Patent ID: 8139281

Claim:
A tunable optical filter apparatus comprising: a filter driver configured to generate a filter driver signal, the filter driver signal comprising a dither signal; a filter device coupled to the filter driver, the filter device configured to receive a filter input signal and the filter driver signal, the filter device configured to generate a filter output signal based on the filter input signal and the filter driver signal, the filter input signal comprising a reference optical signal and an optical input signal; a detector device coupled to the filter device, the detector device configured to receive a detector input signal and to generate a detector output signal, the detector input signal comprising at least a portion of the filter output signal, the detector output signal based on an odd order harmonic signal and an even order harmonic signal of the detector input signal based on a frequency of the dither signal; and a controller device coupled to the detector device, the filter device and the filter driver, the controller device configured to receive the detector output signal, the controller device configured to determine a ratio of the odd order harmonic signal to the even order harmonic signal, to compare the ratio to a predetermined setpoint ratio and to generate a control feedback signal for generating a new filter driver signal, the control feedback signal based on the comparison of the ratio of the odd order harmonic signal to the even order harmonic signal, to the predetermined setpoint ratio.