JPS62223614A - Optical fiber gyro - Google Patents

Abstract

PURPOSE:To stabilize a scale factor through simple constitution by constituting part of a path of constant-polarized-wave optical fibers of specific length which are coupled so that polarization plane maintaining axes are at 45 deg. to each other. CONSTITUTION:A piezoelectric element 7 is wound with a constant-polarized- wave optical fiber 11 and an output error induced by a phase modulator 7 is reduced. One end R of the fiber 11 is coupled with a single-mode optical fiber from an optical directional coupler 4. Further, a part B is composed of a constant-polarized-wave optical fiber 12 and one end Q is coupled with an optical fiber loop 6. The other end P is connected to the fiber 11 at such an angle that their polarization plane maintaining axes are at 45 deg. to each other. Then, the lengths l1 and l2 of the fibers 11 and 12 are so set that polarized wave dispersion is larger than the coherence time of the output light of a light source 1 and l1>2l2 or l2>2l1. Then, the light passed through the part B is not polarized without reference to the polarization state of light propagated in a part A. Similarly, light propagated from the part B to the part A in the opposite direction is not polarized either.

Description

Detailed Description of the Invention [Objective of the Invention] (Industrial Application Field) The present invention detects interference waves of lights propagating in opposite directions through an optical fiber loop to determine the angular velocity of a rotating body with respect to inertial space. This invention relates to an optical fiber gyro for detection.

(Prior art) An optical fiber gyro splits the light emitted from a light source, propagates the light in opposite directions through an optical fiber loop, and then combines it again to detect the phase difference between the left and right lights due to the Sagnac effect. It detects the rotational angular velocity of a moving body, and is expected to be used in many fields such as ships, aviation, and vehicles, and is currently being actively researched.

A fourth example of the configuration of a conventional phase modulation type optical fiber gyro is shown below.
As shown in the figure. In the configuration shown in Fig. 4, the output light from the light source (1) is introduced into a single mode optical fiber, distributed by optical directional couplers (2) and (4), and then connected to an optical fiber loop (6).
The output signal of the 0 photodetector (8), which propagates in opposite directions to each other and detects the interference light with a photodetector (8), is supplied to the signal processing section (9), where the rotational angular velocity is derived. In the phase modulator type optical fiber gyro, the phase modulator (7) is driven by a frequency signal from the signal generator tll, and phase modulation is applied to both lights propagating in opposite directions through the optical fiber loop (6). Then, the signal processing unit (9) extracts the phase modulation frequency component included in the interference light output and
In the method shown in Fig. 4, in order to remove the phase error of the interference light caused by the birefringence of the optical fiber, the A polarizer (3) is inserted to linearly polarize the light from the optical directional coupler (2) and output it.

In addition, an optical directional coupler (4) and an optical fiber loop (6)
A deborahizer (5) is provided between the
By equally distributing it along the axis, deterioration of sensitivity due to polarization distortion of light propagating in the original fiber is prevented and the school 7 actor is kept constant.

In this configuration, the optical power tropic couplers +2), +4) and the optical fiber loop (6) are both composed of 7-mode optical fibers, and the phase modulator (7) is composed of 7-mode optical fibers. A single mode fiber is disposed in the element 8: The deformation of the electric element is used to apply deformation and stress to the original fiber to perform optical phase modulation. However, in this case, when the light passes through the phase modulator, the polarization time of the light changes due to the above deformation and stress, causing an output error. ), but the conventional devolaziizer (5) consists of a combination of a lens and a non-polarizer, which requires a large number of parts and complicates the system.In addition, it is difficult to connect to an optical fiber. In the connection parts and lens systems, the performance of the original fiber gyro deteriorates due to loss of propagating light, 1 reflection, and axis deviation due to temperature changes, φ vibrations, and the like.

Furthermore, the force of two lights with orthogonal polarization planes is
When the polarization plane is converted to the other plane by mode conversion, a phase difference occurs due to the difference in propagation speed, which causes an output error.

(Problems to be Solved by the Invention) The present invention solves the disadvantages of the conventional devolaizer using a combination of a lens and a non-polarizer, namely loss of propagating light, reflection,
It is an object of the present invention to provide an optical fiber gyro with a simple configuration and a stabilized scale 7 actor, which suppresses output errors caused by optical interference due to mode conversion and performance deterioration due to axis misalignment.

[Structure of the invention]

(Means for Solving the Problems) The optical fiber gyro according to the present invention has a part of the path between the optical fiber loop and the distribution means for outputting light propagating in opposite directions through the optical fiber loop. It is constructed of constant polarization optical fibers of a predetermined length that are coupled so that their conservation axes make an angle of 45° to each other.

(Function) With the above configuration, the output light of the constant polarization optical fiber is easily devolized, and alignment is not required when coupling the constant polarization optical fiber to other fibers if only the 45° axis alignment is performed. There is little risk of performance deterioration due to zero loss reflection of propagating light, axis misalignment, etc.

Furthermore, since the lights whose polarization planes are perpendicular to each other from the constant polarization optical fiber are separated so that they do not overlap on the time axis, even if the polarization plane changes during mode conversion, this does not cause an output error.

(Embodiment) The following is a first embodiment of the optical fiber gyro according to the present invention.
This will be explained with reference to FIGS. 3 to 3.

FIG. 1 is a diagram illustrating the configuration of an embodiment of an optical fiber gyro according to the present invention.

The light source (1,) is a light source with a wide spectrum width, good directivity, and high coupling efficiency to the single-mode light 7 fibers.
For example, superluminescent diodes (ILDs)
) is used. The reason for using a light source with a wide spectral width is that the wider the spectral width of the propagating light, the more it is possible to reduce output noise due to interference between signal light and return light due to Rayleigh scattering within the optical fiber, and output drift due to the Kerr effect. It is. The light source (light from 11 is a photonic coupler (2)
It is divided into two parts, the - sword is coupled to the polarizer (3), and the other force is a non-reflective terminal. The light linearly polarized by the polarizer (3) is split into two parts again by the optical directional coupler (4) K, and each of the two parts propagates in opposite directions through an optical fiber loop (6) composed of a single mode optical fiber. At the same time, the phase modulator (force) receives periodic phase modulation corresponding to the inverse number of the signal cylinder from the signal generator (1 (I), interferes on the photodetector (8) surface, and generates a signal in the signal processing section (9). 0 converted to angular velocity signal
In the configuration shown in Fig. 1, the conventionally required debo-2 riser is omitted, and instead, the fixed polarization optical fibers αυ, Ua are connected to the ends (P
), the main axes are connected at an angle of 45 degrees to each other to provide a non-polarizing function.

We are trying to simplify the system. That is, in Figure 2,
In the part where the optical fiber is wound around the piezoelectric element (7), phase modulation is applied to the light propagating through the optical fiber, but since the fiber used is a constant polarization optical fiber, the mode conversion that occurs within the optical fiber is Compared to when a single mode optical fiber is used, one end 4 of the optical fiber is coupled with a single mode optical fiber from an optical directional coupler (4). Also, part B is also
Consisting of a constant polarization optical fiber α2, one end (Q) is coupled to the optical fiber loop (6), and the other end [P] is connected to the constant polarization optical fiber aυ, whose polarization (3) preservation axis (
Xs ), (y) are polarization preserving axes (xt ), (
yt) is connected at an angle rotated by 45°.
and the length 11) of the constant polarization light 7 eye section 4 are the same as the polarization dispersion (1) and the coherence time of the output light of the light source (1) (the time that light with impaired phase and wavelength lasts) (1). The length is greater than 1 〉21z or 1
．． 〉21. 0 As a result, regardless of the light state of the light propagating through part A, the light that passes through part B becomes unpolarized 0 Similarly, it propagates in the opposite direction from part B to part person. Figure 3 shows the polarization component att generated within the polarization constant optical fiber.
) and the coherence time (1) of the light source output.

(S3) shows the state of light propagating in a constant polarization optical fiber in time series, and the state (Sl) shows two lights (XI) and (Yl) with equal amplitude and orthogonal polarization planes.
Indicates the state in which are in phase. In this state (sl), for example, two lights (Xl) and (Yl
) indicates that the phases of these two lights match at the input end of the polarization-constant optical fiber. In addition, the two lights (XI) and (Yl)
The coherence time (1) of is state (81), (8z)
.

It is constant regardless of (S3). Since the propagation speed of light in the X plane and light in the Y plane are different in a constant polarization optical fiber,
A state in which both lights have propagated somewhat within the constant polarization light 7 eyeball (S
2), the analogy is that the element (X2) is more sensitive to time (
t'), that is, polarization dispersion (t') occurs. When light in state (S2) is output from a constant polarization optical fiber and propagated to a single mode optical fiber, for example,
In a single mode optical fiber, the polarization plane of light (X2) is converted from the X plane to the Y plane by mode conversion, and the light (X
2') occurs, and the length of the zero-constant polarization optical fiber where this light (X2') and light (Y2) interfere is in this state (S2).
If the two lights are not separated enough on the time axis and have only a length that causes an overlapping part, as in the case of the two lights, interference will occur between the two lights themselves as they travel in one direction, which will cause an output error.

However, the difficulty of polarization-controlled optical fiber is the state (S3
) In other words, if the length is such that the polarization dispersion (1) occurs in which the light (Xs) and the light (Yl) are separated enough so that they do not overlap on the time axis, then - if the plane of polarization of the sword light is converted. Since both light and the other light have a non-coherent relationship, the interference components are averaged to zero and no output error occurs. Each of the constant polarization light 7 qυ and the length 5) (A't) shown in Fig. 2 is set so that polarization dispersion (1) occurs as shown in this state (S3). O! A! In IIM, the coherence length L (=CXT, where C is the speed of light and T is the coherence time) of light is -λ2 depending on the light source.Semantically, L= (λ is the core wavelength of the spectrum of the light source, Δλ is the light source The beat length (the length of the fiber necessary for two lights whose polarization planes are perpendicular to each other to produce a phase difference of 2), which is one of the specifications of a polarization-controlled optical fiber, is determined by the half value of the spectrum of Since it is determined, the length of the polarization optical fiber αυ, a is G <, ls
) and (1!) are set so as to satisfy L<lh, ls>, respectively. At this time, if 1x=l*, depending on the polarization adjuster of the light after passing through the end (P), the polarization dispersion generated in the -force constant polarization optical fiber is caused by the polarization dispersion caused by the other constant polarization light 7 eye. Since there are cases where they cancel each other out, taking this point into consideration, the length (11), (lz
) is set to 11>21* or lx>zlt. As a result, the light propagating through the constant polarization optical fiber Uυ, (14 length C1t), (l snow) always has a polarization dispersion 11 greater than the coherence time of the light source output + Tl.
) occurs and becomes practically effective.

Regarding the fact that propagating light becomes depolarized when two polarization-preserving optical fibers are coupled so that their polarization preservation axes form an angle of 45°, see, for example, IEICE Technical Research Report 0Q.
E83-42 (Confucianism□Technical Report Vol. 83N0.90
PP, 73-78. Institute of Electronics and Communication Engineers 198
(Published July 26, 2013).

According to the above configuration, since the polarization constant optical fiber υ is used for the optical 7-eyeper constituting the phase modulator (7), the phase modulator (which suppresses the mode conversion that occurs within the optical fiber when the force is deformed, and It is possible to reduce output errors due to state fluctuations.In addition, by simply connecting polarization-maintaining optical fibers aυ, (lz) so that their polarization-maintaining axes form an angle of 45° to each other, the power can be distributed to two orthogonal axes. Since it is equally distributed and has the function of a devolaizer, it is possible to stabilize the scale 7 actor with a simpler configuration than the conventional one, which has a large number of parts and is complicated. Since unpolarized light can be obtained regardless of the polarization state K of the light introduced into the optical fibers υ and α4, there is no need for axis alignment at the coupling groove (QIRJ) between the fixed polarization optical fibers υ and α and other source fibers. , loss of propagating light due to incomplete coupling, 9 reflections, axis misalignment, etc. There is also less risk of performance deterioration.Furthermore, for each of the constant polarization optical fibers υ and (L4), the polarization dispersion is larger than the coherence time of the light source output. Since the length is set to 1, the output error caused by mode conversion is also reduced.

In addition, since the entire system is made of all fibers, the temperature and am
It is less susceptible to the effects of positional displacement due to etc., and environmental resistance is also improved.

Note that it is not necessary to wind part of the long A' portion of the polarization-controlled optical fiber αυ around the phase modulator (7), and after winding other optical fibers, the length lx of the polarization-controlled optical fiber is ) and (12) may be provided.

In addition, the fiber forming the optical fiber loop (6) may be not a single mode optical fiber but other optical fibers, and if a constant polarization optical fiber is used, the optical fiber loop (6) is fixed from the phase modulator (7). It can also be configured with a polarized fiber, and in this case, the polarization state of the propagating light becomes more stable, so the output error reduction effect becomes even greater.

Roughly speaking, the configuration in which the fixed polarization optical fiber αυ part 11) and the fixed polarization optical fiber part (1 length tlx) are coupled is made up of the two ends of the optical fiber loop (6) and the phase modulator ( 7) or between the optical directional coupler (4) and the other end of the optical fiber loop (6), the output light is likely to change the polarization state of the propagating light due to mode conversion etc. Since it propagates through the optical fiber loop (6) without being affected by the phase modulator (7) (11 elements), there is an optical path difference that accurately corresponds to the input angular velocity, and as a result, accurate angular velocity measurement can be expected. , phase modulator (the forces are not limited to those illustrated in FIG. 2).

〔Effect of the invention〕

As explained above, according to the original fiber gyro according to the present invention, it is possible to suppress loss-free reflection of propagating light, performance deterioration due to optical axis deviation, etc., and output error caused due to mode conversion, and it is possible to scale with a simple configuration. It is possible to stabilize the factor and improve environmental resistance, which has a great practical effect.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram illustrating an embodiment of an optical fiber gyro according to the present invention, FIG. 2 is a diagram illustrating a connection part of the polarization-controlled optical fiber shown in FIG. 1, and FIG. FIG. 4, a diagram illustrating the relationship between polarization dispersion and coherence time, is a schematic configuration diagram illustrating a conventional optical fiber gyro. m... light source, f2), (4)... optical directional coupler, (3)... polarizer, (6)... optical 7 eyeball loop, (7)... phase modulator, (8)・°°photodetector, α
O, Ua...constant polarization optical fiber. Agent Patent Attorney Nori Chika Ken Yudo Take Hana

Claims (1)

[Claims] a light output means for outputting polarized light; a distribution means for distributing the output light of the light output means; an optical fiber loop through which each output distributed by the distribution means is propagated in opposite directions; a modulation means disposed between the optical fiber loop and the distribution means for phase modulating the light; and a modulation means provided in a path from the distribution means to the optical fiber loop, the polarization plane preserving axes of each of which make an angle of 45° with respect to each other. What is claimed is: 1. An optical fiber gyro comprising: fixed polarization optical fibers coupled in the same manner; and detection means for detecting interference light of lights propagated in opposite directions through the optical fiber loop.