JPH10311729A - Light interference angular velocity meter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an output error due to a thermal time-dependent disturbance of an optical fiber loop by a method without increasing the number of turns of the optical fiber loop. SOLUTION: A light source 1, a first optical fiber coupler 3, and a second optical fiber coupler 7 are successively connected by an optical fiber string 2 and a polarization beam splitter 22 is connected to the port for branching of the first optical fiber coupler 3. Both terminals of the optical fiber loop 8 are connected to both output ports of the second optical fiber coupler 7. X and Y polarization components being branched by the splitter 22 are photoelectrically converted by wave receivers 10a and 10b, are further detected by synchronous detectors 11a and 11b, respectively, and an interference light intensity of light in both directions of the optical fiber loop 8 is detected. The difference in the output of the detectors 11a and 11b is detected by a subtractor 23, and the detection output is multiplied by a correction coefficient using a multiplication means 24, thus generating a correction signal for the influence of inflation and contraction due to the temperature of the optical fiber loop. The difference between the correction signal and the output of one synchronization detector is detected by the subtractor 23 as the detection signal of an input angular velocity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical interference gyro (also referred to as an interference type optical fiber gyro), and more particularly to a measure against an output error caused by a thermal time-dependent disturbance of an optical fiber loop.

[0002]

2. Description of the Related Art A conventional optical interference gyro will be briefly described with reference to FIG. Polarization maintaining first optical fiber coupler 3 and x
One end of an optical fiber 2 on which a polarizer 5 for selecting polarization and quenching unnecessary y-polarized light is connected to the light source 1, and the other end of the optical fiber 2 is connected to a polarization-maintaining second optical fiber coupler 7. Connected to the input port of The x-polarized light is split into two by an optical fiber coupler 7 and circulates in a polarization maintaining optical fiber loop 8 in opposite directions. That is, this optical fiber loop 8
In the figure, only the x polarization mode is excited. The two circulating lights are multiplexed again by the second optical fiber coupler 7, interfere with each other, return the x mode of the optical fiber 2, and reach the optical receiver 10 via the first optical fiber coupler 3.

Here, when the optical fiber loop 8 has an angular velocity motion about an axis passing through the loop, the phase difference Φ _s due to the Sagnac effect is applied to both circulating lights of the optical fiber loop 8 multiplexed by the second optical fiber coupler 7. = (4πrL / cλ) Ω (1) Then, the input angular velocity Ω can be known from the intensity fluctuation of the interference light detected by the light receiver 10. Here, r and L are the radius and total length of the optical fiber loop 8, respectively, and c and λ are the light speed and light wavelength in vacuum, respectively.

In actual angular velocity measurement, a phase modulation method is performed instead of directly monitoring the light reaching the light receiver. In the simplest case, the optical phase modulator 14 laid at the loop end is driven at a sufficient frequency to generate an oscillating phase difference in the multiplexed light based on the time difference between the two circulating lights passing therethrough. Detection is performed by the synchronous detector 11. As a result, a maximum sensitivity is created near the zero point of the input angular velocity, and its polarity and magnitude can be known.

[0005]

The interference type optical fiber gyro is based on the premise that there is no phase difference other than the Sagnac effect between the two circulating lights passing through the same optical path in the optical fiber loop 8. If, as is the case with the modulation method, there is a point in the loop 8 that causes a temporal variation of the optical path length, the light forming the interference will produce a phase difference indistinguishable from the Sagnac effect due to the time difference passing through it, resulting in an error. Cause.

[0006] Even if the sensing loop 9 is mechanically conservative, application of a heat flux is inevitable. The temperature dependence of the propagation constant of an optical waveguide is significant, and measures against such heat-induced time-dependent disturbances are issues for optical fiber gyros.
This error is described by D.S. M. APPlied Opties Vo by Shupe
l 19,5, P.654; 1980. If the angular rate of light ω, the propagation constant β of the optical fiber, the coefficient of thermal expansion α, and the local temperature change rate of the coil fiber of the total length L are written as T _t , the phase difference generated in the interferometer is Φ = ( _{β / ω) (β T +} βα) ∫ 0 L T t (u) · (2u-L) du = ∫ 0 L / 2 2 {T t (L / 2 + u ') - T t (L / 2u' )｝ U'du '... (2) Here, β _T is the temperature change rate of the propagation constant, u is the distance from one end of the optical fiber loop, u ′ is the distance from the middle point of the optical fiber loop, and u ′ = u−L / 2. From (2), it can be seen that _{Tt at} each point of the fiber contributes to the phase difference Φ in an antisymmetric manner with respect to the center of the coil.

Therefore, conventionally, as a countermeasure, a mechanical method in which the entire coil is insulated, a portion equidistant to the left and right of the coil midpoint is wound on an adjacent layer, and the thermal environment, that is, a winding is performed so that _Tt is symmetrically distributed. Was known. However, in this method, the left and right portions of the optical fiber coil must be alternately wound one layer at a time with respect to the midpoint thereof, resulting in an increase in the number of winding steps and an increase in cost.

The present invention expects that adjacent windings symmetrical with respect to the center of the coil are adjacent to each other, and that _Tt approximately coincides with each other, whereas orthogonal windings in the same fiber sharing _Tt are expected. The polarization mode is used for reference, and a new optical measure is taken against the error to solve the above problem.

[0009]

[Means for Solving the Problems]

(1) In the optical interference gyro according to claim 1, the input port of the first optical branching / coupling means is connected to the light source through the first optical waveguide, and the output port of the first optical branching / coupling means is connected to the output port through the second optical waveguide. Two optical branching / coupling means are connected, and both ends of the optical fiber loop are respectively connected to two output ports of the second optical branching / coupling means. A polarization beam splitter is connected to a branching port of the first optical branching / coupling means.

A sensing loop is formed by the second optical branching / coupling means and the optical fiber loop. The first and second optical waveguides are composed of polarization maintaining optical waveguides having x and y polarization modes, the optical fiber loop is composed of a birefringent polarization maintaining optical fiber loop, and the x and y polarization modes are Excited.
The x and y polarization components branched and output by the polarization beam splitter are respectively input to the first and second optical receivers, and the interference light intensities of the two-way light in the x and y polarization modes of the optical fiber loop are respectively detected. You.

The difference between the output signal components of the first and second photodetectors is detected by a first subtractor, and the output of the first subtractor is multiplied by a predetermined correction coefficient by a multiplying means, and the output is multiplied by the temperature of the optical fiber loop. A correction signal is generated for the effects of expansion and contraction,
The difference between the correction signal and one of the output signal components of the first and second light receivers is detected by the second subtractor as a detection signal of the input angular velocity.

(2) In the invention of claim 2, in the above (1), the first optical branching / coupling means comprises a polarization maintaining optical fiber coupler having polarization independence and having a branching ratio of 3 dB,
The second optical branching / coupling means comprises a polarization maintaining optical fiber coupler or a birefringent substrate type optical branching waveguide.
The optical waveguide comprises a polarization maintaining fiber optic string, and the polarization beam splitter comprises an optical fiber type polarization beam splitter.

(3) In the optical interference gyro according to claim 3, one end of the polarization-maintaining first optical fiber string in which the first optical fiber coupler and the first polarizer for selecting x-polarization are laid is the first. The other end of the first optical fiber string is connected to one input port of a polarization-maintaining second optical fiber coupler, and birefringent and polarized light is connected to two output ports of the second optical fiber coupler. Both ends of the wave maintaining optical fiber loop are connected. One end of a polarization-maintaining second optical fiber string in which a third optical fiber coupler and a second polarizer for selecting y-polarization are laid is connected to a second light source,
The other end of the second optical fiber string is connected to the other input port of the second optical fiber coupler. A sensing loop is formed by the second optical fiber coupler and the optical fiber loop, and the optical fiber loop is excited in both x and y polarization modes.

A first optical receiver is connected to the branch port of the first optical fiber coupler, and the interference light intensity of the two-way light in the x polarization mode of the optical fiber loop is detected. A second optical receiver is connected to the port, and the interference light intensity of the two-way light in the y-polarization mode of the optical fiber loop is detected. The difference between the output signal components of the first and second light receivers is detected by a first subtractor, and the output of the first subtractor is multiplied by a predetermined correction coefficient by a multiplying means, so that the expansion and contraction due to the temperature of the optical fiber loop is reduced. A correction signal for the influence is generated, and a difference between the correction signal and one output signal component of the first and second light receivers is detected by the second subtractor as a detection signal of the input angular velocity.

(4) In the invention of claim 4, in (3), instead of using the light of the first and second light sources, the light of one light source is demultiplexed by an optical fiber type polarizing beam splitter,
Then, the obtained x, y polarization components are used. (5) In the invention of claim 5, in the above (3), the first and second light sources are alternately driven in a certain cycle, and alternately supply light to the sensing loop.

(6) In the optical interference gyro according to claim 6, a polarization maintaining first optical fiber string in which a polarization maintaining first optical fiber coupler and a first polarizer for selecting x polarization are laid. Is connected to the first light source, the other end of the first optical fiber string is connected to one input port of the polarization maintaining second optical fiber coupler, and is connected to two output ports of the second optical fiber coupler. Both ends of the refractive and polarization maintaining optical fiber loop are connected. 3rd polarization maintenance
One end of a polarization-maintaining second optical fiber string having an optical fiber coupler and a second polarizer for selecting y-polarization is connected to a second light source, and the other end of the second optical fiber string is connected to a second optical fiber. Connected to the other input port of the coupler. A sensing loop is configured by the second optical fiber coupler and the optical fiber loop, and the optical fiber loop is
It is excited in both x and y polarization modes.

The light emitted from the first and second light sources is intensity-modulated by the modulating means at frequencies f ₁ and f ₂ , respectively, and the light traveling around the optical fiber loop is converted to the frequency f by the optical phase modulator.
_The phase is modulated by _m , and the first and second optical receivers are respectively connected to the branch ports of the first and third optical fiber couplers. The outputs of the first and second photodetectors are input to the first and second synchronous detectors, respectively, and the frequencies | f ₁ -fm | and | f ₂ -fm
| Components are detected, and x,
The interference light intensities of both round lights in the y-polarization mode are detected.

The difference between the outputs of the first and second synchronous detectors is detected by a first subtractor, and the output of the first subtractor is multiplied by a predetermined correction coefficient by a multiplying means, and the expansion of the optical fiber loop due to the temperature. A correction signal for the effect of contraction is generated, and a difference between the correction signal and one output of the first and second synchronous detectors is detected by the second subtractor as a detection signal of the input angular velocity.

[0019] (7) In the invention of claim 7, in the (6), first, second light source is made of a super luminescent diode, the driving current of the light intensity modulation by the frequency f ₁ and f ₂ is the diode The operation is directly modulated. (8) In the invention of claim 8, in any one of the above (1), (3) and (6), the second optical branching / coupling means or the second optical fiber coupler is a polarization-independent 3 dB branch. Having a ratio.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The Sagnac effect, which is the principle of detecting the angular velocity of an optical fiber gyro, is characterized by being free from the influence of the refractive index of the medium, as shown in equation (1). error depends on the propagation constants β and its temperature change rate B _T of the fiber as seen in equation (2) by. Furthermore, the β and B _T is x in the polarization maintaining property optical fiber, with different values in y both polarization modes.

Therefore, in such an optical fiber gyro that forms a sensing coil with such a polarization maintaining optical fiber,
Conventionally, only one polarization mode was transmitted, but if both polarization modes were excited at the same time and signals were separately extracted, the phase difference output due to angular velocity would be the same wavelength when both modes were excited at the same wavelength. In the case of the light of the formula (1), the outputs match as they are, and even if the light has a significant wavelength difference, the outputs of the angular velocity phase and the like converted by the scale factors corresponding to the coefficients of the appropriate equation (1) match. In general, outputs as errors due to heat-induced time-dependent disturbance differ from each other depending on a constant coefficient ratio. Therefore, if the difference between the two outputs is detected, the difference indicates the error,
It can be used as a correction signal.

If the ring interferometer for detecting the Sagnac effect is composed of an optical fiber loop and a directional coupler (optical branching / coupling means), two ports that can be used for inputting and outputting light can be obtained symmetrically. In a conventional optical fiber gyro, only one of them is used also as an input / output port. That is, a normal polarizer is laid on one port of the directional coupler, light is made to enter from there, and return light to the same place is used. The polarizer is a filter for ensuring the optical path reciprocity of the two light beams forming the interference. The essential point is that the filter for the incident light speed of the optical fiber loop also functions as the filter at the output stage of the feedback light, thereby ensuring the accuracy of the optical fiber gyro.

According to the first aspect of the present invention, both the x and y polarization modes of the polarization maintaining optical fiber loop are excited without using the polarizer, and each interference light in the both deviation modes is excited by the polarization beam splitter. The light is separated, and two interference light outputs are separately detected by two light receivers. Two independent interferometers are formed on one sensing coil. According to the third and sixth aspects of the present invention, both the two ports of the directional coupler are used, and light from the two light sources is made to enter the x and y two polarization modes of the same loop from each port, respectively. Detecting the return light to the port allows two independent ring interferometers to coexist in the same optical fiber loop. At this time, polarizers for x-polarization and y-polarization filtering are laid on each port, but the above-mentioned reciprocity is further secured, that is, mixing of light incident on the other port is eliminated, and two interferometers are used. In order to achieve complete independence, in the invention of claim 6, the first port (for example, x-polarized) incident light and the second port (for example, y-polarized) incident light are amplitude-modulated at different frequencies from each other, and a ring interferometer is used. By detecting a difference frequency component different from the phase modulation effect executed in the first port, the first port incident light component from the first port return light and the second port return light from the second port return light. The component light incident on the loop is separately detected. That is, in the polarization maintaining optical fiber optical system, the mode coupling as an error cannot be actually avoided due to the performance of the device and the accuracy limit of the connection portion, etc., and in terms of eliminating errors due to mixing of unnecessary light. ,
Due to the separate modulation and demodulation, the two-mode two-interferometer is comparable to the conventional reciprocal single interferometer.

Let the non-reciprocal phase difference of the x polarization mode interferometer be Φ
_Assuming that the _x and y polarization modes are Φ _y , these are composed of the Sagnac phase difference Φ _s due to the rotational angular velocity and the phase differences Φ ^T _x and Φ ^T _y which are the heat-induced errors for each mode. Φ _x = Φ _s + Φ ^T _x , Φ ^T _x = C _x ∫ ₀ ^L T _t (2u−L) du (3) Φ _y = Φ _s + Φ ^T _y , Φ ^T _y = C _y ∫ ₀ ^L T _t (2u-L) du ... ( 4) C x, if C _y is a omega angular frequency of the two modes of light are equal _{phase, C x = (β x /} ω) (∂β x / ∂T + β x α) , C _y = (β _y / ω) (∂β _y / ∂T + β _y α) (5) If the angular frequencies of the x and y mode lights are different from ω _x , ω _y , C _x = (β _{x / ω x) (∂β x} / ∂T + β x α), C y = (β y / ω y) (∂β y / ∂T + β y α) ... (5 ') here, β _x, β _y is These are the propagation constants of the x mode and the y mode. Here, if ∫ ₀ ^L T _t (2u−L) du≡I (6), Φ _x = Φ _s −C _x I (3 ′) Φ _y = Φ _s + C _y I (4 ′) ) (3 '), (4') than the erasing _{I, C y Φ x -C x} Φ y = (C y -C x) Φ s ... (7) ∴ Φ s = (C x Φ y -C _y Φ _x ) / (C _x −C _y ) (8) By transforming equation (8) and expressing Φ _s in the form of Φ _x and its correction term, Φ _s = Φ _x − ｛C _x / ( C _x −C _y )｝ (Φ _x −Φ _y ) (9) Similarly, when Φ _s is represented by Φ _y and its correction term, Φ _s = Φ _y − ｛C _y / (C _y − _{C x)} (Φ y -Φ} x) ... (10) (9), if there is a difference [Phi _x, the [Phi _y of (10), it (3) and (4), [Phi _x - [Phi] _y = is ^{_{Φ T x -Φ T y = (}} C x -C y) ∫ 0 L T t (2u-L) du ......... (11). Therefore, this Teikeisu _{C x / (C x -C y} ) or C _y / (C _y -C _x) used, x or y mode output [Phi _x, a [Phi _y (9), corrected by (10) Then, if Φ _s is obtained, an accurate angular velocity output excluding the error can be obtained.

Next, an embodiment will be described. FIG. 1 is a block diagram showing an embodiment of the first and second aspects of the present invention. The light source 1 emits x and y linearly polarized components orthogonal to each other, and is coupled to two polarization modes of an optical fiber (generally, an optical waveguide) 2 that maintains polarization. These are a polarization-independent first optical fiber coupler (generally an optical branching / coupling means) 3 having a branching ratio of 3 dB and a polarization maintaining optical fiber (optical waveguide) 2.
And a polarization-independent second optical fiber coupler having a branching ratio of 3 dB (in some cases, a birefringent substrate-type optical branching waveguide is used, which can be generally referred to as an optical branching / coupling unit). 7, x, y of the polarization maintaining optical fiber loop 8
The light is branched and propagated as both circulating lights of each mode, and is again transmitted to the same coupler 7.
In each mode, it multiplexes and interferes with each other. The interference light formed in each of the x and y modes is guided as feedback light to the polarization beam splitter 22 via the first optical fiber coupler 3 and, if necessary, the polarization maintaining optical fiber 21, and the two x and y polarizations are emitted. Each mode is extracted as a separate light beam, and enters each of the light receivers 10a and 10b.

The synchronous detectors 11a and 11b are
a and 10b are synchronously detected, and the difference between these synchronously detected outputs is made by a first subtractor 23. The difference is further added to the difference by an amplifier (multiplying means) 24 to obtain a constant C _x in the equation (9). / (C _x -C _y) or (1
0) equation in some constant _{C y / (C y -C x} ) is multiplied, the second subtractor to one of the synchronous detection output as a correction signal this to the effects of thermal expansion and contraction due to temperature of the optical fiber loop 8 25 To obtain an output. In FIG. 1, the connection by the solid line on the output side of the synchronous detectors 11a and 11b is a case where correction is performed by the equation (9), and the dotted line is a case where correction is performed by the equation (10).

FIG. 2 is a block diagram of the third embodiment. In this case, the x and y polarization components from the light sources 1a and 1b are respectively polarization-maintaining optical fiber strings 2a and 2a.
2b. Here, for example, the optical fiber string 2a is set to the x polarization mode transmission, and the polarizer 5 that transmits only the x polarization mode via the first optical fiber coupler 3a.
Connect a. A polarizer 5b that transmits only the y-polarization mode is connected to the optical fiber string 2b via a third optical fiber coupler 3b. The two polarized lights enter the optical fiber loop 8 from different branches via the optical fiber string, and further enter the optical fiber loop 8 through the second optical fiber coupler 7 having a polarization independence and a branching ratio of 3 dB. The interference mainly returns to the optical fiber strings 2a and 2b on the incident side.

That is, for example, the x-polarized component light is branched by the coupler 7 from the optical fiber string 2a and becomes interference light after being turned around the loop. If there is no input angular velocity, all the intensities of the optical fiber string 2a are the same. Return to.
The return light of the optical fiber string 2a is extinguished by the polarizer 5a to eliminate the mixing of the y-polarized component, extracts the interference light output of only the pure x component, and reaches the light receiver 10a via the optical fiber coupler 3a. The same applies to the optical fiber string 2b that handles the y polarization component. The signal processing may be exactly the same as the example shown in FIG. When the two light sources 1a and 1b are used, the light sources are alternately emitted while temporally and alternately emitting light, so that one polarization mode light is coupled to the other polarization mode light through mode coupling as an error. It is also possible to prevent an error from being mixed in the output light.

It should be noted, the above-mentioned constant _{C x / (C x -C y} ),
C _y / (C _y −C _x ) is obtained by applying a heat flux to the gyro without inputting the rotational angular velocity, and obtaining Φ _{s of} (9) and (10).
= 0 and _{at, C x / (C x -C} y) = Φ x / (Φ x -Φ y) ...... (12) C y / (C y -C x) = Φ y / (Φ y - Φ _x ) ……………………………………………………………………………………………………………………………… (（)

Instead of using two light sources 1a, 1b,
As shown in FIG. 3, one light source 1 that emits both x and y polarizations is applied to a polarization beam splitter 31 via a polarization maintaining optical fiber 2-0, and the obtained x and y are obtained. Polarized split light can also be used (claim 4). FIG. 4 shows an embodiment of the present invention. 1a and 1b are two semiconductor light sources, and a super luminescent diode is desirable. The output light main mode 1a is coupled to the x polarization mode of the polarization maintaining optical fiber string 2a, and the output light main mode 1b is coupled to the y polarization mode of the polarization maintaining optical fiber string 2b. These are respectively polarization-maintaining and have a branching ratio of 3 dB via optical fiber couplers 3a and 3b.
Each of the polarizer 5a for x polarization transmission and y polarization extinction and the polarizer 5b for y polarization transmission and x polarization extinction are pure linearly polarized light and have polarization-independent 3 dB branching ratio. First port 7 of wave maintaining optical fiber coupler (directional coupler) 7
-1 and the light enters the second port 7-2. The incident light flux is further divided into two, and propagates as left and right circling light of the loop 8.

That is, the x-polarized light incident from the first port is split into two, and circulates in the x-polarization mode of the polarization maintaining optical fiber loop 8 in opposite directions. , And most of the light amount returns to the fiber string 2a from the first port 7-1 again. In particular, if there is no non-reciprocal optical phase shift in the loop, a so-called bright state of interference is formed in the first port 7-1, the entire amount of light returns here, and the second port 7-2 is in a dark state. Apart from the error, there is no feedback of x polarization. The same applies to the y-polarized wave, which enters from the second port 7-2 and branches and circulates around the y-polarized mode of the loop 8, and most of the light enters the second port 7-.
2 and returns to the second fiber string 2b. The two return lights are again filtered through the x polarizer 5a and the y polarizer 5b, respectively, and then reach the light receivers 10a and 10b via the couplers 3a and 3b. That is, 10
“a” performs photoelectric conversion of an x-mode interference light output, and “10b” performs photoelectric conversion of a y-mode interference light output.

Reference numerals 32a and 32b denote light sources 1a and 1b, respectively.
, While the oscillators 33 a and 33
b oscillates signals of frequencies f ₁ and f ₂ , respectively, and the drivers 33a and 33b receive the applied signals and light sources 1a and 1b
Are intensity-modulated at frequencies f ₁ and f ₂ , respectively. The carrier oscillator 13 oscillates the frequency fm and drives the phase modulator 9 laid on the optical fiber loop 8. Due to the effect of the phase modulation, a vibration component of the frequency fm and its integral multiple harmonic is generated in the intensity of the interference light on the surface of the light receiver when the steady light is incident. Here, the loop incident light is already f ₁ and f ₂ respectively.
Since the intensity of the light is modulated by the following equation, the output signal of the photodetector has a difference frequency therefrom, for example, fm in the output signal of the photodetector 10a.
_{-F 1, 2fm -f 1, 3fm} -f 1, includes a ... components, it is the same even light receiver 10b.

In the optical fiber gyro phase modulation method, an odd harmonic component of fm is detected in order to create maximum sensitivity and polarity near the zero point of the measuring instrument. Therefore, using the fundamental wave in this example, to make a fm -f ₁ In the difference-frequency filter 35a, 35b in fm -f _2, respectively, the synchronous detector 11a, 11
b, the respective frequency components of the output signals of the photodetectors 10a and 10b are synchronously detected. Light source 1
a, and the non-reciprocal phase difference equivalent output of the x-polarization mode Sagnac interferometer reaching the light receiver 10a and the phase difference equivalent output Φ _x of the y polarization mode interferometer reaching the light receiver 10b from the light source 1b. , Φ _y are obtained. The subsequent operation is the same as in FIG.

This method corrects the temporal variation of the optical path via temperature as defined by a constant coefficient. If there is a concurrent temporal variation of the optical path via stress, the correction is performed. It is disturbed. Therefore, application to a bobbin-less fiber coil, in which there is no stress fluctuation due to temperature, is excellent and effective. In the third and sixth aspects of the present invention, two light sources are used for a single-axis gyro. However, when a sensor system including two or more gyros is configured, the light emitted from the same light source may be used. Is branched by the optical branching means, and a system for supplying the sensing coil to two or more axes is realized, whereby the number and cost of the devices can be reduced.

[0035]

As described above, the present invention excites both polarization modes of a polarization maintaining optical fiber loop together,
By forming an independent ring interferometer for each mode,
The output error due to the heat-induced time-dependent disturbance in the optical fiber gyro is detected from the difference between the outputs of both modes by using the difference in the coefficient that induces the error, and this error is used as a correction signal for the angular velocity output. An optical fiber gyro having no components can be realized.

In the present invention, a new optical countermeasure is taken in place of a mechanical countermeasure conventionally known as a countermeasure for the error, so that the number of winding steps of the optical fiber coil increases as in the conventional countermeasure. No problem. However, it is of course possible to use both the conventional mechanical countermeasures and the optical countermeasures of the present invention in cases such as when performing more accurate measurements.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a block diagram showing an embodiment of the invention of claim 3;

FIG. 3 is a block diagram showing an embodiment of the invention of claim 4;

FIG. 4 is a block diagram showing an embodiment of the invention of claim 6;

FIG. 5 is a block diagram of a conventional optical interference gyro.

Claims (8)

[Claims] An input port of a first optical branching / coupling means is connected to a light source through a first optical waveguide, and a second optical branching / coupling means is connected to an output port of the first optical branching / coupling means through a second optical waveguide. The two ends of an optical fiber loop are respectively connected to two output ports of the second optical branching / coupling means, a polarization beam splitter is connected to the branching port of the first optical branching / coupling means, And the optical fiber loop constitute a sensing loop. The first and second optical waveguides each comprise a polarization maintaining optical waveguide having x and y polarization modes, and the optical fiber loop comprises a birefringent polarization. X, y, which is composed of a sustaining optical fiber loop, is excited in the x, y polarization mode, and is branched and output by the polarization beam splitter.
The polarization components are input to the first and second optical receivers, respectively, and the interference light intensities of the two-way light in the x and y polarization modes of the optical fiber loop are detected, respectively. The output of the first and second optical receivers The difference between the signal components is detected by a first subtractor, and the output of the first subtracter is multiplied by a multiplying means by a predetermined correction coefficient to generate a correction signal for the effect of expansion and contraction due to the temperature of the optical fiber loop. An optical interference gyro, wherein a difference between the correction signal and one output signal component of the first and second photodetectors is detected by a second subtractor as a detection signal of an input angular velocity. 2. The optical fiber according to claim 1, wherein said first optical branching / coupling means comprises a polarization-maintaining optical fiber coupler having polarization-independence and a branching ratio of 3 dB. A wave maintaining optical fiber coupler or a birefringent substrate type optical branch waveguide; wherein the first and second optical waveguides comprise a polarization maintaining optical fiber string; and the polarizing beam splitter includes an optical fiber type polarization. An optical interference gyro comprising a beam splitter. 3. One end of a polarization-maintaining first optical fiber string having a first optical fiber coupler and a first polarizer for selecting x-polarized light is connected to a first light source, and the first optical fiber string is provided. Is connected to one input port of a polarization maintaining second optical fiber coupler, and both ends of a birefringent, polarization maintaining optical fiber loop are connected to two output ports of the second optical fiber coupler. One end of a polarization-maintaining second optical fiber string in which a third optical fiber coupler and a second polarizer for selecting y polarization are laid is connected to one end of the second optical fiber string. The other end is connected to the other input port of the second optical fiber coupler, and a sensing loop is formed by the second optical fiber coupler and the optical fiber loop.
Excited in the y-polarization mode, a first optical receiver is connected to the branch port of the first optical fiber coupler, and the interference light intensity of the two-way light in the x-polarization mode of the optical fiber loop is detected. A second optical receiver is connected to the branching port of the third optical fiber coupler, and the interference light intensity of the two-way light in the y-polarization mode of the optical fiber loop is detected. The output of the first and second optical receivers The difference between the signal components is detected by a first subtractor, and the output of the first subtracter is multiplied by a multiplying means by a predetermined correction coefficient to generate a correction signal for the effect of expansion and contraction due to the temperature of the optical fiber loop. An optical interference gyro, wherein a difference between the correction signal and one output signal component of the first and second photodetectors is detected by a second subtractor as a detection signal of an input angular velocity. 4. The x and y polarization components according to claim 3, wherein the light of one light source is demultiplexed by an optical fiber type polarization beam splitter instead of using the light of the first and second light sources. An optical interference angular velocity meter characterized by using: 5. The optical interference gyro according to claim 3, wherein the first and second light sources are alternately driven at a certain period, and alternately supply light to the sensing loop. 6. One end of a polarization-maintaining first optical fiber string having a polarization-maintaining first optical fiber coupler and a first polarizer for selecting x-polarization is connected to the first light source,
The other end of the first optical fiber string has a second polarization maintaining property.
A birefringent and polarization maintaining optical fiber loop is connected at one end to an input port of the optical fiber coupler, and two output ports of the second optical fiber coupler are connected to both ends thereof. One end of a polarization-maintaining second optical fiber string having an optical fiber coupler and a second polarizer for selecting y-polarization is connected to a second light source, and the other end of the second optical fiber string is connected to the second optical fiber string. The second optical fiber coupler is connected to the other input port of the optical fiber coupler, the second optical fiber coupler and the optical fiber loop constitute a sensing loop, the optical fiber loop,
The excitation light is excited in the x, y polarization mode, and the light emitted from the first and second light sources has a frequency f
₁ and f ₂ are intensity-modulated, respectively, and the _two-way light of the optical fiber loop is phase-modulated at a frequency fm by an optical phase modulator.
The second light receiver is connected, first, the output of the second photodetector is input to the first, second synchronous detector, a frequency | f ₁ -f _m | and | f ₂ -
f _m | components are detected, respectively, the interference light intensity of both around light is detected, respectively, in the x and y polarization mode of the optical fiber loop, the difference between the first output of the second synchronous detector is first The output of the first subtractor is detected by a subtractor, and the output of the first subtracter is multiplied by a predetermined correction coefficient by a multiplying means to generate a correction signal for the effect of expansion and contraction due to the temperature of the optical fiber loop. 1. An optical interference gyro, wherein a difference from one output of the second synchronous detector is detected by a second subtractor as a detection signal of an input angular velocity. 7. The light source of claim 6, wherein the first and second light sources comprise super luminescent diodes, and the light intensity modulation by the frequencies f ₁ and f ₂ is a direct modulation for controlling a drive current of the diodes. An optical interference angular velocity meter characterized by the above. 8. An optical device according to claim 1, wherein said second optical branching / coupling means or said second optical fiber coupler has a polarization-independent branching ratio of 3 dB. Interferometric gyro.