Optical filter, optical filter module, spectrometric measurement apparatus, and optical apparatus

Abstract

An optical filter includes: a first variable wavelength bandpass filter that can extract light of a first wavelength band (400 to 460 nm), the first wavelength band having a first spectral band having a central wavelength equal to a first wavelength in the first wavelength band and a second spectral band having a central wavelength equal to a second wavelength in the first wavelength band; and a second variable wavelength bandpass filter that can extract light of a second wavelength band (480 to 540 nm) adjacent to the first wavelength band, the second wavelength band having a third spectral band having a central wavelength equal to a third wavelength in the second wavelength band and a fourth spectral band having a central wavelength equal to a fourth wavelength in the second wavelength band.

1 . An optical filter comprising:
 a first variable wavelength bandpass filter;   a second variable wavelength bandpass filter;   a driver that drives each of the first and second variable wavelength bandpass filters; and   a controller that variably controls a spectral band of each of the first and second variable wavelength bandpass filters,   wherein the first variable wavelength bandpass filter extracts light of a first wavelength band located in a desired wavelength band, and the first wavelength band has, at least:
 a first spectral band having a central wavelength equal to a first wavelength in the first wavelength band; and 
 a second spectral band having a central wavelength equal to a second wavelength in the first wavelength band, and 
   the second variable wavelength bandpass filter extracts light of a second wavelength band located in the desired wavelength band and adjacent to the first wavelength band, and the second wavelength band has, at least:
 a third spectral band having a central wavelength equal to a third wavelength in the second wavelength band; and 
 a fourth spectral band having a central wavelength equal to a fourth wavelength in the second wavelength band. 
   
     
     
         2 . The optical filter according to  claim 1 ,
 wherein the first variable wavelength bandpass filter comprises:
 a first substrate; 
 a second substrate that faces the first substrate; 
 a first optical film provided on the first substrate; 
 a second optical film provided on the second substrate and facing the first optical film; 
 a first electrode provided on the first substrate; and 
 a second electrode provided on the second substrate and facing the first electrode, 
   wherein the first variable wavelength bandpass filter extracts light of the first spectral band or the second spectral band after a gap between the first optical film and the second optical film is changed by an electrostatic force induced between the first electrode and the second electrode, and   the second variable wavelength bandpass filter comprises:
 a third substrate; 
 a fourth substrate that faces the third substrate; 
 a third optical film provided on the third substrate; 
 a fourth optical film provided on the fourth substrate and facing the third optical film; 
 a third electrode provided on the third substrate; and 
 a fourth electrode provided on the fourth substrate and facing the third electrode, and wherein 
   the second variable wavelength bandpass filter extracts light of the third spectral band or the fourth spectral band after a gap between the third optical film and the fourth optical film is changed by an electrostatic force induced between the third electrode and the fourth electrode.   
     
     
         3 . The optical filter according to  claim 2 ,
 wherein the first electrode is formed around the first optical film in a plan view viewed in a substrate thickness direction of the first substrate,   the second electrode is formed around the second optical film in a plan view viewed in a substrate thickness direction of the second substrate,   the third electrode is formed around the third optical film in a plan view viewed in a substrate thickness direction of the third substrate, and   the fourth electrode is formed around the fourth optical film in a plan view viewed in a substrate thickness direction of the fourth substrate.   
     
     
         4 . The optical filter according to  claim 3 ,
 wherein the first, second, third, and fourth optical films are made of the same material.   
     
     
         5 . The optical filter according to  claim 1 ,
 wherein the second wavelength band is located on a longer wavelength side of the first wavelength band, and a bandwidth of the second wavelength band is wider than a bandwidth of the first wavelength band.   
     
     
         6 . The optical filter according to  claim 5 ,
 wherein “m” spectral bands are provided in the first wavelength band, and each of the m spectral bands has a predetermined bandwidth,   “n” spectral bands are provided in the second wavelength band, and each of the n spectral bands has the predetermined bandwidth, and   m<n.   
     
     
         7 . The optical filter according to  claim 6 ,
 wherein a holding period Δtm per spectral band when the spectral band of the first variable wavelength bandpass filter is changed “m” times and a holding period Δtn per spectral band when the spectral band of the second variable wavelength bandpass filter is changed “n” times are set to satisfy Δtm>Δtn.   
     
     
         8 . The optical filter according to  claim 7 ,
 wherein the controller sets Δtm and Δtn so that m×Δtm is equal to n×Δtn.   
     
     
         9 . The optical filter according to  claim 1 ,
 further comprising a third variable wavelength bandpass filter that extracts light of a third wavelength band located in the desired wavelength band and adjacent to the second wavelength band,   wherein the third wavelength band is located on a longer wavelength side of the first and second wavelength bands,   a bandwidth of the third wavelength band is set to be wider than a bandwidth of the first wavelength band,   “s” spectral bands are provided in the third wavelength band and each of the s spectral bands has a predetermined bandwidth, and   “m” spectral bands are provided in the first wavelength band, “n” spectral bands are provided in the second wavelength band, and:
 m<n≦s or m≦n<s; and 
 n=m+1 when m<n or s=n+1 when n<s. 
   
     
     
         10 . An optical filter module comprising:
 the optical filter according to  claim 1 ; and   light receiving devices that receive light having passed through the optical filter.   
     
     
         11 . An optical filter module comprising:
 the optical filter according to  claim 2 ; and   light receiving devices that receive light having passed through the optical filter.   
     
     
         12 . An optical filter module comprising:
 the optical filter according to  claim 3 ; and   light receiving devices that receive light having passed through the optical filter.   
     
     
         13 . A spectrometric measurement apparatus comprising:
 the optical filter according to  claim 1 ;   light receiving devices that receive light having passed through the optical filter; and   a signal processor that performs predetermined signal processing based on signals provided from the light receiving devices.   
     
     
         14 . A spectrometric measurement apparatus comprising:
 the optical filter according to  claim 2 ;   light receiving devices that receive light having passed through the optical filter; and   a signal processor that performs predetermined signal processing based on signals provided from the light receiving devices.   
     
     
         15 . A spectrometric measurement apparatus comprising:
 the optical filter according to  claim 3 ;   light receiving devices that receive light having passed through the optical filter; and   a signal processor that performs predetermined signal processing based on signals provided from the light receiving devices.   
     
     
         16 . An optical apparatus comprising the optical filter according to  claim 1 . 
     
     
         17 . An optical apparatus comprising the optical filter according to  claim 2 . 
     
     
         18 . An optical apparatus comprising the optical filter according to  claim 3 . 
     
     
         19 . An optical filter that receives light through a plurality of variable wavelength bandpass filters responsible for respective spectral bands,
 wherein the variable wavelength bandpass filters responsible for adjacent spectral bands include a first variable wavelength bandpass filter that is responsible for the spectral band located on a longer wavelength side,   a second variable wavelength bandpass filter that is responsible for the spectral band located on a shorter wavelength side,   the first variable wavelength bandpass filter having a wider spectral band than the second variable wavelength bandpass filter.