Patent ID: 7031619

Claim:
A control circuit for narrowing the pulse width of electromagnetic signals in communication networks by aligning an electromagnetic signal having a peaked spectrum function including a center wavelength and a wavelength selective device implementing a peaked passband function including a center wavelength, said circuit comprising: mechanism for applying a dither modulation signal at a dither modulation frequency to said electromagnetic signal, and inputting said dither modulated electromagnetic signal to said wavelength selective device to narrow the pulse width of the electromagnetic signal; and a feedback loop including i) mechanism for converting a portion of said dither modulated electromagnetic signal to an electric feedback signal, ii) mechanism for continuously comparing said feedback signal with said dither modulation signal and generating an error signal representing a difference between a frequency characteristic of said feedback signal and a dither modulation frequency, iii) mechanism for applying said error signal to better align the center wavelengths of the electromagnetic signal and the wavelength selective device, wherein said center wavelength of said electromagnetic signal and said wavelength selective device center wavelength become aligned when said frequency characteristic of said feedback signal is two times said dither modulation frequency, and iv) mechanism to selectively prevent said error signal from being applied to better align said center wavelengths.