Optical integrated optical fiber current transformer

Abstract

The invention discloses an optically integrated optical fiber current transformer, and belongs to the technical field of optical fiber sensing. The optical fiber current transformer comprises an integrated optical chip, a lambda / 4 wave plate, a sensing optical fiber ring, a reflecting mirror and a signal processing system, in the integrated optical chip, a light beam emitted by a superradiation light source passes through a first beam splitting / beam combining waveguide, then is subjected to mode filtering through a polarization / polarization waveguide, is split through a second beam splitting / beam combining waveguide and is modulated by a phase modulator in two paths, one path is modulated and then is subjected to mode conversion through a mode conversion waveguide, and the other path is modulated through a phase modulator. After being combined by the polarization beam combining / beam splitting waveguide, the light enters the optical fiber through the optical fiber waveguide coupler; the two beams of light pass through the lambda / 4 wave plate and the sensing optical fiber ring in the optical fiber, then are reflected by the reflector and return along the same path, the two beams of light interfere with each other in the integrated optical chip and then are combined to enter the photoelectric detector to form a photocurrent signal, and the photocurrent signal is input into the signal processing system to be demodulated. And miniaturization and integration of the optical fiber current transformer are realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical fiber sensing, and more specifically, relates to an optically integrated optical fiber current transformer. Background Art

[0002] In recent years, with the increase of electrical equipment and electricity consumption worldwide, all-fiber current transformers have gradually become a field of great interest to researchers. Compared with traditional active electronic current transformers represented by air-core coils, fiber-optic current transformers have the advantages of anti-electromagnetic interference, large dynamic range, small size, light weight, and high precision, making them a valuable asset for the new generation of smart grids.

[0003] However, as all-fiber current transformers have been increasingly put into engineering applications in recent years, they have been working in complex environments such as vibration, high and low temperatures for a long time. These factors will cause the output signal of the transformer to contain interference from environmental vibration, greatly reducing the measurement accuracy of the system. In severe cases, the current transformer will fail and stop operating. Currently, the fiber-optic current transformers reported mostly use discrete components, which cannot fully reflect the advantages of small size and light weight of fiber-optic current transformers. In addition, the connection and fixation between discrete components affect the long-term stability and anti-interference ability of the system to a certain extent. With the continuous development and improvement of micro-nanoscale manufacturing processes, the integration and miniaturization of various optoelectronic devices and systems has become an inevitable trend.

[0004] Therefore, studying an integrated fiber optic current transformer has high research value and practical application significance. Summary of the invention

[0005] In view of the defects of the related art, the purpose of the present invention is to provide an optically integrated fiber optic current transformer, aiming to solve the problems of large size, poor stability and anti-interference ability of the fiber optic current transformer caused by discrete components.

[0006] To achieve the above object, the present invention provides an optically integrated fiber optic current transformer, comprising: an integrated optical chip, a λ / 4 wave plate, a sensing fiber ring, a reflector and a signal processing system;

[0007] One end of the integrated optical chip is connected to the λ / 4 wave plate and the sensing optical fiber ring in sequence through a polarization-maintaining optical fiber, the reflector is arranged at the end of the sensing optical fiber ring, 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 polarizing / polarization waveguide, a first phase modulator, a mode conversion waveguide, a polarization beam combining / splitting waveguide, an optical fiber waveguide coupler, a second beam splitting / combining waveguide and a second phase modulator;

[0009] The incident light beam emitted by the super radiant luminescent light source passes through a first beam splitting / combining waveguide and then passes through a polarizing / polarization waveguide for mode filtering, and is split through a second beam splitting / combining waveguide to obtain a first light beam and a second light beam; the first light beam is modulated by a first phase modulator, and the second light beam is modulated by a second phase modulator, and after the phase modulated first light beam passes through a mode conversion waveguide, its polarization mode is orthogonal to the polarization mode of the second light beam; the first light beam and the second light beam after mode conversion are combined through a polarization combining / splitting waveguide and then pass through a fiber waveguide coupler to enter a polarization-maintaining fiber, pass through a λ / 4 wave plate and a sensing fiber ring, and are reflected by a reflector and return along the original path, the two light beams interfere at the second beam splitting / combining waveguide and then are split through the first beam splitting / combining waveguide, one of the light beams enters a photodetector to form a photocurrent signal, and the photocurrent signal is input into a 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 phase shifts introduced by the first phase modulator and the second phase modulator are equal in magnitude and opposite in sign.

[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 adopts a truncated optical fiber λ / 4 wave plate or an all-optical integrated λ / 4 wave plate;

[0013] The truncated optical fiber λ / 4 wave plate is a 45° axial fusion splicing of a Panda-type polarization-maintaining optical fiber and an elliptical core optical fiber, and is truncated at a quarter of the beat length of the elliptical core polarization-maintaining optical fiber;

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

[0015] Optionally, the thickness of the birefringent crystal is The optical axis is parallel to the surface on which the integrated optical chip is attached, where λ is the wavelength of the incident light beam, and Δn = n o -n e , n o is the fast axis refractive index, n e The slow axis refractive index is 0.0447mm, which is polished and attached to the integrated optical chip and coupled to one end of the optical fiber.

[0016] Optionally, the polarizing / polarization waveguide is a straight waveguide or an S-bend waveguide;

[0017] The polarizing / polarization waveguide is used to perform mode filtering on the incident light beam to obtain a TE mode light beam.

[0018] Optionally, the mode conversion waveguide is an etched waveguide or a sub-wavelength grating waveguide;

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

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

[0021] Optionally, the polarization beam combining / splitting 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 optical fiber waveguide coupler is an optical fiber waveguide end face coupler or a grating coupler.

[0023] Compared with the prior art, the above technical solution conceived by the present invention can achieve the following beneficial effects:

[0024] 1. The present invention provides an optically integrated fiber-optic current transformer. On the basis of the all-fiber-optic current transformer, all components other than the sensing fiber are integrated into the optical chip. Large-scale production can be achieved by using the current micro-nano processing technology. Compared with the original system, there are no discrete components, no spatial optical paths, and the structure is simple and more compact. Through certain packaging technology, the entire system can be made more stable and reliable, reducing the packaging and installation costs of the equipment. At the same time, the reflective structure and phase generation carrier demodulation scheme are adopted to improve the sensitivity while having high demodulation accuracy and anti-interference ability.

[0025] 2. The present invention provides an optically integrated fiber-optic current transformer. Since the on-chip devices have strong polarization correlation, the TM mode loss will be large. In this solution, the second beam splitting / combining waveguide is used for beam splitting in the integrated optical chip. The TE mode is first used for processing and phase modulation is performed in two paths. Then, one of the modulated lights is converted from TE mode to TM mode through a mode conversion waveguide. The two lights are then combined and output through a polarization beam splitting / combining waveguide to reduce losses.

[0026] 3. The present invention provides an optically integrated fiber-optic current transformer. Multiple systems can be manufactured on the same chip to form redundancy and improve reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a schematic diagram of an optically integrated fiber-optic current transformer provided by the present invention;

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

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

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

[0031] Figure 5 Schematic diagram of the birefringent crystal provided by the present invention.

[0032] Among them, the same figure marks have the same meaning, 1—integrated optical chip, 2—λ / 4 wave plate, 3—current-carrying wire, 4—sensing optical fiber ring, 5—reflector, 6—signal processing system, 61—phase-locked amplifier, 62—signal processing device, 8—light source, 9—photodetector, 10—first beam splitting / combining waveguide, 11—polarizing / polarization waveguide, 12—first phase modulator, 13—mode conversion waveguide, 14—polarization beam splitting / combining waveguide, 15—optical fiber waveguide coupler, 16—second beam splitting / combining waveguide, 17—second phase modulator. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0034] The contents involved in the above embodiment are described below in conjunction with a preferred embodiment.

[0035] like Figures 1 to 3 As shown, an optically integrated fiber-optic current transformer comprises: an integrated optical chip 1, a λ / 4 wave plate 2, a sensing fiber 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 wave plate 2 and the sensing optical fiber ring 4 in sequence through a polarization-maintaining optical fiber, the reflector 5 is arranged at the end of the sensing optical fiber ring 4, and 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 splitting / combining waveguide 10, a polarizing / polarization waveguide 11, a first phase modulator 12, a mode conversion waveguide 13, a polarization combining / splitting waveguide 14, an optical fiber waveguide coupler 15, a second beam splitting / combining waveguide 16 and a second phase modulator 17;

[0038] The incident light beam emitted by the super radiant luminescent light source 8 passes through the first beam splitting / combining waveguide 10 and then passes through the polarization / polarization waveguide 11 for mode filtering, and is split by the second beam splitting / combining waveguide 16 to obtain a first light beam and a second light beam; the first light beam is modulated by the first phase modulator 12, and the second light beam is modulated by the second phase modulator 17. After the phase modulated first light beam passes through the mode conversion waveguide 13, its polarization mode is orthogonal to the polarization mode of the second light beam; the first light beam and the second light beam after mode conversion are combined by the polarization combining / splitting waveguide 14 and then pass through the optical fiber waveguide coupler 15 to enter the polarization-maintaining optical fiber, pass through the λ / 4 wave plate 2 and the sensing optical fiber ring 4, and are reflected by the reflector 5 and return along the original path. The two light beams interfere at the second beam splitting / combining waveguide 16 and then are split by the first beam splitting / combining waveguide 10, one of which 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 waveguides connecting the devices are nanowire waveguides. The superluminescent light source 8 emits broadband continuous light, which is coupled to the nanowire waveguide. After mode filtering by the polarizing / polarization waveguide 11, only TE mode light is left.

[0040] The central 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 phase shifts introduced by the first phase modulator 12 and the second phase modulator 17 are equal in magnitude and opposite in sign, so as to introduce a larger phase difference between the two signals and reduce the required modulation voltage.

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

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

[0044] Subsequently, the light beam is output from the integrated optical chip 1 through the polarization-maintaining optical fiber and enters the optical fiber λ / 4 wave plate 2. The two beams of x and y linear polarized light become left-handed and right-handed circularly polarized light and enter the sensing optical fiber ring 4 surrounding the current conductor 3. Due to the Faraday effect caused by the magnetic field generated by the current conductor 3 transmitting the current, the two beams of circularly polarized light with opposite polarization directions are transmitted at different speeds, so that a phase difference related to the current magnitude is generated between the two beams of circularly polarized light. After the two beams of circularly polarized light with different rotation directions are reflected by the reflector, the polarization modes of the two beams of light are interchanged (left-handed light becomes right-handed light, and right-handed light becomes left-handed light). In the process of returning along the original route, they pass through the sensing optical fiber ring 4 surrounding the current conductor 3, and are affected by the Faraday effect again. Due to the non-reciprocity of the Faraday effect, the phase difference caused by the magnetic field between the two beams of light doubles. After passing through the λ / 4 wave plate 2, the two beams of circularly polarized light with opposite rotation directions become orthogonal linear polarized light with interchanged modes, specifically: the x-line polarized light is converted to the y-axis, and the y-axis polarized light is converted to the x-axis. The sensing optical fiber ring 4 is a spiral high birefringence optical fiber.

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

[0046] Among them, Figure 1 and 2 As shown, the signal processing system 6 includes a phase-locked amplifier 61 and a signal processing device 62. The signal processing system 6 collects the current signal for subsequent data processing so as to obtain the magnitude information of the current to be measured in the current conductor 3. During the experiment, the modulation frequency of the first phase modulator 12 and the second phase modulator 17 is consistent with the local reference signal frequency of the phase-locked amplifier 61, so that the first harmonic component of the signal can be extracted.

[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] Where K is the responsivity of the photodetector, I0 is the initial light intensity of the light source, is the modulation phase introduced by the phase modulator, is the phase difference produced by the current.

[0050] The output light intensity is expanded according to the first-order Bessel function, and the first-order component is extracted by the correlation demodulation algorithm in the phase-locked amplifier, and finally it can be obtained:

[0051]

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

[0053] Optionally, the 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 both 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 sub-wavelength grating waveguide.

[0056] Optionally, the polarization beam combining / splitting 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 optical fiber waveguide coupler is an optical fiber waveguide end face coupler or a grating coupler.

[0058] Based on the above embodiment, optionally, the λ / 4 wave plate adopts an optical fiber λ / 4 wave plate or a birefringent crystal.

[0059] Optionally, the optical fiber λ / 4 wave plate adopts a truncated optical fiber λ / 4 wave plate or an all-optical integrated λ / 4 wave plate;

[0060] The truncated optical fiber λ / 4 wave plate is a 45° axial fusion splicing of a Panda-type polarization-maintaining optical fiber and an elliptical core optical fiber, and is truncated at a quarter of the beat length of the elliptical core polarization-maintaining optical fiber;

[0061] The all-fiber integrated λ / 4 wave plate is generated by rotating a panda-type polarization-maintaining optical fiber in one direction at different speeds in a molten state.

[0062] This solution can be implemented in two ways. The first is an optical fiber λ / 4 wave plate, as shown in 1, connected to an integrated optical chip 1 through a polarization-maintaining optical fiber; Figure 4As shown in the figure, the truncated fiber λ / 4 wave plate is composed of a section of elliptical core polarization-maintaining fiber. First, the panda-type polarization-maintaining fiber and the elliptical core fiber are fused at 45°, and then the elliptical core polarization-maintaining fiber is truncated at a quarter of the length. This section of the elliptical core polarization-maintaining fiber constitutes the λ / 4 wave plate. Figure 5 As shown in the figure, the preparation method of the all-fiber integrated λ / 4 glass plate is similar to that of the circular-maintaining fiber. The Panda-type polarization-maintaining fiber with high birefringence is rotated in one direction at different rates in a molten state to cause a difference in birefringence and realize the function of the λ / 4 wave plate. Figure 5 The double helix structure contains two stress regions in the panda fiber. According to the change of the rotation rate, the integrated 1 / 4λ wave plate can be divided into two sections: the starting section (L1) where the rotation rate changes and the ending section (L2) where the rotation rate is uniform and constant. In the L1 section, the spin rate slowly increases from zero (end A) to the maximum value (end B); in the L2 section, the spin rate remains at the maximum value (from end B to end C). The rotation rate affects the performance of the integrated 1 / 4λ wave plate. If the rotation rate is too low, the polarization state conversion will be incomplete. If the rotation rate is too high, the energy coupling may oscillate.

[0063] The second type is a birefringent crystal; the thickness of the birefringent crystal is The optical axis is parallel to the surface on which the integrated optical chip is attached, where λ is the wavelength of the incident light beam, and Δn = n o -n e , n o is the fast axis refractive index, n e The slow axis refractive index is polished and attached to the integrated optical chip and coupled to the optical fiber. Figure 2 shown.

[0064] In this solution, all components other than the sensing optical fiber are integrated into the optical chip, and the micro-nano processing technology can achieve large-scale production. Compared with the original system, there are no discrete components, no spatial optical paths, and the structure is simple and more compact; it solves the technical problems of large size, poor stability and anti-interference ability of the optical fiber current transformer caused by discrete components, and achieves the beneficial effect of improving the stability of the entire system and reducing the packaging and installation costs of the equipment. At the same time, the reflective structure and phase generation carrier demodulation scheme are adopted to improve the sensitivity while having high demodulation accuracy and anti-interference ability.

[0065] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. An optically integrated fiber-optic current transformer, characterized in that: include: Integrated optical chip, λ / 4 wave plate, sensing fiber ring, reflector and signal processing system; One end of the integrated optical chip is connected to the λ / 4 wave plate and the sensing optical fiber ring in sequence through a polarization-maintaining optical fiber, the reflector is arranged at the end of the sensing optical fiber ring, and the other end of the integrated optical chip is connected to the signal processing system; The integrated optical chip integrates a superluminescent light source, a first beam splitting / combining waveguide, a polarizing / polarization waveguide, a first phase modulator, a mode conversion waveguide, a polarization beam combining / splitting waveguide, an optical fiber waveguide coupler, a second beam splitting / combining waveguide and a second phase modulator; The incident light beam emitted by the super radiant luminescent light source passes through a first beam splitting / combining waveguide and then passes through a polarizing / polarization waveguide for mode filtering, and is split through a second beam splitting / combining waveguide to obtain a first light beam and a second light beam; the first light beam is modulated by a first phase modulator, and the second light beam is modulated by a second phase modulator, and after the phase modulated first light beam passes through a mode conversion waveguide, its polarization mode is orthogonal to the polarization mode of the second light beam; the first light beam and the second light beam after mode conversion are combined through a polarization combining / splitting waveguide and then pass through a fiber waveguide coupler to enter a polarization-maintaining fiber, pass through a λ / 4 wave plate and a sensing fiber ring, and are reflected by a reflector and return along the original path, the two light beams interfere at the second beam splitting / combining waveguide and then are split through the first beam splitting / combining waveguide, one of the light beams enters a photodetector to form a photocurrent signal, and the photocurrent signal is input into a signal processing system for demodulation.

2. The optical fiber current transformer according to claim 1, characterized in that: The first phase modulator and the second phase modulator are phase modulators that are thin-film LiNbO3 modulators or silicon-based phase modulators; the phase shifts introduced by the first phase modulator and the second phase modulator are equal in magnitude and opposite in sign.

3. The optical fiber current transformer according to claim 1, characterized in that: The λ / 4 wave plate is an optical fiber λ / 4 wave plate or a birefringent crystal.

4. The optical fiber current transformer according to claim 3, characterized in that: The optical fiber λ / 4 wave plate adopts a truncated optical fiber λ / 4 wave plate or an all-optical integrated λ / 4 wave plate; The truncated optical fiber λ / 4 wave plate is a 45° axial fusion splicing of a Panda-type polarization-maintaining optical fiber and an elliptical core optical fiber, and is truncated at a quarter of the beat length of the elliptical core polarization-maintaining optical fiber; The all-fiber integrated λ / 4 wave plate is generated by rotating a panda-type polarization-maintaining optical fiber in one direction at different speeds in a molten state.

5. The optical fiber current transformer according to claim 3, characterized in that: The thickness of the birefringent crystal is The optical axis is parallel to the surface attached to the integrated optical chip, where λ is the wavelength of the incident light beam, Δn = n o -n e , n o is the fast axis refractive index, n e The slow axis refractive index is 0.0447mm, which is polished and attached to the integrated optical chip and coupled to one end of the optical fiber.

6. The optical fiber current transformer according to claim 1, characterized in that: The polarizing / polarization waveguide is a straight waveguide or an S-bend waveguide; The polarizing / polarization waveguide is used to perform mode filtering on the incident light beam to obtain a TE mode light beam.

7. The optical fiber current transformer according to claim 6, characterized in that: The mode conversion waveguide is an etched waveguide or a sub-wavelength grating waveguide; The mode conversion waveguide is used to convert the phase-modulated first light beam from the TE mode to the TM mode.

8. The optical fiber current transformer according to claim 1, characterized in that: The first beam splitting / combining waveguide and the second beam splitting / combining waveguide are each one of a Y-branch waveguide, a multimode interference waveguide, an adiabatic coupling waveguide and a directional coupling waveguide.

9. The optical fiber current transformer according to claim 1, characterized in that: The polarization beam combining / splitting waveguide is one of a multimode interference waveguide, a directional coupling waveguide, a photonic crystal waveguide, and a Mach-Zehnder interference waveguide.

10. The optical fiber current transformer according to claim 1, characterized in that: The optical fiber waveguide coupler is an optical fiber waveguide end face coupler or a grating coupler.

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