JP2007271694A - Optical wave guide element and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical wave guide element and its manufacturing method which can directly connect the block to the surface of a substrate, without degrading the properties of the optical wave guide and is superior in massproductivity, at low cost. <P>SOLUTION: This optical wave guide element has a substrate 1 mounting an optical wave guide 2 on its surface to guide light wave, and a block 4 provided at an edge of this substrate to cover at least some of the optical wave guides. This substrate and the block are directly connected and the surface of the block in contact with the substrate is polished aslant, and is directed toward the end of the substrate. Preferably, the edge of the substrate is a light input or the output surface of the optical wave guide element, and the gradient δ of the polished surface of the substrate to the optical wave guides is 1/1,000 to 1/10,000. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical waveguide element and a method for manufacturing the same, and in particular, a substrate having an optical waveguide on which light waves are guided, and an end portion of the substrate so as to cover at least a part of the optical waveguide. The present invention relates to an optical waveguide device including a block and a manufacturing method thereof.

Conventionally, in the optical communication field and the optical measurement field, an optical waveguide element having an optical waveguide on a substrate surface, such as an optical modulator and an optical switch, has been put into practical use. For example, on a ferroelectric substrate having an electro-optic effect such as lithium niobate (LiNbO _3, hereinafter referred to as “LN”), a dissimilar element such as Ti is thermally diffused to locally increase the refractive index and lead it. A waveguide-type optical modulator formed by combining a signal wave electrode with a waveguide is a device that forms the core of a high-speed communication system.

  A ferroelectric crystal such as LN generally has a large optical anisotropy (dependence of refractive index on the crystal axis), and therefore the polarization direction of a light wave propagating through a waveguide formed along a specific crystal axis direction. The refractive index perceived by the propagating light differs and the propagation speed changes. As a result, characteristics such as the driving voltage and extinction ratio of the modulator greatly change. Therefore, in order to stabilize the characteristics of the modulator and achieve higher performance, it is preferable that the light waves incident on the waveguide of the modulator are aligned in one direction.

Therefore, as in Patent Document 1 below, a light attracting member such as a ZnLN substrate (LN crystal added with Zn) or the like is attached so as to cover a part of the optical waveguide formed on the LN substrate, and propagates through the optical waveguide. The specific polarization mode light is removed from the light wave.
JP-A-10-68830

  On the other hand, for connecting the optical fiber to the optical waveguide element, a capillary for holding the optical fiber is bonded to the substrate of the optical waveguide element. Since the optical waveguide of the optical waveguide element is formed on the surface of the substrate, sufficient mechanical strength is obtained because only about half the area of the end of the capillary is bonded to the substrate by simply bonding the capillary to the substrate. I can't. In order to solve this problem, a reinforcing plate is bonded onto the substrate at the incident portion or the emitting portion of the optical waveguide element, and the capillary is bonded to the reinforcing plate, thereby increasing the bonding strength between the optical waveguide element and the optical fiber. Things have been done.

  By the way, when a block such as a light attracting member or a reinforcing plate is joined to an LN substrate or the like, it is possible to join the two via an adhesive, but the heat resistance and durability are low, and the adhesive is light. It may affect the light wave propagating through the waveguide and cause light loss. For this reason, the substrate and the block are directly joined. In direct bonding, two members to be bonded are made of a material having the same crystal structure, closely bonded so that the crystal orientations in the plane where the two are bonded are aligned, and heated as necessary, so that they are fixed at the bonding interface. Crystals can be bonded to each other by phase thermal diffusion.

  However, in order to join the substrate and the block by direct joining, it is necessary to smooth the joining surface of both with submicron accuracy (about 10 to 20 nm). In particular, the optical waveguide is thermally diffused by Ti or the like. The optical waveguide element formed by the above method has irregularities of about 10 nm, and it is essential to polish the substrate surface of the optical waveguide element. Moreover, the optical waveguide element is produced using a wafer substrate having a diameter of 3 to 4 inches, and the wafer itself has a warp of about 10 to 50 μm.

  Therefore, it is difficult to flatten the entire wafer substrate with submicron accuracy, and even if local polishing is performed, a step occurs at the boundary between the polishing region on the substrate and other regions. In addition, the light wave propagating through the optical waveguide is also scattered there.

  The problem to be solved by the present invention is to solve the above-described problems, and can directly join a block to the surface of a substrate without deteriorating the characteristics of the optical waveguide. Moreover, the optical waveguide is excellent in mass productivity at low cost. It is providing a device and a method for manufacturing the device.

  In the invention according to claim 1, an optical device comprising: a substrate on which an optical waveguide on which light waves are guided is formed; and a block disposed at an end of the substrate so as to cover at least a part of the optical waveguide. In the waveguide element, the substrate and the block are directly bonded, and a bonding surface of the block in the substrate is polished obliquely toward an end surface of the substrate.

  According to a second aspect of the present invention, in the optical waveguide element according to the first aspect, the end of the substrate is an incident part or an outgoing part of the optical waveguide element.

  The invention according to claim 3 is the optical waveguide element according to claim 2, wherein the gradient of the polishing surface of the substrate with respect to the optical waveguide is 1/1000 to 1/10000.

  In the invention according to claim 4, in the optical waveguide device according to any one of claims 1 to 3, the substrate is a crystal substrate having refractive index anisotropy, and the block has a refractive index of the substrate. Compared with anisotropy, the refractive index in a specific direction is high, the refractive index in other directions is the same or low, and the material has the same crystal structure as the substrate.

  In the invention according to claim 5, in the optical waveguide device according to claim 4, the substrate is lithium niobate, the optical waveguide is formed by Ti diffusion, and the block is made of Zn, Ni, Co or Mg. Lithium niobate containing at least one of the following.

  According to a sixth aspect of the present invention, in the method for manufacturing an optical waveguide element according to any one of the first to fifth aspects, after forming a plurality of optical waveguide elements on a wafer-like substrate, The end portion is polished obliquely, the block is directly joined to the end portion, and then cut and separated into individual optical waveguide elements.

  According to the first aspect of the present invention, an optical device comprising: a substrate having an optical waveguide on which light waves are guided; and a block disposed at an end of the substrate so as to cover at least a part of the optical waveguide. In the waveguide element, the substrate and the block are directly bonded, and the bonding surface of the block in the substrate is polished obliquely toward the end surface of the substrate. In addition to removing the light, the region to be polished is local, and the scattering of the light wave propagating through the optical waveguide can be suppressed, so that the block can be directly bonded to the substrate surface without degrading the characteristics of the optical waveguide. In addition, it is possible to provide an optical waveguide device that is low in cost and excellent in mass productivity.

  According to the invention of claim 2, since the end of the substrate is an incident portion or an emission portion of the optical waveguide element, not only can the block be used as a reinforcing plate at the time of joining with the optical fiber, but also the light of the optical waveguide. It is also possible to improve the mode symmetry and improve the coupling efficiency with the optical fiber.

  According to the invention of claim 3, since the gradient of the polishing surface of the substrate with respect to the optical waveguide is 1/1000 to 1/10000, the light wave propagating through the optical waveguide can be prevented from being reflected by the polishing surface, and the optical waveguide It is also possible to suppress the propagation loss.

  According to the invention of claim 4, the substrate is a crystal substrate having refractive index anisotropy, and the block has a higher refractive index in a specific direction than the refractive index anisotropy of the substrate, and other directions. Since the refractive index is a material having the same or low refractive index and the same crystal structure as that of the substrate, the block can function as a light attracting member and can directly bond the substrate and the block.

  According to the invention of claim 5, since the substrate is lithium niobate, the optical waveguide is formed by Ti diffusion, and the block is lithium niobate containing at least one of Zn, Ni, Co, or Mg, LN Even in an optical waveguide device using a substrate, it is possible to provide an optical waveguide device that can be directly bonded to the surface of the substrate without degrading the characteristics of the optical waveguide, and that is excellent in mass production at low cost. .

  According to the invention of claim 6, in the method of manufacturing an optical waveguide element, after forming a plurality of optical waveguide elements on a wafer-like substrate, the end of the optical waveguide element is polished obliquely, and the block is Since it is directly bonded to the end portion and then cut and separated into individual optical waveguide elements, it is possible to mass-produce optical waveguide elements bonded with blocks at a low cost.

Hereinafter, the present invention will be described in detail using preferred examples.
FIG. 1 is a diagram showing a part of an optical waveguide device according to the present invention.
The optical waveguide device of the present invention includes a substrate 1 on which an optical waveguide 2 on which light waves are guided is formed on a surface, and a block 4 disposed at an end of the substrate 1 so as to cover at least a part of the optical waveguide 2. In particular, the substrate 1 and the block 4 are directly bonded, and the bonding surface 10 of the block in the substrate 1 is polished obliquely (gradient δ) toward the end surface of the substrate. It is characterized by that.

  The end portion of the substrate 1 to which the block 4 is bonded is preferably an incident portion or an emitting portion of the optical waveguide element as shown in FIG. This is because the block 4 can be used as a reinforcing plate when the optical waveguide element and the optical fiber are joined. Further, the optical mode shape 20 of the light wave propagating through the optical waveguide 2 in the arrow A in FIG. 1 has a flat shape in a direction parallel to the substrate surface as shown in FIG. However, by propagating through the junction with the block, the optical mode shape of the light wave extends in the vertical direction as shown in FIG. 2B showing the optical mode shape 21 in the arrow B of FIG. Will be improved. For this reason, the coupling efficiency with the optical fiber is improved, and a more preferable optical waveguide element can be provided.

  The gradient δ of the polished surface 10 is preferably 1/1000 to 1/10000, which can prevent light waves propagating through the optical waveguide from being reflected by the polished surface, and can also prevent propagation loss and quenching of the optical waveguide. It is also possible to suppress the deterioration of the ratio. As a result of actual trial manufacture, an optical waveguide element having an excess loss of about 1 dB or less and an extinction ratio of 25 dB or more is obtained.

For the block bonded to the substrate, if the function as a reinforcing plate is simply expected, the same material as the substrate constituting the optical waveguide element can be used as the block, but as shown in Patent Document 1, When the function as a light attracting member is expected, as a block, the refractive index anisotropy of the specific direction is higher than the refractive index anisotropy of the substrate of the optical waveguide device, and the refractive index of the other direction is the same or lower. It is preferable to use a material having the same crystal structure as the substrate.
As such a material, when an LN substrate is used as the substrate of the optical waveguide device, it is possible to use a material containing at least one of Zn, Ni, Co or Mg in the LN crystal.

The material and structure constituting the optical waveguide element are not particularly limited. For example, lithium niobate or tantalate, which is a substrate having an electrooptic effect frequently used in an optical modulator, an optical switch, or the like. Lithium or the like can be suitably used.
The optical waveguide formed on the substrate can be formed by diffusing Ti or the like on the substrate surface by a thermal diffusion method or a proton exchange method.

Furthermore, if necessary, the control electrode 3 such as a signal electrode or a ground electrode can be provided on the surface of the substrate, etc., which are formed by forming an electrode pattern of Ti / Au, a gold plating method, or the like. Is possible. Furthermore, it is also possible to provide a buffer layer such as dielectric SiO ₂ on the substrate surface after the optical waveguide is formed.

  Note that LN substrates are widely used in general optical waveguide elements, and those with a certain quality can be obtained at low cost. Also, a technique for forming an optical waveguide on the LN substrate by thermal diffusion of Ti is sufficient. Considering that it is established and the like, the optical waveguide element of the present invention uses lithium niobate for the substrate, the optical waveguide is formed by Ti diffusion, and further, lithium niobate containing Zn as a block (Hereinafter referred to as “ZnLN”) is more preferable.

Next, the manufacturing method of the optical waveguide device of the present invention will be described. In the following, an example using an LN substrate is shown, but the present invention is not limited to this.
(1) Formation of optical waveguide Ti is adhered to the substrate surface in a pattern of an optical waveguide on a wafer substrate made of LN crystal, and Ti is thermally diffused into the substrate by heat treatment to form an optical waveguide.
(2) Formation of electrodes, etc. Ti / Au electrode patterns are formed on the wafer substrate, and Au electrodes are formed by a plating method. Before forming the electrode, it is possible to form a buffer layer such as a SiO ₂ film on the optical waveguide. As a method for forming the buffer layer, a sputtering method or a vapor deposition method can be used.

(3) Polishing the substrate A portion of the wafer substrate, particularly a region where the block is joined, is polished obliquely shallowly. As a polishing method, polishing is performed using a polishing sheet or a lapping mop. The polishing process can be performed after all the members required for the optical waveguide device such as the optical waveguide and the electrode are incorporated on the wafer substrate. You may go in stages.

(4) Bonding of substrate and block The wafer substrate and the ZnLN to be the block are washed with sulfuric acid / hydrogen peroxide, etc., dried, and then bonded together at room temperature. It is also possible to reinforce the bonding strength by heating to 80 ° C. or higher after bonding.
The substrate and the block constituting the optical waveguide element can be joined at the wafer substrate stage, but if necessary, the block can be applied to the chip of the optical waveguide element cut out from the wafer substrate. It is also possible to join the chips.

(5) Separation of optical waveguide elements Since a plurality of optical waveguide elements are incorporated in the wafer substrate, the wafer substrate is cut and separated into individual optical waveguide elements. If necessary, a cut surface corresponding to the incident portion or the emitting portion of the optical waveguide element may be polished to perform a polishing process for improving the optical coupling with the optical fiber.

  As described above, according to the present invention, an optical waveguide element capable of directly joining a block to the surface of a substrate without degrading the characteristics of the optical waveguide, and having excellent mass productivity is provided. It becomes possible to do.

It is a figure which shows a part of optical waveguide element concerning this invention. It is a figure which shows the mode of the optical mode shape of the light wave which propagates the optical waveguide element of FIG.

Explanation of symbols

1 Substrate 2 Optical waveguide 3 Electrode 4 Block 10 Bonding surface (polished surface)
20, 21 Optical mode shape

Claims (6)

In an optical waveguide device comprising: a substrate on which an optical waveguide on which light waves are guided is formed; and a block disposed at an end of the substrate so as to cover at least a part of the optical waveguide.
The substrate and the block are directly bonded,
An optical waveguide device, wherein a bonding surface of the block in the substrate is polished obliquely toward an end surface of the substrate.   2. The optical waveguide device according to claim 1, wherein the end portion of the substrate is an incident portion or an emission portion of the optical waveguide device.   3. The optical waveguide element according to claim 2, wherein the gradient of the polishing surface of the substrate with respect to the optical waveguide is 1/1000 to 1/10000.   4. The optical waveguide device according to claim 1, wherein the substrate is a crystal substrate having refractive index anisotropy, and the block is specified in comparison with the refractive index anisotropy of the substrate. An optical waveguide device characterized by being a material having a high refractive index in the direction and the same or low refractive index in the other direction and having the same crystal structure as the substrate.   5. The optical waveguide device according to claim 4, wherein the substrate is lithium niobate, the optical waveguide is formed by Ti diffusion, and the block further includes at least one of Zn, Ni, Co, or Mg. An optical waveguide device characterized by being lithium. In the method for manufacturing an optical waveguide element according to any one of claims 1 to 5, after forming a plurality of optical waveguide elements on a wafer-like substrate, the end of the optical waveguide element is polished obliquely, A method of manufacturing an optical waveguide device, comprising: joining the block directly to the end, and then cutting and separating into individual optical waveguide devices.

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