JP2004264872A - Optical device using photonic crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical device which can be realized only by working of an optical fiber. <P>SOLUTION: This optical device is provided with a 1st function part 7 having a plurality of Faraday crystal replacement columns 5 parallel to each other which mostly penetrate the core 3 of the optical fiber 1 vertically to the optical axis 2 of the optical fiber 1, and a 2nd function part 8 having a plurality of holes 6 parallel to each other which mostly penetrate the core 3 of the optical fiber 1 vertically to the optical axis 2 of the optical fiber 1, in a specified section of the optical fiber 1. The longitudinal direction of the Faraday crystal replacement columns 5 and the longitudinal direction of the plurality of holes form an angle of 45° along the plane vertical to the optical axis 2. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to various optical devices used for optical communication and the like, and more specifically, a dispersion compensator for the wavelength and polarization of an optical fiber, an optical isolator, an optical modulator, a voltage of a transmission line or a distribution line, or the like. The present invention relates to an optical device such as an optical sensor used for detecting a current.

  First, various conventional optical devices will be described below. FIG. 31 is a schematic diagram showing the structure of an optical isolator as a conventional optical device. This optical isolator includes first and second lenses 1003 and 1004 for coupling an optical system between a first optical fiber 1001 and a second optical fiber 1002, and a polarizer 1005 and a Faraday element between them. 1006 and an analyzer 1007. Note that, in FIG. 31, the extension of the light beam 1009 in the optical system is shown as a straight line. Further, the optical isolator has a magnetic field 1008 sufficient to saturate the Faraday element 1006. Further, the polarizer 1005 and the analyzer 1007 make an angle of 45 ° with each other. As the Faraday crystal 1006, a garnet crystal or the like is used.

  Next, the principle of the optical isolator will be described. In the optical isolator shown in FIG. 31, non-polarized light emitted from the first optical fiber 1001 is first converted into linearly polarized light by the polarizer 1005 coupled by the first lens 1003. Next, the plane of polarization of the linearly polarized light is rotated by 45 ° by the Faraday element 1006. All the linearly polarized light whose polarization plane is rotated by 45 ° is coupled to the second optical fiber 1002 via the second lens 1004 by the analyzer 1007 having the above-mentioned angle.

  On the other hand, return light from the second optical fiber 1002 is coupled to the analyzer 1007 via the second lens 1004 and is converted into linearly polarized light. Next, the plane of polarization of the linearly polarized light is rotated by 45 ° by the Faraday element 1006. However, in the polarizer 1005, the plane of polarization of linearly polarized light is orthogonal to the polarization direction of the polarizer 1005. Therefore, no return light is coupled to the first optical fiber 1001 via the first lens 1003. As described above, in the conventional optical isolator, coupling of the optical system between the optical fibers requires two lenses.

  Next, a conventional dispersion compensator will be described. Conventional dispersion compensators are provided between optical fibers. Therefore, coupling of the optical system between the optical fibers requires at least two lenses.

  Next, a conventional optical modulator will be described. For example, the optical modulator functionally includes a polarizer, a λ / 4 plate, a Pockels element, and an analyzer. The linearly polarized light obtained by the polarizer becomes circularly polarized light by the λ / 4 plate, and the circularly polarized light becomes elliptical according to the electric field applied in the Pockels element. Next, in the analyzer, the light quantity changes according to the ellipticalization of the circularly polarized light, so that the light modulation according to the applied electric field can be performed. Thus, the conventional optical modulator also requires at least two lenses for coupling the optical system between the optical fibers.

Further, the configuration of a conventional optical modulator will be described in detail. For example, as shown in FIG. 32, a Mach-Zehnder modulator 2012 used as an optical modulator is formed on a substrate 2001 made of, for example, a LiNbO ₃ crystal. In the Mach-Zehnder modulator 2012, the waveguide unit 2002 has a waveguide on which light of unpolarized light (TM light + TE light) 2005 is incident on the incident side, and polarized light into two polarized lights (TM light and TE light). Includes waveguides that emit separately, and waveguides that combine and emit these polarized lights. Among them, an electrode 2003 for applying an electric field is provided in the waveguide for polarization separation. A predetermined voltage is applied to the electrode 2003 from the signal source 2004. Then, the outgoing light 2010 is coupled to the optical fiber 2006 by the lens 2009. The optical fiber 2006 includes a core 2007 and a clad 2008, and light is transmitted through the core 2007.

  As described above, conventionally, an optical device such as an optical modulator requires an expensive waveguide and at least one lens to couple an optical system from the optical modulator to the optical fiber. In addition, the coupling of the optical system between the waveguide and the optical fiber requires a great deal of time and effort.

  Next, a conventional optical sensor will be described. FIG. 33 is a transparent front view showing a schematic structure of a conventional optical voltage sensor. The optical voltage sensor includes a sensor unit, a light emitting unit, a light receiving unit, and a light emitting side and light receiving side signal processing circuit (not shown). The sensor unit includes a polarizer 241, a quarter-wave plate (also referred to as a “λ / 4 plate”) 242, an electro-optic crystal 243, and an analyzer 244 sequentially arranged on the same optical axis from the light incident side. Be composed. Further, the light emitting unit includes an E / O circuit including a light emitting element such as an LED (Light Emitting Diode) as a light source, and an optical fiber 246a, a ferrule 248a, a GRIN lens 247a, and a holder 245a arranged on the same optical axis. Each of the optical components of the input-side optical system has an optical axis surface that is in contact with each other and is bonded by an adhesive. The light receiving unit converts an optical signal output from the output optical system into an electric signal, which includes an optical fiber 246b, a ferrule 248b, a GRIN lens 247b, and a holder 245b arranged on the same optical axis. And an O / E circuit including a conversion element. The optical components in the output-side optical system are also bonded by an adhesive on optical axis surfaces that are in contact with each other.

  Each of the optical components, that is, the polarizer 241, the λ / 4 plate 242, the electro-optic crystal 243, and the analyzer 244, which are arranged on the same optical axis in the sensor unit of the optical voltage sensor, have optical axes that are in contact with each other. Adhered with adhesive. Here, the optical axis plane refers to a plane perpendicular to the optical axis, and each optical component has two surfaces, a light entrance surface and a light exit surface (the same applies hereinafter). A pair of electrodes 235 is deposited on the electro-optic crystal 243, and each of the pair of electrodes 235 is electrically connected to each of the pair of electrode terminals 249 by a lead wire. The voltage to be measured by the optical voltage sensor (measured voltage) is applied between the pair of electrode terminals 249.

  The light emitting side and light receiving side signal processing circuits are connected to the sensor unit by a light emitting unit and a light receiving unit, respectively. The input side optical axis surface of the polarizer 241 of the sensor unit is the optical axis surface of the GRIN lens 247a of the light emitting unit, the output side optical axis surface of the analyzer 244 of the sensor unit is the optical axis surface of the GRIN lens 247b of the light receiving unit, Each is fixed with an adhesive. The sensor unit, the input side optical system in the light emitting unit, and the output side optical system in the light receiving unit are mechanically fixed to a case (not shown). Note that an epoxy-based or urethane-based resin is used as an adhesive for each optical component in the optical voltage sensor.

In the optical voltage sensor, Bi ₁₂ SiO ₂₀ (BSO), KH ₂ PO ₄ (KDP), LiNbO ₃ having natural birefringence, LiTaO _3, or the like is used as the electro-optic crystal 243.

Next, the operating principle of the optical voltage sensor will be described with reference to FIG. For example, when an LED (Light Emitting Diode) having a center wavelength of 0.85 μm is used as a light source in the light emitting unit, non-polarized light of the LED is emitted from the light emitting unit and is incident on the sensor unit as incident light 109. The incident light 109 becomes linearly polarized light after passing through the polarizer 241 of the sensor unit. The linearly polarized light becomes circularly polarized after passing through lambda / 4 plate 242, the circularly polarized light passes through the electro-optic crystal (LiNbO ₃₎ 243, elliptical in response to the applied voltage Vm to the electro-optic crystal 243 I do. That is, the polarization state of the light passing through the electro-optic crystal 243 changes according to the applied voltage Vm. After passing through the analyzer 244, such elliptically polarized light is received by the light receiving unit as the outgoing light 110. The change in the output intensity, which is the change in the intensity of the outgoing light 110, corresponds to the polarization state of the light passing through the electro-optic crystal 243. Since this polarization state changes according to the applied voltage Vm, the output intensity of the analyzer 244 is monitored at the light receiving unit via the optical fiber 246b on the light receiving side, and the modulation of the light amount (intensity) is calculated to apply the applied voltage. The voltage Vm can be measured. Here, the modulation degree of the light amount is a ratio of the AC component of the light amount to the DC component of the light amount.

By the way, optical voltage sensors are often used under severe outdoor environments, and strict conditions are required for their temperature characteristics, and the modulation degree change at -20 ° C to 80 ° C is ± 1% or less. desired. Factors that cause the temperature characteristics in the above-described conventional optical voltage sensor include a change in the refractive index due to the stress of the bonding portion in the λ / 4 plate 242 and the electro-optic crystal 243 and the temperature characteristics of the birefringence of the λ / 4 plate 242. . When an electro-optic crystal having natural birefringence, such as LiNbO ₃ , is used, the output of the optical voltage sensor changes depending on the state of the beam of light incident on the electro-optic crystal 243.

  FIG. 35 is a graph illustrating the relationship between the axis shift angle α and the axis shift direction β and the output of the optical voltage sensor. In FIG. 35, β1 represented by a dotted line indicates a case where the axis deviation direction is 0, 90, 180, and 270 (degree), and β2 represented by a dashed line indicates a case where the axis deviation direction is 45, 225 (degree). Β3 represented by a normal line represents the case where the axis deviation directions are 135 and 315 (degrees). As shown in FIG. 35, the degree of modulation, which is the output of the optical voltage sensor, changes depending on the beam state of the light incident on the electro-optic crystal 243 (such as the axis shift angle α and the axis shift direction β). Temperature characteristics change.

At present, the following three methods can be cited as an improvement method corresponding to each of such factors.
(1) First, there is a method of improving the temperature characteristics of the electro-optic crystal by relaxing the stress applied to the electro-optic crystal. In this method, the stress applied to the electro-optic crystal is reduced by fixing the electro-optic crystal in a non-adhesive state. This method is disclosed in JP-A-9-145745.
(2) Secondly, there is a method of improving the temperature characteristic of spontaneous birefringence of the electro-optic crystal by reducing the axis shift angle of the incident light. In this method, by improving the mechanical surface accuracy of the optical component itself to reduce the incident angle of light on the electro-optic crystal to 0.2 ° or less, the temperature characteristics due to the axis shift of the incident light are improved. This method is disclosed in JP-A-3-44562.
(3) Third, there is a method of improving the temperature characteristics of the sensor output by changing the incident angle of the incident light on the electro-optical element according to the ambient temperature. According to this method, an incident angle adjustment unit that changes an incident angle of incident light on an electro-optic crystal (Pockels element) in accordance with an ambient temperature, and cancels an output change due to a temperature change with an output change due to the change in the incident angle. Thereby, the temperature characteristic of the sensor output is improved. An optical sensor based on this method is disclosed in Japanese Patent Application Laid-Open No. 7-248339.

  As described above, in the conventional optical device, at least one or two lenses are required to couple the optical system with the optical fiber, and the number of components is increased. In addition, such coupling of optical systems requires a great deal of time and effort. Therefore, according to the configuration of the optical device as described above, there is a problem that the cost of the apparatus is increased.

  Further, in addition to the above-described problems, the optical sensor has a specific problem related to the temperature characteristics. That is, according to the above method (1), it is possible to prevent the fluctuation of the beam state which causes a large temperature characteristic, but when the initial beam state varies, the fluctuation of the temperature characteristic cannot be avoided. The method (2) is easy to use, but the effect of the axis shift is related not only to the axis shift angle but also to the axis shift direction. Therefore, stable characteristics cannot be obtained only by reducing the axis deviation angle based on the method (2). The method (3) requires an incident angle adjustment unit that changes the incident angle of the incident light on the electro-optic crystal in accordance with the ambient temperature, thereby complicating the configuration, reducing the productivity and increasing the cost. Invite. Further, as described above, since the influence of the axis shift relates not only to the axis shift angle but also to the axis shift direction, stable temperature characteristics cannot be obtained only by adjusting the incident angle of the incident light, that is, the axis shift angle.

  On the other hand, the applicant of the present application has disclosed an invention of an optical voltage sensor based on a method of controlling the temperature characteristic of the degree of modulation by utilizing the off-axis characteristic of an electro-optic crystal having a natural birefringence. No. has already been filed. According to the optical voltage sensor according to the invention of the present application, the temperature characteristic of the optical voltage sensor is controlled by controlling the beam state (axis shift angle and axis shift direction or spread angle) of the incident light on the electro-optic crystal. Is improved. That is, the temperature characteristics and the like are improved by appropriately setting the state of the axis deviation in consideration of not only the axis deviation angle but also the axis deviation direction.

  However, the beam state control based on the invention of the present application is disadvantageous in terms of cost because beam state management for preventing variations in the beam state due to tolerances of optical components such as lenses causes an increase in cost. .

  Therefore, at present, it is required to manage the beam state at low cost in order to reduce the price of the optical voltage sensor.

  As described above, an object of the present invention is to provide a low-cost optical device that can easily and inexpensively couple an optical system to an optical fiber and has a small number of components. In the following, as a reference example, an optical sensor such as an optical voltage sensor whose temperature characteristics are stabilized by suppressing variations in a beam state due to tolerances of optical components and the like without increasing costs. Will also be explained.

A first invention provides an optical fiber having an end surface inclined with respect to an optical axis,
An optical device comprising: a photonic crystal that is grown on the end face directly in a direction normal to the end face using the inclined end face as a substrate.
A second invention is an optical device characterized by being formed directly on an end face of a photonic crystal and made of a material whose normal to the end face is parallel to the optical axis of the optical fiber.

  As described above, according to the first and second aspects, it is possible to reduce the manufacturing cost of an optical element having a function that can be realized by a photonic crystal, and to use such an optical element or an optical fiber. It is possible to reduce the number of components of the optical device.

  First, before detailing the configuration of optical devices, the photonic crystals used in polarizers (linear polarizers and circular polarizers), analyzers, λ / 4 plates, Pockels elements, etc., that make up each optical device are outlined. And a method of forming the same will be described.

<Formation of photonic crystal that functions as linear polarizer>
References relating to photonic crystals include, for example, "Photonic crystal", written by John D. Joannopoulos, Robert D. Meade, and Josua N. Winn. Published by Princeton University Press (published in 1995). As described in this document, a photonic crystal has a 1-3 dimensional periodic structure composed of a relatively high refractive index material and a low refractive index material, and is mainly composed of a high refractive index material and a low refractive index material. The periodic structure caused by the refractive index and shape of the material, the period of the spatial change of the refractive index, the direction and wavelength of the incident light beam (hereinafter, referred to as “used beam direction” and “used beam wavelength”, respectively). The light wave is controlled by utilizing the dispersion characteristics of the light wave in the inside. Therefore, when the refractive index and the shape in the photonic crystal, the period of the spatial change of the refractive index, and the used beam direction are appropriately controlled with respect to the used beam wavelength, the two types of linearly polarized light, the TM wave and the TE wave, can be used. By utilizing the phenomenon that the dispersion characteristics are different, a polarizer, a λ / 4 plate, or the like can be realized. For example, a polarizer using such a photonic crystal is disclosed in JP-A-2000-56133. As for the shapes of the high-refractive index material and the low-refractive index material used for the photonic crystal, many types have been proposed and manufactured as described in the above-mentioned literature.

  Therefore, it is possible to form a photonic crystal layer that functions as a linear polarizer or an analyzer on the end face of the optical fiber as used in an eighteenth reference example described later. That is, when a photonic crystal layer made of a high-refractive-index material and a low-refractive-index material is formed on the end face of an optical fiber, only one of the TM wave and the TE wave constituting the light to be transmitted through the optical fiber is used. The refractive index and shape of the high-refractive index material and the low-refractive index material, the period of the spatial change of the refractive index, and the beam direction to be used are set so that the light passes through the photonic crystal layer. (For example, see FIGS. 4 and 6 described in JP-A-2000-56133). A specific method of forming a photonic crystal on the end face of the optical fiber will be described later.

  In a thirteenth reference example described later, when a multilayer film is manufactured as a photonic crystal in which two types of layers, a high refractive index layer and a low refractive index layer, are alternately stacked, the two types of layers are used. The layers are stacked in the direction (optical axis direction) of the incident light on the sensor unit, and are set so that the sum of the thickness of the high refractive index layer and the thickness of the low refractive index layer is １ ／ of the wavelength of the incident light. This makes it possible to prevent both the TM wave and the TE wave from passing through the photonic layer. This means that the multilayer film formed as a one-dimensional photonic crystal functions as a reflection film for the incident light. A specific configuration of an optical device using such a function will be described later in a corresponding reference example.

<Formation of photonic crystal functioning as λ / 4 plate>
As described above, if the refractive index and the shape of the photonic crystal, the period of the spatial change of the refractive index, and the direction of the used beam are appropriately controlled with respect to the used beam wavelength, two types of linearly polarized light TM The λ / 4 plate can be realized by utilizing the phenomenon that the dispersion characteristics of the wave and the TE wave are different. Therefore, a photonic crystal layer functioning as a λ / 4 plate can be formed on the end face of the optical fiber as in a nineteenth reference example described later. That is, when a photonic crystal layer made of a high-refractive-index material and a low-refractive-index material is formed on an end face of an optical fiber (a specific forming method will be described later), light to be transmitted through the optical fiber is formed. Both the TM wave and the TE wave pass through the photonic crystal layer, and the passage causes a phase difference corresponding to 1/4 of the wavelength of the light between the TM wave and the TE wave. It is possible to set the refractive index and shape of the high refractive index material and the low refractive index material, the period of the spatial change of the refractive index, and the beam direction to be used for the wavelength of.

<Formation of photonic crystal layer functioning as circular polarizer>
A circular polarizer, which is a polarizer that converts non-polarized light into circularly polarized light, is realized by a photonic crystal having a 1-3-dimensional periodic structure composed of a material having relatively high permeability and a material having low permeability in the light propagation direction. be able to.

  FIG. 1 is a perspective view illustrating an example of a photonic crystal that functions as a circular polarizer. This photonic crystal has a high magnetic permeability portion 211 and a low magnetic permeability portion 212 formed by periodically disposing a columnar portion made of a high magnetic permeability material in a low magnetic permeability medium (for example, air). Has a periodic structure that is repeated two-dimensionally at a constant period, that is, a periodic structure in which the magnetic permeability changes two-dimensionally and periodically (hereinafter, referred to as “two-dimensional periodic structure regarding magnetic permeability”). The high magnetic permeability portion 211 only needs to have high magnetic permeability in the propagation direction of the incident light to the two-dimensional photonic crystal 210, and does not need to have high magnetic permeability in all directions. The low magnetic permeability portion 212 only needs to have a low magnetic permeability in the direction of propagation of light incident on the two-dimensional photonic crystal 210, and does not need to have a low magnetic permeability in all directions.

  Now, it is assumed that non-polarized light is incident on the photonic crystal 210 having the two-dimensional periodic structure with respect to the magnetic permeability (hereinafter, this non-polarized light is referred to as “non-polarized light incident light”). As shown in FIG. 1, it is assumed that the magnetic permeability is periodically changed in the propagation direction of the non-polarized light 215 and at least one direction perpendicular to the propagation direction. The unpolarized incident light 215 can be generally decomposed into right-handed circularly polarized light 213 in which the electric field vector rotates clockwise and left-handed circularly polarized light 214 in which the electric field vector rotates counterclockwise. The magnetic field of right-handed circularly polarized light 213 (hereinafter, the wave of this magnetic field is referred to as “first magnetic field wave”) and the magnetic field of left-handed circularly polarized light 214 (hereinafter, the wave of this magnetic field is referred to as “second magnetic field wave”) Both are parallel to the propagation direction of the non-polarized incident light 215 and opposite to each other. For the wavelength of the non-polarized light 215, the magnetic permeability of the high magnetic permeability part 211 and the low magnetic permeability part 212 in the two-dimensional photonic crystal 210, the period of the spatial change of magnetic permeability, the non-polarized light 215. Is properly set, the first and second magnetic field waves are reflected at the boundary between the high permeability portion 211 and the low permeability portion 212 in the two-dimensional photonic crystal 210, before the reflection. Is different between the first magnetic field wave and the second magnetic field wave. When the difference in phase difference thus generated satisfies a predetermined condition, scattering acts in a direction to weaken the magnetic field for one of the first and second magnetic field waves, while scattering acts in a direction to strengthen the magnetic field for the other. work. As a result, similarly to the above-described photonic crystal that functions as a linear polarizer, only one of the first and second magnetic field waves passes through the two-dimensional photonic crystal 210. Therefore, in the two-dimensional photonic crystal 210, by appropriately setting the magnetic permeability of the high magnetic permeability part 211 and the low magnetic permeability part 212, the period of the spatial change of the magnetic permeability, and the direction of the non-polarized light 215, The two-dimensional photonic crystal 210 functions as a circular polarizer with respect to the non-polarized incident light 215 to obtain circularly polarized light 216. Therefore, as in a twentieth reference example described below, the photonic crystal layer functioning as a circular polarizer can be formed as a single layer on the end face of the optical fiber (a specific forming method will be described later).

<Formation of photonic crystal layer on optical fiber end face>
Next, a method for producing a photonic crystal on the end face of the optical fiber will be described. FIG. 2 is a diagram for explaining a method of producing a photonic crystal having a periodic structure including three-dimensional high refractive index fine particles 221 and low refractive index portions 222. In this manufacturing method, the photonic crystal 223 is formed on the end face of the optical fiber as described below. In the following, the production of a photonic crystal having a periodic structure with a refractive index will be described. However, a photonic crystal having a periodic structure with a magnetic permeability can be produced in a similar manner.

(1) First, an optical fiber bundle 224 is created by bundling a plurality of optical fibers such that one end face of each optical fiber is substantially aligned on the same plane.
(2) The end face of the optical fiber bundle 224 composed of the end faces aligned on substantially the same plane as described above is used as a substrate, and the wavelength of the light beam to be transmitted by those optical fibers (used beam) is placed on the substrate. The high refractive index fine particles 221 having a particle diameter of about 20 to 80% of the wavelength (wavelength) are periodically laminated.
(3) The optical fiber bundle 224 in which the high refractive index fine particles 221 are periodically laminated on the end face as described above is separated into individual optical fibers.

  Through the above steps (1) to (3), it is possible to mass-produce an optical fiber having a photonic crystal formed on an end face. Of course, the number of the optical fiber bundles 224 is not limited and is not suitable for mass production, but the number may be one.

  In FIG. 2, the cross section of the core 3 of the optical fiber and the high-refractive-index fine particles 221 are drawn with almost the same size. However, the core diameter of a normal optical fiber is 5 to 300 μm, and the beam wavelength used is 0.85 μm. In this case, the particle size of the high refractive index fine particles 221 is 0.17 to 0.68 μm. In the photonic crystal 223 shown in FIG. 2, the low-refractive-index portion 222 is air. However, after laminating the fine particles in the same manner as in the above step (2), the gap between the fine particles is smaller than the refractive index of the fine particles. May be filled with a material having a large refractive index. In this case, a photonic crystal having a periodic structure in which the laminated fine particle portion is a low refractive index portion and the material filled between the fine particles is a high refractive portion is obtained. The photonic crystal 223 shown in FIG. 2 has a periodic structure in which a high refractive index portion and a low refractive index portion are alternately repeated, but a high magnetic permeability portion and a low magnetic permeability portion are alternately repeated. A photonic crystal having a periodic structure can be formed on the end face of the optical fiber in the same manner as described above.

  According to the method of periodically laminating the high-refractive-index fine particles 221 by the steps (1) to (3) as described above, the high-refractive-index fine particles 221 have a regular pattern, typically at regular intervals. Will be arranged. However, when the high refractive index fine particles 221 are arranged in a predetermined pattern on the end face of the optical fiber, an additional process is required.

  For example, in the step (2), before laminating the high refractive index fine particles 221, a step of forming a desired groove pattern on the end face of the optical fiber is added. If the high-refractive-index fine particles 221 are laminated after forming the predetermined groove pattern in this way, the high-refractive-index fine particles 221 can be arranged according to the pattern, and have a desired structure with respect to the optical fiber surface. Photonic crystals can be formed.

  Here, the groove pattern refers to a set of shallow grooves provided for fixing the high refractive index fine particles 221 at predetermined positions. The width and depth of the groove are not particularly limited. The pattern is not limited to a groove pattern as long as it can fix the high-refractive-index fine particles 221 at predetermined positions, and is formed of one or two or more linear or dot-like projections. Pattern or a pattern composed of point-like or planar depressions.

  As a specific method of forming the above groove pattern on the end face of the optical fiber, for example, the following three methods can be considered. The first is a method in which a resin film such as PMMA (polymethyl methacrylate) is formed on a substrate by spin coating or the like, and then a desired groove pattern is drawn by an electron beam and developed to form a groove pattern. . The second is a method in which a mask having a desired groove pattern is arranged on a substrate, and the mask is removed after performing an etching process. A third method is to form a groove pattern by pressing a precision mold having a desired groove pattern against a substrate with a predetermined force.

  The end face of the optical fiber on which the photonic crystal 223 shown in FIG. 2 is formed is perpendicular to the central axis of the core 3 of the optical fiber, but in a direction different from the laminating direction (growing direction) of the photonic crystal 223. May correspond to optimal conditions (or suitable conditions). That is, for example, when a photonic crystal that functions as a polarizer is formed on the end face of an optical fiber, the laminating direction of the photonic crystal is determined by the direction in which light is emitted from the end face of the optical fiber (or the direction in which light is incident on the end face). When the photonic crystal is set in a predetermined direction different from that of the photonic crystal, the photonic crystal may function optimally or suitably as a polarizer. At this time, first, for example, oblique polishing is performed so that the end face on which the photonic crystal is to be formed makes a predetermined angle with respect to the central axis of the optical fiber core 3 (the optical axis 225 of the core 173 in FIG. 3 described later). Process the end face of the optical fiber. That is, as shown in FIG. 3, an optical fiber 148 having an oblique end surface 226 processed so that the angle between the normal direction and the optical axis 225 corresponds to the above-mentioned optimum condition is manufactured. Next, similarly to the step (2), the high refractive index fine particles 221 are periodically laminated in the normal direction 227 of the oblique end face 226. As a result, a photonic crystal having a periodic structure in which the fine particles 221 have high refractive index portions and the air existing in the gaps between the fine particles 221 has low refractive index portions 222 is formed on the oblique end surface 226 of the optical fiber 148.

  As in the above steps (1) to (3), a plurality of optical fibers 148 having the slanted end faces 226 are bundled so that the slanted end faces 226 are aligned on the same plane to form an optical fiber bundle. After forming the photonic crystal on the oblique end face of the optical fiber bundle as described above, the optical fiber bundle may be separated into individual optical fibers. By doing so, it is possible to mass-produce an optical fiber in which a photonic crystal is formed on the oblique end surface 226.

  In addition, as shown in FIG. 3, when a photonic crystal laminated in a direction oblique to the optical axis 225 of the optical fiber 148 is optically coupled to an optical component having a surface perpendicular to the optical axis 225, The end face of the optical fiber 148 on which the photonic crystal is laminated may be used, but a resin or the like is applied onto the diagonally laminated photonic crystal such that the end face of the optical fiber 148 is in close contact with the surface of the optical component. An end face perpendicular to the optical axis 225 may be formed.

  Although the case where a three-dimensional photonic crystal is formed on the end face of the optical fiber has been described above, a multilayer having a periodic structure in the stacking direction instead of a three-dimensional periodic structure on the end face perpendicular or oblique to the optical axis. A similar method can be used for producing a one-dimensional photonic crystal having a film structure.

<Formation of photonic crystal layer in optical fiber>
Next, a method for producing a photonic crystal in an optical fiber will be described. A plurality of cylindrical holes parallel to each other are formed so as to penetrate an optical fiber having a core and a clad, and the cylindrical holes are distributed at regular intervals. Such a cylindrical hole is formed by, for example, mechanical processing using a drill or the like in a direction perpendicular to the optical axis of the optical fiber, optical processing using a laser or the like, heat treatment, or chemical processing such as etching. Then, a plurality of minute holes penetrating the core are created. The etching is performed, for example, by dry etching using anodized alumina as a mask. The thus formed columnar hole may be filled with air or a gas having various refractive indexes, or may be filled with a material having an arbitrary refractive index by, for example, a sol-gel method. Here, if the material to be filled is a functional material such as a Faraday crystal or a liquid crystal, the corresponding portion in the optical fiber has a function such as a polarizer, a Faraday element, and a λ / 4 plate according to the properties of the functional material. Will be. A specific method for fabricating an optical device using them will be described later in each reference example.

  The reason why the plurality of cylindrical holes constitute the photonic crystal is related to the distribution state of the holes. FIG. 4 shows a photonic band obtained as a result of simulation when cylindrical holes are squarely distributed in the core of the optical fiber. In FIG. 4, the horizontal axis corresponds to the light propagation direction, and extends in all directions in the Brillouin zone. The vertical axis corresponds to the normalized frequency. The solid line indicates light in the TM mode, and the dotted line indicates light in the TE mode. The wave vector in the Brillouin zone on the horizontal axis corresponds to the propagation direction of light in the optical fiber, and the standard frequency on the vertical axis corresponds to the light source wavelength.

  In the example of FIG. 4, no light in the TM mode can exist at the light source wavelength in the TM mode forbidden band, and only light in the TE mode can propagate. Moreover, it can be seen that the permissible propagation direction of this TE mode light is limited to a certain propagation direction. Therefore, it is preferable to distribute cylindrical holes so that the direction in which the TE mode can propagate is coincident with the optical axis of the optical fiber. This optical device can function as a polarizer that propagates only the TE mode in a certain propagation direction at the light source wavelength in this frequency band. Therefore, if the cylindrical holes are distributed so that the propagation direction of the polarizer coincides with the optical axis of the optical fiber, the optical fiber also functions as a polarizer for a mode propagating near the optical axis.

  Note that the photonic band shown in FIG. 4 is illustrated as an example in which cylindrical holes are distributed, but the present invention is not limited to this. For example, when a cylindrical hole is filled with various materials to form a cylindrical body, the refractive index of the material constituting the cylindrical body can be changed. Therefore, not only the TE mode but also the TM mode can function as a polarizer in all propagation directions depending on the conditions such as the refractive index, the outer diameter, and the distribution mode of the cylindrical hole portion.

  As described above, when a plurality of parallel cylindrical holes having a refractive index different from the refractive index of the core in a direction perpendicular to the optical axis of the optical fiber are formed at a fixed interval, in addition to the optical waveguide function of the optical fiber, By controlling the refractive index and outer diameter of the cylindrical hole and the distribution of the cylindrical hole, a difference occurs in the dispersion characteristics of the two types of linearly polarized light (TM, TE) with respect to the wavelength of the light source. It is possible to have functions such as a polarizer and a λ / 4 plate. Note that the shape of the hole is not limited to a cylinder, but may be another shape. Hereinafter, embodiments in which the above method is applied to various optical devices will be described as reference examples.

  The optical device according to each of the following reference examples includes a first functional unit and a second functional unit in a certain section along an optical axis of an optical fiber including a core through which light propagates and a clad surrounding the core. , Or three functional units including a third functional unit. These functional units are provided at regular intervals along the optical axis of the optical fiber. The first functional unit includes a plurality of parallel pillars made of a material having a refractive index different from that of the material forming the core, penetrating the optical fiber or its core. Specifically, the columnar body is filled with, for example, a substance having an electro-optic effect or a substance having a Faraday effect. Each of the second and third functional units has a configuration in which a plurality of columnar bodies having a cavity (hole) parallel to each other penetrate the core. Due to having these functional units, the present optical device causes each of the dispersion characteristics of two types of linearly polarized light (TM, TE) to have a difference, and is used as a polarizer, a λ / 4 plate, a Faraday element, or the like. Can function.

(First Reference Example)
Hereinafter, a first reference example of the present invention will be described with reference to the drawings. FIG. 5A is a schematic side view showing the configuration of the optical device according to the first reference example of the present invention. FIG. 5B is a schematic cross-sectional view of the optical device of FIG. 5A taken perpendicularly to the optical axis 2 at the position of line BB ′ in the drawing. FIG. 5C is a schematic cross-sectional view of the optical device of FIG. 5A taken perpendicularly to the optical axis 2 at the position of line CC ′ in the drawing. In FIG. 5A, the optical fiber 1 is shown by extracting only a predetermined section corresponding to the optical device.

  As shown in FIG. 5A, the present optical device is formed on an optical fiber 1, and the optical fiber 1 includes a core 3 for transmitting light and a clad 4 surrounding the core 3. Further, the optical fiber 1 is formed with two functional units including a first functional unit 7 and a second functional unit 8, and functions as an optical device. The first function unit 7 and the second function unit 8 are provided at a predetermined interval along the optical axis 2 of the optical fiber 1. Note that, in the optical fiber 1, portions other than the above-described functional unit only realize an optical transmission function which is a normal function of the optical fiber.

  First, the first functional unit 7 is formed so as to penetrate the core 3 and the clad 4 of the optical fiber 1 in a direction perpendicular to the optical axis 2 for a certain section along the optical axis 2 of the optical fiber 1. And a plurality of Faraday crystal replacement cylinders 5 parallel to each other. The plurality of Faraday crystal-replaced cylinders 5 are used to form a cylindrical hole penetrating the core 3 and the clad 4 of the optical fiber 1 in a direction perpendicular to the optical axis 2 by, for example, a sol-gel method. It is manufactured by filling a Faraday crystal having a refractive index different from the above. The Faraday crystal is, for example, a garnet crystal. The Faraday crystal-substituted cylinders 5 are distributed so as to form a lattice on a plane perpendicular to the longitudinal direction. Here, it is assumed that a magnetic field 20 having sufficient strength to saturate the Faraday rotation of the polarization plane of light exists parallel to the optical axis 2 of the optical fiber 1.

  Next, the second functional unit 8 is formed so as to penetrate the core 3 and the clad 4 of the optical fiber 1 in a direction perpendicular to the optical axis 2 for a certain section along the optical axis 2 of the optical fiber 1. And a plurality of holes 6 having a hollow inside and parallel to each other. Like the Faraday crystal-substituted cylinder 5, the holes 6 are also distributed so as to form a lattice on a plane perpendicular to the longitudinal direction. However, the longitudinal direction of the plurality of holes 6 is set to have an angle of 45 ° along the plane perpendicular to the optical axis 2 with respect to the longitudinal direction of the Faraday crystal replacement column 5 of the first functional unit 7. You. This cylindrical hole 6 also has a refractive index different from the refractive index of the core 3 of the optical fiber 1 due to, for example, natural filling of air.

  The fact that the Faraday crystal-substituted cylinder 5 of the first functional unit 7 and the cylindrical hole 6 of the second functional unit 8 form an angle of 45 ° with each other will be described with reference to FIGS. It is clear from comparison with (c).

  Further, the first and second functional units 7 and 8 will be described in detail. As described above, a column having a refractive index different from that of the core 3 of the optical fiber 1 can be formed in a direction perpendicular to the optical axis 2 of the optical fiber 1 by a method such as drilling, laser, or etching. The first functional unit 7 is composed of a plurality of Faraday crystal-substituted cylinders 5 formed by filling the thus-formed cylindrical holes with Faraday crystals by a sol-gel method, and functions as a polarizer and a Faraday element. Have at the same time. Further, the second functional unit 8 is composed of only a plurality of holes 6, and calculates the outer diameter of the holes 6 and the distribution state of the holes 6 in advance so as to have a function of a polarizer (analyzer). The first functional unit 7 has a hole 6 formed with a longitudinal direction at an angle of 45 ° with the longitudinal direction of the Faraday crystal substitution column 5.

  As described above, a plurality of parallel cylindrical holes having a refractive index different from the refractive index of the core 3 in a direction perpendicular to the optical axis 2 of the optical fiber, or a cylindrical column filled with the functional material is fixed at a predetermined interval. By controlling the refractive index and outer diameter of the hole or the cylinder and the distribution of the hole or the cylinder with respect to the wavelength of the light source, a difference occurs in the dispersion characteristics of the two types of linearly polarized light (TM, TE). As a result, the first functional part 7 of the optical fiber 1 forms a polarizer and a Faraday element, and the second functional part 8 forms an analyzer. Act as an isolator. Therefore, the operation of coupling the optical waveguide to the optical isolator with the lens is eliminated, and the number of components can be reduced, so that the cost can be significantly reduced.

  Next, FIG. 6 is a partial schematic configuration diagram of another example of the optical device according to the first reference example of the present invention. The hole 6 shown in FIG. 6 may be the hole 6 included in the second functional unit 8 in FIG. 5A or the hole before forming the Faraday crystal replacement column 5.

  In the above description, the columnar hole 6 or the hole for forming the Faraday crystal-substituted column 5 is formed so as to penetrate including the clad 4, but as shown in FIG. A hole may be formed in the hole. This is because light actually passes only through the core 3 inside the optical fiber 1, and even if the cylindrical hole penetrates including the cladding 4, or the core 3 alone, This is because the effect of light passing through the inside is hardly changed.

  In the first reference example, the shape of the hole is described as a cylinder, but the shape is not limited to a cylinder, and may be another shape such as a quadrangular prism, a polygonal prism, or an elliptical cylinder. In addition, the above function has been described as being realized by a two-dimensional photonic crystal including a plurality of holes or columns parallel to each other. However, the present invention is not limited to such a case. It may be realized by a two-dimensional photonic crystal.

(Second reference example)
Hereinafter, a second embodiment of the present invention will be described with reference to the drawings. FIG. 7A is a schematic side view showing a configuration of an optical device according to a second reference example of the present invention. FIG. 7B is a schematic cross-sectional view of the optical device of FIG. 7A taken perpendicularly to the optical axis 2 at the position of line BB ′ in the figure. FIG. 7C is a schematic cross-sectional view of the optical device of FIG. 7A taken perpendicularly to the optical axis 2 at the position of line CC ′ in the drawing. In FIG. 7A, the optical fiber 1 is shown by extracting only a predetermined section corresponding to the optical device.

  As shown in FIG. 7, the present device comprises an incident optical fiber 41 having a core 45 and a clad 46 and receiving light, and an output optical fiber having a core 45 and a clad 46 and emitting light. 42, a Faraday element 47 provided between the input side optical fiber 41 and the output side optical fiber 42 and rotating the plane of polarization of light, and an optical axis of the input side optical fiber 41 and an optical axis of the Faraday element 47. And a guide 48 for mechanically adjusting the optical axis of the emission side optical fiber 42. The Faraday element 47 is, for example, a garnet crystal.

  The incident side optical fiber 41 is formed so as to penetrate the core 45 and the clad 46 in a direction perpendicular to the optical axis 49 for a certain section along the optical axis 49, and has a plurality of cylindrical columnar parts parallel to each other. It has one hole 43. The first holes 43 are distributed at regular intervals and have a refractive index different from that of the core 45 in the optical fiber 41.

  Similarly, the output side optical fiber 42 has a plurality of parallel circles formed so as to penetrate the core 45 and the clad 46 in a direction perpendicular to the optical axis 49 for a certain section along the optical axis 49. It has a columnar second hole 44. The second holes 44 are also distributed at regular intervals, and have a refractive index different from that of the core 45 in the optical fiber 42.

  Here, regarding the first hole 43 and the second hole 44, as described in the first reference example, the plurality of first holes 43 and the plurality of second holes 44 are respectively polarizers. Are distributed to act as The arrangement of the first and second holes 43 and 44 only needs to be periodically distributed as described above with reference to FIG. The direction of the first hole 43 and the direction of the second hole are different from each other in the longitudinal direction by 45 °, as is clear from comparison between FIG. 7B and FIG. 7C. Is set to Here, it is assumed that a magnetic field 40 having a strength sufficient to saturate the Faraday rotation of the polarization plane of light exists parallel to the optical axis 49 in relation to the Faraday element 47.

  The method of forming the first and second holes 43 and 44 is the same as that of the first embodiment, and the holes are formed in a direction perpendicular to the optical axis 49 of the optical fiber by using a drill, laser, or etching. To form

  By the way, in the present reference example, the input side optical fiber 41 and the output side optical fiber 42 are mechanically associated with each other by the guide 48, and can be freely rotated around the optical axis 49. Therefore, when the optical axis is adjusted in the guide 48 so that the first hole 43 in the input side optical fiber 41 and the second hole 44 in the output side optical fiber 42 form a relative angle of 45 °, the angle adjustment is performed. May be done. According to the configuration of such an optical device, the first hole 43 in the input side optical fiber 41 and the second hole 44 in the output side optical fiber 42 can be manufactured in the same manner, and the relative angle between them becomes later. Since the adjustment can be made in the above, it can be manufactured at low cost.

  In the above description, the cylindrical hole is formed so as to penetrate including the clad 46, but the hole may be formed only in the core 45 as in the case of FIG. Further, the first hole 43 or the second hole 44 may be filled with a substance such as a Faraday crystal having a refractive index different from that of the core 45 of each optical fiber. Here, when the first hole 43 or the second hole 44 is filled with the Faraday crystal, the Faraday element 47 may be omitted.

  Further, the shape of the hole is also described as a cylinder in the second reference example, but is not limited to a cylinder, and may be another shape such as a quadrangular prism, a polygonal prism, and an elliptical cylinder. Also, the above function has been described as being realized by a two-dimensional photonic crystal composed of a plurality of cylinders parallel to each other. However, the present invention is not limited to such a case, and a three-dimensional photonic crystal having a structure called a jabronobite or a woodpile is provided. It may be realized by a nick crystal. Furthermore, instead of the first hole 43 in the incident side optical fiber 41 and the second hole 44 in the exit side optical fiber 42, a photonic crystal layer is formed on the end faces of the incident side optical fiber 41 and the exit side optical fiber 42. May be used. With respect to a method of forming a photonic crystal on the end face of an optical fiber, for example, a photonic crystal having a periodic structure including three-dimensional high refractive index fine particles 221 and a low refractive index portion 222 is manufactured using FIG. The method has been described above.

  As described above, the polarizer and the analyzer can be formed only by performing the same processing for forming a hole in the optical fiber, and the Faraday element is combined with the optical fiber acting as the polarizer and the analyzer. Thus, an optical isolator can be configured. Therefore, the operation of coupling the optical waveguide to the optical isolator with the lens is eliminated, and the number of components can be reduced, so that the cost can be significantly reduced.

(Third reference example)
Hereinafter, a third embodiment of the present invention will be described with reference to the drawings. FIG. 8 is a schematic side view showing the configuration of the optical device according to the third embodiment of the present invention. In FIG. 8, the optical fiber 51 is shown by extracting only a predetermined section corresponding to the optical device.

  As shown in FIG. 8, the present optical device comprises an optical fiber 51, a pair of electrodes 59 for generating an electric field in a direction perpendicular to the optical axis 52 of the optical fiber, and a signal source for applying a predetermined voltage to the electrode 59. 50. The optical fiber 51 includes a core 53 for transmitting light and a clad 54 surrounding the core 53. Further, the optical fiber 51 is formed with two functional units including a first functional unit 57 and a second functional unit 58, and functions as an optical device. The first functional unit 57 and the second functional unit 58 are provided at a predetermined interval along the optical axis 52 of the optical fiber 51.

First, the first functional part 57 is formed so as to penetrate the core 53 and the clad 54 of the optical fiber 51 in a direction perpendicular to the optical axis 52 for a certain section along the optical axis 52 of the optical fiber 51. And a plurality of Pockels crystal replacement cylinders 55 parallel to each other. The Pockels crystal replacement cylinders 55 are distributed so as to form a lattice on a plane perpendicular to the longitudinal direction. Incidentally, the plurality of Pockels crystal-substituted cylinders 55 are formed by filling Pockels crystals into cylindrical holes by, for example, a sol-gel method. The Pockels crystal is known as a substance exhibiting a primary electro-optic effect, and for example, a LiNbO ₃ crystal, a LiTaO ₃ crystal, an NH ₄ H ₂ PO ₄ crystal, a KH ₂ PO ₄ crystal, or the like can be used.

  Next, the second functional unit 58 is formed so as to penetrate the core 53 and the clad 54 of the optical fiber 51 in a direction perpendicular to the optical axis 52 for a certain section along the optical axis 52 of the optical fiber 51. And a plurality of holes 56 which are hollow and parallel to each other. The plurality of holes 56 are also distributed so as to form a lattice in a plane perpendicular to the longitudinal direction, and have a refractive index different from that of the core 53 of the optical fiber 5.

  Further, the first and second functional units 57 and 58 will be described in detail. As described above, a column having a refractive index different from the refractive index of the core 53 of the optical fiber 51 can be formed in a direction perpendicular to the optical axis 52 of the optical fiber 51 by a method such as drilling, laser, or etching. The first functional unit 57 is configured by the Pockels crystal-substituted cylinder thus formed, and has the functions of a polarizer and a Pockels element at the same time. Further, the second functional unit 58 is composed of only a plurality of holes 56, and calculates the outer diameter of the holes 56 and the distribution state of the holes 56 in advance so as to have a function of a polarizer (analyzer). The first functional portion 57 has a hole 56 formed perpendicularly or parallel to the Pockels crystal replacement cylinder 55 along a plane perpendicular to the optical axis 52. Regarding the arrangement of the holes, it is sufficient that the holes are distributed with the periodic structure as described above with reference to FIG.

  Further, the magnitude of the electric field applied to the electrode 59 by the signal source 50 is controlled so that the refractive index of the Pockels crystal replacement cylinder 55 is changed so that the Pockels crystal replacement cylinder 55 also functions as a λ / 4 plate. Further, the signal source 50 can periodically change the electric field applied to the electrode 59. Then, the refractive index of the Pockels crystal replacement cylinder 55 changes, so that the optical signal transmitted through the first functional unit 57 can be changed.

  As described above, the polarizer, the Pockels element, the λ / 4 plate, and the analyzer can be formed only by processing the optical fiber 51, so that the optical fiber 51 functions as an optical modulator. Therefore, the work of coupling the optical modulator to the waveguide of the optical modulator by the lens is eliminated, and the number of components can be reduced, so that the cost can be significantly reduced.

  In the above description, the cylindrical hole is formed so as to penetrate including the clad 54, but the hole may be formed only in the core 53 as in the case of FIG. Further, the shape of the hole has been described as a cylinder, but the shape is not limited to a cylinder, but may be other shapes such as a quadrangular prism, a polygonal prism, and an elliptical cylinder. Also, the above function has been described as being realized by a two-dimensional photonic crystal composed of a plurality of cylinders parallel to each other. However, the present invention is not limited to such a case, and a three-dimensional photonic crystal having a structure called a jabronobite or a woodpile is provided. It may be realized by a nick crystal.

(Fourth reference example)
Hereinafter, a fourth embodiment of the present invention will be described with reference to the drawings. FIG. 9 is a schematic side view showing an optical device according to a fourth reference example of the present invention. In FIG. 9, the optical fiber 61 is shown by extracting only a predetermined section corresponding to the optical device.

  As shown in FIG. 9, the present optical device includes an optical fiber 61, an electrode 63 for generating an electric field in a direction perpendicular to an optical axis 62 of the optical fiber 61, and a signal source 60 for applying an electric field to the electrode 63. Be composed. The optical fiber 61 includes a core 83 for transmitting light, and a clad 84 surrounding the core 83. Further, the optical fiber 61 is formed with three functional units including a first functional unit 67, a second functional unit 68, and a third functional unit 69, and functions as an optical device. The first to third functional units 67 to 69 are provided at predetermined intervals along the optical axis 62 of the optical fiber 61.

  Here, the first functional unit 67 in the present embodiment is similar to the first functional unit 57 in the third embodiment, with respect to the optical axis 62 for a certain section along the optical axis 62 of the optical fiber 61. It comprises a plurality of Pockels crystal-substituted cylinders 64 parallel to each other and formed to penetrate the core 83 and the clad 84 of the optical fiber 61 in the vertical direction.

  Further, the second and third functional units 68 and 69 in the present reference example are similar to the second functional unit 58 in the third reference example, and are used for a certain section along the optical axis 62 of the optical fiber 61. It is constituted by a plurality of first and second holes 65 and 66 which are hollow and parallel to each other and are formed so as to penetrate the core 83 and the clad 84 of the optical fiber 61 in a direction perpendicular to the axis 62. Is done. The plurality of first and second holes 65 and 66 are distributed so as to form a lattice in a plane perpendicular to the longitudinal direction, and have a refractive index different from that of the core 83 of the optical fiber 61. Having a rate. The first and second holes 65 and 66 are provided perpendicular or parallel to the Pockels crystal replacement cylinder 64 in the first functional unit 67 along a plane perpendicular to the optical axis 62.

  Further, the first to third functional units 67 to 69 will be described in detail. As described above, a cylinder having a refractive index different from that of the core 83 of the optical fiber 61 can be formed in a direction perpendicular to the optical axis 62 of the optical fiber 61 by a method such as drilling, laser, or etching. The first functional unit 67 is constituted by the Pockels crystal-substituted cylinder 64 thus formed, and has the functions of the polarizer and the Pockels element at the same time. Further, the second function part 68 is constituted only by the plurality of first holes 65, and has an outer diameter of the first holes 65 and a distribution of the first holes 65 so as to have a function of a λ / 4 plate. The state is calculated in advance, and the first functional unit 67 has a first hole 65 formed perpendicularly or parallel to the Pockels crystal replacement cylinder 64. As for the arrangement of the holes, it is sufficient that the holes are periodically distributed as described above with reference to FIG. Similarly to the second functional unit 68, the third functional unit 69 is perpendicular to the Pockels crystal replacement cylinder 64 in the first functional unit 67 so as to have a function of a polarizer (analyzer). Or, it has a second hole 66 formed in parallel.

  Further, the signal source 50 changes the optical signal transmitted through the first functional unit 67 by periodically changing the electric field applied to the electrode 59 to change the refractive index of the Pockels crystal replacement cylinder 55. Can be.

  As described above, the polarizer, the Pockels element, the λ / 4 plate, and the analyzer can be formed only by processing the optical fiber 61, so that the optical fiber 61 functions as an optical modulator. Therefore, the work of coupling the optical modulator to the waveguide of the optical modulator by the lens is eliminated, and the number of components can be reduced, so that the cost can be significantly reduced.

  In the above description, the cylindrical hole is formed so as to penetrate including the clad 84, but the hole may be formed only in the core 83 as in the case of FIG. Further, the shape of the hole has been described as a cylinder, but the shape is not limited to a cylinder, but may be other shapes such as a quadrangular prism, a polygonal prism, and an elliptical cylinder. Also, the above function has been described as being realized by a two-dimensional photonic crystal composed of a plurality of cylinders parallel to each other. However, the present invention is not limited to such a case, and a three-dimensional photonic crystal having a structure called a jabronobite or a woodpile is provided. It may be realized by a nick crystal.

(Fifth reference example)
Hereinafter, a fifth embodiment of the present invention will be described with reference to the drawings. FIG. 10 is an overall view of an optical device according to a fifth reference example of the present invention, and FIG. 11 is a schematic view in which the functional unit 78 shown in FIG. FIG.

  As shown in FIG. 11, the present optical device is formed on an optical fiber 71, and the optical fiber 71 includes a core 75 for transmitting light and a clad 76 surrounding the core 75. Further, the optical fiber 71 is provided with a function section 78, which functions as an optical device.

  The function part 78 is formed so as to penetrate the core 75 and the clad 76 of the optical fiber 71 in a direction perpendicular to the optical axis 72 for a certain section along the optical axis 72 of the optical fiber 71. And is constituted by a plurality of holes 77 parallel to each other. The plurality of holes 77 are distributed so as to form a lattice on a plane perpendicular to the longitudinal direction, and have a refractive index different from that of the core 75 of the optical fiber 71. As described above, the hole 77 can be formed in a direction perpendicular to the optical axis 72 of the optical fiber 71 by a method such as drill, laser, or etching.

  As described above, when a plurality of parallel cylindrical holes having a refractive index different from the refractive index of the core 75 are formed at regular intervals in a direction perpendicular to the optical axis 72 of the optical fiber, the light source wavelength can be reduced. By controlling the refractive index and the outer diameter and the distribution of the cylinder, a difference occurs in the dispersion characteristics of the two types of linearly polarized light (TM, TE). As a result, the function section 78 can have a dispersion characteristic that delays the wavelength that is advanced and advances the wavelength that is delayed. As described above, if the phase speed of the light source wavelength can be increased or decreased, the signal 79a spread due to the chromatic dispersion characteristic inherent to the optical fiber also becomes steep like the incident light 73 after passing through the functional unit 78. It can be formed so as to have a wavelength dispersion characteristic that restores to the pulse signal 79b. Therefore, the outgoing light 74 becomes a signal like the incident light 73, and thus the present optical device functions as a dispersion compensator.

  Thus, the optical fiber 71 acts as a dispersion compensator only by processing the optical fiber 71. Therefore, the work of coupling the optical modulator to the waveguide of the optical modulator by the lens is eliminated, and the number of components can be reduced, so that the cost can be significantly reduced.

  In the above description, the cylindrical hole is formed so as to penetrate including the clad 76, but the hole may be formed only in the core 75 as in the case of FIG. Further, the shape of the hole has been described as a cylinder, but the shape is not limited to a cylinder, but may be other shapes such as a quadrangular prism, a polygonal prism, and an elliptical cylinder. Also, the above function has been described as being realized by a two-dimensional photonic crystal composed of a plurality of cylinders parallel to each other. However, the present invention is not limited to such a case, and a three-dimensional photonic crystal having a structure called a jabronobite or a woodpile is provided. It may be realized by a nick crystal. However, when the optical fiber 71 is a polarization-maintaining optical fiber, the arrangement direction becomes a problem, so that it is not suitable for realizing a three-dimensional photonic crystal.

<Specific mounting form to optical fiber>
Next, in the following reference examples, a case where an optical device such as an optical modulator is mounted on an optical fiber will be specifically described. In the following reference example, it is easy to form a plurality of columnar bodies parallel to each other through a core by using a plane formed by partially removing a clad. In addition, since an electrode can be provided on the clad-removed surface, a uniform and stable electric field can be applied to the functional unit. The details will be described below.

(Sixth reference example)
Hereinafter, a sixth embodiment of the present invention will be described with reference to the drawings. FIG. 12 is a horizontal sectional view showing the entire optical device according to the sixth embodiment of the present invention. FIG. 13A is an enlarged side sectional view of a part shown in FIG. FIG. 13B is a schematic cross-sectional view of the optical device of FIG. 13A taken perpendicular to the optical axis 2 at the position of line BB ′ in the figure.

  As shown in FIGS. 12 and 13, the present optical device includes an optical fiber 1 and a capillary 12 that covers the periphery of the optical fiber 1. The optical fiber 1 includes a core 3 for transmitting light and a clad 4 surrounding the core 3. The optical fiber 1 has two function units including a first function unit 7 and a second function unit 8. The first function unit 7 and the second function unit 8 are provided at a predetermined interval along the optical axis 22 of the optical fiber 1. Having these functional units, this optical device can be used as a polarizer or the like by causing a difference in the dispersion characteristics of two types of linearly polarized light (TM, TE) included in the incident light 16. .

  Here, the first and second functional units 7 and 8 according to the present embodiment are the same as the first and second functional units 57 and 58 according to the third embodiment, and the cylinder according to the present embodiment. Since the body 19 and the holes 6 are formed and distributed in the same manner as the Pockels crystal-substituted cylinder 55 and the holes 56 according to the third reference example, the description thereof is omitted. However, the cylindrical body 19 and the hole 6 are arranged so as to be parallel to each other.

  Here, in the optical fiber 1, in order to form the first and second functional units 7 and 8, the clad-removed portion 18 is removed in a predetermined section, and the clad-removed portion 18 is almost in contact with the core 3. Up to the position, it has been removed from both sides of the optical fiber 1. As a result, a pair of parallel boundary surfaces 23 that are parallel to each other across the core 3 and have a rectangular side cross section are formed. Therefore, as shown in FIG. 13 (b), the optical fiber 1 has a shape in which the left and right sides of the optical fiber 1 are cut off in a predetermined section, leaving the unremoved clad residual portions 21 up and down in the figure. , The parallel boundary surface pair 23 is exposed to the outside. By manufacturing in this manner, the columnar body 19 and the hole 6 can be easily formed.

  Further, a pair of electrodes 9 for applying an electric field to the plurality of cylindrical bodies 19 made of Pockels crystal constituting the first functional unit 7 are provided on the above-described parallel boundary surface pair 23. The electrode 9 is provided on the side of the optical fiber 1, and the direction of the applied electric field is parallel to the plurality of cylindrical bodies 19. By arranging the electrode 9 on the parallel boundary surface pair 23 in this manner, an electric field can be easily and accurately applied to the cylindrical body 19. A signal source 10 for applying a voltage to the electrode 9 is provided outside the capillary 12. One of the electrodes 9 is connected to the ground 11.

  Next, the capillary 12 covering the periphery of the optical fiber 1 has an outer diameter substantially equal to that of the ferrule 14 of another optical fiber 13 to be connected. Thus, when this optical device is to be connected to another optical fiber 13, the capillary 12 is pressed by the ferrule of another optical fiber and the split sleeve 15, and the optical axis is adjusted in the same manner as the optical system coupling between the optical fibers. Since the alignment can be performed, the optical systems can be easily combined.

(Seventh Reference Example)
Hereinafter, a seventh embodiment of the present invention will be described with reference to the drawings. FIG. 14A is a schematic side view showing an optical device according to a seventh reference example. FIG. 14B is a schematic cross-sectional view of the optical device of FIG. 14A taken perpendicular to the optical axis 2 at the position of line BB ′ in the figure.

  As shown in FIG. 14, the present optical device has substantially the same configuration as the optical device according to the sixth reference example shown in FIG. 13, but the installation position and the shape of the parallel electrode 24 according to the sixth reference example. Different from electrode 9. The parallel electrode 24 according to the reference example applies an electric field perpendicular to the longitudinal direction of the plurality of cylindrical bodies 19 made of Pockels crystal constituting the first functional unit 7 and perpendicular to the optical axis 22. As described above, parallel electrodes 24 are provided parallel to the optical axis 22 of the optical fiber 1 and perpendicular to the longitudinal direction of the cylindrical body 19. That is, as shown in FIG. 14A, the electrode 9 is different from the electrode 9 in that a pair of parallel electrodes 24 are provided above and below the plurality of cylinders 19 on a plane perpendicular to the longitudinal direction of the cylinder 19. It is different from the case. The plane perpendicular to the longitudinal direction of the cylindrical body 19 is, as shown in FIG. 14B, parallel to each other with the core 3 interposed therebetween, which is formed as a result of the removal of the clad-removed portion 18. Thus, the parallel boundary surface pair 23 has a rectangular side cross section. However, since the pair of parallel electrodes 24 are provided on the same plane, as shown in FIG. 14B, the cladding-removed portions 18 are always removed from the left and right sides of the optical fiber 1 to form two surfaces (parallel boundary surfaces). It is not necessary to form pair 23). Therefore, the cladding-removed portion 18 may be removed so that only one of the planes for arranging the parallel electrodes 24 is formed. With the parallel electrodes 24 arranged as described above, the light modulation function of the first functional unit 7 including the plurality of cylindrical bodies 19 made of Pockels crystal can be adjusted.

  The signal source 10 for applying a voltage to the parallel electrode 24 is provided outside the capillary 12, and the other of the parallel electrodes 24 is connected to the ground 11. Since the configuration is the same as that of the device, the description of the same components will be omitted.

(Eighth Reference Example)
Hereinafter, an eighth embodiment of the present invention will be described with reference to the drawings. FIG. 15A is a schematic side view showing an optical device according to an eighth reference example. FIG. 15B is a schematic cross-sectional view of the optical device of FIG. 15A taken perpendicular to the optical axis 2 at the position of line BB ′ in the figure.

  As shown in FIG. 15, the present optical device has substantially the same configuration as the optical device according to the sixth reference example shown in FIG. 13, but the installation position and shape of the column electrode 25 according to the sixth reference example. Different from electrode 9. The column electrode 25 according to the reference example applies an electric field perpendicular to the longitudinal direction of the plurality of cylindrical bodies 19 made of Pockels crystal constituting the first functional unit 7 and parallel to the optical axis 22. In addition, a column electrode 25 is provided parallel to the optical axis 22 of the optical fiber 1 and perpendicular to the longitudinal direction of the cylindrical body 19. That is, as shown in FIG. 15A, on a plane perpendicular to the longitudinal direction of the cylindrical body 19, the pair of column electrodes 25 is provided on the left and right of the plurality of cylindrical bodies 19. It is different from the case. The plane perpendicular to the longitudinal direction of the cylindrical body 19 is the parallel boundary surface pair 23 shown in FIG. 15B as described above. However, since the pair of tandem electrodes 25 are provided on the same plane, as shown in FIG. 15 (b), the clad-removed portions 18 are always removed from the left and right sides of the optical fiber 1 to form two surfaces (parallel boundary surfaces). It is not necessary to form pair 23). Therefore, the cladding removal portion 18 may be removed so that only one of the planes for arranging the column electrodes 25 is formed. The light modulation function of the first functional unit 7 including the plurality of cylindrical bodies 19 made of Pockels crystal can be adjusted by the cascade electrodes 25 arranged as described above.

  The signal source 10 for applying a voltage to the column electrode 25 is provided outside the capillary 12, and the other of the column electrodes 25 is connected to the ground 11. Since the configuration is the same as that of the device, the same components are denoted by the same reference numerals and description thereof will be omitted.

(Ninth Reference Example)
Hereinafter, a ninth embodiment of the present invention will be described with reference to the drawings. FIG. 16A is a schematic side view showing an optical device according to a ninth reference example. FIG. 16B is a schematic cross-sectional view of the optical device of FIG. 16A taken perpendicularly to the optical axis 2 at the position of line BB ′ in the figure.

  As shown in FIG. 16, the present optical device has substantially the same configuration as the optical device according to the sixth reference example shown in FIG. 13, except that the cladding 4 is further removed and the installation position of the facing electrode 26 is changed to the sixth. Is different from the electrode 9 according to the reference example.

  First, as shown in FIG. 16B, in the optical fiber 1, the first and second functional units 7 and 8 are formed, and the cladding-removed portion 18 is provided in a predetermined section in order to install the facing electrode 26. The cladding-removed portion 18 has been removed from above and below and from the left and right of the optical fiber 1 to a position almost in contact with the core 3. As a result, a first pair of parallel boundary surfaces 31 that are parallel to each other with the core 3 interposed therebetween and have a rectangular side cross section are formed on the left and right sides of the core 3, and a second pair of parallel boundary surfaces 32 are formed on the core 3. Formed above and below. Therefore, as shown in FIG. 16A, the optical fiber 1 has a quadrangular prism having the optical axis 22 as the central axis, in a predetermined section, the unremoved clad residual portion 21 remains so as to surround the core 3. The first and second pairs of parallel boundary surfaces 31 and 32 are exposed to the outside. By manufacturing in this manner, the cylindrical body 19 and the hole 6 can be easily formed, and the facing electrode 26 can be provided on a plane different from that in the sixth embodiment.

  Next, the facing electrode 26 applies an electric field perpendicular to the longitudinal direction of the plurality of cylindrical bodies 19 made of Pockels crystal constituting the first functional unit 7 and perpendicular to the optical axis 22. A facing electrode 26 is provided parallel to the optical axis 22 of the optical fiber 1 and parallel to the longitudinal direction of the cylindrical body 19. That is, as shown in FIGS. 16A and 16B, a plane parallel to the longitudinal direction of the cylindrical body 19 and also parallel to the optical axis 22, that is, a second parallel boundary surface The pair 32 is different from the electrode 9 in that a pair of facing electrodes 26 are provided above and below the plurality of cylindrical bodies 19. The light modulation function of the first functional unit 7 composed of the plurality of cylindrical bodies 19 made of Pockels crystal can be adjusted by the facing electrodes 26 arranged as described above.

  The signal source 10 for applying a voltage to the facing electrode 26 is provided outside the capillary 12, and the other of the facing electrode 26 is connected to the ground 11. Since the configuration is the same as that of the device, the same components are denoted by the same reference numerals and description thereof will be omitted.

(10th reference example)
Hereinafter, a tenth embodiment of the present invention will be described with reference to the drawings. FIG. 17A is a schematic side view showing an optical device according to a tenth reference example. FIG. 17B is a schematic cross-sectional view of the optical device of FIG. 17A taken perpendicularly to the optical axis 2 at the position of line BB ′ in the figure.

  As shown in FIG. 17A, the present optical device has substantially the same configuration as the optical device according to the ninth embodiment shown in FIG. 16 except that the longitudinal direction of the hole 6 is the sixth embodiment. And different. That is, in the optical device according to the present reference example, the longitudinal direction of the plurality of cylindrical bodies 19 constituting the first functional unit 7 provided in the optical fiber 1 and the plurality of holes 6 constituting the second functional unit 8 are different. It is characterized in that the longitudinal directions are perpendicular to each other. That is, in the optical device according to the present reference example, the longitudinal direction of the plurality of cylindrical bodies 19 constituting the first functional unit 7 provided in the optical fiber 1 and the plurality of holes 6 constituting the second functional unit 8 are different. It is characterized in that the longitudinal directions are perpendicular to each other. Specifically, as shown in FIG. 17 (b), the longitudinal direction of the columnar body 19 extends in the horizontal direction in the figure, while the longitudinal direction of the hole 6 extends in the vertical direction in the figure.

  As described above, by setting the longitudinal directions of the cylindrical body 19 and the hole 6 constituting the first and second functional units 7 and 8 to be perpendicular to each other, it is possible to adjust the function of the light modulation function in each functional unit. it can.

  The case where there are two functional units has been described above, but the present invention can be similarly applied to a case where there are three functional units as in the optical device according to the fourth reference example.

(Eleventh Reference Example)
An optical device according to an eleventh reference example of the present invention is characterized in that an electrode for applying an electric field is provided on a surface where the direction of the electric field forms an angle θ with the longitudinal direction of the columnar body constituting the first functional unit. . The light modulation function of the first functional unit can be adjusted by making the longitudinal direction of the columnar body and the direction of the electric field form a constant angle θ in this manner.

  This optical device is different from the optical device according to the ninth or tenth embodiment in that the parallel electrode 87 for applying an electric field is different from the optical device according to the ninth or tenth embodiment in the cross section of the optical fiber 1 shown in FIG. The present embodiment is different from the first embodiment in that the first functional unit 7 is provided at an angle θ with respect to the longitudinal direction of the cylindrical body 19. Specifically, in a predetermined section, the clad 4 is substantially removed except for the core 3, and a pair of parallel electrodes 87 is formed at a position in contact with or substantially in contact with the core 3 so as to form an angle θ with the longitudinal direction of the cylindrical body 19. Is provided. Note that, instead of the flat parallel electrode 87 as shown in FIG. 18A, the present optical device uses a curved electrode 88 which is distorted substantially along the curved surface of the core 3 as shown in FIG. 18B. May be. When the curved electrode 88 is used, the column electrode 19 is provided so that the longitudinal direction of the cylindrical body 19 and the normal direction 35 at the center of the curved surface form an angle θ.

(Twelfth Reference Example)
An optical device according to a twelfth reference example of the present invention is characterized in that the first functional portion of the optical fiber is constituted by a plurality of cylindrical bodies penetrating the core and having a Faraday effect crystal. I do. As described above, since the first functional unit is formed of the columnar body made of the crystal having the Faraday effect, the Faraday rotation angle of the first functional unit can be adjusted by applying a magnetic field. Therefore, the present optical device functions as an optical isolator.

  FIG. 19 is a horizontal sectional view showing an optical device according to a twelfth embodiment of the present invention. As shown in FIG. 19, the present optical device has a Faraday effect in which the first functional unit 7 of the optical fiber 1 penetrates the core 3 as compared with the optical modulator according to the sixth reference example. It is different in that it is composed of a plurality of cylindrical bodies 91 made of crystals. Specifically, the columnar body forming the first functional unit 7 is formed of a crystal having a Faraday effect instead of the Pockels crystal. As the crystal having the Faraday effect, for example, a garnet crystal, a rare earth iron garnet crystal (YIG or the like), or the like can be used. Further, a magnet 95 for applying a magnetic field 94 to the crystal having the Faraday effect is provided on the outer surface of the capillary 12 (or so that the outer surface is processed and fitted). The magnet 95 may be a permanent magnet such as a rare-earth magnet, an electromagnet, or any other magnet that generates a magnetic field having a strength sufficient to substantially saturate the Faraday rotation of the polarization plane of light. . Since the Faraday rotation angle does not depend on the direction of the magnetic field, the direction in which the magnetic field 94 is applied can be selected in various ways.

<Reference example regarding optical sensor>
Next, in the following reference examples, the configuration and operation of an optical sensor such as an optical voltage sensor, a photocurrent sensor, and an optical magnetic field sensor according to the present invention will be specifically described.

(Thirteenth Reference Example)
First, an optical voltage sensor according to a thirteenth embodiment of the present invention will be described.
As shown in FIG. 20, the optical voltage sensor of the present reference example includes a sensor unit, a light emitting unit 118, and a light receiving unit 119, and the sensor unit is arranged on the same optical axis 108 in order from the light incident side. It comprises a polarizer 101, a λ / 4 plate 102, a first conductive reflective film 106, an electro-optic crystal 103, a second conductive reflective film 107, and an analyzer 104, which are arranged.

  The light emitting unit 118 includes an E / O circuit including a light emitting element such as an LED as a light source, and an input optical system including an optical fiber. The light beam emitted from the light source enters the sensor unit via the input side optical system.

In the sensor section, the polarizer 101, the λ / 4 plate 102, the first conductive reflection film 106, the electro-optic crystal 103, the second conductive reflection film 107, and the analyzer 104 are sequentially arranged on the optical path of the light beam. The light beam is emitted after being modulated by the measured voltage Vm by these optical elements. In the present reference example, a Z-axis propagating LiNbO ₃ crystal is used as the electro-optic crystal 103, and the electro-optic crystal 103 is arranged so that its Z-axis (C-axis) matches the optical axis 108. The first conductive reflecting film 106 and the second conductive reflecting film 107 have their reflecting surfaces perpendicular to the optical axis 108, and the first conductive reflecting film 106 and the second conductive reflecting film 107 The distance dr with respect to the sensor 107 is set to be an integral multiple of half the wavelength of the light 109 incident on the sensor unit. As shown in FIG. 20, the coordinate system is set such that the Z axis is along the optical axis 108 and the X and Y axes are along two mutually perpendicular directions in a plane perpendicular to the optical axis 108. And At this time, when an electric field is applied to the Z-axis propagating LiNbO ₃ crystal in the Z-axis direction, that is, the electro-optic constants related to the degree of modulation in the case of vertical modulation are γ33 and γ31, and the Z-axis propagating LiNbO ₃ crystal 103 When the setting direction is the X-axis direction, the setting direction of the polarizer 101 and the analyzer 104 is ± 45 ° with respect to the X-axis, and the setting direction of the λ / 4 plate 102 is the X-axis direction or the Y-axis direction. Here, the setting direction refers to a principal axis direction of an ellipse indicating a refractive index for a light beam incident on an electro-optic crystal, a λ / 4 plate, or the like.

The light receiving unit 119 includes an output optical system including an optical fiber and the like, and an O / E circuit including a photoelectric conversion element that converts an optical signal into an electric signal. The light beam emitted from the sensor unit passes through the output side optical system, is received by a photoelectric conversion element in the O / E circuit, and is converted into an electric signal. This electric signal depends on the polarization state of the light beam after passing through the LiNbO ₃ crystal 103, and the polarization state changes according to the measured voltage Vm. In a light receiving side signal processing circuit (not shown) connected to the light receiving section 119, the value of the voltage to be measured is obtained by calculating the degree of modulation based on this electric signal.

  The specific structure of the optical voltage sensor configured as described above is, for example, a structure as shown in FIG. 24 or FIG. 30 described later. Since the details of these structures will be described later as another reference example, detailed description thereof will be omitted.

  In the optical voltage sensor of this reference example, as described above, the distance dr between the first conductive reflection film 106 and the second conductive reflection film 107 in the sensor unit is an integer of half the wavelength of the light 109 incident on the sensor unit. It is set to double. With this setting, an etalon resonator (also called a “Fabry-Perot resonator”) is formed between the first conductive reflection film 106 and the second conductive reflection film 107. As a result, light propagating in the direction of the optical axis 108 which is a direction perpendicular to the first conductive reflection film 106 and the second conductive reflection film 107 becomes dominant, and as shown in FIG. It becomes steep. That is, even if the central direction and distribution of the incident light 109 vary due to tolerances of optical components, structural variations, and the like, the etalon resonator constituted by the first conductive reflective film 106 and the second conductive reflective film 107. Accordingly, the light passing through the electro-optic crystal 103 has a center direction perpendicular to the reflection surface (parallel to the optical axis 108) and a uniform distribution. Further, the wavelength of light passing through the electro-optic crystal 103 becomes constant by such an etalon resonator.

  As described above, according to the present embodiment, the center direction and distribution of light passing through the electro-optic crystal 103 are fixed by the etalon resonator constituted by the first conductive reflection film 106 and the second conductive reflection film 107. It becomes. That is, the beam states of the light beam incident on the electro-optic crystal 103 and the light beam after passing through the electro-optic crystal 103 are stabilized. As a result, even if the beam state of the incident light 109 to the sensor unit varies due to the tolerance of the optical parts and the like, the modulation degree which is the output of the optical voltage sensor of the present embodiment is stabilized. If the center direction of the incident light 109 on the sensor unit varies, the intensity of the light beam incident on the electro-optic crystal 103 changes, but the distribution is constant. Does not substantially affect the variation in the degree of modulation given as the ratio between the AC component and the DC component of the amount of light received by the light receiving unit 119.

  Note that the above-described beam angle distribution 115 depends on the reflectance of the first conductive reflection film 106 and the second conductive reflection film 107. The higher the reflectance is, the smaller the beam angle distribution 115 is. .6 or more. As described above, when the beam angle distribution 115 becomes smaller, a certain characteristic can be obtained with respect to the axis shift characteristic due to birefringence as shown in FIG.

In the present embodiment, although the vertical modulation scheme field is applied to the Z-axis propagation LiNbO ₃ crystal 103 in a direction of the Z-axis direction, that is the optical axis 108 is employed, instead of this, the Z-axis propagation LiNbO ₃ A lateral modulation method in which an electric field is applied to crystal 103 in the X-axis direction may be employed. As a specific configuration of the optical voltage sensor of the horizontal modulation system, for example, a configuration described later is cited (see FIG. 25).

When the horizontal modulation method is adopted, the electro-optic constant related to the modulation degree of the optical voltage sensor is γ22, and when the setting direction of the Z-axis propagating LiNbO ₃ crystal film 103 is the X-axis direction, the polarizer 101 and the analyzer 104 The setting direction is the X axis direction or the Y axis direction, and the setting direction of the λ / 4 plate 102 is ± 45 ° with respect to the X axis. Since the temperature characteristic of the electro-optic constant γ22 is small, in the case of the lateral modulation method, the change in the output (modulation degree) of the optical voltage sensor due to temperature (hereinafter referred to as “output change due to temperature”) depends on the temperature characteristic of the LiNbO ₃ crystal 103 The contribution is almost negligible, as shown by the dotted line in FIG. 21 (in FIG. 21, the vertical axis represents the relative output change based on the output (modulation degree) of the optical voltage sensor at 25 ° C.). Represents). However, due to the birefringence temperature characteristics of the λ / 4 plate 102, the modulation degree, which is the output of the photovoltaic sensor of the horizontal modulation type, has temperature characteristics. However, since the etalon resonator is formed in the region surrounding the LiNbO ₃ crystal film 103 as described above and the state of the light beam is stabilized, the beam state of the incident light 109 to the sensor unit is changed due to the tolerance of the optical components and the like. Even if there is variation, the temperature characteristics of the output of the optical voltage sensor are stabilized without variation. From this, when the horizontal modulation method is adopted, it can be used as a temperature sensor.

When the vertical modulation method is adopted as in this reference example, as described above, the electro-optic constants related to the modulation degree which is the output of the optical voltage sensor are γ33 and γ31, and the Z-axis propagating LiNbO ₃ crystal is used. When the setting direction of 103 is the X axis direction, the setting direction of the polarizer 101 and the analyzer 104 is ± 45 ° with respect to the X axis, and the setting direction of the λ / 4 plate 102 is the X axis direction or the Y axis direction. It is. In the case of the vertical modulation method, due to the temperature characteristics of the electro-optic constants γ33 and γ31, the contribution of the temperature characteristics of the LiNbO ₃ crystal 103 to the temperature change of the optical voltage sensor is indicated by the dotted line in FIG. become. That is, when the temperature increases, the output of the optical voltage sensor decreases due to the temperature characteristics of the LiNbO ₃ crystal 103. Further, in the output change due to the temperature of the optical voltage sensor, there is a component caused by the temperature characteristic of the birefringence of the λ / 4 plate 102 (hereinafter, this is referred to as “output change due to the temperature characteristic of the λ / 4 plate 102”). ). By the way, the ellipse indicating the refractive index of the λ / 4 plate 102 with respect to the incident light (hereinafter referred to as “refractive index ellipse”) becomes closer to a perfect circle as the temperature increases. On the other hand, the ellipse (refractive index ellipse) indicating the refractive index of the LiNbO ₃ crystal 103 with respect to the incident light becomes a flat ellipse as the temperature increases. Therefore, if the direction of the fast axis of the refractive index ellipse of the λ / 4 plate 102 and the direction of the fast axis of the refractive index ellipse of the LiNbO ₃ crystal 103 are matched, the temperature dependence of the sensor output due to the temperature characteristics of the two. Are canceled out (see the dotted line and the solid line in FIG. 21), and as a result, a change in the output of the optical voltage sensor due to the temperature is reduced. That is, when the setting direction of the LiNbO ₃ crystal 103 is the X-axis direction, the temperature characteristic of the output of the optical voltage sensor can be improved by setting the setting direction of the λ / 4 plate 102 to the X-axis direction. it can.

(14th reference example)
Next, an optical voltage sensor according to a fourteenth embodiment of the present invention will be described.
The optical voltage sensor of the present embodiment has basically the same configuration as that of the thirteenth embodiment, that is, the configuration as shown in FIG. The same components as those in the thirteenth reference example among the components in the optical voltage sensor of the present reference example are denoted by the same reference numerals, and description thereof is omitted. In addition, the overall operation of the optical voltage sensor of the present embodiment is substantially the same as that of the thirteenth embodiment, and a detailed description thereof will be omitted.

  In the present reference example, as shown in FIG. 22, the conductive reflection film for forming the etalon resonator in the sensor unit is realized by a multilayer film including a reflection film and a transparent conductive film. That is, in the present embodiment, the first conductive reflection film 106 in the thirteenth embodiment is realized by a multilayer film composed of the first transparent conductive film 121 and the first reflection film 122 (this multilayer film). The first conductive reflective film of the present embodiment realized by a film is denoted by reference numeral 106b). Further, in the present embodiment, the second conductive reflection film 107 in the thirteenth embodiment is realized by a multilayer film composed of the second transparent conductive film 123 and the second reflection film 124 (this multilayer film). The second conductive reflection film of the present embodiment realized by a film is denoted by reference numeral 107b). Therefore, in this embodiment, the distance dr2 between the first reflection film 122 and the second reflection film 124 is arranged so as to be an integral multiple of half the wavelength of the light 109 incident on the sensor unit. As the first and second transparent conductive films 121 and 123, for example, an ITO (Indium-Tin-Oxide) film or the like can be used.

FIG. 22 shows that the first transparent conductive film 121 forming the first conductive reflective film 106b and the second transparent conductive film 123 forming the second conductive reflective film 107b are both LiNbO ₃ crystals (electrically conductive). Although an example in which the first transparent conductive film 121 and the first reflective film 122 are arranged, and the second transparent conductive film 123 and the second reflective film The order of is arbitrary. However, as described above, regardless of the order, the first reflective film 122 and the second reflective film 124 are arranged such that the distance between the first reflective film 122 and the second reflective film 124 is an integral multiple of half the wavelength of the light 109 incident on the sensor unit. .

  According to this embodiment, the etalon is formed by the first conductive reflection film 106b and the second conductive reflection film 107b, which are realized as a multilayer film including the transparent conductive film and the reflection film, as in the thirteenth embodiment. A resonator is formed, whereby the center direction and distribution of light passing through the electro-optic crystal 103 become constant. As a result, even if the beam state of the incident light 109 to the sensor unit varies due to the tolerance of the optical parts and the like, the modulation degree which is the output of the optical voltage sensor of the present embodiment is stabilized. Further, according to the present embodiment, the first and second conductive reflecting films 106b and 107b are realized as a multilayer film including a transparent conductive film and a reflecting film, and thus the first and second conductive reflecting films 106b and 107b are realized. When fabricating the reflective films 106b and 107b, it is possible to control their conductivity and reflectance separately. Therefore, as compared with the case where a conductive reflection film is realized by a single-layer film, a conductive reflection film having a high reflectance can be easily formed, and the effect of stabilizing the beam state can be further enhanced.

(Fifteenth Reference Example)
Next, an optical voltage sensor according to a fifteenth embodiment of the present invention will be described.
The optical voltage sensor of the present embodiment has basically the same configuration as that of the thirteenth embodiment, that is, the configuration as shown in FIG. The same components as those in the thirteenth reference example among the components in the optical voltage sensor of the present reference example are denoted by the same reference numerals, and description thereof is omitted. Further, the overall operation of the optical voltage sensor according to the present embodiment is substantially the same as that of the thirteenth embodiment, and a detailed description thereof will be omitted.

In the present reference example, two conductive reflection films arranged so as to sandwich the LiNbO ₃ crystal film serving as the electro-optic crystal 103 in the sensor unit are realized by a multilayer film as shown in FIG. That is, in the present embodiment, the first conductive reflective film 106 in the thirteenth embodiment is composed of the first transparent conductive film 121 and the first multilayer film 133 functioning as a reflective film (as described above). In the present embodiment, the first conductive reflection film composed of the first transparent conductive film 121 and the first multilayer film 133 is indicated by reference numeral 106c). Further, the second conductive reflection film 107 in the thirteenth embodiment is composed of the second transparent conductive film 123 and the second multilayer film 134 functioning as a reflection film in this embodiment (as described above). In the present embodiment, the second conductive reflection film composed of the second transparent conductive film 123 and the second multilayer film 134 is indicated by reference numeral 107c). Each of the first multilayer film 133 and the second multilayer film 134 is a multilayer film in which two types of layers, that is, a high refractive index layer 131 and a low refractive index layer 132 are alternately stacked in the direction of the optical axis 108. It has a periodic structure in which the rate changes periodically in the direction of the optical axis 108. That is, the first multilayer film 133 and the second multilayer film 134 are one-dimensional photonic crystals. In this embodiment, the first transparent conductive film 121 is between the first multilayer film 133 and the LiNbO ₃ crystal film 103, and the second transparent conductive film 123 is the second multilayer film 134 and the LiNbO ₃ crystal film 103. Between, each is sandwiched. Then, of the layers constituting the first multilayer film 133, the layer in contact with the first transparent conductive film 121, that is, the layer closest to the LiNbO ₃ crystal film 103 (hereinafter referred to as “first proximity layer”) and the second multilayer Among the layers constituting the film 134, the layer in contact with the second transparent conductive film 123, that is, the layer closest to the LiNbO ₃ crystal film 103 (hereinafter, referred to as “second proximity layer”) is a layer of the same type ( That is, they have the same refractive index). In the example shown in FIG. 23, the first and second proximity layers are both high refractive index layers 131. In addition, as the first and second transparent conductive films 121 and 123, for example, an ITO (Indium-Tin-Oxide) film or the like can be used. In addition, as a material of the high refractive index layer 131, Ta ₂ O ₅ , TiO ₂ , Ge, Si, or the like (for example, a material having a refractive index of about 3.4 to 3.6) can be used. As a material of the layer 132, SiO ₂ (refractive index: about 1.46), air (refractive index: 1), or the like can be used.

  In the above-mentioned first conductive reflection film 106c and second conductive reflection film 107c, the sum of the thickness of one high-refractive index layer 131 and the thickness of one low-refractive index layer 132 is the ratio of the incident light 109 to the sensor unit. Each layer is formed so as to have a wavelength of 1/4. Further, the first multilayer film 133 and the second multilayer film 134 are separated from each other by the distance between the first adjacent layer and the second adjacent layer, that is, the surface of the first multilayer film 133 in contact with the first transparent conductive film 121 and the second multilayer film. The space dr3 between the film 134 and the surface in contact with the second transparent conductive film 123 is arranged so as to be an integral multiple of half the wavelength of the light 109 incident on the sensor unit.

  The first conductive reflecting film 106c and the second conductive reflecting film 107c configured and arranged as described above function as a so-called PBG (Photonic Band Gap) reflecting mirror for the incident light 109, and these PBG reflecting mirrors are used. Strong resonance occurs in the space surrounded by. That is, a stronger effect of the same quality as that of the etalon resonator in the thirteenth embodiment is obtained. Thereby, the center direction and distribution of light passing through the electro-optic crystal 103 become constant, and as a result, even if the beam state of the incident light 109 to the sensor unit varies due to tolerances of optical components and the like, the present embodiment does The degree of modulation, which is the output of the optical voltage sensor, is stabilized.

  By the way, in the above configuration, the first conductive reflection film 106c and the first conductive reflection film 106c are so arranged that the sum of the thickness of the high refractive index layer 131 and the thickness of the low refractive index layer 132 is １ ／ of the wavelength of the light 109 incident on the sensor unit. Although the two conductive reflection films 107c are formed, in order to enhance the above effect, both the thickness of the high refractive index layer 131 and the thickness of the low refractive index layer 132 are set to 1/1 / of the wavelength of the light 109 incident on the sensor unit. It is preferably 8.

  The application of the PBG reflecting mirror has already been introduced in a plurality of documents, and is disclosed in, for example, US Pat. No. 5,365,541.

(16th reference example)
Next, an optical voltage sensor according to a sixteenth embodiment of the present invention will be described.
The optical voltage sensor of this embodiment has the same configuration as that of the thirteenth embodiment, that is, the configuration as shown in FIG. The same components as those in the thirteenth reference example among the components in the optical voltage sensor of the present reference example are denoted by the same reference numerals, and description thereof is omitted. Further, the overall operation of the optical voltage sensor according to the present embodiment is substantially the same as that of the thirteenth embodiment, and a detailed description thereof will be omitted.

FIG. 24 is a transparent front view showing a specific structure of a main part of the optical voltage sensor according to the present reference example. This optical voltage sensor includes a substrate 144, and a polarizer 101, a λ / 4 plate 102, a first conductive reflection film 106, and a LiNbO ₃ crystal film as an electro-optic crystal, which constitute a sensor unit of the optical voltage sensor. A component guide 143 that positions the 103, the second conductive reflection film 107, and the analyzer 104 in close contact with each other and positions them sequentially on a predetermined optical axis 108 is provided at the center of the substrate 144. The component guide 143 is composed of four edges, and the substrate 144 is further provided with optical fiber guides 142a and 142b which are vertically connected to two opposing edges of the four edges. Among these, the optical fiber guide 142a guides the optical fiber 246a so that the optical fiber 246a constituting the input side optical system of the light emitting unit 118 is optically coupled to the polarizer 101 positioned by the component guide 143. The optical fiber guide 142b guides the optical fiber 246b so that the optical fiber 246b constituting the output side optical system of the light receiving unit 119 is optically coupled to the analyzer 104 positioned by the component guide 143. Further, a pair of electrodes 141 is attached to the substrate 144, and one of the pair of electrodes 141 is positioned on the first conductive reflection film 106 positioned by the component guide 143, and the other is positioned by the component guide 143. The second conductive reflection film 107 is electrically connected to each other by a lead wire 145. Therefore, when the measured voltage Vm is applied between the pair of electrodes 141, the voltage Vm is applied to the LiNbO ₃ film 103, which is an electro-optic crystal, in the Z-axis direction (the direction of the optical axis 108).

  In the present embodiment, as in the thirteenth embodiment, the distance dr between the first conductive reflection film 106 and the second conductive reflection film 107 in the sensor unit is half the wavelength of the light 109 incident on the sensor unit. Is set to be an integral multiple of. As a result, an etalon resonator is formed between the first conductive reflection film 106 and the second conductive reflection film 107, so that the direction is perpendicular to the first conductive reflection film 106 and the second conductive reflection film 107. Light propagating in the direction of the optical axis 108 becomes dominant, and the beam angle distribution 115 becomes steep. As a result, even if the beam state of the incident light 109 to the sensor unit varies due to tolerances of the optical components and the like, the modulation degree, which is the output of the optical voltage sensor of the present reference example, is stabilized. This has the effect of improving the directivity of light passing through the sensor section.

According to the present embodiment as described above, the etalon resonator is formed in the region surrounding the LiNbO ₃ crystal film 103 in the sensor portion, so that the directivity of light passing through the sensor portion is improved and the LiNbO ₃ crystal film The deviation of the axis of the light beam incident on the optical axis 103 is suppressed. Further, since each optical component constituting the sensor unit is plate-shaped or film-shaped, and each of the optical components is positioned in close contact with the component guide 143, the optical path length in the sensor unit is conventionally reduced. (See FIG. 33) (the optical path length can be, for example, about 2 to 3 mm). In the present reference example, after increasing the directivity of light passing through the sensor unit and shortening the optical path length in the sensor unit, the optical fiber 246a of the input side optical system is directly polarized by the optical fiber guide 142a. The optical fiber 246b of the output side optical system is directly optically coupled to the analyzer 104 by an optical fiber guide 142b. That is, in this reference example, the coupling loss of the optical fiber 246a on the polarizer 101 side and the analysis loss on the analyzer 104 side can be achieved without using a lens by improving the directivity of light and shortening the optical path length in the sensor section. The coupling loss of the optical fiber 246b can be kept within a range having no practical problem. As described above, according to the present embodiment, it is possible to reduce costs by suppressing the deterioration of the performance as an optical sensor and reducing the number of parts by eliminating the need for a lens.

(17th reference example)
Next, an optical voltage sensor according to a seventeenth embodiment of the present invention will be described.
The optical voltage sensor of the present reference example is a sensor of a horizontal modulation type, in which an electric field is applied in the X-axis direction to a Z-axis propagating LiNbO ₃ crystal film 103 which is an electro-optic crystal (see FIG. 20 for a coordinate system). This is different from the thirteenth reference example and the sixteenth reference example which are optical voltage sensors of the vertical modulation type. In this reference example, since the direction of application of the electric field to the LiNbO ₃ crystal film 103 is not the Z-axis direction (the direction of the optical axis 108) but the X-axis direction, the first conductive reflection A first reflection film 122 is used in place of the film 106, and a second reflection film 124 is used in place of the second conductive reflection film 107 (the first and second reflection films 122 and 124 do not require conductivity). They are arranged a pair of applying electrodes 151 for applying a voltage Vm to be measured is opposed to the X-axis direction in the LiNbO ₃ crystal film 103 so as to sandwich the LiNbO ₃ crystal film 103 in the X-axis direction. Further, the electro-optic constant related to the degree of modulation when an electric field is applied to the Z-axis propagating LiNbO ₃ crystal film 103 in the X-axis direction as in this reference example is γ22, and the setting of the polarizer 101 and the analyzer 104 is performed. The direction is the X axis direction or the Y axis direction, and the setting direction of the λ / 4 plate 102 is ± 45 ° with respect to the X axis.

  Since the basic configuration of this embodiment is the same as that of the thirteenth embodiment shown in FIG. 20 except for the above, the components of the optical voltage sensor according to the thirteenth embodiment are the same as those of the thirteenth embodiment. The same components as those described above are denoted by the same reference numerals, and description thereof will be omitted. Further, the overall operation of the optical voltage sensor according to the present embodiment is substantially the same as that of the thirteenth embodiment, and a detailed description thereof will be omitted.

FIG. 25 is a transparent front view showing a specific structure of a main part of the optical voltage sensor according to this reference example. This optical voltage sensor includes a substrate 144 as in the sixteenth embodiment, and a polarizer 101, a λ / 4 plate 102, a first reflection film 122, an electro-optic crystal constituting a sensor unit of the optical voltage sensor. A component guide 143 for positioning the LiNbO ₃ crystal film 103, the second reflection film 124, and the analyzer 104 in close contact with each other and sequentially arranging them on a predetermined optical axis 108 is provided at the center of the substrate 144. I have. Further, optical fiber guides 142a and 142b having the same configuration as that of the sixteenth embodiment are provided on the substrate 144, and the optical fiber guide 142a connects the optical fiber 246a constituting the input side optical system of the light emitting unit 118. The optical fiber 246a is guided so as to be optically coupled to the polarizer 101 positioned by the component guide 143. The optical fiber guide 142b guides the optical fiber 246b so that the optical fiber 246b constituting the output side optical system of the light receiving unit 119 is optically coupled to the analyzer 104 positioned by the component guide 143. A pair of electrodes 152 is attached to the substrate 144, and one and the other of the pair of electrodes 152 are connected to one and the other of the pair of application electrodes 151 by lead wires, respectively. Therefore, when the measured voltage Vm is applied between the pair of application electrodes 151, the voltage Vm is applied to the LiNbO ₃ film 103, which is an electro-optic crystal, in the X-axis direction.

  In the present embodiment, the distance between the first reflection film 122 and the second reflection film 124 in the sensor unit is set to be an integral multiple of half the wavelength of the light 109 incident on the sensor unit. Thus, similarly to the thirteenth and sixteenth embodiments, an etalon resonator is formed between the first reflection film 122 and the second reflection film 124, and therefore, the etalon resonator is perpendicular to the first reflection film 122 and the second reflection film 124. Light propagating in the direction of the optical axis 108, which is the direction, becomes dominant, and the beam angle distribution 115 becomes steep. As a result, even if the beam state of the incident light 109 to the sensor unit varies due to tolerances of the optical components and the like, the modulation degree which is the output of the optical voltage sensor of the present reference example is stabilized. The effect is obtained that the directivity of light passing through the section is improved.

As described above, according to the present embodiment, as in the sixteenth embodiment, the etalon resonator is formed in a region surrounding the LiNbO ₃ crystal film 103 in the sensor unit, so that the directivity of light passing through the sensor unit is improved. And the axial deviation of the light beam incident on the LiNbO ₃ crystal film 103 is suppressed. Further, since each optical component constituting the sensor unit is in a plate shape or a film shape and is positioned in a state where the optical components are in close contact with each other by the component guide 143, the optical path length in the sensor unit is shortened. (This optical path length can be, for example, about 2 to 3 mm). That is, also in this reference example, the coupling loss of the optical fiber 246a on the polarizer 101 side and the analysis loss on the analyzer 104 side can be achieved without using a lens by improving the directivity of light and shortening the optical path length in the sensor section. The coupling loss of the optical fiber 246b can be kept within a range having no practical problem. Therefore, as in the sixteenth embodiment, the cost can be reduced by reducing the number of parts by eliminating the need for a lens while suppressing a decrease in performance as an optical sensor.

(Eighteenth Reference Example)
Next, an optical voltage sensor according to an eighteenth embodiment of the present invention will be described.
The optical voltage sensor according to the present embodiment has a configuration basically similar to that of the thirteenth embodiment, that is, a configuration as shown in FIG. The same components as those in the thirteenth embodiment among the components in the optical voltage sensor of the present embodiment are denoted by the same reference numerals. Note that the overall operation of the optical voltage sensor of this embodiment is substantially the same as that of the thirteenth embodiment, and a detailed description thereof will be omitted.

  FIG. 26 is a transparent front view showing a specific structure of a main part of the optical voltage sensor of the present reference example. This optical voltage sensor includes a substrate 144, as in the sixteenth embodiment, and a component guide 143 for positioning an optical component constituting a sensor unit of the optical voltage sensor so as to be arranged on a predetermined optical axis 108. And an input-side optical fiber for optically coupling an optical fiber (hereinafter, referred to as an “input-side optical fiber”) 148 a constituting the input-side optical system of the light emitting unit 118 to a predetermined optical component positioned by the component guide 143. An output side for optically coupling a guide 142a and an optical fiber (hereinafter referred to as an “output side optical fiber”) 148b constituting an output side optical system of the light receiving section 119 to a predetermined optical component positioned by the component guide 143. An optical fiber guide 142b is provided on the substrate 144.

In the present reference example, a photonic crystal layer (hereinafter, referred to as a “photonic crystal polarizer”) 171 functioning as a polarizer is formed on one end face of the input side optical fiber 148a. On one end face, a photonic crystal layer 172 functioning as an analyzer (hereinafter referred to as “photonic crystal analyzer”) is formed. The component guide 143 of this embodiment is different from the sixteenth embodiment in that the λ / 4 plate 102, the first conductive reflection film 106, and the LiNbO 2 _{The three-} crystal film 103 and the second conductive reflection film 107 are configured to be in close contact with each other and positioned. Then, the input side optical fiber guide 142 a is configured to optically couple the photonic crystal polarizer 171 formed on the end face of the input side optical fiber 148 a to the λ / 4 plate 102 positioned by the component guide 143. The side optical fiber 148a is guided. The output-side optical fiber guide 142b is configured to optically couple the photonic crystal analyzer 172 formed on the end face of the output-side optical fiber 148b to the second conductive reflective film 107 positioned by the component guide 143. The side optical fiber 148b is guided. In the specific structure of the optical voltage sensor according to the present embodiment, the other points are the same as those of the sixteenth embodiment, and the same components are denoted by the same reference numerals and the description thereof will be omitted. . The formation of the photonic crystal polarizer 171 and the photonic crystal analyzer 172 will be described later.

In the present embodiment as described above, similarly to the sixteenth embodiment, a lens is not required by improving the directivity of light in the sensor section and shortening the optical path length. Photons are formed on the end face of the optical fiber as a photonic crystal layer. For this reason, the number of components of the optical voltage sensor is further reduced, and the cost is further reduced. Forming the polarizer and the analyzer as a photonic crystal layer on the end face of the optical fiber also contributes to shortening the optical path length. In this embodiment, as in the sixteenth embodiment, an etalon resonator is formed in a region surrounding the LiNbO ₃ crystal film 103 in the sensor unit to increase the directivity of the light beam. If the optical path length is sufficiently shortened to eliminate the need for a lens without increasing the performance, it is not necessary to configure an etalon resonator or the like. And 107, a transparent conductive film may be used.

(19th reference example)
Next, an optical voltage sensor according to a nineteenth embodiment of the present invention will be described.
The optical voltage sensor of the present embodiment has basically the same configuration as that of the thirteenth embodiment, that is, the configuration as shown in FIG. The same components as those in the thirteenth embodiment among the components in the optical voltage sensor of this embodiment are denoted by the same reference numerals. Note that the overall operation of the optical voltage sensor of this embodiment is substantially the same as that of the thirteenth embodiment, and a detailed description thereof will be omitted.

  FIG. 27 is a transparent front view showing a specific structure of a main part of the optical voltage sensor of the present reference example. This optical voltage sensor is provided with a substrate 144 similarly to the eighteenth embodiment, and a component guide 143 for positioning an optical component constituting a sensor section of the optical voltage sensor so as to be arranged on a predetermined optical axis 108. And an input-side optical fiber guide 142a for optically coupling the input-side optical fiber 148a constituting the input-side optical system of the light emitting section 118 to a predetermined optical component positioned by the component guide 143; An output optical fiber guide 142b for optically coupling the output optical fiber 148b constituting the output optical system to a predetermined optical component positioned by the component guide 143 is provided on the substrate 144.

  In this embodiment, a photonic crystal polarizer 171 which is a photonic crystal layer functioning as a linear polarizer is formed on one end face of the input side optical fiber 148a, and further functions as a λ / 4 plate. A photonic crystal λ / 4 plate 181 is formed as a photonic crystal layer. That is, a multilayer film of a photonic crystal that functions as a circular polarizer by laminating the photonic crystal polarizer 171 and the photonic crystal λ / 4 plate 181 is formed on one end face of the input-side optical fiber 148a. ing. A photonic crystal analyzer 172, which is a photonic crystal layer functioning as an analyzer, is formed on one end face of the output side optical fiber 148b.

The component guide 143 in this embodiment is different from the eighteenth embodiment in that the first conductive reflective film 106, the LiNbO ₃ crystal film 103 as an electro-optical crystal, and the second conductive It is configured such that the conductive reflective films 107 are positioned in close contact with each other. The input-side optical fiber guide 142a optically couples the photonic crystal λ / 4 plate 181 formed on the end face of the input-side optical fiber 148a to the first conductive reflection film 106 positioned by the component guide 143. As described above, the input side optical fiber 148a is guided. The output-side optical fiber guide 142b is configured to optically couple the photonic crystal analyzer 172 formed on the end face of the output-side optical fiber 148b to the second conductive reflective film 107 positioned by the component guide 143. The side optical fiber 148b is guided.

  In the specific structure of the optical voltage sensor according to the present embodiment, the other points are the same as those of the sixteenth embodiment, and the same components are denoted by the same reference numerals and the description thereof will be omitted. . The formation of the photonic crystal polarizer 171, the photonic crystal λ / 4 plate 181, and the photonic crystal analyzer 172 will be described later.

  As described above, in the present embodiment, similarly to the sixteenth embodiment, a lens is not required by improving the directivity of light in the sensor unit and shortening the optical path length. A linear polarizer and a λ / 4 plate are formed as a photonic crystal layer on the end face of 148a, and an analyzer is formed as a photonic crystal layer on the end face of the output side optical fiber 148b. For this reason, the number of components of the optical voltage sensor is further reduced, and the cost is further reduced. Forming the polarizer, the λ / 4 plate, and the analyzer as a photonic crystal layer on the end face of the optical fiber also contributes to shortening the optical path length.

(20th reference example)
Next, an optical voltage sensor according to a twentieth embodiment of the present invention will be described.
The optical voltage sensor according to the present embodiment has a configuration basically similar to that of the thirteenth embodiment, that is, a configuration as shown in FIG. However, the polarizer 101 and the λ / 4 plate 102 in the thirteenth embodiment are realized as one circular polarizer in this embodiment. The same components as those in the thirteenth embodiment among the components in the optical voltage sensor of this embodiment are denoted by the same reference numerals. Note that the overall operation of the optical voltage sensor of this embodiment is substantially the same as that of the thirteenth embodiment, and a detailed description thereof will be omitted.

  FIG. 28 is a transparent front view showing a specific structure of a main part of the optical voltage sensor of the present reference example. The main part of this optical voltage sensor has substantially the same structure as the main part in the nineteenth embodiment shown in FIG. However, in this embodiment, a photonic crystal layer (hereinafter, referred to as a “photonic crystal circular polarizer”) 191 functioning as a circular polarizer is formed as a single layer on one end face of the input side optical fiber 148a. This is different from the nineteenth embodiment in which a photonic crystal polarizer 171 and a photonic crystal λ / 4 plate 181 are stacked to form a circular polarizer. In the present embodiment, the input-side optical fiber guide 142a is formed by the first conductive reflection film 106 in which the photonic crystal circular polarizer 191 formed on the end face of the input-side optical fiber 148a is positioned by the component guide 143. The input optical fiber 148a is guided so as to be optically coupled to the optical fiber. Since the structure of the present embodiment other than the above points is the same as the structure of the nineteenth embodiment, of the components constituting the main structure of the optical voltage sensor of the nineteenth embodiment, The same portions are denoted by the same reference numerals, and detailed description is omitted. The formation of the photonic crystal circular polarizer 191 and the photonic crystal analyzer 172 is as described above (see FIG. 1).

  As described above, in the present embodiment, as in the nineteenth embodiment, a lens is not required by improving the directivity of light in the sensor unit and shortening the optical path length. A circular polarizer is formed as a photonic crystal layer on the end face of 148a, and an analyzer is formed as a photonic crystal layer on the end face of the output side optical fiber 148b. Therefore, this embodiment has an advantage that the number of components of the optical voltage sensor is reduced and the cost is reduced, as in the nineteenth embodiment. Furthermore, in this embodiment, the photonic crystal polarizer 171 and the photonic crystal λ / 4 plate 181 in the nineteenth embodiment are a single photonic crystal layer functioning as a circular polarizer. Since this embodiment is implemented as the polarizer 191, this embodiment is more advantageous in cost than the nineteenth embodiment.

(Twenty-first reference example)
Next, an optical magnetic field sensor according to a twenty-first embodiment of the present invention will be described.
The optical magnetic field sensor of this embodiment is a λ / 4 plate 102, a first conductive reflection film 106, and a LiNbO ₃ positioned by the component guide 143 in the optical voltage sensor according to the eighteenth embodiment shown in FIG. A magneto-optical crystal film 201 is provided instead of the crystal film 103 and the second conductive reflection film 107. This optical magnetic field sensor is used for applying a magnetic field induced by a current flowing through a transmission line or a distribution line to the magneto-optical crystal film 201 in the X-axis direction (optical axis direction) to measure the magnetic field strength. You. Therefore, electrodes and lead wires for applying an electric field (voltage) to the LiNbO ₃ crystal film 103, which is an electro-optic crystal, are unnecessary. The configuration of the other parts of the optical magnetic field sensor of the present embodiment other than the above is substantially the same as that of the eighteenth embodiment, so that the same components are denoted by the same reference numerals and detailed description thereof will be omitted. In addition, according to such an optical magnetic field sensor, the magnitude of the current can be detected by measuring the intensity of the magnetic field induced by the current flowing in the transmission line, the distribution line, and the like.

  FIG. 29 is a transparent front view showing a specific structure of a main part of the optical magnetic field sensor of the present reference example. This optical magnetic field sensor includes a substrate 144, a component guide 143 for positioning the magneto-optical crystal film 201 so as to be arranged on a predetermined optical axis 108, and an input side constituting an input side optical system of a light emitting unit. The input side optical fiber guide 142a for optically coupling the optical fiber 148a to the magneto-optical crystal film 201 positioned by the component guide 143, and the output side optical fiber 148b constituting the output side optical system of the light receiving unit 119 are parts. An output side optical fiber guide 142b for optically coupling to the magneto-optical crystal film 201 positioned by the guide 143 is provided on the substrate 144.

  In this embodiment, as in the eighteenth embodiment, a photonic crystal polarizer 171 functioning as a linear polarizer is formed on one end face of the input side optical fiber 148a, and one end of the output side optical fiber 148b. A photonic crystal analyzer 172 is formed on an end face of the photonic crystal. Then, the input-side optical fiber guide 142a optically couples the photonic crystal polarizer 171 formed on the end face of the input-side optical fiber 148a to one surface of the magneto-optical crystal film 201 positioned by the component guide 143. As described above, the input side optical fiber 148a is guided. The output side optical fiber guide 142b is configured to optically couple the photonic crystal analyzer 172 formed on the end face of the output side optical fiber 148b to the other surface of the magneto-optical crystal film 201 positioned by the component guide 143. , And the output side optical fiber 148b. As described above, the photonic crystal polarizer 171 and the photonic crystal analyzer 172 optically coupled to the two surfaces of the magneto-optical crystal film 201 are set such that their setting directions are at 45 degrees. . Therefore, the polarization direction of the linearly polarized light after passing through the photonic crystal polarizer 171 and the polarization direction of the linearly polarized light after passing through the photonic crystal analyzer 172 are shifted from each other by 45 degrees.

  In the optical magnetic field sensor configured as described above, the non-polarized light emitted from the light source of the light emitting unit passes through the input side optical fiber 148a and travels toward the magneto-optical crystal film 201, whereupon the input side optical fiber 148a The light passes through the photonic crystal polarizer 171 formed on the end face. Light that has passed through the photonic crystal polarizer 171 becomes linearly polarized light and enters the magneto-optical crystal film 201. When this linearly polarized light passes through the magneto-optical crystal film 201, the polarization direction is an angle corresponding to the intensity of the component of the magnetic field Hm applied to the magneto-optical crystal film 201 in the direction perpendicular to the magneto-optical crystal film 201. Just rotate. The linearly polarized light that has passed through the magneto-optical crystal film 201 passes through a photonic crystal analyzer 172 formed on the end face of the output-side optical fiber 148b, and is transmitted by the output-side optical fiber 148b to the photoelectric conversion element in the light receiving unit, where it is received. And converted into an electric signal. Since the amount of linearly polarized light after passing through the photonic crystal analyzer 172 changes according to the rotation angle of the polarization direction in the magneto-optical crystal film 201, based on the electric signal output from the photoelectric conversion element in the light receiving unit, The intensity of the magnetic field Hm applied to the magneto-optical crystal film 201 can be obtained.

  According to the present embodiment as described above, since the polarizer and the analyzer are formed on the end face of the optical fiber as a photonic crystal layer, the number of components is reduced, and light from the light source in the light emitting unit is input. The optical path length from exiting the side optical fiber 148a to reaching the end face of the output side optical fiber 148b via the polarizer 171, the magneto-optical crystal film 201, and the analyzer 172 is reduced. In this embodiment, a lens is not used by shortening the optical path length, thereby reducing the number of parts. According to this embodiment, the cost can be reduced by reducing the number of components.

(22nd reference example)
Next, an optical voltage sensor according to a twenty-second embodiment of the present invention will be described.
The optical voltage sensor according to the present embodiment is a vertical modulation type optical voltage sensor and has basically the same configuration as the thirteenth embodiment (see FIG. 20). On the other hand, in terms of a specific structure, this optical voltage sensor is similar to the conventional structure shown in FIG. 33, and a right-angle PBS (Polarization Beam Splitter) is used as a polarizer and an analyzer.

  FIG. 30 is a transparent front view showing a specific structure of the optical voltage sensor according to the present reference example. The optical voltage sensor includes a sensor unit, a light emitting unit, a light receiving unit, and a light emitting side and light receiving side signal processing circuit (not shown). The sensor unit includes a right-angled PBS 241 as a polarizer, a λ / 4 plate 242, a first conductive reflection film 106, an electro-optic crystal 243, and a second conductive reflection, which are arranged on the same optical axis in order from the light incident side. It is composed of a membrane 107 and a right-angle PBS 244 as an analyzer. The light-emitting unit includes an input / output circuit including an E / O circuit including a light-emitting element as a light source, an optical fiber 246a, a ferrule 248a, a 0.25-pitch GRIN lens 247a, and a holder 245a arranged on the same optical axis. Each optical component in the input-side optical system has an optical axis surface that is in contact with each other and is bonded with an adhesive. The light receiving unit outputs an output optical system including an optical fiber 246b, a ferrule 248b, a 0.25 pitch GRIN lens 247b, and a holder 245b disposed on the same optical axis, and an optical signal emitted from the output optical system. It is composed of an O / E circuit including a conversion element for converting into an electric signal, and each optical component in the output-side optical system is also bonded by an adhesive on optical axis surfaces that are in contact with each other.

  In the sensor section of the optical voltage sensor, the optical components arranged on the same optical axis, that is, the polarizer 241, the λ / 4 plate 242, the first conductive reflection film 106, the electro-optic crystal 243, and the second conductive reflection The optical axis surfaces of the film 107 and the analyzer 244 that are in contact with each other are all bonded with an adhesive. Further, the first conductive reflection film 106 is connected to one of the pair of electrode terminals 249, and the second conductive reflection film 107 is connected to the other of the pair of electrode terminals 249. The measured voltage Vm of the optical voltage sensor is applied between the pair of electrode terminals 249.

The light emitting side and light receiving side signal processing circuits are connected to the sensor unit by a light emitting unit and a light receiving unit, respectively. The input side optical axis surface of the polarizer 241 of the sensor unit is the optical axis surface of the GRIN lens 247a of the light emitting unit, the output side optical axis surface of the analyzer 244 of the sensor unit is the optical axis surface of the GRIN lens 247b of the light receiving unit, Each is fixed with an adhesive. The sensor unit, the input side optical system in the light emitting unit, and the output side optical system in the light receiving unit are mechanically fixed to a case (not shown). Note that an epoxy-based or urethane-based resin is used as an adhesive for each optical component in the optical voltage sensor. In the optical voltage sensor, Bi ₁₂ SiO ₂₀ (BSO), KH ₂ PO ₄ (KDP), LiNbO ₃ having natural birefringence, and LiTaO ₃ are used as the electro-optic crystal 243.

  By the way, in the above configuration, each optical component in the light emitting section and the light receiving section, and each optical component forming the sensor section are bonded by an adhesive on optical axis surfaces that are in contact with each other, and the light emitting section, the sensor section, and the light receiving section And the sensor unit are also joined by an adhesive on optical axis surfaces that are in contact with each other. However, it is preferable that each optical component forming the sensor unit is configured to be held by a frictional force acting between the respective joining surfaces without using an adhesive. That is, the light-exiting-side optical axis surface of the right-angle PBS that is the polarizer 241 and the incident-side optical-axis surface of the λ / 4 plate 242, the light-exiting-side optical axis surface of the λ / 4 plate 242 and the incident side of the first conductive reflection film 106 The optical axis surface, the emission-side optical axis surface of the first conductive reflection film 106 and the incidence-side optical axis surface of the electro-optic crystal 243, the emission-side optical axis surface of the electro-optic crystal 243, and the incidence side of the second conductive reflection film 107 A λ / 4 wavelength plate is formed through five non-adhesive bonding surfaces of an optical axis surface and an emission optical axis surface of the second conductive reflection film 107 and an incidence optical axis surface of the right angle PBS which is the analyzer 244. 242, the first conductive reflection film 106, the electro-optic crystal 243, and the second conductive reflection film 107 are sandwiched by an appropriate force. The frictional force generated at these five non-adhesive bonding surfaces causes the λ / 4 wavelength plate 242, the first conductive reflection film 106, the electro-optic crystal 243, and the second conductive reflection film 107 to form an input-side optical system. It is fixed and held between the bonded polarizer 241 and the analyzer 244 bonded to the output side optical system. According to such a configuration, the temperature characteristics of the electro-optic crystal are improved by relaxing the stress applied to the electro-optic crystal 243 (see Japanese Patent Application Laid-Open No. 9-145745).

  In the sensor section of the present embodiment, similarly to the thirteenth embodiment, the distance between the first conductive reflecting film 106 and the second conductive reflecting film 107 is an integral multiple of half the wavelength of light incident on the sensor section. The thickness and the like of each optical component constituting the sensor unit are set so that Thus, an etalon resonator is formed in a region surrounding the electro-optic crystal 243 by the first conductive reflection film 106 and the second conductive reflection film 107.

  According to the present embodiment as described above, the etalon resonator is formed in the region surrounding the electro-optic crystal 243 by the first conductive reflection film 106 and the second conductive reflection film 107, and the light beam state is stabilized. Therefore, even if the beam state of the light incident on the sensor unit varies due to the tolerance of the optical components and the like, the temperature characteristics of the output of the optical voltage sensor are stabilized without variation.

  INDUSTRIAL APPLICABILITY The optical device of the present invention has a low manufacturing cost and can contribute to a reduction in the number of components of an optical device, and thus can be used for various optical devices.

FIG. 3 is a perspective view showing a structure of a photonic crystal circular polarizer. FIG. 4 is a diagram illustrating a method for manufacturing a photonic crystal that functions as a polarizer, an analyzer, a circular polarizer, and the like. FIG. 9 is a diagram illustrating another method for manufacturing a photonic crystal that functions as a polarizer, an analyzer, a circular polarizer, and the like. FIG. 4 is a diagram illustrating a photonic band when cylindrical holes are squarely distributed in the core of an optical fiber. FIG. 2 is a schematic diagram illustrating a configuration of an optical device according to a first reference example of the present invention. FIG. 4 is a partial schematic diagram of another example of the optical device according to the first reference example of the present invention. FIG. 9 is a schematic diagram illustrating a configuration of an optical device according to a second reference example of the present invention. FIG. 9 is a schematic side view showing a configuration of an optical device according to a third reference example of the present invention. FIG. 14 is a schematic side view showing a configuration of an optical device according to a fourth reference example of the present invention. FIG. 13 is an overall view of an optical device according to a fifth reference example of the present invention. FIG. 11 is a schematic perspective view of an enlarged view of the functional unit 78 shown in FIG. 10 and viewing the optical fiber 71 from an oblique direction. FIG. 16 is a horizontal sectional view showing the entire optical device according to a sixth reference example of the present invention. FIG. 14 is a schematic diagram illustrating a configuration of an optical device according to a sixth reference example of the present invention. FIG. 14 is a schematic diagram illustrating a configuration of an optical device according to a seventh reference example of the present invention. FIG. 16 is a schematic diagram illustrating a configuration of an optical device according to an eighth reference example of the present invention. FIG. 16 is a schematic diagram illustrating a configuration of an optical device according to a ninth embodiment of the present invention. It is the schematic which showed the structure of the optical device concerning the 10th reference example of this invention. FIG. 27 is a schematic sectional view showing an example of electrode arrangement in an optical device according to an eleventh reference example of the present invention. It is a horizontal sectional view showing the optical device concerning a 12th example of the present invention. It is a mimetic diagram showing composition of an optical voltage sensor concerning a 13th example of the present invention. The output change of the optical voltage sensor due to the temperature characteristic of the quartz λ / 4 plate, the output change of the vertical modulation type optical voltage sensor due to the temperature characteristic of LiNbO ₃ as the electro-optical crystal, and the change of the output of the LiNbO _{3 as} the electro-optical crystal It is a temperature characteristic diagram which shows the output change of the optical voltage sensor of a horizontal modulation system by a temperature characteristic. It is a figure showing the conductive reflective film in the optical voltage sensor concerning the fourteenth example of the present invention. It is a figure which shows the electroconductive reflection film comprised by the multilayer film which the low refractive index layer and the high refractive index layer alternately laminated | stacked in the optical voltage sensor which concerns on the 15th Example of this invention. It is a see-through | perspective front view which shows the principal part structure of the optical voltage sensor which concerns on the 16th Embodiment of this invention. It is a see-through | perspective front view which shows the principal part structure of the optical voltage sensor which concerns on the 17th reference example of this invention. It is a perspective front view which shows the principal part structure of the optical voltage sensor which concerns on the 18th reference example of this invention. It is a perspective front view which shows the principal part structure of the optical voltage sensor which concerns on the nineteenth reference example of this invention. It is a perspective front view which shows the principal part structure of the optical voltage sensor which concerns on the 20th Example of this invention. It is a see-through | perspective front view which shows the principal part structure of the optical magnetic field sensor which concerns on the 21st reference example of this invention. It is a perspective front view which shows the structure of the optical voltage sensor which concerns on the 22nd reference example of this invention. It is the schematic which shows the structure of the optical isolator which is a conventional optical device. FIG. 4 is a schematic diagram illustrating a structure of a conventional Mach-Zehnder modulator. It is a perspective front view which shows the structure of the conventional optical voltage sensor. FIG. 4 is a diagram for explaining the operation principle of the optical voltage sensor. FIG. 9 is a characteristic diagram illustrating a relationship between an output in a conventional optical voltage sensor and an axis shift angle of light incident on an electro-optic crystal.

Explanation of reference numerals

θ Angle between the cylinder and the normal to the electrode surface k Beam direction dr Distance between the first conductive reflection film and the second conductive reflection film Vm Applied voltage (voltage to be measured)
Hm Applied magnetic field (magnetic field to be measured)
DESCRIPTION OF SYMBOLS 1 Optical fiber 2 Optical axis 3 Core 4 Cladding 5 Faraday crystal substitution cylinder 6 Hole 7 1st functional part 8 2nd functional part 9 Electrode 10 Signal source 11 Ground 12 Capillary 13 Optical fiber 14 Ferrule 15 Split sleeve 16 Incident light 17 Outgoing light 18 Cladding-removed part 19 Column 20 Magnetic field 21 Remaining part of clad 22 Optical axis 23 Parallel interface pair 24 Parallel electrode 25 Column electrode 26 Face-to-face electrode 31 First parallel interface pair 32 Second parallel interface pair 35 Method Linear direction 40 Magnetic field 41 Incident optical fiber 42 Exit optical fiber 43 First hole 44 Second hole 45 Core 46 Cladding 47 Faraday element 48 Guide 49 Optical axis 50 Signal source 51 Optical fiber 52 Optical axis 55 Pockels crystal replacement cylinder 56 hole 57 first functional unit 58 second functional unit 59 electrode 60 signal source 61 optical fiber 62 optical axis 63 electrode 64 Pockels crystal-filled cylinder 65 first hole 66 second hole 67 first functional unit 68 second functional unit 69 third functional unit 71 optical fiber 72 Optical axis 73 Incident light 74 Outgoing light 75 Core 76 Cladding 77 Hole 78 Functional part 83 Core 84 Cladding 87 Parallel electrode 88 Curved electrode 91 Cylindrical body 94 Magnetic field 95 Magnet 101 Polarizer 102 λ / 4 plate 103 LiNbO ₃ crystal film (electro-optical crystal)
104 Analyzer 106 First conductive reflective film 107 Second conductive reflective film 108 Optical axis 109 Incident light 110 Outgoing light 115 Beam angle distribution 118 Light emitting unit 119 Light receiving unit 121 First transparent conductive film 122 First reflective film 123 First 2 Transparent conductive film 124 Second reflective film 131 High refractive index layer 132 Low refractive index layer 133 First multilayer film 134 Second multilayer film 141 Electrode (electrode in case of vertical modulation)
142a Input-side optical fiber guide 142b Output-side optical fiber guide 143 Parts guide 148a Input-side optical fiber 148b Output-side optical fiber 148 Optical fiber 151 Applied electrode 152 Electrode (electrode for horizontal modulation)
171 Photonic crystal polarizer 172 Photonic crystal analyzer 181 Photonic crystal λ / 4 plate 191 Photonic crystal circular polarizer 201 Magneto-optical crystal film 210 Two-dimensional photonic crystal 211 Light propagation direction High permeability portion 212 Light propagation direction Low permeability part 213 Right-handed circularly polarized light 214 Left-handed circularly polarized light 215 Non-polarized light incident light 216 Circularly polarized light emission light 221 High refractive index fine particles 222 Low refractive index part 223 Three-dimensional photonic crystal 224 Optical fiber bundle 225 Optical fiber Optical axis 226 Oblique end face 227 Stacking direction 241 PBS polarizer 242 λ / 4 plate 243 LiNbO ₃ crystal 244 PBS analyzer 246a Input optical fiber 246b Output optical fiber 249 Electrode terminal 1010 First optical fiber 1020 Second optical fiber 1030 First lens 104 0 Second lens 1050 Polarizer 1060 Faraday element 1070 Analyzer 1080 Magnetic field 2001 Substrate 2002 Waveguide 2003 Electrode 2004 Signal source 2005 Incident light 2006 Optical fiber 2007 Core 2008 Clad 2009 Lens 2010 Outgoing light 2011 Mach Zehnder) type modulator

Claims (2)

An optical fiber having an end surface inclined with respect to the optical axis,
An optical device comprising: a photonic crystal that is grown directly on the end face in a direction normal to the end face using the inclined end face as a substrate. The optical device according to claim 1, wherein the optical device is formed directly on the end face of the photonic crystal, and is made of a material whose normal line is parallel to the optical axis of the optical fiber.

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