Compact, low-crosstalk, WDM filter elements for multimode ribbon fiber data links

Our WDM filter approach is based upon post-market machining of the commercially available molded plastic "MT" fiber ribbon connector. Current work focuses on 2-port WDM filters suitable for a broadcast and select architecture. To improve crosstalk suppression beyond that attainable with the Lorentzian lineshapes of the single-cavity FP we have investigated some multiple-cavity Fabry-Perot (MC-FP) designs which have a spectral response with a flatter top and sharper passband edges. Filter passband edge sharpness can be quantified by the ratio of the filter 3 dB bandwidth to 18 dB bandwidth. This ratio is 0.48 for our multi-cavity filter, three times sharper than the single-cavity FP devices. This device provides a 5 nm tolerance window for component wavelength variations (at 1 dB excess loss) and is suitable for 10 nm channel spacing with 23 dB crosstalk suppression between adjacent channels. The average insertion loss for the MC-FP devices is 1.6 dB. Our current MC-FP filters have a 3 dB width of 7.6 nm. Fiber to fiber center wavelength variations within a typical filter module are less than 1 nm. The MC-FP devices exhibit cross-talk suppression >30 dB over a 100 nm span.