Optical Device

Abstract

A conductive thin film has first and second surfaces and at least one opening extending through from the first surface to the second surface. At least on one of the first and second surfaces, first and second periodic surface patterns having different period lengths are provided. The period length of the second periodic surface pattern is substantially equal to an odd integral multiple of a half of the period length of the first periodic surface pattern. With this, surface plasmon polaritons excited by the first periodic surface pattern undergo odd-order Bragg reflection by the second periodic surface pattern. As a result, the intensity of the light falling on the first surface and transmitted to the second surface through the opening is increased with high efficiency.

1 . An optical device comprising a conductive thin film having: first and second surfaces; at least one opening extending through the film from the first surface to the second surface; and a periodic surface pattern disposed on at least one of the first and second surfaces, an intensity of light falling on the first surface and transmitted to the second surface through the opening being increased as compared with a case where any periodic surface pattern is not disposed, 
 wherein the periodic surface pattern includes first and second periodic surface patterns having different period lengths, and the period length of the second periodic surface pattern is substantially equal to odd time(s) as much as ½ of the period length of the first periodic surface pattern.    
   
   
       2 . An optical device comprising a conductive thin film having: first and second surfaces; at least one opening extending through the film from the first surface to the second surface; and a periodic surface pattern disposed on at least one of the first and second surfaces, an intensity of light falling on the first surface and transmitted to the second surface through the opening being increased as compared with a case where any periodic surface pattern is not disposed, 
 wherein the periodic surface pattern includes first and second periodic surface patterns having different period lengths, and surface plasmon polaritons excited by the first periodic surface pattern undergo odd-order Bragg reflection by the second periodic surface pattern.    
   
   
       3 . The optical device according to  claim 1 , wherein a ratio P 2 /P 1  of a period length P 2  of the second periodic surface pattern with respect to a period length P 1  of the first periodic surface pattern is within a range of ±0.2 of odd time(s) as much as 0.5.  
   
   
       4 . The optical device according to  claim 1 , wherein a ratio P 2 /P 1  of a period length P 2  of the second periodic surface pattern with respect to a period length P 1  of the first periodic surface pattern is within a range of 0.5±0.2.  
   
   
       5 . The optical device according to  claim 1 , wherein a ratio P 2 /P 1  of a period length P 2  of the second periodic surface pattern with respect to a period length P 1  of the first periodic surface pattern is within a range of 1.5±0.2.  
   
   
       6 . The optical device according to  claim 1 , wherein the intensity of the light transmitted through the opening increases by 20% or more as compared with that of light transmitted through an opening of a device which is not provided with the second periodic surface pattern.  
   
   
       7 . The optical device according to  claim 2 , wherein the intensity of the light transmitted through the opening increases by 20% or more as compared with that of light transmitted through an opening of a device which is not provided with the second periodic surface pattern.  
   
   
       8 . The optical device according to  claim 1 , wherein the first and second periodic surface patterns are disposed on the same plane as the first or second surface.  
   
   
       9 . The optical device according to  claim 2 , wherein the first and second periodic surface patterns are disposed on the same plane as the first or second surface.  
   
   
       10 . The optical device according to  claim 1 , wherein the first periodic surface pattern is disposed so as to correspond to a region on which the light falls, and the second periodic surface pattern is disposed externally from the first periodic surface pattern.  
   
   
       11 . The optical device according to  claim 2 , wherein the first periodic surface pattern is disposed so as to correspond to a region on which the light falls, and the second periodic surface pattern is disposed externally from the first periodic surface pattern.  
   
   
       12 . The optical device according to  claim 10 , wherein the region provided with the first periodic surface pattern is broader than the region on which the light falls.  
   
   
       13 . The optical device according to  claim 11 , wherein the region provided with the first periodic surface pattern is broader than the region on which the light falls.  
   
   
       14 . An optical device comprising a conductive thin film having: first and second surfaces; and a plurality of periodically arranged openings extending through the film from the first surface to the second surface, an intensity of light falling on the first surface and transmitted to the second surface through the plurality of openings being increased as compared with a case where the plurality of openings are not periodically arranged, 
 wherein the plurality of periodically arranged openings are regarded as first periodic openings,    the conductive thin film includes one of second periodic openings and periodic surface patterns formed with a period length which is different from that of the first periodic openings, the second periodic openings including a plurality of openings which are different from the plurality of openings extending through the film from the first surface to the second surface, the periodic surface patterns being formed on one of the first and second surfaces, and    the period length of the second periodic openings or the periodic surface patterns is substantially equal to odd time(s) as much as ½ of the period length of the first periodic openings.    
   
   
       15 . An optical device comprising a conductive thin film having: first and second surfaces; and a plurality of periodically arranged openings extending through the film from the first surface to the second surface, an intensity of light falling on the first surface and transmitted to the second surface through the plurality of openings being increased as compared with a case where the plurality of openings are not periodically arranged, 
 wherein the plurality of periodically arranged openings are regarded as first periodic openings,    the conductive thin film includes one of second periodic openings and periodic surface patterns formed with a period length which is different from that of the first periodic openings, the second periodic openings including a plurality of openings which are different from the plurality of openings extending through the film from the first surface to the second surface, the periodic surface patterns being formed on one of the first and second surfaces, and    surface plasmon polaritons excited by the first periodic openings undergo odd-order Bragg reflection by the second periodic openings or the periodic surface patterns.    
   
   
       16 . The optical device according to  claim 14 , wherein a ratio P 2 /P 1  of a period length P 2  of the second periodic openings or the periodic surface patterns with respect to a period length P 1  of the first periodic openings is within a range of ±0.2 of odd time(s) as much as 0.5.  
   
   
       17 . The optical device according to  claim 14 , wherein a ratio P 2 /P 1  of a period length P 2  of the second periodic openings or the periodic surface patterns with respect to a period length P 1  of the first periodic openings is within a range of 0.5±0.2.  
   
   
       18 . The optical device according to  claim 14 , wherein a ratio P 2 /P 1  of a period length P 2  of the second periodic openings or the periodic surface patterns with respect to a period length P 1  of the first periodic openings is within a range of 1.5±0.2.  
   
   
       19 . The optical device according to  claim 14 , wherein the intensity of the light transmitted through the first periodic openings increases by 20% or more as compared with that of the light transmitted through periodic openings of a device which is not provided with the second periodic openings or the periodic surface patterns.  
   
   
       20 . The optical device according to  claim 15 , wherein the intensity of the light transmitted through the first periodic openings increases by 20% or more as compared with that of light transmitted through periodic openings of a device which is not provided with the second periodic openings or the periodic surface patterns.  
   
   
       21 . The optical device according to  claim 14 , wherein the first periodic openings are disposed so as to correspond to a region on which light falls, and the second periodic openings or the periodic surface patterns are disposed externally from the first periodic openings.  
   
   
       22 . The optical device according to  claim 15 , wherein the first periodic openings are disposed so as to correspond to a region on which light falls, and the second periodic openings or the periodic surface patterns are disposed externally from the first periodic openings.  
   
   
       23 . The optical device according to  claim 14 , wherein a region provided with the first periodic openings is broader than the region on which light falls.  
   
   
       24 . The optical device according to  claim 15 , wherein a region provided with the first periodic openings is broader than the region on which light falls.  
   
   
       25 . An optical device comprising a conductive thin film having: first and second surfaces; at least one opening extending through the film from the first surface to the second surface; and a periodic surface pattern disposed on at least one of the first and second surfaces, an intensity of light falling on the first surface and transmitted to the second surface through the opening being increased as compared with a case where any periodic surface pattern is not disposed, 
 wherein the periodic surface pattern is disposed on the second surface, and a period length of the periodic surface pattern is substantially equal to odd time(s) as much as ½ of a value λ/n d  obtained by dividing a wavelength λ of the transmitted light whose intensity is increased by an effective refractive index n d  of a medium substantially adjacent to the second surface.    
   
   
       26 . An optical device comprising a conductive thin film having: first and second surfaces; at least one opening extending through the film from the first surface to the second surface; and a periodic surface pattern disposed on at least one of the first and second surfaces, an intensity of light falling on the first surface and transmitted to the second surface through the opening being increased as compared with a case where any periodic surface pattern is not disposed, 
 wherein the periodic surface pattern is disposed on the second surface, and assuming that a wavelength of the transmitted light whose intensity is increased is λ, a permittivity of the conductive thin film is ε m , and a permittivity of a medium substantially adjacent to the second surface is ε d , the period length of the periodic surface pattern is substantially equal to odd time(s) as much as ½ of λ/(ε m ·ε d /(ε m +ε d )) 1/2 .    
   
   
       27 . An optical device comprising a conductive thin film having: first and second surfaces; at least one opening extending through the film from the first surface to the second surface; and a periodic surface pattern disposed on at least one of the first and second surfaces, an intensity of light falling on the first surface and transmitted to the second surface through the opening being increased as compared with a case where any periodic surface pattern is not disposed, 
 wherein the periodic surface pattern is disposed on the second surface, and surface plasmon polaritons in the periodic surface pattern undergo odd-order Bragg reflection in the periodic surface pattern.    
   
   
       28 . The optical device according to  claim 25 , wherein a ratio P 3 /(λ/n d ) between a value λ/n d  obtained by dividing the wavelength λ of the transmitted light whose intensity is increased by the effective refractive index n d  of the medium substantially adjacent to the second surface and a period length P 3  of the periodic surface pattern is within a range of ±0.2 of odd time(s) as much as 0.5.  
   
   
       29 . The optical device according to  claim 26 , wherein assuming that the wavelength of the transmitted light whose intensity is increased is λ, the permittivity of the conductive thin film is ε m , and the permittivity of the medium substantially adjacent to the second surface is ε d , a relation formula of the period length P 3  of the periodic surface pattern P 3 /(λ/(ε m ·ε d /(ε m +ε d )) 1/2 ) is within a range of ±0.2 of odd time(s) as much as 0.5.  
   
   
       30 . The optical device according to  claim 25 , wherein a ratio P 3 /(λ/n d ) between a value λ/n d  obtained by dividing the wavelength λ of the transmitted light whose intensity is increased by the effective refractive index n d  of the medium substantially adjacent to the second surface and a period length P 3  of the periodic surface pattern is within a range of 0.5±0.2.  
   
   
       31 . The optical device according to  claim 26 , wherein assuming that the wavelength of the transmitted light whose intensity is increased is λ, the permittivity of the conductive thin film is ε m , and the permittivity of the medium substantially adjacent to the second surface is ε d , a relation formula of the period length P 3  of the periodic surface pattern P 3 /(λ/(ε m ·ε d /(ε m +ε d )) 1/2 ) is within a range of 0.5±0.2.  
   
   
       32 . The optical device according to  claim 25 , wherein a ratio P 3 /(λ/n d ) between a value λ/n d  obtained by dividing the wavelength λ of the transmitted light whose intensity is increased by the effective refractive index n d  of the medium substantially adjacent to the second surface and a period length P 3  of the periodic surface pattern is within a range of 1.5±0.2.  
   
   
       33 . The optical device according to  claim 26 , wherein assuming that the wavelength of the transmitted light whose intensity is increased is λ, the permittivity of the conductive thin film is ε m , and the permittivity of the medium substantially adjacent to the second surface is ε d , a relation formula of the period length P 3  of the periodic surface pattern P 3 /(λ/(ε m ·ε d (ε m +ε d )) 1/2 ) is within a range of 1.5±0.2.  
   
   
       34 . An optical device comprising a conductive thin film having: first and second surfaces; at least one opening extending through the film from the first surface to the second surface; and a plurality of periodic surface patterns disposed on the first and second surfaces, an intensity of light falling on the first surface and transmitted to the second surface through the opening being increased as compared with a case where any periodic surface pattern is not disposed, 
 wherein the plurality of periodic surface patterns include first and second periodic surface patterns disposed on the first surface and having mutually different period lengths, and a third periodic surface pattern disposed on the second surface,    the period length of the second periodic surface pattern is substantially equal to odd time(s) as much as ½ of the period length of the first periodic surface pattern, and    the period length of the third periodic surface pattern is substantially equal to odd time(s) as much as ½ of a value λ/n d  obtained by dividing a wavelength λ of the transmitted light whose intensity is increased by an effective refractive index n d  of a medium substantially adjacent to the second surface.    
   
   
       35 . An optical device comprising a conductive thin film having: first and second surfaces; at least one opening extending through the film from the first surface to the second surface; and a plurality of periodic surface patterns disposed on the first and second surfaces, an intensity of light falling on the first surface and transmitted to the second surface through the opening being increased as compared with a case where any periodic surface pattern is not disposed, 
 wherein the plurality of periodic surface patterns include first and second periodic surface patterns disposed on the first surface and having mutually different period lengths, and a third periodic surface pattern disposed on the second surface,    the period length of the second periodic surface pattern is substantially equal to odd time(s) as much as ½ of the period length of the first periodic surface pattern, and    assuming that a wavelength of the transmitted light whose intensity is increased is λ, a permittivity of the conductive thin film is ε m , and a permittivity of a medium substantially adjacent to the second surface is ε d , the period length of the third periodic surface pattern is substantially equal to odd time(s) as much as ½ of λ/(ε m ·ε d (ε m +ε d )) 1/2 .    
   
   
       36 . An optical device comprising a conductive thin film having: first and second surfaces; at least one opening extending through the film from the first surface to the second surface; and a plurality of periodic surface patterns disposed on the first and second surfaces, an intensity of light falling on the first surface and transmitted to the second surface through the opening being increased as compared with a case where any periodic surface pattern is not disposed, 
 wherein the plurality of periodic surface patterns include first and second periodic surface patterns disposed on the first surface and having mutually different period lengths, and a third periodic surface pattern disposed on the second surface,    surface plasmon polaritons excited by the first periodic surface pattern undergo odd-order Bragg reflection by the second periodic surface pattern, and    surface plasmon polaritons in the third periodic surface pattern undergo odd-order Bragg reflection in the third periodic surface pattern.    
   
   
       37 . The optical device according to  claim 34 , wherein a ratio P 2 /P 1  of a period length P 2  of the second periodic surface pattern with respect to a period length P 1  of the first periodic surface pattern is within a range of ±0.2 of odd time(s) as much as 0.5, and a ratio P 3 /(λ/n d ) between a value λ/n d  obtained by dividing the wavelength λ of the transmitted light whose intensity is increased by the effective refractive index n d  of the medium substantially adjacent to the second surface and a period length P 3  of the third periodic surface pattern is within a range of ±0.2 of odd time(s) as much as 0.5.  
   
   
       38 . The optical device according to  claim 35 , wherein a ratio P 2 /P 1  of a period length P 2  of the second periodic surface pattern with respect to a period length P 1  of the first periodic surface pattern is within a range of ±0.2 of odd time(s) as much as 0.5, and assuming that the wavelength of the transmitted light whose intensity is increased is λ, the permittivity of the conductive thin film is ε m , and the permittivity of the medium substantially adjacent to the second surface is ε d , a relation formula of the period length P 3  of the third periodic surface pattern P 3 /(λ/(ε m ·ε d /(ε m +ε d )) 1/2 ) may be within the range of ±0.2 of odd time(s) as much as 0.5.  
   
   
       39 . The optical device according to  claim 34 , wherein a ratio P 2 /P 1  of a period length P 2  of the second periodic surface pattern with respect to a period length P 1  of the first periodic surface pattern is within a range of 0.5±0.2, and a ratio P 3 /(λ/n d ) between a value λ/n d  obtained by dividing the wavelength λ of the transmitted light whose intensity is increased by the effective refractive index n d  of the medium substantially adjacent to the second surface and a period length P 3  of the third periodic surface pattern is within a range of 0.5±0.2.  
   
   
       40 . The optical device according to  claim 35 , wherein a ratio P 2 /P 1  of a period length P 2  of the second periodic surface pattern with respect to a period length P 1  of the first periodic surface pattern is within a range of 0.5±0.2, and assuming that the wavelength of the transmitted light whose intensity is increased is λ, the permittivity of the conductive thin film is ε m , and the permittivity of the medium substantially adjacent to the second surface is ε d , a relation formula of the period length P 3  of the third periodic surface pattern P 3 /(λ/(ε m ·ε d /(ε m +ε d )) 1/2 ) may be within a range of 0.5±0.2.  
   
   
       41 . The optical device according to  claim 34 , wherein a ratio P 2 /P 1  of a period length P 2  of the second periodic surface pattern with respect to a period length P 1  of the first periodic surface pattern is within a range of 1.5±0.2, and a ratio P 3 /(λ/n d ) between a value λ/n d  obtained by dividing the wavelength λ of the transmitted light whose intensity is increased by the effective refractive index n d  of the medium substantially adjacent to the second surface and a period length P 3  of the third periodic surface pattern is within a range of 1.5±0.2.  
   
   
       42 . The optical device according to  claim 35 , wherein a ratio P 2 /P 1  of a period length P 2  of the second periodic surface pattern with respect to a period length P 1  of the first periodic surface pattern is within a range of 1.5±0.2, and assuming that the wavelength of the transmitted light whose intensity is increased is λ, the permittivity of the conductive thin film is ε m , and the permittivity of the medium substantially adjacent to the second surface is ε d , a relation formula of the period length P 3  of the third periodic surface pattern P 3 /λ/(ε m ·ε d /(ε m +ε d )) 1/2 ) may be within a range of 1.5±0.2.  
   
   
       43 . The optical device according to  claim 2 , wherein an opening diameter of the opening is smaller than a wavelength of the incident light.  
   
   
       44 . The optical device according to  claim 15 , wherein an opening diameter of the opening is smaller than a wavelength of the incident light.  
   
   
       45 . The optical device according to  claim 27 , wherein an opening diameter of the opening is smaller than a wavelength of the incident light.  
   
   
       46 . The optical device according to  claim 36 , wherein an opening diameter of the opening is smaller than a wavelength of the incident light.  
   
   
       47 . The optical device according to  claim 2 , wherein the periodic surface pattern is formed into a concentrically circular shape.  
   
   
       48 . The optical device according to  claim 15 , wherein the periodic surface pattern is formed into a concentrically circular shape.  
   
   
       49 . The optical device according to  claim 27 , wherein the periodic surface pattern is formed into a concentrically circular shape.  
   
   
       50 . The optical device according to  claim 36 , wherein the periodic surface pattern is formed into a concentrically circular shape.  
   
   
       51 . The optical device according to  claim 2 , wherein the periodic surface pattern is periodically disposed centering on the opening.  
   
   
       52 . The optical device according to  claim 15 , wherein the periodic surface pattern is periodically disposed centering on the opening.  
   
   
       53 . The optical device according to  claim 27 , wherein the periodic surface pattern is periodically disposed centering on the opening.  
   
   
       54 . The optical device according to  claim 36 , wherein the periodic surface pattern is periodically disposed centering on the opening.  
   
   
       55 . An optical head which records information in an optical recording medium by light from a light source, the optical head comprising: waveguide means for guiding the output light of the light source; condenser means for condensing the light guided by the waveguide means; and an optical device which irradiates the optical recording medium with a part of the light condensed by the condenser means, 
 the optical device comprising a conductive thin film having: first and second surfaces; at least one opening extending through the film from the first surface to the second surface; and a periodic surface pattern disposed on at least one of the first and second surfaces, an intensity of light falling on the first surface and transmitted to the second surface through the opening being increased as compared with a case where any periodic surface pattern is not disposed,    wherein the periodic surface pattern includes first and second periodic surface patterns having different period lengths, and surface plasmon polaritons excited by the first periodic surface pattern undergo odd-order Bragg reflection by the second periodic surface pattern.    
   
   
       56 . An optical head which records information in an optical recording medium by light from a light source, the optical head comprising: waveguide means for guiding the output light of the light source; condenser means for condensing the light guided by the waveguide means; and an optical device which irradiates the optical recording medium with a part of the light condensed by the condenser means, 
 the optical device comprising a conductive thin film having: first and second surfaces; and a plurality of periodically arranged openings extending through the film from the first surface to the second surface, an intensity of light falling on the first surface and transmitted to the second surface through the plurality of openings being increased as compared with a case where the plurality of openings are not periodically arranged,    wherein the plurality of periodically arranged openings are regarded as first periodic openings,    the conductive thin film includes one of second periodic openings and periodic surface patterns formed with a period length which is different from that of the first periodic openings, the second periodic openings including a plurality of openings which are different from the plurality of openings extending through the film from the first surface to the second surface, the periodic surface patterns being formed on one of the first and second surfaces, and    surface plasmon polaritons excited by the first periodic openings undergo odd-order Bragg reflection by the second periodic openings or the periodic surface patterns.    
   
   
       57 . An optical head which records information in an optical recording medium by light from a light source, the optical head comprising: waveguide means for guiding the output light of the light source; condenser means for condensing the light guided by the waveguide means; and an optical device which irradiates the optical recording medium with a part of the light condensed by the condenser means, 
 the optical device comprising a conductive thin film having: first and second surfaces; at least one opening extending through the film from the first surface to the second surface; and a periodic surface pattern disposed on at least one of the first and second surfaces, an intensity of light falling on the first surface and transmitted to the second surface through the opening being increased as compared with a case where any periodic surface pattern is not disposed,    wherein the periodic surface pattern is disposed on the second surface, and surface plasmon polaritons in the periodic surface pattern undergo odd-order Bragg reflection in the periodic surface pattern.    
   
   
       58 . An optical head which records information in an optical recording medium by light from a light source, the optical head comprising: waveguide means for guiding the output light of the light source; condenser means for condensing the light guided by the waveguide means; and an optical device which irradiates the optical recording medium with a part of the light condensed by the condenser means, 
 the optical device comprising a conductive thin film having: first and second surfaces; at least one opening extending through the film from the first surface to the second surface; and a plurality of periodic surface patterns disposed on the first and second surfaces, an intensity of light falling on the first surface and transmitted to the second surface through the openings being increased as compared with a case where there is not any periodic surface pattern,    wherein the plurality of periodic surface patterns include first and second periodic surface patterns disposed on the first surface and having mutually different period lengths, and a third periodic surface pattern disposed on the second surface,    surface plasmon polaritons excited by the first periodic surface pattern undergo odd-order Bragg reflection by the second periodic surface pattern, and    surface plasmon polaritons in the third periodic surface pattern undergo odd-order Bragg reflection in the third periodic surface pattern.    
   
   
       59 . An optical recording device comprising: an optical head which records information in an optical recording medium by light from a light source, 
 the optical head comprising: waveguide means for guiding the output light of the light source; condenser means for condensing the light guided by the waveguide means; and an optical device which irradiates the optical recording medium with a part of the light condensed by the condenser means,    the optical device comprising a conductive thin film having: first and second surfaces; at least one opening extending through the film from the first surface to the second surface; and a periodic surface pattern disposed on at least one of the first and second surfaces, an intensity of light falling on the first surface and transmitted to the second surface through the opening being increased as compared with a case where any periodic surface pattern is not disposed,    wherein the periodic surface pattern includes first and second periodic surface patterns having different period lengths, and surface plasmon polaritons excited by the first periodic surface pattern undergo odd-order Bragg reflection by the second periodic surface pattern.    
   
   
       60 . An optical recording device comprising: an optical head which records information in an optical recording medium by light from a light source, 
 the optical head comprising: waveguide means for guiding the output light of the light source; condenser means for condensing the light guided by the waveguide means; and an optical device which irradiates the optical recording medium with a part of the light condensed by the condenser means,    the optical device comprising a conductive thin film having: first and second surfaces; and a plurality of periodically arranged openings extending through the film from the first surface to the second surface, an intensity of light falling on the first surface and transmitted to the second surface through the plurality of openings being increased as compared with a case where the plurality of openings are not periodically arranged,    wherein the plurality of periodically arranged openings are regarded as first periodic openings,    the conductive thin film includes one of second periodic openings and periodic surface patterns formed with a period length which is different from that of the first periodic openings, the second periodic openings including a plurality of openings which are different from the plurality of openings extending through the film from the first surface to the second surface, the periodic surface patterns being formed on one of the first and second surfaces, and    surface plasmon polaritons excited by the first periodic openings undergo odd-order Bragg reflection by the second periodic openings or the periodic surface patterns.    
   
   
       61 . An optical recording device comprising: an optical head which records information in an optical recording medium by light from a light source, 
 the optical head comprising: waveguide means for guiding the output light of the light source; condenser means for condensing the light guided by the waveguide means; and an optical device which irradiates the optical recording medium with a part of the light condensed by the condenser means,    the optical device comprising a conductive thin film having: first and second surfaces; at least one opening extending through the film from the first surface to the second surface; and a periodic surface pattern disposed on at least one of the first and second surfaces, an intensity of light falling on the first surface and transmitted to the second surface through the opening being increased as compared with a case where any periodic surface pattern is not disposed,    wherein the periodic surface pattern is disposed on the second surface, and surface plasmon polaritons in the periodic surface pattern undergo odd-order Bragg reflection in the periodic surface pattern.    
   
   
       62 . An optical recording device comprising: an optical head which records information in an optical recording medium by light from a light source, 
 the optical head comprising: waveguide means for guiding the output light of the light source; condenser means for condensing the light guided by the waveguide means; and an optical device which irradiates the optical recording medium with a part of the light condensed by the condenser means,    the optical device comprising a conductive thin film having: first and second surfaces; at least one opening extending through the film from the first surface to the second surface; and a plurality of periodic surface patterns disposed on the first and second surfaces, an intensity of light falling on the first surface and transmitted to the second surface through the openings being increased as compared with a case where there is not any periodic surface pattern,    wherein the plurality of periodic surface patterns include first and second periodic surface patterns disposed on the first surface and having mutually different period lengths, and a third periodic surface pattern disposed on the second surface,    surface plasmon polaritons excited by the first periodic surface pattern undergo odd-order Bragg reflection by the second periodic surface pattern, and    surface plasmon polaritons in the third periodic surface pattern undergo odd-order Bragg reflection in the third periodic surface pattern.    
   
   
       63 . A condensing device which condenses only light having a specific wavelength from light from a light source, comprising: 
 an optical device comprising a conductive thin film having: first and second surfaces; at least one opening extending through the film from the first surface to the second surface; and a periodic surface pattern disposed on at least one of the first and second surfaces, an intensity of light falling on the first surface and transmitted to the second surface through the opening being increased as compared with a case where any periodic surface pattern is not disposed,    wherein the periodic surface pattern includes first and second periodic surface patterns having different period lengths, and surface plasmon polaritons excited by the first periodic surface pattern undergo odd-order Bragg reflection by the second periodic surface pattern.    
   
   
       64 . A condensing device which condenses only light having a specific wavelength from light from a light source, comprising: 
 an optical device comprising: a conductive thin film having: first and second surfaces; and a plurality of periodically arranged openings extending through the film from the first surface to the second surface, an intensity of light falling on the first surface and transmitted to the second surface through the plurality of openings being increased as compared with a case where the plurality of openings are not periodically arranged,    wherein the plurality of periodically arranged openings are regarded as first periodic openings,    the conductive thin film includes one of second periodic openings and periodic surface patterns formed with a period length which is different from that of the first periodic openings, the second periodic openings including a plurality of openings which are different from the plurality of openings extending through the film from the first surface to the second surface, the periodic surface patterns being formed on one of the first and second surfaces, and    surface plasmon polaritons excited by the first periodic openings undergo odd-order Bragg reflection by the second periodic openings or the periodic surface patterns.    
   
   
       65 . A condensing device which condenses only light having a specific wavelength from light from a light source, comprising: 
 an optical device comprising a conductive thin film having: first and second surfaces; at least one opening extending through the film from the first surface to the second surface; and a periodic surface pattern disposed on at least one of the first and second surfaces, an intensity of light falling on the first surface and transmitted to the second surface through the opening being increased as compared with a case where any periodic surface pattern is not disposed,    wherein the periodic surface pattern is disposed on the second surface, and surface plasmon polaritons in the periodic surface pattern undergo odd-order Bragg reflection in the periodic surface pattern.    
   
   
       66 . A condensing device which condenses only light having a specific wavelength from light from a light source, comprising: 
 an optical device comprising a conductive thin film having: first and second surfaces; at least one opening extending through the film from the first surface to the second surface; and a plurality of periodic surface patterns disposed on the first and second surfaces, an intensity of light falling on the first surface and transmitted to the second surface through the openings being increased as compared with a case where there is not any periodic surface pattern,    wherein the plurality of periodic surface patterns include first and second periodic surface patterns disposed on the first surface and having mutually different period lengths, and a third periodic surface pattern disposed on the second surface,    surface plasmon polaritons excited by the first periodic surface pattern undergo odd-order Bragg reflection by the second periodic surface pattern, and    surface plasmon polaritons in the third periodic surface pattern undergo odd-order Bragg reflection in the third periodic surface pattern.    
   
   
       67 . A near-field optical microscope comprising: 
 an optical device which condenses only light having a specific wavelength from light from a light source; and    detection means for receiving the light emitted by the optical device,    the optical device comprising a conductive thin film having: first and second surfaces; at least one opening extending through the film from the first surface to the second surface; and a periodic surface pattern disposed on at least one of the first and second surfaces, an intensity of light falling on the first surface and transmitted to the second surface through the opening being increased as compared with a case where any periodic surface pattern is not disposed,    wherein the periodic surface pattern includes first and second periodic surface patterns having different period lengths, and surface plasmon polaritons excited by the first periodic surface pattern undergo odd-order Bragg reflection by the second periodic surface patter.    
   
   
       68 . A near-field optical microscope comprising: 
 an optical device which condenses only light having a specific wavelength from light from a light source; and    detection means for receiving the light emitted by the optical device,    the optical device comprising: a conductive thin film having: first and second surfaces; and a plurality of periodically arranged openings extending through the film from the first surface to the second surface, an intensity of light falling on the first surface and transmitted to the second surface through the plurality of openings being increased as compared with a case where the plurality of openings are not periodically arranged,    wherein the plurality of periodically arranged openings are regarded as first periodic openings,    the conductive thin film includes one of second periodic openings and periodic surface patterns formed with a period length which is different from that of the first periodic openings, the second periodic openings including a plurality of openings which are different from the plurality of openings extending through the film from the first surface to the second surface, the periodic surface patterns being formed on one of the first and second surfaces, and    surface plasmon polaritons excited by the first periodic openings undergo odd-order Bragg reflection by the second periodic openings or the periodic surface patterns.    
   
   
       69 . A near-field optical microscope comprising: 
 an optical device which condenses only light having a specific wavelength from light from a light source; and    detection means for receiving the light emitted by the optical device,    the optical device comprising a conductive thin film having: first and second surfaces; at least one opening extending through the film from the first surface to the second surface; and a periodic surface pattern disposed on at least one of the first and second surfaces, an intensity of light falling on the first surface and transmitted to the second surface through the opening being increased as compared with a case where any periodic surface pattern is not disposed,    wherein the periodic surface pattern is disposed on the second surface, and surface plasmon polaritons in the periodic surface pattern undergo odd-order Bragg reflection in the periodic surface pattern.    
   
   
       70 . A near-field optical microscope comprising: 
 an optical device which condenses only light having a specific wavelength from light from a light source; and    detection means for receiving the light emitted by the optical device,    the optical device comprising a conductive thin film having: first and second surfaces; at least one opening extending through the film from the first surface to the second surface; and a plurality of periodic surface patterns disposed on the first and second surfaces, an intensity of light falling on the first surface and transmitted to the second surface through the openings being increased as compared with a case where there is not any periodic surface pattern,    wherein the plurality of periodic surface patterns include first and second periodic surface patterns disposed on the first surface and having mutually different period lengths, and a third periodic surface pattern disposed on the second surface,    surface plasmon polaritons excited by the first periodic surface pattern undergo odd-order Bragg reflection by the second periodic surface pattern, and    surface plasmon polaritons in the third periodic surface pattern undergo odd-order Bragg reflection in the third periodic surface pattern.