JP2007322902A - Light processing element - Google Patents

Abstract

An optical processing element made of a novel inorganic material having a high light transmittance, a sufficient phase difference, and a high degree of freedom in design is provided.
An optical processing element has a configuration similar to that obtained by superposing optically flat substrates. On each substrate 2, 3, a pattern is formed by a minute or fine metal structure 4. The incident-side substrate 2 has a function of a polarization separation processing region as a unit processing region that selectively allows light to pass therethrough, and the emission-side substrate 3 serves as a unit processing region that selectively changes the polarization state of light. The function of the polarization rotation processing region.
[Selection] Figure 1

Description

  The present invention relates to an optical processing element that can be used for a display device, an image projection device, optical measurement, and the like.

A polarization control element such as a polarizing plate or a wave plate allows the transmission and transmission of one component of the polarization direction of incident light by providing anisotropy in propagation characteristics and absorption characteristics in two orthogonal directions. It is an element that modulates and polarizes the polarization state from linearly polarized light to circularly polarized light.
Such elements are used, for example, to turn on and off pixels of liquid crystal panels and organic EL displays, as well as various optical instruments and measuring instruments such as optical measurement techniques such as ellipsometry, laser interferometers, and optical shutters. Has been used.
In particular, there is an increasing demand for image projection devices such as liquid crystal projectors.

The polarizing plate is an element that converts natural polarized light into linearly polarized light, and transmits only one of the orthogonal polarized components of incident light and shields the other by absorption (or reflection / scattering).
Many of the polarizing plates currently used for liquid crystal panels are absorbing dichroism by dyeing and adsorbing dichroic materials such as iodine and organic dyes on a substrate film such as polyvinyl alcohol, and highly stretching and orienting them. To be expressed.
On the other hand, a retardation plate (or phase shifter) such as a half-wave plate or a quarter-wave plate is made of a birefringent optical crystal and changes its polarization state due to the difference in refractive index between ordinary and extraordinary rays. Modulate.
A half-wave plate is a half-wave plate in which the optical path difference between the ordinary ray and the extraordinary ray is ½ of a wavelength, and a quarter-wave plate is a quarter. As such a material showing birefringence, calcite or quartz is used.

A polarization control element using absorption is easily affected by heat, and has problems such as a decrease in transparency and scorching, and the amount of irradiation light cannot be increased. In addition, the operating temperature conditions are strict, and when used in a liquid crystal projector or the like, there is a problem that a cold air mechanism is necessary, making it difficult to reduce the size of the apparatus, and causing image quality defects due to dust adhesion.
In addition, in the polarization control element utilizing the anisotropy of the refractive index, the optical crystal material exhibiting birefringence is limited, and there is a problem that the usable wavelength range is limited.
In addition, since the film thickness, that is, the optical path difference is adjusted by bonding the optical crystal material and the polarization state is controlled, the dependence on the optical crystal material is strong and the degree of freedom of polarization controllability is low. In addition, there is a problem that it is difficult to reduce the size and thickness of the polarization control element itself.

In response to such a problem, a wire grid polarizer in which fine wires of gold or aluminum are formed on a transparent substrate has been proposed as a polarization control element that is excellent in mass productivity and can be manufactured at low cost and has excellent heat resistance. This polarizing element has been put to practical use as a polarizing element that functions with respect to light having a wavelength longer than 2.5 μm.
On the other hand, a wire grid structure that can be driven at a visible wavelength (400 to 700 nm) as shown in Patent Document 1 has been proposed due to recent advances in microfabrication technology.

In addition, as a method for realizing a wave plate or phase plate for controlling the polarization state by the interaction of light on a two-dimensional surface, a minute metal pattern is formed on a support substrate as shown in Non-Patent Documents 1 and 2. There are proposals for controlling the polarization state.
In Non-Patent Document 1, an electron beam lithography technique is used to produce asymmetric nano-particles having a gold L-shaped structure on a substrate with a pitch equal to or less than a wavelength, and light is transmitted to such a structure to transmit transmitted light. Shows a different absorption spectrum depending on the direction of the polarization plane of incident light, thereby realizing a polarization selection element.
In Non-Patent Document 2, a smooth Si substrate has a saddle type or C type or a mirror-symmetric metal pattern thereof, and has a chirality in which the end of the pattern is inclined from a right angle. There has been proposed an optical element in which a phase difference occurs in two components of the polarization direction depending on the magnitude of the inclination, and a difference between clockwise and counterclockwise polarization depends on the direction of the pattern edge.

Special table 2003-502708 gazette JP-A-10-153706 Brian Canfield, et. alOptics Express, 12, 5418-5423 (2004) “Linear and Nonlinear Optical Responses Influential Broken Symmetry in an Array of Gold Nanoparts”. Application Number: PCT / GB02 / 05872 “OPTICAL DEVICE”

  In view of the situation as described above, the present invention provides a light processing element made of a novel inorganic material that has a high light transmittance, can provide a sufficient phase difference, and has a high degree of design freedom. For that purpose.

  In order to achieve the above object, according to the first aspect of the present invention, a plurality of minute metal structures having a size D (D <λ) with respect to the wavelength λ of light to be processed are provided at intervals d (<D ) Are arranged in a predetermined arrangement to form a unit arrangement pattern, and a plurality of unit processing regions in which the unit arrangement pattern is two-dimensionally arranged are formed on the optical substrate.

According to a second aspect of the present invention, in the optical processing element according to the first aspect, a unit processing region that selectively transmits light having a wavelength λ and a unit process that selectively changes the polarization state of the light having a wavelength λ. And a region.
According to a third aspect of the present invention, in the optical processing element according to the first aspect, a unit processing region that selectively transmits light of wavelength λ and a unit processing that selectively changes the polarization state of light of wavelength λ. It has the area | region and the unit processing area | region which reflects light, It is characterized by the above-mentioned.

According to a fourth aspect of the present invention, in the optical processing element according to any one of the first to third aspects, the shape of the minute metal structure is a hemispherical shape, a cylindrical shape, a semi-rotating ellipsoidal shape, an elliptical columnar shape. It is any one of a polygonal column shape and a cone shape.
According to a fifth aspect of the present invention, in the optical processing element according to any one of the first to fourth aspects, the minute metal structure is made of gold (Au), silver (Ag), aluminum (Al), platinum ( Pt), nickel (Ni), chromium (Cr), copper (Cu), a combination thereof, or an alloy thereof.

In the invention according to claim 6, in the optical processing element according to any one of claims 1 to 5, the arrangement of the minute metal structures in the unit arrangement pattern is an adjacent arrangement of two metal structures, Or any of V-shaped arrangement or L-shaped arrangement with three or more metal structures, T-shaped arrangement with four or more metal structures, or a cross-shaped arrangement with five or more metal structures It is characterized by.
According to a seventh aspect of the present invention, in the light processing element according to any one of the first to sixth aspects, the light processing element includes a polarizer that is disposed on the light incident side and allows only linearly polarized light to pass therethrough. .
According to an eighth aspect of the present invention, in the optical processing element according to the seventh aspect, the polarizer is a wire grid type.

According to the present invention, light having an arbitrary polarization direction can be selected with high efficiency, and an optical processing element with a high degree of design freedom can be realized.
Also, it is possible to efficiently use the near-field light interaction between the fine structures, and to realize an optical processing element with a high degree of design freedom that can select light having an arbitrary polarization direction with high efficiency. Can do.
Moreover, it is possible to separate incident polarized light with a higher SN ratio, and it is possible to realize an optical processing element with a high degree of design freedom that can select light having an arbitrary polarization direction with high efficiency.

A first embodiment of the present invention will be described below with reference to FIGS.
As shown in FIG. 1, an optical processing element 1 as an inorganic polarizing optical element according to this embodiment has a configuration in which substrates 2 and 3 as optically flat regions or layers are stacked or stacked. Have. On each substrate 2, 3, a pattern is formed by a minute or minute metal structure (hereinafter referred to as “minute metal structure”) 4.
The incident-side substrate 2 has a function of a polarization separation processing region as a unit processing region that selectively allows light to pass therethrough, and the emission-side substrate 3 serves as a unit processing region that selectively changes the polarization state of light. The function of the polarization rotation processing region.

When light is irradiated onto a substrate on which such a metal microstructure pattern is formed, if the minute metal structure exists asymmetrically with respect to the incident polarized light, the resonance frequency of the localized surface plasmon generated in each metal structure is increased. Depending on the near-field interaction that occurs between the minute metal structures, a phase difference occurs between the minute metal structures.
Therefore, a phase difference is also generated in the polarization component of the reflected light or transmitted light on which the light from each minute metal structure is superimposed, and the polarization state in the emitted light can be converted as shown in FIG. Here, an example in which linearly polarized light 5 is converted into elliptically polarized light 6 is shown.

Further, one polarization component can be extracted by utilizing the polarization selectivity due to the resonance effect of dots. Further, the phase and amplitude of the emitted light can be adjusted by adjusting the interval between the dots.
Here, by forming a metal microstructure having a function of separating polarized light on the incident light side (substrate 2) and forming a polarization rotation processing region on the lower side (substrate 3), only a polarized light component in an arbitrary direction is formed. Can be obtained.
By changing the interval between dots formed in the polarization rotation processing region, it is possible to obtain outgoing light having a desired polarization state.
The vertical relationship between the polarization separation functional region (polarization separation processing region) and the polarization rotation processing region may be formed such that the polarization rotation processing region is on the upper side and the polarization separation functional region is on the lower side. In this case, light enters from the substrate 3 side.

Next, the principle that the polarization state of the light incident on the metal composite structure (micro metal structure group) manufactured by such a method changes depending on the structure will be described based on the numerical calculation results.
For the numerical calculation, a finite time domain difference method (FDTD method) is used, which solves the Maxwell equation describing the motion of the electromagnetic field by approximating it to a space-time difference equation. FIG. 3 shows a model used for numerical calculation. Reflection when the distance d between adjacent ends of two Au spheres having a size (diameter) of 40 nm existing in air is changed from 0 to 80 nm. The change of the polarization state in the far field is examined.
As the optical constant of Au, refractive index n = 0.072 and k = 1.497 were used. This value is a value that takes into account the change in the optical constant depending on the size of the metal sphere when the metal sphere is reduced to about 50 nm or less.

In order to obtain the characteristics of far-field light from the electric field distribution in the vicinity of the metal composite structure (Au sphere group) obtained by the FDTD method, a component at an angle θ = 0 ° is extracted by Fourier transformation of the electric field distribution, and shown in FIG. The amplitude ratio and phase difference between the x direction and the y direction were calculated. Calculation was performed using a wavelength of 544 nm, which is near the plasmon resonance wavelength of an Au microsphere of 40 nm, and irradiating a plane wave having an electric field oscillation direction in the direction of 45 ° from the x axis in the xy plane shown in FIG.
FIG. 4 shows the relationship with the amplitude ratio. In the region where d is large, the amplitude ratio approaches 1 and it can be seen that the polarization plane (the vibration direction of the electric field) matches the polarization direction of the incident light. On the other hand, the amplitude ratio increases as it approaches d = 0, that is, the polarization plane tilts in the y direction.
On the other hand, FIG. 5 shows the relationship between the x component of the electric field and the phase difference of the y component. As d approaches zero, the phase difference increases, and when d = 0, the phase difference is about 45 °.

From the simulation results by the FDTD method described above, the polarization plane can be rotated by controlling the interval between Au microspheres (micro metal structures), and the polarization state is converted from linearly polarized light to elliptically polarized light, for example. can do.
FIG. 6 shows the polarization states of incident light and outgoing light. Linearly polarized light incident in the 45 degree direction is converted into circularly polarized light. A similar calculation result is obtained when Ag microspheres are used as the metal material. In this case, the wavelength region in which the polarization state changes is near the wavelength of 400 nm, which is near the plasmon resonance wavelength of the Ag microspheres. .

FIG. 7 shows the results of calculation regarding the relationship between the electric field intensity inside the metal sphere and the resonance wavelength when the diameter of the minute metal structure 4 is changed from 10 nm to 50 nm.
The resonance wavelength in the case of a diameter of 10 nm indicated by a is near 420 nm. However, when the diameter of the fine metal structure is set to 50 nm indicated by e, the resonance wavelength is shifted to the vicinity of 450 nm and the long wavelength side. .
That is, by changing the size of the minute metal structure, the resonance wavelength can be selected, and the action of rotating the polarization plane can be exerted only on the specific incident wavelength.

Here, as shown in FIG. 8, a plurality (two in this case) of fine metal structures 4 having a size D (D <λ) with respect to the wavelength λ of light to be processed, and an interval d (<D). A unit arrangement pattern P is arranged in a predetermined arrangement with a space therebetween, and the unit processing region S in which the unit arrangement pattern p is two-dimensionally arranged is formed on the optical substrate (2, 3), for example, Y When linearly polarized light inclined by 45 degrees with respect to the axial direction is incident, the light transmitted through the substrate becomes elliptically polarized light.
In the present embodiment, the cross-sectional shape of the metal particles (micro metal structure 4) is circular, but other shapes such as an elliptical structure or a polygonal structure may be used. Moreover, the structure which arrange | positions circular structure continuously and forms pseudo-elliptical structure may be sufficient. Such a structure can be manufactured by using a microfabrication technique such as electron beam lithography, DUV / EUV lithography, nanoimprint, and etching utilizing alteration of material properties.
The shape of each minute metal structure 4 need not be particularly limited to the above structure, and may be any one of a hemispherical shape, a cylindrical shape, a semi-rotating ellipsoidal shape, an elliptical columnar shape, a polygonal columnar shape, and a pyramidal shape. It is easy to produce a cylindrical shape or a hemispherical shape.

In FIG. 8, the size (diameter) of the minute metal structure 4 is R (= D), the center distance between the minute metal structure closest to the x direction is d, and the pattern of two adjacent minute metal structures is shown. When PA is the pattern of the fine metal structure most adjacent to PA in the x direction and PB, the distance between PA and PB is d1, and the fine structure adjacent to the y direction is PC. Let the distance between PCs be d2.
At this time, it is desirable that R, d1, and d2 are sufficiently smaller than the wavelength of the incident light. Further, in order to use the near-field interaction generated between the adjacent minute metal structures, it is necessary that at least d <D, and d1 and d2 reduce the influence of the interaction between the patterns of the adjacent minute metal structures. Therefore, it needs to be larger than D.

As shown in FIG. 9, a pattern arranged in a V shape may be formed by a combination of three or a plurality (three or more) of fine metal structures 4.
Further, as shown in FIG. 10, a pattern arranged in an L shape may be formed by combining three or plural (three or more) micro metal structures 4.
Similar to the pattern shown in FIG. 8, the distance between adjacent minute metal structures is sufficiently smaller than the size of the minute metal structure, and the distance between L-shaped or V-shaped patterns is larger than the size of the minute metal structure constituting the same. Is preferably sufficiently large.
Also at this time, the incident light is polarized at an angle that has an asymmetric polarization component with respect to the formed fine metal structure, so that a phase difference of transmitted or reflected light occurs.

As shown in FIG. 11, a pattern arranged in a T shape may be formed by a combination of four or a plurality of (four or more) fine metal structures. Similar to the pattern shown in FIG. 8, the distance between adjacent minute metal structures is sufficiently smaller than the size of the minute metal structure, and the distance between T-shaped patterns is larger than the size of the minute metal structure constituting the same. A sufficiently large size is preferable.
Also at this time, the incident light is polarized at an angle that has an asymmetric polarization component with respect to the formed fine metal structure, so that a phase difference of transmitted or reflected light occurs.
A pattern arranged in a T-shape may be arranged in each divided area, and the size of the minimum constituent structure (pattern) of each minute metal structure in each area may be different in each area. Here, as in the configuration shown in FIG. 8, the distance between adjacent minute metal structures is sufficiently smaller than the size of the minute metal structures, and the distance between the T-shaped patterns is larger than the size of the minute metal structures constituting the structure. Is preferably sufficiently large.
Also at this time, the incident light is polarized at an angle that has an asymmetric polarization component with respect to the formed fine metal structure, so that a phase difference of transmitted or reflected light occurs.

As shown in FIG. 12, a pattern arranged in a cross shape or a cross shape by combining five or plural (five or more) minute metal structures is arranged in each divided region, and each minute in each region. A structure in which the size of the minimum structure of the metal structure is different in each region may be used.
In this case, the same structure as that shown in FIG. Here, as in the configuration shown in FIG. 8, the distance between adjacent minute metal structures is sufficiently smaller than the size of the minute metal structures, and the distance between the cross-shaped or cross-shaped patterns constitutes the minute metal structures. It is preferable that it is sufficiently larger than the size of.
Also at this time, the incident light is polarized at an angle that has an asymmetric polarization component with respect to the formed fine metal structure, so that a phase difference of transmitted or reflected light occurs.

The above-described light processing element can be realized as follows. First, an optical glass substrate is used as an inorganic material, and a metal material such as gold, silver, or aluminum is formed on the flat surface by a film deposition method using chemical vapor deposition such as CVD or physical vapor deposition, or a deposition method such as plating. To form.
A photoresist layer is formed on the metal film, and a resist pattern is formed on the photoresist layer so as to leave a pattern corresponding to a desired fine structure by a technique such as electron beam drawing or X-ray drawing. Thereafter, an unnecessary portion of the metal film is etched by, for example, RIE, so that a desired fine structure metal pattern (micro metal structure pattern) can be formed.

Moreover, optical glass is used as a substrate as an inorganic material, a photoresist layer is formed on the flat surface, and a pattern other than a pattern corresponding to a desired fine structure is formed on the photoresist layer by a technique such as electron beam drawing or X-ray drawing. A resist pattern is formed so as to leave.
Thereafter, a metal material such as gold, silver, and aluminum is formed in a thin film shape on the resist pattern by a chemical vapor deposition method such as CVD, a film formation method using physical vapor deposition, or a deposition method such as plating. Thereafter, by removing the resist film and removing the unnecessary portion of the metal film formed on the resist film, a desired microstructure metal pattern can be formed.
For the substrate as the inorganic material, quartz glass, borosilicate glass such as BK7 and Pyrex (registered trademark), optical crystal material such as CaF ₂ , Si, ZnSe, and Al ₂ O ₃ can be used.

After forming a fine metal structure pattern having a polarization conversion processing function on the substrate, quartz glass, borosilicate glass such as BK7 and Pyrex (registered trademark), optical crystal such as CaF ₂ , Si, ZnSe, Al ₂ O ₃ After forming the material by sputtering or the like, the surface can be polished by CMP (Chemical Mechanical Polishing), and the fine metal pattern having the polarization separation function can be formed again to form a light processing element. .
CMP is a technique for polishing and planarizing a wafer using a polishing slurry (abrasive) and a polishing pad. In a CMP apparatus, the surface of a semiconductor substrate to be polished can be pressed downward against a polishing pad and planarized using a chemical action and a mechanical action while rotating both.
In addition, the polarization direction of the incident light is incident so as to have an asymmetric polarization component with respect to the formed minute metal structure, thereby causing a phase difference between the minute metal structures. The material of the metal particles may be selected so that plasmon is generated at the light source wavelength to be used and a desired phase difference is given to the emitted light. For example, Au, Ag, Al, Pt, Ni, Cr, Cu, etc. Can be used, and alloys of these metals may be used, and Au, Ag, and Al are particularly preferable.

A second embodiment will be described with reference to FIG. Note that the same parts as those in the above embodiment are denoted by the same reference numerals, and unless otherwise specified, description of the configuration and functions already described is omitted, and only the main part will be described (the same applies to other embodiments below).
In the light processing element 7 according to the present embodiment, a substrate 8 which is a light reflection region as a unit processing region for reflecting light is provided on the emission side of the light processing element 1 shown in FIG. Therefore, it is possible to obtain reflected light having only the polarization component.
The polarization separation processing region (substrate 2) and the polarization rotation processing region (substrate 3) have the same functions as those in the embodiment shown in FIG. In this case, a material having high reflectivity is preferable for the light reflection region (substrate 8), and a metal substrate such as Al or Au deposited on the above optical glass or optical crystal material, or a silicon substrate is used. Is preferred.
Further, by using a Cr coating or the like as the partial reflection film, it can be used as a half mirror that uses both transmitted light and reflected light.

A third embodiment will be described with reference to FIG.
The light processing element 10 according to the present embodiment has a polarization rotation processing region (substrate 3) having the same function as shown in FIG. 1 and a wire grid type polarizer 11 formed on the upper surface thereof. is doing.
The wire grid polarizer 31 is a metal fine wire grating having a period smaller than the incident wavelength. When the vibration direction of the electric field of incident light is perpendicular to the thin wire, the wire grid polarizer 31 passes through the grating and is reflected when parallel. Accordingly, the light incident from the upper surface is separated into polarized light in a direction parallel to the fine line by the wire grid polarizer 11, and light having polarized light in an arbitrary direction can be selectively emitted in the polarization rotation processing region. .
The polarizer 11 is not limited to a wire grid polarizer, and a polarizer using an organic film, a polarizer using calcite, and the like can be used.

It is a perspective view of the optical processing element concerning a 1st embodiment. It is a perspective view which shows the function of the optical processing element which concerns on 1st Embodiment. It is explanatory drawing showing the model used for the numerical calculation. It is a graph which shows the amplitude ratio obtained by numerical calculation. It is a graph which shows the phase difference obtained by numerical calculation. It is a figure which shows a polarization state. It is a graph which shows the result of having performed calculation regarding the electric field intensity inside a metal sphere, and a resonance wavelength relation. It is explanatory drawing which shows the arrangement pattern of the micro metal structure which comprises an optical processing element. It is explanatory drawing which shows the arrangement pattern (V shape) of the micro metal structure which comprises a light processing element. It is explanatory drawing which shows the arrangement pattern (L shape) of the micro metal structure which comprises a light processing element. It is explanatory drawing which shows the arrangement pattern (T shape) of the micro metal structure which comprises an optical processing element. It is explanatory drawing which shows the arrangement pattern (letter character) of the micro metal structure which comprises a light processing element. It is a perspective view of the optical processing element which concerns on 2nd Embodiment. It is a perspective view of the optical processing element which concerns on 3rd Embodiment.

Explanation of symbols

2 Polarization separation processing region as a unit processing region that selectively transmits light 3 Polarization rotation processing region as a unit processing region that selectively changes the polarization state of light 4 Micro metal structure 8 Unit processing region that reflects light Reflective region 11 as a wire grid polarizer as a polarizer

Claims (8)

  A plurality of minute metal structures having a size D (D <λ) with respect to the wavelength λ of light to be processed are arranged in a predetermined arrangement with a distance d (<D) to form a unit arrangement pattern, An optical processing element characterized in that a plurality of unit processing regions in which the unit array patterns are two-dimensionally arrayed are formed on an optical substrate. The light processing element according to claim 1,
An optical processing element comprising: a unit processing region that selectively transmits light having a wavelength λ; and a unit processing region that selectively changes a polarization state of light having a wavelength λ. The light processing element according to claim 1,
A unit processing region that selectively transmits light of wavelength λ, a unit processing region that selectively changes the polarization state of light of wavelength λ, and a unit processing region that reflects light Light processing element. In the optical processing element in any one of Claims 1-3,
An optical processing element, wherein the shape of the minute metal structure is any one of a hemispherical shape, a cylindrical shape, a semi-rotating ellipsoidal shape, an elliptical columnar shape, a polygonal columnar shape, and a conical shape. In the optical processing element in any one of Claims 1-4,
The minute metal structure is one of gold (Au), silver (Ag), aluminum (Al), platinum (Pt), nickel (Ni), chromium (Cr), copper (Cu), or these An optical processing element comprising a combination of these or an alloy thereof. In the optical processing element in any one of Claims 1-5,
The arrangement of the minute metal structures in the unit arrangement pattern is a proximity arrangement of two metal structures, a V-shaped arrangement or an L-shaped arrangement of three or more metal structures, or four or more. An optical processing element characterized in that it is either a T-shaped arrangement with a metal structure or a cross-shaped arrangement with five or more metal structures. In the optical processing element in any one of Claims 1-6,
An optical processing element having a polarizer disposed on the light incident side and allowing only linearly polarized light to pass therethrough. The light processing element according to claim 7,
The light processing element, wherein the polarizer is of a wire grid type.

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