JP2011158590A - Optical waveguide device and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical waveguide device and a method of manufacturing the optical waveguide device in which evanescent wave is used as monitoring light, and contamination materials are easily removed or recontamination is suppressed. <P>SOLUTION: The optical waveguide device includes a substrate 1 composed of a material having pyroelectricity or piezoelectricity and an optical waveguide 2 formed at a part of the substrate. The optical waveguide device further includes a light receiving element 3 which is disposed straddling the optical waveguide and a base 4 formed on the substrate for adjusting the distance between the light receiving element and the optical waveguide. The base is composed of a film body and at least a surface material facing the light receiving element is formed of any one of a photocatalytic material, an electric conductive material and a semiconductor material. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical waveguide device and a method for manufacturing the same, and in particular, a diffusion waveguide formed by thermally diffusing a high refractive index material on a dielectric substrate, and disposed above the diffusion waveguide, The present invention relates to an optical waveguide device having a light receiving element that receives a part of a light wave propagating through a diffusion waveguide.

  In an optical waveguide device such as an optical modulator having an optical waveguide, a light receiving element (Photo Detector, PD) is arranged close to the optical waveguide in order to monitor a part of the light wave propagating through the optical waveguide. Yes. As one method for taking out monitor light from an optical waveguide, there is a method using an evanescent wave as shown in Patent Document 1.

In order to use the evanescent wave, the light extraction efficiency to the light receiving element depends on the distance (gap) s from the bottom surface of the light receiving element to the optical waveguide if the structure of the optical waveguide and the light receiving element is determined. For this reason, it is necessary to arrange the distance between the optical waveguide and the light receiving element close to a region that can be coupled as an evanescent wave, and adjustment of the distance requires a highly accurate assembly technique. As an example, if the evanescent wave attenuates exponentially as it moves away from the waveguide surface, and the penetration depth at which the electric field amplitude becomes 1 / e from the waveguide boundary is d, the penetration depth d is It is expressed by equation (1). Γ _{c in} Expression (1) is further expressed by Expression (2).

Each character, kappa, N, n _c is the wave number of the respectively determined in vacuum, the effective refractive index of guided light of formula (2), a cladding refractive index. Here, if the wavelength is 1.55 μm, N = 2.2, and n _c = 1.5, d in Expression (1) is about 0.16 μm. For this reason, in order to obtain reproducibility of the light receiving sensitivity of the monitor light, the distance s from the optical waveguide of the light receiving element needs to be adjusted with an accuracy of about 10 nm.

In order to evaluate the practicality when an evanescent wave is used as monitor light, the distance between the optical waveguide and the light receiving element is adjusted, and the sensitivity of the light receiving element and the ON / OFF extinction ratio detected by the light receiving element are shown in FIG. Show. In the trial production of the vector type modulator with a monitor port, SiO ₂ was used as a gap adjusting film. FIG. 1 is a characteristic evaluation example of wavelength dependency of sensitivity and extinction ratio in the C band and the L band.

  As shown in FIG. 1, the sensitivity varies within 5%, and almost no wavelength dependency is observed. Also, the ON / OFF extinction ratio exceeds 20 dB, which is good. For example, signal sensitivity (monitor PD output signal [A] / signal light intensity [W]) necessary for monitoring and controlling the bias voltage applied to a modulation electrode such as an optical modulator is obtained. Further, it is easily understood that the signal light and the monitor light have the same phase and no phase difference, can be accurately monitored for bias, and have a high practicality.

  By the way, in Patent Document 1, in order to adjust the distance between the optical waveguide and the light receiving element with high accuracy, a high refractive index material used when forming the optical waveguide is used, and the light receiving element is disposed on the substrate on which the optical waveguide is formed. It is proposed to be used as part of the pedestal for support.

  By the way, if there is a contaminant such as dust or deposit between the optical waveguide and the light receiving element chip, the reproduction of the gap (gap) at the time of adhesion deteriorates, and the reproducibility of the characteristics (monitor signal extraction efficiency) is obtained. Absent. For example, if there are dust or deposits of a few hundred nanometers, it becomes a fatal problem that a monitor signal cannot be obtained at all.

For this reason, when adhering the light receiving element chip, contaminants such as dust and adhering matter between the optical waveguide and the light receiving element chip are removed. Effective methods for removing contaminants include scrub cleaning of the waveguide substrate, ultrasonic cleaning, ultraviolet ashing, atmospheric pressure plasma cleaning, and ionizer blow. However, when a pyroelectric or piezoelectric material such as LiNbO ₃ is used as the substrate of the optical waveguide device, it is easy to attract dust due to temperature changes after washing and static electricity generated by external pressure. There is a problem that the product is contaminated again after cleaning, which causes a significant decrease in the yield in manufacturing the optical waveguide device.

Japanese Patent Application No. 2009-69094 (filed on Mar. 19, 2009)

  The problem to be solved by the present invention is to solve the above-mentioned problems, and in the optical waveguide device using the evanescent wave as the monitor light and the method for manufacturing the same, it is easy to remove the contaminants or to re-contaminate. An optical waveguide device capable of being suppressed and a manufacturing method thereof are provided.

  In order to solve the above problems, an invention according to claim 1 is an optical waveguide device comprising a substrate made of a material having pyroelectricity or piezoelectricity, and an optical waveguide partially formed on the substrate. A light receiving element disposed across the optical waveguide; and a pedestal formed on the substrate for adjusting a distance between the light receiving element and the optical waveguide. The pedestal is formed of a film body. The surface material facing at least the light receiving element is formed of any one of a photocatalytic substance, a conductive substance, and a semiconductor substance.

  According to a second aspect of the present invention, in the optical waveguide device according to the first aspect, the light receiving element and the substrate are bonded with an adhesive having a refractive index lower than that of a material constituting the light receiving element. It is characterized by.

  The invention according to claim 3 is the optical waveguide device according to claim 1 or 2, wherein the pedestal is a transparent material having a refractive index of 2.3 or less, and the pedestal is made of a transparent material. It arrange | positions so that it may cover.

  The invention according to claim 4 is the optical waveguide device according to any one of claims 1 to 3, wherein the pedestal has an island-like pattern having a gap.

According to a fifth aspect of the present invention, in the optical waveguide device according to any one of the first to fourth aspects, the surface material uses at least one of TiO _{2 and} ITO.

  According to a sixth aspect of the present invention, in the method of manufacturing an optical waveguide device according to any one of the first to fifth aspects, before the light receiving element is mounted on the substrate, the surface of the pedestal is subjected to optical cleaning and ionizer. One of the blows is performed.

  According to the first aspect of the present invention, in an optical waveguide device having a substrate made of a pyroelectric or piezoelectric material and an optical waveguide partially formed on the substrate, the optical waveguide device is disposed so as to straddle the optical waveguide. And a pedestal formed on the substrate in order to adjust the distance between the light receiving element and the optical waveguide, the pedestal is formed of a film body, and at least faces the light receiving element. Since the surface material is formed of any one of the photocatalytic substance, the conductive substance, and the semiconductor substance, it is possible to easily remove the contaminant. Specifically, due to the photocatalytic effect of the photocatalytic substance, light cleaning can be performed by irradiating light before bonding the light receiving element. In addition, the adhesion of contaminants due to static electricity is weakened by a conductive substance or a semiconductor substance, and the adhered contaminants can be easily removed by ionizer blow or the like. In the case of a conductive material or a semiconductor material, surface charging can be suppressed and reattachment of contaminants can also be suppressed.

  According to the invention of claim 2, since the light receiving element and the substrate are joined with an adhesive having a refractive index lower than the refractive index of the material constituting the light receiving element, the evanescent wave is efficiently introduced into the light receiving element. It becomes possible to do.

  According to the invention of claim 3, since the pedestal is made of a transparent material having a refractive index of 2.3 or less, and is arranged so as to cover the optical waveguide, the arrangement of the pedestal with respect to the optical waveguide Therefore, it is possible to suppress the occurrence of light loss due to the pedestal.

  According to the invention of claim 4, since the pedestal has an island-like pattern having a gap, when the adhesive is used, the adhesive can be easily passed through the gap from between the substrate and the light receiving element. Can flow out or flow in, can suppress uneven thickness of the adhesive, and can appropriately adjust the distance between the optical waveguide formed on the substrate and the light receiving element.

According to the invention of claim 5, since the surface material of the pedestal uses at least one of TiO _{2 and} ITO, the removal effect of the pollutant is high, the reattachment of the pollutant can be suppressed, and the light with a high manufacturing yield. A waveguide device can be provided.

  According to the invention of claim 6, before mounting the light receiving element on the substrate, the surface of the pedestal is subjected to either optical cleaning or ionizer blow. Therefore, an optical waveguide device with a high manufacturing yield can be provided.

It is a graph which shows the wavelength dependence of the sensitivity and extinction ratio of a light receiving element when an evanescent wave is used as monitor light. It is the schematic which shows the optical waveguide device of this invention, and is sectional drawing of a direction parallel to a light propagation direction. It is a 1st Example of the optical waveguide device of this invention, and is a figure which shows sectional drawing in the arrow AA in FIG. It is a 2nd Example of the optical waveguide device of this invention, and is a figure which shows sectional drawing in the arrow AA in FIG. It is a figure which shows the example of application of the base in the optical waveguide device of this invention. It is a figure which shows an example of the structure of the base in the optical waveguide device of this invention. It is a figure which shows the other example of the structure of the base in the optical waveguide device of this invention.

  Hereinafter, the optical waveguide device of the present invention will be described in detail using preferred examples. FIG. 2 is a schematic view showing the optical waveguide device of the present invention, and is a cross-sectional view parallel to the light propagation direction. 3 or 4 is a cross-sectional view taken along arrow AA in FIG. 1, FIG. 3 shows a first embodiment of the present invention, and FIG. 4 shows a second embodiment of the present invention.

  As shown in FIG. 2, the present invention relates to an optical waveguide device having a substrate 1 made of a pyroelectric or piezoelectric material and an optical waveguide 2 partially formed on the substrate. 2 and a pedestal 4 formed on the substrate for adjusting the distance between the light receiving element 3 and the optical waveguide 2, the pedestal 4 being a film And at least a surface material facing the light receiving element is formed of any one of a photocatalytic substance, a conductive substance, and a semiconductor substance.

  In the present invention, “at least the surface material facing the light receiving element” means a constituent material of the pedestal when the entire pedestal is formed of one material, and the pedestal has a plurality of films as shown in FIG. In the case of being composed of a body, it means a material constituting the pedestal portion facing the light receiving element.

As the substrate 1 made of a material having pyroelectricity or piezoelectricity, a single crystal of LiNbO ₃ , LiTaO ₃ or PLZT can be suitably used. These materials are used as substrates for electro-optic devices such as optical modulators, and since optical waveguides are also formed on these devices, the present invention is effective as a means for monitoring light waves propagating through the optical waveguides. It is possible to apply it. When a substrate made of a material having pyroelectricity or piezoelectricity is used, it is required to remove contaminants and prevent reattachment of contaminants, which is the subject of the present invention. Contaminant measures when installing on a substrate are particularly important.

The optical waveguide formed on the substrate is formed by thermally diffusing a high refractive index material such as titanium (Ti) on a LiNbO ₃ substrate (LN substrate). Further, a rib-type optical waveguide in which grooves are formed on both sides of a portion that becomes an optical waveguide and a ridge-type waveguide in which the optical waveguide portion is convex can be used. In the optical waveguide device of the present invention, since a pedestal for supporting the light receiving element is formed on the substrate, thermal diffusion of Ti or the like or a rib-type optical waveguide can be more suitably used.

The width of the light receiving element (the width of the portion denoted by reference numeral 3 in FIG. 3) is about 100 μm to 3 mm, and the size of the pedestal portion is also formed in a range of about half to several times the width of the light receiving element. The pedestal portion formed on the substrate can be formed of only one of a photocatalytic material, a conductive material, and a semiconductor material. The pedestal portion may be composed of a single film body or a plurality of film bodies. What is important is to always coat the surface of the pedestal portion facing the light receiving element with either a photocatalytic substance, a conductive substance or a semiconductor substance. Therefore, an SiO ₂ film is formed on the pedestal part, or a pedestal is formed by Ti thermal diffusion as shown in Patent Document 1, and then the surface of these pedestal parts is either a photocatalytic substance, a conductive substance or a semiconductor substance. It is also possible to cover with.

More specifically, a structure in which the pedestal 4 is formed by a film body made of one material such as the photocatalytic substance described above as shown in FIG. 3, or a pedestal is constituted by a plurality of film bodies (42, 43) as shown in FIG. In addition, a structure in which only the surface material 42 facing the light receiving element 3 is formed of a photocatalytic substance or the like, and further, as shown in FIG. 7, only a base portion 44 facing the light receiving element 3 is formed of a photocatalytic substance or the like. Etc. can be adopted. In FIGS. 6 and 7, the film bodies 43 and 45 are not limited to the photocatalytic substance, and an SiO ₂ film or the like can be used. In particular, as shown in FIG. 7, in the surface portion of the pedestal, contamination 44 is made active by mixing a portion 44 made of a conductive material or a semiconductor material and a portion 45 made of an insulating material such as a SiO ₂ film. In particular, it is also possible to configure so as to separate contaminants from the portion 44 that is collected on the surface portion 45 and faces the light receiving element.

  When the surface of the pedestal part is covered with a photocatalytic substance, the contaminants adhering to or near the photocatalyst can be decomposed and removed by light irradiation (light cleaning), and the light receiving element and the substrate on which the optical waveguide is formed It is possible to adjust the interval between them with high accuracy and reproducibility on the order of several tens of nm.

  In addition, when a conductive material or semiconductor material is used on the surface of the pedestal part, contaminants that are attracted by static electricity due to pyroelectricity or piezoelectricity generated on the substrate on which the optical waveguide is formed are mainly on the pedestal part. Adhere to. This is because the electric potential due to pyroelectricity and piezoelectricity is almost the same for the part where the pedestal is formed and the part where the pedestal is not formed. This is because it becomes easier to attract pollutants that float. Contaminant adhering to the pedestal made of conductive material or semiconductor material is easier to remove by ionizer blow gun treatment than the contaminant adhering to the insulating part, and the distance between the light receiving element and the substrate on which the optical waveguide is formed Can be adjusted with high accuracy and reproducibility on the order of several tens of nanometers.

TiO ₂ , ITO, etc. have both a photocatalytic function and a semiconductor function, and are particularly suitable as the surface material of the pedestal portion used in the present invention. If these substances are used, the contaminants are preferentially captured by the pedestal portion, and not only are they easily removed with an ionizer blow gun or the like, but also an effect of decomposition and removal by light washing can be expected.

  The film portion of the pedestal portion can be formed by a general semiconductor manufacturing process when any material of a photocatalytic substance, a conductive substance, and a semiconductor substance is used. For example, after an optical waveguide is formed on an LN substrate, a film material having a predetermined thickness is formed on the surface of the LN substrate using a sputtering method, a vapor deposition method, or the like (thin film forming step). The pedestal can be formed using a lift-off method or a dry etching method. For example, a pedestal having various patterns to be described later can be formed by using a lift-off method using a photoresist.

  The light receiving element 3 and the substrate 1 use an adhesive 5 having a refractive index lower than the refractive index (n = 3.5) of the material constituting the light receiving element 3. Although it does not specifically limit as an adhesive agent, For example, organic adhesives, such as a thermosetting adhesive, are utilized suitably. Since such a low refractive index adhesive is used, the evanescent wave incident on the adhesive layer can be efficiently introduced into the light receiving element 3.

  Next, a cross-sectional view taken along arrow AA in FIG. 2 will be described. In the first embodiment of the optical waveguide device of the present invention, as shown in FIG. 3, the pedestal portion 4 is arranged so as to sandwich the optical waveguide 2 and not to contact the optical waveguide 2. Reference numeral 31 denotes a light receiving portion of the light receiving element.

  When a metal film (refractive index n> 10) or a semiconductor film (n = 3.5) is used as the conductive material, when such a film body is disposed in contact with the optical waveguide, light propagating through the optical waveguide is absorbed. Light loss is caused by attenuation or by changing the waveguide structure as a photorefractive loading film. The amount of light loss increases exponentially with the length of the film body placed on the optical waveguide. Therefore, when a metal film or a semiconductor film is used, it is desirable not to install it on the optical waveguide as in the structure of FIG. Of course, it is possible to form a pedestal of a metal film or a semiconductor film on the optical waveguide within a range of light loss tolerable as a practical device.

  FIG. 5 shows an application example of the shape of the pedestal. Since the pedestal has an island pattern 42 having a gap, when the adhesive is used, the adhesive can easily flow out or inflow from between the substrate 1 and the light receiving element 3 through the gap. The thickness unevenness of the adhesive can be suppressed, and the distance between the optical waveguide formed on the substrate and the light receiving element can be adjusted appropriately. The island pattern is not limited to the rectangular array arrangement as shown in FIG.

Next, the second embodiment shown in FIG. 4 will be described. In FIG. 4, a pedestal 4 is formed so as to cover the optical waveguide 2. For example, it may be configured by a single continuous film body, or the island pattern shown in FIG. 5 may be modified so that each island portion covers the optical waveguide. However, in order to arrange such a pedestal, it is necessary to suppress the above-described optical loss. Therefore, the wavelength of light propagating through the optical waveguide is transparent with little absorption loss and the same refractive index as that of the substrate. It is preferable that the material is about or less (n <2.3). As such a film body, when the substrate is an LN substrate, a material such as TiO ₂ or ITO can be suitably used.

  The operation of the optical waveguide device of the present invention will be described with reference to FIGS. When the distance between the optical waveguide 2 and the light receiving element 3 is set appropriately, the light wave L propagating through the optical waveguide 2 can take in the evanescent wave E to the light receiving element side. 3 passes through only the adhesive layer 5 in FIG. 3 or the pedestal 4 and the adhesive layer 5 in FIG. 4 and enters the light receiving portion 31 of the light receiving element 3.

  As a manufacturing method related to the optical waveguide device of the present invention, in order to efficiently exhibit the effect of removing contaminants and the effect of preventing reattachment, in the optical waveguide device manufacturing method, before mounting the light receiving element on the substrate on which the pedestal is formed. In addition, it is preferable to perform either optical cleaning or ionizer blow on the surface of the pedestal. Combined with the structure of the pedestal, the removal efficiency of contaminants can be increased, and an optical waveguide device with a high manufacturing yield can be provided.

  In the description of the present invention, for simplicity of explanation, the straight waveguide is minimized as the optical waveguide pattern, but naturally, an optical waveguide having another pattern may be used. For example, by making the optical waveguide a Mach-Zehnder type, the present invention can be applied to an optical waveguide device such as a light intensity modulator. Further, the monitoring method by mounting the light receiving element on the optical waveguide can be used for an integrated optical modulator having a complicated waveguide structure such as DQPSK, DP-QPSK, or 16QAM modulator. This can be used when individually monitoring the bias state of the type waveguide portion (MZI).

In order to investigate improvement in characteristic reproducibility or improvement in production yield in the method for manufacturing an optical waveguide device of the present invention, a manufacturing test was performed under the following conditions.
After forming the optical waveguide by Ti thermal diffusion on the LN substrate, the island-shaped pattern pedestal shown in FIG. Both film thicknesses were 110 nm.

The substrate on which the pedestal was formed was cleaned in the following three ways, and the substrate and the light receiving element were attached using an adhesive (refractive index n = 1.56) to complete the optical waveguide device.
(1) Atmospheric pressure plasma asher (2) Ionizer blow 10 seconds (3) UV light cleaning (UV 100 mw / cm 60 seconds)

The test light was guided through the optical waveguide of the completed optical waveguide device, and a non-defective product or a defective product was judged based on whether or not the light-receiving element could properly detect the evanescent wave of the test light. The determination results are shown in Table 1. From the results in Table 1, it can be easily understood that the production yield of the ITO film of the present invention is remarkably improved as compared with the case of using the SiO ₂ film.

  As described above, according to the present invention, in an optical waveguide device that uses an evanescent wave as monitor light and a method for manufacturing the same, it is easy to remove contaminants or to suppress recontamination. It becomes possible to provide a waveguide device and a manufacturing method thereof.

1 Substrate 2 Optical waveguide 3 Light receiving element (chip)
4, 41 to 45 Base 5 Adhesive 31 Light receiving portion of light receiving element

Claims (6)

In an optical waveguide device having a substrate made of a material having pyroelectricity or piezoelectricity, and an optical waveguide partially formed on the substrate,
A light receiving element arranged to straddle the optical waveguide;
In order to adjust the distance between the light receiving element and the optical waveguide, a pedestal formed on the substrate,
The pedestal is formed of a film body, and at least a surface material facing the light receiving element is formed of any one of a photocatalytic substance, a conductive substance, and a semiconductor substance.   2. The optical waveguide device according to claim 1, wherein the light receiving element and the substrate are bonded with an adhesive having a refractive index lower than a refractive index of a material constituting the light receiving element. Waveguide device.   3. The optical waveguide device according to claim 1, wherein the pedestal is configured so that a material constituting the pedestal is a transparent material having a refractive index of 2.3 or less and covers the optical waveguide. A featured optical waveguide device.   4. The optical waveguide device according to claim 1, wherein the pedestal has an island pattern having a gap. 5. The optical waveguide device according to claim 1, wherein at least one of TiO _{2 and} ITO is used as the surface material. 6.   6. The method of manufacturing an optical waveguide device according to claim 1, wherein the surface of the pedestal is subjected to either optical cleaning or ionizer blow before mounting the light receiving element on the substrate. An optical waveguide device manufacturing method characterized by the above.

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