Abstract
We demonstrate intra- and inter-board level optical interconnects using polymer waveguides and waveguide couplers consisting of both 45 degree total internal reflection (TIR) mirrors and inkjet-printed micro-lenses. Surface normal couplers consisting of 50 µm × 50 µm waveguides with embedded 45 degree mirrors are fabricated using a nickel mold imprint. Micro-lenses, 70 µm in diameter, are inkjet-printed on top of the mirrors. We characterize the optical transmission between waveguides located on different boards in terms of insertion loss, mirror coupling loss, and free space propagation loss as a function of interconnection distance in free space. Each mirror contributes 1.88 dB loss to the system, corresponding to 65% efficiency. The printed micro-lenses improve the transmission by 2-4 dB (per coupler). Data transmission at 10 Gbps reveals that inter-board interconnects has a bit error rate (BER) of 1.1 × 10(-10) and 6.2 × 10(-13) without and with the micro-lenses, respectively.
Highlights
The increasing clock speed in current high performance computing system imposes an increasing demand on data transfer rates with increasingly stringent requirements for latency and power consumption per bit [1]
Optical interconnects consisting of arrays of Vertical Cavity Surface-Emitting Lasers (VCSELs) and Photo-detectors (PDs) have been shown to be superior to copper based electrical interconnects in terms of cost, power, and bandwidth [17, 18]
Free-space optical interconnects between VCSELs and PDs placed on separate boards have been demonstrated in which fixed integrated micro-lens arrays [21, 22] or MEMS controlled lens arrays were used to lower optical loss by reducing the beam divergence [23,24,25,26,27]
Summary
The increasing clock speed in current high performance computing system imposes an increasing demand on data transfer rates with increasingly stringent requirements for latency and power consumption per bit [1]. Inter-board coupling scheme is realized by 45 degree mirrors and integrated inkjet-printed micro-lenses. It provides free-space optical interconnects between waveguides located on different boards. The embedded mirrors together with the inkjet-printed microlenses on top serve as proximity couplers for board-to-board free-space optical interconnects between two molded waveguides on separate boards. The boards are positioned back-to-back to enable the data transfer via the optical couplers In order to investigate the effects of inkjet-printed micro-lens, insertion losses with and without the micro-lenses are compared
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