Integrated tunable optical filter

Abstract

An integrated tunable optical filter comprising a substrate made of a semiconducting material. The substrate includes first and second sections. The first section forms a tunable transmission filter, based on a codirectional coupler having a low selectivity. The second section forms a reflection filter with a reflection spectrum containing a number of peaks. A first injector, designed for current injection into said first section, is provided. Thus, the filter response of the first section is shifted in wavelength over a large wavelength range. There is also a second injector, designed for current injection into the second section. As a result, the reflective spectrum of the second section is slightly shifted in wavelength, in such a way that one reflection peak of the reflection spectrum corresponds to the coupling wavelength of the first section. Consequently, the total filter response has a very narrow bandwidth and wide tunability.

We claim: 
     
       1. An integrated tunable optical filter comprising: a substrate made of semiconducting material,   a first section on said substrate forming a transmission filter having a low spectral selectivity, said first section including a first waveguide system with upper and lower waveguides, a periodic rib shaped structure .[.between said upper and lower.]. .Iadd.adjacent at least one of said .Iaddend.waveguides defining a filter response with a central coupling wavelength, and   a second section on said substrate forming a reflector with a spectral reflection with a plurality of reflection peaks, said second section including a second waveguide coupled with said .[.lower.]. .Iadd.first .Iaddend.waveguide .Iadd.system .Iaddend.in said first section and having a periodically broken short-period reflection structure including short period stripped regions alternating with non-stripped regions;   first means for injecting current into said first section, said filter response of said first section being shifted in wavelength over a range covering a plurality of said reflection peaks of said second section; and   second means for injecting current into said second section, said reflection spectrum of said second section being shifted in wavelength and one reflection peak of said plurality of reflection peaks corresponding to said central coupling wavelength of said first section;   wherein said optical filter has a reflection response .[.in said upper waveguide.]. with a narrow bandwidth and wide tunability.   
     
     
       2. An optical filter according to claim 1, wherein said .[.second.]. .Iadd.first .Iaddend.and second waveguides are formed in a single layer interface. 
     
     
       3. An optical filter according to claim 1, wherein said first section forms a codirectional optical coupler. 
     
     
       4. An optical filter according to claim 3, wherein said short-period reflection structure and said rib-shaped structure are formed in a single layer interface. 
     
     
       5. An optical filter according to claim 3, wherein said rib-shaped structure has a period of 10-50 μm. 
     
     
       6. An optical filter according to claim 5, wherein said short-period reflection structure is sawtooth-shaped. 
     
     
       7. An optical filter according to claim 5, wherein said short-period reflection structure and said rib-shaped structure each have a period and wherein said short period reflection structure has a period less than said period of said rib-shaped structure.