Devices Based on Optical Waveguides with Adjustable Bragg Gratings

Abstract

A system for filtering light propagating in a waveguide is described. The system utilizes an adjustable periodic grating which induces mode coupling of predetermined frequencies of light propagating in the waveguide.

1 . A variable delay apparatus comprising:
 a waveguide segment; and   an adjustable periodic grating moveable along the waveguide segment in the direction of light propagation in the waveguide, the adjustable periodic grating inducing Bragg reflection in the waveguide.   
   
   
       2 . The variable delay apparatus of  claim 1  further comprising:
 a circulator to transmit light to the waveguide segment and to receive light reflected within the waveguide segment.   
   
   
       3 . The variable delay apparatus of  claim 1  wherein the adjustable periodic grating is moved by a screw. 
   
   
       4 . A method of transferring a light signal from a first polarization maintaining fiber to a second polarization maintaining fiber comprising
 coupling the first polarization maintaining fiber to the second polarization maintaining fiber at a joint to form a combination polarization maintaining fiber;   position a periodic grating to induce mode coupling of one frequency of light in the combination polarization maintaining fiber;   adjusting pressure between the periodic grating and the combination polarization maintaining fiber to couple power between a fast mode and a slow mode of the combination polarization maintaining fiber.   
   
   
       5 . A tunable polarizer comprising:
 a polarization maintaining fiber including a core and a cladding; and   a periodic grating coupled to the polarization maintaining fiber to couple a first polarization mode of a first wavelength into the cladding.   
   
   
       6 . The tunable apparatus of  claim 5  wherein the periodic grating presses against the polarization maintaining fiber to induce a periodic change in a refractive index of the polarization maintaining fiber to couple the first polarization mode of the first wavelength into the cladding.