Optical system and method for locking a wavelength of a tunable laser

Abstract

An optical system can lock a wavelength of a tunable laser to a specified wavelength of a temperature-insensitive spectral profile of a spectral filter. In some examples, the spectral filter, such as a Fabry-Perot filter, can have a temperature-insensitive peak wavelength and increasing attenuation at wavelengths away from the peak wavelength. The spectral filter can spectrally filter the laser light to form filtered laser light. A detector can detect at least a fraction of the filtered laser light. Circuitry coupled to the detector and the laser can tune the tunable laser to set a signal from the detector to a specified value corresponding to a specified wavelength in the spectral profile, and thereby adjust the selectable wavelength of the tunable laser to match the specified wavelength. In some examples, the optical system can include a polarization rotator, and can use polarization to separate incident light from return light.

What is claimed is: 
     
         1 . An optical system, comprising:
 a tunable laser to generate light at a selectable wavelength;   a splitter that forms a output light and a split light portion from the light;   an interference based optical filter that filters the split light portion to form a filtered light, the interference based optical filter having a peak wavelength at which an output of the interference based optical filter attenuates at wavelengths away from the peak wavelength;   a detector to detect the filtered light; and   control circuitry to lock a wavelength of the output light to match the peak wavelength of the interference based optical filter by changing the selectable wavelength of the tunable laser such that a signal that is generated by the detector from the filtered light is at a maximum.   
     
     
         2 . The optical system of  claim 1 , wherein the interference based optical filter is a Fabry-Perot optical filter. 
     
     
         3 . The optical system of  claim 1 , wherein the interference based optical filter comprises a first reflective surface, a second reflective surface, and a cavity between the first reflective surface and the second reflective surface. 
     
     
         4 . The optical system of  claim 1 , wherein the interference based optical filter is configured to compensate for temperature changes to one or more components of the optical system. 
     
     
         5 . The optical system of  claim 4 , wherein the interference based optical filter compensates for temperature changes by balancing a path of a cavity of the interference based optical filter and a refractive index of material that forms the cavity. 
     
     
         6 . The optical system of  claim 1 , wherein the tunable laser and the interference based optical filter are formed in a photonic integrated circuit. 
     
     
         7 . The optical system of  claim 1 , wherein the optical system further comprises an optical modulator to modulate the light from the tunable laser. 
     
     
         8 . The optical system of  claim 1 , wherein the optical system further comprises a port that directs modulated light to an optical receiver. 
     
     
         9 . The optical system of  claim 1 , wherein the splitter is an optical tap that taps a portion of the light from the tunable laser to form the split light portion. 
     
     
         10 . The optical system of  claim 1 , wherein the splitter is a grating. 
     
     
         11 . A method for tuning a tunable laser, the method comprising:
 generating light at a selectable wavelength with the tunable laser;   splitting the light using a splitter for form an output light and a split light portion;   filtering the split light portion of the light using an interference based optical filter to form a filtered light, the interference based optical filter having a peak wavelength at which an output of the interference based optical filter attenuates at wavelengths away from the peak wavelength;   detecting the filtered light using a detector; and   locking a wavelength of the output light to match the peak wavelength of the interference based optical filter using control circuitry that changes the selectable wavelength of the tunable laser such that a signal that is generated by the detector from the filtered light is at a maximum.   
     
     
         12 . The method of  claim 11 , wherein the interference based optical filter is a Fabry-Perot optical filter. 
     
     
         13 . The method of  claim 11 , wherein the interference based optical filter comprises a first reflective surface, a second reflective surface, and a cavity between the first reflective surface and the second reflective surface. 
     
     
         14 . The method of  claim 11 , wherein the interference based optical filter is configured to compensate for temperature changes to the tunable laser. 
     
     
         15 . The method of  claim 14 , wherein the interference based optical filter compensates for temperature changes by balancing a path of a cavity of the interference based optical filter and a refractive index of material that forms the cavity. 
     
     
         16 . The method of  claim 11 , wherein the tunable laser and the interference based optical filter are formed in a photonic integrated circuit. 
     
     
         17 . The method of  claim 11 , further comprising: modulating the light using a modulator to form a modulated light. 
     
     
         18 . The method of  claim 17 , further comprising: directing the modulated light to an optical receiver. 
     
     
         19 . The method of  claim 11 , wherein the splitter is an optical tap that taps a portion of the light from the tunable laser to form the split light portion. 
     
     
         20 . The method of  claim 11 , wherein the splitter is a grating.