Method and apparatus for a low parasitic capacitance butt-joined passive waveguide connected to an active structure

Abstract

Undoped layers are introduced in the passive waveguide section of a butt-joined passive waveguide connected to an active structure. This reduces the parasitic capacitance of the structure.

1 . An active-passive butt-joint structure for reduced parasitic capacitance comprising:
 a III-V substrate;   an active structure disposed over said substrate comprised of an active region sandwiched between two separate confinement heterostructure layers; and   a passive butt-joint structure comprised of a passive Q-waveguide core sandwiched between two undoped III-V layers, said passive butt-joint structure disposed over said substrate and aligned adjacent to said active structure such that said active region is adjacent to said passive Q-waveguide core.   
   
   
       2 . The structure of  claim 1  wherein said undoped III-V layers are comprised of InP. 
   
   
       3 . The structure of  claim 1  wherein said substrate is comprised of N-InP. 
   
   
       4 . The structure of  claim 1  wherein a first thickness of each said two undoped III-V layers is adjusted to control parasitic capacitance. 
   
   
       5 . The structure of  claim 1  wherein said active structure comprises an EA-modulator. 
   
   
       6 . The structure of  claim 1  wherein a second thickness of said passive Q-waveguide core is selected to achieve a good mode match to said active region. 
   
   
       7 . The structure of  claim 1  wherein a composition of said passive Q-waveguide core is selected to achieve a good mode match to said active region. 
   
   
       8 . The structure of  claim 1  wherein said active structure comprises a laser. 
   
   
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