Wavelength locking filter

Abstract

An optical system can automatically lock an adjustable spectral filter to a first wavelength of an incoming light signal, and can automatically filter an additional incoming light signal at the first wavelength. A tunable filter can have a filtering spectrum with an adjustable peak wavelength and increasing attenuation at wavelengths away from the adjustable peak wavelength. The tunable filter can receive first input light, having a first wavelength, and can spectrally filter the first input light to form first output light. A detector can detect at least a fraction of the first output light. Circuitry coupled to the detector and the tunable filter can tune the tunable filter to maximize a signal from the detector and thereby adjust the peak wavelength to match the first wavelength. The tunable filter further can receive second input light and spectrally filter the second input light at the first wavelength.

What is claimed is: 
     
         1 . An optical device comprising:
 a first waveguide to propagate a first light;   a second waveguide to propagate a second light;   a tunable filter coupled to the first waveguide and the second waveguide, the tunable filter having an adjustable peak wavelength, the tunable filter to generate, from the second light, tuned light that has a wavelength of the first light, the tunable filter generating the tuned light by tuning the second light using the adjustable peak wavelength; and   a third waveguide to output the tuned light.   
     
     
         2 . The optical device of  claim 1 , wherein attenuation from the tunable filter increases at wavelengths away from the adjustable peak wavelength. 
     
     
         3 . The optical device of  claim 1 , wherein the first light is an incoming light received using the first waveguide. 
     
     
         4 . The optical device of  claim 3 , wherein the optical device further comprises an optical modulator, wherein the second light is generated by a light source and the second light is an outgoing light that is modulated by the optical modulator. 
     
     
         5 . The optical device of  claim 4 , wherein the incoming light and the outgoing light simultaneously propagate on one or more optical paths in the tunable filter. 
     
     
         6 . The optical device of  claim 4 , wherein the incoming light and the outgoing light counter-propagate in opposite directions on one or more optical paths of the tunable filter. 
     
     
         7 . The optical device of  claim 1 , further comprising:
 a detector to detect a portion of the first light.   
     
     
         8 . The optical device of  claim 7 , further comprising control circuitry coupled to the detector to tune the tunable filter to the wavelength of the first light. 
     
     
         9 . The optical device of  claim 1 , wherein the tunable filter is an optical ring resonator. 
     
     
         10 . The optical device of  claim 9 , wherein the optical ring resonator is tuned by a heater in the optical device. 
     
     
         11 . The optical device of  claim 1 , wherein the tunable filter has a free spectral range that is greater than a range of wavelengths than the wavelength of the first light. 
     
     
         12 . The optical device of  claim 1 , wherein the second light is generated by a tunable laser. 
     
     
         13 . A method for propagating light in an optical device comprising:
 propagating a first light on a first waveguide of the optical device;   propagating a second light on a second waveguide of the optical device;   tuning the second light using a tunable filter of the optical device to form a tuned light having a wavelength of the first light, the tunable filter being coupled to the first waveguide and second waveguide, the tunable filter comprising an adjustable peak wavelength, the tunable filter forming the tuned light by tuning the second light using the adjustable peak wavelength; and   outputting the tuned light on a third waveguide.   
     
     
         14 . The method of  claim 13 , wherein the first light is an incoming light that is received using the first waveguide. 
     
     
         15 . The method of  claim 14 , wherein the optical device further comprises an optical modulator, wherein the first light is generated by a light source is an outgoing light that is modulated by the optical modulator. 
     
     
         16 . The method of  claim 15 , wherein the incoming light and the outgoing light simultaneously propagate on one or more optical paths in the tunable filter. 
     
     
         17 . The method of  claim 15 , wherein the incoming light and the outgoing light counter-propagate in opposite directions on one or more optical paths of the tunable filter. 
     
     
         18 . The method of  claim 13 , wherein the optical device further comprises a detector to detect a portion of the first light. 
     
     
         19 . The method of  claim 18 , wherein the optical device further comprises control circuitry coupled to the detector to tune the tunable filter to the wavelength of the first light. 
     
     
         20 . The method of  claim 13 , wherein the tunable filter is an optical ring resonator.