JPS5987315A - Optical fiber gyroscope - Google Patents

Abstract

PURPOSE:To simplify an optical system and to reduce the number of parts, by arranging one ends of the first and the second optical fibers on one line while interposing between them a half mirror, where a dielectric multilayered film is formed on one face of an optical substrate. CONSTITUTION:Optical fibers F1 and F2 have optical axes arranged on one line through a half mirror HF. An optical fiber F3 forms an optical fiber loop, and its both ends are arranged in parallel with optical fibers F1 and F2. Optical fibers have the property that the plane of polarization is preserved, and an incident laser light has the plane of polarization preserved and is emitted. A multilayered dielectric film HL is formed on one face of an optical substrate SUB to constitute the half mirror HF. By this invention, a phase modulator, depolarizer, etc. are unnecessary becasue the dielectric multilayered film is used to shift the phase, and thus, the constitution is simplified, and the number of parts is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to a gyronoscope used for determining the attitude of an aircraft, space vehicle, or the like.

A fiber optic gyroscope has been proposed that utilizes the Sagnac effect.

That is, the laser light from the laser diode LD is incident on the polarizing plate POL via the beam splitter BS, where only light having a specific polarization plane is incident, and is incident on the optical fiber directional coupler DCO.

The optical fiber directional coupler DCO divides the incident laser beam into 3 dB units and outputs the divided beams to points a and b.

The laser beam emitted to the point a is modulated by the deborerizer, and the light emitted to the point is modulated by the optical modulator PM.
4 and enters the optical fiber loop FL.

The laser beams traveling in opposite directions through the optical fiber loop FL enter the optical fiber directional coupler DLO again, are combined there, and enter the polarizing plate POL.

Here, only the laser beam with a specific polarization plane is emitted again, enters the beam splitter BS, and is reflected there and enters the photodetector DET.

The electrical signal from the photodetector DKT is sent to the lock-in amplifier LA.
Here, the gate opens and amplification is performed only when the light from the optical fiber loop FL returns. This improves S/'N.

Here, the laser light traveling clockwise and the laser light traveling counterclockwise through the optical fiber loop FL undergo a phase shift due to the Sagnac effect, and are represented by (ωχ10) and photo (ωZZθ).

These two laser beams are combined, and the combined laser beam has the following formula: (ωl + θ) 10 parts (ω × 〇) = 2 min ω difference・μsθ.

Therefore, by detecting the value of force θ, the rotational angular velocity can be detected.

However, when the value of θ is used, the sign is the same around "0" regardless of the direction of rotation, and there is a drawback that the direction of rotation cannot be determined.

Therefore, the phase of the light traveling in the counterclockwise direction is shifted by π by the optical modulator PM.

As a result, the light traveling in the counterclockwise direction becomes phobic (ω difference − θ + π
), and the combined light is α4 (ωzu 10) + α6 (ωl - θ1π) = 2α6ω
Su fist becomes sinθ.

Since the sign of the value indicated by θ is reversed around "0", the direction of rotation can be detected.

Furthermore, since the coupling degree of the optical fiber directional coupler largely depends on the plane of polarization, it is necessary to use a polarizing plate POL to obtain the best coupling degree.

Furthermore, the plane of polarization of the light returning from the optical fiber loop FL is rotated by the earth's magnetism, etc., and there is a risk that the optical fiber directional coupler may not be able to obtain the best coupling degree. I have to.

As described above, the conventional optical fiber gyrocator requires a polarizing plate, a depolarizer, and an optical modulator, and has the disadvantage of having a large number of parts.

OBJECT AND CONSTRUCTION OF THE INVENTION The present invention aims to eliminate such drawbacks,
For this purpose, a half mirror with a dielectric multilayer film formed on one side of an optical substrate is sandwiched, one end of the first optical fiber and the second optical fiber are arranged in a straight line, and an optical fiber loop is further inserted. Both ends of the formed single mode fiber having polarization preserving properties are placed between the first and second half mirrors.
arranged so as to be parallel to a second optical fiber, one end of the first and second fibers and both ends of the single mode fiber are inclined surfaces with respect to the optical axis of these optical fibers; A single mode laser beam with constant polarization is input from the other end of the first optical fiber, the laser beam emitted from one end of the first optical fiber is split into two by the half mirror, and the two ends of the single mode fiber are split into two. The light enters the single mode fiber, propagates in opposite directions to each other, and the light emitted from both ends is combined by the half mirror, enters one end of the second optical fiber, and the light of the second optical fiber. This is achieved by an optical fiber gyrocator characterized in that the laser beam emitted from the other end is detected by a photodetector.

Examples of the invention Hereinafter, the present invention will be explained based on examples.

FIG. 2 is a diagram showing an embodiment of the present invention, in which Fl,
F2. F3 is a single mode optical fiber, HF' is a half mirror, and the same members as in FIG. 1 are given the same symbols. Here, optical fiber F1. F2 is half mirror H
The optical axes are arranged in a straight line through F.

The optical fiber F3 forms an optical fiber loop, and both ends thereof are arranged parallel to the optical fibers F, , F2.

Furthermore, the optical fiber has a property of preserving the plane of polarization, and the incident laser beam is emitted with the plane of polarization preserved.

Optical fibers Fl, F2. End face of FB F+s, F2
1. F31. As shown in detail in FIG. 3, F32 is an inclined surface having a predetermined angle.

Further, as shown in detail in FIG. 4, the half mirror HF is constructed by forming multilayer dielectric films H and L on one side of an optical substrate SUB.

Also, the end faces F12 . of the optical fibers Fl and F2. F22 is sloped so as to form a Brewster's angle with respect to the laser diode LD and the photodetector DIT.

In the present invention, the optical directional coupler is configured with the configuration shown in FIG. 3, and the half mirror shown in FIG. 4 gives a phase difference of π to the laser light traveling in both directions through the optical fiber loop. That's what I do.

Next, the tilt angle will be explained in detail with reference to FIG. 3. In the figure, the optical fiber end face F++, the optical axis ox of Fs2
1. Let the inclination with respect to ox2 be θp, and the end face F21. F3
The inclination with respect to the optical axes OXI and OX2 K of 1 is -θp,
θO is the input/output angle of the light with respect to the optical axis, L is the length from the light input/output point to the half mirror, and the optical fiber Fl
, If the distance between the optical axis of F3 and the mechanical axis MX (half mirror T (passing through the reflection point of F) is h, then the end face F2
Incident angle with respect to + and human exit angle θ2 with respect to end face F32
and optical fiber F2. The distance x2 between the optical axis of F3 and the mechanical axis Mx (half mirror T (passing through the reflection point of light of F)) is expressed by the following equation using a ray matrix.

minus) = (total) (later) (points) Therefore X2: h + 2L”θ0 θ2-00 becomes.

Here, in order to set x2=-h, 11=L·θO.

Therefore, by arranging optical fibers whose end faces are polished according to the above formula, the exit angles are equalized and optimum coupling can be obtained.

Next, the reason why the phase difference π occurs will be explained with reference to FIG.

The multilayer film is made of a material with a high refractive index (for example, TiOz) layer H
and layers of a material with a small refractive index (for example, 5 iOz) are laminated alternately, and the thickness of each layer is approximately 1/4 of the wavelength of the laser beam used.

The outermost layer is a material layer H having a high refractive index.

The ray matrix of this half mirror is calculated by the following equation, where na is the refractive index of the layer H and nb is the refractive index of the layer.

Here, φ2λ・2πδ/λ0, λ6 is the center wavelength of the half mirror at the time of design (λo/4=nadl or nbdb)
.

δ is the degree of deviation of the used wavelength from the designed wavelength, which is 1.2
Takes a value between 5 and 0.8.

Here, it becomes Mll2M22”M.

From now on, the electric field Eo of the laser light inside the half mirror,
The magnetic field H, is as follows.

Further, the reflectance IR of a film is generally expressed by the following formula.

Therefore, if the light enters the half mirror from the direction of arrow A,
'The light reflected in the force direction and the light incident from the direction of arrow B and the light reflected in the direction of arrow B
The amplitude and phase of the light reflected in the ' direction are K as follows.

From the above formula, 01. θ2 is becomes.

In each equation, the second term is the same, the first term only has a different sign, and the absolute values are the same.

By injecting light almost perpendicularly into the multilayer film,
It can be seen that the amplitudes are the same and the phase is shifted by π.

On the other hand, the phase of the light transmitted through the half mirror HF is not affected in any way.

Applying this to Figure 2, half mirror H
The light that is reflected at F and travels counterclockwise through the optical fiber F3, and the light that passes through the half mirror corresponds to the light that travels clockwise through the optical fiber F3.

Therefore, at the time of entering the optical fiber F2, the phase is λ/
It will be shifted by 4+θ.

FIG. 5 shows another embodiment of the invention.

The figure shows a configuration in which ball lenses L@, L7 are arranged in addition to the configuration shown in FIG. 2, and in this case, the end faces Fu, F21. F3
The slope of 1°F32 is opposite to that in FIG.

Regarding the angle of inclination in this case, please refer to the magazine rOptical.
Sosje'ty of America J Vot
Paper written on pages 3484-3488 of I9, A19
physical directional couple
Since it is explained in detail in r J, it will be omitted here.

Effects of the Invention As described above, according to the present invention, the phase shift is performed using a dielectric multilayer film, so there is no need for a conventional phase modulator, and the optical directional coupler does not have polarization plane dependence. ,
There is no need for a debolarizer or the like, and as a result, the optical system becomes extremely simple.

[Brief explanation of drawings]

Figure 1 is a diagram showing a conventional fiber optic gyroscope.
FIG. 2 is a diagram showing an embodiment of the present invention, and FIG. 3 is a diagram showing a light directional coupling section used in the present invention. 11- FIG. 4 is a diagram showing a half mirror used in the present invention. FIG. 5 is a diagram showing another embodiment of the present invention. In the figure, LD is a laser diode, HF is a half mirror,
Fl, F2. F3 is an optical fiber and DBT is a photodetector. 12-

Claims (1)

[Scope of Claims] One end of a first optical fiber and a second optical fiber are arranged in a straight line with a nof mirror formed with a dielectric multilayer film formed on one side of an optical substrate, and an optical fiber Both ends of a single mode fiber having polarization preserving property formed into a loop are sandwiched between the half mirror and the first fiber. The second optical fiber is arranged parallel to the first optical fiber. One end of the second fiber and both ends of the single-mode 7-eyes are inclined surfaces with respect to the optical axis of these optical fibers, and a single-mode laser beam with constant polarization is emitted from the other end of the first optical fiber. enters the first optical fiber, and the laser beam emitted from one end of the first optical fiber is split into two by the half mirror, enters both ends of the single mode fiber, and propagates through the single mode fiber in opposite directions. , the laser light emitted from both ends is combined by the barforer, and enters one end of the second optical fiber, and the laser light emitted from the other end of the second optical fiber is detected by a photodetector. An optical fiber gyroscope characterized by: