JPH09318367A - Optical fiber gyro and optical integrated circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent occurrence of fixed bias and scale actor errors caused by fluctuation of erroneous light by providing a light shielding film or plate to a front end surface of an optical integrated circuit and shielding the erroneous light among radiation mode light generated, at the front end surface of the optical integrate circuit. SOLUTION: A Y branch 26 formed on an upper surface 20B of an optical integrated circuit 20 contains a main wave guide 23 and two branch wave guides 26A and 26B. On the upper surface 20B of the circuit 20, grooves 56 and 57 are formed, and the main wave guide 23 spirally extends between the grooves 56 and 57, while bending in S-like. With the grooves 56 and 57, radiation mode light is shielded, and the radiation mode light is prevented from being propagated to two branched 26A and 26B and a joint part between the circuit 20 and an optical fiber loop 103. In addition, the radiation mode light is shielded, and the radiation mode light is prevented from being propagated to a joint part between the circuit 20 and an optical fiber on a light source side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber gyro for measuring an angular velocity by utilizing the Sagnac effect and an optical integrated circuit used therein. More specifically,
The present invention relates to a light blocking device or a light blocking structure for blocking radiation mode light leaked or diffused from a light propagation path in an optical fiber gyro and an 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, and has an advantage that it has high reliability and can downsize the device.

FIG. 21 shows an example of a phase difference modulation type optical fiber gyro among conventional interferometric optical fiber gyros. The optical fiber gyro includes a light source 101 such as a semiconductor laser and a light emitting diode, and a light receiver 1 that converts incident light into an electric current.
02 and an optical fiber loop 103 formed by winding one optical fiber a plurality of times, a polarizer 104, and couplers 105 and 106 that combine or branch light propagating through the optical fiber.

The light output from the light source 101 passes through the first coupler 105 and the polarizer 104,
It is led to 6, where it is branched into two. The two lights propagate in the optical fiber loop 103 in opposite directions. That is, one propagates right through the optical fiber loop 103,
The other propagates to the left.

When an angular velocity Ω is applied to the optical fiber loop 103, the optical fiber loop 10
3, a phase difference Δφ occurs between the lights propagating 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 output from the light source 101. , C represent the speed of light.

This optical fiber gyro is further provided with an electric current
Voltage converter 107, phase modulator 108, and signal generator 10
9 and a synchronous detector 110. The current output from the light receiver 102 is converted into a voltage by the current / voltage converter 107 and output as a voltage. The phase modulator 108 is arranged at one end of the optical fiber loop 103, and is operated by the reference signal supplied from the signal generator 109. The optical fiber loop 103 by the phase modulator 108
The light propagating in the opposite directions to each other is phase-modulated. When the angular frequency of the signal supplied from the signal generator 109 is ω _P , the output voltage V of the current / voltage converter 107 is represented by the following equation.

[0009]

## EQU2 ## I = K [1 + cos Δφ · {J ₀ (z) -2J
₂ (z) cos2ω _P t + ··｝ −sinΔφ · ｛2J
₁ (z) cosω _P t -...}]

Where z is the degree of phase modulation, J ₀ , J ₁ , J
_2, ... are Bessel functions, K is a proportionality constant, t is time.

A reference signal of angular frequency ω _P is supplied from the signal generator 109 to the synchronous detector 110, and the first harmonic angular frequency component ω _P of the angular frequency nω _P component of the output voltage V is synchronized by this reference signal. Is detected. Synchronous detector 110
Is an output 2KJ ₁ (z) sinΔ proportional to sinΔφ.
Output φ. From the output of the synchronous detector 110, Δφ is obtained, and the angular velocity Ω is obtained from the equation (1).

A serrodyne optical fiber gyro is known as an improved version of the phase difference modulation optical fiber gyro. In the serrodyne system, the phase modulator 108
Besides, a serrodyne phase modulator 108 'is further provided. For details of the serrodyne type optical fiber gyro, Japanese Patent Application No.
See 306975.

As shown by the broken line in FIG. 21, two couplers 105 and 106, a polarizer 104, and a phase modulator 10 are provided.
8, 108 'may be replaced by the optical integrated circuit 115. Further, the polarizer 104, the second coupler 106, and the phase modulators 108 and 108 ′ may be replaced by the optical integrated circuit 20.

Another example of the conventional optical fiber gyro will be described with reference to FIG. This example is described in Japanese Patent Application No. Hei 7-189363 filed on July 25, 1995 by the same applicant as the present applicant. For details, refer to the same application.

The optical fiber gyroscope of this embodiment includes a light source 101, a light receiver 102, a beam splitter 10, and an optical integrated circuit 20.
And the optical fiber loop 103, and the optical fiber loop 103 is connected to the waveguide of the optical integrated circuit 20 via the connection device 35.

As the optical fiber loop 103, a single mode optical fiber or a polarization maintaining optical fiber is used.
When the single mode optical fiber loop is used, the depolarizers 31 and 32 are inserted between the optical integrated circuit 20 and the optical fiber loop 103. If the polarization maintaining optical fiber is used, the depolarizers 31 and 32 are unnecessary.

The depolarizers 31 and 32 are respectively two polarization maintaining optical fibers 31A and 31B and 32A and 32.
An optical fiber type including B may be used. The two polarization-maintaining optical fibers 31A and 31B, 32A and 32B are connected to each other by a fusion surface inclined by 45 ° with respect to the optical axis as shown, and both ends thereof are inclined by an arbitrary angle with respect to the optical axis. The connection device 35 and the optical fiber loop 1 by the fused surface
It is connected to the optical fiber end (Pigtail) from 03.

In FIG. 22, the control circuit including the current-voltage converter 107, the synchronous detector 110, the signal generator 109, etc. connected to the photodetector 102 as shown in FIG. 21 is omitted.

The beam splitter 10 is arranged in the optical path between the light source 101 and the front end face 20A of the optical integrated circuit 20, and has the function of the first coupler 105 in the example shown in FIG.
The beam splitter 10 has a half mirror 11 inclined at 45 ° with respect to the optical path, and first and second condenser lenses 12 and 13 arranged along the optical path. Half mirror 1
1 may be formed by a right angle prism.

The distance between the light source 101 and the first condenser lens 12 and the distance between the second condenser lens 13 and the front end face 20A of the optical integrated circuit 20 are actually several tens of μm to several mm. You may

On the upper surface of the optical integrated circuit 20, a waveguide 23 and a Y branch 26 composed of the waveguide are formed, and phase modulators 27, 28 are formed on both sides of each branch 26A, 26B of the Y branch 26. .

The light from the light source 101 is a beam splitter 1
It reaches 0, is condensed by the first condenser lens 12, is transmitted through the half mirror 11, and is guided by the waveguide 23 of the optical integrated circuit 20.
Be led to. The light that has propagated through the waveguide 23 is split by the Y-branch 26 into two propagating lights. One propagating light propagates clockwise through the optical fiber loop 103 via the first branch 26A and the depolarizer 31, and the other light propagates in the second branch 2
The optical fiber loop 103 propagates counterclockwise through the 6B and the depolarizer 32.

The light propagating rightward and the light propagating counterclockwise in the optical fiber loop 103 are respectively arranged along the branches 26A and 26B of the Y branch 26, and the phase modulator 2 is arranged.
7 and 28 are phase modulated. Second phase modulator 2
8 may be a serrodyne phase modulator.

The lights propagating through the two branches 26A and 26B are combined by the Y branch 26, and the interference light is guided by the waveguide 23.
To reach the beam splitter 10. The interference light reaching the beam splitter 10 is condensed by the second condenser lens 13, reflected by the half mirror 11 and reflected by the light receiver 102.
Is detected by

The optical integrated circuit 20 is manufactured by forming the waveguide 23, the Y-branch 26 and the phase modulators 27 and 28 on the upper surface of the substrate by using the photolithography technique. As the substrate, for example, lithium niobate (LiNb
O ₃ ) or lithium tantalate (LiTaO ₃ ) is used. As a method of forming the waveguide, there are a thermal diffusion method, a proton exchange method and the like.

The light output from the light source 101 has two polarized lights having polarization planes orthogonal to each other and having the same intensity, that is, TE.
Includes polarized light and TM polarized light. In a fiber optic gyro, polarized light with a single plane of polarization is used to obtain high measurement accuracy. Therefore, the optical fiber gyro is usually provided with a polarization separation function for obtaining polarized light from light from the light source 101. In the optical fiber gyro shown in FIG. 21, a polarizer 104 is provided in the optical path. In the optical fiber gyro shown in FIG. 22, the optical integrated circuit 20 has a polarization separation function.

Since the waveguide itself of the proton exchange type has a function of a polarizer, it is not necessary to provide the polarizer 104 in the optical integrated circuit. In the proton exchange type waveguide, T
E-polarized light is confined in the waveguide and propagates in the waveguide,
TM polarized light diffuses from the waveguide and propagates through the substrate. As a result, the proton exchange type waveguide propagates only TE polarized light. However, since the titanium diffusion type waveguide does not have the function of the polarizer, it is necessary to form the polarizer in the optical integrated circuit. Such a polarizer may be formed in a metal loaded form.

In an optical fiber gyro utilizing the Sagnac effect of light, light other than the signal light is mixed into the optical transmission line to affect the Sagnac phase difference Δφ, which causes an error.

FIG. 23 shows only the optical integrated circuit 20 of the optical fiber gyro shown in FIG. The light 101P output from the light source 101 is generated by the coupler 105 and the polarizer 10.
4 propagates through the waveguide 23 of the optical integrated circuit 20. When the light 101P reaches the end of the waveguide 23 on the front end face 20A of the optical integrated circuit 20, the emitted light P ₁ is generated there. The radiated light P ₁ is generated due to misalignment at the junction between the optical fiber and the waveguide 23 of the optical integrated circuit 20 and mode coupling loss.

The emitted light P ₁ is transmitted through the waveguide 2 of the optical integrated circuit 20.
It also occurs because 3 is a proton exchange type. When the incident light 101P to the optical integrated circuit 20 is linearly polarized light, the emitted light P ₁ is generated due to the deviation between the polarization plane of the linearly polarized light and the transmission axis (polarization plane of the TE polarized light) of the waveguide. When the incident light 101P to the optical integrated circuit 20 is not linearly polarized light, radiated light P _{1 in the} direction of the cutoff axis of the waveguide (polarization plane of TM polarized light) is generated and propagates through the substrate.

When the light propagating along the waveguide 23 of the optical integrated circuit 20 reaches the Y branch 26, the emitted light P ₂ is generated there. Similarly, the radiated light P ₂ propagated through the substrate is recombined with the signal light at the connection between the branch branches 26A and 26B, the optical fiber loop 103 and the optical integrated circuit 20. The emitted light P ₂ is
It occurs due to the propagation loss of the Y branch 26.

The emitted light P ₁ propagating through the substrate is Y-branched 26.
And the branch branches 26A, 26B, the optical fiber loop 103, and the optical integrated circuit 20 are re-coupled (coupled) with the signal light. The radiated light P ₂ also propagates through the substrate in the same manner and is recombined (coupled) with the signal light at the connection between the branch branches 26A and 26B, the optical fiber loop 103 and the optical integrated circuit 20. If the polarization planes of the emitted lights P ₁ and P ₂ match the polarization plane SP of the signal light, the two lights are directly recombined, and if they are different, they are recombined as crosstalk.

The coupling light propagates in the optical fiber loop 103 in opposite directions as signal light. However, the paths of the emitted lights P ₁ and P ₂ from the generation point to the recombination are different from each other, and when they are recombined, their phases are slightly changed from each other. Therefore, the coupling light propagating clockwise in the optical fiber loop 103 and the coupling light propagating counterclockwise differ in the amount of change in the phase due to the coupling, which results in an error in the Sagnac phase difference generated in the interference light. .

Description will be made with reference to FIG. The light propagating through the optical fiber loop 103 propagates to branch branches (waveguides) 26A and 26B (waveguide) of the optical integrated circuit 20, respectively. When the light reaches the ends of the branched branches (waveguides) 26A and 26B on the rear end face of the optical integrated circuit 20, the emitted light Q ₁ is generated. The emitted light Q ₁ is similar to the emitted light P _{1 in} that both ends of the optical fiber loop 103 and the branch branches 26 of the optical integrated circuit 20.
It occurs due to misalignment of the junction of A and 26B and mode coupling loss.

The emitted light Q ₁ is also generated due to the optical characteristics of the optical fiber loop 103. Optical fiber loop 103
Is a polarization maintaining optical fiber, the optical fiber loop 103
Light propagating from the branched branches 26A and 26B is linearly polarized light. At this time, the plane of polarization of the linearly polarized light and the transmission axis (T
Radiated light Q ₁ is generated due to the deviation of the polarization plane of E-polarized light. When the optical fiber loop 103 is a single-mode optical fiber, the optical fiber loop 103 branches off from the optical fiber loop 103,
The light propagating to 26B is not linearly polarized. At this time, in the case of a proton exchange type waveguide, the cutoff axis (T
Radiation light Q _{1 in the} M polarization plane) is generated and propagates through the substrate.

When the light propagating along the two branches 26A and 26B reaches the Y branch 26, the emitted light Q ₂ is generated there. The emitted light Q ₂ is generated by phase modulation by the phase modulators 27 and 28.

The emitted light Q ₁ is recombined (coupled) with the signal light at the branch branches 26A and 26B. Synchrotron radiation Q ₂
It is recombined (coupling) with the interference light guided to the light receiver 102. Therefore, the emitted light Q ₁ , Q ₂ is the emitted light P ₁ ,
Like P _2, it causes an error.

By the same applicant as the applicant of the present application
In Japanese Patent Application No. 7-101340 and Japanese Patent Application No. 7-101344, which were filed on April 25, 2014, in an optical fiber gyro using an optical integrated circuit, a mode filter is provided in the waveguide of the optical integrated circuit. Is listed. The mode filter blocks the radiation mode light diffused from the waveguide to the substrate, and prevents the radiation mode light from being recombined with the light propagating in the waveguide to cause an error.

[0039]

However, in an optical fiber gyro using an optical integrated circuit, errors due to various causes other than these occur.

This will be described with reference to FIGS. 25, 26 and 27. FIG. 25 is a perspective view of the optical fiber gyro shown in FIG. When a single mode optical fiber is used as the optical fiber loop 103, as shown in the figure,
Depolarizers 31 and 32 are inserted between the optical fiber loop 103 and the optical integrated circuit 20. Optical fiber loop 10
When the polarization maintaining fiber is used as 3, the depolarizers 31 and 32 are unnecessary.

As described above, the Y branch structures 26, 26A and 26B of the optical integrated circuit 20 are waveguides. Therefore, the optical transmission line in the optical integrated circuit 20 is a waveguide. The propagating light is not completely confined in the waveguide but leaks or diffuses into the substrate, as indicated by reference signs A, B, and C in FIG.

Light confined in the waveguide and propagating is called a waveguide mode, and light leaking or diffusing from the waveguide to the substrate is called a radiation mode. Here, three cases in which the radiation mode occurs will be described.

(1) Radiation mode light A generated due to the Y branch 26. This occurs regardless of whether a single mode optical fiber is used as the optical fiber loop 103 or a polarization maintaining fiber. . Further, the radiation mode light A is generated even when the Y branch structures 26, 26A and 26B form a perfect intensity coupler.

Description will be made with reference to FIG. 26A. Usually light collection
The Y branch of the product circuit 20 and the waveguide 23 are single mode waveguides.
It consists of a waveguide. Two branches 26A and 26B of the Y branch 26
Light propagating through₀Is a single mode light, that is, the 0th mode
Light, and on both sides with respect to the center of the waveguide as shown.
It has a symmetrical optical field distribution. Two branches 26A, 26
Two 0th-order mode lights M propagating in B₀Is due to phase modulation
Have a phase difference with each other, and when passing through the Y branch 26, 1
Next mode light M₁Is generated. First-order mode light M ₁Is waveguide
Has an asymmetric optical field distribution on both sides with respect to the center of the path
You. This optical electric field distribution has a substantially cosine waveform as shown in the figure.
A convex shape with opposite polarity on both sides of the center of the waveguide.
This is a line-symmetrical curve.

Eventually, the 0th mode light M ₀ and the 1st mode light M ₁ propagate in the waveguide 23. Normally, since the waveguide 23 is a single mode waveguide, the 0th-order mode light M ₀ is not attenuated, but the 1st-order mode light M ₁ is diffused and attenuated in the substrate outside the waveguide.

The radiation mode light A propagates through the waveguide 23 and is directed to the beam splitter 10 and the light receiver 102.
The amount of light changes with the opposite polarity to the next mode light M ₀ . Therefore, when the radiation mode light A from the Y branch 26 is incident on the light receiver 102, the 0th mode light M ₀ propagated through the waveguide 23.
Acts to cancel the gyro signal. That is the scale factor error of the gyro signal.

(2) Radiation mode light B caused by the fact that the Y branch 26 is not a perfect intensity coupling structure. Also, when the single mode optical fiber is used as the optical fiber loop 103, the polarization maintaining fiber is used. Cases occur in both cases.

Description will be made with reference to FIG. 26B. When the Y branch structures 26, 26A and 26B do not form a complete intensity coupler structure, the 0th mode light M ₀ propagating through the two branches 26A and 26B leaks from the waveguide. As shown, these leaked lights interfere near the Y-branch 26 and inside the two waveguides (26C). as a result,
Radiation mode light B is induced at the Y-branch 26.

The distribution and quantity of this radiation mode light B is 2
The output signal of the photodetector 102 is affected by changes in the phase difference of the 0th-order mode light M ₀ running in parallel on the two branches 26A and 26B, that is, changes in synchronization with the phase modulation signal. It becomes a fixed bias of the gyro signal and causes an error in the gyro signal.

Description will be made with reference to FIG. FIG. 27 shows a state in which the emission mode lights A and B from the Y branch 26 of the optical integrated circuit 20 reach the front end face 20A of the optical integrated circuit 20. For example, when the distance from the Y-branch 26 to the front end face 20A of the optical integrated circuit 20 is 6 mm, the regions 20C and 20D where the radiation mode lights A and B appear are about 500 μm from the waveguide 23.
Range.

The center positions of the regions 20C and 20D are 100 to 200 μm deep from the upper surface of the substrate and about 100 μm on both sides of the waveguide 23.

(3) Radiation mode light C caused by using a single mode optical fiber as the optical fiber loop 103. When a single mode optical fiber is used as the optical fiber loop 103, the optical fiber loop is as described above. 1
The depolarizers 31 and 32 are inserted between 03 and the optical integrated circuit 20.

Referring again to FIG. The light from the light source 101 is linearly polarized by the optical integrated circuit 20, circularly polarized by the depolarizers 31 and 32, and then propagates in the single mode optical fiber loops 103 in opposite directions. The single-mode circularly polarized light exiting the single-mode optical fiber loop 103 propagates through the two branches 26A and 26B of the Y branch 26 of the optical integrated circuit 20 and the waveguide 23.

When the optical integrated circuit 20 is a proton exchange type,
Of the two polarization components, TM polarization and TE polarization, TM polarization having a polarization plane perpendicular to the upper surface of the optical integrated circuit 20 is shown in FIG.
As shown by the broken line C at,
Only E polarized light propagates in the waveguide. The TM polarized light diffused outside the waveguide generates interference fringes D at the front end face 20A of the optical integrated circuit 20. This interference fringe D is the phase modulator 27, 2.
The signal is phase-modulated by 8 and changes in synchronization with the phase-modulated signal. The change in the interference fringe D is caused by the light receiver 10
2 affects the output signal.

Of the radiation light or radiation mode light generated in the optical integrated circuit 20, the radiation light P ₁ , P ₂ , Q ₁ and Q ₂ described with reference to FIGS. 23 and 24 is the substrate of the optical integrated circuit 20. Propagates along the upper surface 20B of the. Synchrotron radiation P ₁ , P ₂ , Q
_The error caused by Q ₁ and Q ₂ is removed by the optical fiber gyro having the coupler 105 including the optical fiber as shown in FIG. 21 and the optical integrated circuit 20 and the optical fiber gyro having the beam splitter 10 as shown in FIG. Is also necessary.

However, since the radiation mode lights A, B, and C described with reference to FIGS. 25 to 27 appear on the front end face 20A of the optical integrated circuit 20 at a position below the upper face 20B, the radiation mode light A , B, C error removal,
Although not important in the case of an optical fiber gyro having the coupler 105 including the optical fiber and the optical integrated circuit 20 as shown in FIG. 21, the beam splitter 1 as shown in FIG.
Required for fiber optic gyros with zeros.

In view of this point, the present invention is directed to the optical integrated circuit 2
An object of the present invention is to provide an optical fiber gyro having no fixed bias and scale factor error of a gyro signal caused by radiated light generated by a junction between a waveguide of 0 and an optical fiber, a Y branch of an optical integrated circuit, and the like.

In view of such a point, the present invention is directed to the optical integrated circuit 2
(EN) An optical fiber gyro having no fixed bias and scale factor error of a gyro signal caused by changes in interference fringes D generated on the front end face 20A of an optical integrated circuit 20 and radiation mode lights A, B, C from a 0 waveguide. The purpose is to

[0059]

According to the present invention, an optical integrated circuit having a light source and a Y-branch for branching or combining light, an optical fiber loop for propagating two lights emitted from the optical integrated circuit, and an optical integrated circuit. In an optical fiber gyro having a light receiver for detecting interference light emitted from the circuit, the Y branch includes a main waveguide and two branch waveguides connected to the main waveguide, and the optical integrated circuit has grooves on both sides of the main waveguide. And the grooves are staggered so as to overlap each other so as to block the propagation path of the radiation mode light propagating through the substrate of the optical integrated circuit, and the main waveguide is curved and extended so as to pass between the grooves. Existence

According to the present invention, in the optical fiber gyro, the groove is provided between the two branch waveguides on the upper surface of the optical integrated circuit, and the groove emits the radiation mode light generated at the ends of the two branch waveguides. Are arranged so as to prevent them from propagating to the main waveguide.

According to the present invention, in an optical integrated circuit having a substrate and a Y-branch formed on the substrate, the Y-branch includes a main waveguide and two branch waveguides connected to the main waveguide, each of which is provided on each side of the main waveguide. Grooves are provided, the grooves are alternately arranged so as to overlap with each other so as to block a propagation path of radiation mode light propagating through the substrate, and the main waveguide is curved and extends so as to pass between the grooves. There is. A groove is provided between the two branch waveguides, and the groove is arranged so as to prevent the radiation mode light generated at the ends of the two branch waveguides from propagating to the main waveguide.

According to the present invention, an optical integrated circuit having a light source and a Y branch for branching or combining the light, an optical fiber loop for propagating two lights emitted from the optical integrated circuit, and an interference light emitted from the optical integrated circuit. In a fiber optic gyro having a beam splitter for deflecting light and a light receiver for detecting light from the beam splitter, light diffused to the outside of a waveguide forming a Y branch is transmitted to a beam splitter via an end face of an optical integrated circuit. A light shielding device is provided between the optical integrated circuit and the beam splitter to prevent leakage.

According to the present invention, in the optical fiber gyro, the light shielding device is a light shielding film formed on the end face of the optical integrated circuit. The light shielding device is a light shielding plate arranged on the end surface of the optical integrated circuit. The light shielding device has a window for propagating the interference light from the main waveguide. The window diameter is several to 20 times the diameter of the main waveguide.

According to the present invention, a light source and an optical integrated circuit having a Y branch for splitting or combining light, an optical fiber loop, a beam splitter for deflecting interference light emitted from the optical integrated circuit, and light from the beam splitter. In a fiber optic gyro having a photodetector for detecting light, a light shielding film is attached to the front end face of the optical integrated circuit facing the beam splitter, except for a band-shaped light-transmitting part along the upper edge. Has a dimension corresponding to the depth dimension of the cross section of the waveguide of the optical integrated circuit.

According to the present invention, in the optical fiber gyro, a light shielding plate having a window is attached to the front end face of the optical integrated circuit, and the width of the window in the lateral direction is the lateral width dimension of the cross section of the waveguide of the optical integrated circuit. The width of the window in the longitudinal direction has a corresponding dimension and is sufficiently larger than the depth dimension of the cross section of the waveguide of the optical integrated circuit. Grooves are formed on both sides of the waveguide and close to the waveguide on the upper surface of the optical integrated circuit, and the depth dimension of the groove has a dimension corresponding to the depth dimension of the cross section of the waveguide of the optical integrated circuit. . The grooves are arranged in a staggered and overlapping manner so as to block the propagation path of the radiation mode light propagating outside the waveguides, and the waveguides extend between the grooves in a curved manner. The groove is formed by a laser processing method.

According to the present invention, a light source and an optical integrated circuit having a Y-branch for branching or combining light, an optical fiber loop, a beam splitter for deflecting interference light emitted from the optical integrated circuit, and light from the beam splitter. In a fiber optic gyroscope having a photodetector for detecting light, an inclined surface is formed on the front end surface facing the beam splitter of the optical integrated circuit, except for a band-shaped light-transmitting portion along the upper edge. It is inclined at a predetermined angle to the upper surface of the optical integrated circuit so that the radiation mode light parallel to the upper surface of the integrated circuit is totally reflected, and the width of the light transmitting portion is the depth dimension of the cross section of the waveguide of the optical integrated circuit. Has dimensions corresponding to.

According to the present invention, in the optical fiber gyro, a light shielding plate having a window is attached to the front end face of the optical integrated circuit, and the width of the window in the lateral direction is the width of the cross section of the waveguide of the optical integrated circuit. The width of the window in the longitudinal direction has a corresponding dimension and is sufficiently larger than the depth dimension of the cross section of the waveguide of the optical integrated circuit. Grooves are formed on both sides of the waveguide and close to the waveguide on the upper surface of the optical integrated circuit, and the depth dimension of the groove has a dimension corresponding to the depth dimension of the cross section of the waveguide of the optical integrated circuit. . The grooves are arranged in a staggered and overlapping manner so as to block the propagation path of the radiation mode light propagating outside the waveguides, and the waveguides extend between the grooves in a curved manner. The groove is formed by a laser processing method.

According to the present invention, an optical integrated circuit having a light source and a Y branch for branching or combining the light, a single mode optical fiber loop for propagating two lights emitted from the optical integrated circuit, an optical integrated circuit and an optical fiber. In an optical fiber gyro having a depolarizer connected between the loops, a beam splitter for deflecting the interference light emitted from the optical integrated circuit, and a light receiver for detecting the light from the beam splitter, the optical integrated circuit is a proton exchange type. A polarizer for removing TM polarized light propagating through the waveguide of the optical integrated circuit is provided.

According to the present invention, in the optical fiber gyroscope, the connecting device is provided between the optical integrated circuit and the depolarizer, and the connecting device includes the V groove formed on the upper surface of the substrate and the optical fiber end arranged in the V groove. Have. The polarizer is arranged in the connection device. The polarizer is arranged between the optical integrated circuit and the beam splitter. The polarizer is a laminated polarizer.

According to the present invention, an optical integrated circuit having a light source and a Y-branch for branching or combining the light, an optical fiber loop for propagating two lights emitted from the optical integrated circuit, and an interference light emitted from the optical integrated circuit. In a fiber optic gyro having a beam splitter for deflecting light and a light receiver for detecting light from the beam splitter, a shield plate is provided so as to surround the light receiver, and the light leaked from the light source reaches the light receiver by the shield plate. Is configured to be prevented.

According to the present invention, an optical integrated circuit having a light source and a Y-branch for branching or combining the light, an optical fiber loop for propagating two lights emitted from the optical integrated circuit, and an interference light emitted from the optical integrated circuit. In a fiber optic gyro having a beam splitter for deflecting light and a light receiver for detecting light from the beam splitter, the optical integrated circuit is a titanium diffusion type, and a first for polarizing the light propagating from the light source to the optical fiber loop. And a second polarizer that polarizes the light propagating from the optical fiber loop to the optical integrated circuit.

[0072]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of an optical fiber gyro according to the present invention and an optical integrated circuit used therein will be described with reference to FIGS. 1 to 4, components other than the optical integrated circuit 20 and the optical fiber loop 103 are omitted. The optical fiber gyro of this example may be of a type including a coupler 105 as shown in FIG.
It may be of a type including the beam splitter 10 as shown in FIG.

FIG. 1 shows a first example of the present invention. The Y branch 26 formed on the upper surface 20B of the optical integrated circuit 20 includes a main waveguide 23 and two branch branch waveguides 26A and 26B. According to this example, the groove 56, is formed on the upper surface 20B of the optical integrated circuit 20,
57 is formed, and the main waveguide 23 extends meandering between the grooves 56 and 57 and is curved in an S shape.

The grooves 56 and 57 are provided alternately on both sides of the waveguide 23, but only two grooves are provided in total.
Plural pieces may be provided on both sides of 3. Also, the grooves 56, 5
The inside of 7 may be filled with a light shielding material.

The radiating mode light P ₁ described with reference to FIG. 23 is blocked by the grooves 56 and 57 of this example, and the radiating mode light P ₁ is divided into the two branches 26A and 26B, the optical integrated circuit 20 and the optical fiber. Propagation to the junction of loop 103 is prevented. Further, the radiation mode light Q ₂ to which has been described with reference blocked Figure 24, the radiation mode light Q ₂ is an optical integrated circuit 2
Propagation to the junction between 0 and the optical fiber on the light source side is prevented.

Description will be made with reference to FIG. FIG. 2 shows a waveguide 23 formed on the upper surface 20B of the front end portion of the optical integrated circuit 20.
And grooves 56, 57 are shown. As shown in the figure, on the upper surface 20B of the optical integrated circuit 20, the X axis is set along the front end surface 20A, and the Z axis is set so as to be orthogonal thereto. As shown in FIG. 2A, the two grooves 56, 57 are staggered and are arranged to have overlapping or overlapping portions along the X axis. The length of this overlapping portion or the overlapping portion is ΔZ. By arranging in this way, the optical integrated circuit 2
Light propagating in the Z-axis direction along the 0 upper surface 20B is blocked.

Description will be made with reference to FIG. 2B. Optical integrated circuit 2
Light propagating in the positive direction of the Z-axis along the upper surface 20B of 0
BE₁, BE_TwoFirst reaches the first groove 56, part of which
BE ₁Is blocked, but some other BE_TwoIs not cut off
Sow. However, it is blocked by the first groove 56
Light BE propagated without_TwoIs always blocked by the second groove 57
Is done.

When the length ΔZ of the overlapped portion or the overlapped portion of the two grooves 56, 57 is sufficiently large, the light BE ₂ propagated without being blocked by the first groove 56 is completely transmitted by the second groove 57. It can be blocked, but if this length ΔZ is small, this light BE ₂ cannot be completely blocked.

Similarly, the light BE propagating in the negative direction of the Z-axis
₃ and BE ₄ reach the second groove 57 first and partially BE
₃ is blocked, but part of other BE ₄ is not blocked and propagates. However, the light BE ₄ propagated without being blocked by the second groove 57 is always blocked by the first groove 56.

The two grooves 56, 57 are formed between the two waveguides 2 and 5.
3 are arranged so that they are spaced from each other. The two grooves 56 and 57 may be arranged to extend along the X axis and be spaced apart in the Z axis direction.

The waveguide 23 extends meanderingly in an S shape between the two grooves 56 and 57, and the front end face 20 of the optical integrated circuit 20.
It may be configured to include a first portion 23A near A, a third portion 23C near the Y-branch 26 and a curved second portion 23B therebetween. The first groove 56 is formed in the waveguide 23.
Of the optical integrated circuit 20 is arranged near the portion 23A near the front end face 20A, and the second groove 57 is arranged near the portion 23C of the waveguide 23 near the Y branch 26 of the optical integrated circuit 20. May be done.

The dimension L _X of the grooves 56 and 57 in the lateral direction (X-axis direction) may be sufficiently large, and is formed so as to extend from a position close to the waveguide 23 to a side edge of the optical integrated circuit 20. Good. Dimension L _{Z of the} grooves 56, 57 in the width direction (Z-axis direction)
May be several tens of μm to 1 mm. The depths of the grooves 56 and 57 may be formed to be substantially the same as or slightly larger than the outer diameter of the cross section of the waveguide 23.

The grooves 56 and 57 may be formed by the well-known fine processing method used in the manufacture of semiconductor devices.
For example, it may be manufactured by forming a metal foil pattern in advance on the portions where the grooves 56 and 57 are to be formed and scraping off the portions with a laser beam machine.

FIG. 3 shows a second example of the present invention. According to this example, a groove 58 is formed between the two branch branches 26A and 26B immediately behind the Y branch 26 on the upper surface 20B of the optical integrated circuit 20. The groove 58 extends substantially along the X-axis direction. By the grooves 58 of the present embodiment, the radiation mode light P ₂ described with reference blocked Figure 23, the radiation mode light P ₂ is 2
Propagation to the junction between the two branches 26A and 26B and the optical integrated circuit 20 and the optical fiber loop 103 is prevented.
Further, the radiation mode light Q ₁ described with reference to FIG. 24 is blocked, and the radiation mode light Q ₁ is prevented from propagating to the waveguide 23 and the junction between the optical integrated circuit 20 and the optical fiber on the light source side. .

FIG. 4 shows a third example of the present invention. This example is a combination of the first example of FIG. 1 and the second example of FIG. According to this example, the groove 5 is formed on the upper surface 20B of the optical integrated circuit 20.
6A, 56B, 57A, 57B, 58 are formed, and the main waveguide 23 extends meandering between the grooves 56A, 56B, 57A, 57B and is curved in an S shape.

Four grooves 56A, 56B, 57A, 57B
Of these, the two grooves 56A and 57A are the same as the grooves shown in FIG. 1 and are essential, but the other two grooves 56B and 57B.
Is not always required and may be omitted. Y branch 26
The groove 58 on the rear side of is similar to the example shown in FIG.
Further, the inside of the grooves 56, 57, 58 may be filled with a light shielding material.

Four grooves 56A, 56 on both sides of the waveguide 23
B, 57A, 57B and the groove 58 on the rear side of the Y-branch 26, the radiation mode light P ₁ described with reference to FIG.
P ₂ and the radiation mode lights Q ₁ , Q described with reference to FIG.
₂ is cut off.

An example of an optical fiber gyro according to the present invention and an optical integrated circuit used therein will be described with reference to FIGS. The optical fiber gyro according to this example is different from the optical fiber gyro of the type including the conventional beam splitter 10 described with reference to FIG. 22 in a light shielding device at the front end (end on the light source side) of the optical integrated circuit 20. Alternatively, the structure may be different, and the other structures may be the same. Therefore, in FIG. 5 to FIG. 14, components other than the optical integrated circuit 20 and the light shielding device or structure are omitted. Further, on the upper surface 20B of the optical integrated circuit 20, as shown in FIG. 22, the phase modulator 2 is provided in two branches of the Y branch 26.
7, 28 are provided, but they are omitted in FIGS.

FIG. 5 shows a fourth example of the present invention. According to this example, the front end face 20A of the optical integrated circuit 20 is coated with the light shielding film 51. The light shielding film 51 is formed with a small window 51A for passing the light propagated through the waveguide 23.

Referring to FIG. 6, the light shielding film 51 of the example of FIG.
An example of a method of forming the will be described. The light shielding film 51 of this example may be formed by a metal thin film forming method known in the semiconductor manufacturing technology. As shown in FIG. 6A, first, the optical integrated circuit 20
6B, a resist film 111 is applied to the front end face 20A thereof, and then, as shown in FIG.
3 is propagated in the direction of the front end face 20A of the optical integrated circuit 20. As a result, the portion 111A of the resist film 111 that covers the exposed end face of the waveguide 23 is exposed.
Next, as shown in FIG. 6C, the resist film 111 is developed to remove portions of the resist film 111 other than the exposed portions 111A.

Next, as shown in FIG. 6D, the optical integrated circuit 2
On the front end face 20A of 0, a metal thin film 11 of chromium, titanium, etc.
2 is formed into a film. The film forming method includes spattering, vacuum deposition and the like. Finally, as shown in FIG. 6E, the optical integrated circuit 2
The resist film 111A remaining on the front end face 20A of 0 is removed. As a result, the light shielding film 51 having the window 51A is formed on the front end face 20A of the optical integrated circuit 20.

In the example shown in FIGS. 7 and 8, the optical integrated circuit 2
The light shielding plate 52 is arranged on the front end face 20A of 0.
The light shielding plate 52 shown in FIG. 7 is formed by applying a light shielding film on the surface of a plate made of a transparent material, for example, a glass plate, and the light shielding film is provided for passing the light propagated through the waveguide 23. A small window 52A is formed. The light shield plate 52 shown in FIG. 8 is formed of a plate made of a light shield material, and has a small cutout window 52B for passing the light propagated through the waveguide 23.

According to this example, the Y branch 2 of the optical integrated circuit 20 is
Even if the radiation mode lights A and B are generated at 6, the radiation mode light is blocked and removed by the light blocking film 51 or the light blocking plate 52 at the front end face 20A of the optical integrated circuit 20. Therefore, only the interference light propagating through the waveguide 23 is transmitted through the windows 51A, 52A, 5
It is guided to the beam splitter 10 through 2B.

Next, the dimensions of the light shielding film 51 or the light shielding plate 52 and the windows 51A, 52A and 52B thereof will be described.
These dimensions are set so that the radiation mode lights A and B appearing on the front end face 20A of the optical integrated circuit 20 can be sufficiently blocked.

As described with reference to FIG. 27, when the distance from the Y-branch 26 to the front end face 20A of the optical integrated circuit 20 is about 6 mm, the emission mode lights A and B are the front end faces 20A of the optical integrated circuit 20. The center positions of the regions 20C and 20D appearing in (1) are 100 to 200 μm below the waveguide 23 and about 100 μm on both sides of the waveguide 23. The regions 20C and 20D of the radiation mode lights A and B each have a depthwise dimension of about 100 μm and a lateral dimension of about 100 to 20 μm.
200 μm.

Therefore, it is sufficient that the light shielding film 51 or the light shielding plate 52 has a length of about 400 μm and a width of about 400 μm. Therefore, as shown in FIG. 5, the light shielding film 51 may be applied to the entire front end face 20A of the optical integrated circuit 20 except the window 51A, but may be applied to a part of the front end face 20A. Good. Similarly, the light shield plate 52 may have the same external dimensions as the front end face 20A of the optical integrated circuit 20, but may have a smaller size.

The diameter of the window 51A of the light shielding film 51 may be about 5 to 50 μm, assuming that the cross-sectional dimension of the waveguide 23 is about 5 μm. Window 52A of the light shielding plate 52,
The diameters H _Y and W _X of 52B may be larger than the cross-sectional dimension of the waveguide 23 and may be about 5 to 50 μm.

FIG. 9 shows a seventh example of the present invention. According to this example, the light shielding film 51 is formed on the front end face 20A of the optical integrated circuit 20, and the light shielding plate 52 is further arranged. The light shielding film 51 has a band-shaped light transmitting portion along the upper edge, that is, a window 51C. The light shielding plate 52 has a vertically long and slender window 52C.

By overlapping the light shielding plate 52 on the light shielding film 51, the common portion of the window 51C of the light shielding film 51 and the window 52C of the light shielding plate 52 becomes a substantial window. The window 51C of the light shielding film 51 has a strip shape extending along the upper edge of the front end face 20A of the optical integrated circuit 20, and shields most of the radiation mode light propagating through the front end of the optical integrated circuit 20. However, the radiation mode light along the upper surface 20B of the optical integrated circuit 20 cannot be completely blocked. Window 5 of light shielding film 51
The radiation mode light that has passed through 1C is blocked and removed by the light blocking plate 52.

As described above, by stacking the light shielding plate 52 on the light shielding film 51 as in this example, the radiation mode light is almost completely shielded like the light shielding film 51 of the fourth example shown in FIG. Therefore, only the interference light propagating through the waveguide 23 is guided to the beam splitter 10.

An eighth example of the present invention will be described with reference to FIG. According to this example, the inclined surface 5 is formed on the front end surface 20A of the optical integrated circuit 20.
3 is provided, and the light shielding plate 52 is further mounted. The inclined surface 53 is formed leaving a strip-shaped portion 53C along the upper edge of the front end surface 20A of the optical integrated circuit 20. The strip-shaped portion 53C corresponds to the window 51C of the seventh example in FIG. 9 and has the same dimensions as the window 51C.

As shown in the figure, the light shield plate 52 has the inclined surface 5
It may be mounted on the support members 54A and 54B mounted on both sides of the sheet. The light shielding plate 52 has a vertically long and slender window 52C. The light shield plate 52 of this example may be the same as the light shield plate 52 used in the seventh example of the present invention in FIG. 9.

The inclined surface 53 is a total reflection surface for radiation mode light. The radiation mode light propagated to the front end of the optical integrated circuit 20 is totally reflected by the inclined surface 53, and the beam splitter 1
0 and the light receiver 102 (FIG. 22) are never reached. Therefore, the inclined surface 53 constitutes a light shielding device or structure similarly to the light shielding film.

The inclination angle of the inclined surface 53 will be described. It is assumed that the radiation mode light propagating to the front end of the optical integrated circuit 20 is parallel to the upper surface 20B of the optical integrated circuit 20. The inclined surface 53 is provided on the upper surface 20B of the optical integrated circuit 20 so that radiation mode light parallel to the upper surface 20B of the optical integrated circuit 20 is totally reflected.
Is inclined with a predetermined inclination angle θ ₁ .
The inclination angle θ ₁ of the inclined surface 53 with respect to the upper surface 20B of the optical integrated circuit 20 is equal to the incident angle of the radiation mode light. The condition for total reflection is expressed as follows.

[0105]

[Equation 3] θ ₁ ≧ sin ⁻¹ (n ₁ / n ₂ )

Here, n ₂ is the refractive index of the substrate of the optical integrated circuit 20, and n ₁ is the refractive index of air. When lithium niobate is used as the substrate of the optical integrated circuit 20, n ₂ =
2.2, assuming that the refractive index of air is n ₁ = 1.0, θ ₁ ≧
It becomes 27 °. Therefore, the inclination angle θ ₁ of the inclined surface 53 is changed to θ ₁
= 30 ° may be used.

Similar to the example of FIG. 9, by overlapping the light shielding plate 52 on the inclined surface 53, the common portion of the window 53C of the inclined surface 53 and the window 52C of the light shielding plate 52 becomes a substantial window.
By overlapping the light shielding plate 52 on the inclined surface 53, the radiation mode light can be almost completely shielded, and only the interference light propagating through the waveguide 23 is guided to the beam splitter 10.

On the front end face 20A of the optical integrated circuit 20, as shown in the drawing, the X axis is taken in the width direction and the Y axis is taken in the depth direction. The vertical width of the window 51C of the light shielding film 51 and the window 53C of the inclined surface 53, that is, the upper surface 2 of the optical integrated circuit 20.
The dimension h from 0B may be at least larger than the depth dimension of the cross section of the waveguide 23, and may be, for example, several to several tens of μm.

The dimension W _X of the window 52C of the light shielding plate 52 in the lateral direction (X-axis direction) is slightly larger than the dimension of the cross section of the waveguide 23 in the width direction, and may be several to several tens of μm. Also,
The dimension H _Y of the window 52C in the vertical direction (Y-axis direction) may be sufficiently larger than the width h of the window 51C of the light shielding film 51 or the window 53C of the inclined surface 53.

In the example shown in FIGS. 9 and 10, the light blocking device or structure includes two parts. In the seventh example of FIG. 9,
The light shielding film 51 and the light shielding plate 52 are included, and in the eighth example of FIG. 10, the light inclined surface 53 and the light shielding plate 52 are included. Therefore, as compared with the case of the example of FIGS. 5 to 8, there are more components of the light shielding device or structure. However, the examples shown in FIGS. 9 and 10 have the advantage that the manufacturing and alignment operations of the light shielding device or structure are easier.

In the seventh example of FIG. 9, the window 5 of the light shielding film 51 is used.
1C has a strip shape, and the light shielding film 51 has a rectangular shape. Therefore, as compared with the case of the light shielding film 51 having the small window 51A as in the case of the fourth example of FIG. 5, the manufacturing process of the light shielding film 51 is simpler. Further, as in the eighth example of FIG. 10, in order to form the inclined surface 53, the triangular columnar portion 53 ′ (FIG. 12) shown by the broken line from the rectangular parallelepiped optical integrated circuit 20 is formed.
Can be removed, and the manufacturing process can be shortened.

The dimension H _Y of the window 52C of the light shield plate 52 in the vertical direction (Y-axis direction) is formed sufficiently large so that alignment work in the Y-axis direction is unnecessary. After all, when mounting the light shielding plate 52 on the front end face 20A of the optical integrated circuit 20, only the alignment work in the X-axis direction is required.
Alignment in the X-axis direction may be performed by moving the light shielding plate 52 in the X-axis direction, monitoring the output of the light receiver 102, and detecting the position where the output of the light receiver 102 is maximized.

FIG. 11 shows a ninth example of the present invention. According to this example, the light shielding film 51 is formed on the front end face 20A of the optical integrated circuit 20.
And a groove 56 is formed on the upper surface 20B of the optical integrated circuit 20.
A and 56B are formed. The light shielding film 51 is similar to the example shown in FIG. 8 and has a band-shaped light transmitting portion along the upper edge, that is, a window 51C.

The grooves 56A and 56B are arranged at the front end of the optical integrated circuit 20 on both sides of the waveguide 23 and close to the waveguide 23. In the illustrated example, the grooves 56A and 56B are the waveguide 2
Only two pieces are provided on each side of the waveguide 3, but a plurality of pieces may be provided on both sides of the waveguide 23. Also, groove 5
A light shielding material may be filled inside 6A and 56B.

The dimension L _X of the grooves 56A and 56B in the lateral direction (X-axis direction) may be sufficiently large, and is formed so as to extend from a position close to the waveguide 23 to a side edge of the optical integrated circuit 20. You may Width direction of grooves 56A, 56B (Z-axis direction)
The dimension L _Z may be several tens of μm to 1 mm. Groove 5
The depths of 6A and 56B may be formed to be substantially the same as or slightly larger than the outer diameter of the cross section of the waveguide 23 or the width h of the window 51C.

The grooves 56A and 56B have the same function as that of the light shielding plate 52 in the example of FIGS. 9 and 10. The window 51C of the light shielding film 51 has a strip shape extending along the upper edge of the front end face 20A of the optical integrated circuit 20, and shields most of the radiation mode light propagating through the front end of the optical integrated circuit 20. However, the radiation mode light along the upper surface 20B of the optical integrated circuit 20 cannot be completely blocked.

Radiation mode light along the upper surface 20B of the optical integrated circuit 20 is blocked by the grooves 56A and 56B. The light that has propagated below the grooves 56A and 56B is blocked by the light blocking film 51. Therefore, in this example, the radiation mode light can be shielded almost completely.

The trenches 56A and 56B may be formed by a well-known fine processing method used in the manufacture of semiconductor devices. For example, it may be manufactured by forming a metal foil pattern in advance on the portions where the grooves 56A and 56B are to be formed and scraping off the portions with a laser beam machine.

FIG. 12 shows a tenth example of the present invention. According to this example, the inclined surface 53 is formed on the front end surface 20A of the optical integrated circuit 20.
And a groove 56 is formed on the upper surface 20B of the optical integrated circuit 20.
A and 56B are formed. The inclined surface 53 is similar to the example shown in FIG. 10, and has a band-shaped light transmitting portion along the upper edge, that is, a window 53C.

The grooves 56A and 56B are similar to those of the example shown in FIG. 11, and are arranged on both sides of the waveguide 23 and in the vicinity of the waveguide 23 at the front end portion of the optical integrated circuit 20.

Similar to the example of FIG. 11, the radiation mode light along the upper surface 20B of the optical integrated circuit 20 is blocked by the grooves 56A and 56B. The light propagating under the grooves 56A and 56B is blocked by the inclined surface 53. Therefore, in this example, the radiation mode light can be shielded almost completely.

13 and 14 show the eleventh and twelfth examples of the present invention. According to these examples, the optical integrated circuit 20
The waveguide 23 is curved at the front end thereof. First of FIG.
In the first example, the light shielding film 51 is formed on the front end surface 20A of the optical integrated circuit 20, and the grooves 56A and 57A are further formed on the upper surface 20B of the optical integrated circuit 20. The light shielding film 51 is similar to the example shown in FIG. 9 and has a band-shaped light transmitting portion along the upper edge, that is, a window 51C.

In the twelfth example shown in FIG. 14, the optical integrated circuit 20 is used.
An inclined surface 53 is formed on the front end surface 20A of the optical disk, and grooves 56A and 57A are formed on the upper surface 20B of the optical integrated circuit 20. The inclined surface 53 is similar to the example shown in FIG. 10, and has a band-shaped light transmitting portion along the upper edge, that is, a window 53C.

The relative positional relationship and function between the positions of the grooves 56A and 57A and the curved waveguide 23 have been described with reference to FIG. The dimensions of the grooves 56A and 57A are similar to those in the examples of FIGS. 11 and 12. The grooves 56A and 57A are provided alternately on both sides of the waveguide 23, but the broken line 56A
As shown by B and 57A, plural pieces may be provided on both sides of the waveguide 23. Further, a light shielding material may be filled inside the grooves 56A and 57A.

A thirteenth example of the optical fiber gyro according to the present invention will be described with reference to FIG. In this example, the laminated polarizer 40 is arranged on the front end face 20A of the optical integrated circuit 20. Details of the laminated polarizer 40 will be described later with reference to FIG. In the optical fiber gyro of this example, as compared with the example of the conventional optical fiber gyro shown in FIG. 22, the optical integrated circuit 20 is a proton exchange type, and the polarizer 40 is provided on the front end face 20A of the optical integrated circuit 20. Is different,
The other configurations may be the same.

The polarizer 40 may provide a suitable polarizing function such as a polarizing plate or a polarizing prism.
It may be a laminated polarizing plate commercially available under the trade name of Lamipol. The laminated polarizing plate will be described with reference to FIG.

Since the proton exchange type waveguide has the function of a polarizer, it is not necessary to provide the optical integrated circuit 20 with a polarizer.
In this example, the laminated polarizer 40 is provided to shield and remove the TM polarized light diffused outside the waveguide of the optical integrated circuit 20. Therefore, the TM fringes diffused from the waveguide cause interference fringes D (FIG. 25) on the front end face 20A of the optical integrated circuit 20.
Even if (reference) is generated, the interference fringe D is absorbed by the laminated polarizer 40 and removed. Therefore, the waveguide 2
Of the interference light propagating through No. 3, only the TE polarized light is guided to the beam splitter 10. The thirteenth example of FIG. 15 is a modification of the example shown in FIG. 16B later, and details of the operation are omitted here.

A fourteenth example of the optical fiber gyro according to the present invention will be described with reference to FIG. 16A and FIG.
The optical fiber gyro shown in B is a light source 101 and a light receiver 10.
2, a beam splitter 10, a proton exchange type optical integrated circuit 20, polarizers 40 and 40, optical fiber type depolarizers 31 and 32, and a single mode optical fiber loop 103.

On the upper surface of the optical integrated circuit 20, a waveguide 23, a Y branch 26 composed of the waveguide and each branch 26A of the Y branch 26,
The phase modulators 27 and 28 arranged on both sides of 26B are formed. The second phase modulator 28 may be a serrodyne phase modulator. The optical integrated circuit 20 of this example is a proton exchange type, and since the waveguide has a function of a polarizer, it is not necessary to provide a separate polarizer 104 in the optical integrated circuit 20.

According to this example, the TM polarized light which produces the interference fringe D on the front end face 20A of the optical integrated circuit 20 as shown by the broken line C in FIG. 25 is absorbed by the polarizers 40, 40 and removed. Therefore, the interference fringe D is not generated on the front end face 20A of the optical integrated circuit 20. The TM polarized light has a polarization plane perpendicular to the upper surface of the integrated circuit 20, and
0 is configured to remove only such TM polarized light.

In the example shown in FIG. 16A, the polarizers 40, 40
Is an optical fiber end (pig tail) 36 of the connection device 35,
37 and the optical fiber type depolarizers 31 and 32. In the example shown in FIG. 16B, the polarizers 40, 40
Are inserted into the optical fiber ends (pig tails) 36 and 37 in the connection device 35.

The polarizers 40, 40 may be those which provide an appropriate polarizing function such as polarizing plates or polarizing prisms, and may be, for example, laminated polarizing plates commercially available under the trade name of Lamipol.

Light from the light source 101 is emitted from the beam splitter 1
Is guided to the waveguide 23 of the optical integrated circuit 20 via 0, and Y
Reach branch 26. The propagating light is split into two at the Y branch 26. One light propagates clockwise in the optical fiber loop 103 via the first branch 26A and the optical fiber end 36, and the other light propagates in the second branch 26B and the optical fiber end 37.
Propagates counterclockwise through the optical fiber loop 103 via

The light emitted from the optical integrated circuit 20 is linearly polarized by the polarization function of the proton exchange type optical integrated circuit 20, and circularly polarized by the depolarizers 31 and 32, respectively. The circularly polarized light propagates right and left in the optical fiber loop 103, and the optical integrated circuit 20
to go into. Such light is transmitted to the polarizer 4 in front of the optical integrated circuit 20.
The TM polarized light is removed by 0 and 40, and the TE polarized light only becomes linearly polarized light. Therefore, the optical integrated circuit 2 as shown in FIG.
The interference fringe D is not generated on the front end face 20A of 0.

Such linearly polarized light is combined by the Y branch 26 to generate interference light. Such interference light is guided to the beam splitter 10 via the waveguide 23, and the light receiver 1
Detected by 02.

The configuration and operation of the laminated polarizer 40 will be described with reference to FIG. The laminated polarizer 40 has excellent characteristics such as a high extinction ratio, a small light loss, a small size in the optical path direction, a stable function, and excellent mass productivity. The laminated polarizer 40 is typically
A metal layer 40A having a thickness L _M of several nm and a thickness L _D of several hundred nm
Of dielectric layers 40B alternately.

As shown, three orthogonal axes are set on the laminated polarizer 40. The X axis and the Z axis are taken on the plane parallel to the metal layer 40A and the dielectric layer 40B, and the Y axis is taken in the thickness direction of the layers 40A and 40B. Each of the layers 40A and 40B is formed in a substantially rectangular shape, and the X axis is in the long side direction and the Z axis is in the short side direction of the rectangle. The thickness t of the laminated polarizer 40 in the Z-axis direction
Is typically t = about 30 μm or less.

The laminated polarizer 40 has its layers 40A and 40A.
B (that is, the XZ plane) is arranged to be parallel to the optical path 100, and preferably the Z axis is arranged to be parallel to the optical path 100. Layers 40A and 40 of stacked polarizer 40
When B (that is, the YZ plane) is arranged to be inclined with respect to the optical path 100, the optical loss becomes large.

The laminated polarizer 40 has an absorption-type polarization function of transmitting the polarized light having the polarization plane in the Y-axis direction and absorbing the polarized light having the polarization plane in the X-axis direction among the incident light. For example, of the incident light, TE polarized light has a polarization plane in the Y-axis direction and
The M-polarized light has a plane of polarization in the X-axis direction. TE polarized light is transmitted and TM polarized light is absorbed.

The structure of the connection device 35 of this embodiment will be described with reference to FIG. As shown in FIG. 18A, the connection device 35 of this example is a substrate 3 having a V-groove 35A formed on the upper surface 35B.
Including 5C. As shown in FIG. 18B, an optical fiber end (pig tail) 36 is arranged in the V groove 35A.

FIG. 18C shows the connection device 35 of the example shown in FIG. 16B. In this example, the laminated polarizer 40 is arranged so as to traverse the optical fiber end (pig tail) 36. A method of manufacturing the connection device 35 of this example will be described. First, as shown in FIG. 18B, the optical fiber end (pig tail) 36 is arranged in the V groove 35A and is bonded by an appropriate method.
Next, a groove is formed so as to cross the optical fiber end (pig tail) 36, and the laminated polarizer 40 is inserted into the groove. The laminated polarizer 40 is arranged in an orientation that absorbs and removes TM polarized light.

Still another example of the optical fiber gyro of the present invention will be described with reference to FIG. According to the optical fiber gyro of this example, since the optical integrated circuit 20 is a titanium diffusion type and the waveguide does not have the function of a polarizer, the optical integrated circuit 20 is provided with the polarizers 104A and 104B. Such a polarizer may be, for example, a metal loaded type made of an aluminum (Al) thin film.

The optical fiber gyro of this example is different from the fourteenth example of the present invention shown in FIG. 16 in that the titanium diffusion type optical integrated circuit 2 is used instead of the proton exchange type optical integrated circuit 20.
0 is used, and instead of providing the polarizers 40, 40, metal-loaded polarizers 104A, 104B are provided in the optical integrated circuit 20.
Is different. The other configurations may be the same.

The operation of the optical fiber gyro of this example will be described. The light from the light source 101 is beam splitter 10
Is guided to the waveguide 23 of the optical integrated circuit 20 via. Such light is linearly polarized by the polarizer 104A, circularly polarized by the Y branch 26 and the depolarizers 31 and 32, and guided to the single mode optical fiber loop 103.

The circularly polarized propagating light emitted from the optical fiber loop 103 is the polarizers 104 A and 104 of the optical integrated circuit 20.
The TM polarized light is removed by B, and the TE polarized light only becomes linearly polarized light. Such linearly polarized light is combined by the Y branch 26 to generate interference light. Such interference light is guided to the beam splitter 10 via the waveguide 23, and is further received by the light receiver 102.
Is detected by

Thus, according to this example, the light emitted from the optical fiber loop 103 is reflected by the polarizers 104A, 1A of the optical integrated circuit 20.
Since TM polarized light is removed by 04B and only TE polarized light becomes linearly polarized light, the interference fringe D is not generated on the front end face 20A of the optical integrated circuit 20.

Another example of the present invention will be described with reference to FIG. FIG. 20 shows the light source 101, the light receiver 102, the beam splitter 10, and the front end of the optical integrated circuit 20 of the optical fiber gyro. According to this example, shield plates 102A and 102B are arranged around the light receiver 102. Although the rear end portion of the optical integrated circuit 20 and the optical fiber loop portion are omitted in FIG. 20, the optical fiber loop is composed of a single mode or polarization maintaining optical fiber. The optical integrated circuit 20 may be either a proton exchange type or a titanium diffusion type.

The shield plates 102A and 102B function so as to block the leaked light reaching the light receiver 102 directly from the light source 101. Therefore, the light receiver 102 is the beam splitter 1
Only the interference light passing through 0 is detected. Thus, according to the optical fiber gyro of this example, the light receiver 102 is the light source 101.
Since the leaked light reaching the light receiver 102 directly or indirectly from the light source 101 is not detected, unlike the conventional example, the light source 101
There is no DC bias in the output signal of the photodetector 102 due to the leaked light. Therefore, D of the first stage amplifier
The C amplification factor can be increased, and a gyro signal with less noise can be obtained.

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

[0150]

The present invention has the advantage that radiation mode light propagating along the top surface of an optical integrated circuit can be blocked by a relatively simple method and structure.

According to the present invention, since the light shielding film or the light shielding plate is provided on the front end face of the optical integrated circuit, the error light of the radiation mode light generated on the front end face of the optical integrated circuit is shielded. Such an error light is not detected by the light receiver, and there is an advantage that a fixed bias and a scale factor error of the output signal of the light receiver do not occur due to the fluctuation of the error light.

According to the present invention, the manufacturing process and the alignment work of the light shielding device are easy and can be performed in a short time, so that there is an advantage that the manufacturing process of the optical fiber gyro can be shortened.

According to the present invention, when the light shielding device is mounted on the front end portion of the optical integrated circuit, the alignment work is extremely easy and can be performed in a short time, so that the manufacturing process of the optical fiber gyro can be shortened. It has the advantage that

According to the present invention, there is an advantage that the radiation mode light can be almost completely blocked by appropriately combining and using a plurality of light shielding devices.

According to the present invention, there is an advantage that the light shielding device can be formed only by machining such as cutting.

According to the present invention, a polarizer is provided between the proton exchange type optical integrated circuit and the depolarizer, whereby the TM polarized light is removed from the light emitted from the optical fiber loop and the light guided to the optical integrated circuit is TE. Since only the polarized light is used, there is an advantage that no interference fringes are generated on the front end face of the optical integrated circuit and an error is not generated in the output signal of the optical receiver due to the fluctuation of the interference fringes.

According to the present invention, the titanium-diffused optical integrated circuit is provided with the metal-bearing-type polarizer, whereby the TM polarized light is removed from the light exiting the optical fiber loop, and the guided light to the optical integrated circuit is Since only TE polarized light is used, no interference fringe is generated on the front end face of the optical integrated circuit, and there is an advantage that an error does not occur in the output signal of the optical receiver due to the variation of the interference fringe. .

According to the present invention, in an optical fiber gyro having a beam splitter, an optical integrated circuit, a single mode optical fiber loop and a depolarizer, it is possible to remove interference fringes generated on the front end face of the optical integrated circuit with a simple device. There are advantages.

[Brief description of drawings]

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

FIG. 2 is an explanatory diagram showing a relationship between a curved waveguide and a groove of the optical integrated circuit of the optical fiber gyro of FIG.

FIG. 3 is a diagram showing a second example of the optical fiber gyro of the present invention.

FIG. 4 is a diagram showing a third example of the optical fiber gyro of the present invention.

FIG. 5 is an explanatory diagram showing a fourth example of the optical fiber gyro of the present invention.

FIG. 6 is an explanatory diagram showing an example of a method of forming a light shielding film.

FIG. 7 is an explanatory diagram showing a fifth example of the optical fiber gyro of the present invention.

FIG. 8 is an explanatory diagram showing a sixth example of the optical fiber gyro of the present invention.

FIG. 9 is an explanatory diagram showing a seventh example of the optical fiber gyro of the present invention.

FIG. 10 is an explanatory diagram showing an eighth example of the optical fiber gyro of the present invention.

FIG. 11 is an explanatory diagram showing a ninth example of the optical fiber gyro of the present invention.

FIG. 12 is an explanatory diagram showing a tenth example of the optical fiber gyro of the present invention.

FIG. 13 is an explanatory diagram showing an eleventh example of an optical fiber gyro of the present invention.

FIG. 14 is an explanatory diagram showing a twelfth example of the optical fiber gyro of the present invention.

FIG. 15 is an explanatory diagram showing a thirteenth example of the optical fiber gyro of the present invention.

FIG. 16 is an explanatory diagram for explaining a fourteenth example of the optical fiber gyro of the present invention.

FIG. 17 is an explanatory diagram for explaining the structure of a laminated polarizer used in the optical fiber gyro of the present invention.

FIG. 18 is an explanatory diagram for explaining the structure of the optical fiber gyro connection device of the present invention.

FIG. 19 is an explanatory diagram for explaining a modified example of the fifteenth example of the optical fiber gyro of the present invention.

FIG. 20 is an explanatory diagram for explaining a structural example of a light receiver of the optical fiber gyro of the present invention.

FIG. 21 is a diagram showing an example of a conventional optical fiber gyro.

FIG. 22 is a diagram showing another example of a conventional optical fiber gyro.

FIG. 23 is an explanatory diagram for explaining radiation mode light generated on the upper surface of the optical integrated circuit.

FIG. 24 is an explanatory diagram for explaining radiation mode light generated on the upper surface of the optical integrated circuit.

FIG. 25 is an explanatory diagram for explaining radiation mode light generated on the upper surface of the optical integrated circuit of the optical fiber gyro of FIG. 22.

FIG. 26 is an explanatory diagram for explaining that radiation mode light is generated in the Y branch of the optical integrated circuit.

FIG. 27 is an explanatory diagram for explaining a state in which radiation mode light appears on the end surface of the optical integrated circuit.

[Explanation of symbols]

 10 Beam Splitter 11 Half Mirror 12, 13 Condenser Lens 20 Optical Integrated Circuit 20A Front End Facet 20B Top Surface 23 Waveguide 26 Y Branch 27, 28 Phase Modulator 31, 32 Depolarizer 35 Connection Device 36, 37 Optical Fiber End 51 Light Shielding Film 51A, 51C window 52 light shielding plate 52A, 52B, 52C window 53 inclined surface 53C window 54A, 54B support member 56, 57, 58 groove 101 light source 102 light receiver 103 optical fiber loop 104A, 104B polarizer 105, 106 coupler 107 current Voltage converter 108, 108 'Phase modulator 109 Signal generator 110 Synchronous detector 115 Optical integrated circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ryuichiro Sasaki 2-16-46 Minami-Kamata, Ota-ku, Tokyo Within Tokimec Co., Ltd. (72) In-house Kensuke Masushima 2-chome 46, Minami-Kamata, Ota-ku, Tokyo No. Within Tokimec Co., Ltd. (72) Ryohiro Cho, Inventor 2-16-46 Minami Kamata, Ota-ku, Tokyo Within Tokimec Co., Ltd.

Claims (26)

[Claims] 1. An optical integrated circuit having a light source and a Y branch for branching or synthesizing light, an optical fiber loop for propagating two lights emitted from the optical integrated circuit, and an interference light emitted from the optical integrated circuit. In an optical fiber gyro having a photodetector for detecting, the Y branch includes a main waveguide and two branch waveguides connected thereto, and the optical integrated circuit is provided with grooves on both sides of the main waveguide, respectively. The grooves are alternately arranged so as to overlap each other so as to block a propagation path of radiation mode light propagating through the substrate of the optical integrated circuit, and the main waveguide is curved and extends so as to pass between the grooves. An optical fiber gyro characterized by being present. 2. The optical fiber gyro according to claim 1, wherein a groove is provided on the upper surface of the optical integrated circuit between the two branch waveguides, and the groove is provided at an end portion of the two branch waveguides. An optical fiber gyro arranged so as to prevent the generated radiation mode light from propagating to the main waveguide. 3. An optical integrated circuit having a substrate and a Y-branch formed on the substrate, wherein the Y-branch includes a main waveguide and two branch waveguides connected to the main waveguide, and the Y-branch is provided on each side of the main waveguide. Grooves are provided, the grooves are alternately arranged so as to overlap each other so as to block a propagation path of radiation mode light propagating in the substrate, and the main waveguide is curved so as to pass between the grooves. An optical integrated circuit characterized by being extended. 4. The optical integrated circuit according to claim 3, wherein a groove is provided between the two branch waveguides, and the groove is provided with radiation mode light generated at an end portion of the two branch waveguides. An optical integrated circuit, which is arranged so as to prevent it from propagating to a main waveguide. 5. An optical integrated circuit having a light source and a Y branch for branching or combining the light, an optical fiber loop for propagating two lights emitted from the optical integrated circuit, and an interference light emitted from the optical integrated circuit. In an optical fiber gyro having a beam splitter for deflecting and a photodetector for detecting light from the beam splitter, the light diffused to the outside of the waveguide forming the Y branch is passed through the end face of the optical integrated circuit to An optical fiber gyro, wherein a light shielding device is provided between the optical integrated circuit and the beam splitter so as not to leak to the beam splitter. 6. The optical fiber gyro according to claim 5, wherein the light shielding device is a light shielding film formed on an end face of the optical integrated circuit. 7. The optical fiber gyro according to claim 5, wherein the light shielding device is a light shielding plate arranged on an end face of the optical integrated circuit. 8. The optical fiber gyro according to claim 5, wherein the light shielding device has a window for propagating interference light from the main waveguide. 9. The optical fiber gyro according to claim 8, wherein the diameter of the window is several times to 20 times the diameter of the main waveguide. 10. An optical integrated circuit having a light source and a Y branch for splitting or combining light, an optical fiber loop, a beam splitter for deflecting interference light emitted from the optical integrated circuit, and a light from the beam splitter. In a fiber optic gyro having a photodetector for detection, a light shielding film is attached to a front end face of the optical integrated circuit facing the beam splitter, except for a band-shaped light transmitting portion along an upper edge. An optical fiber gyro, wherein the width of the optical part has a dimension corresponding to the depth dimension of the cross section of the waveguide of the optical integrated circuit. 11. The optical fiber gyro according to claim 10, wherein a light shielding plate having a window is attached to a front end face of the optical integrated circuit, and a width of the window in a lateral direction is a waveguide of the optical integrated circuit. An optical fiber gyro having a dimension corresponding to a lateral width dimension of a cross section, and a vertical width of the window being sufficiently larger than a depth dimension of a cross section of a waveguide of the optical integrated circuit. 12. The optical fiber gyro according to claim 10, wherein a groove is formed on the upper surface of the optical integrated circuit on both sides of the waveguide and in the vicinity of the waveguide, and the depth of the groove. An optical fiber gyro having dimensions corresponding to a depth of a cross section of a waveguide of the optical integrated circuit. 13. The optical fiber gyro according to claim 12, wherein the grooves are arranged in a staggered and overlapping manner so as to block a propagation path of radiation mode light propagating outside the waveguide, and the waveguides are arranged. An optical fiber gyro, wherein the groove extends between the grooves in a curved manner. 14. The optical fiber gyro according to claim 12 or 13, wherein the groove is formed by a laser processing method. 15. A light source, an optical integrated circuit having a Y branch for splitting or combining light, an optical fiber loop, a beam splitter for deflecting interference light emitted from the optical integrated circuit, and a light from the beam splitter. In an optical fiber gyro having a photodetector for detecting, an inclined surface is formed on a front end surface of the optical integrated circuit facing the beam splitter, except for a belt-shaped light transmitting portion along an upper edge, and the inclined surface Is inclined at a predetermined angle with respect to the upper surface of the optical integrated circuit so as to totally reflect radiation mode light parallel to the upper surface of the optical integrated circuit, and the width of the light transmitting portion is the waveguide of the optical integrated circuit. An optical fiber gyro having a dimension corresponding to a depth dimension of a cross section of the optical fiber gyro. 16. The optical fiber gyro according to claim 15, wherein a light shielding plate having a window is attached to a front end surface of the optical integrated circuit, and a width of the window in a lateral direction is a waveguide of the optical integrated circuit. An optical fiber gyro having a dimension corresponding to a lateral width dimension of a cross section, and a vertical width of the window being sufficiently larger than a depth dimension of a cross section of a waveguide of the optical integrated circuit. 17. The optical fiber gyro according to claim 15 or 16, wherein grooves are formed on the upper surface of the optical integrated circuit on both sides of the waveguide and in proximity to the waveguide, and the depth of the groove. An optical fiber gyro having dimensions corresponding to a depth of a cross section of a waveguide of the optical integrated circuit. 18. The optical fiber gyro according to claim 17, wherein the grooves are arranged in a staggered and overlapping manner so as to block a propagation path of radiation mode light propagating outside the waveguide, and the waveguides are arranged. An optical fiber gyro, wherein the groove extends between the grooves in a curved manner. 19. The optical fiber gyro according to claim 17 or 18, wherein the groove is formed by a laser processing method. 20. A light source and a Y for splitting or combining light
An optical integrated circuit having a branch, a single mode optical fiber loop for propagating two lights emitted from the optical integrated circuit, a depolarizer connected between the optical integrated circuit and the optical fiber loop, and an optical integrated circuit emitted from the optical integrated circuit In an optical fiber gyro having a beam splitter for deflecting interference light and a light receiver for detecting light from the beam splitter, the optical integrated circuit is a proton exchange type, and TM polarized light propagating in a waveguide of the optical integrated circuit is used. An optical fiber gyro, which is provided with a polarizer for removal. 21. The optical fiber gyro according to claim 20, wherein a connection device is provided between the optical integrated circuit and the depolarizer, and the connection device is arranged in a V groove formed on the upper surface of the substrate and the V groove. An optical fiber gyro having a closed optical fiber end. 22. The optical fiber gyro according to claim 21, wherein the polarizer is arranged in the connection device. 23. The optical fiber gyro according to claim 21, wherein the polarizer is arranged between the optical integrated circuit and the beam splitter. 24. The optical fiber gyro according to claim 20, 21, 22 or 23, wherein the polarizer is a laminated polarizer. 25. A light source and a Y for splitting or combining light
An optical integrated circuit having a branch, an optical fiber loop for propagating two lights emitted from the optical integrated circuit, a beam splitter for deflecting interference light emitted from the optical integrated circuit, and a light receiver for detecting the light from the beam splitter An optical fiber gyro having a shield plate is provided so as to surround the light receiver, and the shield plate is configured to prevent light leaking from the light source from reaching the light receiver. An optical fiber gyro characterized by. 26. Y for splitting or combining a light source and light
An optical integrated circuit having a branch, an optical fiber loop for propagating two lights emitted from the optical integrated circuit, a beam splitter for deflecting interference light emitted from the optical integrated circuit, and a light receiver for detecting the light from the beam splitter And a first polarizer for polarizing light propagating from the light source to the optical fiber loop, and the optical integrated circuit from the optical fiber loop. And a second polarizer that polarizes light propagating to the optical fiber gyro.