JPH0694465A - Optical wave guide and ring interferometer - Google Patents

Abstract

PURPOSE:To form a one corresponding to a fiber coil with one base, integrate optical members and reduce cost by forming a plurality of circular optical paths different in diameter so that those having larger diameters include those having smaller diameters, and adjacent optical paths are not concentric but partly situated in positions close to each other. CONSTITUTION:A circular optical path II is provided on the inside of the most outside optical path I, an optical path III on the inside thereof, and an optical path IV further on the inside thereof, whereby an optical wave guide is formed to be an aggregate of a number of eccentric optical paths. The optical paths I, II or the optical paths II, III have an evanescent coupling part A or B, respectively. For example, a right-handed light CW advances in the optical path I from an end part (a), enters the optical path II from the evanescent coupling part A, further enters the optical path III in the evanescent coupling part B. Since the coupling efficiency is 100%, the light is perfectly exchanged in two optical paths, turned clockwise in the optical path III, returned again to the optical path II, and returned to the optical path I in the point A through the optical path II, reaching an end part (b). Since the light reaching the inside goes out to the outside again, thus, no intersection is present.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide used in an optical device which requires a circular optical path with a large number of turns, as represented by an optical fiber gyro. In particular, the present invention relates to an optical waveguide having a large number of turns of a circular optical path, which has high mass productivity and can be manufactured at low cost. Further, it relates to a ring interferometer using this optical waveguide path.

[0002]

2. Description of the Related Art A conventional technique will be described by taking a fiber coil of an optical fiber gyro as an example. The optical fiber gyro is a sensor that propagates light to the left-handed light and the right-handed light in an optical fiber wound in a coil shape many times, and detects the angular velocity of the fiber coil from the difference in the propagation time of both lights. The propagation time difference between the two lights is obtained from the interference light intensity of the two lights having different phases depending on the light receiving element. The phase difference φ of the clockwise light and the counterclockwise light is relative to the angular velocity Ω of the fiber coil,

Φ = (4πLaΩ / cλ) (1)

There is a relationship of Here, c is the speed of light, λ is the wavelength of light, L is the fiber length of the fiber coil, and a is the radius of the coil. For the same angular velocity, the larger 4πLa / cλ, the larger the phase difference φ and the greater the sensitivity. The detection sensitivity can be increased by increasing this coefficient. c is the speed of light and is a constant. Since λ is the wavelength of light, it can be lowered, but if a practically advantageous semiconductor light source is used, the range of λ is also determined.

Only the fiber length L or the radius a of the coil can be easily changed as a design condition. However, the coil radius a affects the size of the entire device. If the radius of the fiber coil is large, the size of the entire device becomes large. There is a problem when it is necessary to downsize the device. The length of the fiber L is increased by increasing the number of turns, and the size of the entire device is not increased. However, the fact that the fiber length is long means that the fiber is used a lot, which increases the cost.

In order to solve this problem, it has been proposed that a spiral continuous optical waveguide equivalent to a fiber coil is two-dimensionally provided on the substrate. Since it is a two-dimensional optical waveguide, it can be formed by photolithography and does not require an optical fiber. However, since it is a two-dimensional optical waveguide formed on the substrate, it is difficult to take the innermost end to the outside.

For example, in JP-A-64-64283, a spiral optical waveguide is formed on one semiconductor chip, and a light emitting element and a light receiving element are also provided on the same substrate. It is an integrated ring laser gyro. The spiral optical waveguide can be formed on the substrate by photolithography. Since it is made equivalent to a fiber coil, it becomes a continuous spiral optical waveguide. Since it is spiral, the radius changes gradually. The outermost edge with the largest radius and the innermost edge with the smallest radius are created. The innermost optical path must be taken out. For this purpose, an extraction optical path portion is provided which is orthogonal to all the other spiral optical paths. That is, the optical paths intersect each other.

In Japanese Patent Laid-Open No. 1-191803, a spiral continuous optical path that is close to a rectangle is formed on a substrate. Then, the outermost optical path is curved and guided to the center of the spiral to form the innermost optical path and coupler. Also in this case, the outermost optical path is guided inward so as to be orthogonal to all the other spiral optical paths. Again, the optical paths intersect. 2 on the plane
Since they are three-dimensionally formed optical paths, they intersect each other.

Japanese Unexamined Patent Publication No. 2-251189 is also a ring laser gyro in which a spiral optical path is formed on a semiconductor substrate. A light emitting element, a light receiving element, a frequency modulator, a beam splitter, an amplifier and the like are provided. Also in this case, in order to draw out the innermost end of the spiral optical path to the outside, an extraction optical path portion is provided which is orthogonal to the other optical paths from the innermost end. Since it is a two-dimensional optical path, it is unavoidable that there are intersecting optical paths.

Japanese Unexamined Patent Publication No. 61-184417 discloses that a spiral optical path is formed on both sides of a single substrate by photolithography, and a hole is formed at one place inside the spiral, and a high refractive index portion is also provided on the surface to form a surface. The inner ends of the spiral optical paths on the back side are connected by holes. In this way, the internal optical path can be pulled out without crossing the optical paths.

Japanese Unexamined Patent Publication (Kokai) No. 62-247209 is an optical fiber gyro having a spiral optical path formed on a substrate.
This joins the inner end of the spiral optical path to the end of an independent optical fiber and pulls it out by the optical fiber. This avoids the drawback of intersecting optical paths.

Japanese Unexamined Patent Publication No. 1-143914 proposes a ring interferometer in which a two-dimensional spiral optical path is similarly formed on a substrate. Creates a continuous optical path from the outside to the inside like a groove in a record. An independent optical fiber is connected to the inner end. An independent optical fiber is also connected to the outer end. This also does not have the drawback that the optical paths intersect each other.

The above is the prior art relating to the fiber coil. The optical fiber gyro has another demand for integration and one chip. Since the conventional optical fiber gyro is a combination of independent optical components, the cost is inevitably high. One chip is desired. It is possible to form a phase modulator, a polarizer, and a coupler on a substrate in a plane, and an optical fiber gyro as shown in FIG. 6 has been proposed.

This is one in which a polarizer, a phase modulator, a coupler, an optical waveguide and the like are provided on one substrate. However, due to the inability to integrate the fiber coil, this results in many couplings between the fiber and the optical path on the substrate. This is an obstacle to practical use. It is desirable to have few joints.

[0015]

Forming a spiral optical path on a semiconductor or dielectric substrate by photolithography is economically advantageous because it does not require the use of long fibers. Further, if other light receiving elements, light emitting elements, amplifiers, etc. are integrally formed on the substrate, they can be coupled with each other by the optical path formed on the substrate, and the work of assembling independent optical components can be reduced. However, ring interferometers and ring laser gyros that use these continuous spiral optical paths have the following drawbacks.

Japanese Patent Laid-Open Nos. 64-64283 and 1-1
No. 91803, JP-A-2-21189, etc., in order to draw the inner end of the spiral optical path to the outside, an extraction optical path portion orthogonal to all the other optical paths is provided. The orthogonal parts are on the same plane. Since light travels straight, it may be considered that there is no coupling between orthogonal waveguides.

However, this is not the case. Light travels straight only when it propagates in free space. In the waveguide, light is guided in both the oblique direction and the perpendicular direction depending on the shape of the waveguide and the refractive index distribution. In addition, since there is no cladding at the intersection, there is no waveguide function. In this part, light is diffracted and becomes a loss. The smaller the waveguide, the greater the diffraction.

In addition, light coupling occurs between the intersecting waveguides. Part of the light bends at a right angle at the intersection and enters the partner's waveguide. Then, the light components having different optical path lengths are superimposed. This is a serious problem for a device such as an optical fiber gyro or a ring laser gyro that detects the phase of light as a signal element. Light loss due to diffraction scattering weakens the signal light. The mixing of light between the waveguides further adds noise. These reduce the sensitivity of the detector and reduce the S / N ratio. That is, the loss of light and the mixing of light at the intersection are the drawbacks of such a two-dimensional waveguide.

Further, a spiral optical path provided on the front surface and the back surface and coupled by a through hole does not support the design technology enabling such a configuration or the process technology of the three-dimensional waveguide. Since the light travels straight, it is not possible to connect the optical paths above and below the surface with a through hole.
Different from current. This is just an idea.

Japanese Unexamined Patent Publication No. 1-143914 mentions that an optical fiber is directly attached to the inner end of the waveguide, but it is not clear how the optical fiber can be coupled.

Optical fiber gyros have long required long optical fibers. This was one of the reasons for raising the cost. In order to solve this, an attempt is made to provide a spiral optical path on a single semiconductor or dielectric substrate, but this has not been realized due to the drawbacks already mentioned.

According to the present invention, an optical path which does not intersect with each other is formed on a single substrate, and thereby an angular velocity measuring device is constructed. This is called a ring interferometer here since it does not use an optical fiber.

The object of the present invention is to make a fiber coil corresponding to one substrate. Another object is to provide a ring interferometer in which components corresponding to a fiber coil, a light receiving element, a light emitting element, and an amplifier are configured by one substrate.

[0024]

The optical waveguide of the present invention is an optical path formed by providing a high refractive index portion on a substrate which is transparent to light, and has a plurality of circular shapes with different diameters. The optical paths of (1) and (2) have a large diameter and a small diameter, and adjacent circular optical paths are not concentric with each other, but are formed at positions close to each other such that some of them are optically coupled.

FIG. 1 shows the principle of the optical waveguide of the present invention. A plurality of closed circular optical paths with different diameters are arranged so that the larger ones include the smaller ones. The optical paths adjacent to each other are not concentric with each other, but are close enough to each other to evanescently couple at one place. Although it is evanescent coupling, the interval refractive index distribution of the waveguide is determined so that the coupling efficiency is 100% or close to 100%. 100
A coupling efficiency of% means that all light energy is completely exchanged between the two optical waveguides. The outermost optical path is not closed, and both ends are guided to the ends of the substrate.

The individual optical paths need not be strictly circular.
It may be oval. Each curve is a smooth curve, and each one is closed. The circular shape includes an ellipse, an ellipse, etc. in addition to a perfect circle. Since it is easy to form the evanescent joint portion in a straight line portion, an ellipse or an ellipse is more advantageous in terms of producing the evanescent joint portion.

The evanescent joint is also called a distributed joint. Circular optical paths I, II, III, IV, V from the outermost circumference
・ ・I and II are evanescently bound at point A.
II and III are evanescently bound at point B. III and I
V is evanescently coupled at point C. The same applies hereinafter.

[0028]

The operation of the present invention will be described with reference to FIGS.
In FIG. 2, a circular optical path II is provided inside the outermost optical path I, an optical path III is provided inside the circular optical path II, and an optical path IV is provided further inside. The same applies to the following, and the optical waveguide of the present invention is a set of a large number of non-concentric optical paths. Here, the operation will be described by using three optical waveguides. A and B are evanescent coupling portions of I and II optical paths or II optical paths and III optical paths, respectively. The traveling path of light is shown in FIG. All of these are optical waveguides, but individual optical waveguides are called optical paths and are distinguished as optical waveguides as a whole.

The clockwise light (CW) travels along the optical path I from (a), enters the optical path II from the evanescent coupling section A, and further enters the optical path III at the evanescent coupling section B. Coupling efficiency is 10
Since it is 0%, the light is completely exchanged in the two optical paths. Turn right on the optical path III and return to the optical path II again at the point B. This light passes through the optical path II and returns to the optical path I at the point A. And it appears at the end.

The counterclockwise light (CCW) travels along the optical path I from A, enters the optical path II from the evanescent coupling portion A, and further enters the optical path III at the evanescent coupling portion B. Coupling efficiency is 1
Since it is 00%, the light is completely exchanged in the two optical paths. Turn left in the optical path III and return to the optical path II again at the point B.
This light passes through the optical path II and returns to the optical path I at the point A. And it appears at the end.

Actually, there are more optical paths, and the left-handed light and the right-handed light travel from the outside to the inside over the evanescent joint many times. When it reaches the innermost circumference, it proceeds from the inside to the outside through the evanescent joint. Light passes through an optical path about half each. In other words, it goes through a part of the optical path when going from the outside to the inside. This light travels through the rest of this path as it travels from the inside to the outside. In other words, the left-handed light and the right-handed light propagate for one round in every optical path. Such left-handed light and right-handed light propagate in the opposite directions in the exact same optical path. This is a little different from propagating in a continuous spiral optical path, but it can be said that the propagation distances of left-handed light and right-handed light are the same.

The advantage of the optical waveguide comprising the multiple optical paths of the present invention is that there is no intersection. Multiple circular optical paths are formed in a non-concentric manner, but there is no intersection because the large and small ones are always included. In the case of the conventional continuous optical path, there is always an intersection. With N turns, there were N intersections.
However, in the case of the present invention, there is no intersection. The light that reaches the inside also goes out to the outside, thus eliminating the need for an intersection.

The outermost peripheral edges a and b can be provided at the edge of the substrate. This is a structure suitable for coupling with an external optical fiber or coupling with a light emitting element or a light receiving element via a lens.

[0034]

EXAMPLE An example in which a ring interferometer is constructed using the optical waveguide according to the present invention is shown in FIGS. Although it has the same principle as an optical fiber gyro, it is called a ring interferometer because it does not use an optical fiber.

[Example (FIG. 4)] This is an example in which the waveguide of the present invention is used instead of the sensing loop of the conventional optical fiber gyro. In this case, a flat substrate 1 provided with a large number of non-concentric optical waveguides 2 is used instead of a fiber coil. Other elements are the same as the conventional ones. The light emitted from the light source 3 passes through the coupler 4 and the polarizer 5
Through the second coupler 6. Here, the light is divided into two and enters both ends a and a of the optical waveguide 2 on the substrate 1.

The light entering from A propagates in the optical path as clockwise light and travels from the innermost peripheral portion to the outer side through the distributed coupling portions A, B, C, ... . Then, it is emitted from a and passes through the coupler 6 in the opposite direction. Further, the light passes through the polarizer 5 and the coupler 4 and enters the light receiving element 7.

The light entering from (i) propagates in the optical waveguide as counterclockwise light. Then, the light exits from A, passes through the coupler 6, the polarizer 5 and the coupler 4, and enters the light receiving element 7. The counterclockwise light and the clockwise light interfere with each other, and the intensity of the interference light is detected by the light receiving element. Such a principle is similar to that of the conventional optical fiber gyro. The optical fibers 10 to 15 are single mode fibers outside the substrate.

The material of the waveguide may be glass, a semiconductor, a dielectric or the like and is transparent to light. If only a passive optical waveguide is used as in this example, it is preferable to use glass, especially quartz. This is because the waveguide loss is small. Such a waveguide is formed by forming a waveguide pattern using a photolithography technique and locally increasing the refractive index with respect to this pattern.

In the case of a semiconductor substrate, the formation of the refractive index distribution is
Epitaxial growth, diffusion for a dielectric substrate, proton exchange, ion exchange for a glass substrate, and CVD for quartz are suitable. Of course, the refractive index distribution can be formed by using a method other than this.

Next, the sensitivity of the optical waveguide of the present invention can be explained by comparison with the conventional one. The waveguide to be actually formed on the substrate according to the present invention is a weak waveguide. For light with a wavelength of about 1 μm, the waveguide width is 5 to 10 μm. It is the distance of the waveguide of the distributed coupling portion, but the distance is approximately the same as the width of the waveguide although it depends on the length of the coupling. Light energy is here 1
The length of the distributed coupling portion and the optical path interval are determined so that they are exchanged by 100%.

It is necessary to prevent the two optical paths from being coupled except in the distributed coupling section. In this case, the distance between adjacent optical paths should be 25 μm or more. If they are separated by this amount, they will not combine. That is, the radius of the nth optical path counted from the outside is r
_{If n} , then r _n −r _{n + 1} > 25 μm. The sensitivity of an optical fiber gyro is as shown in the following formula.

Φ = (4πLaΩ / cλ) (2)

It is proportional to La. L is the fiber length and a is the radius of the coil. This is the formula when the radii are the same. In the case of a fiber coil, since the thin fiber is wound around a bobbin having a large diameter, the radius is considered to be approximately constant. However, since the two-dimensional optical waveguide is formed in the present invention, the radius differs depending on the optical path. Since the radius of the _nth optical path is r _n , the partial length of this optical path is 2πr _n . The La part of the equation (2) can be replaced as follows.

[0044]

[Equation 3]

N is a number counted from the outside of the optical path. N
Is the number of the innermost optical path. The difference between the radii of adjacent optical paths is Δ
Let r.

Δr = r _n −r _{n + 1} (4)

This need not be constant. Here, let's calculate (3) with a constant value.

[0048]

[Equation 5]

[0049]

[Equation 6]

[0050]

[Equation 7]

The coefficient expression (7) for determining the sensitivity is determined by the radius r ₀ of the outermost optical path, the number N of optical paths, and the radius difference Δr between adjacent optical paths. To increase the sensitivity, the number N of optical paths may be increased. However, since the size of the substrate is limited, in order to increase the number N of optical paths, the optical path width must be narrowed. As described above, the distance between adjacent optical paths must be 25 μm or more for a wavelength of 1 μm. Since the minimum distance between adjacent optical paths is thus limited, the maximum number of optical paths is determined when the size of the substrate is determined.

Photolithography for wafers with diameters on the order of 4 inches is now easy. In this case, the radius r ₀ of the outermost optical path can be set to 50 × 10 ⁻³ m. The maximum number of optical paths N is determined from the size of the substrate and the radius of the innermost peripheral optical path. Assume a minimum bend radius of 10 mm. r _N = 10 × 10 ⁻³ m. The distance Δr between the adjacent optical paths can be set to Δr = 30 μm as the minimum value when the optical path width is 5 μm and the interval is 25 μm. The number of optical paths N is

N = (r ₀ −r _N ) / Δr = 40 × 10 ⁻³ / 30 × 10 ⁻⁶ = 1333 (8)

It becomes N = 1333, r ₀ = 50 × 10
Substituting the value of ^-3 m and Δr = 30 μm into (7),

[0055]

[Equation 9]

It becomes This amount of La can be obtained by an optical waveguide formed on a 4-inch substrate.

A comparison will now be made with the fiber coil of an actual optical fiber gyro. Currently used for automobiles is L = 100 m and a = 65 × 10 ⁻³ m. In this case, the value of La is 6.5 m ² . In comparison with this, it can be seen that the optical waveguide of the present invention has sufficient sensitivity.

[Embodiment (FIG. 5)] FIG. 5 shows a second embodiment of the present invention.
An example of is shown. This is one in which a phase modulator and a polarizer are also integrally manufactured on a substrate forming an optical waveguide.
The substrate 1 is made of a material having an electro-optical effect. For example LiN
bO ₃ . The optical concentric circular optical waveguide 2 is the substrate 1
Formed on. The outermost optical path is coupled at one place outside the loop to form a coupler 16.

A phase modulator 18 is provided on both sides of the outermost optical path.
There is 19. This is a pair of electrodes, and when a voltage is applied, the optical path near the electrodes expands and contracts due to the electro-optic effect. It is made on the substrate of the polarizer 20. Two optical waveguides 21 and 22 are provided in front of the polarizer 20 and are coupled by the coupler 17.

The light emitted from the light source 3 passes through the optical fiber 23 and enters the end portion of the optical waveguide 21. This coupling can also be done with a lens. The light emitted from the optical waveguide 22 passes through the optical fiber 24 and enters the light receiving element 7 outside the substrate. The connection of this portion can also be performed by a lens or the like.
Since the sensor coil is photolithographically fabricated on the substrate in this embodiment, the coupler, phase modulator and polarizer can be formed on the same substrate and coupled by the coil and the waveguide on the substrate.

As already mentioned, the phase modulator, the polarizer,
There has been proposed an optical fiber gyro as shown in FIG. 6 in which a coupler is planarly formed on a substrate. However, this has not been put to practical use because there are many coupling portions between the fiber and the optical path on the substrate. It is desirable to have fewer joints.

The embodiment of FIG. 5 answers such a demand. It suffices to pay attention only to the coupling between the light source and the end of the optical waveguide 21. A multimode fiber may be used to guide the light of the optical waveguide 22 to the light receiving element 7. Alternatively, the light receiving element 7 may be directly attached to the end of the optical waveguide 22 on the substrate. Further, if a material capable of forming a light source or a light receiving element such as a semiconductor is used as the substrate material, the light source and the light receiving element shown in FIG. 5 can be formed on the same substrate.

As shown in the figure, when an active element such as a phase modulator is also formed on the substrate, it is necessary to use a material having an electro-optical effect, such as a LiNbO ₃ single crystal substrate. If a phase modulator is not needed, it is cost effective to use a glass substrate. Even if there is a phase modulator, the glass substrate can be used when the thermo-optical effect is used instead of the electro-optical effect.

Alternatively, the fiber coil portion of FIG. 6 can be replaced with the sensing coil of FIG. That is, as shown in FIG. 6, a phase modulator, a polarizer, an optical waveguide connecting them, and the like are formed on one substrate, and
As described above, a large number of circular optical paths are formed on another substrate, these two substrates are coupled by a fiber, and further, a light source and a light receiving element are coupled to these by a fiber.

[0065]

According to the conventional optical fiber gyro, a fiber coil formed by winding an optical fiber is used as a sensing coil. The present invention can form a sensing coil on a substrate. This can reduce the manufacturing cost of the optical fiber gyro. Further, in the conventional optical fiber gyro, each optical component is made of an optical fiber and a bulk component and then assembled.

The present invention can provide a long-awaited one-chip ring interferometer. Since optical parts can be integrated, material costs, processing costs, etc. can be significantly reduced. An inexpensive ring interferometer suitable for mass production can be provided. In the case where the spiral optical path that has been proposed so far is formed on a substrate, an intersection is always formed, so that a high S / N ratio sensor cannot be obtained because of high light loss and noise and high sensitivity. The present invention can overcome such difficulties.

The evanescent coupling between adjacent optical paths is 10
Having a 0% exchange ratio is a rather difficult condition, but this is possible due to the choice of waveguide design and process conditions based on material constants.

[Brief description of drawings]

FIG. 1 is a plan view of an optical waveguide of the present invention.

FIG. 2 is a plan view for explaining the operation of the optical waveguide of the present invention.

FIG. 3 is a diagram illustrating paths of CW light and CCW light in the configuration of FIG.

FIG. 4 is a configuration diagram of a ring interferometer according to an embodiment of the present invention.

FIG. 5 is a configuration diagram of a ring interferometer according to another embodiment of the present invention.

FIG. 6 is a plan view of a proposed example of an optical fiber gyro in which a polarizer, a coupler, and a phase modulator are integrated on a substrate.

[Explanation of symbols]

 1 substrate 2 optical waveguide 3 light source 4 coupler 5 polarizer 6 coupler 7 light receiving element

Claims (6)

[Claims] 1. An optical path formed by providing a high refractive index portion on a substrate transparent to light, wherein a plurality of circular optical paths having different diameters have a large diameter and a small diameter. And the adjacent circular optical paths are not concentric with each other, but are formed at positions close to each other such that some of them are optically coupled. 2. An optical path formed by providing a high refractive index on a multi-component glass or quartz substrate, wherein a plurality of circular optical paths having different diameters have a large diameter and a small diameter. An optical waveguide characterized in that adjacent circular optical paths are not concentric with each other, but are formed at positions close to each other such that some of them are optically coupled. 3. An optical path formed by providing a high refractive index portion on a substrate transparent to light, wherein a plurality of circular optical paths having different diameters have a large diameter and a small diameter. The adjacent circular optical paths are not concentric with each other and are formed at positions close to each other so that some of them are optically coupled, and a polarizer or a branching / merging element is formed on the other part of the substrate. An optical waveguide characterized in that a child, a branching / merging element, and the outermost one of the circular optical paths are coupled by an optical path. 4. An optical path formed by providing a high refractive index portion on a substrate transparent to light, wherein a plurality of circular optical paths having different diameters have a large diameter and a small diameter. The adjacent circular optical paths are not concentric and are formed at positions close to each other such that some of them are optically coupled, and the outermost optical path has its both ends aligned with the ends of the substrate. The optical waveguide is used as a coil for angular velocity detection, and the light source, the light receiving element, the polarizer, the branching and merging element, etc. are coupled by a single mode fiber, and the single mode fibers at both ends of the branching and merging element are connected to the above-mentioned optical waveguide. A ring interferometer characterized in that it is coupled to both ends of the outer optical path. 5. An optical path formed by providing a high refractive index portion on a first substrate which is transparent to light,
A plurality of circular optical paths having different diameters, one having a large diameter and one having a small diameter are included, and adjacent circular optical paths are not concentric with each other, but are formed in positions close to each other so that some of them are optically coupled. , The outermost optical path is such that both ends of the optical path are aligned with the ends of the substrate, and the optical waveguide is used as a coil for angular velocity detection. An optical waveguide that connects the child, the first and second branching and joining elements and an optical waveguide connecting them, and branches from the outermost optical path end on the first substrate and the second branching and joining element of the second substrate. A ring interferometer characterized in that the optical waveguides at both ends of the first branching / merging element of the second substrate, the light source, and the light receiving element are coupled to each other by a fiber or directly. 6. A set of optical paths formed by providing a high refractive index portion on a substrate which is transparent to light,
A plurality of circular optical paths having different diameters, one having a large diameter and one having a small diameter are included, and adjacent circular optical paths are not concentric with each other, but are formed in positions close to each other so that some of them are optically coupled. , The outermost optical path is provided with an optical waveguide that is a set of multiple optical paths in which both ends are aligned with the ends of the substrate, and the modulator, the polarizer, and the first and second branches are provided on the same substrate. A converging element and an optical path connecting them are formed, and the outermost optical path of the optical waveguide of the multiple optical path set and the optical path branched from the second branching converging element are coupled to each other to form the first branching converging element. A ring interferometer, which is characterized in that an optical waveguide at both ends of a light source and a light receiving element are combined.