The implementation of optical fiber transversal filters incorporating single-mode fibers and bidirectional couplers using a cascade synthesis procedure is discussed. The filter structures fabricated by this method exhibit good filtering characteristics in a broad frequency region. Single cascaded filters with first passband center frequencies from few MHz to over 3 GHz and with quality factors over 250 have been demonstrated. Many single cascades can also be cascaded together to form a multicascaded structure for shifting the first passband to higher frequencies or for suppression of the out-of-band attenuation level. Multicascaded filters with more than 30 dB out-off-band attenuation level have been demonstrated. The cascade synthesis procedure is very simple and cost-effective.
C C. WANG, C C. WANG,
"Cascaded Single-Mode Fiber Optic Transversal Filters", Proc. SPIE 0716, High Frequency Optical Communications, (23 February 1987); doi: 10.1117/12.937450; https://doi.org/10.1117/12.937450