JPS6326326B2 - - Google Patents

Description

[Detailed Description of the Invention] Technical Field of the Invention The present invention relates to a laser beam using the Sagnatsk effect.
The present invention relates to a gyroscope, and particularly to an optical fiber gyroscope system that uses a rotation prism to perform polarization separation and combination of light.

Prior Art and Problems Optical fiber gyroscope systems are already known, which detect the rotational angular velocity of an object by utilizing the sagnac effect produced in an optical fiber.

FIG. 1 shows the basic form of an optical fiber gyroscope system. In the same figure, laser 1
The output light passes through beam splitter 2 and becomes clockwise light 3.
and counterclockwise light 4 are generated, both lights propagate through an optical fiber loop 5, are combined in a beam splitter 6, and detected by a light receiver 7. When the optical system shown in Fig. 1 is rotating at an angular velocity Ω in the direction of the arrow, a phase difference of △θ=2πRL/λc·Ω occurs between the two output lights. Here, R is the radius of the optical fiber loop, L is the fiber length, λ is the wavelength, and c is the speed of light. This is known as the Sagnac effect, and it allows us to know the rotational angular velocity that the optical system has with respect to inertial space.

Various methods have been researched and proposed in the past as methods for determining the rotational angular velocity by measuring the phase difference between the two output lights generated in such an optical fiber gyroscope system. However, all of the conventional methods have had drawbacks or problems in some sense. In other words, in the basic form shown in Figure 1, ring-shaped interference fringes are obtained by adjusting the position of the fiber excitation lens, and the light is received at a position where the brightness of the fringe is the average of the maximum and minimum values, for example. By arranging the vessels, sin△
The defocus method that obtains an output proportional to θ, the use of a wave plate to propagate left and right-handed light in an optical fiber with orthogonal polarization, and the use of the anisotropy of an electro-optic modulator to generate a π/2 In the orthogonal polarization method, which optimizes sensitivity by obtaining an output proportional to sin△θ by applying a phase difference bias, if there is an optical path difference between the left and right optical paths, the temperature fluctuation and the laser diode spectrum will be affected. The disadvantage is that fluctuations cause output fluctuations.

In addition, when a frequency difference △ω is given between the lights in both directions in the optical fiber using an acousto-optic modulator, the phase difference △θ between the two lights on the receiver surface is expressed as follows: The equivalent refractive index is given by △θ=nL/c・△ω and is proportional to the frequency difference. Therefore, in the laser frequency variation method, which determines the phase difference by measuring the frequency, it is necessary to If there is a frequency difference between the circulating lights, there is a drawback that output fluctuations occur due to temperature fluctuations in the optical fiber.

Furthermore, in these various methods and other conventional methods, the output varies due to variations in the state of polarization in the optical fiber. In other words, in a general single mode optical fiber, even if it is excited with a linearly polarized wave, the output will be an elliptically polarized wave, and if the two lights are made to interfere in this state, the output will fluctuate due to changes in the polarization state in the fiber due to temperature etc. There's a problem. It is also known that variations in the state of polarization in optical fibers occur due to the influence of geomagnetism, and this also causes output variations.

In all methods, if the light source has good coherence, the return light from the optical fiber and other parts will interfere with the signal light, thereby causing output fluctuations.

As described above, all conventional optical fiber gyroscope systems have some kind of drawback or problem, and are not necessarily ideal.

Purpose of the Invention The present invention is intended to solve the problems of the prior art, and its purpose is to reduce the rotational angular velocity by eliminating various causes of noise that could not be avoided in the conventional system as described above. An object of the present invention is to provide an optical fiber gyroscope system that can improve the detection limit of the sensor and achieve high reliability, high stability, and low power consumption.

Embodiment of the Invention FIG. 2 is a diagram showing the configuration of an embodiment of the optical fiber gyroscope system of the present invention. In the figure, 11 is a laser diode which is a light source, and 12 is a laser diode which is a light source.
is an output monitor terminal, 13 is a lens, 14 is a Glan-Thompson prism that extracts only linearly polarized light from the output light of the laser diode 11, 15 is a lens, 16 is a λ/4 phase plate, 17 is an input/output optical fiber, 18 is a lens; 19 is a rotation prism that separates circularly polarized light into extraordinary light and ordinary light; and reversely combines the circularly polarized light; 20 is a lens; 21 is a constant polarization optical fiber loop; 22 and 23 are both ends of the fiber loop 21. , 24 and 25 are optical directional couplers, 26 is an output monitor terminal, 27 is a λ/4 phase plate, 28 is a photodetector, and 29 is a phase difference output terminal.

In FIG. 2, the output light of the laser diode 11 is input to the Glan-Thompson prism 14 through the lens 13, and the linearly polarized light component is extracted. This is because, although the light generated by the laser diode 11 is generally linearly polarized light, it inevitably contains some other polarized light components. So Grant Thompson Prism 1
4 to remove unnecessary polarized light components, for example.
It can attenuate about 60dB. Note that the output level of the laser diode 11 at this time can be monitored by the output of the monitor terminal 12.

The output light from the Glan-Thompson prism 14 is applied to a λ/4 phase plate 16 via a lens 15, where it is converted into circularly polarized light. Since completely linearly polarized light is applied to the phase plate 16 as described above, completely circularly polarized light is obtained as its output light. The output of the phase plate 16 is applied to a lens 18 via an optical fiber 17, and then input to a rotation prism 19 via the lens 18. A portion of the light on the optical fiber 17 is taken out to a terminal 26 through an optical directional coupler 24, so that the input light level to the rotation prism 19 can be monitored. The rotation prism 19 separates the input circularly polarized light into extraordinary light and ordinary light, and the separated extraordinary light and ordinary light pass through the lens 20 and enter the end portions 22 and 23, respectively, and enter the fixed polarization optical fiber loop 21, respectively. Generates a rotating light and a counterclockwise light. The constant polarization optical fiber loop 21 is formed by forming a constant polarization optical fiber into a loop shape that transmits only one type of polarized light, and its both ends 22 and 23 are held such that the planes of polarization are perpendicular to each other at the respective end faces. , are capable of selectively inputting and outputting extraordinary light and ordinary light, respectively.

The clockwise light and counterclockwise light in the fiber loop 21 are transmitted from the ends 23 and 22 to the lens 20, respectively.
The light then enters the Rotion prism 19, where it is multiplexed again to generate circularly polarized light. The output of the rotation prism 19 passes through the lens 18, returns to the optical fiber 17, is taken out via the optical directional coupler 25, and is applied to the λ/4 phase plate 27, so that only one polarized light has a π/2 phase. It shifts. The output of the λ/4 phase plate 27 is applied to the photodetector 28 and converted into an electrical output, and the output is sent to the terminal 2.
taken out from 9.

When the optical system shown in FIG. 2 is stationary with respect to inertial space, no phase difference occurs between the two-way beams in the fiber loop 21. Therefore, the phase difference between the two polarized lights in the output of the λ/4 phase plate 27 due to the combined output light of the Rotion prism 19 is π/2, and the combined output is 0. The electrical output produced at is 0.

FIG. 2 shows that when the optical system has a rotational angular velocity with respect to inertial space, a phase difference occurs between the two directions of light as explained in FIG. 1, and the λ/4 phase plate 2
The phase difference between the two polarized lights at the output of 7 is not π/2, so the photodetector 28 generates an electrical output proportional to cos θ for the deviation angle θ of the phase difference from π/2. do. The λ/4 phase plate 27 thus shifts the phase of only one of the polarized lights by π/2 to obtain an output that changes almost linearly with respect to the phase difference between the two polarized lights in the fiber loop 21. It is used for.

FIG. 3 shows the input/output optical fiber 17, lens 18, and rotation prism 1 in the embodiment shown in FIG.
9, a lens 20, and a polarization-constant optical fiber loop 21. In this figure, the same parts as in FIG. 2 are represented by the same numbers, 31 and 32 are both end surfaces of the rotation prism 19, and 33 is its mechanical axis.

In FIG. 3, the rotion prism 19 has end faces 31 and 32 having the same inclination angle α ₁ . The input optical fiber 17 has an optical axis parallel to the mechanical axis 33 of the rotation prism 19 and is disposed at a distance h from the mechanical axis 33, and has an inclination angle θp at the output end face. The ball lens 18 is located between the optical fiber 17 and the rotation prism 19 and has a center O at a distance 1 ₁ from the upper end surface 31 of the mechanical axis 33 . Further, the output optical fibers 22 and 23 are arranged parallel to an axis parallel to the mechanical axis passing through the equivalent optical branch point M of the rotary prism 19 at a distance h from the axis, and have inclination angles θp and -θp at their incident end faces, respectively. optical fiber 22,
23 constitutes both ends of the constant polarization optical fiber loop 21, and the planes of polarization thereof are arranged to be orthogonal as described above. The ball lens 20 is located between the rowsion prism 19 and both optical fibers 22 and 23, on an axis parallel to the mechanical axis passing through the equivalent light branch point of the rowsion prism 19, and at a distance of 1 from the equivalent light branch point.
It has a center O' at ₁ . Now, the inclination angle α ₁ of the rotation prism 19, the output angle θ ₀ of the input optical fiber 17,
Assuming that the incident angle of the output optical fibers 22 and 23 is θr, and the focal length of both lenses is F, these are determined by the following relationship.

α ₁ = (+n _e /n _e +n _p -2)・δ θo=θr = sin ^-1 (n _c /n _a・sinθp)−θp θo=θr=(1 ₁ −F)h/F ^2where n _e is the refractive index of the Roschill prism for extraordinary light n _p is the refractive index of the Roschill prism for ordinary light δ is the separation angle of the Roschill prism for extraordinary light and ordinary light n _c is the refractive index of the input/output optical fiber core n _a is the air When this is done, the light emitted from the optical fiber 17 with an output angle θo is separated into extraordinary light and ordinary light, and the light is emitted from the optical fiber 2 with an incident angle θr.
2 and 23, respectively, and are transmitted through the fiber loop 21 as clockwise and counterclockwise lights, respectively, and exit from the optical fibers 23 and 22 with an output angle θr, and are combined again and sent to the optical fiber 17. The incident angle is θr and returns to the original direction, but the incident and exit angles at this time are all equal from the above relationship,
The symmetry of input and output is completely maintained. The optical polarization separation/synthesis system shown in FIG. 3 has already been filed by the same applicant.

The fiber optic gyroscope system of the present invention includes:
By using the optical polarization separation/synthesis system shown in FIG. 3, the noise factors that have been problematic in conventional fiber optic gyroscope systems are eliminated. That is, as is clear from FIG. 3, there is no optical path difference between the clockwise light and the counterclockwise light in the fiber loop 21 when viewed from the input optical fiber 17, and therefore the output fluctuation is based on the optical path difference between the two directions. does not occur.

Further, the clockwise light and the counterclockwise light in the fiber loop 21 are composed of extraordinary light and ordinary light separated from the same input light, and have the same frequency.
Therefore, no output fluctuation occurs due to the frequency difference between the two directions of light.

Also, the optical fibers 17, 22, 2 in FIG.
The input/output end faces of No. 3 and the input/output end faces of the lowsion prism 19 are not perpendicular to the optical path, so the return loss on these surfaces is kept sufficiently small, and is based on the interference between the returned light and the input light. No output fluctuation occurs.

Furthermore, a constant polarization optical fiber is used for the fiber loop 21 in FIG. No output fluctuation occurs due to polarization state fluctuation.

In the optical fiber gyroscope system of the present invention, all noise factors based on these causes are removed, and as a result, the detection limit of rotational angular velocity can be significantly improved compared to conventional systems.

Furthermore, in the optical polarization separation/synthesis system shown in FIG. The optical fiber can be easily held by fixing it in a V-shaped groove etched on a silicon substrate by a well-known method.
There is no fear of positional changes after fixation, and the stability and reliability of the device configuration and performance can be significantly increased.

In addition, in the case of the conventional laser frequency variation method, it is necessary to perform optical modulation to give a frequency difference between the left and right beams, which increases power consumption, but in the system of the present invention, this is not necessary.
Power consumption can be kept low.

Effects of the Invention As explained above, according to the optical fiber gyro system of the present invention, it is possible to improve the detection limit of rotational angular velocity, and to achieve high stability and reliability of the device and performance. Furthermore, it is extremely advantageous due to its low power consumption.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the basic configuration of an optical fiber wiring system, FIG. 2 is a diagram showing the configuration of an embodiment of the optical fiber wiring system of the present invention, and FIG. 3 is a diagram showing the configuration of an embodiment of the optical fiber wiring system of the present invention. - It is a diagram showing an example of the configuration of an optical polarization separation/synthesis system in a gyro system. 1...Laser, 2...Beam splitter, 3...
...Clockwise light, 4...Counterclockwise light, 5...Optical fiber loop, 6...Beam splitter, 7...Photo receiver, 11...Laser diode, 12...Output monitor terminal, 13...Lens, 14...Grand Thompson prism, 15...lens, 16...λ/
4 phase plate, 17... optical fiber, 18... lens, 19... rotation prism, 20... lens, 21... constant polarization optical fiber loop, 22,2
3...Both ends of the fiber loop 21, 24, 25
...Optical directional coupler, 26...Output monitor terminal,
27...λ/4 phase plate, 28... Photodetector, 29
...Phase difference output terminal.

Claims (1)

[Claims] 1. A light source device that generates circularly polarized light, an optical fiber coupled to the output side of the light source device and having an inclination angle α ₁ at the output end, and a distance h from the optical axis of the optical fiber and A rostion prism having parallel mechanical axes and the same inclination angle α ₁ on the entrance and exit end faces, and a rostion prism located between the rostion prism and the optical fiber and at a distance of 1 ₁ from the entrance end face of the rostion prism on the mechanical axis. It consists of a first lens having a focal length F at the center and a constant polarization optical fiber formed in a loop shape, each end of which is at a distance from an axis parallel to the mechanical axis passing through the equivalent optical branch point of the Rotion prism. h, and both end faces have an inclination angle θp-
a constant polarization optical fiber loop having θp and arranged so that its polarization planes are orthogonal to each other at both end faces, and an equivalent light of the rotation prism located between the constant polarization optical fiber loop and the rotation prism. a second lens of focal length F, centered at a distance 1 ₁ from the axially equivalent light branch point parallel to the mechanical axis passing through the branch point, and coupled to the optical fiber to transmit the transmitted light back from the Rotion prism; It comprises an optical directional coupler to take out, and a photodetector to detect the intensity of the output light of the optical directional coupler, and the inclination angle α ₁ of the rotation prism, the input/output angle θo of the optical fiber, and the constant polarization light. Between the entrance and exit angles θr at both ends of the fiber loop and the focal lengths F of both lenses, α ₁ = (+n _e /n _e +n _p −2)・δ θo=θr = sin ⁻¹ (n _c /n _a・sinθp) −θp θo=θr=(1 ₁ −F) h/F ² where n _e is the refractive index of the Rochon prism for extraordinary light n _p is the refractive index of the Rochion prism for ordinary light δ is the extraordinary light in the Rochion prism and the separation angle n _c with respect to ordinary light has a relationship with the refractive index n _a of the input/output optical fiber core portion and the refractive index of air. A patent characterized in that it consists of a Glan-Thompson prism that extracts only a single polarized light from the light generated by a semiconductor laser, and a quarter-wavelength phase plate that converts the output light of the Glan-Thompson prism into circularly polarized light. An optical fiber gyroscope system according to claim 1. 3. The photodetector includes a 1/4 wavelength phase plate in the optical path, and produces an output proportional to the cosine of the deviation angle from π/2 of the phase difference between the extraordinary light and the ordinary light in the input light. An optical fiber gyroscope system according to claim 1 or 2.