CN209764932U - Polarization-detecting closed-loop all-fiber current transformer - Google Patents
Polarization-detecting closed-loop all-fiber current transformer Download PDFInfo
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Abstract
the utility model provides a polarization-detecting closed loop all-fiber current transformer. The method comprises the following steps: the device comprises a broadband light source, a detector, a polarization maintaining optical fiber beam splitting polarizer, a phase modulator, a lambda/4 wave plate, a sensing optical fiber, a reflector, a detector and a control circuit. The broadband light source emits broadband light to the polarization maintaining fiber beam splitting polarizer, the polarization maintaining fiber beam splitting polarizer outputs light waves to the phase modulator and the lambda/4 wave plate, and the lambda/4 wave plate decomposes the polarized light into left-handed circular polarized light and right-handed circular polarized light and transmits the left-handed circular polarized light and the right-handed circular polarized light to the sensing fiber. The polarized light reflected by the reflector at the tail end of the sensing optical fiber is synthesized into linearly polarized light after passing through a lambda/4 wave plate, the light power of the linearly polarized light after polarization detection processing is detected through a detector and a control circuit to obtain a digital signal, and the digital signal is fed back to a phase modulator as an open-loop digital quantity to realize closed-loop feedback. The utility model discloses can realize big dynamic range, high accuracy, high stable current detection.
Description
Technical Field
The utility model relates to an optical fiber sensing technical field especially relates to a polarization detection formula closed loop all-fiber current transformer.
Background
Compared with the traditional electromagnetic mutual inductor, the optical fiber current mutual inductor has the following advantages; the safety advantage is that: the insulation structure is simple, green and environment-friendly, and has no explosion, no oil gas, no SF6 and no secondary open circuit danger; the cost advantage is as follows: when the voltage is more than 220kV, the optical fiber is adopted, so that the insulation cost is greatly reduced; the performance advantage is as follows: the volume is small and the weight is light; the dynamic range is large, alternating current/direct current can be measured, magnetic saturation is avoided, the frequency band response is wide, the anti-interference capability is strong, and the digital output is suitable; the optical fiber current transformer meets the requirements of national intelligent power grid development planning.
According to different working mechanisms of 2 different optical phase modulators, there are 2 optical path structure schemes of the optical fiber current transformer at present:
The first optical path structure scheme: one prior art Sagnac interferometric optical structure employing an integrated optical multifunction phase modulator MIOC as a core is shown in fig. 1. The scheme has the advantages that: the working principle of a fiber optic gyroscope based on the Sagnac interferometer is mature in theory; the disadvantages are: the optical structure has large insertion loss, and environmental factors such as temperature, vibration and the like can influence the system performance.
The following is a list of patents for existing fiber optic current transformers that employ a phase modulator scheme.
except for the "reflective all-fiber current transformer" of the No.15 patent, application No. 201320439007.4, which explains the function of the polarizer as polarizing and analyzing, all other patents falsely describe the interference of light waves at the polarizer position. However, the patent No.15 describes a laser as a light source, not a broadband light source such as SLD or ASE light source, and thus it is inevitable that an error is caused by a nonlinear effect in the optical fiber; the function of the phase modulator for controlling the polarization rotation of the light wave is not properly explained.
The following is a prior art article describing a fiber optic current transformer.
none of the above published references has a proper understanding of the function of the phase modulator. Are all misinterpreted, interference occurs at the polarizer location;
The above-mentioned false physical phenomena interpretation of the prior art patents and documents introduces false mathematical model description, which leads to false conclusions and false structural design of the optical system, thereby also causing serious false design in the circuit and closed-loop control software; the net result is that this highly advantageous optical structure does not allow for engineering applications.
for the optical fiber current transformer sensing system of the polarization direction rotation switch optical structure adopting the phase modulator as the lambda/2 wave plate, the requirements for the optical device are as follows:
1. the light source must be broadband;
2. The system needs polarization-maintaining fiber beam splitting to maintain the polarization characteristic of the light wave.
3. The polarization extinction ratio of the polarizer requires >60 dB.
Wherein: the optical power splitting is usually performed by using a conventional fiber coupler, and there are also a circulator scheme and a polarization beam splitter scheme. However, there are insurmountable weaknesses with the latter 2 solutions:
1. Fiber optic circulators have weaknesses: due to the limitations of the working mechanism, there is a large Wavelength Dependent Loss (WDL), Polarization Dependent Loss (PDL). Temperature Dependent Loss (TDL), and various loss cross-effects, can significantly reduce other system performance such as system linearity and system measurement errors, so commercial systems prefer to use conventional fiber couplers rather than fiber circulators;
2. the polarization beam splitter/combiner has weak points: the working mechanism is as follows: based on the fact that light waves propagate in the birefringent crystal and deviate from the direction of an optical axis, o light and e light leave away, and therefore 2 polarized light beams are separated; or a Glan prism, a Wollaston prism, a polarization beam splitter prism and the like are adopted to realize the separation of the 2-polarization light beams. Due to volume limitation, commercial polarization beam splitters mostly adopt a birefringent crystal scheme, and due to light wave propagation limitation, 2-polarization beams still partially overlap in a space separation part, so that the performance is greatly reduced, and particularly, a fiber sensing system for simulation cannot achieve a polarization extinction ratio of more than 60 dB. Commercial systems prefer to use conventional fiber couplers and also fiber polarization splitters/combiners.
3. compared with an optical fiber circulator and a polarization beam splitter/combiner, the traditional optical fiber coupler comprising the polarization-maintaining optical fiber coupler and the optical fiber polarizer is combined, so that relatively good WDL, PDL and TDL can be obtained, and reciprocity meeting objective laws of physics can be met, and the optical fiber coupler is the best choice of the traditional scheme.
4. the weakness of conventional fiber optic couplers, see the optical device patents granted to the present invention
| No. | Application number | patent name |
| 1 | 200920216913.1 | 2 x 2 polarization-maintaining optical fiber beam splitter |
| 2 | 201520663325.8 | 2 x 2 polarization-maintaining optical fiber beam splitter |
There are known patents for optical fiber polarizers that,
| No. | Patent name | application number |
| 1 | crystal wrapped polarization-maintaining optical fiber polarizer | 02217755.8 |
| 2 | Micro-optical fiber polarizer | 200420003467.3 |
and current commercial optics, are not able to achieve polarization extinction ratios >60 dB.
SUMMERY OF THE UTILITY MODEL
The embodiment of the utility model provides a polarization detection formula closed loop's full fiber current transformer to overcome prior art's shortcoming.
In order to achieve the purpose, the utility model adopts the following technical scheme.
A polarization-analyzing closed-loop all-fiber current transformer, comprising: the device comprises a broadband light source, a detector, a polarization maintaining optical fiber beam splitting polarizer, a phase modulator, a lambda/4 wave plate, a sensing optical fiber, a reflector, a detector and a control circuit;
the broadband light source emits broad-spectrum light, and the broad-spectrum light is transmitted to the polarization maintaining optical fiber beam splitting polarizer;
The polarization maintaining fiber beam splitting polarizer splits the power of light waves output by the broadband light source and realizes polarization, and the light waves enter the phase modulator at an incident angle of 45 degrees; analyzing and polarizing the light wave returned from the phase modulator, splitting the light power, and realizing secondary analysis of the light power entering the detector so as to multiply the polarization extinction ratio of the detected polarized light wave;
The phase modulator is used as a polarization direction rotating switch and is used for rotating the polarization direction of the received light wave through an external electric signal and transmitting the output polarized light to the lambda/4 wave plate through the polarization maintaining optical fiber delay coil;
the lambda/4 wave plate is used for decomposing the received polarized light into left circularly polarized light and right circularly polarized light and transmitting the left circularly polarized light and the right circularly polarized light to the sensing optical fiber;
when current flows through the sensing optical fiber, the light wave polarization state is caused to rotate by a magnetic field generated by the current through the Faraday effect, the left circularly polarized light and the right circularly polarized light reflected by the reflector at the tail end of the sensing optical fiber are synthesized into linearly polarized light after passing through the lambda/4 wave plate, and the polarization angle of the linearly polarized light is superposed with the deflection angle caused by the current induced magnetic field of the Faraday effect; the linearly polarized light returns to the polarization-maintaining fiber beam splitting polarizer again through the phase modulator, and the polarization-maintaining fiber beam splitting polarizer performs polarization analysis processing on the linearly polarized light;
the detector is used for detecting the optical power of the linearly polarized light after the polarization detection processing of the polarization-maintaining optical fiber beam splitting polarizer, converting the optical power into an electric signal and outputting the electric signal to the control circuit;
The control circuit performs analog-to-digital conversion sampling, digital filtering and demodulation processing on the electric signal transmitted by the detector to obtain a digital signal, and outputs the digital signal; and feeding back the digital signal as an open-loop digital quantity to the phase modulator to realize closed-loop feedback.
Preferably, when the broadband light source is an SLD light source output by a polarization maintaining fiber, the output polarization maintaining pigtail of the SLD light source is aligned at 0 degree or 90 degrees with the input polarization maintaining pigtail of the polarization maintaining fiber beam splitting polarizer, and the polarization of the polarization maintaining fiber beam splitting polarizer is a single polarized light;
When the broadband light source is an SLD light source or an ASE light source output by a common single-mode fiber, the angle alignment direction of the single-mode fiber and the input polarization-maintaining tail fiber of the polarization-maintaining fiber beam splitting polarizer is not limited, and the polarization-maintaining fiber beam splitting polarizer realizes the polarization function.
preferably, the polarization maintaining pigtail of the polarization maintaining fiber beam splitting polarizer is welded with the polarization maintaining pigtail at the input end of the phase modulator at an angle of 45 degrees, and the phase modulator is used as a lambda/2 wave plate capable of adjusting the polarization direction of the optical wave.
Preferably, the output polarization-maintaining tail fiber of the phase modulator is aligned and welded with the birefringence principal axis 0 degree of the polarization-maintaining fiber delay coil, the tail fiber of the polarization-maintaining fiber delay coil forms a 45-degree angle with the tail fiber angle of the lambda/4 wave plate, and the light wave enters the lambda/4 wave plate at the 45-degree angle.
Preferably, the polarization extinction ratio of the polarization maintaining fiber beam splitting polarizer is higher than 60 dB.
Preferably, the phase modulator is a lithium niobate phase modulator, and the lithium niobate phase modulator realizes a pi/2 deflection angle of a light wave polarization plane.
by the technical scheme that the embodiment of the utility model provides can see out, the polarization-maintaining optical fiber beam splitting polarizer is adopted to the polarization-analyzing closed-loop all-fiber current transformer of the embodiment of the utility model, and the phase modulator is adopted as the closed-loop control method of the adjustable lambda/2 wave plate, so that the insertion loss of the optical system is small; the polarization rotation of the light wave output by the phase modulator is only completed in 1 optical fiber, the temperature and vibration stability is good, and the engineering application is facilitated. The polarization extinction ratio of the polarization maintaining optical fiber beam splitting polarizer in the polarization analyzing type closed-loop all-fiber current transformer provided by the embodiment of the utility model can be improved to more than 60dB, even as high as 80 dB; thereby enabling practical engineering applications of the advantageous optical design.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to these drawings without creative efforts.
FIG. 1 is a prior art diagram of a Sagnac interferometric optical configuration using an integrated optical multi-function phase modulator MIOC as the core;
Fig. 2 is an optical structure diagram of a polarization direction rotating switch using a phase modulator as a λ/2 wave plate according to an embodiment of the present invention;
Fig. 3 is a schematic diagram of the response of a square-wave modulated electrical signal applied to a phase modulator and an output optical signal in the prior art.
Detailed Description
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below by referring to the drawings are exemplary only for explaining the present invention, and should not be construed as limiting the present invention.
As used herein, the singular forms "a", "an", "the" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. It will be understood that when an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element or intervening elements may also be present. Further, "connected" or "coupled" as used herein may include wirelessly connected or coupled. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.
It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the prior art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
For the convenience of understanding the embodiments of the present invention, the following description will be given by way of example only with reference to the accompanying drawings, and the embodiments are not limited thereto.
the embodiment of the utility model provides an actual physics background to the optic fibre current transformer optical structure who adopts the phase modulator scheme explains as follows:
1. When the interference of light waves only exists in the condition that 2 different optical fibers are combined into 1 optical fiber, the mode field distribution spatial positions of the 2 optical waves are different, and the effect is that the light power loss or the power separation is generated; the optical waves transmitted in the same optical fiber have the same optical mode field distribution spatial position, and under the condition of no nonlinear effect and even on the premise of the existence of the nonlinear effect, the interference effect cannot occur in the physical mechanism, namely the optical power cannot be lost or separated; even if the optical wave mode field distribution returns to the polaroid, the spatial position of the optical wave mode field distribution is still the same, the optical power is not lost, and the interference effect is not generated.
2. The real application of the polaroid is the traditional polarizing and analyzing function; the optical power loss observed in the optical system of the fiber optic current transformer is due to the polarization plate analysis. In the application of the analog optical fiber sensing system, the polarization extinction ratio is required to reach 80dB similar to the waveguide of the MIOC modulator, at least the polarization extinction ratio is required to reach more than 60dB, so that the polarization error can be inhibited, and the signal-to-noise ratio of the system is improved, which is the core content to be described in the embodiment of the utility model; the single polaroid and the device at present can not reach 60dB magnitude basically, and the polarization extinction ratio reaching 80dB is more difficult; even if 2 polarizers are cascaded to improve the polarization extinction ratio, the alignment accuracy requirement is very high, namely, 0.1 degrees or even higher; in addition, the alignment accuracy of fusion splicing the polarizer fiber to the phase modulator fiber can significantly reduce the polarization extinction ratio that can be achieved.
3. the true use of a phase modulator is: an optical structure as a polarization direction rotating switch for a lambda/2 wave plate. The input light wave is incident at an angle of 45 degrees with the TE or TM mode of the modulator waveguide in a single polarization state; the working voltage of the phase modulator can be adjusted to realize the pi/2 radian rotation of the polarization state of the incident light wave; the working voltage of the phase modulator is the voltage corresponding to the realization of the pi/2 radian rotation of the light wave.
The advantage of the solution of the phase modulator as an adjustable lambda/2 plate compared to the interferometric solution of the MIOC phase modulator is: the insertion loss of the system is 6dB less than that of the MIOC scheme, namely, the loss of each of split beams and combined beams after MIOC is 3dB, and if the insertion loss of a device is considered, the loss is about 7 dB; the polarization rotation of the light wave output by the phase modulator is only completed in 1 optical fiber, so that the temperature and vibration stability is good, and the engineering application is facilitated; theoretically, instead of using a low birefringence single mode fiber, only a normal single mode fiber may be used; thereby, the cost can be greatly reduced.
The utility model discloses content that polarization detection formula closed loop all-fiber current transformer relates to includes:
1. Adopting a polarization maintaining fiber beam splitting polarizer;
2. The polarization extinction ratio is required to reach more than 60dB for an optical system to be industrially used;
3. the working mechanism of the optical structure of the optical fiber current transformer is that the polarization state of light waves is deflected by utilizing Faraday magneto-optical effect, so that the measured current is measured through polarization and analysis;
4. the phase modulator is used as the working mechanism of a polarization direction rotation switch capable of adjusting the lambda/2 wave plate;
5. The phase modulator is used as a voltage calculation method for a polarization direction rotation switch of an adjustable lambda/2 wave plate;
6. the phase modulator is used as a current transformer closed-loop control method of a polarization direction rotary switch of an adjustable lambda/2 wave plate, and can realize a large measurement range and high measurement linearity.
The utility model discloses polarization-detecting formula closed loop all-fiber current transformer adopts the polarization direction rotary switch optical structure as lambda/2 wave plate based on the phase modulator, can realize the general current detection function of interchange, direct current of big dynamic range, high accuracy, high stability.
The phase modulator of the rotary switch capable of adjusting the polarization direction of the lambda/2 wave plate is adopted, and the polarization state deflection of the light wave caused by the Faraday magneto-optical effect is utilized, so that the measured current is measured through polarization and analysis, and the most fundamental working mechanism is an optical polarization and analysis principle.
The embodiment of the utility model provides an adopt the polarization direction rotary switch optical structure of phase modulator as lambda/2 wave plate is shown in figure 2. The optical components of the optical path scheme comprise a broadband light source, a detector, a polarization maintaining optical fiber beam splitting polarizer, a phase modulator, a polarization maintaining optical fiber, a lambda/4 wave plate, a sensing optical fiber and a reflecting mirror.
the optical path fusion diagram is described as follows:
1. an SLD (Super luminescent Diode) light source is used as a broadband light source, broad spectrum light emitted from the SLD light source firstly passes through a polarization-maintaining optical fiber beam splitting polarizer, and polarization of the polarization-maintaining optical fiber beam splitting polarizer is single polarized light; the output polarization-maintaining pigtail of the SLD light source can be aligned 0 degrees, or 90 degrees, with the input polarization-maintaining pigtail of the polarization-maintaining fiber splitting polarizer to take advantage of 1 polarization mode of the SLD light source. If an ASE (Amplified spontaneous emission) light source is adopted, the polarization state of the ASE light source is natural light, and the ASE light source can be aligned at will and outputs stable single polarized light;
2. The polarization maintaining tail fiber of the polarization maintaining fiber beam splitting polarizer is welded with the polarization maintaining tail fiber at the input end of the phase modulator at an angle of 45 degrees; the light wave output by the polarization maintaining fiber beam splitting polarizer enters the phase modulator at an incident angle of 45 degrees. The phase modulator decomposes the received light wave into orthogonal 2 beams of polarized light, wherein the phase modulator functions as a lambda/2 wave plate capable of adjusting the polarization direction of the light wave;
3. The output polarization-maintaining tail fiber of the phase modulator is aligned and welded with the birefringence main shaft 0 degree of the polarization-maintaining fiber delay coil; the polarized light output by the phase modulator is transmitted to the polarization-maintaining optical fiber delay coil, and then the polarization-maintaining optical fiber delay coil transmits the polarized light to the lambda/4 wave plate.
4. the angle between the tail fiber of the polarization-maintaining fiber delay coil and the tail fiber of the lambda/4 wave plate forms a 45-degree angle, and the light waves enter the lambda/4 wave plate at the 45-degree angle and are decomposed into circularly polarized light with the opposite rotation directions of levorotatory light and dextrorotatory light 2.
and the left circularly polarized light and the right circularly polarized light output by the 5-1 lambda/4 wave plate enter the low-birefringence sensing optical fiber.
5-2, if current flows in the sensing optical fiber, the magnetic field generated by the current causes the polarization state of the light wave to rotate through the Faraday effect;
And 6-1, reflecting the tail end of the sensing optical fiber by a reflector, wherein the left circularly polarized light is changed into right circularly polarized light, and the right circularly polarized light is changed into left circularly polarized light.
And 6-2, under the condition that current flows in the sensing optical fiber, after the current is reflected by the reflector, the rotation angle of the polarization state of the light wave caused by the magnetic field generated by the current is multiplied.
7. After 2 left-handed and right-handed circularly polarized lights returned by the reflector pass through the lambda/4 wave plate, linearly polarized lights with a single polarization angle are synthesized again, but the angle is superposed with a deflection angle caused by a current induced magnetic field of a Faraday effect;
8. therefore, the angle of the linearly polarized light reversely incident to the phase modulator is a 45-degree angle and is superposed with the polarization angle change caused by the current induction magnetic field;
9. The linearly polarized light finally returns to the polarization maintaining fiber beam splitting polarizer:
9-1. due to the current flowing in the sensing fiber, the light wave can generate polarization rotation,
9-2. after the light wave is analyzed and polarized by a polarizer,
9-3, reflecting by a partial reflector,
9-4, analyzing the polarization again by the polarizer, and multiplying the analyzing effect;
10. finally, returning to the detector, detecting the optical power after the polarization detection by the detector, converting the optical power into an electric signal and outputting the electric signal to the control circuit;
11. The analog-to-digital conversion and sampling of the control circuit are carried out, then the control circuit is input into controller software to carry out digital filtering processing and demodulation, and the demodulated electric signals are used for controlling the phase voltage of the modulator so as to realize closed-loop feedback and output digital signals at the same time.
wherein, the light wave passes through the polarization maintaining fiber beam splitting polarizer twice, and each time, the light wave has an inherent 3dB loss; phase modulator insertion loss 4 dB; the additional loss of the polarization-maintaining fiber beam splitting polarizer is about 1dB, and the inherent optical insertion loss of the whole optical path structure is about 15 dB.
2. The closed-loop control method of the optical fiber current transformer comprises the following steps:
2.1 according to the Faraday magneto-optical effect and Malus law, the output response of a FOCT when a square wave bias modulation is applied is:
I(t)＝I0cos2[Δφf+φ(t)]
In the formula phifFor the phase shift, Δ φ, induced by the current-induced magnetic fieldfV is the Verdet constant of the fiber, I is the current, and N is the number of turns of the sensing fiber wound on the current cable.
phi (t) is the amplitude applied to the phase modulator of Vπ/4And 1/2T (eigenfrequency of the delay loop of the round-trip polarization-maintaining fiber).
Fig. 3 is a schematic diagram showing the response of a square-wave modulated electrical signal applied to a phase modulator and an output optical signal in the prior art, as shown in fig. 3, when no current flows in a sensing optical fiber loop, the output is a straight line (which often contains error pulses of 2 times the eigenfrequency in an undesirable situation).
When current flows through the sensing optical fiber ring, the polarization plane of the light wave is rotated by the Faraday effect, the polarization is detected at the polarizer, the movement of the working point is finally shown, and the output is changed into a square wave signal with the same frequency as the modulation square wave.
Sampling is carried out in each half period of the square wave output signal, and the sampling values of two adjacent half periods are subtracted to give an open-loop digital quantity of the optical fiber current transformer, which can be expressed as:
VOut＝G sin2φs
wherein G is a constant relating to output light intensity, circuit gain, and the like.
in the closed loop state, the feedback loop generates a digital step wave to be synchronously superposed with the square wave modulation signal, and the duration time of the step is equal to the round-trip transmission time of the optical fiber in the polarization-maintaining optical fiber delay loop;
When the step height delta phi f is used for closed-loop processing, the step height delta phi f is used for offsetting the phase deviation of polarization rotation caused by a magnetic field generated by current, and the voltage output after FOCT demodulation is as follows:
VOut＝G sin2(φs+φτ)
Only by means of software program control feedback loop to make the detector receive positive and negative half-cycle voltage difference VOutWhen the value is 0, the FOCT can work in a closed loop state. The all-digital processing technology actually combines digital demodulation and digital closed-loop feedback by using a programmable logic unit and peripheral circuits thereof. Because sampling is that the sampling values of two adjacent half periods are subtracted in each half period of the square wave signal to give an open-loop digital quantity of the FOCT, and a feedback loop generates a proper phase step according to the digital quantity, the temperature stability problem of a phase modulator and the drift caused by an electronic circuit in analog demodulation are avoided, and the dynamic range of the FOCT and the linearity of a scale factor are greatly improved. And can meet the high-precision and high-stability AC and DC universal detection function.
3. The polarization extinction ratio of the polarization-maintaining fiber beam splitting polarizer must be higher than 60dB
Since the detector output is a multivalued function of the Veldert phase shift, corresponding to a + -pi/2 phase shift, the maximum measurement range for closed-loop FOCT is:
The minimum measurement limit is limited by the detector photon shot noise, typically about 1 μ rad;
measuring range of the closed-loop optical fiber current transformer: 1 micro radian-pi/2 radian and 60dB dynamic range.
Output response of FOCT is
I(t)＝I0cos2[Δφf+φ(t)]～I0·cos[2·(Δφf+φ(t))+1]/2
ΔφfHas a range of + -pi/2, 2 delta phifWithin a range of + -pi/;
The extinction ratio is the differential of the light intensity,
therefore, the comprehensive polarization extinction ratio of the polaroid must be higher than 60dB to improve the performance index in micro-current measurement.
In addition, because the polarization maintaining function of polarization maintaining fiber is limited, and the output coupling is aligned with the angle limitation, even the polarization extinction ratio of the device measured is in the range of 20-30 dB, because the utility model discloses the polarization maintaining fiber beam splitting polarizer that adopts has very ingenious design, also can satisfy the actual use requirement completely.
The polarization-maintaining fiber beam splitting polarizer is a fiber passive optical device which realizes optical power beam splitting, integrates an optical polarizer and realizes polarization or polarization detection functions at the same time, and particularly is a 2 multiplied by 2 polarization-maintaining fiber beam splitting polarizer which can maintain the polarization state of light waves.
The polarization-maintaining optical fiber beam splitting polarizer integrates the functions of beam splitting and polarization (polarization or polarization analysis) of an optical fiber device, namely, the function of single polarization state selection or polarization analysis of the polarization direction of optical waves is realized while the optical power beam splitting is realized.
The polarization-maintaining fiber beam splitting polarizer can enable light waves to pass through the same polaroid for 2 times in a reciprocating mode, 2 polaroids do not need to be adopted, the angles of the 2 polaroids do not need to be aligned, the production and assembly processes are simplified, and polarization extinction ratio multiplication can be easily achieved.
The polarization-maintaining optical fiber beam splitter polarizer inherits the advantages of simple process, stability and reliable performance of the polarization-maintaining optical fiber beam splitter; the input and output optical fibers have the same type as the connected optical fibers, and have the advantages of wide working wavelength range, high yield, small insertion loss, wide working temperature range and short total length, and the problem of high welding difficulty in the optical path of the polarization maintaining optical fiber which needs to be aligned at a specific angle can be solved.
4. The voltage calculation method for realizing the pi/2 deflection angle of the light wave polarization plane by the lithium niobate phase modulator comprises the following steps:
For X-cut Y-transmission lithium niobate crystal (or other electro-optical crystal material or semiconductor material, material capable of realizing double polarization state light wave passing and phase modulation function), half-wave voltage V of TE (transverse electric) modeπhalf-wave voltage V of (TE, TM (transverse magnetic) modeπ(TM); e light corresponding to TE mode, and using electro-optical coefficient component of gamma33(ii) a O light corresponding to TM mode, and gamma as the component of electrooptical coefficient13(ii) a The refractive index changes are caused by the electric field component in the Z-axis direction of the lithium niobate crystal:
wherein n isoand neRefractive indices of o light and e light, respectively; gamma-shapedTEAnd ΓTMthe overlap integral of the interaction of the Z-direction electric field with the TE or TM mode, respectively.
For a wavelength λ 1310nm, there are
| 1 | no＝2.2218 | ne＝2.14502 | (ne/no)3＝0.90 |
| 2 | γ13＝8.39 | γ33＝28.8 | γ33/γ13＝3.43 |
| 3 | ΓTM＝0.48 | ΓTE＝0.56 | ΓTE/ΓTM＝1.15 |
Then there is theoretical calculation that:Measured actuallytherefore, within the error range of the system measurement, selectingwherein the content of the first and second substances,Is the half-wave voltage of the TE mode,is the half-wave voltage of the TM mode.
Because the lambda/2 wave plate can make the linearly polarized light vibration surface rotate by an angle of 2 times of included angle, the voltage V for realizing the 2 pi radian deflection of the light wave polarization directionπComprises the following steps:
theoretical calculation of：Actual measurement
Within the error range of system measurement, selecting
Obtaining:
Thus realizing a pi/2 radian deflection, requiring an applied voltage VπA/2 is
if it is notThen there is Vπ/2＝3.3V
see fig. 2, the voltage V is supplied by the control circuitπApplied to a phase modulator for a polarization rotating switch. Light wave deflection angle gets into phase modulator with 45 degrees incidences, and through the voltage that changes phase modulator, the phase place of change light wave can adjust the polarization angle of the light wave of phase modulator output, realizes the function of adjustable lambda 2 wave plate, just is the utility model provides an in the embodiment of a polarization rotary switch's of phase modulator function.
to sum up, the polarization-detecting closed-loop all-fiber current transformer of the embodiment of the present invention employs a polarization-maintaining fiber beam splitting polarizer, and employs a phase modulator as a closed-loop control method of an adjustable 1/2 wave plate, so that the insertion loss of the optical system is small; the polarization rotation of the light wave output by the phase modulator is only completed in 1 optical fiber, the temperature and vibration stability is good, and the engineering application is facilitated. The polarization extinction ratio of the polarization maintaining optical fiber beam splitting polarizer in the polarization analyzing type closed-loop all-fiber current transformer provided by the embodiment of the utility model can be improved to more than 60dB, even as high as 80 dB; thereby enabling practical engineering applications of the advantageous optical design. The defect that a traditional polarization-maintaining optical fiber coupler has large polarization-related loss PDL is overcome, the minimum measurement current precision (3-5 times) of the system can be improved, and the universal current detection function of alternating current and direct current with large dynamic range, high precision and high stability can be realized.
The utility model discloses polarization-detecting formula closed loop all-fiber current transformer has overcome the weakness that adopts wavelength dependent loss WDL, the temperature dependent loss TDL that traditional fiber coupler exists. The light path assembly process of the polarization-detecting closed-loop all-fiber current transformer provided by the embodiment of the utility model is simple, the fiber type of the polarization-maintaining fiber beam splitter is the same as that of the light source and the phase modulator, and the problem can not occur; the phase modulator is used as a current transformer closed-loop control method of a polarization direction rotary switch of an adjustable lambda/2 wave plate, and can realize a large measurement range and high measurement linearity.
The utility model discloses polarization detection formula closed loop all-fiber current transformer can improve system reliability, including the device reliability to and the fused reliability of light path. Ultimately, the advantageous optical structures can be truly put to industrial use.
Those of ordinary skill in the art will understand that: the figures are schematic representations of one embodiment, and the blocks or processes in the figures are not necessarily required to practice the present invention.
the embodiments in the present specification are described in a progressive manner, and the same and similar parts among the embodiments are referred to each other, and each embodiment focuses on the differences from the other embodiments. In particular, for apparatus or system embodiments, since they are substantially similar to method embodiments, they are described in relative terms, as long as they are described in partial descriptions of method embodiments. The above-described embodiments of the apparatus and system are merely illustrative, and the units described as separate parts may or may not be physically separate, and the parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution of the present embodiment. One of ordinary skill in the art can understand and implement it without inventive effort.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention should be covered by the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.
Claims (6)
1. The utility model provides a polarization detection formula closed loop all-fiber current transformer which characterized in that includes: the device comprises a broadband light source, a detector, a polarization maintaining optical fiber beam splitting polarizer, a phase modulator, a lambda/4 wave plate, a sensing optical fiber, a reflector, a detector and a control circuit;
The broadband light source emits broad-spectrum light, and the broad-spectrum light is transmitted to the polarization maintaining optical fiber beam splitting polarizer;
the polarization maintaining fiber beam splitting polarizer splits the power of light waves output by the broadband light source and realizes polarization, and the light waves enter the phase modulator at an incident angle of 45 degrees; analyzing and polarizing the light wave returned from the phase modulator, splitting the light power, and realizing secondary analysis of the light power entering the detector so as to multiply the polarization extinction ratio of the detected polarized light wave;
The phase modulator is used as a polarization direction rotating switch and is used for rotating the polarization direction of the received light wave through an external electric signal and transmitting the output polarized light to the lambda/4 wave plate through the polarization maintaining optical fiber delay coil;
the lambda/4 wave plate is used for decomposing the received polarized light into left circularly polarized light and right circularly polarized light and transmitting the left circularly polarized light and the right circularly polarized light to the sensing optical fiber;
When current flows through the sensing optical fiber, the light wave polarization state is caused to rotate by a magnetic field generated by the current through the Faraday effect, the left circularly polarized light and the right circularly polarized light reflected by the reflector at the tail end of the sensing optical fiber are synthesized into linearly polarized light after passing through the lambda/4 wave plate, and the polarization angle of the linearly polarized light is superposed with the deflection angle caused by the current induced magnetic field of the Faraday effect; the linearly polarized light returns to the polarization-maintaining fiber beam splitting polarizer again through the phase modulator, and the polarization-maintaining fiber beam splitting polarizer performs polarization analysis processing on the linearly polarized light;
The detector is used for detecting the optical power of the linearly polarized light after the polarization detection processing of the polarization-maintaining optical fiber beam splitting polarizer, converting the optical power into an electric signal and outputting the electric signal to the control circuit;
the control circuit performs analog-to-digital conversion sampling, digital filtering and demodulation processing on the electric signal transmitted by the detector to obtain a digital signal, and outputs the digital signal; and feeding back the digital signal as an open-loop digital quantity to the phase modulator to realize closed-loop feedback.
2. the polarization-detecting closed-loop all-fiber current transformer of claim 1, wherein when the broadband light source is an SLD light source output by a polarization-maintaining fiber, an output polarization-maintaining pigtail of the SLD light source is aligned at 0 degree or 90 degrees with an input polarization-maintaining pigtail of a polarization-maintaining fiber beam-splitting polarizer, and polarization of the polarization-maintaining fiber beam-splitting polarizer is a single polarized light;
When the broadband light source is an SLD light source or an ASE light source output by a common single-mode fiber, the angle alignment direction of the single-mode fiber and the input polarization-maintaining tail fiber of the polarization-maintaining fiber beam splitting polarizer is not limited, and the polarization-maintaining fiber beam splitting polarizer realizes the polarization function.
3. The polarization-detecting closed-loop all-fiber current transformer of claim 1, wherein the polarization-maintaining pigtail of the polarization-maintaining fiber splitter polarizer is fused at an angle of 45 degrees with the polarization-maintaining pigtail at the input end of the phase modulator, and the phase modulator is used as a λ/2 wave plate capable of adjusting the polarization direction of the optical wave.
4. The polarization-analyzing closed-loop all-fiber current transformer of claim 1, wherein the output polarization-maintaining pigtail of the phase modulator is fusion-spliced with the polarization-maintaining fiber of the polarization-maintaining fiber delay coil in alignment with the 0 degree of birefringence principal axis, the pigtail of the polarization-maintaining fiber delay coil forms a 45 degree angle with the pigtail of the λ/4 plate, and the light wave enters the λ/4 plate at a 45 degree angle.
5. the polarization-detecting closed-loop all-fiber current transformer of claim 1, wherein the polarization extinction ratio of the polarization-maintaining fiber splitting polarizer is higher than 60 dB.
6. The polarization-analyzing closed-loop all-fiber current transformer of claim 1, wherein the phase modulator is a lithium niobate phase modulator, and the lithium niobate phase modulator implements a pi/2 deflection angle of the polarization plane of the light wave.
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109752581A (en) * | 2019-03-14 | 2019-05-14 | 北京交通大学 | Polarize analyzing formula closed loop all-fiber current transformator |
| CN111239464A (en) * | 2020-02-25 | 2020-06-05 | 中国科学院半导体研究所 | High signal-to-noise ratio optical current transformer based on modular design |
| CN113138302A (en) * | 2020-01-20 | 2021-07-20 | 南京南瑞继保电气有限公司 | Optical current transformer |
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2019
- 2019-03-14 CN CN201920326845.8U patent/CN209764932U/en active Active
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109752581A (en) * | 2019-03-14 | 2019-05-14 | 北京交通大学 | Polarize analyzing formula closed loop all-fiber current transformator |
| CN113138302A (en) * | 2020-01-20 | 2021-07-20 | 南京南瑞继保电气有限公司 | Optical current transformer |
| CN111239464A (en) * | 2020-02-25 | 2020-06-05 | 中国科学院半导体研究所 | High signal-to-noise ratio optical current transformer based on modular design |
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