CN102590577B - Full-optical fiber heterodyning current sensor - Google Patents

Abstract

An all-fiber heterodyne current sensor, including a semiconductor laser light source, a common optical fiber polarization controller, an optical fiber current sensing unit, a section of optical fiber with a sub-wavelength metal grating on the end face, and the first and second optical power meters, the first The first and the second two optical fiber circulators, wherein the output end of the semiconductor laser light source is connected to the first optical fiber circulator through the optical fiber polarization controller and then connected to the optical fiber current sensing unit; the third end of the first optical fiber circulator is connected to the second optical fiber in parallel The first port of the circulator, the second end of the second optical fiber circulator are provided with an end face metal grating and the first optical power meter, and the third end of the second optical fiber circulator is connected with the second optical power meter. Using the all-fiber optical path based on the nano-metal wire grid at the end of the fiber, the current sensor has greatly improved in terms of sensitivity, stability, and simplification of the device itself.

Description

An all-fiber heterodyne current sensor

technical field

The invention belongs to the field of optoelectronic technology, and in particular relates to a method for measuring optical quantities and the polarization selection characteristics of metal wire grids, and a manufacturing method and application of an optical fiber current sensor for realizing heterodyne current measurement under the condition of all optical fibers.

Background technique

The conventional current mutual induction technology based on the principle of electromagnetic induction used in current industrial applications has exposed a series of problems: oil-filled transformers may be broken down and explode in ultra-high voltage environments, and there are magnetic saturation and magnetic The adverse effects of the hysteresis effect, large volume and weight, high price, and susceptibility to electromagnetic interference, etc., are difficult to meet the needs of the development of the new generation of smart grid power system. In comparison, optical fiber sensing technology has the following significant advantages: insulating dielectric materials have strong anti-interference ability, can work in extremely harsh environments, small size, light weight and free layout, large measurement range and good linearity, easy to integrate with optical fiber Combination of communication systems. Therefore, the fiber optic current sensor that introduces the fiber optic sensing technology into the current detection becomes a good method to be applied to the new generation smart grid power system.

Fiber-optic current transformer is a new type of optical-mechanical-electrical integration equipment, which can be widely used in many fields of smart grid. However, due to the difficulty in calculating the influence of temperature and stress on measurement performance, the difficulty of product manufacturing process, poor consistency of components, and high manufacturing costs, it is still difficult to apply fiber optic current transformers on a large scale. The all-fiber current sensor based on metal nanowire grids developed by us adopts all-fiber sensing optical path, which aims to improve the stability and accuracy of optical fiber sensing and greatly reduce product costs.

With the influence of Japan's nuclear power plant leakage incident, China has suspended the approval of some new nuclear power projects. In addition, the country will invest 500 billion yuan in the construction of UHV power grids during the "Twelfth Five-Year Plan" period, and the development of smart grids is bound to usher in spring. The UHV power grid based on smart grid technology will be a big stage for the application of new technologies such as digital power station technology, control systems based on optical fiber communication, and intelligent sensing. The traditional current mutual inductance has been difficult to meet the development needs of the new generation of smart grid power system on-line detection, high-precision fault diagnosis, operation under high interference, large current measurement, and power digital network. The fiber optic current sensor that introduces fiber optic sensing technology into current detection is the best way to solve the above problems.

It is estimated that the value of photoelectric transformers used in the next-generation UHV smart grid system will exceed 10 billion yuan, and the fiber optic current sensor that leads the technology development trend is bound to occupy a large share. Therefore, the market prospect of fiber optic current sensors for smart grids is extremely optimistic.

Based on all the research at home and abroad, the optical fiber technology current sensor is mainly divided into the following two categories:

The first category is temperature equivalent sensing based on current heating effects, such as distributed current sensors based on fiber Bragg gratings. The advantage of this type of technology is that there are many basic temperature sensing technologies. Temperature sensing has a slow response time and is easily affected by environmental conditions, which greatly limits its industrial application.

The second category is current sensing based on the Faraday magneto-optic effect of fiber optic media. The advantages are accurate sensing and fast response time. ) is small, so that the sensing sensitivity is low.

The optical fiber current sensor described in this work is based on the magneto-optical effect current sensing of the reflective optical fiber optical path. There are also many researches on fiber optic current sensing based on this technology in the world, but almost all the research is on the sensing head (such as the introduction of micro-fiber ring, resonant cavity technology), or the sensing optical path (such as using Sagnac interference optical path) For improvement, there is no research to introduce all-fiber heterodyne technology at the polarization detection end. Heterodyne technology plays a key role in improving measurement accuracy in sensing. The existing practice is to use an independent crystal-like beamsplitter prism at the light detection end, and the introduction of discrete components causes the same disadvantages as the above-mentioned use of magneto-optic crystals, namely It has a great impact on the miniaturization and performance reliability of the device. In addition to the general advantages of optical fiber current sensing, this work also has the unique advantage of citing the polarization analysis technology of optical fiber metal nanowire grids, which enables the first realization of an all-fiber heterodyne current sensing system without any discrete components. It is conducive to the miniaturization and cost reduction of the device, and the introduction of the heterodyne method can also greatly improve the stability of the device, and it can also work normally under extreme conditions such as large fluctuations in light source and temperature.

Contents of the invention

The purpose of the present invention is to prepare a novel all-optical fiber heterodyne current sensor and an all-fiber heterodyne current sensing method by using the optical signal polarization detection technology of the metal wire grid on the end face of the optical fiber.

The technical scheme of the present invention is: an all-fiber heterodyne current sensor, including a semiconductor laser light source input end, a fiber optic polarization controller, a fiber optic current sensing unit, a section of optical fiber with a subwavelength metal grating on the end face and the first and second Two optical power meters, the first and the second two optical fiber circulators, in which the input end of the semiconductor laser light source is connected to the first optical fiber circulator through the optical fiber polarization controller and then connected to the optical fiber current sensing unit; the first optical fiber circulator The third end is connected in parallel with the first port of the second optical fiber circulator, the second end of the second optical fiber circulator is provided with an end face metal grating and the first optical power meter, and the second end of the second optical fiber circulator is connected to the second Optical power meter.

The optical fiber current sensing unit adopts a structure in which an optical fiber ring and a current ring are intertwined. One end of the optical fiber ring is connected to a Faraday rotating mirror, and the other end of the optical fiber ring is connected to the output end of the first optical fiber circulator to exchange optical signals. The input and output of the current ring The current circuit of the current sensing unit to be tested is connected; the signal light reflected from the current sensing unit enters the first port of the second circulator through the first circulator.

The metal grating on the end face is a sub-wavelength metal grating, which is an all-fiber optical polarization controller that controls the transmittance and polarization rate of incident light with different polarization states on the end face of the fiber.

Adopt the method that realizes heterodyne measurement under the condition of all-optical fiber, set optical path characteristic as: when the incident light of semiconductor laser light source input end passes through described all-fiber optical polarization controller, transmitted light is measured light intensity I _t by optical power meter, reflected light Introduce another section of optical fiber through an optical fiber circulator to measure the light intensity I _r , and obtain the heterodyne result after signal processing The incident light goes to the first port of the fiber circulator 1, the third port of the circulator 1 is directly connected to the second optical power meter through the optical fiber, and the incident light passes through the first port of the circulator to the second port of the fiber circulator and the full-fiber optical polarization control The transmitted light of the device is coupled into a section of optical fiber through a fiber coupling V-shaped groove to measure the light intensity of the first optical power meter; the transmitted light is coupled into a section of optical fiber through a fiber coupling V-shaped groove to measure the light intensity I _t , and the reflected light passes through a The optical fiber circulator introduces another section of optical fiber to measure the light intensity I _r , the transmitted light intensity I _t =I ₀ sin ² (δ/2), the reflected light intensity I _r =I ₀ cos ² (δ/2), where δ is the phase difference, and I ₀ is the light intensity of incident polarized light; the results of transmitted light and reflected light intensity are only related to the light phase difference δ caused by current changes, and have nothing to do with current sensing, such as light source fluctuations, ambient temperature changes, weak Unfavorable factors such as mechanical vibration can be excluded.

A circulator 1 is used to connect the light source, the current sensing unit and the all-fiber heterodyne optical path; the light source includes a semiconductor laser light source and an ordinary optical fiber polarization controller.

The metal wire grid is directly or indirectly prepared on the end face of the optical fiber by micro-processing technology, and the selective reflection or transmission effect of the metal wire grid on specific polarized light is used to realize the polarization control of the reflected or transmitted light of a specific optical band.

The basic sensing principle used by the optical fiber current sensor of the present invention is the Faraday magneto-optical effect. When plane polarized light propagates in some non-optical substances with magnetic field action, if the propagation direction is along the direction of magnetic field action, the polarization plane of the light wave will rotate, and the rotation angle is proportional to the strength of the magnetic field and the length of the medium it passes through, β =γ∫Hdl, where γ is the magneto-optical coefficient (Vander coefficient), H is the magnetic field strength, l is the space length of the magneto-optical effect interaction, and β is the azimuth polarization angle of polarized light. In the present invention, the optical fiber is used not only as the transmission carrier of the signal light, but also as the sensing substance that produces the Faraday magneto-optical effect, that is, the Faraday sensing effect occurs directly during the transmission process of the signal light in the optical fiber.

Fig. 1 is a schematic diagram showing the structure of wires and optical fibers wound with each other according to the present invention. Multiple coils of optical fiber are parallel and tightly wound on a cylinder with a hollow in the center (the dark part in the figure), and the wires are evenly spirally wound around the inner and outer walls of the cylinder (the straight line marked with current I in the figure), then this structure The direction of the magnetic field generated by the current is along the circumferential direction of the cylinder wall (that is, the transmission direction of light in the optical fiber), so that the Faraday magneto-optic effect shown in Figure 1 can be used directly in the optical fiber ring to measure the change of the current in the wire.

In the polarization optical fiber sensing system, the polarization analysis technology of polarized light plays a key role in the overall sensing system. In the present invention, a brand-new polarized light analyzer based on metal nanowire grid is used, which has the advantages of small size, high measurement accuracy, and easy combination with optical fiber system to construct an all-fiber system.

The structure of the metal nanowire grid is shown in Figure 2. One-dimensional infinitely long strips of metal (such as gold, silver, etc.) and strips of air are periodically arranged on the substrate (such as silicon dioxide), and the incident light is vertical incident on the surface of the wire grid. According to the effective medium theory, when the period of the grating (on the order of nanometers) is much smaller than the wavelength of the incident light, the grating can be equivalent to an overall birefringent material, and the incident light whose polarization is parallel to the direction of the wire grid is almost completely reflected, while the polarization Almost all incident light perpendicular to the direction of the wire grid can be transmitted. Thus, an analyzer function for incident polarized light is formed.

The method of optical heterodyne has played a great role in improving the precision of polarization detection. The conventional optical signal polarization detection method is to add a splitter prism (composed of multiple birefringent crystals) at the output end of the signal light to be detected, and divide the outgoing light into two beams (or multiple beams). There is a fixed phase difference determined by the beam-splitting prism, and the optical power meter (or spectrometer) is used to collect information such as the light intensity, frequency and phase of each beam of light, and then use mathematical operations to obtain pure sensing signals that exclude external interference. External interference factors that can be excluded generally include fluctuations in light source intensity, disturbances in ambient temperature, and weak mechanical vibrations in the measurement optical path. However, the obvious disadvantage of this heterodyne technique is that the beam splitting prisms used are all bulk crystal materials, and the reference of bulk materials inevitably makes the measurement need to be carried out in the free optical path, thus losing the all-fiber device Small size, light weight, good mechanical stability advantages.

The beneficial effects of the present invention are:

(1) In the present invention, the optical path polarization analysis technology based on the nano-metal wire grid at the end face of the optical fiber is used to realize the acquisition of all-fiber heterodyne data, greatly improve the stability of the device, and can be used under extreme conditions such as large fluctuations in light sources and large temperature fluctuations. normal work.

(2) The present invention realizes all-optical current sensing without any discrete components for the first time, improves system reliability, miniaturizes devices, and is more conducive to flexible layout in actual smart grids.

(3) The key component used in the current sensor—fiber nanometal wire grid can be mass-produced by nanoimprinting technology, and the product cost can be controlled to be very low.

Description of drawings

Fig. 1 Schematic diagram of the structure of the mutual winding of wires and optical fibers in the induction unit;

Figure 2 The working principle of the metal wire grid polarizer: the incident TE light is reflected, and the TM light is transmitted;

Figure 3 is an all-fiber heterodyne measurement optical path based on a metal wire grid at an optical fiber end face;

The structural setting and working principle of the all-fiber heterodyne current sensor of Fig. 4;

Fig. 5 is the metal grating structure obtained at the core of the fiber section by using the FIB method. Figure 5(a) is a photo of a metal grating; Figure 5(b) is a photo of a cross-section of an optical fiber with a wire grid structure at the core;

Fig. 6 is the optical signal current sensing measurement result and the heterodyne calculation result in embodiment 2;

Figure 7 shows the comparative measurement curves of heterodyne measurement and common measurement. The curve shown in Figure 7(a) is the transmission signal of the light source under the condition of pure intensity instability; the curve shown in Figure 7(b) is the reflection signal of the light source under the condition of pure intensity instability (optical power meter 2 Signal) measurement results; Figure 7(c) shows the measurement curve of the integrated transmission and reflection signals after heterodyne processing.

Detailed ways

The method and application of the present invention will be further illustrated by the following examples, but these examples are not intended to limit the present invention.

All-fiber heterodyne current sensors based on fiber-optic wire grids include:

(1) Fabrication of the metal wire grid at the end face of the optical fiber. Using micro-nano processing technology, metal wire grids are fabricated on the surface of optical fibers by direct or indirect methods. Direct methods include focused ion beam etching (FIB), micro-nano shield directional deposition technology, and soft template printing (metal); indirect methods include nanoimprinting, photolithography, holographic interference, and electron beam direct writing (EBL). Specifically: the focused ion beam etching technology in the direct method is to use the focused gallium ion beam to sputter off the metal film layer in the target area of the fiber end face to obtain a metal wire grid structure; the directional deposition technology of the micro-nano shield is to use the space of the shield Shielding effect, direct deposition of metal wire grids on the end faces of optical fibers; soft template printing technology deposits metal film layers on the surface of micro-nano structures of soft templates, and prints transfer metal wire grids to the end faces of optical fibers. The indirect method can also be divided into two categories. One is to use micro-nano processing technology to prepare a structural barrier layer on the metal film layer deposited on the end face of the optical fiber, and use this as a barrier to etch the groove by wet etching or dry etching. Finally, the barrier layer is eluted to obtain a metal wire grid structure; another solution is to prepare a microstructure barrier layer first, then deposit the metal, and then elute the barrier layer and the metal deposited on it to obtain the target metal wire grid structure.

The optical fiber end metal grating used in the present invention is made into a polarization controller, which can easily eliminate these shortcomings and realize the purpose of current sensing under the condition of all optical fibers, because it has the inherent advantage of external optical fiber heterodyne, the method is shown in Figure 3 . The metal nanowire grid shown in Fig. 2 is used to make the fiber end face to control the transmittance and polarization rate of the incident light with different polarization states on the fiber end face, which is an all-fiber optical polarization controller.

Figure 4 shows the working principle diagram of the all-fiber heterodyne current sensor, and the specific description is as follows: first, the semiconductor laser light source generates a single-wavelength (such as infrared with a wavelength of 1550 nanometers) signal light that is input into an ordinary single-mode optical fiber, and the signal light passes through The online fiber optic polarization controller adjusts the polarization characteristics of the input light, and then inputs it to the current sensing head made of wire loop/fiber surround, and a Faraday rotating mirror is added to the reflection end to rotate the reflected light by 90 degrees relative to the incident light axis to eliminate Unfavorable factors such as inherent birefringence and stress birefringence in fiber optic rings. The circulator 1 is used to collect the signal light reflected from the sensor head, and then input into the circulator 2 . The signal light is incident on the metal nanowire grid on the end face of the optical fiber through the circulator 2, the transmitted light of the wire grid is measured by the optical power meter 1, and the reflected light of the wire grid is collected by the circulator 2 and then input to the optical power meter 2 for measurement. The measured values of the two optical power meters are heterodyned. When the current in the wire on the sensing unit changes, it causes a change in the magnetic field around the fiber, which in turn causes a change in the polarization state of the transmitted light in the fiber. The change in the polarization state is obtained on the metal nanowire grid at the fiber end face. .

The general operation steps of the first scheme of the indirect method are as follows:

(a) Deposit a layer of metal film (film thickness 0.01-2 microns) on the end face of the optical fiber.

(b) Coating photoresist or resist layer on the end face of the optical fiber

(c) Patterning photoresist or resist layer using micro-nano processing technology

(d) Develop and remove glue or remove residue

(e) Use wet etching or dry etching to etch away the metal that is not covered by photoresist

(f) Dissolve and remove the remaining photoresist layer with a solvent to obtain the desired grating structure

The operation steps of the second option of the indirect method include:

(a) Coating photoresist or resist layer on the fiber end face

(b) Patterning photoresist or resist layer using micro-nano processing technology

(c) Develop and remove glue or remove residue

(d) Deposit a metal film with a specific thickness (0.01-2 microns) on the surface of the pattern

(e) Remove the photoresist layer by dissolving with a solvent to obtain the desired grating structure

The period of the metal wire grid is 0.05-50 microns, the duty cycle is any value between 0-1, and the metal film thickness is 0.01-2 microns.

(2) The setting of the heterodyne current sensing optical path under the condition of all-fiber. Using the optical fiber end-face metal grating prepared by the above method, construct the heterodyne measurement optical path under the condition of optical fiber as shown in Fig. 1 . The light transmitted in the optical fiber is affected by the change of the current of the sensing unit, so that the polarization state of the light incident on the detection end changes, and the light intensity of the transmitted light and reflected light of the metal grating at the end of the fiber will change accordingly. The transmitted light is coupled into a section of optical fiber through a fiber coupling V-groove to measure the light intensity I _t , the reflected light is introduced into another section of optical fiber through a fiber circulator to measure the light intensity I _r , and the heterodyne result is obtained after signal processing Thus, the classic heterodyne measurement method is realized under the condition of all-fiber, and the heterodyne results can eliminate external factors such as fluctuations in light source intensity, disturbances in ambient temperature, and weak mechanical vibrations in the measurement optical path that are not related to specific sensing.

Example 1

The single-mode fiber was cut with a fiber cleaver to obtain a flat fiber end face, and a 0.07 μm thick gold film was plated on the fiber end face by sputtering. Using the focused ion beam etching system (Strata FIB 201, FEI company, 30keV gallium ion source), under the condition of 7pA beam current, use the focused gallium ion beam to sputter off the metal film layer in the target area of the fiber end face, so that A gold wire grid with an area of 10 μm×10 μm, a period of 0.2 μm, and a duty ratio of 0.5 is obtained at the core, as shown in FIG. 5 .

Example 2

As shown in Figure 4, the all-fiber heterodyne current sensor uses the metal wire grid on the end face of the fiber made in Example 1, together with the circulator 2, the optical power meter 1, and the optical power meter 2 to form an all-fiber heterodyne sensor light path. In the induction unit, there are 420 rings of optical fiber and 60 rings of wire. The current range in the optical fiber is 0 to 10A, so the equivalent current range is 0-600A. Figure 6 shows the current sensing curve, the detection sensitivity reaches 0.528degree/A, and the minimum detection accuracy is 0.5mA. Since the optical fiber sensing is not in direct contact with the current, the sensor itself has no maximum measurement limit (only limited by the wire that conducts the current) . Figure 7 shows the comparative measurement curves of heterodyne measurement and common measurement. When there are unfavorable factors such as light source instability, mechanical disturbance, and environmental temperature changes in the measurement system, the results obtained by non-heterodyne measurement will be inaccurate. The curve shown in Figure 7(a) is the measurement result of the transmitted signal (signal of optical power meter 1) when the light source is purely unstable in intensity, and the curve shown in Figure 7(b) is the measurement result of the light source purely in the case of unstable intensity The measurement results of the reflected signal (optical power meter 2 signal) below are all affected by external adverse factors, resulting in poor linearity. Figure 7(c) shows the measurement curve of the integrated transmission and reflection signals after heterodyne processing, which eliminates the influence of external factors on the measurement curve.

Claims (10)

1. An all-fiber heterodyne current sensor is characterized in that it includes a semiconductor laser light source, a common optical fiber polarization controller, an optical fiber current sensing unit, an optical fiber with a sub-wavelength metal grating on the end face, and the first and second two An optical power meter, the first and the second two optical fiber circulators, wherein the output end of the semiconductor laser light source is connected to the first optical fiber circulator through the optical fiber polarization controller and then connected to the optical fiber current sensing unit; the first optical fiber circulator the second The three terminals are connected in parallel with the first port of the second optical fiber circulator, the second end of the second optical fiber circulator is provided with an end face metal grating and the first optical power meter, and the third end of the second optical fiber circulator is connected to the second optical fiber circulator. dynamometer. 2. The all-fiber heterodyne current sensor according to claim 1, characterized in that: the fiber optic current sensing unit adopts a structure in which a fiber optic ring and a current ring are intertwined, one end of the fiber optic ring is connected to a Faraday rotating mirror, and the other end of the fiber optic ring is connected to The second end of the first optical fiber circulator functions as the input and output of optical signals, and the current loop is connected to the circuit of the current sensing unit to be tested; the signal light reflected from the current sensing unit passes through the third port of the first circulator is incident on the first port of the second circulator. 3. The all-optical fiber heterodyne current sensor according to claim 1, characterized in that: the metal grating on the end face is a sub-wavelength metal grating, which is a full control of the transmittance and the polarization rate of the different polarization states of the incident light on the end face of the optical fiber. Fiber optic polarization controller; the fiber optic current sensing unit is tightly wound in parallel on a cylinder with a hollow in the center by multiple coils of optical fiber, and the wire is wound evenly and spirally around the inner and outer walls of the cylinder. Light effect to measure changes in current in a wire. 4. a kind of all-fiber heterodyne current sensing method utilizing all-fiber heterodyne current sensor claimed in claim 1, is characterized in that: adopt the method for realizing heterodyne measurement under a kind of all-fiber condition, set optical path characteristic as: When the incident light at the input end of the semiconductor laser light source passes through the all-fiber optical polarization controller, the transmitted light passes through the optical power meter to measure the light intensity I _t , the reflected light is introduced into another section of optical fiber through the fiber looper to measure the light intensity I _r , and passes through the signal Processing to get heterodyned results Specifically, the incident light enters the first port of the first optical fiber circulator, the third port of the first optical fiber circulator is connected with the first port of the second optical fiber circulator, and the second port of the second optical fiber circulator The second port couples light to the first optical power meter through the optical fiber to measure the transmitted light intensity I _t , and the third port of the second fiber optic circulator is directly connected to the second optical power meter through the optical fiber to measure the reflected light intensity I _r ; Intensity I _t =I ₀ sin ² (δ/2), reflected light intensity I _r =I ₀ cos ² (δ/2), where δ is the phase difference, and I ₀ is the light intensity of the incident polarized light; the transmitted light and The result of reflected light is only related to the optical phase difference δ caused by current changes, and unfavorable factors that are not related to current sensing, including light source fluctuations, environmental temperature changes, and weak mechanical vibrations, can be excluded. 5. The all-fiber heterodyne current sensing method according to claim 4, characterized in that: use the first optical fiber circulator to connect the light source, the current sensing unit and the all-fiber heterodyne optical path; the light source comprises a semiconductor laser light source and Ordinary fiber optic polarization controller. 6. The all-fiber heterodyne current sensing method according to claim 4 or 5, characterized in that: utilize micro-nano processing technology to directly or indirectly prepare metal wire grids on the end faces of optical fibers, and use metal wire grids to detect specific polarized light Selective reflection or transmission effect realizes polarization control of reflected light or transmitted light in a specific light band. 7. The all-fiber heterodyne current sensing method according to claim 4 or 5, wherein the semiconductor laser light source produces a single-wavelength signal light that is input into a common single-mode optical fiber, and the signal light passes through an online optical fiber polarization controller Adjust the polarization characteristics of the input light, and then input it to the current sensing head made of wire loop/fiber surround, and add a Faraday rotation mirror at the reflection end to rotate the reflected light by 90 degrees relative to the incident light axis to eliminate the inherent birefringence in the fiber loop , Unfavorable factors of stress birefringence; the first optical fiber circulator is used to collect the signal light reflected from the sensor head end, and then input into the second optical fiber circulator; the signal light is incident on the fiber end face through the second optical fiber circulator On the metal nanowire grid, the transmitted light of the wire grid is measured by the first optical power meter, and the reflected light of the wire grid is collected by the second optical fiber circulator and then input to the second optical power meter for measurement; the measured values of the two optical power meters are Heterodyne calculation; when the current in the wire on the induction unit changes, it causes a change in the magnetic field around the fiber, which in turn causes a change in the polarization state of the transmitted light in the fiber. The change in the polarization state is obtained on the metal nanowire grid at the fiber end. Heterodyne detection. 8. according to claim 4 or 5 described all-fiber heterodyne current sensing methods, it is characterized in that optical fiber comprises single-mode optical fiber, multimode optical fiber, polarization-maintaining optical fiber, has smooth optical fiber end face; Semiconductor laser light source, common optical fiber polarization Controllers, fiber optic circulators, optical power meters, and Faraday rotating mirrors are all commercially available. 9. The all-fiber heterodyne current sensing method according to claim 6, characterized in that the metal wire grid is characterized in that the material includes gold, silver, aluminum, copper, platinum or chromium metal, and the wire grid structure period 0.05-50 microns, the film thickness of the wire grid is 0.01-2 microns, and the structure area covers the fiber core. 10. The all-fiber heterodyne current sensing method according to claim 5, characterized in that the method for realizing heterodyne measurement is applied to optical information processing systems, optical fiber sensing and precision optical measurement systems.