JPH01299412A - Sensor of angular velocity of rotation - Google Patents

Abstract

PURPOSE:To simplify an optical system and to reduce noise, by a method wherein a photocoupler using double-refraction fibers showing a difference in an attenuation amount in an orthogonal polarization mode is connected with a sensing coil formed by winding a double-refraction fiber in a coil. CONSTITUTION:A photocoupler 13 is formed of a double-refraction fiber leading a light from a light source and showing a difference in an attenuation amount in an orthogonal polarization mode, and a double-refraction fiber leading the light to a photosensor 6, and the ends thereof are wound as denoted by 130, so as to construct a transmitting-receiving photocoupler unit. Next, a sensing coil 5 is formed by winding a double-refraction fiber in a coil, and a light-phase converter 4 is provided at one end thereof. Both ends of the coil 5 are connected with the coupler 13 at points denoted by X. Accordingly, a light emitted from the coil 5 turns to be the same polarized wave and a zero-point drift and noise can be reduced. According to this method, construction and manufacture of the title device are simplified and miniaturization and cost reduction can be attained.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a rotational angular velocity sensor.

[Prior art] Rotational angular velocity sensors detect rotational angular velocity by applying the Sagnac effect, and there are two types: negotiation type and ring resonance type.
There are different types. A ring resonance type rotational angular velocity sensor detects rotation in a frequency range by utilizing the optical resonance phenomenon caused by a ring resonator. Therefore, compared to the interference type, it has the advantage of being able to perform highly sensitive measurements with a shorter optical fiber loop and providing a wider dynamic range. However, it is sensitive to expansion and contraction of the loop due to changes in humidity, etc., and has the drawbacks of requiring a narrow spectrum light source (frequency width Δf≦100 KHz), so not much research is currently underway.

FIG. 7 shows the basic configuration of a conventional interferometric rotational angular velocity sensor. Polarizer 33 Phase modulator 4. Sensing coil5. One detector 6 and two optical couplers are used.

The light from the light source l is split by an optical coupler 2a, one of which is split by a polarizer 3. It is guided to the sensing coil 5 via the optical coupler 2b. The left and right light propagated through the sensing coil 5 is recombined by the optical coupler 2b and guided to the detector 6 via the polarizer 3.

When the sensing coil 5 rotates at an angular velocity Ω, a phase difference occurs between the left and right light propagating through the sensing loop (
Sagnac effect), the light output reaching the detector 6 changes. Conventionally, the rotational angular velocity has been detected by directly detecting this change in optical output. Note that the phase modulator 4 is
This is to provide a phase difference of π/2 on the same side to the left and right rotational lights to improve the accuracy of rotational angular velocity detection.

Since the interferometric rotational angular velocity sensor detects the rotational angular velocity from changes in light intensity due to interference between left and right lights, it has the restriction that the light coupled to the sensing coil 5 and emitted from the sensing coil must be of the same polarization. receive. This is because if the polarizations are not the same, a zero point drift or noise will occur in the rotational angular velocity sensor output. Therefore, conventionally, two optical couplers 2a and 2b were used as shown in FIG. 7, and a polarizer 3 had to be inserted between them.

FIG. 9 shows the basic configuration of a conventional ring resonance type rotational angular velocity sensor, including one light source 1.

4 optical couplers 14 and 2 detectors 16.17
and one phase modulator 19.

A triangular wave voltage is applied to the phase modulator 19.

In the case of this ring resonance type rotational angular velocity sensor as well, the rotational speed is detected from the movement of the resonance peak (Figure 10) of the light rotating in the ring.5 The restriction is that the light propagating through the ring must be of the same polarization. receive.

[Problems to be Solved by the Invention] A polarization-maintaining optical coupler is currently manufactured by digging a groove with a curvature in a quartz substrate 7 and removing the coating from the embedded part, as shown in FIGS. 8(A) and 8(B). The polarization-maintaining optical fiber 8 is embedded so that the long sleeve of the elliptical jacket 11, which is the stress applying part, is perpendicular to the surface of the substrate 7 and fixed with resin. They use an advanced method of producing two polished pieces and combining them into one. Therefore, the price is also very high.

A conventional interferometric rotational angular velocity sensor uses two optical couplers.
It is expensive and difficult to manufacture because it requires the use of a stand. Furthermore, since the prior art requires at least four connection points indicated by "x" marks in FIG. 7, reflections at the connection points are large and become a major noise factor in the output of the rotational angular velocity sensor.

On the other hand, in a ring resonant rotational angular velocity sensor, as already mentioned, the light propagating through the ring must be of the same polarization. Conventionally, no consideration was given to this point.

Figure 11 shows an experimental example of resonance characteristics (Transactions of the Institute of Electronics and Communication Engineers '8
Ei/7 Voli89-CNa,7) However, in this experimental example, since a single mode fiber optic was used in the ring resonator 18 in Fig. 9, two independent polarization modes were generated, and FSR ( Free 5pect
ral Range), two resonance peaks appear. For this reason, there is a problem in that rotational angular velocity resolution is reduced and noise is generated due to fluctuations in polarization.

Even when a polarization-maintaining optical fiber is used as a resonator, polarization mode coupling occurs at the optical coupling section.

There was a problem that two resonance peaks appeared in the FSR.

Next, we will return to the problem of interferometric rotational angular velocity sensors.In general, a light source with a short coherence distance must be used to prevent interference noise due to reflected light from the connection part, Ray scattering light, etc. However, A light source with a short coherence length (light emitting diode LED'4) generally has a small output, and direct detection cannot provide sufficient sensitivity. On the other hand, the laser diode L
When D is used as a light source, the sensitivity decreases to J due to interference noise.
There are no two. Furthermore, although SLDs with short coherence distances have a higher output than LEDs, they are expensive and lack reliability.

An object of the present invention is to solve the problem of polarization noise in the above-mentioned interference type and ring resonance type rotational angular velocity sensors, and to provide a highly accurate rotational angular velocity sensor that can be manufactured easily at low cost and has little polarization noise. It is in.

Another object of the invention is to eliminate the drawbacks of the above-mentioned interferometric rotational angular velocity sensor and to significantly improve reception sensitivity by adopting heterodyne detection, even when using a light source with a short coherence distance and low output. The object of the present invention is to provide a rotational angular velocity sensor capable of highly sensitive detection of rotational angular velocity.

[Means for Solving the Problems] The rotational angular velocity sensor of the present invention includes a first birefringent fiber having a difference in attenuation in orthogonal polarization modes that guides light from a light source, and a second birefringent fiber that guides light to a light receiver. A branch at one end of the refractive fiber.
A coupling optical system is constructed, and its output end is bent under predetermined conditions to form a light transmitting/receiving coupler unit, and a third birefringent fiber is wound in a coil shape to connect both ends of a sensing coil having an optical phase modulator at at least one end. , connected to the light transmitting/receiving coupler unit.

In another form, a coupling optical system is configured in a ring shape using birefringent fibers having different attenuation amounts in orthogonal polarization modes, and a phase modulator is provided in the middle of the ring, and furthermore, a phase modulator is provided at both ends of the coupling optical system. A ring resonator formed by bending a birefringent fiber under predetermined conditions is connected to a processing unit equipped with a branching/coupling optical system that guides light to a receiver at both output ends of a birefringent fiber coupler that guides light from a light source. .

In yet another form, a light source, a polarizer, an optical coupler,
In a phase modulation rotary angular velocity sensor consisting of a sensing coil, phase modulator, receiver light, and fiber,
The structure includes a frequency shifter that branches and frequency shifts the light from the light source.

In this case, one frequency shifter has 2x2 terminals, one end guides the light from the light source, one of the two branched ends guides the light to the polarizer, and the other is connected to the other terminal on the light source side, and the do 2
It is possible to have a configuration in which the frequencies of the light in the optical path are different, and a light emitting diode (LED) can be used as the light source.

[Function] Claim 1 uses a birefringent (ASP) fiber in which orthogonal polarization modes have a difference in attenuation as the optical fiber for the optical coupler, thereby simplifying the optical system and facilitating manufacturing. This also reduces noise by reducing the number of connection points.

According to a second aspect of the present invention, an ASP fiber is used as the optical fiber for ring resonance, thereby resonating with a single polarized wave and reducing noise.

According to claims 3 to 5, heterogain detection is used as the detection method, and a frequency shifter for branching and frequency shifting the light from the light source is used as the means for this, thereby significantly improving reception sensitivity.

An acousto-optic device (AOM) can be used as the frequency shifter. In addition, the sensor part uses not only optical fibers, but also
An integrated waveguide using LiNbO3 or the like, which has a large loss, can also be applied.

[Example] The present invention will be described below based on illustrated embodiments.

FIG. 1 shows an example of an interferometric rotational angular velocity sensor of the present invention.

In Fig. 1, numeral 13 is an optical coupler using two birefringent (ASP) fibers with different attenuation amounts in orthogonal polarization modes, and the end thereof is bent under predetermined conditions as shown at 130 to detect polarized light. Make it a child. 5 is a sensing coil made of ASP fiber, and the winding diameter and optical fiber length are determined by the system design. Both ends of this sensing coil 5 can be connected to an optical coupler 13 at locations indicated by "X". Reference numeral 4 denotes a phase modulator included in one end of the sensing coil 5, which imparts a phase difference of π/2 on the same side to the left and right rotational lights to improve the precision of rotational angular velocity detection.

The ASP fiber uses an elliptical jacket type polarization maintaining optical fiber whose cross section is shown in Figure 2(a), and the refractive index n (r) of the radial distance #r from the center is as shown in Figure 2(b) ( c.
), and by designing this refractive index distribution, the Y-polarized wave has a high bending loss, and the X-polarized wave has a low bending loss.

A prototype example for a wavelength of 0.858 Lm is shown below.

Core radius a = 2.32pm shown in Figure 2(b)(c)
, ellipse long sleeve radius b c = 13.935gm, ellipse short axis radius bt = 6. +935gm, cladding thickness/core radius δ=t, relative refractive index difference Δ◆= between core and cladding
+0.2%, relative refractive index difference Δ-=-0.2% between the cladding and the elliptical jacket part, and ellipticity ε=38.5%. When the end of the optical fiber was wound with a bending radius of 4 ha and a number of turns of 15 (intersection = 3.8111), the extinction ratio was -45.
dB, and an optical coupler unit with an excess loss of 0.7 dB has been obtained.

If an optical system is configured using the above optical coupler unit, the light coupled to the sensing coil 5 and emitted from the sensing coil 5 will have the same polarization, so zero point drift and noise can be reduced. Moreover, since only one optical coupler is required, the configuration and manufacturing can be carried out in a cylinder, making it possible to downsize and lower the price of the one-rotation angular velocity sensor. Furthermore, since there are only two connection points, assembly is simplified and noise due to reflection can be reduced.

Note that the bending position applied to the ASP fiber of the optical coupler unit may be on the light source or detector side.

FIG. 3 shows an embodiment of a ring resonator type rotational angular velocity sensor. 1 is a light source, 14a, 14b.

14c and 14d are optical couplers, 15 is a sensing unit, 16.17 is a detector, 18 is a ring resonator, 1
9 is a phase modulator. An ASP fiber is used for the ring resonator 18, and the end portion 180 and the portion to be wound as the phase modulator 19 are bent under predetermined conditions to serve as a polarizer. The phase modulator 19 applies 2π to the light in the ring.
This provides a phase difference of 100 kHz to enable confirmation of resonance phenomena on the time axis.

The ASP fiber uses the elliptical jacket type polarization maintaining optical fiber explained in Fig. 2, and the optical coupler 14
c is constituted by the optical coupler unit of the prototype example already mentioned.

In this way, using the ASP fiber, the optical coupler 14
0. If the ring resonator 189 phase modulator 19 is configured,
Since only a single polarized wave propagates, noise can be reduced.

The reason why the two detectors 16 and 17 are used is to detect the expansion and contraction of the ring resonance from the amount of deviation of the resonance peaks of the clockwise light and the counterclockwise light.

The optical system shown in FIG. 3 can be applied not only as a one-rotation angular velocity sensor but also as an optical system for stabilizing the frequency of a light source.

FIG. 4 shows an embodiment in the case of an interference type rotational angular velocity sensor.

Light from a light source 21 is split into two directions by a frequency shifter 22 having 2×2 terminals, and the frequency-shifted light is sent to a polarizer 23 . Sensing coil 2 via optical coupler 24a
6. The left and right lights propagated through the sensing coil 26 are combined by the optical coupler 24a and returned to the frequency shifter 22 via the polarizer 23. This return light is
Light branched from the light source 21 and not frequency shifted;
The light is combined by the optical coupler 24b, and the intensity of the light is detected by the detector 27.

The selection level meter 28 is a device that detects the intensity of the difference frequency component (heterodyne detection signal) of the two beams branched by the frequency shifter 22, and the lock-in amplifier 29 detects the intensity of the difference frequency component of the two beams branched by the frequency shifter 22. A device for synchronously detecting a phase-shifted signal, 30 is an oscillator.

The signal obtained by the above system is converted into a rotational angular velocity signal by a signal processing system 31.

FIG. 5 shows a system for measuring reception sensitivity of hetero gain detection. 32, 36.39 are objective lenses, 33.38 are polarizers, 34.37 are variable optical attenuators, and 35 are half mirrors.
shows.

Figure 6 shows the results of adjusting the optical output with the variable optical attenuators 34 and 37 and measuring the receiving sensitivity. The light intensity at a level considered to be 1) was defined as the minimum detection sensitivity. The wavelength is 1.32 tau.

When the light source 21 is an LED, the output that can be input into single mode is approximately -20 dBm from the zero frequency shifter 22.
Even if it is branched 1:1 and there is an additional 3 dB loss, the local light output will be 129 dB (3 dB loss due to the branching of the optical coupler), so approximately -80
It is possible to detect light up to dBm, so an LED can be used as a light source for a rotational angular velocity sensor. The coherence distance of LED is 1
Since it is as short as 00100p, highly accurate angular velocity detection is possible.

The configuration shown in FIG. 4 can also be applied to an orthogonal polarization type rotational angular velocity sensor or an integrated rotational angle sensor.

[Effects of the Invention] Since the present invention is configured as described above, it produces the following effects.

In the rotation angle sensor according to claim 1, the optical coupler includes one
Since only a stand is required, the configuration and manufacture are simple, and the rotational angular velocity sensor can be made smaller and lower in price. Furthermore, since there are only two connection points, assembly is simplified and noise due to reflection can be reduced.

In the rotation angle sensor according to claim 2, since an ASP fiber is used for the ring resonator, polarization noise is removed.
A highly accurate rotational angular velocity sensor can be obtained.

In the rotation angle sensor of claim 3, heterodyne detection is used as the detection method, and a frequency shifter that shifts the frequency of the light from the light source by one branch is used as the means, so the detection sensitivity of light intensity is greatly improved. Ru.

As a result, (1) a light source such as an LED with a short coherence distance and low optical output can be used, so the detection sensitivity of one rotational angular velocity is increased, and an inexpensive and highly reliable rotational angular velocity sensor can be obtained.

(2) Since the light source can be driven with a low current, the life of the rotational angular velocity sensor is extended.

(3) Since it can be applied to an integrated rotational angular velocity sensor with a large waveguide loss, miniaturization is possible.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram showing an embodiment of the rotational angular velocity sensor of the present invention, and Fig. 2 shows the structure of an elliptical Jackent type polarization-maintaining optical fiber, (a) is a cross-sectional view, (b) (C ) is a diagram showing an example of refractive index distribution. Fig. 3 is a block diagram showing another embodiment of the rotational angular velocity sensor of the present invention, Fig. 4 is a block diagram showing still another embodiment of the rotational angular velocity sensor of the present invention, and Fig. 5 is the reception sensitivity of hetero gain detection. Figure 6 is a diagram showing the measurement results of hetero gain detection reception sensitivity, Figure 7 is a basic configuration diagram of a conventional interferometric rotational angular velocity sensor, and Figures 8 (A) and (B) are optical A cross-sectional view of a fiber optic coupler, Figure 9 is a basic configuration diagram of a ring resonant rotational angular velocity sensor, Figure 10 is a diagram showing resonance characteristics when a triangular wave with a frequency of 17FSR is applied to a phase modulator, and Figure 11 is a diagram showing resonance characteristics. FIG. 3 is a diagram showing an example of measurement of characteristics. In the figure, l is a light source, 2 is an optical coupler, 3 is a polarizer, 4 is a phase modulator, 5 is a sensing coil, 6 is a detector, 9
is the core, 10 is the cladding, 11 is the oval jacket, 12
13° is a support, 14a, 14b, 14c, and 14d are optical couplers, 15 is a sensing coil, 16 and 17 are detectors, 18 is a ring resonator, and 19 is a phase modulator. 21 is a light source, 22 is a frequency shifter, 23 is a polarizer, 24
a, 24b are optical couplers, 25 is a phase modulator, 26 is a sensing coil, 27 is a detector, 28 is a selection level meter, 29 is a lock-in amplifier, 30 is an oscillator, 31
34 and 37 are variable optical attenuators, and 35 is a half mirror.

Claims (5)

[Claims] 1. A branching/combining optical system is configured at one end of a first birefringent fiber that guides light from a light source and has a difference in attenuation in orthogonal polarization modes and a second birefringent fiber that guides light to a light receiver. The ends are bent under predetermined conditions to form a transmitting/receiving coupler unit, and a third birefringent fiber is wound in a coil shape, and both ends of a sensing coil having an optical phase modulator at at least one end are connected to the transmitting/receiving coupler unit. A rotational angular velocity sensor featuring: 2. A coupling optical system is formed into a ring shape by constructing a birefringent fiber having a difference in attenuation in orthogonal polarization modes, a phase modulator is provided in the middle of the ring, and both ends of the coupling optical system are bent under predetermined conditions. A rotational angular velocity sensor characterized in that the configured ring resonator is connected to a sensing unit provided with a branching/coupling optical system that guides light to a light receiver at both output ends of a birefringent fiber coupler that guides light from a light source. . 3. Light source, polarizer, optical coupler, sensing coil,
A rotational angular velocity sensor comprising a phase modulator, a light receiver, and a fiber, the rotational angular velocity sensor comprising a frequency shifter for branching and frequency shifting light from a light source. 4. The frequency shifter has 2 x 2 terminals, one end guides the light from the light source, one of the two branched ends guides the light to the polarizer, and the other is connected to the other terminal on the light source side, creating two optical paths to be combined. 4. The rotational angular velocity sensor according to claim 3, wherein the frequencies of the lights are different. 5. 5. The rotational angular velocity sensor according to claim 3, wherein the light source is a light emitting diode.