Tuning the index of a waveguide structure

Abstract

The index of refraction of waveguide structures can be varied by altering carrier concentration. The waveguides preferably comprise semiconductors like silicon that are substantially optically transmissive at certain wavelengths. Variation of the carrier density in these semiconductors may be effectuated by inducing an electric field within the semiconductor for example by apply a voltage to electrodes associated with the semiconductor. Variable control of the index of refraction may be used to implement a variety of functionalites including, but not limited to, tunable waveguide gratings and resonant cavities, switchable couplers, modulators, and optical switches.

What is claimed is:  
     
         1 . A waveguide grating comprising a waveguide for propagating light in a longitudinal direction, comprising a plurality of elongate members oriented transverse to said longitudinal direction, said members disposed relative to said waveguide to form a grating for coupling light out of the waveguide, said waveguide having a carrier density at each of said members, said members including respective electrodes for applying an electric field to said waveguide, said electric field altering said carrier density in said waveguide such that said coupling is altered.  
     
     
         2 . The waveguide grating of  claim 1 , wherein the waveguide comprises semiconductor.  
     
     
         3 . The waveguide grating of  claim 2 , wherein the waveguide comprises silicon.  
     
     
         4 . The waveguide grating of  claim 2 , further comprising an insulating layer disposed between said elongated members and said waveguide.  
     
     
         5 . The waveguide grating of  claim 1 , wherein said waveguide comprises a strip loaded waveguide.  
     
     
         6 . The waveguide grating of  claim 1 , wherein said strip loaded waveguide comprises a slab, a strip formed thereon, and an intermediate layer between said strip and said slab.  
     
     
         7 . The waveguide grating of  claim 6 , wherein said slab comprises semiconductor and said intermediate layer comprises dielectric material.  
     
     
         8 . The waveguide grating of  claim 7 , further comprising at least one electrode juxtaposed with respect to said slab to induce an electric field through said dielectric intermediate layer and into said semiconductor slab to alter the distribution of carriers in said semiconductor slab thereby altering the effective index of said strip loaded waveguide.