JPH03295410A - Interferometer type optical fiber gyro - Google Patents

Abstract

PURPOSE:To reduce the quantity of variation in modulation degree due to temperature variation by vibrating the piezoelectric material of a phase modulator at a frequency other than the resonance frequency and antiresonance frequency of the piezoelectric material itself, and thus applying an optical bias. CONSTITUTION:The piezoelectric material 1 is applied with a voltage from the phase modulator 3 to vibrate radially and thus light which is transmitted in an optical fiber is shifted in phase, which is utilized to apply the optical bias. In this case, the frequency which is applied is set to neither the resonance frequency nor antiresonance frequency of the piezoelectric material 1. For example, when lead zirconate titanate is used for the piezoelectric material 1, the resonance frequency 27kHz and the antiresonance frequency is 54kHz, so when 7.8kHz is applied and the quantity of modulation corresponding to -20 - 80 deg.C temperature variation is checked, the modulation rate can be suppressed to variation which is nearly a half as large as that when the material is driven at the resonance frequency and antiresonance frequency.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an interferometer type optical fiber gyro.

(Prior Art) The basic form of an interferometer type optical fiber gyro is shown in FIG. This optical fiber gyro has low sensitivity as shown in Figure 3, so conventionally a bias circuit A was added as shown in Figure 4 to provide an optical bias and improve the sensitivity as shown in Figure 5. There is.

Conventionally, a phase modulator has been used to provide this optical bias. As shown in FIG. 6, this phase modulator has an optical fiber 2 wound around the outer periphery of a cylindrical piezoelectric material 1.
When a voltage is applied to the piezoelectric material 1 from the power source 3, the piezoelectric material 1 vibrates in the radial direction, and this vibration causes the optical fiber 2 to expand and contract in the longitudinal direction, changing the fiber length. Optical bias is performed by utilizing the change in the phase of transmitted light. Incidentally, piezoelectric ceramics (such as lead zirconate titanate) and piezoelectric polymers (PVDF) are used as the piezoelectric material 1.

In the interferometer type optical fiber gyro, an optical bias is applied by setting the amount of change in this phase to a predetermined value 1 Bessel function 1&J (η=1.84)).

Piezoelectric materials have a large degree of modulation (phase change N) at the resonant frequency or anti-resonant frequency, so conventionally piezoelectric materials have been used at the resonant frequency or anti-resonant frequency where a large degree of modulation can be obtained.

(Problem to be solved by the invention) However, when a piezoelectric material is vibrated at a resonant frequency or an anti-resonant frequency, a large degree of modulation can be obtained, but the degree of modulation (amount of phase change) varies with temperature changes. There was a problem.

(Object of the Invention) An object of the present invention is to provide an interferometer-type optical fiber gyro in which the degree of modulation varies little due to temperature changes.

(Means for Solving the Problem) When synchronous detection is performed at the frequency of the voltage applied to the piezoelectric material, the output of the interferometer type optical fiber gyro is expressed by the following formula 6 Gyro output = IJ, (η) SINΔΩ...■Where, I: Received light power, J, (η) - Next Bessel function ΔΩ: In the phase difference interferometer type optical fiber gyro, the angular velocity is determined by detecting this phase difference. In the interferometer type optical fiber gyro, the first-order Bessel function j1 (η)
is set to be maximum (n=1.84), and η is expressed by the following formula.

n=2czsIN (nxfL/C) - ■where, a: modulation degree of piezoelectric material (amount of phase change) f: applied frequency of piezoelectric material n: refractive index of fiber 1, ,: fiber length C・light velocity, therefore, By suppressing fluctuations in the degree of modulation of the piezoelectric material, it is possible to stabilize the gyro output.

The interferometer type optical fiber gyro of the present invention was developed based on the above-mentioned principle. That is, in the interferometer type optical fiber gyro of the present invention, as shown in FIG. In an interferometer type optical fiber gyro in which an optical bias is applied by a phase modulator 3 that changes the phase of light transmitted through the fiber 2 by vibration, the phase phase modulator 3 described in iii.
The electric material 1 is driven at a frequency other than the resonance frequency and anti-resonance frequency of the piezoelectric material 1 itself to apply an optical bias.

The piezoelectric material 1 in the interferometer type optical fiber gyro of the present invention is piezoelectric ceramics, piezoelectric polymers, etc., and the piezoelectric ceramics are barium titanate, lead zirconate titanate, lead cobalt niobium, lead bismuth niobate. .

The piezoelectric polymer is polyvinylidene fluoride (PVll) F
), vinylidene fluoride/tetrafluoroethylene copolymer (P
(VDF/TFE)), and vinylidene fluoride/trifluoroethylene (P(VDF/TrFE)).

(Function) In the interferometer type optical fiber gyro of the present invention, the phase modulator 3
A resonant layer l11 in which the piezoelectric material l itself has a piezoelectric material l of
Since we applied optical bias by vibrating at a frequency other than the 7-frequency and anti-resonant frequencies, we cannot obtain as large a modulation degree as when vibrating at the resonant or anti-resonant frequencies, but as shown in Figure 7. As shown by the circle, the modulation degree (phase change amount) fluctuates little with respect to temperature changes.

(Example) An example of an interferometer type optical fiber gyro of the present invention will be described below.

The piezoelectric material l of the phase modulator 3 in FIG. 1 is made of lead zirconate titanate, and is a cylindrical body with an outer diameter of 35 mm and a thickness of 1.5 mm. The optical fiber 2 was wound around this by about 2 m, and the applied voltage was adjusted so that a predetermined amount of phase change was achieved.

This piezoelectric material I has a resonant frequency of 27 kHz and an anti-resonant frequency of 54 kHz.

Next, using an evaluation system as shown in Figure 7,
The amount of variation in modulation degree with respect to temperature change.

Resonant frequency, anti-resonant frequency and frequencies other than the above (f=
7.8kHz). By the way, in Fig. 7, 11 is a light source, 12 is a doubler, 3 is a phase modulator, 4 is a driving power source, 15 is a doubler, 16 is a light receiver, and 17 is an FFT.
It is an analyzer.

The measurement results obtained by the measurement system are shown in FIG. 8. FIG. 8 shows a change in the degree of modulation in the temperature range in which an arbitrary temperature is maintained for a predetermined period of time. As is clear from the figure, there is a large variation in the modulation degree with respect to temperature changes, as shown by the X mark in the case of the resonant frequency (27 KH) and the △ mark in the case of the 1 anti-resonant frequency (54 KHz). f=7
．． The variation in modulation depth at 8 kHz is about half compared to the case of driving at the resonant frequency and the anti-resonant frequency.

Furthermore, FIG. 9 shows the results of investigating the relationship between the modulation degree (amount of phase change) and the applied frequency. As shown in the figure, the resonance frequency (27KHz) and anti-resonance frequency (54KHz)
), the modulation degree changes greatly due to a slight change in the applied frequency, whereas at frequencies other than the above (f = 7.8
kHz), it can be seen that the variation in the modulation degree is very small.

(Effects of the Invention) With the interferometer type optical fiber gyro of the present invention, it is possible to reduce fluctuations (scale factor) in the output of the gyro due to temperature fluctuations. Furthermore, variations in the frequency applied to the piezoelectric material have little effect on the output of the gyro.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing one embodiment of the interferometer type optical fiber gyro of the present invention, Fig. 2 is a diagram of the basic principle of the interferometer type optical fiber gyro, and Fig. 3 is the sensitivity of the optical fiber gyro shown in Fig. 2. Fig. 4 is an explanatory diagram of an interferometer type optical fiber gyro equipped with a bias circuit, Fig. 5 is an explanatory diagram of the sensitivity of the optical fiber gyro shown in Fig. 4, and Fig. 6 is an illustration of the phase modulation of the optical fiber gyro. An explanatory diagram of the instrument, Figure 7 is an explanatory diagram of the measurement system,
FIG. 8 is an explanatory diagram showing the relationship between temperature and the modulation degree, and FIG. 9 is an explanatory diagram showing the relationship between the frequency applied to the piezoelectric material and the modulation degree. 1 is a piezoelectric material 2 is an optical fiber 3 is a phase modulator I (Fig.

Claims (1)

[Claims] When an optical fiber 2 is wound around a piezoelectric material 1 and a voltage is applied to the piezoelectric material 1 to vibrate the piezoelectric material 1 in the radial direction, the phase of the light transmitted through the optical fiber 2 changes due to the vibration. In the interferometer-type optical fiber gyro in which an optical bias is applied by the phase modulator 3, the piezoelectric material 1 of the phase modulator 3 is operated at a frequency other than the resonance frequency and anti-resonance frequency of the piezoelectric material 1 itself. An interferometer-type optical fiber gyro characterized by applying optical bias through vibration.