JPS60140115A - Optical fiber rate sensor - Google Patents

Abstract

PURPOSE:To reduce noise output by suppressing drift, by constituting a light path, which reaches a light detector from a non-polarized light source having a wide spectrum band through an optical directional coupler and an optical fiber, by single mode fibers. CONSTITUTION:Light from a light source 11 having a wide spectrum band and outputting non-polarized light is supplied to an optical directional coupler 13 through a single mode fiber 12. This light further transmits a single mode fiber 16 to be supplied to an optical directional coupler 19 and propagates the optical fiber loop 23 wound around a drum in a clockwise direction and a counterclockwise direction through single mode fibers 20, 21. The lights of the loop 23 are respectively modulated by a phase modulator 24. Lights, which propagated the loop 23 in directions opposite to each other, are again guided to the optical directional coupler 13 and supplied to a light detector 29 through a fiber 28. A component having the same frequency as phase modulation frequency is synchronously detected from outputs of the light detector 29 by using a lock-in amplifier.

Description

[Detailed Description of the Invention] [Amazing technical field] This article describes an optical fiber that detects interference waves of light propagating in opposite directions through an optical fiber to obtain information on the rotational angular velocity of a rotating body. Regarding rate sensor.

``'vgusi'' Self 1/+-14 upper level; Me II, λ7 El
l-7-n-110ank) Among the control devices used for moving objects such as various aircraft and ships, sensors that detect the rotational angular velocity of rotating bodies are used to detect the current position of aircraft and ships. , and is one of the most important factors in controlling posture. Conventionally, as this type of sensor, there is a mechanical type sensor that maintains a rotation axis of a gyro rotor rotating at high speed in a constant direction in an inertial space. Mechanical sensors using this gyro rotor have extremely short service life because they use high-speed mechanical rotation, and have the disadvantage of requiring high-precision machining technology.
It is very expensive.

Furthermore, one type of gyro that is not based on a mechanical structure but has an optical structure is a ring laser gyro that uses the Sagnac effect. This is composed of a ring resonator in which the optical path is formed into a ring shape.
- The rotational angular velocity is determined by inserting the laser light and measuring the beat frequency of Mmt'i (the root of each light generated when the ring resonator rotates). This ring laser gyro has advantages such as a longer lifespan and superior reliability than mechanical gyros, a digital output for counting beat frequencies, and a short start-up time.

However, in a laser gyro using a ring resonator, since the laser medium is nonlinear, when the oscillation frequencies of the lights in opposite directions approach each other to a certain extent, they are pulled together and oscillate at the same frequency. Therefore, it is not possible to measure the rotation speed within the limit rotation speed where this phenomenon (lock-in) occurs, and even if the beat frequency can be measured, the linearity of the beat frequency vs. rotation speed will be extremely poor near the limit rotation speed. Therefore, the rotation speed cannot be determined accurately. The first method to avoid this is to apply mechanical rotational vibration around the rotation axis of the laser gyro, or to create a periodic phase difference between light waves in opposite directions to reduce the difference in oscillation frequency. There is a way to change it periodically. However, with the Towara method, an inverse piezoelectric element or a phase shifter must be installed around the laser gyro or in the resonator, which complicates the configuration.In addition, the characteristics of the inserted parts may change due to changes in the surrounding environment such as temperature. Therefore, it is difficult to accurately measure rotational angular velocity.

On the other hand, in contrast to such a ring laser gyro, there is an inexpensive and highly accurate optical fiber sensor (also called an optical fiber gyro) that detects rotational angular velocity using an optical fiber.
development is underway. Fiber optic sensor is
Light enters from both ends of a circularly wound optical fiber, and after passing through the optical fiber, the interference light of the two lights emitted from both ends is detected and propagates in opposite directions caused by rotation. It measures the phase difference of light and detects the rotational angular velocity. This optical 7-eye pared sensor is configured as shown in FIG. 1, for example. In other words, the light source (
The light from 1) is supplied to the beam sinter (2) and
divided. One of the two halves of the light is passed through a polarizer (3
) is supplied to the light directional coupler (4). The light directional combiner (4) divides the light from the polarizer (3) into two parts.
supply to both ends of the loop mode optical fiber loose (5). The lights propagated in opposite directions through the single mode loose optical fiber (5) pass through the devolaizer (6) and the phase modulator (7), respectively, and are recombined by the optical directional coupler (4). The light recombined by the optical directional coupler (4) passes through the polarizer (3) and the beam slitter (2) and is guided to the photodetector (8).

The phase f adjuster (7) adjusts the oscillation frequency f from the oscillator (9).
0 photodetector (8) that is driven by 0 and phase modulates the oppositely directed light passing through the single mode loose optical fiber (5)
The component of the phase modulation frequency rO among the output 1N components of is
This phase modulation is proportional to the sine component 5in (Δφ) of the phase difference Δφ between the two lights (this is the Sagnac phase difference and is proportional to the rotational angular velocity) caused by the rotation of the single mode optical fiber loose (5). Therefore, this phase modulation A photodetector detects the same frequency component as the frequency fO! A lock-in amplifier (11) is used to detect the output from among the 81 outputs by synchronous detection.

In such a rate sensor that uses single-mode optical 7-eyes, if the polarization state of the light changes due to changes in the birefringence of the single-mode optical fiber, the output signal will drift, and the input and output scale factors will also fluctuate. Therefore, in the optical fiber sensor shown in FIG. 1, in order to avoid this, the polarizer (3) and the riser (
6) has been inserted. That is, the polarizer (3) serves to prevent drift due to changes in fiber birefringence, and the depolarizer (6) serves to prevent changes in the scale 7 actor.

Conventionally, rate sensors using optical fibers require a device to fix or adjust the polarization plane of light propagating within the fiber, which complicates the overall configuration of the optical system. Even if an optical system was configured, the characteristics of each device were not necessarily the best, it was difficult to obtain sufficient measurement accuracy, and it took a lot of time to adjust the optical system.

[Purpose of the invention]

The present invention has been made in consideration of the above-mentioned circumstances, and is an optical fiber that does not require devices for fixing or adjusting the plane of polarization, such as polarizers and devolaizers, and can suppress drift and reduce noise output with a simple configuration. The purpose is to provide a rate sensor.

[Summary of the invention]

According to the present invention, a light source that outputs unpolarized light with a wide spectrum width is used, and the optical path from the light source to the photodetector via the optical directional coupler and loose fiber is configured with a single mode fiber. The pressure is applied so that the light propagates in an unpolarized state.

[Embodiments of the invention]

An embodiment of the optical fiber sensor according to the present invention will be described with reference to FIG.

A light source aυ is a light source that outputs unpolarized light with a wide spectrum width, such as a light emitting diode. Furthermore, when performing highly accurate measurements, a light emitting diode with high output and good directivity is used. A superluminescent diode can also be used as the light source αυ, but in this case, measures may be taken to keep the degree of polarization low. Superluminescent diodes have a smaller light-emitting surface than light-emitting diodes and output high-intensity light, are easily coupled to optical fibers, and have a wide spectrum width of output light. light source aυ
The reason why light with a wide spectral width is used as the spectral width is that the wider the spectral width, the less noise caused by the superimposition of returned light due to Rayleigh scattering within the 7-eyeper and the output drift due to the Kerr effect are reduced.

Light from such a light source αυ is coupled to a single mode fiber (I2).Single mode fiber 02 is an optical fiber that propagates only one mode of light.

The light from this single mode fiber a4 is supplied to an optical directional coupler 09. Optical directional coupler (on the first floor, for example, two fibers (141) (1!9 cores are arranged closely and utilizes the coupling of evanescent waves between adjacent cores, and the coupling from the single mode fiber θ2) The light is separated into one that passes through the single-mode fiber 4 and one that is coupled to the α-power side of the single-mode fiber.

The terminal decoy of the single mode fiber Uη is a non-reflection PZM. Only the light transmitted through the single mode 7 eyeballs 4 is supplied to the optical directional coupler u1.

This light is still separated by the optical directional coupler 4 into what is transmitted to the single mode fiber (a) side and what is coupled to the single mode fiber QD side. The single mode fiber 1 was transmitted clockwise through the optical fiber RUG TJ31, which was composed of a single mode fiber and wound around the drum (2), and was coupled to the single mode fiber C2υ. The light propagates counterclockwise through the single mode loose optical fiber (23). ) is phase-modulated by a phase modulator 04).The phase modulator ff141 uses, for example, an inverse piezoelectric effect, and mechanically modulates the optical fiber in response to a high-frequency signal from an oscillator (2). The high frequency signal frequency becomes the phase modulation frequency.

The light propagated in opposite directions through the single mode loose optical fiber (2) is guided again to the optical directional coupler (ILJ).The end (2) of the single mode fiber (A) is a non-reflective end.Single mode The light transmitted from the fiber (A) and the light combined from the single mode fiber (2I) are guided to the single mode fiber (I [9).The light from this single mode fiber The light guided to α9 and coupled here is supplied to a photodetector (to) via a single mode fiber plate.The photodetector is a single mode optical fiber loose (to).
(to)) detects interference light of light propagating in opposite directions.

The amplitude of the phase modulation frequency component among the output signal components of this photodetector is the sine component 5 inches (Δφ ) is proportional to Then, the lock-in amplifier 6 (power) is used to extract the same frequency component as the phase modulation frequency from the output signal of the photodetector (21) by synchronous detection. Since it is proportional to the rotational angular velocity of the fiber loop) 231, rotational angular velocity information can be easily obtained even with a minute angular elongation.

In the optical fiber rate sensor shown in FIG.
126) is composed of a single optical fiber, and its temperature is kept constant and uniform over the entire length of the fiber, including the fiber on the detector side. However, the entire sensor is magnetically shielded to suppress drift caused by the Faraday effect due to magnetic fields. As shown in Figure 2, when the optical path of an optical fiber loop or the like is constructed entirely of optical fibers, there are no optical coupling parts or optical fiber joints, which reduces coupling loss and reflection, and enables highly sensitive signal detection. It is possible.

In the optical fiber sensor shown in FIG. 2, the light from the light source 0υ is non-polarized light. Therefore, since the light is propagated in an unpolarized state during the optical path from the light source αυ to the photodetector (2 trenches), even if there are temperature changes or fiber birefringence, the polarization state will not fluctuate statistically. There are no annoying noise factors and it is possible to suppress output drift.

〔Effect of the invention〕

As explained above, according to the optical fiber sensor according to the present invention, a light source that outputs unpolarized light is used,
Since this unpolarized light is used to detect interference light, there is no need for a device to fix or adjust the plane of polarization as in the past, and a simple configuration suppresses output drift and reduces noise output. can be reduced.

Since all the light from the light source can be guided to the photodetector through a single-mode fiber, coupling loss and reflection can be reduced, and highly sensitive signal detection is possible, which has a great practical effect. Ru.

[Brief explanation of drawings]

FIG. 2 is a diagram illustrating an embodiment of the optical fiber sensor according to the present invention. ... Single mode fiber, 031, (l... Optical directional coupler, +
231...Optical fiber loose, (Sakaki...Photodetector.

Claims (1)

[Claims] a light source that outputs unpolarized light; a single mode fiber to which the light from the light source is supplied; means for separating the light from the single mode fiber into two waves; and a single mode fiber to which the two waves from the means are supplied. An optical fiber sensor comprising an optical optical fiber loop 2 formed of a mode fiber and in which two waves propagate in opposite directions, and a photodetector that detects interference waves of the two waves propagated through the optical fiber loop.