JPS58137766A - Detector of rotation angular speed of optical fiber - Google Patents

Abstract

PURPOSE:To prevent the influence of a dark current and a DC drift even if the rotation angular speed is constant, by using an optical switch to switch alternately directions of the incident light to an optical fiber ring and obtaining the quantity of phase shift on a basis of the difference of the intensity of detected light between respective cases. CONSTITUTION:The light from a light source 1 is divided into two by a translucent mirror 7, and one divided light is incident to a photodetector 6 as a reference light through a reflective mirror 8 and a translucent mirror 9, and the other is incident to an optical fiber ring 5 through an optical switch 10. This light becomes a counterclockwise light 4 when the optical switch is turned on as shown in figure by (a), and the light becomes a clockwise light 3 when the optical switch is turned off as shown in figure by (b), and thus, the light is transmitted through the ring 5 and is synthesized with the reference light by the photodetector. Though the quantity of phase shift between the reference light and the light transmitted through the ring includes rotation angular speed information, the optical switch is switched alternately to measure the difference of the intensity of detected light between respective cases of detect the quantity of phase shift in AC.

Description

Detailed Description of the Invention [Technical Field to which the Invention Pertains] The present invention relates to an optical fiber rotation angular velocity detector (optical 7 eye verge gyroscope) for an optical fiber used in optical communications, and more specifically, This invention relates to an optical fiber rotational angular velocity detector that utilizes the fact that there is a difference in transmission time between light propagating in the circular direction and light propagating in the counterclockwise direction, which is proportional to the rotational angular velocity of the original fiber ring.

[Description of prior art]

The phenomenon in which a difference in propagation time occurs between clockwise and counterclockwise light due to the rotational angular velocity of the optical fiber ring is called the Sagnac effect.

As shown in Figure 1, the light emitted from light source 1 is transferred to a half mirror.
Divided into two by 2, the origin of the clockwise rotation (arrow 3 in the diagram) and the y of the left rotation
It enters from both ends of the original fiber ring 50 with a radius a1 that is divided into t (arrow 4 in the figure), and then a half mirror.
2 constitutes an optical system for detection by a photodetector 6. When the clockwise light that has propagated through the original fiber ring 5 and the counterclockwise light are combined again by the half mirror 4, if the optical fiber ring 5 is rotating at an angular velocity Ω, then the clockwise light and the counterclockwise light)
Since there is a difference in propagation time with light, a phase difference Δφ occurs.

This phase difference Δφ is determined by the well-known formula: However, L: total length of optical fiber ring Ω: radius of optical fiber ring Ω: Rotation angular velocity of optical fiber ring C: Speed of light λ: Mitsukocho It is expressed as

Using this phase difference Δφ, the intensity of the composite light synthesized by the half mirror 2 is calculated as follows: Intensity of composite light = m (1-) - cos Δφ) However, m is a constant, and when receiving this combined light, The photodetector 6Fi outputs an output proportional to the intensity of this combined light, allowing the rotational angular velocity of the ring 50 to be determined.

Many research papers have been published regarding original fiber gyros that utilize this characteristic. However, in those conventional fiber optic gyros, when the rotational angular velocity Ω is constant,
Since the signal output from the photodetector 6 is only a DC component,
Clearance of photodetector 6 tk.

Accurate measurement is difficult due to the temperature characteristics of the sensor and DC drift of the electric circuit that processes the detection signal.

The above-mentioned research publications include, for example, [Measurement and Control J VOL, 20 No. 10 ("Laser Gyro", written by Kazuo Hotate).

[Object of the present invention]

The present invention is an optical system that makes it possible to measure the rotational angular velocity of the original fiber ring with high precision by preventing the output signal from the photodetector from being affected by the dark current of the photodetector or the DC drift of the electric circuit. An object of the present invention is to provide a fiber rotational angular velocity detector.

[Pros of the present invention]

The present invention switches between clockwise light and counterclockwise light by a light tube light switch propagating in the light 7 eye ring,
The present invention is characterized in that the output of the photodetector can be detected as an alternating current component by measuring the amount of phase shift of each original and detecting the difference.

The present invention also provides an optical fiber rotational angular velocity detector in which the original fiber is formed into a ring shape and utilizes the configuration of a q-ring interference needle, which includes a light source, an optical system that divides the light emitted from the light source into two, and one of the optical fibers. An optical system configured to make the reference light enter the photodetector as a reference light, and an optical switch having a means for switching the other light so that it enters the optical fiber ring alternately clockwise and counterclockwise. An optical fiber rotation angle comprising an optical system configured to enter the optical fiber ring through the optical fiber ring, enter the light emitted from the optical fiber ring again into the photodetector via the optical switch, and combine it with the reference source. It can be configured as a detector.

[Explanation based on examples]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A device according to an embodiment of the present invention will be explained below based on the drawings.

FIG. 2 is a configuration diagram of the device according to the first embodiment of the present invention. In the same figure, nine beams emitted from light source l, half mirror
7, one part of the light enters the photodetector 6 as a reference source through a mirror 8 and a half mirror 9, and the other part enters the original fiber ring 5 through the original switch (optical switching device) 10. do. When the optical switch 10 is on, the source incident on the optical fiber ring 5 becomes a counterclockwise source 4 that propagates counterclockwise through the original fiber ring 5.
After exiting the optical fiber ring 5, the light enters the photodetector 6 through the optical fiber ring 9, where it is combined with the reference light described above (see FIG. 3). Furthermore, when the source switch 1O is in the off state, the light passes through the optical ear ring 5 as clockwise light 3, and is combined with the reference source at the photodetector 6 in the same manner as described above (see FIG. 4).

FIG. 5 is a characteristic diagram of the light intensity at the photodetector 6 with respect to the on/off time of the optical switch 100, and the horizontal axis indicates the time axis.

In the figure, the on/off switching time interval of the original switch IO is respectively T (seconds), the time for light to pass through the optical fiber ring 5 is T/(seconds), and these are T )
It is assumed that there is a relationship T'. It is assumed that the optical switch 10 is switched from off to on at time to, from on to off at time t2, and again from off to on at time t4.

For 71 seconds from time tg to time tl (Guanxia), the clockwise source 3 that entered the original fiber ring 5 when the optical switch 10 was in the OFF state continues to be emitted from the original fiber ring 5, so that the emitted light remains unchanged from the original fiber ring 5. The light passes through the switch 10 and is emitted toward the half-circuit -7, and only the reference source enters the photodetector 6. Time t.

In the period from tl to tl (interval layer), the device operates in the state shown in FIG.

Similarly, 71 seconds from time t2 to t5 (section ■
), the left mDjt4 that entered the original fiber ring 5 when the optical switch lO was in the on state propagated inside the original fiber ring 5 and was emitted from the optical switch 10 that was in the off state, so this emitted light was in the section I. As in the case of , it does not reach the photodetector 6. Between time t8 and t4 (section y)
Here, the light passing through the optical fiber 5 as the clockwise light 3 when the original switch 10 is in the OFF state and the reference light passing through the mirror 8 described above are combined by the photodetector 6.

Furthermore, after time t4, the same operation as t(1% t4) is repeated.

The amplitude of the reference source on the photodetector 6 is
Let B be the amplitude of the light emitted from the optical fiber ring 5 above. In addition, the amount of phase shift from the half mirror 7 to the half mirror 9 through the mirror 8 is ψ, the phase shift lid of the light from the half mirror 7 to the optical switch 10j is ψ1, and the amount of phase shift from the half mirror 7 to the optical switch 10j is ψ1, and from the original switch lO to the half mirror. The phase shift of light up to 9 is ψ9 and [7, and the phase shift of 9 in the original fiber ring 5 is ψ5-Δφ/2 (9'5-2 x n L /λ, Δφ=4r
Let LaΩ/Cλ. ) Then, 1 reference light BA and the output light EB from the original fiber ring 5 are expressed on the photodetector 6 by the following equation.

For this reason, the strength of the party under control at the beginning of the period is 1. is 1,=I
CA-Rmu-A evil fl! 1 [The intensity of light 1 meter at a time is g = (
k! , + PiB)・(KA-11B)”=A2-1
−B2+2μBaas((ψ7+ψ9+ψ5−ψ8)−
Δφ/2).

Here, by adjusting the reflectance and position of the mirror 80, A=B ψ7+ψ9+ψ5-ψ8=7(2n+1), where n
: If n is made to be an integer, the above-mentioned ■1 and the import are ■1; m2 1m=2A2 (1±sinΔφ/2), and the sign is + if n is an even number and - if it is an odd number.

Next, the light intensity ■ when in the interval layer is the interval! Since it is the same as in the case of , ■ shoes = A2.

Regarding the light intensity -9 in section V, compared to the case of section layer, this is the difference only in whether the party moves counterclockwise inside the original fiber ring 5 or counterclockwise 9. Therefore, the amount of phase shift within Party 7 Aipari/G 5 is an interval! The difference is that ψ, +Δφ/2 is different from the case of . Therefore, the light intensity 19 becomes as shown in the following equation.

凰, = 2 A2 (14-sin Δφ72
) Figure 5 shows the relationship between the above-mentioned light intensity and time, and is for the case of n=1.

In the same figure, the light intensity in the interval layer and the interval y is 2A2 when the angular velocity Ω is zero, and when the angular velocity Ω has a certain magnitude, the light intensity in the interval 1 and the interval A difference occurs between the light intensity IW at y. This II and 1.
Find the difference value with 4 A25inΔφ/29,
Under the condition of Δφ<<1, this difference value is proportional to 4φ, so that Δφ can be detected as an AC signal.

Next, the section in Figure 5! and section ■ are parts unrelated to the angular velocity Ω, but if T is set to a value sufficiently larger than T' (for example, T ) 1000T/), as shown in Fig. 6, You can ignore this part. Alternatively, as shown in FIG. 7, only values related to the angular velocity Ω can be obtained by sampling the output at appropriate times t5 and t6 between the interval V.

Note that the value of T' in the aIs diagram is approximately 5 μa@C if the fiber length is I Km, so in the case of Figure 6, if the original switch 4 is switched at a timing later than approximately 200 Hz, good. Further, as is clear from FIGS. 5 and 6, the faster the switching speed, the better.

FIG. 8 is a block diagram of a device according to a second embodiment of the present invention. In the device of the first embodiment shown in FIG. 2, since there is a section ■ and a period amount time which are unrelated to the angular velocity Ω,
It is necessary to take measures as explained using the diagram. Second
The apparatus of this embodiment is designed so that it is possible to obtain an output related to the angular velocity Ω even in the interval l and the interval quantity.

In FIG. 8, the structures of the parts denoted by the same reference numerals as in FIG. M2 are the same as those of the first embodiment. The difference is that jt, rj passing through half mirror 9, mirror 11,
The light enters the photodetector 6 through the half mirror 12, and the light enters the half mirror 7 from the optical switch IO.
The light passes through the mirror 13 and the half mirror 12 and enters the photodetector 6.

In FIG. 9, sections t, i, m, Wlifa211
It is explained in J and takes about the same amount of time.

In section 1, the source emitted from the source fiber ring 5 is output from the source switch 10 to the half mirror 7. In the case of the iron rack of the first embodiment, KIIi, this original fiber ring 5
The 9th beam emitted was not combined with the reference beam, but the 2nd beam
In the case of the embodiment, this emitted light passes through the half mirror 7, passes through the mirror 13, and the half mirror 12, and then reaches the photodetector 6.
reach.

On the other hand, the reference light is reflected by the half mirror 9, passes through the mirror 11, is combined with the aforementioned light emitted from the original fiber ring 5 at the half mirror 12, and is input to the photodetector 6. A similar optical path is taken for interval quantities.

Regarding the interval quantity W, in Fig. 8,
The originals synthesized by half mirror 9 are further mirrored by mirror 11,
The light passes through the half mirror 12 and enters the photodetector 6, where it is detected. Therefore, the light intensity input to the photodetector 6 is only a value related to the angular velocity Ω through sections 1, I, II, and W as shown in FIG. 9, so that value is detected as an AC signal L, To find the wR width, 19 angles of reach Ω
The value of can be found. However, in this case, if the reflectance of the Eve-11, 130 is 1 and the reflectance of the half mirror 12 is [L5, the intensity of the combined light will be 1/2 compared to the case of the first embodiment. Become.

Many types of optical switches can be used, one of which is an original switch using a waveguide as shown in FIG. In FIG. 10, a substrate 14 (eg [, Link) is made of Os. ) Upper K 15.16
．． Nine waveguides are formed with 17 and 18 as input and output parts, and electrode 1
9. Deposit 20. Now, when an applied voltage is applied to the electrodes 19 and 20, the refractive index of the waveguide and the light around it changes, and the coupling coefficient between the two waveguides changes. Therefore, depending on the presence or absence of voltage applied to the electrodes 19 and 20, the input/output section 15
．． 16.17.18 can be switched between a state where questions 15, 17 and 16, 18 are connected, and a state where questions 15, 18 and 16, 17 are connected. A device with an applied voltage of 10v1 and a switching time of 100 MHI has been developed and can be used to implement the present invention.

As for the original switch, it is also possible to use a system other than the one explained in Fig. 10, and there is also an A/A switch on the optical path.
Wavelength changes like an O modulator! I! It is also possible to adopt a method of inserting a device into the device and detecting the phase difference between the beat signals. Furthermore, although the explanation has been made using a C=7 mirror or a mirror as the optical component, it is clear that a waveguide-shaped component such as the one illustrated as a switch may also be used.

[Description of Effects] As described above, according to the present invention, the clockwise light and the counterclockwise light are alternately incident on the source fiber ring using the source switch, and the phase difference between the output lights is determined. By detecting this, it is possible to detect the output signal of the photodetector as a variable current signal with a width corresponding to the rotational angular velocity, and it is possible to detect dark current in the photodetector or DC drift in the electrical section. It is possible to perform highly accurate measurements without being affected.

[Brief explanation of drawings]

Figure 1 is a diagram showing the configuration of a conventional original fiber rotation angular velocity Yokota device. FIG. 2 is a configuration diagram of an apparatus according to a first embodiment of the present invention. 5 and 4 are explanatory diagrams of the operation of the apparatus according to the first embodiment of the present invention. Figure 5 is a photodetector output characteristic diagram in the first embodiment device.
Japanese Patent Publication No. 58-137766
(5) FIGS. 6 and 7 are photodetector output characteristics diagrams for other embodiment devices. FIG. 8 is a configuration diagram of an fjg2 embodiment of the present invention. FIG. 9 is a photodetector output characteristic diagram in the second embodiment device. FIG. 10 is a configuration diagram of a specific example of an optical switch. DESCRIPTION OF SYMBOLS 1... Light source, 5... Original fiber ring, 6... Photodetector, 10... Optical switch. Patent applicant NEC Corporation Representative Patent attorney Nao Ide Takaha 1 Figure 2 Figure 3 M4 Figure 7 Figure 7 1073 Shoulder 9 Mouth

Claims (1)

[Claims] (1) A light source, an optical means that divides the light from the light source into a reference source and a measurement light, an optical fiber ring through which the light enters and exits, and a measurement light that enters the optical fiber ring from the optical means. A light switching means for periodically switching the original fiber ring between a clockwise propagation and output direction and a counterclockwise propagation and output direction, and a reference source from the optical means and the optical fiber ring. 1. An optical fiber rotation angular velocity detector comprising: a photodetector into which emitted light enters.