A system and method for detecting the optical spectrum of an optical input signal. The system includes a tunable optical filter having a microresonator that is tunable across a plurality of states and a processor. The input signal is coupled into the microresonator, which is continuously tuned across a spectral range that is narrow relative to the targeted detection range. Signal information such as center wavelength, power distribution, and power strength are extracted from the measured output intensities resulting from the interaction of the unknown input signal with the tunable resonator at various tuned states. The processor includes a transfer function database with the resonant spectra of the tunable optical filter at predefined states. The processor applies an iterative non-linear deconvolution algorithm, and preferably an accelerated Richardson-Lucy algorithm, to calculate the spectrum of the input signal using the transfer function information and the intensity measurements.