A tuning technique for 10 GHz spaced, 128-channelfrequency-selection switches is described. It utilizes optical frequencydivision multiplexing (OFDM) information distribution systems with afrequency-shift-keying-direct-detection (FSK-DD) configuration. Thefrequencies of seven Mach-Zehnder (MZ) filters can be locked to thecenter frequency of the desired FSK signal by making use of FSK-ASKconversion effects of the transmittance characteristics of the MZfilters. The frequency offset and fluctuation of the MZ filters can becompressed to within 2% of their frequency spacing. This percentage islow enough to construct OFDM information distribution systems
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