<title>Beam extractor card for free-space optical backplanes</title>

Abstract

The fabrication of an interface card to extract free-space beams from an optical backplane and deliver them to either photodetectors on a printed circuit board or to fiber, is described. Experimental results are presented for polymer waveguides with 45 degree end reflectors and refractive polymer microlens arrays used in the fabrication of the card. Results for 1 by 4 and 4 by 4 prototypes which intercept 4 and 16 free-space beams, respectively, are also discussed. The 1 by 4 prototype extractor card coupled 4 free-space beams on 500 micrometer centers to direct-dispensed polymer waveguides with 45 degree end reflectors and finally to 100 micrometer core multimode fibers. Total throughput losses (free-space to fiber) for each of the four channels were 2.1, 2.4, 2.5, and 2.8 dB. In order to implement a fully connected 4 by 4 extractor card, laser-written waveguides were developed which have smaller cross-sections thereby allowing more channels and standard 62.5 micrometer core fiber to be used. The second prototype card intercepts 16 free-space beams in a 4 by 4 array (500 micrometer centers) and couples them into two sets of eight laser-written waveguides (50 by 50 micrometer cross-sections), which in turn are coupled to two multimode fiber ribbon cables with 62.5 micron cores on 250 micrometer centers. Total insertion losses from free-space to fiber ribbon are typically 4 - 5 dB. The refractive microlens arrays, which are used to focus the light onto the waveguide end-reflectors, are fabricated using an extremely simple direct- dispense technique which achieves excellent quality and uniformity. Experimental results are reported.