JP2006053407A - Optical element, and optical module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To simplify a structure of an optical element, to heighten its reliability and to downsize it by eliminating its mechanical driving part in switching between optical paths. <P>SOLUTION: In the optical element, a photonic crystal structure 10 in which media with mutually different light refractive indexes are periodically aligned, a line defect waveguide 13 arranged on a part of the periodical alignment in the photonic crystal structure 10, an electro-optic material 14, aligned on first and second output side line defect waveguides 13b, 13c branched from the line defect waveguide 13, of which the optical state is controllable and first and second electrodes 24, 25 to vary optical characteristics of the electro-optic material 14 are provided. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical element or the like used in an optical transmission communication system or the like, and more particularly to an optical element or the like that switches a light path.

  In recent years, the full-scale broadband network era has entered, and the capacity and speed of information transmission have been remarkably advanced. In order to dramatically increase the transmission capacity, optical communication technology capable of large-capacity transmission has been rapidly developed. Until now, communication networks using optical fibers, which have been mainly introduced in backbone transmission systems connecting large cities, have shown momentum to expand to ordinary homes (so-called FTTH (Fiber to the home)) within the next few years. At the same time, the communication capacity is dramatically increasing and is expected to reach several hundred Tb / sec or more.

  In order to organically and functionally manage and operate such separation and integration of information in an optical communication network, an optical switch in a network node is one of the indispensable functions. The performance required for optical switches is low insertion loss, high-speed switching, high extinction ratio, low stroke, wavelength and polarization independence, small size, low power consumption, high reliability, low cost, etc. In the area close to the subscriber system as well as the basic performance, cost reduction becomes an important issue especially in the area of expansion.

In the future, it is considered that the high-speed information communication network infrastructure that can be always connected will increase, and the establishment of a so-called all-optical network using a new communication technology such as optical packet communication is expected. In an all-optical network, signal processing that is performed after converting an optical signal into an electrical signal in a current optical communication system can be performed directly in an optical state, so that a high-speed response in the order of picoseconds to nanoseconds is achieved. It is said that a possible optical switch and an optical wavelength tunable filter are necessary.
As an optical switch used in such an optical communication system, a mechanical (mechanical control type) optical switch using mechanical movement of a prism, a mirror, an optical fiber, etc., a micrometer of about several hundreds μm created by using a semiconductor manufacturing technology. Mirror type optical switch using micro electro mechanical system (MEMS) that mechanically drives a simple mirror, thermal type that deflects light using refractive index change due to thermo-optic effect of optical transmission medium (Thermal control type) optical switches have been proposed.

  As an example of a method of mechanically switching with a conventional optical switch, for example, light input to, for example, two input optical fibers that constitute an input channel, and, for example, two output optical fibers that constitute an output channel In order to output the light as it is or in place, optical path switching mirrors are provided at the four intersections of the input light and the output light, and this optical path switching mirror is moved by the drive mechanism so that it can be taken in and out of the optical path and output. The destination is controlled. In addition, for example, a technique has been proposed in which the angle of two optical path switching mirrors is changed in an analog manner so that it can be input to any of the output destination optical fibers (see, for example, Patent Document 1).

  In addition, as an example of switching by a conventional optical switch in a non-mechanical manner, a switch element is provided between an input-side optical waveguide and an output-side optical waveguide, and the switch element includes a photonic crystal and its switch A technology is disclosed that includes a pair of electrodes formed so as to sandwich a photonic crystal, and controls the voltage applied to the electrodes to turn on and off the transmission of light of a specific wavelength (for example, (See Patent Document 2).

JP 2000-162520 A (pages 3 to 5, FIG. 4) Japanese Patent Laying-Open No. 2003-215646 (pages 4-5, FIG. 1)

  However, as described in Patent Document 1, when switching mechanically, a mirror and a drive element are required, so that the number of elements is large, the structure is complicated, and the size tends to be large. Furthermore, since the optical components are moved and rotated mechanically, it is necessary to strictly control the angle of the optical path switching mirror using a servo mechanism or the like, which complicates the drive mechanism and makes it difficult to reduce the size. In addition, it is difficult to maintain long-term characteristics, and there is a problem in adopting it in an optical communication system that requires long-term reliability. Further, in addition to the mechanical switch, the one using the thermo-optic effect or liquid crystal cannot satisfy the required high speed because the response speed is slow on the order of milliseconds. Furthermore, although the technique of Patent Document 2 can take two states, a state in which light of a specific wavelength can be transmitted and a state in which light of a specific wavelength is blocked, a method for switching paths is not disclosed.

The present invention has been made to solve the technical problems as described above, and the object of the present invention is to simplify the structure by eliminating the mechanical drive part when switching the light path. Another object of the present invention is to provide an optical element that increases the reliability and enables downsizing.
Another object is to provide an optical element with a high response speed.

  For this purpose, an optical element to which the present invention is applied includes a photonic crystal structure in which a second optical medium having a different refractive index is periodically arranged in a first optical medium, A line defect waveguide provided in a part of a periodic arrangement in a photonic crystal structure, a switch waveguide including a constituent medium arranged in connection with the line defect waveguide and capable of controlling an optical state, and the switch Control means for changing the optical characteristics of the constituent medium of the waveguide.

  Here, the constituent medium of this switch waveguide is a substance having an electro-optic effect, and the refractive index can be changed by voltage control by the control means. Further, the constituent medium of the switch waveguide is provided in each of the plurality of waveguides branched in the line defect waveguide, and the control means is a switch waveguide provided in the plurality of branched waveguides. The path of the propagating light can be switched by changing the optical state of any one of the constituent media. Further, the constituent medium of the switch waveguide may be provided at a branch point in addition to the case where it is provided in the whole of the plurality of branched waveguides.

  In addition, the control means changes the optical state of the constituent medium of the switch waveguide, and outputs the light output by propagating through the line defect waveguide to a plurality of output lights provided adjacent to the photonic crystal structure. It can be characterized by outputting to any one of the fibers. The control means can also change the optical state of the constituent medium of the switch waveguide and delay the light that is propagated through the line defect waveguide and output.

On the other hand, when the present invention is regarded as an optical module, the optical module to which the present invention is applied is such that a second optical medium having a different refractive index is periodically arranged in the first optical medium. A line defect waveguide is provided in a part of the optical waveguide, and a switch medium which is a plurality of branched output side line defect waveguides constituting the line defect waveguide is provided with a constituent medium capable of controlling an optical state A crystal structure, an input optical fiber for entering light into a line defect waveguide of this photonic crystal structure, and a plurality of outputs receiving light propagated respectively to a plurality of output side line defect waveguides of the photonic crystal structure Optical characteristics of the constituent medium provided in the optical fiber and the switch waveguide, which is a plurality of output-side line defect waveguides of a photonic crystal structure, in units of a plurality of output-side line defect waveguides, respectively. And a control unit for reduction.
Here, the constituent medium of the switch waveguide provided in each of the plurality of output-side line defect waveguides of this photonic crystal structure is a substance having an electro-optic effect, and the refractive index is changed by voltage control by the control unit. It can be.

  According to the present invention, it is possible to obtain an optical element that simplifies the structure by eliminating the mechanical drive portion when switching the light path, increases the reliability, and enables downsizing.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
[Embodiment 1]
FIG. 1 and FIG. 2 are explanatory diagrams showing the configuration of an optical element by an optical switch using a photonic crystal to which the present embodiment is applied. FIG. 1 shows the overall configuration, and FIG. 2 shows a cross section of the line defect waveguide portion on the emission side. As shown in FIGS. 1 and 2, the optical element to which this exemplary embodiment is applied includes a photonic crystal structure 10, a first electrode 24, and a second electrode 25. 1 and / or 2, an input optical fiber 21 that emits a light beam to the photonic crystal structure 10 and a first output optical fiber that enters the light that has passed through the photonic crystal structure 10 are shown. 22 and a second output optical fiber 23 are shown. The optical switch includes the photonic crystal structure 10, the first electrode 24 and the second electrode 25, and the input optical fiber 21, the first output optical fiber 22, and the second output optical fiber 23. As an optical module that functions as

  The photonic crystal structure 10 includes a structure 11 having a high refractive index, for example, as a first optical medium (material), and a periodic structure 12 having, for example, a low refractive index, as a second optical medium. The periodic structure 12 is periodically arranged in the structure 11 that is the first optical medium. In the present embodiment, cylindrical dielectrics are arranged in a square lattice type as the second optical medium. Here, the region in which the periodic structures 12 are periodically arranged in the first optical medium is a photonic band gap region, and is a region where the input light cannot propagate. In the photonic crystal structure 10 shown in the figure, a region where the second optical medium does not exist is formed linearly in the photonic band gap region. The light input only in this region can propagate, and this is called a line defect waveguide 13. The line defect waveguide 13 is formed in a T-shape as in this example, for example, and is branched on the output side. The line defect waveguide 13 includes an input side line defect waveguide 13a that guides light input from the input fiber 21 and a first output that guides light to the first output optical fiber 22 as a branched output side. The side line defect waveguide 13b and the second output side line defect waveguide 13c for guiding light to the second output optical fiber 23 are included. In the first output-side line defect waveguide 13b and the second output-side line defect waveguide 13c, for example, the electro-optic material 14 is formed in one row by a periodic structure similar to the periodic structure 12. In the present embodiment, the electro-optical material 14 is disposed only in a region where the refractive index is desired to be changed in advance. When a voltage is applied, the electro-optical material 14 has a high refractive index similar to that of the structure 11, for example, and forms a conductive waveguide. In addition, when no voltage is applied, the electro-optical material 14 has a low refractive index similar to that of the periodic structure 12, for example, and forms a photonic band gap region.

  As shown in FIGS. 1 and 2, the optical switch control means includes a pair of electrodes formed vertically so as to sandwich the electro-optic material 14 arranged on the first output-side line defect waveguide 13b. A first electrode 24 and a second electrode 25 composed of a pair of electrodes formed vertically so as to sandwich the electro-optic material 14 arranged on the second output-side line defect waveguide 13c are provided. In addition, a control unit 26 that controls voltage application to the first electrode 24 and the second electrode 25 is provided. Furthermore, a voltage generation source 27 that supplies voltages to the first electrode 24 and the second electrode 25 is provided, and the control unit 26 controls voltage application from the voltage generation source 27 by an input switching signal. Yes. As described above, the optical switch to which this embodiment is applied includes a switch element that switches to the first output-side line defect waveguide 13b and the second output-side line defect waveguide 13c. The state is electrically changed by the control unit 26. The line defect waveguide on the output side is also referred to as a switch waveguide.

  In the photonic crystal structure 10, the light wave has no propagation mode due to the energy structure in the photonic crystal region other than the line defect waveguide 13 in the two-dimensional plane. That is, the energy of incident light is strongly confined in the line defect waveguide 13 because light cannot propagate outside the line defect waveguide 13 in the two-dimensional plane, that is, in the photonic band gap region. Therefore, it is possible to realize a minute waveguide having a size of the submicron which is the size of the grating pitch.

  In the present embodiment, by applying a voltage to one of the first electrode 24 and the second electrode 25 formed on the line defect waveguide 13, the first output side line defect waveguide 13b and the first electrode The refractive index of the electro-optical material 14 of any one of the two output-side line defect waveguides 13c is changed, and the optical path is changed in the direction of the line defect waveguide 13 to which a voltage is applied. For example, when a voltage is applied to the first electrode 24 under the control of the control unit 26, the light emitted from the input optical fiber 21 passes through the first output-side line defect waveguide 13b from the input-side line defect waveguide 13a. Then, the light is guided to the first output optical fiber 22. At this time, the second output side line defect waveguide 13c is turned off. For example, when a voltage is applied to the second electrode 25 under the control of the control unit 26, the light emitted from the input optical fiber 21 is transmitted from the input side line defect waveguide 13 a to the second output side line defect waveguide. The light is guided to the second output optical fiber 23 through 13c. At this time, the first output-side line defect waveguide 13b is turned off. The dotted arrows in the figure indicate two paths through which light is switched and propagated. The first output-side line defect waveguide 13b and the second output-side line defect waveguide 13c are switched between an on state in which light can be transmitted (transmitted) and an off state in which light is blocked by the electric field control of the control unit 26. By switching to each other, the direction of the emitted light can be switched.

As described above, the photonic crystal structure 10 is periodically arranged in the structure 11 as the first optical medium, which is an optical substrate, and the periodic structure 12 having a refractive index different from that of the optical substrate as the optical medium. ing. Here, many optical substrates such as Si, quartz, various oxide substrates including glass, or various organic material substrates can be used, and may be selected according to the application.
In addition, when the optical medium such as the periodic structure 12 is arranged in the optical substrate, in addition to the formation using the semiconductor process technique, a method of arranging the spherical body as the optical medium, etc. This method can be adopted.

Here, in this embodiment, a square lattice type array is used as the photonic liquid crystal, but other two-dimensional photonic crystals such as a two-dimensional triangular lattice and a regular hexagonal lattice, or a diamond structure 3 It is also possible to construct a dimensional photonic crystal as a basic structure.
Further, although voltage application by the first electrode 24 and the second electrode 25 has been described as an example of means for changing the refractive index, it is not limited to this as long as the same effect is obtained.

  FIG. 3 is a view showing a modification of the optical switch shown in FIG. In the example shown in FIG. 3, the electro-optical material 14 is provided only at a switching portion (branch point) that is a part of the line defect waveguide 13 to reduce the range in which the electro-optical material 14 occupies the waveguide. There is a feature in the point. Therefore, in FIG. 3, at the branch point between the input-side line defect waveguide 13a and the first output-side line defect waveguide 13b and at the branch point between the input-side line defect waveguide 13a and the second output-side line defect waveguide 13c. The electro-optic material 14 is provided, and the electro-optic material 14 is not provided in the first output-side line defect waveguide 13b and the second output-side line defect waveguide 13c that are separated from the branch point. In the example shown in FIG. 1, the first electrode 24 covering the entire first output side line defect waveguide 13b, and the second electrode 25 covering the entire second output side line defect waveguide 13c, However, in the example shown in FIG. 3, the first electrode 31 and the second electrode 32 are provided in the portion of the electro-optical material 14 placed at the branch point. The control unit 26 shown in FIG. 2 applies a voltage to the first electrode 31 or the second electrode 32 when switching the waveguide, and controls the electro-optical material 14 on the side that transmits light by electric field control, as described above. The light can be transmitted (transmitted). This makes it possible to easily switch the light path. As described above, in the example shown in FIG. 3, the switch elements include the input-side optical waveguide (input-side line defect waveguide 13a) and the respective output-side waveguides (first output-side line defect waveguide 13b and second waveguide). It is inserted in the propagation path between the output side line defect waveguide 13c). In the example shown in FIG. 3, the electro-optic material 14 does not need to affect the entire waveguide (the first output-side line defect waveguide 13b and the second output-side line defect waveguide 13c), and the electrode also branches. It is excellent in that it is sufficient if it is provided only in the vicinity of the point.

  FIG. 4 is a view showing another modification of the optical switch for switching the output to the output optical fiber. In the example of the photonic crystal structure 10 shown in FIG. 4, three output optical fibers, a first output optical fiber 51, a second output optical fiber 52, and a third output optical fiber 53, are provided. Yes. The line defect waveguide 13 is divided into a first output side line defect waveguide 13d, a second output side line defect waveguide 13e, and a third output defect waveguide 13f in addition to the input side line defect waveguide 13a. Yes. In addition, a first switching waveguide 13g and a second switching waveguide 13h are provided as switching paths. The electro-optic material 14 is used as a switch element used for switching each waveguide, as in the example shown in FIG. Further, in the example shown in FIG. 4, five electrodes for applying an electric field to the electro-optical material 14 are provided as switch elements. The five electrodes include a first electrode 41 that switches between an on state (light transmissive state) and an off state (light blocking state) with respect to the first output side line defect waveguide 13d, and a second output side line. A second electrode 42 that switches an on state or an off state with respect to the defect waveguide 13e and a third electrode 43 that switches an on state or an off state with respect to the third output defect waveguide 13f are provided. In addition, a fourth electrode 44 that switches an on state or an off state of the first switching waveguide 13g and a fifth electrode 45 that switches an on state or an off state of the second switching waveguide 13h are provided.

In the optical element shown in FIG. 4, when the light input from the input optical fiber 21 is output to the first output optical fiber 51, the first electrode is controlled by the control unit 26 shown in FIG. 41, the first output-side line defect waveguide 13d portion is turned on (light transmissive state), and the fourth electrode 44 is used to turn the first switching waveguide 13g off (light blocking state). As a result, the input light propagates through the input-side line defect waveguide 13a and the first output-side line defect waveguide 13d, and is output to the first output optical fiber 51.
When the light input from the input optical fiber 21 is output to the second output optical fiber 52, the first output side line defect waveguide 13d portion is turned off by the first electrode 41, and the fifth The second switching waveguide 13h is turned off by the electrode 45, the first switching waveguide 13g is turned on by the fourth electrode 44, and the second output-side line defect waveguide 13e is turned on by the second electrode 42. Put it in a state. As a result, the input light propagates through the input-side line defect waveguide 13a, the first switching waveguide 13g, and the second output-side line defect waveguide 13e, and is output to the second output optical fiber 52.
Furthermore, when the light input from the input optical fiber 21 is output to the third output optical fiber 53, the first output side line defect waveguide 13d portion is turned off by the first electrode 41, The second output-side line defect waveguide 13e is turned off by the electrode 42, the first switching waveguide 13g is turned on by the fourth electrode 44, and the second switching waveguide 13h is turned on by the fifth electrode 45. In this state, the third output-side line defect waveguide 13 f is turned on by the third electrode 43. As a result, the input light propagates through the input-side line defect waveguide 13a, the first switching waveguide 13g, the second switching waveguide 13h, and the third output-side line defect waveguide 13f. It is output to the output optical fiber 53.

  As described above, according to the present embodiment, it is possible to use as an optical switch by inserting a switch element between an input-side optical waveguide and an output-side optical waveguide. This switch element changes the refractive index by applying a voltage to the element of the electro-optical material 14 disposed in the optical path, and changes the traveling direction of light. At this time, as shown in FIG. 1 and FIG. 3, in addition to the case of switching two outputs, as shown in FIG. 4, a plurality of output side line defect waveguides are provided, and a plurality of switches are switched. It can also be configured. Such a configuration is effective when configuring and controlling a multi-channel optical switch.

[Embodiment 2]
In the first embodiment, an example of an optical switch that switches light paths and emits light to different output optical fibers has been described. In the second embodiment, an optical switch used as a delay circuit by switching light paths will be described.
The same functions as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  FIG. 5 is a diagram showing a photonic crystal structure 10 that changes a light propagation path as a delay circuit. In FIG. 5, an output optical fiber 71 is provided for receiving light output from the input optical fiber 21 and passing through the photonic crystal structure 10. The line defect waveguide 13 through which light propagates in the photonic crystal structure 10 has an input side line defect waveguide 13a, an output side line defect waveguide 13i, a straight waveguide 13j, and a detour waveguide 13k. The straight waveguide 13j and the detour waveguide 13k are provided with an electro-optical material 14 as a switch element, and in order to apply an electric field to the electro-optical material 14, the first structure is sandwiched between the first and second crystal waveguides as shown in FIG. An electrode 61 and a second electrode 62 are disposed.

In the example shown in FIG. 5, when the light is first propagated to the output optical fiber 71 without detouring, the electro-optic material 14 provided in the straight waveguide 13j is controlled by the control unit 26, for example. The electrode 61 is turned on (light transmissive state), and the electro-optic substance 14 provided in the bypass waveguide 13k is turned off (light blocking state) by the second electrode 62. As a result, the light input to the line defect waveguide 13 by the input optical fiber 21 propagates through the input side line defect waveguide 13 a, the straight waveguide 13 j, and the output side line defect waveguide 13 i, and enters the output optical fiber 71. Emitted.
On the other hand, when delaying, the electro-optic material 14 provided in the straight waveguide 13j is turned off by the first electrode 61, and the electro-optic material 14 provided in the detour waveguide 13k is turned on by the second electrode 62. To. The light input to the line defect waveguide 13 by the input optical fiber 21 is diverted from the input side line defect waveguide 13a to the detour waveguide 13k, and emitted to the output optical fiber 71 via the output side line defect waveguide 13i. Is done. As a result, an optical switch using a photonic crystal can be used for the delay circuit.

  FIG. 6 is a diagram showing a modification of the delay circuit shown in FIG. In FIG. 6, as in FIG. 5, the line defect waveguide 13 through which light is propagated includes an input side line defect waveguide 13a, an output side line defect waveguide 13i, a straight waveguide 13j, and a detour waveguide 13k. Yes. However, the arrangement of the electro-optical material 14 as a switch element is different from that in FIG. In the example shown in FIG. 6, the electro-optical material 14 is provided on the IN side and the OUT side that are the branch points of the straight waveguide 13j, and on the IN side and the OUT side that are the branch points of the detour waveguide 13k. The waveguide is composed of the structure 11 alone. In the example shown in FIG. 6, the first electrode 63 is provided so as to apply an electric field to the electro-optical material 14 of the straight waveguide 13j, and the second electrode 63 is applied to apply the electric field to the electro-optical material 14 of the detour waveguide 13k. The electrode 64 is provided.

In the example shown in FIG. 6, when the light is first propagated to the output optical fiber 71 without detouring, the electro-optic material 14 provided in the straight waveguide 13j is controlled by the control unit 26, for example. The electrode 63 is turned on (light transmissive state), and the electro-optic substance 14 provided on the IN side and OUT side of the bypass waveguide 13k is turned off (light blocking state) by the second electrode 64. As a result, the light input to the line defect waveguide 13 by the input optical fiber 21 propagates through the input side line defect waveguide 13 a, the straight waveguide 13 j, and the output side line defect waveguide 13 i, and enters the output optical fiber 71. Emitted.
On the other hand, when delaying, the electro-optic material 14 provided on the IN side and the OUT side of the straight waveguide 13j is turned off by the first electrode 63, and the electro-optic material 14 provided in the detour waveguide 13k is turned on. The second electrode 64 is turned on. The light input to the line defect waveguide 13 by the input optical fiber 21 is diverted from the input side line defect waveguide 13a to the detour waveguide 13k, and emitted to the output optical fiber 71 via the output side line defect waveguide 13i. Is done. As a result, an optical switch using a photonic crystal can be used for the delay circuit. Further, it can be used as a circuit for switching and controlling the phase of propagating light.

As described above in detail, the present embodiment (Embodiment 1 and Embodiment 2) is an optical switch that cuts off or switches a light propagation path, is made of a photonic crystal, and is used as a light propagation path. A switch element that is inserted and cuts off or switches a light propagation path according to a state change, and a control unit that electrically changes a refractive index of a constituent material of the switch element so as to change the state of the switch element. With this configuration, the element can be reduced in size.
In the present embodiment, a multi-channel switching optical switch that can be switched to a plurality of channels with one optical switch is realized, and the multi-channel switch is made compact.

  In general, the photonic crystal has a structure in which a second optical medium having a refractive index n2 is arranged as a periodic structure in a first optical medium having a refractive index n1. This structure forms a region where signal light cannot be propagated. This is called a photonic band gap region (PBG region). This photonic band gap region is a two-dimensional array of structures that are second optical media, for example, in a substrate forming the first optical medium, with an optical long period interval of about one-half of the wavelength of incident light. Arranged in a shape. The structure that is the second optical medium is formed in a cylindrical shape, for example. It is also possible to use a prism or a spherical structure. Further, the periodic structure is not limited to the square lattice as shown in FIG. 1, and various two-dimensional periodic structures or three-dimensional periodic structures such as a triangular lattice, a rectangular lattice, and an orthorhombic lattice can be employed.

  In the photonic band gap region having such a structure, when a region where the second optical medium does not exist (a region where only the first optical medium exists) is formed in a part, for example, a linear shape, the region is formed of signal light. This is an area where propagation is possible. When signal light enters the end of this region, the light selectively propagates through this region. This region is called a line defect waveguide. In the photonic crystal of the present embodiment (Embodiment 1 and Embodiment 2), the photonic band gap region and the line defect waveguide have the same structure as described above. The manufacturing method will be described below.

First, a material to be a first optical medium having a refractive index n1 is used as a substrate. A periodic structure such as a cylindrical hole is formed on the substrate by lithography or etching. A second optical medium having a refractive index n2 is embedded therein. For example, Si or the like can be used for the first optical medium serving as the substrate. It can also be produced using a material such as GaN or GaAs that is transparent at the operating wavelength. For the second optical medium, a dielectric material such as SiO ₂ , Al ₂ O ₃ , Ta ₂ O ₅ , or TiO ₂ can be used. It is also possible to use no material, that is, air as the second optical medium. Alternatively, on the contrary, it is possible to leave the second optical medium in the form of a cylinder, for example, by etching the substrate, and to configure the first optical medium as air. As described above, air, liquid, or vacuum can be used for one of the two optical media having different refractive indexes.

A cylindrical hole formed in the two output-side line defect waveguide portions (switch waveguides) that are switched as output paths has a material whose refractive index changes due to application of an electric field, that is, an electro-optic effect. Filled with a substance having As this substance, for example, KH ₂ PO ₄ : (KDP), BaTiO ₃ , LiNbO ₃ , LiTaO ₃ , BiSiO, GaAs, Pb (Zr, Ti) O ₃ : (PZT), (Pb, La) (Zr, Ti) O ₃ : (PLZT), PbNb ₂ O ₆ , (Sr, Ba) Nb ₂ O ₆ , Ba ₂ NaNb ₅ O ₁₅ , Fe ₂ O ₃ —Bi ₂ O ₃ —PbTiO _3, or the like can be used.
As a method for filling these electro-optical materials into the cylindrical hole portion formed in the Si substrate, a method of filling fine particles of the material into the hole portion and firing it under pressure or normal pressure in an oxygen atmosphere (Solid-phase reaction method). It can also be synthesized by a chemical reaction method using a liquid material such as an alkoxide compound as a starting material.

Next, a specific configuration example will be shown as an example of the present case. Here, an optical switch is configured to enter light having a wavelength of 1.55 μm and switch the output optical path.
First, SiO ₂ having a thickness of about 5 μm was laminated on a Si substrate. Then, a 2 μm thick Si layer was laminated thereon. This is called an SOI (Silicon On Insulator) substrate. The SiO ₂ layer becomes the lower cladding layer and the Si layer becomes the core layer. The photonic crystal was formed by processing the Si layer on the surface of the SOI substrate using a lithography technique and an etching technique. That is, after forming a resist mask patterned into a desired shape on this SOI substrate, the Si layer was etched so that the portion corresponding to the second optical medium was removed by a dry etching apparatus. In this case, a columnar hole having a diameter of 0.3 μm and an arrangement period of 0.4 μm was formed in a square lattice pattern in the Si layer by reactive ion etching. The photonic band gap region was filled with SiO ₂ in cylindrical holes.

Then, lanthanum-doped lead zirconate titanate (PLZT) was used as an electro-optical material. PLZT is obtained by substituting Pb of Pb (Zr, Ti) O _{3 in} the perovskite crystal with La. Generally, it is represented by the following composition formula.
_{(Pb 1-x, La x} ) (Zr y, Ti z) 1-x / 4O 3
It is assumed that the composition of PLZT is expressed using the set of (x, y, z). Among them, a substance having a composition ratio of PLZT (9/65/35) was used here. This material transmits light having a wavelength of about 1.55 μm, which is the signal wavelength used in this embodiment in this composition. This material exhibits a secondary electro-optic effect. The PLZT fine particles having an average diameter of about 5 nm are filled in the holes formed in the switch waveguide, and subjected to a baking process such as 10 hours at 800 ° C. under a pressure of 200 kg / cm ² in an oxygen atmosphere. did.
Thus, 2.5 μm of SiO ₂ was laminated on the entire surface of the substrate on which the PBG region, the line defect waveguide, and the switch waveguide were formed to form a cladding layer.
Then, the respective electrodes were formed of Cu so as to cover the electro-optic material at the lower and upper portions of the respective switch waveguides.

The switching operation was confirmed in the photonic crystal optical switch configured as described above.
As shown schematically in FIG. 1, an optical fiber is connected to the input side line defect waveguide and the two output side line defect waveguides (switch waveguides), and a signal having a wavelength of 1.55 μm is input to the input side linear waveguide. Incident light. In a state where no voltage is applied, the refractive index of the electro-optic material embedded in the switch waveguide has a value close to that of the substrate that is the first optical medium, and thus the propagation of incident light is allowed. The refractive index of the electro-optical material PLZT decreases when a voltage is applied. Therefore, when a voltage is applied to the switch waveguide through the electrode, the switch waveguide enters the PBG state, and the incident light cannot be propagated. In the photonic crystal optical switch of the present embodiment, by applying a voltage of 300 V to one side of the first electrode or the second electrode, a switch operation that allows only propagation to the side to which no voltage is applied is performed. I confirmed that I can do it.
In addition, in an electro-optic material, a material having a first-order electro-optic effect has a hysteresis in a change in electric polarization with respect to an applied voltage. In this embodiment, the switch waveguide is configured using PLZT (8/65/35) which is a substance having this property. In this device, even if the voltage application is stopped after the waveguide is switched by applying a voltage, the selected optical path can be preserved as it is.

In addition, it is possible to design the photonic band gap region of the photonic crystal to an arbitrary wavelength band by appropriately designing the material, period, interval, etc. of each optical medium, and can be used as an optical switch of an arbitrary wavelength. can do. Further, since the shift amount (change amount) of the photonic band gap region of the switch waveguide can be adjusted according to the applied voltage, it can also be used as an optical wavelength variable filter.
In the photonic crystal of the present embodiment, optical fibers are used for both the input side and the output side, but instead, it may be configured with an optical waveguide formed on the same substrate as the photonic crystal. . According to this configuration, the signal input / output path and the photonic crystal can be easily coupled.

  Examples of utilization of the present invention include utilization in optical transmission communication systems, optical elements and optical modules used in optical transmission communication systems.

It is the figure which showed the whole structure of the optical element by the optical switch using the photonic crystal to which this Embodiment is applied. It is the figure which showed the cross section of the line defect waveguide part of the output side of the optical element using the photonic crystal to which this Embodiment is applied. It is the figure which showed the modification of the optical switch shown in FIG. It is the figure which showed the other modification of the optical switch which switches the output to the optical fiber for output. It is the figure which showed the photonic crystal structure which changes the path | route which light propagates as a delay circuit. FIG. 6 is a diagram showing a modification of the delay circuit shown in FIG. 5.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Photonic crystal structure, 11 ... Structure, 12 ... Periodic structure, 13 ... Line defect waveguide, 14 ... Electro-optic substance, 21 ... Input optical fiber, 22 ... 1st output optical fiber, 23 2nd output optical fiber, 24 ... 1st electrode, 25 ... 2nd electrode, 31 ... 1st electrode, 32 ... 2nd electrode, 41 ... 1st electrode, 42 ... 2nd electrode , 43 ... third electrode, 44 ... fourth electrode, 45 ... fifth electrode, 51 ... first output optical fiber, 52 ... second output optical fiber, 53 ... third output light. Fibers 61 ... first electrode 62 ... second electrode 63 ... first electrode 64 ... second electrode 71 ... output optical fiber

Claims (8)

A photonic crystal structure in which a second optical medium having a different refractive index is periodically arranged in the first optical medium;
A line defect waveguide provided in a part of a periodic array in the photonic crystal structure;
A switch waveguide including a constituent medium disposed in connection with the line defect waveguide and capable of controlling an optical state;
An optical element comprising: control means for changing an optical characteristic in the constituent medium of the switch waveguide.   2. The optical element according to claim 1, wherein the constituent medium of the switch waveguide is a substance having an electro-optic effect, and a refractive index is changed by voltage control by the control means. The constituent medium of the switch waveguide is provided in each of a plurality of waveguides branched in the line defect waveguide,
The control means switches a path of light to propagate by changing an optical state of any one of the constituent media of the switch waveguide provided in the plurality of branched waveguides. Item 5. The optical element according to Item 1.   4. The optical element according to claim 3, wherein the constituent medium of the switch waveguide is provided at a branch point of the plurality of branched waveguides.   The control means is configured to change the optical state in the constituent medium of the switch waveguide, and to output light that propagates through the line defect waveguide and is adjacent to the photonic crystal structure. 4. The optical element according to claim 3, wherein the optical element is output to any one of the output optical fibers.   4. The optical element according to claim 3, wherein the control means changes the optical state of the constituent medium of the switch waveguide and delays the light that is propagated through the line defect waveguide and output. . A second optical medium having a different refractive index is periodically arranged in the first optical medium, and a line defect waveguide is provided in a part of the arrangement, and the line defect waveguide is configured. A photonic crystal structure in which a constituent medium capable of controlling an optical state is provided in a switch waveguide that is a plurality of branched output-side line defect waveguides;
An input optical fiber for entering light into the line defect waveguide of the photonic crystal structure;
A plurality of output optical fibers each receiving light propagated to the plurality of output-side line defect waveguides of the photonic crystal structure;
A control unit that changes optical characteristics of the constituent medium provided in the switch waveguide that is the plurality of output-side line defect waveguides of the photonic crystal structure in units of the plurality of output-side line defect waveguides, respectively. Optical module.   The constituent medium of the switch waveguide provided in each of the plurality of output-side line defect waveguides of the photonic crystal structure is a substance having an electro-optic effect, and a refractive index is changed by voltage control by the control unit. The optical module according to claim 7.

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