Tunable resonant cavity based on the field effect in semiconductors

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.

1 . (canceled)  
   
   
       2 . A method comprising: 
 propagating light in an optical resonator comprising doped semiconductor;    forward biasing the doped semiconductor to accumulate free carriers in at least a portion of the doped semiconductor; and    applying an electric field though an insulator to at least a portion of the doped semiconductor to alter free carrier distribution in the doped semiconductor, thereby changing a resonant frequency of the optical resonator.    
   
   
       3 . The method of  claim 2 , wherein the doped semiconductor comprises p-type and n-type regions.  
   
   
       4 . The method of  claim 3 , wherein forward biasing comprises coupling the p-type region to a relatively higher voltage and coupling the n-type region to a relatively lower voltage.  
   
   
       5 . The method of  claim 2 , wherein the optical resonator guides light along a closed path.  
   
   
       6 . The method of  claim 2 , wherein the optical resonator guides light along a circular path.  
   
   
       7 . The method of  claim 2 , wherein altering the free carrier distribution in the doped semiconductor introduces refractive index variations in the optical resonator.  
   
   
       8 . The method of  claim 2 , wherein the free carrier distribution is altered through a field effect.  
   
   
       9 . The method of  claim 2 , wherein the optical resonator is formed on a semiconductor substrate.  
   
   
       10 . The method of  claim 9 , further comprising an optical waveguide formed on the semiconductor substrate.  
   
   
       11 . The method of  claim 10 , wherein light is coupled from the optical waveguide to the optical resonator.  
   
   
       12 . An apparatus comprising: 
 an optical resonator comprising doped semiconductor, wherein the doped semiconductor is forward biased to accumulate free carriers in at least a portion of the doped semiconductor; and    at least one electrode positioned to apply an electric field through an insulator to a portion of the semiconductor to alter free carrier distribution in the doped semiconductor, thereby changing a resonant frequency of the optical resonator.    
   
   
       13 . The apparatus of  claim 12 , wherein the doped semiconductor is forward biased by applying a positive voltage to a p-type region and a negative voltage to an n-type region of the doped semiconductor.  
   
   
       14 . The apparatus of  claim 12 , wherein the electrode is coupled to a variable voltage source that controls a magnitude of the applied electric field.  
   
   
       15 . The apparatus of  claim 12 , wherein the optical resonator is a strip loaded waveguide having a closed optical path.  
   
   
       16 . The apparatus of  claim 12 , wherein altering the free carrier distribution in a region of the doped semiconductor changes a refractive index for that region of the doped semiconductor.  
   
   
       17 . The apparatus of  claim 12 , wherein the free carrier distribution in the doped semiconductor is modulated though a field effect.  
   
   
       18 . The apparatus of  claim 12 , further comprising a waveguide that is juxtaposed with the optical resonator to permit coupling of light between the waveguide and the optical resonator.  
   
   
       19 . The apparatus of  claim 18 , wherein a coupling coefficient between the waveguide and the optical resonator is modulated by separately controlling a first refractive index in the waveguide and a second refractive index in the optical resonator.