JP2001264553A - Optical ic - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical IC capable of being manufactured with an efficient yield and also capable of reducing the danger of a substrate being broken. SOLUTION: An optical waveguide 14 is formed on the surface of the substrate 12, and a groove 12a, which nearly faces the optical waveguide 14 and extends nearly parallel to the optical waveguide 14 and moreover which has a surface not orthogonal and not parallel to the rear surface of the substrate mainly on the surface side of the substrate, is formed on the rear surface of the substrate 12. A TE wave of light coupled to the optical waveguide from the input part of the optical IC 10 propagates the inside of the optical waveguide as it is and advances toward the output part. On the other hand, although a TM wave leaks out and spreads within the substrate 12, the TM wave which reaches a part facing the optical waveguide 14 of the wave reaching the rear surface of the substrate is reflected in the direction straying from the optical waveguide 14 by the surface of the surface side of the substrate of the groove 12a, and whereby re-coupling in the output part of the optical waveguide 14 is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical IC having a polarizer function which can be used for optical communication or an optical fiber gyro, and more particularly to an optical IC whose extinction ratio can be improved.

[0002]

2. Description of the Related Art Conventionally, an optical IC having a polarizer function has been known.
Is, for example, an optical communication or an optical fiber gyro (FO)
G). The FOG is an angular velocity sensor using the Sagnac effect in which a phase difference is generated between clockwise light and counterclockwise light around an optical fiber loop (also referred to as a sensing coil) according to angular velocity. In this FOG, the role of the optical IC is to combine and split light into right-handed light and left-handed light, or to combine them again, and a phase modulator, that is, right-handed light. And a role to intentionally add a phase difference to the counterclockwise light, or a role to remove a polarizer, that is, an extra polarization component.

The necessity of a role as a polarizer will be described. In the FOG, the angular velocity of a pair of lights that rotate around the sensing coil in a direction opposite to each other is detected using the Sagnac effect. The phase difference generated by the Sagnac effect can be detected as a change in light intensity by combining and interfering clockwise light and counterclockwise light.
However, when light other than the pair of lights is generated, a new interference light component other than the original interference light is newly generated, which causes a bias error of the FOG.

[0004] In particular, when a polarization component that is orthogonal to the polarization direction of the original pair of light is generated, these cause serious errors. The polarization component orthogonal to the original pair of light is
Although the phase is generally different from the original polarization component,
In addition, when the ambient temperature around the FOG changes, their refractive index temperature coefficients differ, resulting in a periodic fluctuation of the bias. Therefore, it is important to prevent the generation of this harmful polarization component, but if it does, it is necessary to remove it with a polarizer.

Therefore, for example, a polarization component (TE) corresponding to an extraordinary ray of a substrate crystal is added to an optical waveguide formed on a LiNbO ₃ or LiTaO ₃ substrate by a proton exchange method.
Wave), and a polarization component (TM) corresponding to the extraordinary ray
An optical IC has been developed which has a principle of obtaining a polarizer function by leaking a wave) into a substrate crystal. However, some of the TM waves leaked into the substrate crystal are reflected on the back surface of the substrate and return to the front surface side of the substrate again, and the optical IC
Is recombined with the connected fiber. Although this ratio is very small, the improvement of the extinction ratio of the optical IC,
That is, in order to further improve the polarizer function, it is necessary to prevent the reflected light from being recombined with the fiber.

Conventionally, as a method for preventing the reflected wave from the back surface of the optical IC from being recombined with the fiber and improving the extinction ratio, for example, Japanese Patent No. 2791414, Japanese Patent No. 2737030, JP-A-11-132
No. 772 is known.

Japanese Patent No. 2791414 discloses an optical IC.
It is described that the two side surfaces and the back surface parallel to the optical waveguide are roughened so as to scatter light, or the side surface and the back surface of the optical IC are covered with an antireflection film or an absorption film.

Japanese Patent Application Laid-Open No. H11-132772 describes that an absorption film is deposited on the back surface of an optical IC and attached to a mount via an adhesive film.

Also, Japanese Patent No. 2737030 discloses that
As one example, a waveguide and a 45 °
It is described that a large number of micro-groove arrays at an angle of degree are provided. The minute groove array roughens the back surface of the substrate crystal, deflects the TM mode light leaking into the substrate crystal to an angle of about 90 degrees, and prevents recombination with the optical fiber. Alternatively, it is described that a plurality of equally-spaced deformed portions are formed on the back surface of the optical IC, and the leakage light that has reached the back surface of the optical IC is attenuated by hitting any of the deformed portions.

[0010]

However, the improvement of the extinction ratio in the conventional optical IC has the following problems.

That is, when a rough surface is formed on the back surface of an optical IC as described in Japanese Patent No. 2791414, any rough surface is not a problem, and reflected light is eliminated. It is necessary to satisfy the condition of a rough surface that is scattered. This appropriate condition is a rather limited condition, and to meet this requirement, a very precise condition is required for the processing apparatus. It is difficult to control this condition, and it is difficult to manufacture an optimum rough surface with a good yield, and the extinction ratio varies greatly. Also,
Making the substrate rough means that the substrate is innumerably scratched, and there is also a problem that the substrate may be damaged.

When the back surface of an optical IC is covered with an antireflection film or an absorption film as disclosed in Japanese Patent No. 2791414 or JP-A-11-132772, the refractive index and the thickness of the film attached to the back surface must be adjusted under appropriate conditions. Without the film, the reflected light cannot be eliminated. For example, when the refractive index of the film is smaller than the refractive index of the substrate, the incident angle must be equal to or less than the critical angle at which total reflection occurs. (Relationship between length and thickness) is usually difficult. Even when the refractive index of the film is larger than the refractive index of the substrate, it is necessary to strictly control the film forming conditions of the film forming apparatus so that the film has the desired refractive index and thickness. It is difficult to manage this apparatus under optimum conditions, it is difficult to obtain a desired film with good yield, and the extinction ratio varies widely. Further, it is difficult to form a film having a high adhesion strength, and there is a problem that the film is easily peeled off. It is also difficult to deposit an absorbing film.

In the case where an array of minute grooves at an angle of 45 degrees is provided on the back surface of an optical IC as described in Japanese Patent No. 2737030, a large number of minute grooves must be formed over a wide range. Any angle may be used as long as it is a degree angle, and it is necessary to optimize the depth, pitch, and shape of each groove, and there is a problem that the processing is difficult and it is difficult to process with good yield. Further, since a large number of microgroove arrays are formed on the substrate, there is a problem that the degree of damage to the substrate is increased and there is a risk of breakage.

In the case where a deformed portion is provided in an optical IC, there is a problem that it is difficult to adjust the shape and size of the deformed portion and the position where the deformed portion is provided. Further, since a large number of deformed portions must be formed. As in the case of forming a large number of grooves, there is a problem that the degree of damage increases and there is a risk of breakage.

An object of the present invention is to provide an optical IC that can be manufactured with a high yield and can reduce the risk of damaging a substrate.

[0016]

According to a first aspect of the present invention, there is provided an optical IC having a substrate and an optical waveguide formed on a surface of the substrate, wherein the optical waveguide is formed on the back surface of the substrate. A groove extending substantially in parallel with the optical waveguide substantially in opposition to the optical waveguide and mainly having a non-perpendicular and non-parallel surface to the back surface of the substrate is formed on the front surface side of the substrate. Optical IC
Out of the light coupled from the input part to the optical waveguide, the TE wave propagates in the optical waveguide as it is and goes to the output part. On the other hand, the TM wave leaks and spreads conically into the substrate without being confined in the optical waveguide of the optical IC. Of the TM waves,
The light that reaches the portion of the back surface of the substrate facing the optical waveguide is reflected on the surface of the groove on the substrate surface side according to the rule of incident angle = reflection angle. The surface of the groove extending substantially parallel to the optical waveguide on the front surface side of the substrate is mainly non-perpendicular and non-parallel to the back surface of the substrate, so that the light is reflected in a direction deviating from the optical waveguide and separates from the optical waveguide. Propagating in the direction. Therefore, recombination at the output section of the optical waveguide can be prevented.

The invention according to claim 2 is characterized in that the groove has a triangular or polygonal cross section. By making the cross-sectional shape of the groove triangular or polygonal, the surface of the groove on the substrate surface side can be an inclined surface.
The slope ensures that the reflected light is reflected away from the optical waveguide.

According to a third aspect of the present invention, a vertex of a triangular or polygonal cross-sectional shape of the groove according to the second aspect is shifted from immediately below the optical waveguide.
The apex can be a sloped surface of the groove directly below the optical waveguide, and light reflected immediately below the optical waveguide most likely to recombine can be reliably reflected in a direction deviating from the optical waveguide. .

The invention described in claim 4 is the first to third aspects of the present invention.
Wherein the substrate is LiNbO ₃ or LiTaO ₃ .

The invention according to claim 5 is the invention according to claims 1 to 4.
The gist of the invention is an optical fiber gyro using the described optical IC as an optical multiplexer / demultiplexer and a polarizer.

[0021]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 6 show an optical IC according to an embodiment of the present invention.
An optical waveguide 14 is provided on a substrate 12 made of an anisotropic optical crystal such as iNbO ₃ or LiTaO ₃ . The optical waveguide 14 can be manufactured by a proton exchange method or the like. The optical IC 10 of this embodiment also functions as an optical multiplexer / demultiplexer and a polarizer, and the optical waveguide 14 has an input side optical waveguide 14a having one input side fiber 16a.
And two optical waveguides 14 in the middle thereof.
b, 14b and the two optical waveguides 14b, 1b
4b are each coupled to two output fibers 18.

On the back surface of the substrate 12, as shown in FIG.
Substantially parallel to the optical waveguide 14 and substantially immediately below the optical waveguide 14,
One triangular groove 12a is formed. This triangular groove 12a
Has a triangular shape whose cross-sectional shape is convex upward. The triangular groove 12a is formed by turning the substrate 12 upside down after manufacturing the optical waveguide 14, and passing the cutting blade of the dicing saw once at the center of the substrate 12 so as to be parallel to the optical waveguide 14. be able to. Light I
Usually, a plurality of C10s can be obtained from one wafer. In the case of the present invention, the separation of a plurality of chips and the formation of the triangular grooves 12a are performed by a dicing saw using a dicing saw.
It can be performed in one step, and an increase in the number of steps can be prevented. Further, in forming the triangular groove 12a, unlike the configuration of the conventional publication, it is not necessary to strictly control the precision as described later, and the triangular groove 12a can be formed easily.

The operation of the optical IC 10 configured as described above will be described. Of the light coupled from the input fiber 16 to the optical waveguide 14 of the optical IC 10, the TE wave propagates in the optical waveguide 14 (14 a, 14 b) of the optical IC 10 as it is, and is recoupled to the output fiber 18 on the opposite side. On the other hand, the TM wave is not restrained in the optical waveguide 14 of the optical IC 10,
It leaks and spreads conically in the substrate 12 crystal. Of those, the one that reaches the back surface of the substrate 12 has an incident angle = on the groove surface of the groove 12a formed on the back surface of the substrate 12, as shown in FIG.
The reflected wave is reflected in accordance with the law of the reflection angle. However, as shown in FIGS.
No recombination occurs.

FIG. 6 is an explanatory sectional view for obtaining a condition for preventing the recombination from occurring. Assuming that the thickness of the substrate is h, the angle (base angle) formed by the inclined surface of the triangular groove 12a with respect to the back surface of the substrate 12 is θ, and as shown in FIG. Assuming that the X axis is taken in the direction and the Y axis is taken in the vertical direction, the groove surface on one side of the triangular groove 12a is

[0025]

(Equation 1) Can be expressed as Here, xc is the x coordinate of the vertex at one end of the bottom of the triangular groove 12a. The arrival position x2 when the light reflected on the slope of the triangular groove 12a reaches the surface of the substrate 12 again is represented by the following equation.

[0026]

(Equation 2) Here, φ is the angle between the TM wave leaking through the substrate 12 and the X axis when viewed on the XY plane. For any φ or such that recombination can occur (ie,
φ ≦ tan ^-1 (2h / x ₁ ))

[0027]

(Equation 3) May be selected within a range that satisfies the following condition. The x-coordinate of the input fiber 16 is 0, the x-coordinate of one output fiber 18 is x1, and the x-coordinate of the other output fiber 18 is -x1. The above equation can be easily satisfied by the combination of θ and xc, and the range of the combination is wide. For example, when the thickness of the substrate 12 is 1.0 mm and x1 = 150 μm, as an example, the shape and dimensions of the triangular groove 12a are such that the apex angle ξ = π−2θ
= 150 ° and the bottom of the groove = 700 μm.
However, under the same groove bottom length conditions, the apex angle has an acceptable range between 30 ° and 170 °. If the apex angle is reduced, the groove bottom becomes smaller and the groove depth becomes larger, and if the apex angle is made larger, the groove base becomes larger and the groove depth becomes smaller. In addition, the minimum range of the groove bottom where the triangular groove 12a needs to be formed is that, when there is no triangular groove 12a, the TM wave emitted from the input fiber can be reflected on the back surface and reach the output fiber. Within the range of ± x1 / 2. If this range is covered, the triangular groove 12a
The x-coordinate of the vertex does not necessarily need to be x = 0, that is, at the same position as the input side fiber, and does not need to be an isosceles triangle. Depending on the configuration of the optical waveguide 14, rather, by shifting the apex of the triangular groove 12 a from immediately below the optical waveguide 14, light reflected immediately below the optical waveguide 14 where recombination is most likely to be separated from the optical waveguide 14. In some cases, the light can be reliably reflected in a certain direction.

Specifically, for example, when the apex angle is 150 °, the base of the groove is 700 μm, and the thickness of the substrate is 1 mm, the displacement of the triangular groove is allowed up to 150 μm. The actual values of the apex angle and the bottom of the groove depend on the size of the bottom of the groove that can be cut by the dicing saw and the set value of the ratio of the groove depth to the substrate thickness. Although it is preferable to determine the groove depth so as not to be too large with respect to the thickness of the substrate, the dimensional accuracy in the triangular groove processing is very gentle.

The groove is not limited to a groove such as a triangular groove shown in FIG. 7A, but the groove on the substrate surface side may be a slope, and may be a groove 12'a having a curved surface (FIG. 7A). Alternatively, a polygonal groove 12 ″ a may be used (FIG. 7B).
Any groove may be used as long as it has a surface that is non-perpendicular and non-parallel to the back surface of the substrate 12 mainly in the range of x | ≦ x1 / 2 on the front surface side of the substrate.

Further, in the above description, the primary reflection, in which one reflection is mainly performed on the back surface, is mainly considered, but since the TM wave deviates from the optical waveguide 14 in the first reflection, the secondary reflection or more. It is considered that the influence of reflection is small.

FIG. 8 illustrates a case where this optical IC is used for FOG. In the figure, 20 is a light source, 22 is an optical coupler,
24 is a sensing coil and 26 is a detector. The optical IC 10 of the present invention is used as a polarizer and an optical multiplexer / demultiplexer.

However, the present invention is not limited to the example shown in FIG. 1 which is used for an optical multiplexer / demultiplexer having one input side waveguide and two output side waveguides, and a polarizer having only one waveguide. IC functioning only as a light or light I functioning as an optical modulator
The same can be applied to C. In this case, 1
A groove may be formed on the back surface of the substrate so as to face the two waveguides in parallel with the waveguides. In other words, a groove may be formed on the back surface so as to be parallel to and opposite to the line connecting the input side and the output side. In this case, the conditions of the apex angle of the groove and the bottom side of the groove become milder.

[0033]

As described above, according to the present invention, a groove is formed on the back surface of a substrate, light is reflected on the surface of the groove on the substrate surface side, and is propagated in a direction away from the optical waveguide. Recombination to the output side of the optical waveguide can be prevented, and the extinction ratio of light can be improved. There is no need to form a large number of grooves, and since there is a large tolerance in the accuracy of the position of the groove and the shape of the groove, the risk of damaging the substrate can be reduced, and manufacturing can be performed with high yield.

[Brief description of the drawings]

FIG. 1 is a perspective view illustrating an embodiment of an optical IC according to the present invention.

FIG. 2 is a bottom view of the optical IC of FIG. 1;

FIG. 3 is a cross-sectional view taken along line 3-3 in FIG. 1, and a dashed line indicates T which leaks from the input side of the optical waveguide to the back surface of the substrate.
Represents M waves.

FIG. 4 is a cross-sectional view taken along line 3-3 in FIG. 1, and a dashed line indicates a TM wave reflected on the back surface of the substrate.

FIG. 5 is a plan view of the optical IC of FIG. 1; a dashed line indicates a TM wave that leaks and spreads from the input side of the optical waveguide to the back surface of the substrate and is further reflected on the back surface and the groove.

FIG. 6 is an explanatory cross-sectional view for obtaining a condition for preventing recombination of a TM wave.

FIGS. 7A and 7B are views corresponding to FIG. 3, showing another example of the groove.

FIG. 8 is a block diagram showing a configuration in which an optical IC according to the present invention is used in an optical fiber gyro.

[Explanation of symbols]

 Reference Signs List 10 optical IC 12 substrate 12a, 12'a, 12 "a groove 14 optical waveguide

Claims (5)

[Claims] 1. An optical IC comprising a substrate and an optical waveguide formed on the surface of the substrate, wherein the optical IC extends substantially parallel to the optical waveguide on the back surface of the substrate, substantially opposite to the optical waveguide, and is non-conductive with respect to the back surface of the substrate. An optical IC characterized by forming a groove mainly having a vertical and non-parallel surface on a substrate surface side. 2. The light I according to claim 1, wherein said groove has a triangular or polygonal cross section.
C. 3. The optical IC according to claim 2, wherein a vertex of a triangular or polygonal cross-sectional shape of the groove is shifted from immediately below the optical waveguide. 4. The method according to claim 1, wherein the substrate is LiNbO ₃ or LiTa.
The optical IC according to claim 1, wherein the optical IC is O ₃ . 5. An optical fiber gyro using the optical IC according to claim 1 as an optical multiplexer / demultiplexer and a polarizer.