{'fraction_non_alphanumeric': 0.03291139240506329, 'fraction_numerical': 0.021518987341772152, 'mean_word_length': 4.833948339483395, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Board-to-board optical interconnects utilizing molded embedded 45 degree mirrors and print-on-demand micro-lenses as proximity vertical coupler

We demonstrate board-to-board optical communication utilizing 45 degree mirrors and print-on-demand micro-lenses as surface-normal coupler. The presented system which includes polymer waveguides, embedded 45 degree mirrors and micro-lenses, realizes back-to-back optical interconnects between two boards. The waveguide and mirrors are fabricated using molding method using a low-cost electroplated nickel mold. Micro-lenses (80 μm in diameter) are fabricated using a material inkjet-printer, on top of the 45 degree mirrors. Experimental results show that each 45 degree mirror contributes about 1.88 dB loss (65% coupling efficiency) to the total optical loss. When propagating in free space without a lens, a 2 mm separation between boards results in a 9.9 dB loss, which is reduced to 7.5 dB when a micro-lens is inserted in the path. High speed data transmission test is performed at various separations. At a separation of 1mm, the system can provide 10Gbps error free transmission. At 2mm separation, the maximum error free data rate was measured to be 3.5Gbps and 7.5Gbps, with and without the micro-lens, respectively. Printing the micro-lenses on both the input 45 degree mirror and the photodiode or the receiving 45 degree mirror in a confocal setup will significantly reduce the freespace propagation loss. To the best of our knowledge, this is the first report of free-space coupling between waveguides on separate boards.