CN111458553B - High-sensitivity all-fiber current measuring device and method with double-circulation structure - Google Patents

High-sensitivity all-fiber current measuring device and method with double-circulation structure Download PDF

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CN111458553B
CN111458553B CN202010354031.2A CN202010354031A CN111458553B CN 111458553 B CN111458553 B CN 111458553B CN 202010354031 A CN202010354031 A CN 202010354031A CN 111458553 B CN111458553 B CN 111458553B
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coupler
linearly polarized
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polarized light
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CN111458553A (en
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许少毅
李威
朱真才
陈�光
邢方方
王禹桥
范孟豹
杨雪锋
薛宏宇
彭强
董峰
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China University of Mining and Technology CUMT
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
    • G01R19/0092—Arrangements for measuring currents or voltages or for indicating presence or sign thereof measuring current only
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R15/00—Details of measuring arrangements of the types provided for in groups G01R17/00 - G01R29/00, G01R33/00 - G01R33/26 or G01R35/00
    • G01R15/14—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks
    • G01R15/24—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using light-modulating devices
    • G01R15/245—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using light-modulating devices using magneto-optical modulators, e.g. based on the Faraday or Cotton-Mouton effect
    • G01R15/246—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using light-modulating devices using magneto-optical modulators, e.g. based on the Faraday or Cotton-Mouton effect based on the Faraday, i.e. linear magneto-optic, effect

Abstract

The invention discloses a high-sensitivity all-fiber current measuring device with a double-circulation structure and a method thereof. The sensor of the invention utilizes the combination of the polarization beam splitter, the first coupler, the double Faraday rotation mirror and the second coupler to form a double circulation structure, so that optical signals realize multiple circulation in a sensing optical path, the stability of the system is enhanced, the sensitivity of the sensor is improved, and the influence of the linear birefringence effect is reduced.

Description

High-sensitivity all-fiber current measuring device and method with double-circulation structure
Technical Field
The invention belongs to the technical field of optical fiber sensing, and particularly relates to a high-sensitivity all-optical fiber current measuring device and method with a double-circulation structure.
Background
The optical fiber current sensor has the advantages of good insulating property, strong anti-electromagnetic interference, simple structure, safety and the like, and is very suitable for being applied in the aspect of current.
The working principle of the fiber optic current sensor is based on the faraday magneto-optical effect, namely: the current to be measured forms Faraday phase shift in a linear relation with the current to be measured in the sensor, an interference light path is constructed in the current mainstream scheme, a phase modulator is utilized, a closed-loop control algorithm is introduced, the Faraday phase shift is demodulated according to an interference light intensity signal, and the current to be measured is obtained from a demodulation result. Because the demodulation of the Faraday phase shift depends on an interference light intensity signal, and the interference light intensity is influenced by the power of a light source, how to eliminate the influence of the fluctuation of the power of the light source is one of the problems that the existing scheme needs to be straight; the interference light intensity and Faraday phase shift are in a cosine function relationship, which is a nonlinear function relationship, in addition, the Faraday phase shift is a weak signal, and in this case, the first derivative value of the cosine function is close to 0, so how to improve the measurement sensitivity of the sensor and solve the problem that the nonlinear problem is the second problem that the existing scheme needs to be straight; the modulation and demodulation of the Faraday phase shift are realized through a phase modulator, the modulation period is related to the transit time of the sensor, the transit time depends on the length of a polarization-maintaining delay optical fiber ring, the bandwidth of the sensor is limited, the currently known highest bandwidth is about 100kHz, and the polarization-maintaining optical fiber ring also increases the use cost of the sensor, which is the third problem that the existing scheme needs to be straight; the high price of the phase modulator directly increases the use cost of the sensor, which is four of the problems that the existing scheme needs to be straight. Some of these problems have been solved by complex control algorithms, but some of the intrinsic difficulties attributed to sensing schemes are difficult to overcome.
Disclosure of Invention
The purpose of the invention is as follows: aiming at the problems, the invention provides a high-sensitivity all-fiber current measuring device with a double-circulation structure and a method thereof, the device and the method can realize high-sensitivity measurement of current, are suitable for weak current measurement and most industrial applications, and have the advantages of high sensitivity, high precision, good linearity, no influence of light source power fluctuation, no need of a complex closed-loop control method, no limit of detection bandwidth and the like.
The technical scheme is as follows: a high-sensitivity all-fiber current measuring device with a double-circulation structure comprises a broadband light source (1), a polarizer (2), a polarization controller (3), a first polarization beam splitter (4), a first coupler (5), a circulator (6), a second coupler (7), a sensing fiber ring (8), a current-carrying conductor (9), a first Faraday rotating mirror (10), a second Faraday rotating mirror (11), a second polarization beam splitter (12), a first photoelectric detector (13) and a second photoelectric detector (14); the broadband light source (1) is connected with a port (21) of the polarizer (2), a port (22) of the polarizer (2) is connected with a port (31) of the polarization controller (3), a port (32) of the polarization controller (3) is connected with a port (41) of the first polarization beam splitter (4), a port (42) of the first polarization beam splitter (4) is connected with a port (51) of the first coupler (5), a port (52) of the first coupler (5) is connected with a port (61) of the circulator (6), a port (62) of the circulator (6) is connected with a port (72) of the second coupler (7), a port (63) of the circulator (6) is connected with a port (43) of the first polarization beam splitter (4), a port (71) of the second coupler (7) is connected with the second Faraday rotator mirror (11), and a port (73) of the second coupler (7) is connected with one end of the sensing optical fiber ring (8), a sensing optical fiber ring (8) is wound on a current-carrying conductor (9), the other end of the sensing optical fiber ring (8) is connected with a first Faraday rotator mirror (10), a port (121) of a second polarization beam splitter (12) is connected with a port (53) of a first coupler (5), a port (122) of the second polarization beam splitter (12) is connected with a first photoelectric detector (13), and a port (123) of the second polarization beam splitter (12) is connected with a second photoelectric detector (14).
Furthermore, the first polarization beam splitter (4) has a light beam coupling function, a tail fiber of a port (41) of the first polarization beam splitter (4) and a tail fiber of a port (32) of the polarization controller (3) are in slow axis alignment fusion, and a tail fiber of a port (42) of the first polarization beam splitter (4) and a tail fiber of a port (51) of the first coupler (5) are in slow axis alignment fusion.
Further, the first coupler (5) has the function of power splitting, and the coupling ratio is 80:20, wherein: the optical power output from the port 52 is 20% and the optical power output from the port 53 is 80%.
Furthermore, the tail fiber of the port (121) of the second polarization beam splitter (12) is welded with the tail fiber of the port (53) of the first coupler (5) at an angle of 45 degrees.
Further, the second coupler (7) has a coupling ratio of 50:50, wherein: the optical power output from the port 71 is 50% and the optical power output from the port 72 is 50%.
Furthermore, the first Faraday rotator mirror (10) and the second Faraday rotator mirror (11) are both 45-degree Faraday rotator mirrors.
The invention also provides a high-sensitivity all-fiber current measuring method with a double-circulation structure, which comprises the following steps:
a: the output light of the broadband light source (1) enters the polarizer (2) from the port (21), linearly polarized light is formed in the process from the port (21) to the port (22), and the linearly polarized light is output from the port (22); linearly polarized light output from the port (22) enters the polarization controller (3) from the port (31) and is output from the port (32); linearly polarized light output from the port (32) enters the first polarization beam splitter (4) from the port (41) and is output from the port (42); linearly polarized light output from the port (42) enters the first coupler (5) from the port (51) and is divided into two linearly polarized light beams A0 and B0, the linearly polarized light beam A0 is output from the port (52), and the linearly polarized light beam B0 is output from the port (53);
b: linearly polarized light A0 output from port 52 enters circulator 6 from port 61 and is output from port 62; linearly polarized A0 light output from the port (62) enters the second coupler (7) from the port (72) and is output from the port (73); a0 linearly polarized light output from the port (73) enters the sensing optical fiber ring (8) and is received byA magneto-optical phase shift is produced by the action of a magnetic field excited by a current flowing in a current-carrying conductor (9)
Figure BDA0002472859740000031
Then returns to the sensing optical fiber ring (8) under the action of a first Faraday rotation mirror (10) and generates a magneto-optical phase shift again under the action of the same magnetic field
Figure BDA0002472859740000032
Return to port (73); the A0 linearly polarized light returned to the port (73) enters the second coupler (7) and is divided into two linearly polarized light beams of C1 and D1, the C1 linearly polarized light beam is output from the port (71), and the D1 linearly polarized light beam is output from the port (72);
c: c1 linearly polarized light output from the port (71) reaches the second Faraday rotation mirror (11), is reflected back, enters the second coupler (7) from the port (71) again, and is output from the port (73); c1 linear polarized light output from the port (73) enters the sensing optical fiber ring (8) and generates a magneto-optical phase shift under the action of a magnetic field excited by current on the current-carrying conductor (9)
Figure BDA0002472859740000034
Then returns to the sensing optical fiber ring (8) under the action of a first Faraday rotation mirror (10) and generates a magneto-optical phase shift again under the action of the same magnetic field
Figure BDA0002472859740000033
Return to port (73); c1 linearly polarized light returning to the port (73) enters the second coupler (7) and is divided into two linearly polarized light beams of C2 and D2, the linearly polarized light beam of C2 is output from the port (71), and the linearly polarized light beam of D2 is output from the port (72);
d: according to the above description, the linearly polarized light finally output from the port (72) is: d1, D2, D3, …, Dn;
e: linearly polarized light D1, D2, D3, … and Dn output from the port (72) enter the circulator (6) from the port (62) and are output from the port (63); d1, D2, D3, … and Dn linearly polarized light output from the port (63) enters the first polarization beam splitter (4) from the port (43) and is output from the port (42); d1, D2, D3, … and Dn linearly polarized light output from the port (42) enter the first coupler (5) from the port (51) and are divided into Ai linearly polarized light and Bi linearly polarized light, the Ai linearly polarized light is output from the port (52), the Bi linearly polarized light is output from the port (53), and i is more than or equal to 1 and less than or equal to n;
e: from the above description, the linearly polarized light finally output from the port 53 is: b1, B2, B3, …, Bn;
linearly polarized light B1, B2, B3, … and Bn output from the port (53) respectively enter the second polarization beam splitter (12) from the port (121) and are divided into two beams of orthogonal linearly polarized light which are respectively output from the port (122) and the port (123); linearly polarized light output from the port (122) enters a first photodetector (13), and linearly polarized light output from the port (123) enters a second photodetector (14);
and G, resolving to obtain the current to be measured on the current-carrying conductor (9) after the linearly polarized light entering the first photoelectric detector (13) and the linearly polarized light entering the second photoelectric detector (14) are subjected to photoelectric conversion.
Further, the current to be measured on the current-carrying conductor (9) is calculated as follows:
let the light vector emitted by the light source be Ein＝[Ex；Ey]The Jones matrix of the polarizer (2) is JpJones matrix J of the polarization controller (3)1The Jones matrix of the first polarization beam splitter (4) is J2The Jones matrix of the first coupler (5) is Jo1The loop 6 has a Jones matrix J from port 1 to port 2h12The Jones matrix of the second coupler (7) is Jo2The Jones matrix of the sensing optical fiber ring (8) is Jf1The Jones matrixes of the first Faraday rotator mirror (10) and the second Faraday rotator mirror (11) are Jm(ii) a During reflection, the Jones matrix of the sensing fiber ring 8 is Jf2The circulator (5) has a matrix J from port 2 to port 3h23The Jones matrix of the second polarization beam splitter (12) is J31And J32The included angle between the main shaft of the second polarization beam splitter (12) and the polarization-maintaining optical fiber is 45 degrees, and the Jones matrix J is introduced45°The jones matrices are respectively as follows:
Figure BDA0002472859740000041
Figure BDA0002472859740000042
Figure BDA0002472859740000043
in the formula: f is the Faraday phase shift generated between polarized lights in the sensing optical fiber (8) by a magnetic field excited by current to be measured on the current-carrying conductor (9), F is VNI, V is the Verdet constant of the sensing optical fiber ring (8), N is the number of turns of the sensing optical fiber ring (8), and I is the current to be measured on the current-carrying conductor (9); omega0Is the center frequency, omega, of the broadband light source0t is the modulation delay time;
as can be seen from the process E, Di output from the port (42) and linearly polarized light enter the first coupler (5) from the port (51) and are divided into Ai and Bi linearly polarized light, Ai linearly polarized light is output from the port (52), Bi linearly polarized light is output from the port (53), wherein linearly polarized light Bi output from the port (53) enters the second polarization beam splitter (12) from the port (121) and is divided into two orthogonal linearly polarized light which is output from the port (122) and the port (123) respectively, and light vectors output by the second polarization beam splitter (12) are defined as Eo respectivelyut1And Eout2I.e. for linearly polarized light Bi:
let JF＝Jf2·Jm·Jf1Therefore:
Figure BDA0002472859740000051
Figure BDA0002472859740000052
according to the malus theorem, the optical power of the polarized light Bi in two orthogonal directions is:
Figure BDA0002472859740000053
Figure BDA0002472859740000054
wherein E isxIs the amplitude of the input light vector in the horizontal direction;
due to the limitation of the optical path condition, the optical power in the channel is gradually weakened due to the relation of the coupling ratio when the channel is recycled, and the detection capability is reduced, so that the recycling cannot be infinitely recycled, therefore, the linearly polarized light Bi is output from the second polarization beam splitter (12), and if the optical power of the linearly polarized light Bi in two orthogonal directions is smaller than a set value
Figure BDA0002472859740000055
In time, the light circulation in the channel is not considered, i.e. the linearly polarized light B output from the port (53) is again output from the timei+1Considering no longer as detection light, P is the power of the light source;
after the linearly polarized light Bi is output from the second polarization beam splitter (12), if the light power of the linearly polarized light Bi in two orthogonal directions is not less than a set value
Figure BDA0002472859740000056
To measure the optical power P1-BiAnd P2-BiInput to a first photodetector (13), a second photodetector (14) and perform a difference sum, that is:
Figure BDA0002472859740000057
since F ═ VNI, substituting this equation into (1) can result in the current I to be measured being:
Figure BDA0002472859740000058
f is the Faraday phase shift generated between polarized lights in the sensing optical fiber (8) by a magnetic field excited by current to be measured on the current-carrying conductor (9), and can be calculated according to the formula (1); v is the Verdet constant of the sensing fiber ring (8); n is the winding turns of the sensing optical fiber ring (8).
The beneficial technical effects are as follows: compared with the prior art, the technical scheme of the invention has the following beneficial technical effects:
the invention provides a high-sensitivity all-fiber current measuring device and method with a double-circulation structure, wherein a polarization beam splitter, a first coupler, a double Faraday rotation mirror and a second coupler are introduced to form the double-circulation structure, a sensing light path can detect alternating current as weak as 1.5mA and has linear response to current amplitude, which indicates that the system has very good performance in weak current detection, and the high sensitivity is suitable for current measurement in most industrial applications, particularly in the weak current applications; compared with the prior art, the invention utilizes the combination of the polarization beam splitter, the first coupler, the double Faraday rotation mirror and the second coupler to form a double-circulation structure, so that the optical signal is circulated for many times in a sensing optical path, the stability of the system is enhanced, the sensitivity of the sensor is improved, and the influence of the linear birefringence effect is reduced, thereby avoiding the influence of the fluctuation of the power of the light source, solving the problems of small sensitivity and nonlinearity, needing no phase modulator, needing no complex closed-loop control method and having no limiting factor for the detection bandwidth.
Drawings
Fig. 1 is a schematic diagram of the optical path structure of the present invention.
The optical device in the figure is specifically as follows: 1. the device comprises a broadband light source, 2, a polarizer, 3, a polarization controller, 4, a first polarization beam splitter, 5, a first coupler, 6, a circulator, 7, a second coupler, 8, a sensing optical fiber ring, 9, a current-carrying conductor, 10, a first Faraday rotator mirror, 11, a second Faraday rotator mirror, 12, a second polarization beam splitter, 13, a first photoelectric detector, 14 and a second photoelectric detector.
Detailed Description
The technical solution of the present invention will be further explained with reference to the drawings and the embodiments.
The high-sensitivity all-fiber current measuring device with the double-circulation structure is characterized in that the sensor comprises a broadband light source 1, a polarizer 2, a polarization controller 3, a first polarization beam splitter 4, a first coupler 5, a circulator 6, a second coupler 7, a sensing fiber ring 8, a current-carrying conductor 9, a first Faraday rotator mirror 10, a second Faraday rotator mirror 11, a second polarization beam splitter 12, a first photoelectric detector 13 and a second photoelectric detector 14, wherein the broadband light source 1 is arranged on the broadband light source, and the polarization controller 3 is arranged on the broadband light source;
the broadband light source 1 is connected with a port 21 of a polarizer 2, a port 22 of the polarizer 2 is connected with a port 31 of a polarization controller 3, a port 32 of the polarization controller 3 is connected with a port 41 of a first polarization beam splitter 4, a port 42 of the first polarization beam splitter 4 is connected with a port 51 of a first coupler 5, a port 52 of the first coupler 5 is connected with a port 61 of a circulator 6, a port 62 of the circulator 6 is connected with a port 72 of a second coupler 7, a port 63 of the circulator 6 is connected with a port 43 of the first polarization beam splitter 4, a port 71 of the second coupler 7 is connected with a second Faraday rotator 11, a port 73 of the second coupler 7 is connected with one end of a sensing fiber ring 8, the sensing fiber ring 8 is wound on a current-carrying conductor 9, the other end of the sensing fiber ring 8 is connected with a first Faraday rotator 10, a port 121 of the second polarization beam splitter 12 is connected with a port 53 of the first coupler 5, the port 122 of the second polarization beam splitter 12 is connected to the first photodetector 13, and the port 123 of the second polarization beam splitter 12 is connected to the second photodetector 14;
the first polarization beam splitter 4 has the function of beam coupling, the tail fiber of the port 41 of the first polarization beam splitter 4 and the tail fiber of the port 32 of the polarization controller 3 are in slow axis alignment and fusion, and the tail fiber of the port 42 of the first polarization beam splitter 4 and the tail fiber of the port 51 of the first coupler 5 are in slow axis alignment and fusion;
the first coupler 5 has the function of power splitting, and the coupling ratio is 80:20, wherein: the optical power ratio output from the port 52 is 20%, and the optical power ratio output from the port 53 is 50%;
the pigtail of the port 121 of the second polarization beam splitter 12 is fused at 45 ° to the pigtail of the port 53 of the first coupler 5;
the coupling ratio of the second coupler 7 is 50:50, wherein: the optical power ratio output from the port 71 is 50%, and the optical power ratio output from the port 72 is 50%;
the first Faraday rotator mirror 10 and the second Faraday rotator mirror 11 are both 45-degree Faraday rotator mirrors;
a high-sensitivity all-fiber current measuring method with a double-circulation structure is characterized by comprising the following steps:
a: the output light of the broadband light source 1 enters the polarizer 2 from the port 21, forms linearly polarized light in the process from the port 21 to the port 22 and is output from the port 22; linearly polarized light output from the port 22 enters the polarization controller 3 from the port 31 and is output from the port 32; linearly polarized light output from the port 32 enters the first polarization beam splitter 4 from the port 41 and is output from the port 42; linearly polarized light output from the port 42 enters the first coupler 5 from the port 51 and is divided into two linearly polarized light beams A0 and B0, linearly polarized light beam A0 is output from the port 52, and linearly polarized light beam B0 is output from the port 53;
b: linearly polarized a0 light output from port 52 enters circulator 6 from port 61 and is output from port 62; linearly polarized a0 light output from port 62 enters second coupler 7 from port 72 and is output from port 73; a0 linearly polarized light output from port 73 enters into sensing optical fiber ring 8, and generates a magneto-optical phase shift under the action of magnetic field excited by current on current-carrying conductor 9
Figure BDA0002472859740000071
Then returns to the sensing fiber ring 8 under the action of the first Faraday rotator mirror 10, and generates a magneto-optical phase shift again under the action of the same magnetic field
Figure BDA0002472859740000072
Back to port 73; the A0 linearly polarized light returning to the port 73 enters the second coupler 7 and is divided into two linearly polarized light beams of C1 and D1, the C1 linearly polarized light beam is output from the port 71, and the D1 linearly polarized light beam is output from the port 72;
c: c1 line bias output from port 71The vibration light reaches the second faraday rotator 11, is reflected back, enters the second coupler 7 from the port 71 again, and is output from the port 73; the C1 linear polarized light output from the port 73 enters the sensing optical fiber ring 8 and generates a magneto-optical phase shift under the action of a magnetic field excited by the current on the current-carrying conductor 9
Figure BDA0002472859740000074
Then returns to the sensing fiber ring 8 under the action of the first Faraday rotator mirror 10, and generates a magneto-optical phase shift again under the action of the same magnetic field
Figure BDA0002472859740000073
Back to port 73; the C1 linearly polarized light returning to the port 73 enters the second coupler 7 and is divided into two linearly polarized light beams of C2 and C2, the C2 linearly polarized light beam is output from the port 71, and the D2 linearly polarized light beam is output from the port 72;
d: from the above description, the linearly polarized light that is ultimately output from port 72 is: d1, D2, D3, …, Dn, (this result is due to the first structural cycle);
e: linearly polarized light D1, D2, D3, …, Dn output from port 72 enters circulator 6 from port 62 and is output from port 63; d1, D2, D3, … and Dn linearly polarized light output from the port 63 enter the first polarization beam splitter 4 from the port 43 and are output from the port 42; d1, D2, D3, … and Dn linearly polarized light output from the port 42 enter the first coupler 5 from the port 51 and are divided into two linearly polarized light beams of Ai and Bi, the Ai linearly polarized light beam is output from the port 52, and the Bi linearly polarized light beam is output from the port 53;
e: from the above description, the linearly polarized light finally output from the port 53 is: b1, B2, B3, …, Bn, (this result is due to the first structural cycle);
linearly polarized light B1, B2, B3, … and Bn output from the port 53 respectively enter the second polarization beam splitter 12 from the port 121 and are divided into two orthogonal linearly polarized light beams which are respectively output from the port 122 and the port 123; linearly polarized light output from port 122 enters first photodetector 13 and linearly polarized light output from port 123 enters second photodetector 14.
And G, resolving to obtain the current to be measured on the current-carrying conductor 9 after the linearly polarized light entering the first photoelectric detector 13 and the linearly polarized light entering the second photoelectric detector 14 are subjected to photoelectric conversion.
The method for calculating the current to be measured on the current-carrying conductor 9 is as follows:
the light vector emitted by the light source is Ein＝[Ex；Ey]The Jones matrix of the polarizer 2 is JpJones matrix J of the polarization controller 31The Jones matrix of the first polarizing beam splitter 4 is J2The Jones matrix of the first coupler 5 is Jo1The circulator 6 has a J-matrix from port 1 to port 2h12The Jones matrix of the second coupler 7 is Jo2The Jones matrix of the sensing fiber ring 8 is Jf1The Jones matrices of the first Faraday rotator mirror 10 and the second Faraday rotator mirror 11 are both Jm(ii) a During reflection, the Jones matrix of the sensing fiber ring 8 is Jf2Circulator 5 has a J matrix from port 2 to port 3h23The Jones matrix of the second polarizing beam splitter 12 is J31And J32The included angle between the main shaft of the second polarization beam splitter 12 and the polarization maintaining fiber is 45 degrees, and the Jones matrix J is introduced45°. Thus, the jones matrices are respectively as follows:
Figure BDA0002472859740000081
Figure BDA0002472859740000091
Figure BDA0002472859740000092
in the formula: f is the faraday phase shift generated between polarized lights in the sensing optical fiber 8 by the magnetic field excited by the current to be measured on the current-carrying conductor 9, F is VNI, V is the verdet constant of the sensing optical fiber ring 8, N is the number of winding turns of the sensing optical fiber ring 8, and I is the current to be measured on the current-carrying conductor 9; omega0Is the center frequency, omega, of the broadband light source0t is the modulation delay time.
As can be seen from the above process E, Di output from the port 42, linearly polarized light enters the first coupler 5 from the port 51 and is divided into two linearly polarized lights Ai and Bi, the linearly polarized light Ai is output from the port 52, the linearly polarized light Bi is output from the port 53, wherein the linearly polarized light Bi output from the port 53 enters the second polarization beam splitter 12 from the port 121 and is divided into two orthogonal linearly polarized lights output from the port 122 and the port 123 respectively, and the light vectors output by the second polarization beam splitter 12 are defined as Eo respectivelyut1And Eout2I.e. for linearly polarized light Bi:
let JF＝Jf2·Jm·Jf1Therefore:
Figure BDA0002472859740000093
Figure BDA0002472859740000094
according to the malus theorem, the optical power of the polarized light Bi in two orthogonal directions is:
Figure BDA0002472859740000095
Figure BDA0002472859740000096
wherein E isxIs the amplitude of the input light vector in the horizontal direction;
due to the limitation of the optical path condition, the optical power in the channel will gradually decrease due to the relationship of the coupling ratio when the channel is recycled, and the detection capability will also decrease, so the recycling cannot be infinitely recycled, therefore, the linearly polarized light Bi is output from the second polarization beam splitter 12, if the optical power of the linearly polarized light Bi in two orthogonal directions is less than a set value
Figure BDA0002472859740000097
In time, the light recycling in the channel is not considered, i.e. the linearly polarized light B output from the port 53 is again started from this timei+1Considering no longer as detection light, P is the power of the light source;
after the linearly polarized light Bi is output from the second polarization beam splitter 12, if the optical power of the linearly polarized light Bi in two orthogonal directions is not less than a set value
Figure BDA0002472859740000101
To measure the optical power P1-BiAnd P2-BiInput to the first photodetector 13, the second photodetector 14 and perform a difference-sum, that is:
Figure BDA0002472859740000102
since F ═ VNI, substituting this equation into (1) can result in the current I to be measured being:
Figure BDA0002472859740000103
wherein, F is the faraday phase shift generated between polarized lights in the sensing fiber 8 by the magnetic field excited by the current to be measured on the current-carrying conductor 9, and can be calculated according to the formula (1); v is the verdet constant of the sensing fiber ring 8; and N is the winding turns of the sensing optical fiber ring 8.

Claims (9)

1. A high-sensitivity all-fiber current measuring device with a double-circulation structure is characterized by comprising a broadband light source (1), a polarizer (2), a polarization controller (3), a first polarization beam splitter (4), a first coupler (5), a circulator (6), a second coupler (7), a sensing fiber ring (8), a current-carrying conductor (9), a first Faraday rotating mirror (10), a second Faraday rotating mirror (11), a second polarization beam splitter (12), a first photoelectric detector (13) and a second photoelectric detector (14); the broadband light source (1) is connected with a first port (21) of the polarizer (2), a second port (22) of the polarizer (2) is connected with a first port (31) of the polarization controller (3), a second port (32) of the polarization controller (3) is connected with a first port (41) of the first polarization beam splitter (4), a second port (42) of the first polarization beam splitter (4) is connected with a first port (51) of the first coupler (5), a second port (52) of the first coupler (5) is connected with a first port (61) of the circulator (6), a second port (62) of the circulator (6) is connected with a second port (72) of the second coupler (7), a third port (63) of the circulator (6) is connected with a third port (43) of the first polarization beam splitter (4), and a first port (71) of the second coupler (7) is connected with the second Faraday rotator mirror (11), a third port (73) of the second coupler (7) is connected with one end of a sensing optical fiber ring (8), the sensing optical fiber ring (8) is wound on a current-carrying conductor (9), the other end of the sensing optical fiber ring (8) is connected with a first Faraday rotation mirror (10), a first port (121) of a second polarization beam splitter (12) is connected with a third port (53) of the first coupler (5), a second port (122) of the second polarization beam splitter (12) is connected with a first photoelectric detector (13), and a third port (123) of the second polarization beam splitter (12) is connected with a second photoelectric detector (14).
2. The high-sensitivity all-fiber current measuring device with a dual-cycle structure as claimed in claim 1, wherein: the first polarization beam splitter (4) has a light beam coupling effect, a tail fiber of a first port (41) of the first polarization beam splitter (4) and a tail fiber of a second port (32) of the polarization controller (3) are in slow axis alignment fusion, and a tail fiber of a second port (42) of the first polarization beam splitter (4) and a tail fiber of a first port (51) of the first coupler (5) are in slow axis alignment fusion.
3. The high-sensitivity all-fiber current measuring device with a dual-cycle structure as claimed in claim 1, wherein: the first coupler (5) has the function of power splitting, and the coupling ratio is 80:20, wherein: the optical power output from the port 52 is 20% and the optical power output from the third port 53 of the first coupler 5 is 80%.
4. The high-sensitivity all-fiber current measuring device with a dual-cycle structure as claimed in claim 1, wherein: the pigtail of the first port (121) of the second polarization beam splitter (12) is fused at 45 ° to the pigtail of the third port (53) of the first coupler (5).
5. The high-sensitivity all-fiber current measuring device with a dual-cycle structure as claimed in claim 1, wherein: the second coupler (7) has a coupling ratio of 50:50, wherein: the optical power output from the first port (71) of the second coupler (7) accounts for 50%, and the optical power output from the second port (72) accounts for 50%.
6. The high-sensitivity all-fiber current measuring device with a dual-cycle structure as claimed in claim 1, wherein: the first Faraday rotator mirror (10) and the second Faraday rotator mirror (11) are both 45-degree Faraday rotator mirrors.
7. The method for measuring the high-sensitivity all-fiber current with the double-cycle structure, which is realized by the device according to claim 1, is characterized by comprising the following steps:
a: the output light of the broadband light source (1) enters the polarizer (2) from the first port (21) of the polarizer (2), forms linearly polarized light in the process from the first port (21) of the polarizer (2) to the second port (22) of the polarizer (2), and is output from the second port (22) of the polarizer (2); linearly polarized light output from the second port (22) of the polarizer (2) enters the polarization controller (3) from the first port (31) of the polarization controller (3) and is output from the second port (32) of the polarization controller (3); linearly polarized light output from the second port (32) of the polarization controller (3) enters the first polarization beam splitter (4) from the first port (41) of the first polarization beam splitter (4) and is output from the second port (42) of the first polarization beam splitter (4); linearly polarized light output from the second port (42) of the first polarization beam splitter (4) enters the first coupler (5) from the first port (51) of the first coupler (5) and is divided into two linearly polarized light beams A0 and B0, the linearly polarized light beam A0 is output from the second port (52) of the first coupler (5), and the linearly polarized light beam B0 is output from the third port (53) of the first coupler (5);
b: linearly polarized A0 light output from the second port (52) of the first coupler (5) enters the circulator (6) from the first port (61) of the circulator (6) and is output from the second port (62) of the circulator (6); linearly polarized A0 light output from the second port (62) of the circulator (6) enters the second coupler (7) from the second port (72) of the second coupler (7) and is output from the third port (73) of the second coupler (7); a0 linearly polarized light output from the third port (73) of the second coupler (7) enters the sensing optical fiber ring (8) and generates a magneto-optical phase shift under the action of a magnetic field excited by current on the current-carrying conductor (9)
Figure FDA0002907636400000021
Then returns to the sensing optical fiber ring (8) under the action of a first Faraday rotation mirror (10) and generates a magneto-optical phase shift again under the action of the same magnetic field
Figure FDA0002907636400000022
A third port (73) returning to the second coupler (7); the A0 linearly polarized light returned to the third port (73) of the second coupler (7) enters the second coupler (7) and is divided into two linearly polarized lights of C1 and D1, the C1 linearly polarized light is output from the first port (71) of the second coupler (7), and the D1 linearly polarized light is output from the second port (72) of the second coupler (7);
c: c1 linearly polarized light output from the first port (71) of the second coupler (7) reaches the second Faraday rotation mirror (11), is reflected back, enters the second coupler (7) from the first port (71) of the second coupler (7) again, and is output from the third port (73) of the second coupler (7); c1 linearly polarized light output from the third port (73) of the second coupler (7) enters the sensing optical fiber ring (8) and generates a magneto-optical phase shift under the action of a magnetic field excited by current on the current-carrying conductor (9)
Figure FDA0002907636400000031
Then returns to the sensing optical fiber ring (8) under the action of a first Faraday rotation mirror (10) and generates a magneto-optical phase shift again under the action of the same magnetic field
Figure FDA0002907636400000032
A third port (73) returning to the second coupler (7); the C1 linearly polarized light returned to the third port (73) of the second coupler (7) enters the second coupler (7) and is divided into two linearly polarized lights of C2 and D2, the C2 linearly polarized light is output from the first port (71) of the second coupler (7), and the D2 linearly polarized light is output from the second port (72) of the second coupler (7);
d: according to the above description, the linearly polarized light finally output from the second port (72) of the second coupler (7) is set to: d1, D2, D3, …, Dn;
e: linearly polarized light D1, D2, D3, …, Dn output from the second port (72) of the second coupler (7) enters the circulator (6) from the second port (62) of the circulator (6) and is output from the third port (63) of the circulator (6); d1, D2, D3, … and Dn linearly polarized light output from the third port (63) of the circulator (6) enters the first polarization beam splitter (4) from the third port (43) of the first polarization beam splitter (4) and is output from the second port (42) of the first polarization beam splitter (4); d1, D2, D3, … and Dn linearly polarized light output from the second port (42) of the first polarization beam splitter (4) enters the first coupler (5) from the first port (51) of the first coupler (5) and is divided into Ai and Bi linearly polarized light, the Ai linearly polarized light is output from the second port (52) of the first coupler (5), the Bi linearly polarized light is output from the third port (53) of the first coupler (5), and i is more than or equal to 1 and less than or equal to n;
from the above description, the linearly polarized light finally output from the port 53 is: b1, B2, B3, …, Bn;
linearly polarized light B1, B2, B3, … and Bn output from a third port (53) of the first coupler (5) respectively enter the second polarization beam splitter (12) from a first port (121) of the second polarization beam splitter (12), and are divided into two orthogonal linearly polarized light beams which are respectively output from a second port (122) of the second polarization beam splitter (12) and a third port (123) of the second polarization beam splitter (12); linearly polarized light output from a second port (122) of the second polarization beam splitter (12) enters a first photodetector (13), and linearly polarized light output from a third port (123) of the second polarization beam splitter (12) enters a second photodetector (14);
and G, resolving to obtain the current to be measured on the current-carrying conductor (9) after the linearly polarized light entering the first photoelectric detector (13) and the linearly polarized light entering the second photoelectric detector (14) are subjected to photoelectric conversion.
8. The high-sensitivity all-fiber current measuring method with the dual-cycle structure as claimed in claim 7, wherein the current to be measured on the current-carrying conductor (9) is calculated as follows:
let the light vector emitted by the light source be Ein＝[Ex；Ey]The Jones matrix of the polarizer (2) is JpJones matrix J of the polarization controller (3)1The Jones matrix of the first polarization beam splitter (4) is J2The Jones matrix of the first coupler (5) is Jo1The Jones matrix of the circulator (6) from the first port (61) of the circulator (6) to the second port (62) of the circulator (6) is Jh12The Jones matrix of the second coupler (7) is Jo2The Jones matrix of the sensing optical fiber ring (8) is Jf1The Jones matrixes of the first Faraday rotator mirror (10) and the second Faraday rotator mirror (11) are Jm(ii) a During reflection, the Jones matrix of the sensing fiber ring 8 is Jf2The Jones matrix of the circulator (6) from the second port (62) of the circulator (6) to the third port (63) of the circulator (6) is Jh23The Jones matrix of the second polarization beam splitter (12) is J31And J32The included angle between the main shaft of the second polarization beam splitter (12) and the polarization-maintaining optical fiber is 45 degrees, and the Jones matrix J is introduced45°The jones matrices are respectively as follows:
Figure FDA0002907636400000041
Figure FDA0002907636400000042
Figure FDA0002907636400000043
in the formula: f is the Faraday phase shift generated between polarized lights in the sensing optical fiber (8) by a magnetic field excited by current to be measured on the current-carrying conductor (9), F is VNI, V is the Verdet constant of the sensing optical fiber ring (8), N is the number of turns of the sensing optical fiber ring (8), and I is the current to be measured on the current-carrying conductor (9); omega0Is the center frequency, omega, of the broadband light source0t is the modulation delay time;
from the step E, it can be seen that: di output from the second port (42) of the first polarization beam splitter (4), linearly polarized light enters the first coupler (5) from the first port (51) of the first coupler (5) and is divided into Ai and Bi linearly polarized light, the Ai linearly polarized light is output from the second port (52) of the first coupler (5), and the Bi linearly polarized light is output from the third port (53) of the first coupler (5), linearly polarized light Bi output from a third port (53) of the first coupler (5) enters the second polarization beam splitter (12) from a first port (121) of the second polarization beam splitter (12), the linearly polarized light Bi is divided into two beams of orthogonal linearly polarized light which are respectively output from a second port (122) of the second polarization beam splitter (12) and a third port (123) of the second polarization beam splitter (12), and light vectors output by the second polarization beam splitter (12) are respectively defined as E.out1And Eout2I.e. for linearly polarized light Bi:
let JF＝Jf2·Jm·Jf1Therefore:
Figure FDA0002907636400000051
Figure FDA0002907636400000052
according to the malus theorem, the optical power of the polarized light Bi in two orthogonal directions is:
Figure FDA0002907636400000053
Figure FDA0002907636400000054
wherein E isxIs the amplitude of the input light vector in the horizontal direction;
if the light power of the linearly polarized light Bi in two orthogonal directions is smaller than a set value, the light circulation in the channel is not considered, namely the linearly polarized light B output from the third port (53) of the first coupler (5) is re-considered from the momenti+1Will no longer be considered as detection light;
after the linearly polarized light Bi is output from the second polarization beam splitter (12), if the light power of the linearly polarized light Bi in two orthogonal directions is not less than a set value
Figure FDA0002907636400000055
To measure the optical power P1-BiAnd P2-BiInput to a first photodetector (13), a second photodetector (14) and perform a difference sum, that is:
Figure FDA0002907636400000056
since F ═ VNI, substituting this equation into (1) can result in the current I to be measured being:
Figure FDA0002907636400000057
f is the Faraday phase shift generated between polarized lights in the sensing optical fiber (8) by a magnetic field excited by current to be measured on the current-carrying conductor (9), and can be calculated according to the formula (1); v is the Verdet constant of the sensing fiber ring (8); n is the winding turns of the sensing optical fiber ring (8).
9. The method of claim 8, wherein the set values are:
Figure FDA0002907636400000058
p is the power of the light source.
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