JP2006276519A - Waveguide type optical device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a waveguide type optical device, using a substrate including a part of ≤20 μm in thickness, which is free of breakage of the substrate and peeling of a polarizing means, such as a metal film breaking off the substrate and has a high yield and high productivity. <P>SOLUTION: The optical waveguide type optical device, which has the substrate 1 of ≤20 μm in thickness having electro-optical effects, an optical waveguide 2 formed on the top surface of the substrate, and a control electrode (not illustrated) for controlling light waves to be propagated in the optical waveguide 3 and also has a reinforcing plate 11 jointed to the reverse surface of the substrate 1 is characterized in that the polarizing means 10, formed of a metal film or high-refractive-index film, is provided between the substrate 1 and reinforcing plate 11. Preferably, the polarizing means 10 is jointed to only the reinforcing plate 11. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a waveguide-type optical device, and in particular, a substrate formed of a material having an electro-optic effect and having a portion with a thickness of 20 μm or less, and a reinforcing plate bonded to the back surface of the substrate and having a thickness larger than that of the substrate The present invention relates to a waveguide type optical device including:

Conventionally, in the optical communication field and the optical measurement field, a waveguide type optical device such as a waveguide type optical modulator in which an optical waveguide or a modulation electrode is formed on a substrate having an electrooptic effect has been widely used.
In particular, with the development of multimedia, the amount of information transmission is also increasing, and it is necessary to realize a broadband optical modulation frequency. As one of means for realizing these, there is an external modulation system using a LiNbO ₃ (hereinafter referred to as “LN”) modulator or the like. However, in order to realize a wide band of the LN modulator, it is necessary to achieve speed matching between the microwave and the light wave that are the modulation signals and to reduce the driving voltage.

As means for solving the above-described problems, it has been conventionally known that, by reducing the thickness of the substrate, the speed matching condition between the microwave and the speed of the light wave is satisfied and the driving voltage is simultaneously reduced.
In the following Patent Documents 1 to 3, an optical waveguide and a modulation electrode are incorporated in a thin substrate (hereinafter referred to as a “first substrate”) having a thickness of 30 μm or less, and another substrate having a lower dielectric constant than the first substrate. The effective refractive index with respect to the microwave is lowered, the speed matching between the microwave and the light wave is achieved, and the mechanical strength of the substrate is maintained.
JP-A 64-18121 JP 2003-215519 A Japanese Patent Laid-Open No. 10-133159

On the other hand, optical intensity modulators, optical switches, variable optical attenuators (VOA), phase modulators and the like have been developed and put into practical use as waveguide type optical devices. For example, in a VOA element, in a single-arm branching waveguide constituting a Mach-Zehnder interferometer, the refractive index of the waveguide is changed by the electro-optic effect, the thermo-optic effect, etc., and the output light intensity is adjusted.
However, when a substrate having optical anisotropy is used, the applied voltage and the heating amount differ depending on the incident light polarization. For this reason, only specific polarization is guided.

As a method of selecting a specific polarization, as shown in Patent Document 4 below, as shown in FIG. 1A, a method of attaching the polarizer 2 to the entrance end face of the substrate 1 of the waveguide type optical device, When an LN substrate is used, a method of attaching the metal film 4 on the optical waveguide 3 in the X-cut plate (see FIG. 1B), and a slab is applied to the side surface of the optical waveguide in the Z-cut plate. There are methods.
JP 2000-266951 A

  However, when a thin plate having a thickness of 20 μm or less is used, it is difficult to attach a polarizer to the end face of the substrate with high accuracy as shown in FIG. 1A, and FIG. When the metal film 4 is attached to the surface of the thin plate as described above, there is an increased risk of the substrate being damaged due to the difference in coefficient of thermal expansion between the substrate and the metal film, and the metal film is installed on the optical waveguide 3 in the first place. In such a case, there arises a problem that not only the specific polarized wave is absorbed but also the light wave of another polarization plane is attenuated.

  In addition, in order to increase the adhesion strength between the metal film 4 and the substrate, film formation is performed while heating the substrate in the vacuum film formation method such as sputtering or vacuum evaporation. Has a problem that it easily breaks due to the thermal stress due to the difference in thermal expansion coefficient described above.

  The problem to be solved by the present invention is to solve the above-mentioned problems, and in a waveguide type optical device using a substrate including a part having a thickness of 20 μm or less, polarizing means such as substrate breakage and metal film are peeled off from the substrate. It is another object of the present invention to provide a waveguide type optical device that has a high yield and high productivity.

  In order to solve the above-described problem, in the invention according to claim 1, a substrate having an electrooptic effect with a thickness of 20 μm or less, an optical waveguide formed on the surface of the substrate, and a light wave propagating through the optical waveguide In a waveguide type optical device having a control electrode for controlling and having a reinforcing plate bonded to the back surface of the substrate, at least a portion between the substrate and the reinforcing plate has a metal film or a high refractive index. A polarizing means using an index film is provided.

  The invention according to claim 2 is characterized in that, in the waveguide type optical device according to claim 1, the polarizing means is bonded only to the reinforcing plate.

  According to a third aspect of the present invention, in the waveguide type optical device according to the first aspect, the polarizing means is formed on the reinforcing plate by a film forming process.

  The invention according to claim 4 is the waveguide type optical device according to any one of claims 1 to 3, wherein the polarizing means has a thickness of 50 to 1000 nm.

  According to a fifth aspect of the present invention, in the waveguide type optical device according to any one of the first to fourth aspects, the position where the polarizing means is formed is located on the back surface of the substrate where the optical waveguide is formed. It is a region.

  The invention according to claim 6 is the waveguide optical device according to any one of claims 1 to 5, characterized in that the polarizing means is in direct contact with the back surface of the substrate.

  The invention according to claim 7 is the waveguide optical device according to any one of claims 1 to 6, wherein the bonding between the substrate and the reinforcing plate is direct bonding.

  According to an eighth aspect of the present invention, in the waveguide type optical device according to any one of the first to seventh aspects, the substrate and the reinforcing plate are bonded to a region excluding a portion where the polarizing means is formed. It is characterized by being carried out by forming a layer.

  The invention according to claim 9 is the waveguide type optical device according to claim 8, wherein the thickness of the bonding layer is substantially the same as the thickness of the polarizing means.

  According to a tenth aspect of the present invention, in the waveguide type optical device according to any one of the first to ninth aspects, the region between the substrate and the reinforcing plate is a region excluding the portion where the polarizing means is formed. A spacer corresponding to the thickness of the polarizing means is arranged.

  According to an eleventh aspect of the present invention, in the waveguide type optical device according to the tenth aspect, the spacer is formed by providing a recess in a region including a portion where the polarizing means is formed on the surface of the reinforcing plate. It is characterized by being.

  According to a twelfth aspect of the present invention, in the waveguide type optical device according to the first to eleventh aspects, at least the surface portion of the reinforcing plate on the side where the polarizing means is formed has a lower refractive index than the substrate. It is composed of a material.

  According to the first aspect of the present invention, since the polarizing means by the metal film or the high refractive index film is provided in at least a part between the substrate and the reinforcing plate, there is no peeling of the polarizing means and the control formed on the surface of the substrate. It is possible to increase the degree of freedom of design related to the waveguide type optical device, for example, the polarizing means can be arranged at a required place without being affected by the configuration of the electrode for the use. Moreover, since the thickness of the substrate is 20 μm or less, the optical waveguide formed from the front surface of the substrate reaches the vicinity of the back surface of the substrate or reaches the back surface of the substrate, and propagates through the optical waveguide by the polarization means disposed on the back surface of the substrate. It is possible to effectively remove the specific polarization of the light wave.

  According to the invention of claim 2, since the polarizing means is bonded only to the reinforcing plate, there is no need to bond the polarizing means to a substrate having a thickness of 20 μm or less, and the substrate may be damaged by heat treatment such as vacuum evaporation. Further, it is possible to avoid alteration of the polarizing means due to heat by heat treatment performed after providing a waveguide or the like on the substrate.

  According to the invention of claim 3, since the polarizing means is formed on the reinforcing plate by film formation, the shape, thickness and composition of the polarizing means can be freely controlled, and the polarizing means and the reinforcing plate Thus, it is possible to provide a waveguide type optical device having a polarizing means with excellent polarization function and durability.

  According to the invention of claim 4, since the thickness of the polarizing means is 50 to 1000 nm, the substrate and the reinforcing plate can be disposed close to each other, and the under cladding function of the optical waveguide in which the reinforcing plate is formed on the substrate is provided. Various characteristics of the reinforcing plate can be exhibited.

  According to the invention of claim 5, since the position where the polarization means is formed is a region located on the back surface of the substrate where the optical waveguide is formed, the specific polarization is efficiently generated from the light wave propagating through the optical waveguide. It can be removed.

  According to the invention of claim 6, since the polarizing means is in direct contact with the back surface of the substrate, it is possible to increase the polarization efficiency of the polarizing means.

  According to the invention of claim 7, since the bonding between the substrate and the reinforcing plate is direct bonding, the bonding strength between the two can be increased and the reinforcing plate is formed on the substrate in order to bring the substrate and the reinforcing plate into close contact with each other. Various properties brought about by the reinforcing plate on the substrate, such as having an underclad function of the optical waveguide, can be effectively exhibited.

  According to the invention of claim 8, since the bonding between the substrate and the reinforcing plate is performed by forming a bonding layer in a region excluding the portion where the polarizing means is formed, the substrate and the polarizing means are in contact with each other. Therefore, it is possible to provide a waveguide type optical device having a stable temperature characteristic without causing thermal stress due to a difference in linear expansion coefficient between the substrates and the polarizing means.

  According to the invention of claim 9, since the thickness of the bonding layer described above is substantially the same as the thickness of the polarizing means, the distance between the substrate and the reinforcing plate is kept constant, and the various properties that the reinforcing plate gives to the substrate. The effect can be made uniform over the entire substrate. Moreover, even if the polarizing means is disposed between the substrate and the reinforcing plate, it is possible to suppress the occurrence of mechanical stress strain in the bonding between the substrate and the reinforcing plate.

  According to the invention of claim 10, since the spacer corresponding to the thickness of the polarizing means is disposed between the substrate and the reinforcing plate in the region excluding the portion where the polarizing means is formed, the thickness of the polarizing means Even when becomes thicker, the distance between the substrate and the reinforcing plate can be kept constant.

  According to the eleventh aspect of the present invention, the spacer described above is formed by providing a recess in a region including the portion where the polarizing means is formed on the surface of the reinforcing plate. It is possible to make the surface of the reinforcing plate closer to the back surface of the substrate. Further, by making the depth of the recess substantially the same as the thickness of the polarizing means, the polarizing means can be brought close to the back surface of the substrate.

  According to the twelfth aspect of the present invention, at least the surface portion of the reinforcing plate on the side where the polarizing means is formed is made of a material having a refractive index lower than that of the substrate. It becomes possible to fulfill the under-cladding function of the waveguide.

Hereinafter, the present invention will be described in detail using preferred examples.
As shown in FIG. 2, the waveguide type optical device according to the present invention has a substrate 1 having a thickness of 20 μm or less having an electrooptic effect, an optical waveguide 2 formed on the surface of the substrate, and the optical waveguide 3. In a waveguide type optical device having a control electrode (not shown) for controlling a light wave propagating through the substrate 1 and having a reinforcing 11 plate bonded to the back surface of the substrate 1, the substrate 1 and the reinforcing plate 11. The polarizing means 10 made of a metal film or a high refractive index film is provided at least at a part between the two. In particular, the polarizing means 10 is characterized by being bonded only to the reinforcing plate 11.

  In the state where the substrate 1 and the reinforcing plate 11 of FIG. 2 are joined, the polarization means 10 is disposed in a region located on the back surface of the substrate 1 in the portion where the optical waveguide 3 is formed. It is possible to efficiently remove a specific polarization from the propagating light wave. Moreover, since the polarizing means 10 is in direct contact with the back surface of the substrate 1, the polarization efficiency by the polarizing means can be further increased.

  In the present invention, since the substrate 1 having a thickness of 20 μm or less is used, a specific polarization of the light wave (especially on the substrate surface) can be obtained from the back surface of the substrate with respect to the light wave propagating through the optical waveguide formed on the substrate surface. It is possible to efficiently remove a light wave having a polarization plane in a vertical direction.

  As a material having an electro-optic effect constituting the substrate 1, for example, lithium niobate, lithium tantalate, PLZT (lead lanthanum zirconate titanate), quartz-based materials, and combinations thereof can be used. In particular, a lithium niobate (LN) crystal having a high electro-optic effect is preferably used. Further, as the substrate 1, an X cut plate or a Y cut plate can be suitably used.

  Various materials can be used as the reinforcing plate 11. For example, in addition to using the same material as that of the substrate 1, a lower dielectric constant than that of the substrate 1 such as quartz, glass, alumina, etc. It is also possible to use a material or a material having a crystal orientation different from that of the substrate 1. However, it is preferable to select a material having a linear expansion coefficient equivalent to that of the substrate 1 in order to stabilize the temperature characteristics of the waveguide type optical device against temperature changes. If it is difficult to select an equivalent material, a material having a linear expansion coefficient equivalent to that of the substrate is selected as an adhesive for joining the substrate and the reinforcing plate as in Patent Document 2.

  For bonding the substrate 1 and the reinforcing plate 11, an epoxy adhesive, a thermosetting adhesive, an ultraviolet curable adhesive, solder glass, a thermosetting, photocurable or photothickening resin adhesive is used as an adhesive layer. Various adhesive materials such as agent sheets can be used. It is also possible to directly bond the substrate 1 and the reinforcing plate 11 without using an adhesive by direct bonding (direct bonding method) while applying pressure to bring the substrate 1 and the reinforcing plate 11 into close contact with each other.

  The polarizing means can be formed using a metal film (conductive material film) such as Al or Zn, or a high refractive index film such as Ta2O5 or Nb2O5. In the case of using a metal film, a method of forming an opening of a predetermined pattern with a photoresist film in advance and vapor-depositing on the opening, or a method of removing other vapor-deposited film leaving a predetermined region on the entire substrate surface after vapor deposition There is. The thickness of the polarizing means is preferably set in the range of 50 to 1000 nm. When the thickness is small, the substrate 1 and the reinforcing plate 11 can be joined by direct bonding. In addition, when the thickness is large, it is preferable that an adhesive layer or a spacer, which will be described later, be disposed on the surface of the reinforcing plate other than the polarizing means, and the substrate 1 and the reinforcing plate 11 are joined.

As a method for forming the optical waveguide of the waveguide type optical device, it can be formed by diffusing Ti or the like on the substrate surface by a thermal diffusion method or the like as in the prior art.
Control electrodes such as a signal electrode and a ground electrode can be formed by forming a Ti / Au electrode pattern, a gold plating method, or the like. Further, if necessary, a buffer layer such as a dielectric SiO ₂ can be provided on the substrate surface.

As an example of a method for manufacturing a waveguide type optical device, the above-described optical waveguide is formed on a substrate having a thickness of several hundreds μm, and the back surface of the substrate is polished to produce a thin plate having a thickness of 20 μm or less. Then, a modulation electrode is formed on the surface of the thin plate. It is also possible to polish the back surface of the substrate after making the optical waveguide, the modulation electrode, and the like. In addition, there is a risk that the thin plate may be damaged when a thermal shock during the formation of the optical waveguide or a mechanical shock due to the handling of the thin film during various treatments. It is preferably performed before the substrate is polished and thinned.
On the other hand, a polarizing means is formed on the surface of the reinforcing plate 11 by vacuum deposition or the like, and the substrate 1 and the reinforcing plate 11 are bonded by a direct bonding method.

FIG. 3 shows another embodiment of the waveguide type optical device according to the present invention.
FIG. 3 shows an example in which the polarizing means 10 such as a metal film or a high refractive index film is formed on the base film 13 such as glass. However, when the thickness of the polarizing means is increased in this way, the substrate It is difficult to directly join 1 and the reinforcing plate 11. For this reason, it is preferable to join both through the adhesive layer 12 which has substantially the same thickness as the thickness of the polarizing means portions (10 and 13).

Further, instead of the adhesive layer 12, a spacer can be arranged to keep the distance between the substrate 1 and the reinforcing plate 11 at a predetermined distance.
Furthermore, the spacer does not necessarily need to be a separate member from the reinforcing plate 11, and a concave portion is formed on the surface of the reinforcing plate 11 where the polarizing means is disposed, and a convex portion on the surface other than the concave portion is used as the spacer. Is also possible.

In the waveguide type optical device according to the present invention, since the polarization means is disposed between the substrate and the reinforcing plate, as shown in FIG. Without being affected, the polarizing means can be arranged at the necessary locations (A to C), and the degree of freedom in designing the waveguide type optical device can be increased.
When the Mach-Zehnder type optical waveguide 3 as shown in FIG. 4 is used, the polarization means may be arranged in any of the incident side optical waveguide portion A, the branching waveguide portion B, or the emission side optical waveguide portion C. In the portion where the branching waveguides are combined, mode conversion may occur. When only polarized light is output, it is most efficient to place it in the portion C.

Next, specific examples and tests related to the optical modulator of the present invention will be described.
(Example)
The thin plate light modulation element uses an X-cut LN substrate having a thickness of 500 μm for the substrate, and forms a linear optical waveguide (width 7 μm) on the substrate surface by a Ti diffusion process or the like. The back surface of the substrate was polished with a polishing machine until the thickness of the substrate reached 10 μm.
Next, using the same substrate (X-cut LN substrate having a thickness of 500 μm), forming polarizing means on the surface of the substrate, forming Al with a thickness of 200 nm and a length of 1 mm along the optical waveguide, and reinforcing with polarizing means I got a plate. The polished substrate and the reinforcing plate were pressed and directly bonded to produce a waveguide type optical device.

(Comparative example)
A waveguide type optical device was prepared in the same manner as in the example except that the polarizing means of the example was not formed.

When the polarization extinction ratio in the example and the comparative example was measured, it was 10 to 15 dB in the example and 0.5 to 3 dB in the comparative example.
From this, it is understood that the polarization means of the present invention effectively attenuates the mode light of the longitudinal polarization plane.

  As described above, according to the present invention, in the waveguide type optical device using the substrate including a portion having a thickness of 20 μm or less, the polarizing means such as the substrate damage or the metal film is not peeled off from the substrate, In addition, it is possible to provide a waveguide type optical device with a high yield and high productivity.

It is a figure which shows the polarization means of the conventional waveguide type optical device. It is a figure which shows the outline of the waveguide type optical device which concerns on this invention. It is a figure which shows the other Example of the waveguide type optical device which concerns on this invention. It is a figure which shows the arrangement position of the polarization means in the waveguide type optical device which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Polarizer 3 Optical waveguide 4 Metal film 10 Polarizing means 11 Reinforcing plate 12 Adhesive layer 13 Base film

Claims (12)

A substrate having an electro-optic effect with a thickness of 20 μm or less; an optical waveguide formed on the surface of the substrate; and a control electrode for controlling a light wave propagating through the optical waveguide; In the waveguide type optical device to which the reinforcing plate is joined,
A waveguide type optical device comprising a polarizing means comprising a metal film or a high refractive index film at least partially between the substrate and the reinforcing plate.   2. The waveguide type optical device according to claim 1, wherein the polarization means is bonded only to the reinforcing plate.   2. The waveguide type optical device according to claim 1, wherein the polarizing means is formed on a reinforcing plate by a film forming process.   4. The waveguide type optical device according to claim 1, wherein the polarizing means has a thickness of 50 to 1000 nm.   5. The waveguide type optical device according to claim 1, wherein a position where the polarization means is formed is a region located on a back surface of the substrate where the optical waveguide is formed. Waveguide type optical device.   6. The waveguide optical device according to claim 1, wherein the polarization means is in direct contact with the back surface of the substrate.   7. The waveguide type optical device according to claim 1, wherein the bonding between the substrate and the reinforcing plate is direct bonding.   8. The waveguide type optical device according to claim 1, wherein the substrate and the reinforcing plate are bonded by forming a bonding layer in a region excluding a portion where the polarizing means is formed. A waveguide type optical device.   9. The waveguide optical device according to claim 8, wherein the thickness of the bonding layer is substantially the same as the thickness of the polarizing means.   10. The waveguide type optical device according to claim 1, wherein a region between the substrate and the reinforcing plate except for a portion where the polarizing means is formed corresponds to a thickness of the polarizing means. A waveguide type optical device characterized in that a spacer is arranged.   11. The waveguide type optical device according to claim 10, wherein the spacer is formed by providing a recess in a region including a portion where the polarizing means is formed on the surface of the reinforcing plate. A waveguide type optical device. 12. The waveguide type optical device according to claim 1, wherein at least a surface portion of the reinforcing plate on the side where the polarizing means is formed is made of a material having a refractive index lower than that of the substrate. A waveguide-type optical device.

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