Optoelectronic Packaging for 16-Channel Optical Backplane Bus with VHOEs

A novel 16-channel optical backplane bus with volume holographic optical elements (VHOEs), operating as diffraction grating beam alignment guides, was designed and fabricated for a high-performance computing system multi-slot bus. These thin film VHOEs were fabricated to diffract light beams for each bus slot into a glass wave-guiding plate (refractive index 1.52) for total internal reflection to other slot positions. Slot-to-slot optical alignment issues, including channel crosstalk and beam alignment tolerances, were computer modeled to optimize a low cost and simple optical packaging structure. For each slot position, a 4 X 8 element optical packaging plate was then fabricated to allow insertion of 16 VCSELs and 16 Photodiodes, each in an individual TO-46 can. Through the VHOE, the slot-to-slot fan-out received beam intensities were experimentally measured for each of the 16 channels and found to be in the range of 90 μW ~ 150 μW. This 90 μW minimum fan-out power is 5dB greater than the receiver sensitivity requirement. In this study, the maximum 10 Gbps single channel bandwidth was tested and a 1.6 Gbps aggregate bandwidth was also demonstrated through a three slot 16-channel optical backplane bus. This aggregate bandwidth was limited by an electronic element in the receiver circuit (155 Mbps PD-TIA) and processor (100 Mbps FPGA). With the system’s measured optical isolation of greater than 80dB, and suitably fast receiver electronics, simulation modeling indicates that Terabit per second bus data rates can be achieved in inexpensive, mechanically robust and reliable form factors. Index Term – Optical Backplane Bus, Volume Holographic Optical Elements (VHOEs), VCSEL, Photodiode, Lateral and Angular Misalignment, Optical Packaging Plate.