Controlling back scattering in optical waveguide systems

Abstract

Back scattering in an optical waveguide at an operating wavelength is controlled by adjusting an optical phase of light propagating in the waveguide at one or more locations along the waveguide. A portion of the back scattered light is tapped off near an input port and coupled into a photodetector. A controller detects changes in the photodetector signal and adjusts an optical phase tuner configured to control the optical phase of light in the waveguide at the selected location or locations. The optical phase tuner may be configured to vary the refractive index of at least a portion of the waveguide.

1 - 20 . (canceled) 
     
     
         21 . A method for controlling back scattering of input light in an optical waveguide system, the method comprising:
 coupling a portion of backscattered light into a first photodetector (PD), the backscattered light produced by back-scattering of the input light in the optical waveguide system; and,   acting upon at least one optical waveguide in the optical waveguide system so as to vary an optical phase of the backscattered light at one or more locations along the at least one optical waveguide in dependence upon a first electrical PD signal from the first PD, or a signal derived at least in part therefrom, so as to control an optical power of the portion of the backscattered light coupled into the first PD.   
     
     
         22 . The method of  claim 21 , wherein the acting comprises adjusting a temperature of at least a portion of the at least one optical waveguide in dependence upon the first electrical PD signal. 
     
     
         23 . The method of  claim 21 , including measuring a return optical loss of the optical waveguide system based at least in part upon the first electrical PD signal, wherein the acting is performed so as to reduce the return optical loss at an operating wavelength. 
     
     
         24 . The method of  claim 21  wherein the at least one optical waveguide comprises two waveguide sections optically connected in sequence, and wherein the acting comprises changing the optical phase of the backscattered light between the two waveguide sections. 
     
     
         25 . The method of  claim 21  wherein the acting comprises locally varying a refractive index of the at least one optical waveguide at the one or more locations. 
     
     
         26 . The method of  claim 25  comprising tapping off the portion of the backscattered light at or near an input port to form first tapped-off light, wherein the acting comprises varying the optical phase of the backscattered light in dependence at least in part upon the first electrical PD signal so as to decrease, or at least stabilize, the optical power of the backscattered light at the input port. 
     
     
         27 . The method of  claim 25  wherein the acting comprises:
 varying a refractive index of the at least one optical waveguide at the one or more locations by:
 applying an electrical voltage or current at the one or more locations responsive to the first electrical PD signal, or 
 heating the at least one optical waveguide at the one or more locations responsive to the first electrical PD signal. 
 
 
     
     
         28 . The method of  claim 21  comprising providing a plurality of tunable local phase shifters disposed at a plurality of locations in the optical waveguide system, wherein the acting comprises selecting a first subset of the tunable local phase shifters for tuning in dependence upon the first electrical PD signal when the input light comprises a first operating wavelength, and selecting a second subset of the tunable local phase shifters for tuning in dependence upon the first electrical PD signal when the input light comprises a second operating wavelength that is different from the first operating wavelength, wherein the second subset is different from the first subset. 
     
     
         29 . The method of  claim 21  for controlling the back scattering in a selected wavelength range, further comprising blocking wavelengths of the backscattered light outside of the selected wavelength range from coupling into the first PD. 
     
     
         30 . The method of  claim 23  comprising measuring an optical power of the input light to determine the optical return loss.