Wavelength locker

Abstract

Conventionally, wavelength locking and monitoring has been achieved used various components, including calibrated etalon filters, gratings, and arrays of color filters, which offer fairly bulky solutions that require complicated controls. An improved on-chip wavelength monitor comprises: a combination comb filter comprising a plurality of comb filters, each for receiving a test beams, and each comb filter including a substantially different FSR, e.g. 10× to 20× the next closest FSR. A controller dithers a phase tuning section of each comb filter to generate a maximum or minimum output in a corresponding photodetector indicative of the wavelength of the test signal.

We claim: 
     
         1 . An apparatus, comprising
 a laser source to generate a laser signal and a wavelength monitor, wherein the wavelength monitor comprises:
 a tap for tapping a portion of the laser signal from the laser source to form a test signal; 
 a splitter for splitting the test signal into a plurality of test beams; 
 a combination comb filter comprising a plurality of comb filters, each one of the plurality of comb filters connected to receive a respective one of the test beams, each comb filter having a different FSR; 
 a plurality of photodetectors, each one of the photodetectors configured for measuring light output from a respective one of the plurality of comb filters; 
 a plurality of phase tuning sections, each of the plurality of phase tuning sections for tuning a corresponding one of the comb filters; and 
 a controller to control the plurality of phase tuning sections to determine a wavelength of the test signal by generating a maximum output or a minimum output in some of the plurality of photodetectors, and configured to tune the laser source based on the determined wavelength of the test signal. 
   
     
     
         2 . The apparatus according to  claim 1 , wherein the controller is configured to determine the wavelength of the test signal based on values of pre-calibration values of electrical signals for controlling the some of the phase tuning sections to tune corresponding ones of the plurality of comb filters. 
     
     
         3 . The apparatus according to  claim 2 , wherein the controller is configured to dither the some of the plurality of phase tuning sections such that some of the test beams are locked to a peak or a null point of the corresponding ones of the plurality of comb filters. 
     
     
         4 . The apparatus according to  claim 1 , wherein the plurality of comb filters comprises at least a first of the comb filters and a second of the comb filters; and
 wherein the FSR of the second of the comb filters is at least 10 times larger than the FSR of the first of the comb filters.   
     
     
         5 . The apparatus according to  claim 4 , wherein the plurality of comb filters further comprises a third of the comb filters; wherein the FSR of the third of the comb filters is at least 10 times larger than the FSR of the second of the comb filters. 
     
     
         6 . The apparatus according to  claim 5 , wherein the FSR of the first of the comb filters is between 10 GHz to 40 GHz;
 wherein the FSR of the second of the comb filters is between 100 GHz to 800 GHz; and   wherein the FSR of the third of the comb filters is between 2000 GHz to 16000 GHz.   
     
     
         7 . The wavelength monitor according to  claim 5 , wherein each of the plurality of phase tuning sections are configured to provide wavelength accuracy of at least 10 to 30 times finer than the first FSR, the second FSR and the third FSR. 
     
     
         8 . The apparatus according to  claim 1 , wherein each one of the plurality of comb filters comprises a ring resonator. 
     
     
         9 . The apparatus according to  claim 8 , wherein at least one of the ring resonators comprises waveguides with positive and negative thermal coefficients on each side thereof to minimize temperature sensitivity between each side. 
     
     
         10 . The apparatus according to  claim 8 , wherein each ring resonator comprises a drop port and a through port; and wherein one of the plurality of photodetectors is coupled to each drop port. 
     
     
         11 . The apparatus according to  claim 1 , wherein each of the plurality of comb filters comprises a Mach-Zehnder filter. 
     
     
         12 . The apparatus according to  claim 11 , wherein at least one of the Mach-Zehnder filters comprises a first arm and a second arm; and wherein the first arm includes a first polarization rotator for rotating a polarization of light in the first arm, and a second polarization rotator for rotating back the polarization of light in the first arm. 
     
     
         13 . The apparatus according to  claim 12 , wherein the first arm comprises Silicon and the second arm comprises Silicon Nitride. 
     
     
         14 . The apparatus according to  claim 12 , wherein the first arm comprises a strip waveguide, and the second arm comprises a rib waveguide. 
     
     
         15 . The apparatus according to  claim 12 , wherein the first arm includes a width that is different than a width of the second arm. 
     
     
         16 . The apparatus according to  claim 1 , further comprising a temperature sensor; wherein the temperature sensor comprises at least three temperature sensors; and wherein a heat source is placed outside an area defined by the at least three sensors. 
     
     
         17 . The apparatus according to  claim 16 , wherein each of the at least three temperature sensors comprises two diodes with different lengths.