JP2003505670A - Optical fiber current sensor reduced to minimum configuration - Google Patents

Abstract

(57) [Summary] Reduced to a minimum configuration including a sensing coil or sensing area, a light source, and an optical path disposed between a front output side of the light source and the fiber optic sensing coil / sensing area ( RMC) fiber optic current sensors (FOCS) are provided. At least one quarter-wave plate is disposed between the light path and the sensing coil / region to convert the linearly polarized light beam into a circularly polarized light beam propagating through the sensing coil / region. Has been established. The circularly polarized light beam propagating through the sensing area undergoes a phase difference shift caused by a magnetic field or current flowing through a conductor near the sensing coil. A photodetector is located at the output behind the light source and generates an output signal in response to the intensity of the return light transmitted through the light source. Return light intensity is a measure of the magnetic field at the sensor / area. A magnetic field can be generated by the current flowing through the wire. The sensing coil can be wound around a wire. An electronic device has been described that minimizes the effects caused by changes in environmental conditions.

Description

Detailed Description of the Invention

CROSS REFERENCE TO RELATED PATENT APPLICATION This patent application is a continuation application of US patent application Ser. No. 09 / 459,438, now waived and filed on April 15, 1996 in the United States. Provisional application No. 60 /
This is a continuation-in-part application of U.S. patent application Ser. No. 09 / 459,438 filed December 13, 1999, claiming the benefit of 014,884. This patent application also claims the benefits of US Provisional Patent Application No. 60 / 143,847, filed July 15, 1999.

FIELD OF THE INVENTION The present invention relates to fiber optic sensors. In particular, the present invention relates to fiber optic current sensors and their signal processing electronics.

BACKGROUND OF THE INVENTION Interferometric fiber optic sensors (FOS) are angular rotations (interferometric fiber optic gyroscopes, FOGs) and magnetic fields (interfering or polarized fiber optic current sensors, FOCs).
It is an established technique for accurately measuring S). FOCS does not directly detect the current,
Rather, it is understood to detect the effect of the magnetic field generated by the current. Because FOS is an optical, solid-state structure with no moving parts, it can be used for long-lived, highly reliable applications such as vehicle navigation and remote detection of electrical current. it can.

The basic operating principle behind FOS is the Sagnac effect for rotation sensors (FOG) and the Faraday effect for current sensors (FOCS). In FOG rotation measurements, two counter-propagating light waves traversing a loop interferometer acquire a phase difference as the loop rotates about its axis.
When FOCS measuring the current flowing through a wire passing through the coil plane, the magnetic field associated with the current causes a phase difference. Depending on the configuration of the optical path of the light wave, the FOS can incorporate interference or polarization phase modulation. To accurately measure the phase difference induced by rotation or current, it is necessary to suppress the parasitic phase difference that can change depending on the environment. For this reason, the principle of optical reciprocity is used to select the portion of the wave propagating in the opposite direction through the interferometer or polarimeter along a common path. In the following description, "interferometer" is meant to refer to both an interferometer or a polariser. Variations induced in the system by the environment evenly change the phase of both waves, so no phase delay difference occurs and the sensor is environmentally stable.

In a conventional interferometric fiber optic gyroscope (FOG), light emitted from a suitable light source passes through a first 3 dB coupler where half of the light is dissipated and half through a polarizer. Sent to the interferometer. A second 3 dB coupler splits the light into two substantially equal intensity, counter-propagating beams that traverse the coil.
The two light beams are then recombined at the second combiner, where they interfere. The light beam thus combined then undergoes a second pass of the polarizer in the opposite direction, half of the light being guided by the first coupler to the detector.
The first coupler is an optically reciprocating motion.
cal) Not part of the Sagnac interferometer. Its sole purpose is to direct some of the returning light into the photodetector, minimizing direct coupling of light energy from the light source to the detector. An optical split ratio of 3 dB is chosen to maximize the optical power that the combiner impinges on the detector. This results in an inherent 6 dB system loss as it passes through this coupler twice.

In conventional interferometric fiber optic current sensors (FOCS), the light beam also
It passes through a first directional coupler separating the photodetectors and then through a polarizer that produces linearly polarized light. The linearly polarized light beam is then split by a second directional coupler into two beams, one of which is directed to one end of a detection coil comprising a loop of non-birefringent fiber. The other of the two light beams is guided through the phase modulator into the other end of the detection coil. Each of the linearly polarized light beams passes through their respective quarter-wave plate before entering the detector coil and exits therefrom as circularly polarized light, which is the light entering the detector coil. Light exiting the two fiber ends of the detection coil again passes through the quarter wave plate to produce linearly polarized return light. The returning light is recombined by the second directional coupler and the intensity of this recombined light is detected by the photodetector.

Another type of conventional FOCS is based on a reflected current sensing coil, which eliminates the second directional coupler and simplifies the design. A diagonally linearly polarized light beam passes through the quarter-wave plate and emerges therefrom as circularly polarized light rotating in the opposite direction before entering the detection coil. Reflected at the end of the fiber, the directions of rotation of the two light waves are reversed and the light returns through the detection region, after which the light is converted back into linearly polarized light. The intensity of the recombined light is detected by the photodetector. If a birefringence modulator is used instead of a phase modulator, it is necessary to insert a 45 degree splice before the light enters the modulator.

The phase modulator may be, for example, a piezoelectric transducer (PZT). Other methods of modulating the phase difference may be used, for example electro-optical materials such as lithium niobate. If an integrated optical assembly (IOC) is used for modulation, a Y-connected power splitter may be included instead of the directional coupler connected to the detection coil. This phase modulation serves two purposes. One purpose is to dynamically bias the interferometer to a more sensitive operating point, and also to detect rotational direction. The other purpose is to move the detected signal from direct current (DC) to alternating current (AC) to increase the accuracy of the electrical signal processing. With sinusoidal phase modulation in an open loop signal processing configuration, the output signal of the interferometer is an infinite series of sinusoidal and cosine waveforms, the maximum amplitude of which is the Bessel function associated with the phase modulation amplitude. The maximum amplitude of the Bessel function is proportional to the sine (odd harmonics) and cosine (even harmonics) of the measured quantity. The fundamental signal is located at the applied modulation frequency with subsequent even and odd harmonic signals. Many signal processing methods have been proposed for detecting rotational speed and / or magnetic field and at the same time using the ratio of the fundamental signal to the lowest third harmonic signal amplitude while maintaining a stable linear output scale factor. It was However, implementing these methods on analog and / or digital electronic hardware is complicated and expensive. Therefore, a much simpler signal processing design that is not affected by errors in the relative amplitudes of the sensor harmonic signals is desired.

The inherent linearity of the Sagnac and Faraday effects for small measured current or magnetic field values maintains the linearity of the scale factor (ie measured current or magnetic field vs. applied current or magnetic field). It Environmental change (
Higher rates (i.e. temperature, vibration, etc.) and over the life of the sensor (i.e.
rate) or higher current, conventional signal processing techniques can be used to maintain linearity.

Therefore, it is desirable to provide a fiber optic current sensor that has fewer optical elements and is easier and cheaper to manufacture. It is also desirable to provide an electronic system for processing the output signal of the current sensor to maintain a constant scale factor during environmental changes.

SUMMARY OF THE INVENTION The present invention is directed to a reduced minimum configuration (RMC) fiber optic current sensor (FOCS) system for measuring magnetic fields, particularly current induced magnetic fields. According to one aspect of the invention, an RMC FOCS system may also include a fiber sensing coil, a light source having a front output side and a back output side and emitting light at an associated light source intensity, and a polarizer. Often, an optical coupler disposed between the front output side and the rear output side and receiving light from a light source, the light forming two linearly polarized light beams of substantially equal intensity. A coupler and a fiber sensing coil disposed proximate the first end of the fiber sensing coil for receiving a first beam of the two linearly polarized light beams and providing a first linearly polarized light beam to the first linearly polarized light beam. A first quarter-wave plate for converting into first circularly polarized light propagating through the sensing coil in one direction and a second end of the fiber detection coil, 2 A second linearly polarized light beam and a second linearly polarized light beam A second quarter-wave plate for converting into a second circularly polarized light propagating through the sensing coil in a second direction opposite the first direction, the first and second Circularly polarized light of the fiber passes through the sensing coil and undergoes a phase difference shift caused by a magnetic field or a current flowing through a conductor in the vicinity of the sensing coil, the fiber sensing coil having first and second quarter wavelengths. The phase-shifted and circularly-polarized return light is supplied to the plate, and the first and second quarter-wave plates convert the phase-shifted and circularly-polarized return light into linearly-polarized return light. And wherein the optical combiner is a photodetector that combines and interferes with linearly polarized return light to produce a combined light beam, and is operatively coupled to a rear output side of the light source. Detection in response to a combined light beam transmitted through a light source And including a light detector providing an output signal.

According to another aspect of the present invention, a reduced minimum configuration (RMC) fiber optic current sensor (FOCS) system includes a fiber optic sensing area having an optical fiber and a front output side and a rear output side. A light source for emitting light having an associated light source intensity, and an optical fiber sensing area and a front output side of the light source for transmitting two linearly polarized light beams from the light source along the optical path. And an optical path portion connected to. At least one quarter wave plate is provided for converting the two linearly polarized light beams into two opposing circularly polarized light beams propagating through the sensing area portion, the optical path portion and the sensing area portion. Two opposing circularly polarized light beams, which are disposed between the two and propagate through the sensing region, undergo a phase difference shift caused by a magnetic field or a current flowing through a conductor near the sensing coil. The sensing area portion of the fiber includes a reflector disposed at an end portion of the fiber sensing area portion, the reflector reflecting the circularly polarized light beam and providing a phase-shifted and circularly polarized return light. Feeding at least one quarter wave plate, which converts the phase-shifted circularly polarized return light into an interfering linearly polarized return light beam. A photodetector operatively coupled to the rear output side of the light source detects the interfering return light beam transmitted through the light source and outputs an output signal in response to the interfering return light beam transmitted through the light source. give.

Embodiments of the RMC FOCS system can include one or more of the following features. R
The MC-FOCS includes a polarizer disposed between the front output side and the sensor coil, which polarizes the light emitted from the light source and the return light beam. Reflective R
In MC FOCS, a 45 degree twist can be inserted between the polarizer and the sensor coil. An optical phase or birefringence modulator may be coupled to the sensor coil.
An oscillator controlling the modulation amplitude may be coupled to the modulator. An electrical amplifier receiving the output signal is coupled to the detector, and a DC block, rectifier, integrating comparator and light source driving means are coupled to the amplifier to control the intensity of the associated light source. Process the output signal,
Electrical signal processing means may also be coupled to the amplifier to provide a value for the output that is correlated with the magnetic field or current.

Detailed Description of Certain Illustrated Embodiments While the invention is susceptible to various modifications and alternative forms, specific embodiments are shown by way of example in the drawings and will herein be described in detail. However, this is not intended to limit the invention to the particular forms disclosed, but rather to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined below.

The present invention is a “minimized configuration reduced” (RMC) fiber optic current sensor (FOC).
S). Unlike conventional FOCS, the first combiner is omitted and the output of the interferometer is read by a detector positioned on the output side behind the light source. Referring first to FIG. 1, the light source 1a emits light from the front output surface 1b, which light is polarized by a polarizer 2. Laser diode (LD), super light emitting diode (SL)
D), and several types of light sources may be used, including light emitting diodes (LEDs) or super radiating fiber amplifiers. The polarizer 2 may be, for example, a fiber polarizer, a lithium niobate polarizer, or a polymer waveguide polarizer. The combiner 3 splits the light into two substantially equal intensity counter-propagating beams. Quarter-wave plates 14 and 16 are inserted in the optical paths at both ends of the sensing coil. Quarter-wave plate 14, 16
Converts the linearly polarized light formed by the polarizer 2 into circularly polarized light propagating in the opposite direction in the sensing coil 4. A magnetic field introduces a phase shift (Faraday rotation) of a circularly polarized light beam propagating in the opposite direction, where the direction of the phase shift is determined by the direction of propagation of the circularly polarized light beam with respect to the direction of the magnetic field. . The quarter-wave plates 14, 16 convert each returned circularly polarized light beam that passed through the sensing coil back into a linearly polarized light beam, which is then again in the optical combiner 3. Be combined. The coupler can be a directional coupler formed from optical fibers or integrated optical elements.

The recombined light beam then passes through the light source 1a and is received by the detector 5 at the output 1c behind the light source 1a. The detector 5 converts an optical input into an output voltage, for example an amplifier 6 which is a transimpedance amplifier.
A photodetector coupled to the. The output of the detector 5 passes through a suitable amplifier 6 which provides a voltage gain of eg 1 million. The output of the amplifier is applied to the demodulator 7. The demodulator 7 may be a phase sensitive detector (PSD) that receives a signal from an oscillator 8. FOCS
On the other hand, the output of the demodulator 7 is a function of the magnetic flux through the sensing coil 4 and is sinusoidal and can be approximated by a linear function to be low to relax the magnetic field or current. If the two signals entering demodulator 7 are the same in phase and frequency, the output is maximum, and if they are different, the output is reduced. The oscillator 8 and the phase modulator 9 maintain the phase modulation interference depth, as will be described in detail below. Alternatively, other phase modulators may be used, such as those constructed from lithium niobate or another electro-optical material. The light source controller / driver 10 for adjusting the intensity of the light source may include additional elements such as filters, rectifiers, integrating comparators, as described in detail below.

Referring now to FIG. 2, which illustrates another embodiment of the RMC FOCS system according to the present invention, the light source 1 a emits light from the front output surface 1 b, which light is polarized by the polarizer 2. The birefringence modulator 9 modulates the polarization direction of the polarized light. Polarizer 2
A 45-degree slice 11 is inserted between the birefringence modulator 9 and the birefringence modulator 9 to provide light linearly polarized in the diagonal direction. A single quarter wave plate 12 disposed between one end of the sensing coil 4'and the phase modulator 9 provides two opposing circles for propagating the modulated, linearly polarized light through the sensing area. Convert to a polarized light beam. Unlike the first embodiment, light is introduced into only one end of the sensing coil 4 '. The other end of the sensing coil 4'is
It has a reflector 13 which reflects the circularly polarized light back to the sensing coil 4'while reversing the polarization direction. The shape of the reflective sensing coil has the additional advantage of being less sensitive to mechanical vibrations and rotation of the sensing coil.

The scale factor of the sensing coil can be designed such that this maximum current range is well within the essentially linear region of the transfer function of the output of the sensor. Alternatively, electron linearization techniques known in the art may be used. The fiber coil length of the sensing coil depends on the current range to be measured and may be between 1 meter and 1000 meters, preferably between 1 meter and 20 meters. The coil is wound so that the conductor can pass through the opening of the coil. A first directional coupler and a sense coil, λ / 4
The respective separation between the wave plate is the first directional coupler and the sensing coil or λ.
20 meters to 1.0 to employ a polarization maintaining fiber with a quarter wave plate
It may be between 00 meters. Due to this type of structure, the current is
It can be determined directly from the amplitude of F1). Since the phase and frequency of the fundamental signal are known, an effective way to determine the amplitude is synchronous demodulation.

Referring now to FIG. 3, the broadband signal current detected by the detector is passed through a transimpedance preamplifier 26 which converts the detected photocurrent into a voltage and an amplifier 27 which provides the voltage signal gain. To be done. The amplified voltage signal is then fed to a low pass filter (LPF) whose corner frequency is at the fundamental frequency (F1) before being synchronously demodulated in the synchronous demodulator 29. The low pass filter 28 attenuates all harmonics from the voltage signal, leaving only the fundamental frequency (F1). The other input of the synchronous demodulator 29 is a voltage signal from a self-resonant oscillator and an AGC amplifier that may use a Colpitts oscillator and an AGS amplifier to provide a stable amplitude and self-resonant frequency to the modulator 9, as described below. To receive. However, as is known in the art, the circuit 8 may be a crystal oscillator that provides a constant amplitude, a digital synthesizer, a crystal oscillator that provides a fixed frequency signal, or a Colpitts that provides a fixed amplitude self-resonant signal to the modulator. An oscillator (only) is enough.

The output of the circuit 8 is passed through a phase shifter and a low pass filter 32 whose corner frequency is equal to or higher than the fundamental frequency (F1). The output of demodulator 29 is maximum when the phase and frequency of its input signals are equal and is proportional to the magnitude of the sensor output signal at the fundamental frequency (F1) which is a function of magnetic field or current.
This output may be passed through another low pass filter 30 which produces a DC signal proportional to the magnetic field or current. Finally, the DC signal is amplified in DC amplifier 31 to set the desired sensor scale factor. Demodulation produces a linear output over a wide dynamic magnetic field and / or current range. The resolution of the magnetic field measurement depends on the noise figure of the transimpedance preamplifier 26 and the measurement band.

Those skilled in the art will appreciate, for example, that AC power
It is recognized that the output of a current sensor that measures the AC magnetic field produced by the AC current flowing through the line produces a corresponding AC signal that includes the fundamental frequency of the AC power line as well as its harmonics.

Maintaining a constant scale factor during environmental changes requires that the operating points of the two sensors be accurately maintained. First, the magnitude of the sensor signal at the output of the amplifier 6 must be constant. In order to achieve this, one aspect of the present invention provides a second harmonic signal (F2) for a sensor with a short coil length.
Capitalizes on the fact that the amplitude of is relatively constant over the entire rate / field range. Thus, the broadband sensor signal is high pass filtered (HP) at the second harmonic frequency (F2) by the high pass filter 35.
F), rectified by the rectifier 36, integrated by the integration comparator 37, compared with the reference, and applied to the light source 21 by the light source driving device 10. The resulting D
The C signal changes the optical power output of the light source 1a by increasing or decreasing the current of the light source,
And is therefore used to control the emitted optical power. The high pass filter 35 may be needed to reduce the effect of the reference signal (F1) on the accuracy of the light source control circuit in high magnetic fields or currents. As known in the art,
The high pass filter 35 is replaced with a DC block or a band pass filter,
The rectifier 36 may be a full-wave rectifier or a half-wave rectifier.

The second sensor operating point to be maintained is the phase modulation interference depth controlled in the PZT phase modulator 9. The depth of phase modulation is set by the amplitude of the sinusoidal drive voltage applied to the PZT phase modulator 9. However, simply maintaining a sinusoidal drive with a fixed frequency and amplitude does not guarantee a fixed depth of phase modulation. The resonance frequency (Fr) of the PZT modulator 9 may drift over time and due to changes in temperature. Also, the mechanical to optical phase shift conversion scale factor (Q _m ) of the PZT modulator 9 may vary. As mentioned above, the present invention allows the phase modulator 9 to be activated by applying the output of the self-resonant oscillator and the adjustable gain control (AGC) amplifier circuit 8 to the phase shifter and low pass filter 32. To use as. Since the modulator 9 is part of the active feedback circuit, any movement in frequency of the resonant modulator is tracked. Qm and Fr
Also changes the dynamic impedance of the modulator, which affects the drive amplitude. Although other self-resonant oscillators known in the art may be used, the self-resonant oscillator and AG
The C amplifier circuit 8 is used to maintain a stable sine wave drive amplitude through changes in the environment.

Thus, where the basic sensor signal amplitude is synchronously demodulated to determine the magnetic field or current, a FOCS system with simplified signal processing electronics is provided. The second harmonic sensor signal (F2) is used to control the intensity of the light source. It is not necessary to take the ratio of these signals. The depth of phase modulation is maintained by using the self-resonant oscillator method with the phase modulator as part of the active electrical circuit.

Such a configuration eliminates non-essential optical elements and slices from the system and enables a low cost FOCS system configuration. The use of RMC FOCS in conjunction with a simplified signal processing electronics approach provides a very attractive cost effective magnetic field sensor that can be used to measure current. FOCS
The signal processing system is simple, low cost to manufacture, accurately determines external quantities affecting the sensing coil, and has a constant scale factor during changes in environmental conditions. To maintain.

Referring now to FIG. 4, the same signal processing electronics as described above with reference to FIG. 3 can be used with the reflective fiber optic current sensor of FIG. The use of RMC FOCS with a simplified signal processing electronics approach provides a very attractive, cost-effective magnetic and current sensor that is rather immune to mechanical vibrations and coil rotation. .

While the present invention has been disclosed in connection with the preferred embodiments shown and described in detail, various modifications and improvements will immediately become apparent to those skilled in the art. Therefore, the spirit and scope of the invention should be limited only by the claims.

[Brief description of drawings]

[Figure 1]   1 is a schematic diagram of a first embodiment of an RMC / FOCS system according to the present invention.

[Fig. 2]   FIG. 6 is a schematic diagram of a second embodiment of an RMC / FOCS system according to the present invention.

FIG. 3 is a detailed diagram of an electronic control circuit of the first embodiment of the RMC / FOCS system shown in FIG.

FIG. 4 is a detailed diagram of an electronic control circuit of a second embodiment of the RMC / FOCS system shown in FIG.

─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Bennett, Sydney M             Chicago, Illinois, USA 60610,             North Dearborn Parkway             1301, unit 706 (72) Inventor Diot, Richard Bee             Ohio, Illinois, United States 60463             Ku Lone, South Minique Avenue             ー 9832 F-term (reference) 2G025 AA00 AB09 AB10 AC06

Claims (20)

[Claims] 1. A reduced configuration (RMC) fiber optic current sensor (F)
OCS) system, a fiber sensing coil, a light source having a front output side and a back output side and emitting light at an intensity of an associated light source, and disposed between the front output side and the coil, An optocoupler for receiving light from the light source, the optocoupler forming two linearly polarized light beams of substantially equal intensity, and an optical coupler disposed near the first end of the fiber sensing coil. A first circularly polarized light that is provided and receives a first one of the two linearly polarized light beams and propagates the first linearly polarized light beam in a first direction through the sensing coil. A first quarter-wave plate for converting into a first quarter-wave plate and a second one of the two linearly polarized light beams disposed near the second end of the fiber sensing coil, Two linearly polarized light beams in a second direction opposite to the first direction A second quarter-wave plate for converting into second circularly polarized light propagating through the sensing coil in a direction, the first and second circularly polarized light passing through the sensing coil. And a second quarter-wave plate that is subject to a phase difference shift caused by a magnetic field or a current flowing through a conductor near the sensing coil, the fiber sensing coil being phase-shifted and circularly polarized return light. Are supplied to the first and second quarter-wave plates, and the first and second quarter-wave plates convert the phase-shifted and circularly-polarized return light into linearly-polarized return light. And the optical coupler converts
A photodetector operatively coupled to the output side behind the light source for combining and interfering the linearly polarized light, the light beam being transmitted through the light source. Reduced to minimum configuration (RMC) fiber optic current sensor (FOCS) with a photodetector that detects and provides an output signal in response to a combined light beam. 2. An optical modulator coupled to the coil and having a modulation depth, an oscillator coupled to the modulator for controlling the amplitude of phase modulation, and an electrical coupler coupled to the detector for receiving an output signal. An amplifier, a light source driving means coupled to the amplifier for controlling the intensity of an associated light source, and an electrical signal coupled to the amplifier for processing the amplified output signal and providing a value of the output corresponding to a magnetic field or current The RMC / FOCS system according to claim 1, further comprising processing means. 3. The RM of claim 1, further comprising a polarizer coupled between the front output side and the optocoupler to polarize the light emitted from the light source and the return light beam.
C / FOCS system. 4. The RMS FOCS system of claim 1, wherein the light source is selected from the group comprising a semiconductor light source and a rare earth element-doped fiber light source. 5. The RMC / FOCS system according to claim 2, wherein the light source driving means includes a DC block, a rectifier and an integrating comparator. 6. The RMC FOCS system of claim 5, wherein the DC block comprises a high pass filter. 7. The RMC · F according to claim 5, wherein the rectifier is a half-wave rectifier.
OCS system. 8. The RMC according to claim 2, wherein the oscillator is a phase modulator driving device of a piezoelectric converter which supplies a periodic waveform having a fixed amplitude and a fixed frequency.
FOCS system. 9. The RMC / FOC according to claim 2, wherein the oscillator is a phase modulator driving device of a piezoelectric converter which supplies a fixed amplitude and a self-resonant frequency waveform.
S system. 10. The RM of claim 2, wherein the oscillator is a piezoelectric modulator phase modulator driver providing an adjustable gain controlled self-resonant frequency waveform.
C / FOCS system. 11. The RMC according to claim 5, wherein the rectifier is a full-wave rectifier.
FOCS system. 12. The RMC FOCS system of claim 5, wherein the DC block comprises a bandpass filter. 13. A reduced configuration (RMC) fiber optic current sensor (F).
OCS) system, a fiber optic sensing region comprising an optical fiber, a light source having a front output side and a back output side, emitting light at the intensity of the associated light source, and from said light source along the optical path. An optical path portion operatively connecting the front output side of the light source to the fiber optic sensing area portion for transmitting two linearly polarized light beams; At least one quarter-wave plate arranged to convert the two linearly polarized light beams into two opposing circularly polarized light beams propagating through the sensing region. Two opposing circularly polarized light beams propagating through the sensing region undergo a phase difference shift caused by a magnetic field or a current flowing through a conductor in the vicinity of the sensing coil, and the fiber sensing region portion is phase shifted. The circularly polarized return light to at least one quarter corrugated plate, which at least one quarter corrugated plate shifts the phase-shifted circularly polarized return light into a coherent straight line. A photodetector for converting into a polarized return light beam and operatively coupled to an output side behind the light source, the photodetector being responsive to a coherent return light beam transmitted through the light source. Reduced to Minimal Configuration (RMC) Fiber Optic Current Sensor (FOCS) system with a photodetector that detects and provides an output signal. 14. An optical modulator for providing a modulation depth and coupled to said optical fiber sensing area portion, an oscillator coupled to said modulator for controlling phase modulation amplitude, and coupled to said detector, An electrical amplifier for receiving an output signal, a light source driving means coupled to the amplifier for controlling the intensity of an associated light source, a value of the output coupled to the amplifier for processing the output signal and correlated to a magnetic field or current 14. The RMC FOCS system of claim 13, further comprising electrical signal processing means for providing. 15. A polarizer coupled between the front output side and the fiber optic sensing region, the polarizer further comprising: polarizing light emitted from the light source and a return light beam. The RMC / FOCS system according to claim 13. 16. The RMC FOCS system according to claim 13, wherein the light source is selected from the group including a semiconductor light source and a rare earth element-doped fiber light source. 17. The RM of claim 14, wherein the oscillator is a piezoelectric modulator phase modulator driver that provides a periodic waveform of fixed amplitude and fixed frequency.
C / FOCS system. 18. The RMC · F according to claim 14, wherein the oscillator is a phase modulator driving device of a piezoelectric converter that supplies a fixed amplitude and a self-resonant frequency waveform.
OCS system. 19. The R of claim 14, wherein the oscillator is a piezoelectric transducer phase modulator driver that provides an adjustable gain controlled self-resonant frequency waveform.
MC / FOCS system. 20. The RMC / FOCS system according to claim 14, wherein the light source driving means includes a DC block, a rectifier and an integrating comparator.