A Novel Locking Technique for Very Narrow Tunable Optical Filters With Sub-GHz 3-dB Bandpass

We demonstrate a novel locking technique for very narrow bandpass optical tunable filters. Locking stability within 1% of the 3-dB bandwidth was achieved experimentally on filters with 3-dB bandwidths ranging from 1 GHz, 25 MHz, to 1 MHz.