JPH08261768A - Optical integrated circuit and optical-fiber gyro - Google Patents

Abstract

PURPOSE: To provide an optical integrated circuit having a simple structure easy to assemble by providing a base board, waveguides and electrodes for modulation. CONSTITUTION: A phase modulation optical integrated circuit 120 comprises a base board 10, waveguides 11, 12 and modulation electrodes 13A, 13B and 14A, 14B. Optical fibers are connected to both sides of the circuit 120 via connection members 31, 32. For example, a first connection member 31 has optical fibers 103A, 103B disposed on both ends of an optical fiber loop 103 and a second connection member 32 has optical fibers 106A, 1O6B disposed on both ends of a second coupler 106. Connection faces between the circuit 120 and connection member 31, 32 are inclined with respect to an optical path. That is, connection faces of the circuit 120 permit the loss of a light in the connection section between the waveguide 11, 12 and optical fiber not to be increased so that it is possible to minimize bad influence owing to the reflection. Therefore, one phase modulation optical integrated circuit provides two functions of a phase modulator, thereby reducing the number of parts.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical integrated circuit and an optical fiber gyro using the optical integrated circuit.

[0002]

2. Description of the Related Art An optical fiber gyro is configured to measure an angular velocity by utilizing the Sagnac effect of light (Sagnac effect), and has an advantage that it has high reliability and can miniaturize an apparatus. Out of fiber optic gyro
There is a type called an interference type optical fiber gyro,
This is configured so that light is propagated in opposite directions through one long optical path formed by an optical fiber loop wound a plurality of times, and the angular velocity is obtained from the phase difference between the two propagating lights.

FIG. 3 shows an example of a phase modulation type optical fiber gyro. The optical fiber gyro is a light source 101 such as a semiconductor laser or a light emitting diode, a light receiver 102 for converting incident light into an electric current, an optical fiber loop 103 formed by winding one optical fiber a plurality of times, a polarizer 104, and an optical fiber. Couplers 105, 1 for combining or splitting light propagating in light
06 and. The optical fiber gyro further includes a current / voltage converter 107, a phase modulator 108, a signal generator 109, and a synchronous detector 110.

The light beam output from the light source 101 passes through the first coupler 105 and the polarizer 104, and then the second coupler 1
It is led to 06. The light beam is branched by the second coupler 106, and the two light beams thus branched propagate in the optical fiber loop 103 in opposite directions. That is, one propagates clockwise through the optical fiber loop 103, and the other propagates counterclockwise.

When the angular velocity Ω is applied to the optical fiber loop 103, the optical fiber loop 10 is caused by the Sagnac effect.
A phase difference Δφ occurs in the lights propagating in 3 in opposite directions. The phase difference Δφ is proportional to the angular velocity Ω and is represented by the following equation.

[0006]

## EQU1 ## Δφ = (2πLD / λC) Ω

Where Ω is the angular velocity around the central axis of the optical fiber loop 103, D is the loop diameter of the optical fiber loop 103, L is the length of the optical fiber loop 103, and λ is the wavelength of the light beam output from the light source 101. , C represent the speed of light.

The signal generator 109 generates a reference signal having an angular frequency of ω _P and supplies it to the phase modulator 108 and the synchronous detector 110. The phase modulator 108 is the signal generator 1
The optical signals propagating in the optical fiber loop 103 in opposite directions are phase-modulated by the reference signal of ω _{P with} the angular frequency supplied from 09.

The phase modulator 108 is an optical fiber loop 10.
The light propagating rightward in the optical fiber loop 103 is phase-modulated at the exit of the optical fiber loop 103, and the light propagating counterclockwise is phase-modulated at the entrance of the optical fiber loop 103. It

The phase-modulated light is combined by the second coupler 106 to generate interference light. The interference light passes through the polarizer 104 and the first coupler 105, and then the light receiver 1
Detected by 02. The current signal output by the light receiver 102 is converted into a voltage signal V by the current / voltage converter 107. The voltage signal V is represented as follows.

[0011]

[Expression 2] V = K [1 + cos Δφ · {J ₀ (z) -2J ₂ (z) cos 2ω _P t + ··} −sin Δφ · {2J ₁ (z) cosω _P t −...}]

Where z is the degree of phase modulation, J ₀ , J ₁ , J
₂ , ... Bessel function, K is a proportional constant, and t is time.

The synchronous detector 110 synchronously detects the voltage signal V from the angular frequency supplied from the signal generator 109 by the reference signal of ω _P. As a result, the angular frequency component ω _P of the angular frequency nω _P components included in the output voltage V is synchronously detected, and the output 2KJ ₁ (z) si proportional to sin Δφ is output.
nΔφ is output. In this way, Δφ is obtained, and the angular velocity Ω is obtained from the equation (1).

An example of a serrodyne optical fiber gyro will be described with reference to FIG. The serrodyne optical fiber gyro is an improvement of the phase modulation optical fiber gyro. In the serrodyne optical fiber gyro, the phase modulator 10 is provided at one end of the optical fiber loop 103.
8 is arranged, and the serrodyne phase modulator 108 'is arranged at the other end.

Light propagating clockwise in the optical fiber loop 103 is serrodyne-modulated by the serrodyne phase modulator 108 ′ at the entrance of the optical fiber loop 103 and phase-modulated by the phase modulator 108 at the exit of the optical fiber loop 103. It The light propagating counterclockwise in the optical fiber loop 103 is phase-modulated by the phase modulator 108 at the entrance of the optical fiber loop 103, and the optical fiber loop 1
The output of 03 is serrodyne modulated by the serrodyne phase modulator 108 '.

For details of the serrodyne type optical fiber gyro, refer to Japanese Patent Application No. 4-306975 filed by the same applicant as the present applicant.

FIG. 5 shows a conventional phase modulator 108, 108 '.
For example: A waveguide type optical phase modulator is used as the conventional phase modulators 108 and 108 '. The waveguide type optical phase modulator includes a waveguide 51 formed on the upper surface of the substrate 50 and modulation electrodes 53A and 5A formed on both sides of the waveguide 51.
3B and. The substrate 50 is lithium niobate LiN
It is composed of a dielectric crystal plate that exhibits an electro-optical effect such as bO ₃ .
The waveguide 51 is formed by diffusing a metal such as titanium Ti. The phase modulators 108 and 108 'are configured to change the refractive index of the waveguide by applying an electric field to the modulation electrodes 53A and 53B.

[0018]

The light output from the light source 101 includes TE polarized light and TM polarized light having two planes of polarization orthogonal to each other. The two polarized lights have slightly different propagation velocities in the optical fiber loop 103, which causes an error in the phase difference Δφ of the interference light. Therefore, in the optical fiber gyro, in order to obtain high measurement accuracy, the polarizer 104 is provided and the polarized light having a single polarization plane is used. A polarization-maintaining fiber is used for the optical fiber loop 103.

However, in the conventional optical fiber gyro, the polarization state of the linearly polarized light generated by the polarizer 104 changes when passing through the second coupler 106 and when propagating through the long optical fiber loop 103. However, a polarization component perpendicular to the polarization direction is generated. Thereby, the linearly polarized light is changed to the elliptically polarized light, and the gyro measurement accuracy is deteriorated.

Further, in the conventional serrodyne type optical fiber gyro, since two phase modulators 108 and 108 'are used, there is a tendency that the assembly takes time and the manufacturing cost becomes high.

In view of the above problems, an object of the present invention is to provide a serrodyne type optical fiber gyro having a simple structure and easy to assemble.

In view of the above problems, an object of the present invention is to provide an optical integrated circuit suitable for a serrodyne optical fiber gyro having a simple structure and easy to assemble.

[0023]

According to the present invention, as shown in FIG. 1, for example, an optical integrated circuit includes a substrate and two waveguides formed along the upper surface of the substrate and each of the two waveguides. And a modulation electrode formed along both sides, and the waveguide is formed by a proton exchange method.

According to the present invention, in the optical integrated circuit, one of the modulation electrodes is configured as a serrodyne modulator, and the other is configured as a phase modulator.

According to the present invention, the optical fiber loop has a light source, an optical fiber loop and a light receiver, and splits the light from the light source into two and propagates the optical fiber loops in opposite directions. In an optical fiber gyro configured to detect interference light of two lights propagating in mutually opposite directions by the photodetector, an optical integrated circuit for phase modulation is connected to both ends of the optical fiber loop, and the phase modulation The optical integration circuit has a substrate, two waveguides formed along the upper surface of the substrate, and modulation electrodes formed on both sides of each of the two waveguides. The waveguide is a proton exchange method. It is characterized by being formed by.

According to the present invention, in the optical fiber gyro, one of the modulation electrodes is configured as a serrodyne modulator, and the other is configured as a phase modulator.

[0027]

Since the optical integrated circuit 120 of the present invention has the functions of two phase modulators, the number of parts of the optical fiber gyro can be reduced. The optical integrated circuit 120 has a polarization separation function because it is formed by the proton exchange method. Therefore, even if the polarization characteristics are deteriorated by the coupler or the like, the polarization characteristics can be restored.

[0028]

Embodiments of the present invention will be described below with reference to FIGS. FIG. 1 shows an example of a serrodyne optical fiber gyro according to the present invention. The optical fiber gyro of this example has two phase modulators 108 and 10 as compared with the conventional serrodyne optical fiber gyro shown in FIG.
8'is different in that a phase modulation optical integrated circuit 120 is arranged, and the other parts may be the same.

That is, the optical fiber gyro of this example is the light source 1
01, a light receiver 102, a polarizer 104, an optical fiber loop 103, two couplers 105 and 106, and an optical integrated circuit 120 for phase modulation. The optical fiber gyro of this example further includes a current-voltage converter 107, a signal generator 109, and a synchronous detector 110.

The phase modulation optical integrated circuit 120 of this example has the functions of two phase modulators 108 and 108 '.

FIG. 2 shows an example of an optical integrated circuit 120 for phase modulation according to the present invention. Optical modulation circuit 120 for phase modulation of this example
Is a substrate 10, two waveguides 11 and 12 formed on the upper surface of the substrate 10, and modulation electrodes 13A, 13B and 14A formed along both sides of the waveguides 11 and 12,
14B and.

The modulation electrodes 13A and 13B formed along both sides of the first waveguide 11 are serrodyne phase modulators, and the modulation electrodes 14A formed along both sides of the second waveguide 12, 14B may be a phase modulator.

The optical integrated circuit 120 may be manufactured by forming the waveguides 11 and 12 and the modulation electrodes 13A, 13B and 14A, 14B on the upper surface of the substrate 10 by using a photolithography technique.

The substrate 10 is a dielectric crystal plate exhibiting an appropriate electro-optical effect, such as lithium niobate (LiNb).
O ₃ ), lithium tantalate (LiTaO ₃ ) and the like. Generally, there are a titanium diffusion method, a proton diffusion method and the like as a method of forming a waveguide. The waveguide formed by the titanium diffusion method does not have the polarization separation function, but the waveguide formed by the proton exchange method has the polarization separation function.

The waveguides 11 and 12 of this example are formed by the proton exchange method. Therefore, the phase modulation optical integrated circuit 120 according to the present example has a function of recovering the polarization characteristic deteriorated by the second coupler 106.

Connection members 3 are provided on both sides of the optical integrated circuit 120.
Optical fibers are connected via 1, 32. In this example, the first connecting member 31 has the optical fibers 103A and 103B at both ends of the optical fiber loop 103, and the second connecting member 32 is the optical fiber 1 at both ends of the second coupler 106.
06A and 106B.

The joint surface between the optical integrated circuit 120 and the connecting members 31 and 32 is inclined with respect to the optical path. That is, the joint surface of the optical integrated circuit 120 is inclined with respect to the waveguides 11 and 12, whereby the waveguides 11 and 1 of the optical integrated circuit 120 are inclined.
The adverse effects of reflection can be minimized without increasing the loss of light at the junction of the optical fiber and the optical fiber.

Although the embodiments of the present invention have been described above in detail, those skilled in the art will understand that the present invention is not limited to the above-mentioned embodiments and various other configurations can be adopted without departing from the gist of the present invention. Easy to understand.

[0039]

According to the optical integrated circuit of the present invention, since it has the functions of two phase modulators, there is an advantage that the structure of the optical fiber gyro can be simplified.

According to the optical integrated circuit of the present invention, since the waveguide is formed by the proton exchange method, it has a polarization separation function, and therefore, the polarization function deteriorated by the second coupler or the like can be recovered. is there.

According to the optical fiber gyro of the present invention, 1
Since one phase modulation optical integrated circuit provides the functions of two phase modulators, there is an advantage that the number of assembly parts can be reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of an optical fiber gyro of the present invention.

FIG. 2 is a diagram showing an example of an optical integrated circuit of the present invention.

FIG. 3 is a diagram showing an example of a conventional phase modulation type optical fiber gyro.

FIG. 4 is a diagram showing an example of a conventional serrodyne modulation type optical fiber gyro.

FIG. 5 is a diagram showing an example of a conventional phase modulator.

[Explanation of symbols]

 10 substrate 11, 12 waveguide 13A, 13B, 14A, 14B modulation electrode 31, 32 connecting member 50 substrate 51 waveguide 53A, 53B modulation electrode 101 light source 102 light receiver 103 optical fiber loop 104 polarizer 105, 106 coupler 107 Current-voltage converter 108, 108 'Phase modulator 109 Signal generator 110 Synchronous detector 120 Phase modulation optical integrated circuit

Claims (4)

[Claims] 1. A substrate, two waveguides formed along an upper surface of the substrate, and modulation electrodes formed on both sides of each of the two waveguides. The waveguide is a proton exchange method. An optical integrated circuit characterized by being formed by. 2. The optical integrated circuit according to claim 1, wherein one of the modulation electrodes is configured as a serrodyne modulator, and the other is configured as a phase modulator. 3. A light source, an optical fiber loop, and a light receiver, wherein the light from the light source is split into two to propagate the optical fiber loops in opposite directions, and the optical fiber loops in opposite directions. In the optical fiber gyro configured to detect the interference light of the two lights propagating to the optical receiver, the phase modulation optical integrated circuit is connected to both ends of the optical fiber loop, and the phase modulation optical integrated circuit is connected. Has a substrate, two waveguides formed along the upper surface of the substrate, and modulation electrodes formed on both sides of each of the two waveguides, and the waveguide is formed by a proton exchange method. An optical fiber gyro characterized by the above. 4. The optical fiber gyro according to claim 4, wherein one of the modulation electrodes is configured as a serrodyne modulator, and the other is configured as a phase modulator.