Spectral alignment of a wdm device to a specified frequency grid

Abstract

A WDM device having a controller that individually controls the operating parameters of tunable lasers and the temperatures of an optical multiplexer and etalon. The device employs a spectral analyzer to measure the spectral composition of the optical output signal produced by the device. Based on the analyses of the measured spectral composition, the controller sets the temperatures of the tunable lasers, optical multiplexer, and optical etalon to values that cause: (i) middle frequencies of transmission bands of the optical multiplexer to be spectrally aligned with the corresponding frequencies of the specified frequency grid, (ii) each laser line to be properly positioned within the corresponding transmission band, and (iii) transmission resonances of the optical etalon to be properly positioned with respect to the laser lines.

What is claimed is: 
     
         1 . An optical method, comprising:
 receiving light from a plurality of lasers, each laser lasing at a corresponding lasing wavelength and being connected to a different optical input port of an optical multiplexer that is periodic in its frequency response;   multiplexing, using the optical multiplexer, the light received from the lasers to produce an optical output signal;   measuring, using a spectral analyzer, a spectral composition of the optical output signal over one or more wavelength ranges, wherein each of said one or more wavelength ranges excludes the lasing wavelengths; and   adjusting a spectral location of optical pass bands of the optical multiplexer based on the spectral composition measured by the spectral analyzer, said adjustment being performed by changing a temperature of the optical multiplexer.   
     
     
         2 . The method of  claim 1 , wherein the adjusting includes operating a first temperature-control unit to change the temperature of the optical multiplexer based on the spectral composition measured by the spectral analyzer. 
     
     
         3 . The method of  claim 1 , wherein the adjusting includes adjusting a heater or cooler located along part of the optical multiplexer. 
     
     
         4 . The method of  claim 1 , wherein the adjusting includes changing the temperature of the optical multiplexer to cause a series of regularly spaced pass bands thereof to be spectrally aligned with a regular grid. 
     
     
         5 . The method of  claim 1 , wherein the one or more wavelength ranges include a first wavelength range and a second wavelength range, said first and second wavelength ranges being disjoint from one another by a wavelength interval that includes the lasing wavelengths. 
     
     
         6 . The method of  claim 5 , wherein one or each of the first and second wavelength ranges has a respective width of at least a free spectral range of the optical multiplexer. 
     
     
         7 - 8 . (canceled) 
     
     
         9 . The method of  claim 5 , wherein wavelengths of the first wavelength range are shorter than wavelengths in the wavelength interval, and wavelengths of the second wavelength range are longer than the wavelengths in the wavelength interval. 
     
     
         10 . The method of  claim 1 , further comprising measuring, using the spectral analyzer, a spectral composition of the optical output signal over a wavelength interval that includes the lasing wavelengths. 
     
     
         11 . The method of  claim 10 , further comprising operating a plurality of laser-control units, each laser-control unit coupled to a corresponding one of the lasers, to change at least one of the lasing wavelengths of the lasers based on the spectral composition measured over said wavelength interval. 
     
     
         12 . The method of  claim 11 , wherein the change of the at least one of the lasing wavelengths is performed by changing at least one of a temperature and an injection current of at least one of the lasers. 
     
     
         13 . The method of  claim 2 , wherein the multiplexing includes:
 passing light received from an output port of the optical multiplexer through an optical etalon to produce a filtered optical signal, wherein said filtered optical signal is the optical output signal; and   operating a second temperature-control unit to change a temperature of the optical etalon based on the spectral composition measured by the spectral analyzer.   
     
     
         14 . The method of  claim 13 , wherein the change of the temperature of the optical etalon is configured to cause a transmission spectrum of the optical etalon to shift by at least a free spectral range of the optical etalon. 
     
     
         15 . The method of  claim 13 , wherein the measuring includes:
 recording the spectral composition at a first temperature of the optical etalon;   recording the spectral composition at a different second temperature of the optical etalon; and   adding or averaging the spectral compositions recorded at the first temperature and the second temperatures.   
     
     
         16 - 20 . (canceled)