JP5087043B2 - ELECTRO-OPTICAL ELEMENT AND MANUFACTURING METHOD THEREOF - Google Patents

Description

  The present invention relates to an electro-optical element and a manufacturing method thereof, and more particularly to a method of manufacturing an electro-optical element using an electro-optical material.

  The effect of changing the refractive index by applying an electric field to a substance is called an electro-optic effect. It is used for intensity modulators used in optical communications, Q-switch elements for obtaining laser oscillation pulse operations, and light beam scanners for controlling the traveling direction of light. The refractive index change Δn due to the electro-optic effect is given by the following equation in the case of the first-order Pockels effect.

  Δn∝rij × V / d (1)

  Here, rij is an electro-optic constant (Pockels constant), V is an applied voltage, and d is an interval between electrodes to which a voltage is applied.

  In practical use of such an electro-optic element, it is required to respond at a low voltage and in a wide frequency band. For this purpose, the electric field strength may be increased by reducing the electrode distance d in the above formula (1). As the electrode interval is reduced, the element often takes an optical waveguide structure.

  A typical example of a conventional waveguide type electro-optic element is an intensity modulator in optical communication. In the intensity modulator, an optical waveguide structure is manufactured by locally diffusing titanium into a lithium niobate crystal to increase the refractive index of only that portion. Examples of the method of forming an optical waveguide by such impurity diffusion include methods by zinc diffusion and proton diffusion in addition to titanium diffusion. Such a diffusion waveguide is also used for an optical wavelength conversion element using a nonlinear optical effect.

  As another waveguide manufacturing method, a method of manufacturing an optical waveguide structure by bonding an electro-optic material or a nonlinear optical material to another material directly or by bonding with an adhesive and thinning it by polishing is used.

  This method of bonding / polishing or bonding / polishing is conventionally used as a method of manufacturing an optical wavelength conversion element. This method is also applicable to the manufacture of electro-optic elements. According to this method, since the waveguide structure can be manufactured while maintaining the original performance of the electro-optic material and the nonlinear optical material, it is an effective production method for low-voltage operation of the electro-optic element. Is already known.

  An outline of the conventional bonding polishing process will be described below. A substrate serving as a base and a substrate serving as a core of a waveguide are bonded together with an adhesive. Next, the substrate serving as the core is polished and thinned to a thickness that can confine light. In the waveguide type element, it is important to make the thickness of the core layer uniform. This is because the effective refractive index of the waveguide changes as the thickness of the core layer changes, and there is a problem that the optical beam quality such as the conversion efficiency decreases in the optical wavelength conversion element and the wavefront distortion decreases in the electro-optical element. This is because it occurs. The uniformity of the thickness of the core layer reflects the in-plane uniformity of the polishing amount and the in-plane uniformity of the thickness of the adhesive layer in the polishing process. In order to improve the in-plane uniformity of the thickness of the adhesive layer, there is a method of relatively reducing the non-uniformity by thinning the adhesive layer. However, the method of increasing the uniformity of the thickness of the adhesive layer by thinning the adhesive as described above has a problem that the mechanical strength of the element is lowered because the adhesive strength is reduced due to the phenomenon of the thickness of the adhesive layer. there were. In order to make the thickness of the adhesive layer uniform, it is preferable to use an adhesive having a low viscosity. However, such an adhesive should be selected in order to select the optimum one for guaranteeing the performance of the element. There was also a problem that the degree of freedom of. Therefore, in order to solve these problems, in Patent Document 1, the viscosity of the adhesive is small for the purpose of uniforming the distribution of the thickness of the adhesive layer formed by bonding and curing the adhesive. It has been proposed that a viscosity of 100 cp or less is preferable. Further, in Patent Document 1, when the thickness of the adhesive layer exceeds 10 μm, the thickness accuracy of the adhesive layer itself decreases and the fluctuation range increases, so that the thickness of the subsequent ferroelectric single crystal substrate is reduced. It is also disclosed that the process becomes difficult and the thickness fluctuation range of the final thinned ferroelectric single crystal substrate cannot be within a predetermined range.

  However, in the method of increasing the uniformity of the thickness of the adhesive layer by reducing the thickness of the adhesive layer in this way, the adhesive strength also decreases as the thickness of the adhesive layer decreases, and the mechanical strength of the device decreases. There was a problem. Further, in order to make the adhesive layer thickness uniform, it is preferable to use an adhesive having a small viscosity, but such an adhesive is selected in order to select the optimum one for guaranteeing the performance of the element. There was also a problem that the degree of freedom became narrow.

  The present invention is for solving these problems, can obtain a uniform thickness regardless of the thickness of the adhesive layer, and achieves both the mechanical strength of the electro-optic element and the quality of the light beam, An object of the present invention is to provide an electro-optical element and a method for manufacturing the same, which can ensure the degree of freedom in selecting an optimum adhesive for assuring the performance of the element regardless of the thickness.

  In order to solve the above problems, the electro-optical element of the present invention is configured by bonding a first and second substrate formed of an electro-optical material with an adhesive, and the adhesive includes the first substrate and the first substrate. The gap member that defines the gap of the second substrate is mixed. Therefore, it is possible to achieve both the mechanical strength of the element and the quality of the light beam by obtaining a uniform thickness uniformity regardless of the thickness of the adhesive layer. The degree of freedom in selecting the optimum adhesive can be ensured in order to guarantee the performance.

  Further, by providing a clad layer on one surface of either the first or second substrate to be thinned by polishing, for example, in an optical element in which the substrate is a substrate serving as a waveguide core, a gap material Scattering generated by the can be suppressed.

  Further, by providing a clad layer on both surfaces of either the first or second substrate to be thinned by polishing, for example, in an optical element in which the substrate is a substrate serving as a core of a waveguide, a gap material It is possible to further suppress the scattering generated by.

  Moreover, it is preferable to have a clad layer and an electrode layer on both surfaces of either the first or second substrate to be thinned by polishing.

  Furthermore, it is preferable that a part of one of the first and second substrates to be thinned by polishing is reversed in polarity and has a clad layer and an electrode layer on both surfaces of the substrate.

  As another invention, in a method of manufacturing an electro-optic element in which first and second substrates formed of an electro-optic material are bonded with an adhesive, a gap between the first substrate and the second substrate is provided. The first substrate and the second substrate are adhered to each other using an adhesive mixed with a gap member that defines Accordingly, it is possible to provide a method for manufacturing an electro-optical element that makes the core layer manufactured by polishing uniform in thickness, thereby making it possible to achieve both the mechanical strength of the element and the quality of the light beam.

  According to the present invention, the first substrate and the second substrate are bonded using the adhesive in which the gap member that defines the gap between the first and second substrates formed of the electro-optic material is mixed. Thus, the thickness of the core layer manufactured by polishing becomes uniform, and both the mechanical strength of the element and the quality of the light beam can be achieved.

1 is a cross-sectional view illustrating a configuration of an electro-optical element according to a first embodiment of the invention. FIG. 6 is a cross-sectional view illustrating a configuration of an electro-optical element according to a second embodiment of the invention. FIG. 6 is a cross-sectional view illustrating another configuration of the electro-optic element according to the second embodiment. FIG. 6 is a cross-sectional view illustrating a configuration of an electro-optical element according to a third embodiment of the invention. FIG. 10 is a cross-sectional view illustrating another configuration of an electro-optic element according to a third embodiment.

  FIG. 1 is a cross-sectional view showing the configuration of the electro-optic element according to the first embodiment of the present invention. According to the electro-optic element 10 of the present embodiment shown in FIG. 4A, the base substrate 11 and the substrate 12 serving as the core layer are bonded by the adhesive 13. At this time, the gap material 14, which is a member having a high size uniformity, is mixed with the layer of the adhesive 13. The gap material 14 includes beads made of silica or resin. As a mixing method, there is a method of mixing with the adhesive 13 in advance. Alternatively, a method in which the gap material 14 is spread on the base substrate 11 in advance and the adhesive 13 is applied thereto is also possible. Furthermore, the shape of the gap member 14 does not need to be spherical, and any shape is possible as long as the distance between the base substrate 11 and the substrate 12 serving as the core layer can be kept constant. Examples include a cylinder and a prism. Further, a photoresist formed in a columnar shape by photolithography after spin coating of a photoresist may be used. Further, since the gap member 14 is used to make the gap between the base substrates, that is, the thickness of the adhesive layer, constant when the base substrate 11 is bonded, the gap material 14 is evenly distributed throughout the base substrate at the time of bonding. It only has to be. Therefore, it is not always necessary to include a gap material in individual elements obtained after dividing the base substrate by dicing or the like. In the actual production, lithium niobate having a diameter of 3 inches and a thickness of 300 μm is used for both the substrate 12 serving as the core layer and the pedestal substrate 11, and a true ball made of silica having a diameter of 10 μm as the gap material 14 (JGC) For the adhesive 13, a UV curable resin adhesive was used. When the thickness was measured after bonding, the uniformity of the thickness within a 3 inch plane was as high as 500 nanometers or less. Thereafter, the substrate 12 serving as the core layer was thinned by polishing to form a waveguide as shown in FIG. At this time, since the layer of the adhesive 13 had a thickness of 10 micrometers and had sufficient adhesive strength, the problem that the substrate 12 serving as the core layer peeled during polishing did not occur. When the thickness of the core layer 15 was measured after polishing, a thickness uniformity as high as 10 ± 0.5 micrometers was obtained within a 3-inch plane. By adopting the structure of the present invention in this way, the thickness of the adhesive layer can be increased to maintain the mechanical strength while maintaining the uniform core layer thickness. Therefore, the mechanical strength of the device and the quality of the light beam Can be made compatible.

  FIG. 2 is a cross-sectional view showing a configuration of an electro-optic element according to the second embodiment of the present invention. 2, the same reference numerals as those in FIG. 1 denote the same components. The first embodiment of FIG. 1 is an example in which an adhesive layer functions as a cladding layer of a waveguide, but guided light may be scattered by the gap material 14. Therefore, in the second embodiment shown in FIG. 2, in order to prevent this scattering, the clad layer 16 is formed between the substrate 12 serving as the core layer and the adhesive 13 layer. In addition, as a formation method of the clad layer 16, methods, such as a sputtering and vapor deposition, are previously mentioned to the board | substrate 12 used as a core layer. Furthermore, as shown in FIG. 3, the clad layer 17 may be formed on the core layer 15 after the core layer 15 is manufactured by polishing.

  FIG. 4 is a cross-sectional view showing a configuration of an electro-optic element according to the third embodiment of the present invention. In the figure, the same reference numerals as those in FIG. 3 denote the same components. In the present embodiment, as shown in FIG. 4A, the clad layer 16 and the electrode layer 18 are formed on the substrate 12 serving as the core layer prior to bonding, and then the bonding to the base substrate 11 is performed. Thereafter, as shown in FIG. 4B, the core layer 15 is formed by polishing, and the clad layer 17 and the electrode layer 19 are formed on the core layer 15. In addition, as a formation method of a clad layer and an electrode layer, methods, such as a sputtering and vapor deposition, are previously mentioned to the board | substrate used as a core layer. Moreover, the electrode by the upper and lower electrode layers may be a uniform electrode or may have an arbitrary pattern. Furthermore, the shape of the electrode by the upper and lower electrode layers may be different. Examples of the pattern include a prism shape electrode as shown in FIG. 4C and a lens shape electrode as shown in FIG. Further, as shown in FIG. 5, before the clad layer 16 and the electrode layer 18 are formed on the substrate 12 serving as the core layer, the polarization of the substrate 12 serving as the core layer is controlled. The polarization control is performed by polarization inversion by a direct electric field application method. In this electro-optical element, the upper electrode and the lower electrode may be uniform electrodes or may have an arbitrary pattern. When a voltage is applied between these electrodes, the light beam propagating through the waveguide layer is deflected in the prism-shaped polarization-inverted electro-optic element as shown in FIG. Further, in the electro-optic element in which the lens-shaped polarization inversion is performed as shown in FIG. 5D, the light beam propagating through the waveguide layer is condensed.

  The present invention is not limited to the above-described embodiments, and various modifications, substitutions, and applications are possible as long as they are described within the scope of the claims.

10: Electro-optic element, 11: Base substrate, 12: Substrate serving as a core layer,
13; adhesive, 14; gap material, 15; core layer,
16, 17; Cladding layer, 18, 19; Electrode layer.

JP 2003-107545 A

Claims (6)

In an electro-optic element configured by adhering first and second substrates formed of an electro-optic material with an adhesive,
An electro-optic element, wherein a gap member that defines a gap between the first substrate and the second substrate is mixed with the adhesive.   2. The electro-optical element according to claim 1, further comprising a clad layer on one surface of either the first or second substrate to be thinned by polishing.   2. The electro-optic element according to claim 1, further comprising a clad layer on both surfaces of either the first or second substrate to be thinned by polishing.   2. The electro-optical element according to claim 1, further comprising a clad layer and an electrode layer on both surfaces of either the first or second substrate to be thinned by polishing.   2. The substrate according to claim 1, wherein a part of the first or second substrate to be thinned by polishing is partly inverted, and has a clad layer and an electrode layer on both surfaces of the substrate. Electro-optic element. In a method for manufacturing an electro-optic element, in which the first and second substrates formed of an electro-optic material are bonded with an adhesive,
An electro-optical device characterized in that the first substrate and the second substrate are bonded using the adhesive in which a gap member defining a gap between the first substrate and the second substrate is mixed. Device manufacturing method.

Images