JPH10319361A - Optical modulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical modulator smaller in size and easy to produce. SOLUTION: Incident light from a light incident hole 10 propagates through a first optical waveguide 3, and its part transmits through a partial transmission/partial reflection film 5, and its part is reflected by the film 5 to be branched to a first optical waveguide 3 and a second optical waveguide 4. The branched light propagate through respective waveguides to be reflected by a first total reflection film 6 and a second total reflection film 7 of waveguide ends. The reflected light return respectively through the waveguides again, and are reflected/transmitted again by the partial transmission/partial reflection film 5 to be emitted from a light emission hole 11 while interfering with each other. When an electric field based on a required modulation signal is applied to the second part 4b of the second optical waveguide 4 by an electrode 8, the phase of the light propagating through the waveguide is changed by an electrooptic effect, and an intensity of interference light is changed according to this phase change, and the light is modulated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a small-sized optical wiring part for use in optical communication and automobiles, or optical signal processing, optical control, optical measurement, etc. of industrial equipment.
The present invention relates to an optical modulator that can be easily manufactured.

[0002]

2. Description of the Related Art With the development of optical communication technology and optical signal processing technology, optical wiring of automobiles via optical fibers, optical measurement and optical signal processing for controlling various industrial equipment using optical signals, and the like. Is being put to practical use. As such a waveguide type optical modulator used for optical information transmission and optical signal processing,
An Mach-Zehnder interferometer is used.

FIG. 3 shows a Machender type optical modulator used so far. As shown in FIG. 3, the Mach-Zehnder optical modulator 90 includes two opposing Y-branch waveguides 91 _-1 and 91 _-2 and two linear waveguides 9 connecting the Y-branch waveguides 91 _-1 and 91 _-2.
2 _-1 and 92 _-2 . And two waveguides 9
Electrodes 93 are provided on both sides of 2 _-1 and 92 _-2 . An electric field based on the modulation signal is applied to the waveguide 92 through the electrode 93.
_-1 and 92 _-2 , the phase of the light propagating through the waveguide changes due to the electro-optic effect, and the intensity of the output interference light changes according to the phase change, thereby modulating the light. You.

[0004]

However, this Mach-Zehnder type optical modulator has a problem that it is difficult to reduce the size because of the dimensional restrictions. Specifically, referring to FIG. 4, since the propagating light must be in a single mode in the optical modulator, the Y-branch type waveguide 91 constituting the modulator is designed to have a branch angle and a branch optical path length. Subject to the above restrictions. For example, in the case of a Y-type branch waveguide using lithium niobate, the input waveguide and the output two waveguide are almost straight because the branch angle for branching while maintaining a single mode is very small, about 1 °. It must be connected in a shape.

[0005] Further, since the difference between the refractive indices of the core and the clad of the waveguide is reduced to form a single mode waveguide,
In order to draw the 1 ° gradient parallel to the input waveguide as a waveguide parallel to the end face of the rectangular substrate, the curvature R of the waveguide is set to 50 mm or more to prevent light from leaking out of the waveguide. It is necessary to make the curvature portion a 5 to 10 mm. Further, the waveguide width at the connection portion of the waveguide is doubled when viewed from the side of the one input waveguide, and when simply connected, transmission loss increases due to light reflection and transmission mode conversion. Therefore, an extra length b for converting the transmission mode slowly by making the connection portion tapered is required to be several mm.

Further, in order to transmit a signal from the two-branch waveguide to the input linear waveguide, a linear waveguide c (for example, at least a certain level) is used to alleviate the disturbance of the transmission mode at the connection point.
3 mm or more) is required. In total, the total length of the conventional Y-branch is about 15 mm or more. In the Mach-Zehnder type optical modulator 90 described above, two sets of such Y-branch type waveguides must be opposed to each other, and a linear waveguide for applying an electric field must be provided therebetween. Therefore, the entire modulator has a length of 40 to 50 mm or more. In addition, in the modulator having such a length, the width of the substrate needs to be 6 mm or more in consideration of the subsequent processing and deformation of the component, which results in a very large component.

As described above, in the Mach-Zehnder type optical modulator, since it is difficult to reduce the size and the size is large, the number of elements that can be obtained from one substrate is smaller than that of a normal semiconductor element. For example, a Mach-Zehnder type optical modulator 90 shown here may be formed from a 3-inch substrate generally used for manufacturing optical components.
Is less than 10 pieces. This is extremely small in comparison with the fact that many semiconductor elements taking the same steps are 1 mm square or less. As a result, the conventional Mach-Zehnder type optical modulator has a problem that the productivity is low and the cost cannot be reduced.

The Mach-Zehnder type optical modulator also has a problem that its structure is complicated and its manufacture is difficult.
The shape of the connection portion of the Y-branch of the Mach-Zehnder optical modulator 90 affects the branching characteristics and the loss, and therefore must be manufactured very precisely. In particular, the branch center conical portion requires a processing accuracy of about 0.1 μm. As a result, very high-precision processing is also required, which causes a problem that the cost is further increased.

Accordingly, it is an object of the present invention to provide an optical modulator that is smaller and easy to manufacture.

[0010]

In order to solve the above-mentioned problems, two optical waveguides are crossed on the same plane, and an optical thin film of partial transmission and partial reflection is provided at the intersection, and the input light is reflected by reflected light. A Y-branch waveguide, which is a cause of miniaturization and requires high-precision processing, is not used.

Accordingly, an optical modulator according to the present invention comprises a base material, a first optical waveguide formed on the base material, made of an electro-optic material, and having one end having a light incident portion; A second optical waveguide formed on a material so as to intersect the first optical waveguide at a predetermined angle, made of an electro-optic material, and having one end as a light emitting portion; and the first optical waveguide. A first total reflection optical member provided at the other end of the
A second total reflection optical member provided at the other end of the optical waveguide, an optical waveguide provided at an intersection of the first optical waveguide and the second optical waveguide, and incident on the first optical waveguide. The reflected light is partially reflected, made incident in the direction of the end of the second optical waveguide on which the second totally reflecting optical member is provided, partially transmitted, and the first light is transmitted through the first optical waveguide. The light is made incident in the direction of the first total reflection optical member of the waveguide, and a part of each of the light reflected by the first and second total reflection optical members is reflected. A partially reflecting optical member that guides the guided optical waveguide to another waveguide different from the guided optical waveguide, and partially transmits the guided optical waveguide; and the first optical waveguide. Between the partial reflection optical member and the first total reflection optical member, and the partial reflection of the second optical waveguide. Between the undergraduate member second total reflection optical member, provided on at least one,
An electrode for applying an electric field based on a desired modulation signal to the optical waveguide.

In the optical modulator having such a configuration, the light incident on one end of the first optical waveguide is partially reflected by the partially reflecting optical member and is incident on the second optical waveguide. , And a part is branched by being transmitted as it is. Each split light is totally reflected by the second and first total reflection optical members, respectively, and is incident on the partially reflection optical member again. The light totally reflected by the second totally reflecting optical member and transmitted through the partially reflecting optical member, and the light totally reflected by the first totally reflecting optical member and reflected by the partially reflecting optical member. Are respectively interfered to form an output optical signal, which is output from one end of the second optical waveguide. Therefore, if the phase of the propagating light reciprocating in the waveguide is changed by the electro-optic effect via the electrode, the intensity of the interference light due to the reflected light between the two optical paths will be electrically controlled, and as an optical modulator. Can work.

Specifically, the substrate has a groove having a side wall including a cross section of the optical waveguide at an intersection of the first optical waveguide and the second optical waveguide, The partially reflecting optical member is used to obtain a desired light splitting ratio.
It is formed by inserting a film member on which a partially reflective film is formed into the groove. More specifically, in the base, a groove having a side wall including a cross section of the optical waveguide is formed at an intersection of the first optical waveguide and the second optical waveguide, and the partial reflection The optical member is configured such that a partial transmission / partial reflection film for obtaining a desired light branching ratio is formed directly on a side wall of the groove.

Preferably, the first optical waveguide and the second optical waveguide
Are formed to intersect at a relatively large intersection angle, such as 45 ° to 90 °. And specifically, the first and second optical waveguides intersect at right angles to each other, and the partially reflecting optical member intersects the first and second optical waveguides at 45 °, respectively, and the first and second optical waveguides intersect at 45 °. An interferometer composed of two optical waveguides and a total reflection member constitutes a Michelson interferometer.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a top view illustrating the optical modulator according to the present embodiment. FIG. 2 is a perspective view showing the optical branch waveguide section 10 of the optical modulator shown in FIG.

First, the structure of the optical modulator 1 will be described. As shown, in the optical modulator 1, two linear first optical modulators made of an electro-optical material are formed on the same plane of a substrate 2.
The optical waveguide 3 and the second optical waveguide 4 are formed. The first optical waveguide 3 and the second optical waveguide 4 are:
Crossed at 90 °. In addition, the first optical waveguide 3 and the second optical waveguide 4 are provided with a partial transmission / partial reflection film 5 described later.
The two parts 3a, 3b and 4a, 4 respectively
b. Further, the end of the first portion 3a of the first optical waveguide 3 is connected to the light entrance 10 and the second optical waveguide 4
The end of the second portion 4b is used as the light exit 11.

The first optical waveguide 3 and the second optical waveguide 4
Is provided with a partial transmission / partial reflection film 5 that reflects part of incident light and transmits part of the light. The partial transmission / partial reflection film 5 is incident on the first optical waveguide 3, transmits a part of the light guided through the first portion 3 a, and transmits the second portion of the first optical waveguide 3. 3b, and reflects a part of the light to form a second portion 4 of the second optical waveguide 4.
b. In addition, a part of light guided by the second portion 3b of the first optical waveguide 3 and reflected by the first total reflection film 6 and the second total reflection film 7, which will be described later, and the second light. A part of the light guided through the second portion 4b of the optical waveguide 4 is reflected and transmitted, respectively, so that the second optical waveguide 4
To the first portion 4a.

This partial transmission / partial reflection film 5 is shown in FIG.
This will be described in detail with reference to FIG. First optical waveguide 3 of substrate 2
At the intersection of the first and second optical waveguides 4 and 4, an angle of 45 ° is formed with the two optical waveguides 3 and 4, the width is about 30 μm, and the depth is the first and second optical waveguides 3 and 4. A groove 9 having a depth of 4 or more (10 μm or more in the present embodiment) is formed. Then, the partial transmission / partial reflection film 5 that reflects a part of the incident light and transmits a part of the light is inserted into the groove 9. The partial transmission / partial reflection film 5 is formed by forming an optical thin film of semi-transmissive reflection on an organic film transparent to guided light, or an optical thin film similar to a thin plate made of an inorganic material transparent to guided light. Is formed. In addition,
The optical thin film is composed of, for example, a multilayer interference film or a metal film.

First optical waveguide 3 and second optical waveguide 4
On the end faces of the second portions 3b and 4b, which are different from the light entrance and the light exit, the first total reflection film 6 and the first total reflection film 6 which reflect the propagation light back into the waveguide are provided. A second total reflection film 7 is provided. The first optical waveguide 3, the second optical waveguide 4, the partial transmission / partial reflection film 5, the first total reflection film 6, and the second total reflection film 7 form a Michelson-type optical interferometer. Is configured.

An electrode for applying an electric field to the second optical waveguide 4 is provided on a second portion 4b of the second optical waveguide 4 between the partial transmission / partial reflection film 5 and the second total reflection film 7. 8 are provided. A voltage based on an arbitrary modulation signal is applied to the electrode 8, an electric field is applied to the electrode 8, and the phase of the light propagating back and forth in the second optical waveguide 4 is changed by the electro-optic effect, thereby obtaining a partial transmission / reception. It is possible to electrically control the intensity of the interference light due to the reflected light between the two optical paths, which is emitted through the first portion 4a of the second optical waveguide 4 via the partial reflection film 5, and is thus controlled. An element having a simple structure can be operated as an optical modulator.

The operation of performing optical modulation using the optical modulator 1 having such a structure will be described together. Light incident from the light entrance 10 of the first optical waveguide 3 is guided through the first portion 3 a of the first optical waveguide 3 and is incident on the partial transmission / partial reflection film 5. In the partially transmitting / partially reflecting film 5, the second part 4b of the second optical waveguide 4 that transmits a part of the light and crosses the partially reflected light of the film
To effectively split the input light. The branched light propagates through each waveguide, and is reflected by total reflection mirrors 6 and 7 installed at the ends of the waveguide, and returns inside the waveguide again.

The returned light is reflected or transmitted again by the partial transmission / reflection film 5, respectively, and propagates through the first portion 4a of the second optical waveguide 4 while interfering with each other. The light exits from the light exit port 11 as output light. At this time, the second portion 4b of the second optical waveguide 4
, The partial transmission / partial reflection film 5 and the second total reflection film 7
When an electric field is applied to the electrode 8 disposed between the two, the phase of light propagating through the waveguide changes due to the electro-optic effect. Thus, the intensity of the interference light propagating through the first portion 4a of the second optical waveguide 4 changes according to the phase change. Therefore, by applying an electric field composed of a desired modulation signal to this electrode, it becomes possible to modulate light, and it functions as an optical modulator.

As described above, the optical modulator 1 of the present embodiment does not require a complicated tapered optical waveguide portion, a large radius curved waveguide portion, or the like of a branch waveguide in a conventional optical modulator. Therefore, the shape is significantly smaller than that of the conventional parts. Specifically, the length of the substrate is
The length of the electrode 8 for phase control occupies the majority because the branching part using the partial reflection film 5 is sufficient at about 1-2 mm.
The total length of the substrate is 20 mm or less. The width of the substrate can be made 3 mm or less, which is thinner than the conventional one, because the entire length of the substrate becomes shorter and the electrodes need only be equivalent to one waveguide. From the above, the size of the substrate is the same as the conventional one.
/ 4 or less.

Further, since the size of the element is 1/4 or less of that of the conventional device, the number of parts produced from one material substrate is calculated to be about four times if calculated simply, and the cost per one is greatly reduced. it can. Further, since the two waveguides forming the branch have a relatively large intersection angle (90 ° in the optical modulator 1 of the present embodiment), the branch can be easily manufactured. In addition, since the characteristics of the component such as the loss and the branching ratio depend on the partial transmission / partial reflection film, the characteristics can be easily managed.

Since this element is small, in order to facilitate handling, this element is fixed to a supporting substrate which is larger and cheaper than this substrate, and a V-groove is provided in the supporting substrate to connect the fibers. Alternatively, it is also possible to fix the light receiving element or the light emitting element to the indication substrate and connect it to the waveguide.
Further, for connection to the outside, an optical fiber can be directly connected, and further, a light receiving element or a light emitting element can be directly bonded to the waveguide opening on the end face of the substrate.

Next, a method for manufacturing the optical modulator 1 will be described with reference to two specific examples. First, as a first example, a case where the optical modulator 1 is manufactured using a lithium niobate (LiNbO ₃ ) substrate will be described. First, two orthogonal single-mode linear waveguides are formed on a lithium niobate (LiNbO ₃ ) substrate by a Ti thermal diffusion method. Next, a groove having a depth of 10 μm or more, which intersects each orthogonal optical waveguide at an angle of 45 ° with a dicing saw using a metal blade having a thickness of 30 μm and perpendicular to the substrate, with a dicing saw. Is provided.

Next, a partial reflection / partial transmission film made of an optical thin film such as a multilayer interference film or a metal film for obtaining a desired light branching ratio for each optical waveguide is formed in the groove. This partial reflection / partial thin film is made of lithium niobate (L
A thin flake of iNbO ₃ ) with a partially reflecting and partially transmitting film formed thereon is formed by inserting it into a groove provided. Next, using a dicing saw, a rectangular region that is perpendicular to the waveguide and includes an intersection is cut out as a modulator substrate. Finally, for each of the cross waveguides, a total reflection film made of a dielectric thin film or a metal thin film is formed on one end face of each of the waveguides, and an electrode for applying an electric field is formed on one of the waveguides. A space between the partial reflection / partial transmission film and the optical waveguide in the groove is filled with a refractive index regulator having a refractive index equivalent to that of the lithium niobate substrate. Thus, the optical modulator of the present embodiment can be manufactured.

Next, as a second example, as an optical waveguide,
A case where a nonlinear organic waveguide formed on a Si substrate is used will be described. First, a polymer having a lower refractive index than the core layer and a non-linear organic polymer of the core layer are applied as a cladding layer on the Si wafer on which the lower electrode layer is formed by spin coating or the like. Each film thickness is controlled so as to be a single mode waveguide from the relationship between the final waveguide width and the film thickness. In the present embodiment, the core layer is 2 μm and the cladding layer is 3 μm. A resist pattern having a width of 3 to 6 μm, preferably 4 to 5 μm, which crosses the cross, is formed thereon by photolithography.

Next, this is subjected to RIE treatment in oxygen gas to etch only the core layer, thereby forming a rectangular optical waveguide having a resist shape width and a core layer thin film. Then, a clad layer is formed again on the surface by spin coating or the like.
Next, an upper electrode layer is formed on one clad layer so as to sandwich the core layer with the lower electrode layer. Thereafter, a groove having a depth of 10 μm perpendicular to the substrate and formed at an angle of 45 ° with the orthogonal optical waveguide is formed in the intersection using a dicing saw using a metal blade having a thickness of 30 μm. Next, a partial reflection / partial transmission film made of an optical thin film such as a multilayer interference film or a metal film is formed in the groove to obtain a desired light branching ratio for each optical waveguide. To form the partial reflection / partial transmission film, a ribbon-like partial reflection / partial transmission film is inserted into a groove, and fixed using a transparent adhesive so that the film adheres tightly to the cut surface.

Thereafter, using a dicing saw, a rectangular portion perpendicular to the waveguide and including an intersection is cut out as a modulator substrate. Finally, for each of the cross waveguides, a total reflection film made of a dielectric thin film or a metal thin film is formed on one end face of each waveguide, and an electrode for applying an electric field is formed on one waveguide. Thus, the optical modulator of the present embodiment can be manufactured. In addition, by forming a V-groove used for fiber connection on the Si substrate in advance by etching, it becomes easy to align the fiber, the number of component creation steps can be reduced, and the connection step can be simplified.
You may do so.

The optical modulator according to the present invention is not limited to the embodiment, and various modifications can be made. For example, in the optical modulator 1 of the present embodiment, the first optical waveguide 3 and the second optical waveguide 4 intersect at an angle of 90 ° and partially intersect with each of the waveguides at an angle of 45 °. Although the transmission / partial reflection film 5 is provided, the invention is not limited to this. The two waveguides may intersect at any angle, although it is advantageous for ease of manufacture to intersect at a relatively large angle such as close to 90 °. In addition, partial transmission
The partial reflection film 5 is such that the reflected light of the light that has been propagated through one of the waveguides and entered is appropriately determined so that the reflected light is incident on the other waveguide. And the arrangement of the second optical waveguide 4.

A method of forming a partial reflection / partial transmission film at an intersection of two optical waveguides may be any method. For example, a method in which a thin flake of lithium niobate (LiNbO ₃ ) with a partially reflecting / partially transmitting film formed thereon is inserted into the groove may be used. Further, the optical waveguide substrate is inclined so that the partial reflection / partial transmission film is formed on one side wall of the groove, and an optical thin film such as a multilayer interference film or a metal film is deposited or sputtered. LiN
bO ₃ ) A partially reflective / partially transmissive film may be formed by filling a refractive index regulator having the same refractive index as the substrate.

As the partial reflection / partial transmission film, various members usually used as a half mirror in the spatial light optical system may be used. Of course, the manufacturing technique may be manufactured and formed by the same method as that of the half mirror. Further, the material of the waveguide may be arbitrarily changed. Further, the method of manufacturing the optical modulator according to the present invention is not limited to the two examples described above.
The method for forming the partially transmitting film, the method for forming the waveguide, and the like may be arbitrarily changed.

[0034]

As described above, according to the optical modulator of the present invention, an optical semipermeable membrane is provided at the intersection of two optical waveguides without using a long and large Y branch waveguide. Is provided, and a branch waveguide for dividing input light into reflected light and transmitted light is used, so that the optical modulator can be significantly reduced in size. In addition, this makes it possible to obtain a larger number of light modulators in a series of manufacturing steps from one wafer, while improving the operation efficiency per unit of equipment, while maintaining the same process as the conventional one.
Cost reduction can be realized. Further, since the degree of demand for process uniformity can be made lower than before by the downsizing of the element, the yield is improved and the cost can be further reduced.

Further, in the optical modulator of the present invention, since there is no sharp bent portion or curved portion, and the processing accuracy is eased as compared with the conventional optical modulator, the manufacture becomes easy. In addition, the yield can be improved, and the manufacturing can be performed with less expensive equipment, so that the cost can be reduced in this respect as well.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a structure of an optical modulator according to an embodiment of the present invention.

FIG. 2 is a perspective view showing an optical branch waveguide section of the optical modulator shown in FIG.

FIG. 3 is a diagram illustrating a structure of a conventional optical modulator.

FIG. 4 is a diagram illustrating a Y-type optical branch waveguide section of the optical modulator illustrated in FIG. 3;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Optical modulator 2 ... Substrate 3 ... 1st optical waveguide 4 ... 2nd optical waveguide 5 ... Partial transmission / partial reflection film 6 ... 1st total reflection film 7 ... 2nd total reflection film 8 ... Electrode 9 ... Groove 10 ... Light entrance 11 ... Light exit

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yasuhiro Kubota Inside Wakkadai 25 NKK, Tsukuba, Ibaraki Prefecture (72) Inventor Shinji Ushijima 25 Waikadai, Tsukuba, Ibaraki Inside NOK Corporation

Claims (5)

[Claims] A first optical waveguide formed on the substrate, made of an electro-optical material, and having one end as a light incident portion; and a first optical waveguide on the substrate. A second optical waveguide formed so as to intersect the waveguide at a predetermined angle, made of an electro-optical material, and having one end as a light emitting portion; and a second optical waveguide provided at the other end of the first optical waveguide. A first total reflection optical member, a second total reflection optical member provided at the other end of the second optical waveguide, and an intersection of the first optical waveguide and the second optical waveguide. And a portion of the light incident on the first optical waveguide, which is partially reflected, in a direction toward the end of the second optical waveguide where the second total reflection optical member is provided. The first waveguide is transmitted through a part of the first waveguide and is incident in the direction of the first total reflection optical member. Respect of light incident is reflected by the total reflection optical member, each thereof,
A partially reflecting optical member that partially reflects and guides the guided optical waveguide to another waveguide different from the guided optical waveguide, and partially transmits the guided optical waveguide; A first reflecting optical member of the first optical waveguide;
Between the total reflection optical member, and between the partial reflection optical member and the second total reflection optical member of the second optical waveguide, at least one of the And an electrode for applying an electric field based on a desired modulation signal. 2. The substrate has a groove having a side wall including a cross section of the optical waveguide at an intersection of the first optical waveguide and the second optical waveguide. 2. The optical modulator according to claim 1, wherein the member is formed by inserting a film member on which a partial transmission / partial reflection film having a desired light branching ratio is formed into the groove. 3. The substrate according to claim 1, wherein a groove having a side wall including a cross section of the optical waveguide is formed at an intersection of the first optical waveguide and the second optical waveguide. 2. The optical modulator according to claim 1, wherein the member is formed by directly forming a partial transmission / partial reflection film for obtaining a desired light branching ratio on a side wall of the groove. 4. The optical modulation device according to claim 1, wherein the first optical waveguide and the second optical waveguide are formed so as to intersect at a large intersection angle of 45 ° to 90 °. vessel. 5. The optical system according to claim 1, wherein the first and second optical waveguides intersect at right angles to each other, and the partially reflecting optical member intersects the first and second optical waveguides at 45 °. The optical modulator according to claim 4, wherein