JP2005172651A - Optical gyroscope - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize an optical gyroscope allowing for detection of gyration and its direction without the use of members by special design. <P>SOLUTION: A polarizing prism 3 separates low coherence light generated in a broadband luminous source 7 into p-polarized light and s-polarized light. After the p-polarized light propagated clockwise while the s-polarized light propagates counterclockwise in a sensing loop 4, both the lights multiplex again in the sensing loop 4 and the multiplexed light wave is injected into a photodetector 8 via transmitting through a polarizer 6. The sensing loop 4 has birefringence with π/2 of phase difference between the both polarized lights between the terminals of 4a and 4b, and the polarizer 6 is arranged such as its transmission axis has a angle of 45° to the plane of a substrate 1. The electric signals corresponding with intensity of the light wave received in the photodetector 8 can function as an optical gyroscope because of its variation responding to gyration of the whole system. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical gyro that enables autonomous navigation of a moving body.

  With the rapid development of automatic control in recent years, the demand for control accuracy of moving bodies has been increasing year by year. Autonomous navigation technology is divided into a global positioning system (GPS) and an inertial navigation system (INS). Conventionally, a system using both GPS and INS has been applied to navigation of aircraft and ships, but a GPS-only system has been mainly applied to systems for consumer use such as car navigation. This is because the device constituting the INS is expensive, and its downsizing and maintenance are not easy.

  One of the indispensable devices for INS is an optical gyro. This is a rotational angular velocity sensor that uses the Sagnac effect, which is one of the nonreciprocal principles of light. The optical gyro has advantages such as small size and maintenance-free as compared with the conventional mechanical gyro, but there is still a barrier for introduction into the above-mentioned consumer system. In other words, the optical parts necessary for realizing the optical gyro are expensive, and it is essentially difficult to reduce the cost.

  However, recently, an optical gyro using an optical waveguide capable of reducing the cost (hereinafter referred to as a waveguide type optical gyro) has been proposed by a plurality of research institutions [Non-patent Document 1: P. Mottier and P.Pouteau “Solid state optical gyrometer integrated on Silicon. ELECTRONICS LETTERS Vol.33 No.23 P.1975-1977 (1997)]. The prospect of realizing a low-cost optical gyro has been obtained by using an optical waveguide that has been energetically introduced into consumer applications, among which quartz-based materials are used. Quartz-based planar lightwave circuits (PLCs) are excellent in terms of stability over time, mass productivity, and optical characteristics, and are actively researched and developed.

  FIG. 3 is a diagram showing an outline of a waveguide-type optical gyro using the conventional silica-based optical waveguide disclosed in Non-Patent Document 1. The operation of the gyro in FIG. 3 is as follows.

  The low coherence light output from the broadband light source 101 enters the input optical waveguide 104 on the gyro substrate 103 via the optical fiber 102. The input optical waveguide 104 is connected to the 3 × 3 optical coupler 105, and the input low-coherence light is branched and input to the sensing loop 106 from both terminals 106 a and 106 b of the sensing loop 106. The low coherence light propagating in the clockwise and counterclockwise directions in the sensing loop 106 enters the 3 × 3 optical coupler 105 again. The low coherence light from the 3 × 3 optical coupler 105 propagates to the optical fiber 109 and the optical fiber 110 via the output optical waveguide 107 and the output optical waveguide 108, and is finally converted into an electrical signal in the light receivers 111 and 112. The

  Here, when the entire system rotates, the low coherence light propagating through the sensing loop 106 is subjected to different phase changes clockwise and counterclockwise due to the Sagnac effect. When the rotational angular velocity of the entire system is Ω, the difference ΔI in the light intensity received by the light receiver 111 and the light receiver 112 is expressed by Expression (1). Here, K is a constant determined by the characteristics of the 3 × 3 optical coupler 105.

  FIG. 4 shows the result of detecting the rotational angular velocity in the optical gyro having the conventional configuration shown in FIG. The sensing loop 106 has a sensing loop length of 80 cm, and the sensing loop 106 has a diameter of 3 cm. It can be seen that rotation is detected from −900 ° / sec to 900 ° / sec with good linearity.

  That is, in this conventional example, unlike a normal interference type optical fiber gyro, by using a 3 × 3 optical coupler 105 having an asymmetric output at the input / output of the sensing loop 106, the response to the rotation of the entire system is made a sine function. The rotation detection sensitivity can be improved and the rotation direction can be detected.

P.Mottier and P.Pouteau "Solid state optical gyrometer integrated on Silicon. ELECTRONICS LETTERS Vol.33 No.23 P.1975-1977 (1997)

  As described above, the conventional waveguide-type optical gyro is capable of detecting a good rotational angular velocity. However, as is apparent from the equation (1), the difference ΔI between the light receiving intensities of the two light receivers 111 and 112 representing the sensing information varies depending on the manufacturing error of the 3 × 3 optical coupler 105, and the sensitivity is asymmetric. The manufacture of the 3 × 3 optical coupler 105 having an output is difficult to realize because it requires a special design technique.

  Further, as shown in FIG. 3, the conventional method requires two light receivers, and it is difficult to reduce the cost of the members, and sensitivity correction of the two light receivers is necessary.

The outline of the optical gyro disclosed in the present invention will be described below.
That is, the present invention for solving the above-described problems has an input terminal, an output terminal, a first connection terminal, and a second connection terminal. When low-coherence light is input from the input terminal, p-polarized light and s Separated into polarized light, p-polarized light and s-polarized light are individually output from the first connection terminal and the second connection terminal, and s-polarized light and p-polarized light are individually input from the first connection terminal and the second connection terminal. A polarizing prism that combines the two polarized lights and outputs the combined light wave from the output terminal;
One terminal is connected to the first connection terminal of the polarizing prism, the other terminal is connected to the second connection terminal of the polarizing prism, and the p-polarized light and the other terminal propagate from one terminal to the other terminal. A sensing loop having birefringence with a phase difference of π / 2 between the s-polarized light propagating from the terminal to one terminal;
Input light transmission means connected to the input terminal of the polarizing prism, for introducing low coherence light into the polarizing prism;
An output light transmission means connected to the output terminal of the polarizing prism and for deriving the light wave combined by the polarizing prism;
It is interposed in the middle of the output light transmission means, and is arranged with its transmission axis set at an angle of 45 degrees with respect to the p-polarization polarization plane or s-polarization polarization plane of the light wave propagated by this output light transmission means. A polarizer,
It is characterized by having.

In this case, according to the present invention, the input light transmission means and the output light transmission means have a birefringence of zero,
It further has a light source that generates low-coherence light and transmits the low-coherence light to the input light transmission means, and a light receiver that receives the light wave output from the output light transmission means.

The present invention is also characterized in that the polarizing prism, the sensing loop, the input light transmission means, and the output light transmission means are formed by an optical waveguide structure formed on a substrate.
In this case, the present invention is characterized in that the polarizer is arranged with its transmission axis set at an angle of 45 degrees with respect to the surface of the substrate.

In the present invention, the output light transmission means is constituted by a polarization maintaining optical fiber,
The polarizer is arranged such that its transmission axis is set at an angle of 45 degrees with respect to the fast axis of the polarization maintaining optical fiber.

The effects obtained by the representative ones of the inventions disclosed in the present application will be briefly described as follows.
According to the present invention, it is possible to detect the rotation direction and perform high-sensitivity rotation without using a 3 × 3 optical coupler that is sensitive to manufacturing errors and requires a special design, which has been used in conventional waveguide-type optical gyros. An optical gyro capable of detection can be realized.
Further, in the conventional method, two light receivers are necessary. However, in the optical gyro according to the present invention, it is possible to detect the rotation direction and increase the sensitivity with only one light receiver.
That is, according to the present invention, it is possible to realize an optical gyro having a performance equivalent to that of a conventional waveguide optical gyro with a simpler configuration.

  The best mode for carrying out the present invention will be described below in detail based on examples.

  FIG. 1 shows a configuration of a waveguide type optical gyroscope 20 according to Embodiment 1 of the present invention. As shown in the figure, an input optical waveguide 2, a polarizing prism 3, a sensing loop 4, and an output optical waveguide 5 are formed on a waveguide type gyro substrate 1 by an optical waveguide structure having a core and a cladding. ing.

  The polarizing prism 3 having an optical waveguide structure has an input terminal 3a, a first connection terminal 3b, a second connection terminal 3c, and an output terminal 3d. When the low-coherence light is input from the input terminal 3a, the polarizing prism 3 separates the low-coherence light into p-polarized light and s-polarized light, and outputs the p-polarized light from the first connection terminal 3b. The optical characteristics are output from the two connection terminals 3c. When s-polarized light and p-polarized light are individually input from the connection terminals 3b and 3c, both polarized lights are combined, and the combined light wave is output from the output terminal 3c.

  The input optical waveguide 2 having an optical waveguide structure is an optical waveguide having zero birefringence, and is connected to the input terminal 3 a of the polarizing prism 3. The output optical waveguide 5 having an optical waveguide structure is an optical waveguide having zero birefringence, and is connected to the output terminal 3 d of the polarizing prism 3.

  The sensing loop 4 having the optical waveguide structure has one terminal 4 a connected to the first connection terminal 3 b of the polarizing prism 3, and the other terminal 4 b connected to the second connection terminal 3 c of the polarizing prism 3. It is connected. As will be described later, in the sensing loop 4, p-polarized light propagates clockwise and s-polarized light propagates counterclockwise. From the terminal 4a (or 4b) to the terminal 4b (or 4a) of the sensing loop 4 , The birefringence of the sensing loop 4 is set so that the phase difference between the p-polarized light and the s-polarized light that is input to the sensing loop 4 and propagates is π / 2.

  In the output optical waveguide 5, a polarizer 6 whose transmission axis is set at an oblique angle of 45 degrees with respect to the surface of the waveguide type gyro substrate 1 is disposed (intervened). That is, the output waveguide 5 is cut halfway, and the polarizer 6 is inserted into this cut portion. As a result, the light wave propagating through the output waveguide 5 is polarized by passing through the polarizer 6.

  A broadband light source 7 that outputs low coherence light and a light receiver 8 are disposed outside the waveguide gyro substrate 1. The broadband light source 7 is connected to the input optical waveguide 2 via an optical fiber 9, and the light receiver 8 is connected to the output optical waveguide 5 via an optical fiber 10. As the broadband light source 7 that outputs low coherence light, for example, a superluminescent diode having an emission band of 1550 nm ± 15 nm can be used.

  In the waveguide type optical gyro 20 having the above-described configuration, the low coherence light (wavelength is, for example, 1550 nm ± 15 nm) output from the broadband light source 7 is incident on the input optical waveguide 2 through the optical fiber 9. The input optical waveguide 2 is connected to the input terminal 3 a of the polarizing prism 3, and the low coherence light is separated into p-polarized light and s-polarized light by the polarizing prism 3.

  The p-polarized light and the s-polarized light separated by the polarizing prism 3 propagate from the first connection terminal 3b and the second connection terminal 3c to the sensing loop 4. At this time, p-polarized light emitted from the first connection terminal 3b propagates clockwise in the sensing loop 4, and s-polarized light emitted from the second connection terminal 3c propagates counterclockwise in the sensing loop 4. The p-polarized light and the s-polarized light propagated in the clockwise and counterclockwise directions again enter the polarizing prism 3 and are combined by the polarizing prism 3, and the combined light wave is output from the output terminal 3c to the output optical waveguide 5. Is done.

  The combined light wave is propagated in the output optical waveguide 5 and polarized when passing through the polarizer 6, further propagated in the optical fiber 10 and received by the light receiver 8. The light receiver 8 optically / electrically converts the received light wave and outputs an electric signal having a value corresponding to the intensity of the light wave.

  When the entire system (the entire waveguide-type optical gyro 20) rotates at an angular velocity Ω with respect to the inertial space, the phase change received during propagation through the sensing loop 4 is expressed by Equation (2) for p-polarized light and s-polarized light, respectively. expressed. Here, βp and βs are propagation constants for p-polarized light and s-polarized light, L is the length of the sensing loop 4, k is the wave number of light, S is the area surrounded by the sensing loop 4, and c is high speed in vacuum. Φ represents a phase change due to the Sagnac effect.

  On the other hand, the transfer function T of the clockwise light and the counterclockwise light from the broadband light source 7 to the light receiver 8 is expressed by Expression (3) using βpL and βsL. Here, θ is an angle formed by the transmission axis of the polarizer 6 and the surface of the waveguide type gyro substrate 1.

When the light wave from the broadband light source 7 has the same intensity for both p-polarized light and s-polarized light, and its Jones vector is expressed by E = (1/2 ^1/2 , ^{1/2 1/2} ), θ = 45 ° The intensity I of the light wave received by the light receiver 8 is expressed by equation (4).

  Further, when the entire system is stationary, that is, when the phase change due to the Sagnac effect is zero, by setting the difference in phase change for p-polarized light and s-polarized light to π / 2, that is, Thus, equation (4) can be transformed into equation (6) using equation (2).

  Here, m is an integer, and is a value within which the phase amount represented by Equation (5) falls within the coherence length of the low coherence light source. As is apparent from the equation (6), the output of the light receiver 8 responds to the rotational angular velocity Ω of the system with a sine function, which enables highly sensitive rotation detection and rotation direction detection.

  FIG. 2 shows an experimental example in which the waveguide type optical gyroscope 20 of this embodiment is configured and the rotational angular velocity is detected. The waveguide type gyro substrate 1 was manufactured using a quartz optical waveguide technique by flame deposition and reactive ion etching. The sensing loop length and diameter of the sensing loop 4 were 80 cm and 3 cm, respectively, as in the conventional example. As the low coherence light source, a superluminescent diode having an emission band of 1550 nm ± 15 nm was used. As can be seen from FIG. 2, rotation can be detected with good linearity from −1000 ° / sec to 1000 ° / sec.

  In this embodiment, a waveguide-type polarizing prism is used as the polarizing prism 3, but it can also be realized by mounting a crystal-type polarizing prism such as a Glan-Thompson prism or a Grand Taylor prism. Further, although the silica-based optical waveguide is used as the optical waveguide, it can be realized by using a semiconductor optical waveguide such as InP or a polymer optical waveguide.

  In the first embodiment shown in FIG. 1, an input optical waveguide 2 that is input light transmission means, a polarizing prism 3, a sensing loop 4, and an output optical waveguide 5 that is output light transmission means are formed by an optical waveguide structure. However, the input light transmission means and the output light transmission means are composed of polarization-maintaining optical fibers, the polarization prism is a crystal type, and the sensing loop is an optical fiber. Can also be configured. This configuration is referred to as Example 2.

In the second embodiment, similarly to the first embodiment, a polarizer is interposed in the polarization maintaining optical fiber as the output light transmission means. At this time, the transmission axis of the polarizer is the fast axis of the polarization maintaining optical fiber ( The polarizer is arranged so as to be set at an angle of 45 degrees with respect to the axis along the line connecting the two stress applying portions of the polarization maintaining optical fiber. That is, the polarizer is arranged so that the transmission axis of the polarizer is set at an angle of 45 degrees with respect to the p-polarization polarization plane or the s-polarization polarization plane of the light wave propagated by the output light transmission means.
The configuration of other parts, for example, the configuration of the broadband light source, the light receiver, and the optical fiber is the same as in the first embodiment.

It is a conceptual diagram which shows the structure of the waveguide type optical gyro which concerns on Example 1 of this invention. It is a characteristic view which shows the rotation detection characteristic of the waveguide type gyro which concerns on Example 1 of this invention. It is a conceptual diagram which shows the structure of the conventional waveguide type optical gyro. It is a characteristic view which shows the rotation detection characteristic of the conventional waveguide type optical gyro.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Waveguide-type optical gyro 2 Input optical waveguide 3 Polarizing prism 4 Sensing loop 4a, 4b Terminal 5 Output optical waveguide 6 Polarizer 7 Broadband light source 8 Light receiver 9, 10 Optical fiber

Claims (6)

It has an input terminal, an output terminal, a first connection terminal, and a second connection terminal. When low coherence light is input from the input terminal, it is separated into p-polarized light and s-polarized light, and p-polarized light and s-polarized light are separated. When the s-polarized light and the p-polarized light are individually input from the first connection terminal and the second connection terminal, the two polarized lights are combined and combined. A polarizing prism that outputs the output light wave from the output terminal;
One terminal is connected to the first connection terminal of the polarizing prism, the other terminal is connected to the second connection terminal of the polarizing prism, and the p-polarized light and the other terminal propagate from one terminal to the other terminal. A sensing loop having birefringence with a phase difference of π / 2 between the s-polarized light propagating from the terminal to one terminal;
Input light transmission means connected to the input terminal of the polarizing prism, for introducing low coherence light into the polarizing prism;
An output light transmission means connected to the output terminal of the polarizing prism and for deriving the light wave combined by the polarizing prism;
It is interposed in the middle of the output light transmission means, and is arranged with its transmission axis set at an angle of 45 degrees with respect to the p-polarization polarization plane or s-polarization polarization plane of the light wave propagated by this output light transmission means. A polarizer,
An optical gyro characterized by comprising: The optical gyro of claim 1,
An optical gyro characterized in that the input light transmission means and the output light transmission means have zero birefringence. In the optical gyro of Claim 1 or Claim 2,
A light source that generates low coherence light and sends the low coherence light to the input light transmission means;
An optical gyro further comprising a light receiver that receives the light wave output from the output light transmission means. In claim 1 or claim 2 or claim 3,
The optical gyro, wherein the polarizing prism, the sensing loop, the input light transmission means, and the output light transmission means are formed by an optical waveguide structure formed on a substrate.   5. The optical gyro according to claim 4, wherein the polarizer is arranged with its transmission axis set at an angle of 45 degrees with respect to the surface of the substrate. In claim 1 or claim 2 or claim 3,
The output light transmission means is composed of a polarization maintaining optical fiber,
The optical gyro is characterized in that the polarizer is arranged with its transmission axis set at an angle of 45 degrees with respect to the fast axis of the polarization maintaining optical fiber.

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