according to the first Bessel function, and the first order component is extracted through a correlation demodulation algorithm in a phase-locked amplifier, and finally the current information is obtained.

[0051]

[0052] wherein, is the first Bessel function of , is a parameter related to the modulation voltage and the modulation frequency. The above formula represents the information about the phase difference of the current, and then the current information is obtained through a correlation signal processing algorithm.

[0053] Optionally, the polarizing / polarization waveguide 11 is a straight waveguide or an S-bend waveguide.

[0054] Optionally, the first beam splitting / combining waveguide 10 and the second beam splitting / combining waveguide 16 are one of a Y-branch waveguide, a multimode interference waveguide, an adiabatic coupling waveguide and a directional coupling waveguide.

[0055] Optionally, the mode conversion waveguide 13 is an etched waveguide or a subwavelength grating waveguide.

[0056] Optionally, the polarization beam splitting / combining waveguide 14 is one of a multimode interference waveguide, a directional coupling waveguide, a photonic crystal waveguide and a Mach-Zehnder interference waveguide.

[0057] Optionally, the fiber waveguide coupler is a fiber waveguide end face coupler or a grating coupler.

[0058] On the basis of the above embodiment, optionally, the fiber λ / 4 waveplate is a fiber λ / 4 waveplate or a birefringent crystal.

[0059] Optionally, the fiber λ / 4 waveplate is a truncated fiber λ / 4 waveplate or a full-fiber integrated λ / 4 waveplate.

[0060] The truncated fiber λ / 4 waveplate is a panda polarization maintaining fiber and an elliptical core fiber which are axially fused at 45°, and the elliptical core polarization maintaining fiber is truncated at a quarter beat length.

[0061] The full-fiber integrated λ / 4 waveplate is a panda polarization maintaining fiber which is rotated at different speeds in one direction in a molten state.

[0062] The present scheme can adopt two implementation manners, the first one is a fiber λ / 4 waveplate, as shown in 1, which is connected with a polarization maintaining fiber and an integrated optical chip 1; as shown in 2, the fiber λ / 4 waveplate is connected with a polarization maintaining fiber and a polarization maintaining fiber integrated chip 2. Figure 4As shown, the truncated optical fiber λ / 4 wave plate is composed of a section of elliptical core polarization maintaining optical fiber; first, the panda type polarization maintaining optical fiber is axially fused with the elliptical core optical fiber at 45°, and then the elliptical core polarization maintaining optical fiber is truncated at the quarter beat length, and the section of the elliptical core polarization maintaining optical fiber constitutes the λ / 4 wave plate. As shown in Figure 5 As shown, the preparation method of the all-fiber integrated λ / 4 wave plate is similar to the polarization maintaining optical fiber, and the panda type polarization maintaining optical fiber with high birefringence is rotated at different rates in a direction in a molten state, so that the difference of birefringence is caused, and the function of the λ / 4 wave plate is realized. Referring to Figure 5 , the double helix structure includes two stress regions in the panda fiber, and according to the change of the rotation rate, the integrated 1 / 4λ wave plate can be divided into two sections: the initial section (L1) of the change of the rotation rate and the tail section (L2) of the uniform and constant rotation rate. In the L1 section, the rotation rate slowly increases from zero (A end) to the maximum value (B end); in the L2 section, the rotation rate remains the maximum value (from B end to C end). The rotation rate affects the performance of the integrated 1 / 4λ wave plate, and too low rotation rate will cause incomplete conversion of the polarization state, and too high rotation rate may cause oscillation of energy coupling.

[0063] The second is a birefringent crystal; the thickness of the birefringent crystal is The optical axis is parallel to the surface of the integrated optical chip, wherein λ is the wavelength of the incident light beam, Δn = n o -n e , n o is the fast axis refractive index, and n e is the slow axis refractive index, which is polished and attached to the integrated optical chip to be coupled with the optical fiber at one end, as shown in Figure 2

[0064] In this scheme, all components except the sensing optical fiber are integrated on the optical chip, and the micro-nano processing technology can realize large-scale production. Compared with the original system, there are no discrete components, no spatial light path, simple structure and more compact; solve the technical problems of large volume, poor stability and anti-interference ability of optical fiber current transformer caused by discrete components, realize the beneficial effects of improving the stability of the whole system and reducing the packaging and installation cost of the equipment. At the same time, the reflective structure and the phase generation carrier demodulation scheme are adopted, which improves the sensitivity and has high demodulation precision and anti-interference ability.

[0065] Those skilled in the art will readily understand that the above description is only the preferred embodiment of the present application, and is not intended to limit the present application, and any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.​

Claims

1. An optically integrated fiber-optic current transformer, characterized by, The application relates to an integrated optical chip, a lambda / 4 wave plate, a sensing optical fiber ring, a mirror and a signal processing system. One end of the integrated optical chip is connected with the lambda / 4 wave plate and the sensing optical fiber ring in sequence through a polarization maintaining optical fiber, the mirror is arranged at the tail end of the sensing optical fiber ring, and the other end of the integrated optical chip is connected with the signal processing system. The integrated optical chip is integrated with a super-radiation light source, a first beam splitting / combining waveguide, a polarization / deflection waveguide, a first phase modulator, a mode conversion waveguide, a polarization combining / splitting waveguide, a fiber waveguide coupler, a second beam splitting / combining waveguide and a second phase modulator. The incident light beam emitted by the super-radiation light source is filtered through the polarization / deflection waveguide after passing through the first beam splitting / combining waveguide, is split through the second beam splitting / combining waveguide, and first and second light beams are obtained; the first light beam is modulated through the first phase modulator, and the second light beam is modulated through the second phase modulator; the polarization mode of the first light beam after phase modulation is orthogonal to the polarization mode of the second light beam after passing through the mode conversion waveguide; the first and second light beams after mode conversion are combined through the polarization combining / splitting waveguide, enter the polarization maintaining optical fiber through the fiber waveguide coupler, are reflected by the mirror after passing through the lambda / 4 wave plate and the sensing optical fiber ring, and return along the original path; the two light beams interfere at the second beam splitting / combining waveguide, are split through the first beam splitting / combining waveguide, one of the light beams enters a photodetector to form a photoelectric current signal, and the photoelectric current signal is input into the signal processing system for demodulation. The lambda / 4 wave plate is an optical fiber lambda / 4 wave plate or a birefringent crystal; the optical fiber lambda / 4 wave plate is a truncated optical fiber lambda / 4 wave plate or a full optical fiber integrated lambda / 4 wave plate. The truncated optical fiber lambda / 4 wave plate is a panda-type polarization maintaining optical fiber and an elliptical core optical fiber which are axially fused at 45 degrees, and the elliptical core polarization maintaining optical fiber is truncated at a quarter of the beating length; the full optical fiber integrated lambda / 4 wave plate is generated by rotating a panda-type polarization maintaining optical fiber at different speeds in one direction in a molten state. The polarization / deflection waveguide is a straight-through waveguide or an S-bend waveguide; the polarization / deflection waveguide is used for mode filtering of the incident light beam to obtain a TE mode light beam. The mode conversion waveguide is an etched waveguide or a subwavelength grating waveguide; the mode conversion waveguide is used for converting the first light beam after phase modulation from a TE mode into a TM mode. The first and second phase modulators are thin-film LiNbO3 modulators or silicon-based phase modulators; the first and second phase modulators introduce phase shifts of equal size and opposite signs.

2. The fiber-optic current transformer of claim 1, wherein, The first and second beam splitting / combining waveguides are one of a Y-branch waveguide, a multimode interference waveguide, an adiabatic coupling waveguide and a directional coupling waveguide.

3. The optical current transformer of claim 1, wherein, The thickness of the birefringent crystal is , the optical axis is parallel to the surface adhered to the integrated optical chip, wherein λ is the wavelength of the incident light beam, , is the fast axis refractive index, is the slow axis refractive index, and the birefringent crystal is polished and adhered to the integrated optical chip at the fiber coupling end.

4. The optical current transformer of claim 1, wherein, The polarization combining / splitting waveguide is one of a multimode interference waveguide, a directional coupling waveguide, a photonic crystal waveguide and a Mach-Zehnder interference waveguide.

5. The fiber optic current transformer of claim 1, wherein, The fiber waveguide coupler is a fiber waveguide end face coupler or a grating coupler.

6. The optical current transformer of claim 1, wherein, ​

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