JP4695916B2 - Optical modulator and spatial light modulator provided with the optical modulator - Google Patents

Description

  The present invention relates to an optical modulator and a spatial light modulator including the optical modulator, and more particularly to an optical modulator capable of controlling the wavelength of light transmitted through a metal thin plate, and the spatial light including the optical modulator. Relates to the modulator.

Conventionally, a specific wavelength that penetrates a metal thin film when the metal thin film is irradiated with light by periodically arranging minute openings and surface shapes (protrusions, depressions, etc.) having a size equivalent to the light wavelength on the metal thin film. It is known that the light intensity increases.
Furthermore, it has also been clarified that the cause of this increase in transmitted light intensity is due to resonance interaction between the light incident on the surface of the metal thin film and the surface plasmon mode excited by the metal thin film. .
Also, by using a material with a variable refractive index on one surface of the metal thin film and changing the refractive index, the transmitted light intensity at a specific wavelength is increased, or the increase in transmitted light intensity at a specific wavelength is suppressed. There have been reports on optical modulators that modulate the intensity of transmitted light.

Patent Document 1 proposes that a plurality of metal thin films as described above are arranged and applied to a display device by independently controlling the refractive index variable material.
Also, compared to the case where the surface of the metal thin film is sandwiched between media having different refractive indexes, the rate of increase in transmitted light intensity of a specific wavelength is greater when sandwiched between media having substantially the same refractive index. Has also been reported. Furthermore, Patent Document 2 proposes that such a phenomenon is used to configure a probe for a near-field optical microscope, an exposure mask, a condensing device, and the like.
US Pat. No. 6,040,936 JP 2001-133618 A

By the way, in the above prior art, the refractive index is changed by arranging a material having a variable refractive index on the surface of the metal thin film having a periodic structure such as periodically arranged microscopic apertures, thereby transmitting the metal thin film. The main focus is on modulating the intensity of light, and the consideration of controlling the transmission wavelength is not sufficient. That is, in the above prior art, the wavelength of the light transmitted through the metal thin film can only obtain a specific wavelength according to the periodic structure formed on the surface of the metal thin film. In order to obtain a desired transmission wavelength, the periodic structure formed on the surface of the metal thin film is changed in accordance with the desired transmission wavelength, for example, by changing the periodic arrangement of periodically arranged microscopic apertures. It will be necessary.
However, in order to change the periodic structure formed on the surface of the metal thin film according to the desired transmission wavelength, the periodic arrangement of the micro openings periodically arranged on the surface of the metal thin film according to each transmission wavelength, etc. It is necessary to start from design to production from the beginning, which leads to an increase in the number of processes and an increase in cost.

  In view of the above problems, the present invention makes it possible to control not only the intensity of light transmitted through a thin metal plate, but also the wavelength of light without changing the periodic structure by the microscopic openings periodically arranged on the thin metal plate. An object of the present invention is to provide an optical modulator and a spatial light modulator provided with the optical modulator.

The present invention, in order to achieve the above object, there is provided an optical modulator which is constructed as follows.
That is, the optical modulator of the present invention is an optical modulator that modulates light,
A metal thin film having periodically arranged microscopic apertures, and a dielectric disposed opposite the metal thin film,
Wherein the metal thin film dielectric and are relatively moved in the opposite direction, anda moving means for Ru is adhered to said metal thin film and the dielectric,
The controller controls the by adhesion or control of the release of the metal thin film and the dielectric to change the dielectric constant of the surrounding of the metal thin film, the wavelength dependence of the transmittance of light passing through the thin metal film of said moving means It is a feature.

  According to the present invention, an optical modulator capable of controlling not only the intensity of light transmitted through the metal thin plate but also the wavelength of the light without changing the periodic structure by the micro openings periodically arranged on the metal thin plate. A spatial light modulator including the light modulator can be realized.

The best mode for carrying out the present invention will be described by the following examples.

[Example 1]
In the first embodiment, the present invention is applied to configure an optical modulator.
FIG. 1 is a schematic diagram illustrating the configuration of the optical modulator of this embodiment. FIG. 1A is an exploded perspective view of a three-layer configuration of a first dielectric, a metal thin film, and a second dielectric in the optical modulator, and FIG. 1B is a diagram showing a cross-sectional configuration of the optical modulator.
FIG. 2 shows a configuration in which a light source is arranged in the optical modulator in this embodiment.
In FIG. 1, 100 is an optical modulator, 101 is a metal thin film, 102 is a first dielectric, 103 is a second dielectric, and 104 is a support member.

The optical modulator 100 includes a metal thin film 101, a first dielectric 102 disposed to face one surface of the metal thin film 101, and a second dielectric disposed to face the other surface of the metal thin film 101. The dielectric 103 and the support member 104 are configured.
As shown in FIG. 1A, the optical modulator 100 includes three layers of a first dielectric, a metal thin film, and a second dielectric. In addition, as shown in FIG. 1B, the support member 104 provides a gap between the first dielectric, the second dielectric, and the metal thin film.
In addition, holes having a diameter d are arranged in the metal thin film 101 as minute openings having a period equal to or less than the wavelength of light that is periodically transmitted with a period P that is approximately the wavelength of the transmitted light. The periodic arrangement at this time may be arranged in a square lattice pattern in the period P or may be arranged in a triangular lattice shape, and the arrangement method is not limited. A space between the metal thin film 101 and the first and second dielectrics is filled with a medium having a certain dielectric constant (dielectric constant of air at this time: εair) such as air.

Next, the operation of the optical modulator of this embodiment will be described.
As shown in FIG. 2, when the illumination light 202 having a broad wavelength is introduced from the light source 201 to the optical modulator 100, the diameter of the holes formed in the metal thin film 101, the period of the arrangement, the dielectric constant of the metal thin film, and The surface plasmon mode corresponding to the dielectric constant around the metal thin film is excited. The light (λ1) having a specific wavelength included in the illumination light 202 corresponding to the surface plasmon mode interacts, and the intensity of the light (λ1) transmitted through the metal thin film is increased.
At this time, the transmittance of the light (λ1) having an increased intensity is greatly different from the transmittance of light of other wavelengths. The state at this time is referred to as “state (1)”, the transmittance is shown in FIG. 3, and the positional relationship between the metal thin film 101, the first dielectric 102 and the second dielectric 103 in the optical modulator is shown in FIG. Shown in

  Next, the metal thin film 101 is moved by using a relative movement means (not shown), and the metal thin film 101 is brought into close contact with the first dielectric 102 substantially (see FIG. 4B). At this time, the dielectric constant ε1 of the first dielectric is larger than that of air. Since the dielectric constant around the metal thin film 101 changes, the surface plasmon mode excited on the metal surface changes, the transmittance of light (λ2) corresponding to the plasmon mode increases, and light with a wavelength of λ2 is unique. Therefore, the metal thin film 101 is transmitted. The state at this time is “state (2)”, the transmittance is shown in FIG. 3, and the contact state between the metal thin film 101 and the first dielectric 102 is shown in FIG.

  Further, the metal thin film 101 adhered in the state (2) is peeled off from the first dielectric 102 using a relative moving means (not shown), and the metal thin film 101 is substantially adhered to the second dielectric 103 (see FIG. (Refer FIG.4 (c)). At this time, the dielectric constant ε2 of the second dielectric is assumed to be larger than the dielectric constant ε1 of the first dielectric. Since the dielectric constant around the metal thin film 101 is changed further from the state (2), the surface plasmon mode excited on the metal surface is changed, and the transmittance of light (λ3) corresponding to the plasmon mode is increased. Then, light having a wavelength of λ2 is transmitted through the metal thin film 101 specifically. The state at this time is referred to as “state (3)”, the transmittance is shown in FIG. 3, and the contact state between the metal thin film 101 and the second dielectric 103 is shown in FIG.

These phenomena can be qualitatively understood from the following equation (cited from Patent Document 1).

Here, λmax is the wavelength at which the transmitted light intensity is maximum, P is the period of the arrangement of holes formed in the metal thin film, εm is the dielectric constant of the metal thin film, and εd is the dielectric constant of the dielectric around the metal thin film. . In the case of the state (1), εd is a dielectric constant of air and is considered to be approximately 1.
Also, i and j are diffraction orders. When the refractive index around the metal thin film 101 changes from 1 to 1.4, the period P = 400 nm, the metal thin film dielectric constant εm = −10.545 + 0.835i, and the minimum order of transmitted light is (i, j) = ( 0, 1), from the above formula, the wavelength at which the transmittance is maximum shifts from about 440 nm to 690 nm toward the long wavelength side. Actually, the above equation can represent a qualitative phenomenon, but various correction terms need to be used for quantitative discussion.
Therefore, an example in which numerical calculation is performed with correction added will be shown. When gold (Au) formed on a quartz substrate was used as the metal thin film and the rectangular opening was a 50 nm × 300 nm rectangular opening, the transmittance through the metal thin film was as shown in the graph of FIG.

FIG. 7 is a diagram showing three types of spectra when a material having a refractive index of 1, 1.33, and 1.375 is present on Au. As can be seen from this figure, when the refractive index of one surface of the metal thin film increases from 1 to 1.33, the peak wavelength at which the transmittance is maximized shifts from 1040 nm to 1260 nm toward the longer wavelength side.
In the case of the configuration used for this calculation, a peak having a large transmittance at a value of 660 nm / index shifted to the long wavelength side. Since the above equation is an equation that can be considered from the surface plasmon wavelength excited at the interface between the metal and the dielectric, the wavelength of the light transmitted through the metal thin film is the above equation for one surface of the metal thin film and the dielectric facing it. And the relationship between the other surface of the metal thin film and the relationship of the above equation for the dielectric facing the metal thin film. However, it has become clear from the calculation results that the transmission wavelength shifts to a long wavelength only by increasing the dielectric constant of the dielectric facing one surface of the metal thin film.

  In the optical modulator of this embodiment described above, there are three states, and in each state, air (state (1)), first dielectric and air (state (2)), second around the metal thin film. And dielectric (air (3)) exist, and the dielectric constants of these three dielectrics have a relationship of εair <ε1 <ε2. The relationship of the wavelength at which the transmittance is increased is λ1 <λ2 <λ3, and the wavelength at which the transmitted light intensity is increased is shifted to the longer wavelength side when the dielectric having a large dielectric constant is around the metal thin film. .

By configuring as described above, an optical modulator capable of dividing the wavelength of transmitted light into three types can be realized.
Further, a spatial light modulator can be realized by two-dimensionally arranging the light modulators and driving each light modulator. In that case, the structure which drives these optical modulators independently can be taken.
Also, the portion filled with air between the first dielectric and the second dielectric described in this embodiment does not need to be air, and depends on the wavelength to be transmitted in the state (1). The material can be selected, and various flowable materials such as vacuum, water, and alcohol may be filled, and the present invention is not limited to air. Any dielectric may be selected as the first and second dielectrics.
In that case, when the dielectric constant of the fluid medium is ε0, the dielectric constant of the first dielectric is ε1, and the dielectric constant of the second dielectric is ε2, these dielectric constants are:
The relation satisfying ε0 <ε1 <ε2.

In this embodiment, the illumination light 202 having a broad wavelength is emitted from the light source 201. However, in the states (1), (2), and (3), the transmittances of the wavelengths λ1, λ2, and λ3 are high. Three types of monochromatic light may be illuminated simultaneously, and the wavelength of the illumination light 202 emitted from the light source 201 is not limited to broad light or the like.
Further, as a metal thin film driving device not shown in the present embodiment, voltage applying means for applying a voltage between the metal thin film 101 and the first dielectric 102 and the second dielectric 103 as shown in FIG. The device driven by the electrostatic force generated in 801 may be used, or as shown in FIG. 9, the metal thin film is bent by pressure using pressure control means 901 that changes the pressure in the space between the dielectric and the metal thin film. In the present invention, any driving method may be used as long as it is a driving method for driving the metal thin film 101 so that the first dielectric 102 and the second dielectric 103 are substantially in close contact with each other. The method is not limited.

[Example 2]
In the second embodiment, the present invention is applied to configure an optical modulator of a different form from the first embodiment.
FIG. 5 is a schematic diagram for explaining the configuration of the optical modulator of this embodiment. In FIG. 5, 301 is a metal thin film, 302 is a metal thin film supporting dielectric, 303 is a dielectric, 304 is a supporting member, and 305 is a light source.

In the optical modulator 300, a metal thin film 301 is formed on a metal thin film supporting dielectric 302, a dielectric 303 is disposed opposite to the metal thin film 301, and the metal thin film 301 and the metal thin film supporting dielectric 302 are supported by a support member 304. Is supported.
It is assumed that, for example, air (εair≈1) is filled between the metal thin film 301 and the dielectric 303. The dielectric constants of the dielectric 303 and the metal thin film supporting dielectric 302 at this time are εa and εb.
Further, the metal thin film 301 and the support member 304 are driven by a metal thin film driving device (not shown), and the metal thin film 301 is in close contact with the dielectric 303 substantially on the entire surface.
As the metal thin film driving device, as shown in the first embodiment, various driving methods such as driving by electrostatic force and driving by pressure control can be mentioned, but the present invention is limited to such driving method. is not.

In the metal thin film 301, as in the first embodiment, holes having a diameter d are arranged as minute openings having a period equal to or less than the wavelength of light that is periodically transmitted with a period P approximately equal to the wavelength of the transmitted light. Examples of the proper arrangement include a square lattice shape and a triangular lattice shape, but the present invention is not limited to such a lattice type.
When light having a broad wavelength is irradiated from the side of the metal thin film 301 / metal thin film supporting dielectric 302, the dielectric constant of the metal thin film 301, the dielectric constant of the metal thin film supporting dielectric 302, and the period P of the minute aperture are obtained. The corresponding wavelength light (λa) is specifically transmitted through the metal thin film. This state is referred to as “state A”.

Next, the metal thin film 301 / metal thin film supporting dielectric 302 is driven using a metal thin film drive device (not shown) as shown in FIG. 6 so that the entire surface of the metal thin film 301 is in close contact with the dielectric 303. As a result, the dielectric constant on the surface of the metal thin film 301 changes from εair to εa, so that the wavelength of light transmitted through the metal thin film 301 changes. Alternatively, as described in Patent Document 2, by setting εa = εb, the transmitted light intensity at a specific wavelength is further increased. This state is referred to as “state B”.
Further, by peeling the metal thin film 301 / metal thin film supporting dielectric 302 from the dielectric 303 using the metal thin film driving device and returning to the “state A”, the wavelength and intensity of the light transmitted through the metal thin film 301 are also “ It can return to state A ”.

  In this way, by driving the metal thin film 301 and controlling the adhesion and peeling between the metal thin film 301 and the dielectric 303, the wavelength and intensity of the light transmitted through the optical modulator 300 can be changed. Furthermore, a spatial light modulator can be realized by two-dimensionally arranging this optical modulator and driving each optical modulator.

BRIEF DESCRIPTION OF THE DRAWINGS It is the schematic explaining the structure of the optical modulator in Example 1 of this invention, (a) is a disassembled perspective view of the 3 layer structure by the 1st dielectric material in the optical modulator, a metal thin film, and the 2nd dielectric material, FIG. 4B is a diagram illustrating a cross-sectional configuration of the optical modulator. Schematic which shows the structure of the optical modulator and light source in Example 1 of this invention. The schematic diagram of the spectrum of the transmitted light modulated by the optical modulator in Example 1 of this invention. FIG. 3 is an explanatory diagram of a state during operation of the optical modulator according to the first embodiment of the present invention. FIG. 5 is a schematic diagram of a configuration of an optical modulator according to a second embodiment of the present invention. Explanatory drawing at the time of operation | movement of the optical modulator in Example 2 of this invention. The figure which shows the calculation result explaining the principle of this invention. The figure which shows the structural example by the electrostatic force used for the operation means of the optical modulator in the Example of this invention. The figure which shows the structural example by the pressure control used for the operation means of the optical modulator in the Example of this invention.

Explanation of symbols

100: light modulator 101: metal thin film 102: first dielectric 103: second dielectric 104: support member 201: light source 202: illumination light

Claims (8)

An optical modulator for modulating light,
A metal thin film having periodically arranged microscopic apertures, and a dielectric disposed opposite the metal thin film,
Moving the metal thin film and the dielectric relative to each other in a facing direction, and bringing the metal thin film and the dielectric into close contact with each other;
The wavelength dependence of the transmittance of the light transmitted through the metal thin film is controlled by changing the dielectric constant around the metal thin film by controlling the adhesion or peeling between the metal thin film and the dielectric by the moving means. Characteristic light modulator.   The dielectric disposed opposite the metal thin film includes a first dielectric disposed opposite the surface of the metal thin film and a second dielectric disposed opposite the back surface of the metal thin film. The optical modulator according to claim 1, comprising: A flowable medium is filled between the metal thin film and the first dielectric and the second dielectric. The dielectric constant of the medium is ε0, and the dielectric constant of the first dielectric is ε1. The optical modulator according to claim 2, wherein when the dielectric constant of the second dielectric is ε2, these dielectric constants satisfy the relationship of the following equation.
ε0 <ε1 <ε2 The metal thin film is deposited on the metal thin supporting dielectric having equal dielectric constant to the dielectric constant of the dielectric which is disposed opposite to the metal thin film, and the metal thin film by the moving means and the dielectric 2. The optical modulator according to claim 1, wherein a wavelength and intensity of light transmitted through the metal thin film are changed by changing a dielectric constant around the metal thin film by controlling adhesion or peeling of the metal thin film .   The optical modulator according to claim 1, wherein the moving unit is a driving unit using electrostatic force.   The optical modulator according to claim 1, wherein the moving unit is a driving unit using pressure.   A spatial light modulator comprising a plurality of the optical modulators according to any one of claims 1 to 6 and two-dimensionally arranging these optical modulators.   The spatial light modulator according to claim 7, wherein the spatial light modulator is configured such that each of the two-dimensionally arranged light modulators can be driven independently.

Images