JP2009139524A - Light deflection method and device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of freely controlling an advancing direction of light by an external field, and to provide a device contributing to an active element such as an optical switch and a light modulator for constituting an optical network system, by executing the method. <P>SOLUTION: The method controls the advancing direction of light by the constitution of the device including an input part for receiving light, an output part for emitting light, a guide member positioned in an optical path between the input part and the output part to guide the light, and a magnetic field applying means for applying a magnetic field onto the guide member. In the method, a substance with a nondiagonal component of a refractive index tensor responding to the magnetic field is used as a raw material of the guide member, the guide member is constituted of an aggregate of small pieces, micro-fine structure is formed by arraying the small pieces in arrangement thereof regularly and periodically with a prescribed interval of about a wavelength of the light received in the input part or less, the guide member is applied with the magnetic field to change a refractive index of the light passed therethrough, and the advancing direction is changed by interference of the light in the micro-fine structure. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for controlling the traveling direction of light and an apparatus for implementing the method.

In the past, in order to deflect light, methods such as a photoacoustic effect, an electro-optic effect, a thermo-optic effect, and a mechanical mirror have been used.
However, the deflection angle of light according to these conventional techniques is as small as about 10 ° except for the mirror, and in principle, it does not reach 90 °. In addition, since the return light returned from the receiver side is the same as the forward path, there is a risk of crosstalk.

In a network system using such light, a switch, filter, multiplexer / demultiplexer,
Various optical devices such as modulators are used, and technological developments for realizing high speed, large capacity, high reliability, miniaturization, cost reduction, etc. are being promoted.

As a breakthrough for miniaturization of optical devices, photonic crystals that can form devices such as prisms and filters with a size of several micrometers are drawing attention.
A photonic crystal is a structure in which a plurality of substances having different refractive indexes are regularly and periodically arranged with a size equal to or smaller than the wavelength of light.

The propagation of light in a photonic crystal has the same basic equation as the conduction of electrons in a semiconductor, and the wave nature is also similar. Similar to the conduction band, valence band, and forbidden band of electrons in a semiconductor, there are wavelength bands and forbidden bands in which propagation of electromagnetic waves is allowed in photonic crystals.
Photonic crystals use light diffraction, scattering, and interference inside the nanostructure,
The period of the structure of the photonic crystal used in the visible light band is about half the wavelength of light, that is, 20
It is extremely fine at around 0 nm.
In the photonic crystal, the light band structure is modulated in the same manner as the electron band structure in a semiconductor or the like according to the arrangement period, shape, refractive index, etc., and a unique band structure is formed. For example, in the vicinity of the Brillouin zone, a light forbidden band called a photonic band gap is formed, and light cannot exist inside the photonic crystal in that frequency band. In addition, the band in the vicinity of the photonic band gap is greatly modulated, and its frequency dispersion plane is greatly different from that of a normal optical crystal.

A photonic crystal is expected as an elemental technology for downsizing a conventional optical device to a size of several microns.
For example, in an optical waveguide type optical switch, it is essential to adjust the deflection angle of light in response to speeding up and multi-channeling. In an optical waveguide type optical switch, attention has been paid to using a photonic crystal in order to obtain a large deflection angle.

A photonic crystal fiber is known as an application product of a two-dimensional periodic photonic crystal.
The nonlinear effect is high, the degree of freedom in design of the dispersion characteristics is high, and the light is not leaked even if it is steeply bent.
Lasers that oscillate in a large area using a group velocity of light at the band edge of a two-dimensional photonic crystal are also being developed.
As a research to apply two-dimensional photonic crystals to optical devices, it is confirmed that resonators and waveguides can be created in the structure to accumulate hundreds of thousands of cycles of light, and the traveling speed can be reduced by about two orders of magnitude from that in vacuum. Application to quantum communication, computation, slow light, and stopping light is expected.

As a 3D photonic crystal optical device, a self-molding process that utilizes the characteristics of bias sputtering has been developed, and is expected to be applied to image sensors, optical disk recording / reproducing elements, measurement systems, and communication devices. Yes.

Conventional techniques related to optical devices using photonic crystals include Patent Documents 1-3.

Japanese Patent Application Laid-Open No. 2005-49705 “Optical Device Using Photonic Crystal and Method for Determining Incidence Angle when Light is Incident to Photonic Crystal” JP 2003-279762 “Optical deflection element” Japanese Patent Application Laid-Open No. 2004-145317 “Optical Deflector, Optical Switch Constructed by Optical Deflector, Optical Scanning Apparatus, and Optical Deflection Method”

However, photonic crystals according to the prior art are mainly passive elements, and it has not been possible to freely change characteristics such as the polarization angle and transmission band of light.

Therefore, the present invention implements a method for freely controlling the traveling direction of light by an external field, and the method,
It is an object of the present invention to provide an apparatus that contributes to active elements such as an optical switch and an optical modulator for configuring an optical network system.

In order to solve the above-described problems, the light deflection apparatus of the present invention has the following configuration.
That is, an element that controls the traveling direction of light, and includes an input unit that receives light, an output unit that emits light, and a guide member that is positioned in an optical path between the input unit and the output unit to guide light And a magnetic field applying means for applying a magnetic field to the induction member, the induction member is composed of a collection of small pieces, and the arrangement of the small pieces is equal to or less than the wavelength of light received by the input unit. It is a structure that is regularly and periodically arranged at intervals, and the material of the guiding member is a substance in which the off-diagonal component of the refractive index tensor responds to a magnetic field.

  Here, when the material of the induction member is a dielectric, it is suitable for application of a magnetic field.

In the unit structure repeated in the periodic structure of the guide member pieces, the interval between any of the guide member pieces constituting the unit structure is d, the angle at which the light is deflected is θ, and the wavelength of the light is λ. When the structure satisfies 2dsinθ = nλ (n is an integer), the deflection is accurate.

  Such an optical deflecting device is usefully used as a component of an optical communication device.

Examples of the optical communication device include a circulator and an optical waveguide type optical switch that have three terminals and guide and circulate a signal input at each terminal to an adjacent terminal.

If the periodic arrangement of the guide member pieces is an arrangement in which dot-like defects are introduced, it can be used to control light emission.

Such devices include single mode light emitting diodes and zero threshold lasers.

The light deflection method of the present invention has the following configuration.
That is, an input unit that receives light, an output unit that emits light, a guide member that guides light in an optical path between the input unit and the output unit, and a magnetic field applying unit that applies a magnetic field to the guide member And a method of controlling the traveling direction of light, using a material whose off-diagonal component of the refractive index tensor responds to a magnetic field as a material of the guiding member, and the guiding member is a collection of small pieces. The fine structure is formed by arranging and arranging the small pieces regularly and regularly at a predetermined interval equal to or less than the wavelength of light received at the input unit, and a magnetic field is applied to the induction member And while changing the refractive index of the light which passes there, the advancing direction is changed by interference of the light in a fine structure, It is characterized by the above-mentioned.

Here, the direction in which the magnetic field is applied to the guiding member may be perpendicular to the light traveling direction, thereby contributing to the efficiency of deflection.

  Moreover, you may make it contribute to the application efficiency of a magnetic field using a dielectric material for the raw material of an induction | guidance | derivation member.

In the unit structure in which the arrangement of the guide member pieces is repeated in the periodic structure, the interval between any of the guide member pieces constituting the unit structure is d, the angle at which the light is deflected is θ, and the wavelength of the light is λ. , It may be set so as to satisfy 2dsinθ = nλ (n is an integer) to contribute to the accuracy of deflection.

Depending on the adjustment of the refractive index or the arrangement of the guide member pieces, the light deflection angle may be controlled to a wide angle up to 360 °, thereby contributing to an increase in the application of deflection.

Even if a point-like defect is introduced into the periodic arrangement of the guiding member pieces, a defect level is formed in the band gap, and light emission can be controlled at the defect level, thereby contributing to diversification of optical devices. Good.

The arrangement of the guide member pieces may be circular orbital, and the light may be cyclotron moved to contribute to the use of a research probe or the like.

  In that case, the Landau level may be determined by the wavelength of light.

The present invention has the following effects by providing the above configuration.
That is, since the small pieces of the inductive member such as a dielectric are arranged like a crystal, the refractive index can be changed by applying a magnetic field, and the traveling direction of light can be controlled. In particular, the traveling direction can be bent at a wide angle, which contributes to application to optical devices for communication.

Hereinafter, embodiments of the present invention will be described based on examples shown in the drawings. The embodiment is not limited to the following examples, and the design can be changed as appropriate using a conventionally known technique such as the above-mentioned patent document without departing from the gist of the present invention.
1 and 2 are schematic diagrams showing light deflection by refractive index distribution.
The refractive index is usually a scalar quantity as shown in FIG. 1 (a) and expressed as grad as shown in FIG. 1 (b). When light is incident here, the light travels against an arrow indicating a refractive index gradient as shown in FIG. When light is incident again from the emission position, it returns to the original incident position as shown in FIG. 1 (d), and the light forward path and return path are the same.

On the other hand, if there is a vector-type refractive index distribution as shown in FIG.
It is expressed as rot. When light is incident here, it proceeds against the arrow indicating the refractive index gradient as shown in FIG. 2C, and when light is incident again from its exit position, the original is obtained as shown in FIG. Thus, the light outgoing path and the return path are different.
If the path of traveling light and return light can be changed, it is useful for suppressing crosstalk in communications.

A means for providing such a refractive index distribution is an external field.
When an external field such as an electric field, a magnetic field, stress, or heat is applied to a substance, its electronic state changes, and a change in refractive index can occur with a change in polarizability. For example, anisotropy of an isotropic liquid or solid appears when an external field is applied, and the main refractive index of an anisotropic material changes when the external field is applied.

The inventor paid attention to the influence of the magnetic field in the external field.
The effect of a magnetic field on light is applied to reading of magnetic recording light represented by a magneto-optical disk, and an optical isolator as a communication device.
A magneto-optic effect is known as an effect on a substance by a magnetic field. This is a phenomenon based on the fact that electron spin is polarized by application of a magnetic field, and orbital motion of electrons becomes asymmetrical in the clockwise and counterclockwise directions.
Also, Faraday effect, cotton mouton effect (forked effect), magnetic car effect,
The Zeeman effect is also known.

The Faraday effect is a difference in the complex refractive index for left and right circularly polarized light with respect to light traveling parallel to the magnetic field. As a result, a phenomenon similar to optical rotation and circular dichroism is observed. The natural optical rotation of a chiral substance means that polarized light rotates depending on the magnetization direction. When light is reflected by the mirror through the medium and returns through the medium again, for natural optical rotation, k
Since the vector is reversed, the rotation direction of the polarized light is canceled, but in Faraday rotation, the rotation angle is doubled and returned.
Therefore, it can be used for an optical isolator or the like for blocking reflected light when laser light is introduced into an optical fiber.

The Cotton Mouton effect involves the presence of linearly polarized light in which the direction of vibration of the electric field is orthogonal to the linearly polarized light parallel to the magnetic field for light traveling perpendicular to the magnetic field. Thereby, birefringence and linear dichroism appear.

In the magnetic Kerr effect, both the Faraday effect and the Cotton Mouton effect are obtained by observing changes in the refractive index due to light transmission, and changes in the refractive index also appear in the reflection coefficient.
That is, it is a phenomenon in which the state of the reflected light changes depending on the magnetic field, and is classified into polar kerr, vertical kerr, and horizontal kerr according to the relationship between the polarization of incident light and reflected light. For example, it is used for reading the direction of magnetization recorded perpendicularly to the disk surface of a magneto-optical disk by the polar Kerr rotation of a semiconductor laser.

3 is a perspective explanatory view showing a state in which a magnetic field is applied to the light guiding member piece, and FIGS.
These are top | planar explanatory drawing which shows the advance of the light in that case.
A magnetic field is applied by a magnet or the like to a dielectric serving as a guiding member that guides light positioned in an optical path between an input unit such as a terminal that receives light to be deflected and an output unit such as a terminal that emits the light. Light is incident in the applied state. The application direction of the magnetic field is preferably perpendicular to the incident light.
As a material of the induction member, any substance such as a dielectric material whose off-diagonal component of the refractive index tensor responds to a magnetic field can be used. As the dielectric, any of a paraelectric, a piezoelectric, a pyroelectric, and a ferroelectric can be used.

When no magnetic field is applied, as shown in FIG. 4, the energy level of electrons remains double degenerate and incident light travels straight without being deflected.
When a magnetic field is applied, as shown in FIG. 5, the degeneracy of the energy level of electrons is solved by the Zeeman effect and a difference occurs in the frequency, and the emitted light is deflected in relation to the radiation lifetime.

FIG. 6 is an explanatory plan view showing the progress of light when the dielectrics are arranged in a line, and FIG. 7 is an explanatory plan view showing the progress of light when the dielectrics are arranged in a grid.
If a dielectric is further arranged in the deflection direction of the emitted light in FIG. 5, the deflection direction can be further changed. In this way, by arranging the dielectrics one after another at the deflection destination, the deflection angle can be set large.
Since light always undergoes deflection perpendicular to the traveling direction, it can be deflected up to 360 ° as shown in FIG.

This wide angle deflection corresponds to the movement of charged particles in a magnetic field, so using similar equipment,
It is possible to perform cyclotron motion by controlling the progress of light by a predetermined arrangement of dielectrics to which a magnetic field is applied. If the motion is quantized and the energy level is discretized, the Landau level is determined by the wavelength of light.

Further, since the time-reversal symmetry is broken in the deflection by the refractive index, as shown in FIG. 2, the incident light and the return light do not return to the original path through different paths.
For this reason, the response light from the receiver side has a different path, and thus has a feature that it is difficult to cross-link.
For example, it can be used for a circulator that sequentially connects a plurality of lines. The circulator is a three-terminal high-frequency component, which is a circuit element that guides and circulates the signal that has entered each terminal next to it. .

FIG. 8 is a schematic diagram showing deflection in a bulk crystal.
Unlike discrete photonic crystals, bulk crystals are a continuum, so light only shifts sideways and does not change direction. Therefore, the present invention that deflects light by applying a magnetic field to a dielectric is different from the Cotton Mouton effect.

In the present invention, the dielectric is only required to have a predetermined lattice arrangement, which is different from a narrowly defined crystal.
Its structure corresponds to a photonic crystal.
FIG. 9 is an explanatory diagram showing an example of the arrangement of dielectrics.
In the illustrated example, four dielectrics are arranged in a square shape. Here, the optical path difference (a√2−a) from two dielectrics adjacent to each other in the plane perpendicular to the light traveling direction to the dielectric adjacent to the downstream side in the light traveling direction is the light wavelength. Set to be an integer multiple and set the dielectric spacing to
A fine structure is formed by regularly and periodically arranging at predetermined intervals equal to or less than the wavelength of light.

FIG. 10 is an explanatory diagram showing an example in which dielectrics are arranged in a triangular lattice shape.
In the illustrated example, three types of deflection are shown. The interval (d) between any of the dielectrics arranged in a triangular lattice shape is
The fine structure may be formed by arranging so as to satisfy 2dsinθ = nλ in the relationship between the angle (θ) of light deflection and the wavelength (λ) of light. Here, n is an integer.

11 and 12 are explanatory views showing an example in which dielectrics are arranged in a square lattice pattern.
In the example of FIG. 11, five types of deflection are shown. In FIG. 12, the incident direction of light is different for the same square lattice array. In either case, the distance (d) between the dielectrics arranged in the form of a square lattice is the relationship between the light deflection angle (θ) and the light wavelength (λ).
A fine structure may be formed by arranging so as to satisfy 2dsinθ = nλ. Here, n is an integer.

As described above, there are various patterns in the unit structure repeated in the periodic structure of the guide member piece and the light deflected by the unit structure, but it is only necessary to satisfy the same conditions as the Bragg conditions in X-ray crystal diffraction.
Therefore, the induction member of the present invention includes triclinic, monoclinic, orthorhombic, hexagonal, trigonal, tetragonal, cubic 7-crystal, simple triclinic, simple monoclinic, bottom monoclinic , Simple oblique, body-centered oblique, face-centered oblique, bottom-centered oblique, simple hexagonal, simple rhombohedral, simple square, body-centered square, simple cube, body-centered cube, face-centered cubic Any of which can be used.

The phenomenon in which the traveling direction changes due to the interference of light inside the fine structure corresponding to the photonic crystal is similar to light diffraction. Diffraction is applied to various applications such as spectroscopic techniques that divide light into wavelengths, devices that select laser oscillation wavelengths, holography, and optical filters. Therefore, various optical functions can be similarly controlled by the element according to the present invention.

The device according to the present invention having the above-described fine structure can produce a structure having a three-dimensional refractive index distribution and a structure having a two-dimensional refractive index distribution, as in the case of a photonic crystal.
In such a structure, the electron wave is subjected to Bragg reflection due to the periodic potential of the nucleus in the semiconductor, and a band gap is formed. Is formed.

Since no light can exist in the band gap, the light can be freely controlled. For example,
Spontaneous emission light can be suppressed by introducing a material that emits light with a wavelength equal to the band gap into the device.
Also, if the periodicity in the device is partially disturbed and a defect level is formed in the band gap, light emission is allowed only at the defect level, so a highly efficient single mode light emitting diode, It can be applied to a zero threshold laser.

According to the present invention, the light traveling direction can be controlled at a wide angle by applying a magnetic field, so that it can be applied to various optical devices such as switches for optical communication, logic gates for optical computers, and light beam control devices for monitors. And industrial value is high.

Schematic diagram showing light deflection by scalar refractive index distribution Schematic diagram showing deflection of light by vector-type refractive index distribution Perspective explanatory view showing a state in which a magnetic field is applied to the light guiding member piece Plane explanatory diagram showing the progression of light when no magnetic field is applied Plane explanatory diagram showing the progression of light when a magnetic field is applied Plane explanatory drawing showing the progression of light when dielectrics are arranged in a line Plane explanatory diagram showing the progression of light when dielectrics are arranged in a grid Schematic showing deflection in bulk crystal Explanatory drawing showing an example of the arrangement of dielectrics Explanatory drawing showing an example in which dielectrics are arranged in a triangular lattice shape Explanatory drawing showing an example in which dielectrics are arranged in a square lattice pattern Explanatory drawing showing an example in which dielectrics are arranged in a square lattice and the incident directions are different

Claims (17)

An element for controlling the traveling direction of light,
An input unit that receives light; an output unit that emits light; a guide member that guides light positioned in an optical path between the input unit and the output unit; and a magnetic field application unit that applies a magnetic field to the guide member Prepared,
The guiding member is composed of a collection of small pieces, and the arrangement of the small pieces is a structure that is regularly and periodically arranged at a predetermined interval equal to or less than the wavelength of light received by the input unit,
The light deflecting device, wherein the material of the guiding member is a substance whose off-diagonal component of the refractive index tensor responds to a magnetic field. The light deflecting device according to claim 1, wherein a material of the guide member is a dielectric. The unit structure repeated in the periodic structure of the guide member pieces is
It is a structure that satisfies 2dsinθ = nλ (n is an integer), where d is the interval between any of the guiding member pieces constituting the unit structure, θ is the angle at which the light is deflected, and λ is the wavelength of the light. The light deflection apparatus according to claim 1 or 2. The deflection apparatus according to claim 1, wherein the deflection apparatus is a component of an optical communication device. Optical communication device
The light deflecting device according to claim 4, wherein the light deflecting device is a circulator that has three terminals and circulates a signal input at each terminal by guiding it to an adjacent terminal. The light deflection apparatus according to claim 4, wherein the optical communication device is an optical waveguide type optical switch. The light deflecting device according to claim 1, wherein the periodic arrangement of the guide member pieces is an arrangement into which point-like defects are introduced. The light deflecting device according to claim 7, wherein the light deflecting device is a component of a single mode light emitting diode. The deflecting device according to claim 7 is a component of a zero threshold laser. An optical deflecting device. An input unit that receives light; an output unit that emits light; a guide member that guides light positioned in an optical path between the input unit and the output unit; and a magnetic field application unit that applies a magnetic field to the guide member With the configuration
A method for controlling the direction of travel of light,
For the material of the induction member, a substance whose off-diagonal component of the refractive index tensor responds to a magnetic field is used.
The guiding member is composed of a collection of small pieces, and the arrangement of the small pieces is regularly and periodically arranged at predetermined intervals equal to or less than the wavelength of light received by the input unit, thereby forming a fine structure. And
A method of deflecting light, comprising: applying a magnetic field to an induction member to change a refractive index of light passing therethrough, and changing a traveling direction thereof by interference of light in a fine structure. The light deflection method according to claim 10, wherein a direction in which a magnetic field is applied to the guide member is perpendicular to a light traveling direction. The light deflection method according to claim 10, wherein a dielectric is used as a material of the guide member. The arrangement of the guide member pieces
The unit structure repeated in the periodic structure is 2d when the interval between any of the guiding member pieces constituting the unit structure is d, the angle at which the light is deflected is θ, and the wavelength of the light is λ.
The light deflection method according to claim 10, wherein it is set so as to satisfy sin θ = nλ (n is an integer). The light deflection method according to claim 10, wherein the deflection angle of the light can be controlled to a wide angle up to 360 ° in accordance with the adjustment of the refractive index or the arrangement of the guide member pieces. The light deflection according to any one of claims 10 to 14, wherein a point-like defect is introduced into the periodic arrangement of the guiding member pieces, a defect level is formed in the band gap, and light emission can be controlled at the defect level. Method. The light deflection method according to any one of claims 10 to 15, wherein the guide member small pieces are arranged in a circular orbit to cause the light to perform cyclotron motion. The light deflection method according to claim 16, wherein the Landau level is determined by a wavelength of light.

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