Synchro-scanned rotating tunable optical disk filter for wavelength discrimination

We propose a novel wavelength-discrimination scheme using a rotating tunable optical disk filter with a circularly graded cavity thickness. The transmittance peak of the filter varies linearly with the angular position of the beam on the disk while the bandwidth remains constant. The rotation is synchronized to an electrical signal, enabling temporal measurement of an optical spectrum. The first experimental demonstration was performed at 670 r/m using a filter that ranged from 1560 to 1615 nm under a 3-dB bandwidth of 5 nm. Single-mode laser light was correctly discriminated. Good linearity of the transmittance-peak variation was confirmed by analyzing the measured trace waveform.