Integrated optical filters utilizing resonators

Abstract

A filtering method and optical filter structure are presented. The structure comprises an input waveguide, an output waveguide, and a filter stage formed by at least one closed loop resonator optically coupled to the input and output waveguides. A level of the coupling from each of the waveguides to the resonator is at least 5 times greater than a loss-per-revolution of the resonator. The filter structure thus provides for reducing a bandwidth and insertion loss while filtering at least one optical channel from a multi-channel light signal.

1 . An optical filter structure comprising an input waveguide, an output waveguide, and a filter stage formed by at least one closed loop resonator optically coupled to the input and output waveguides, wherein a level of the coupling from each of the waveguides to the resonator is at least 5 times greater than a loss-per-revolution of the resonator, the filter structure providing for reducing a bandwidth and insertion loss while filtering at least one optical channel from a multi-channel light signal.  
   
   
       2 . The structure according to  claim 1 , wherein said at least one resonator and the waveguides are made of at least one dielectric material with a refractive index different from a refractive index of a surrounding medium.  
   
   
       3 . The structure according to  claim 1 , wherein the at least one closed loop resonator has a free spectral range of about 200-1000 GHz.  
   
   
       4 . The structure according to  claim 1 , comprising at least one additional closed loop resonator, the at least two closed loop resonators being optically coupled to each other.  
   
   
       5 . The structure according to  claim 4 , wherein the at least two closed loop resonators are arranged in a serial-cascaded relationship between the input and output waveguides and are directly optically coupled to each other.  
   
   
       6 . The structure according to  claim 4 , wherein the at least two closed loop resonators are arranged in a spaced-apart relationship between the input and output waveguides, each of the resonators being optically coupled to said waveguides, and the resonators being optically coupled to each other via segments of said waveguides between the resonators, thereby forming a compound closed loop resonator.  
   
   
       7 . The structure according to  claim 4 , wherein the at least two closed loop resonators are arranged in a serial-cascaded relationship and are optically coupled to each other via at least one additional waveguide, the resonators at opposite sides of the additional waveguides thereby forming first and second filter stages, respectively.  
   
   
       8 . The structure according to  claim 5 , comprising an additional filter stage formed by one of said two waveguides, an additional waveguide spaced-apart therefrom and at least one additional closed loop resonator accommodated between said one of said two waveguides and said additional waveguide.  
   
   
       9 . The structure according to  claim 8 , wherein the closed loop resonators between said one of said two waveguides and said additional waveguide are arranged in a serial-cascaded relationship being directly optically coupled to each other.  
   
   
       10 . The structure according to  claim 8 , wherein the closed loop resonators between said one of said two waveguides and said additional waveguide are arranged in a spaced-apart relationship, each being optically coupled to these waveguides and optically coupled to the adjacent resonator via segments of these waveguides between the adjacent resonators.  
   
   
       11 . The structure according to  claim 6 , comprising an additional filter stage formed by one of said two waveguides, an additional waveguide spaced-apart therefrom and at least one additional closed loop resonator accommodated between said one of said two waveguides and said additional waveguide.  
   
   
       12 . The structure according to  claim 11 , wherein the closed loop resonators between said one of said two waveguides and said additional waveguide are arranged in a serial-cascaded relationship being directly optically coupled to each other.  
   
   
       13 . The structure according to  claim 11 , wherein the closed loop resonators between said one of said two waveguides and said additional waveguide are arranged in a spaced-apart relationship, each being optically coupled to these waveguides and optically coupled to the adjacent resonator via segments of these waveguides between the adjacent resonators.  
   
   
       14 . The structure according to  claim 7 , wherein the resonators of the first filter stage are arranged in a serial-cascaded relationship being directly optically coupled to each other.  
   
   
       15 . The structure according to  claim 7 , wherein the resonators of the second filter stage are arranged in a serial-cascaded relationship being directly optically coupled to each other.  
   
   
       16 . The structure according to  claim 7 , wherein the resonators of the first filter stage are arranged in a spaced-apart parallel relationship, each being optically coupled to said input and said additional waveguides and optically coupled to the adjacent resonator via segments of these waveguides between the adjacent resonators.  
   
   
       17 . The structure according to  claim 7 , wherein the resonators of the second filter stage are arranged in a spaced-apart parallel relationship, each being optically coupled to said additional and said output waveguides and optically coupled to the adjacent resonator via segments of these waveguides between the adjacent resonators.  
   
   
       18 . The structure according to  claim 4 , wherein the closed loop resonators are characterized by the at least one of the following: 
 the resonators have equal free spectral ranges;    the resonators have different free spectral ranges;    a free spectral range of the closed loop resonator is about 200-1000 GHz;    each of the resonators is wavelength tunable at least across its own free spectral range;    a ratio between the largest free spectral range and a bandwidth of the filter structure substantially does not exceed 30;    the coupling level between the waveguides and the resonators is higher than 12%.    
   
   
       19 . A tunable optical filter structure comprising at least two waveguides and at least two closed loop resonator optically coupled to the waveguides and to each other, wherein a level of the coupling from each of the waveguides to the resonator is at least 5 times greater than a loss-per-revolution of the resonator.  
   
   
       20 . The structure according to  claim 19 , wherein the closed loop resonators are characterized by the at least one of the following: 
 the resonators have equal free spectral ranges;    the resonators have different free spectral ranges;    a free spectral range of the closed loop resonator is about 200-1000 GHZ;    each of the resonators is wavelength tunable at least across its own free spectral range;    a ratio between the largest free spectral range and a bandwidth of the filter structure substantially does not exceed 30;    the coupling level between the waveguides and the resonators is higher than 12%.    
   
   
       21 . An optical filter structure for filtering at least one optical channel from a multi-channel light signal, the filter structure comprising an input waveguide, an output waveguide, and a filter stage formed by at least one closed loop resonator optically coupled to the input and output waveguides, wherein a level of the coupling from each of the waveguides to the resonator is at least 5 times greater than a loss-per-revolution of the resonator, the filter structure thereby reducing a bandwidth and insertion loss of the filtering.  
   
   
       22 . A method for reducing a bandwidth and insertion loss while filtering at least one optical channel from a multi-channel light signal, the method comprising inputting the light signal into an input waveguide of an optical filter structure that comprises at least one closed loop resonator optically coupled to said input waveguide and at least one output waveguide with a level of the coupling from each of the waveguides to the resonator being at least 5 times greater than a loss-per-revolution of the resonator.  
   
   
       23 . The method according to  claim 22 , wherein a free spectral range of the closed loop resonator is about 200-1000 GHz.  
   
   
       24 . A method for reducing a bandwidth and insertion loss while filtering at least one optical channel from a multi-channel light signal, the method comprising passing the light signal through an input waveguide of an optical filter structure, that comprises at least two closed loop resonators optically coupled to said input waveguide and at least one output waveguide and to each other, with a level of the coupling from each of the waveguides to the resonator being at least 5 times greater than a loss-per-revolution of the resonator.  
   
   
       25 . The method according to  claim 24 , wherein the resonators have equal free spectral ranges.  
   
   
       26 . The method according to  claim 24 , wherein at least some of the resonators have different free spectral ranges.  
   
   
       27 . The method according to  claim 24 , wherein a free spectral range of the closed loop resonator is about 200-1000 GHz.  
   
   
       28 . The method according to  claim 24 , wherein each of the resonators is wavelength tunable at least across its own free spectral range.  
   
   
       29 . The method according to  claim 24 , wherein a ratio between the largest free spectral range and a bandwidth of the filter structure substantially does not exceed 30.  
   
   
       30 . The method according to  claim 24 , wherein the coupling level between the waveguides and the resonators is higher than 12%.