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|Glass with Embedded Waveguides for Photonic Packaging|
|Keywords: optical interconnects, photonic packaging, electro optical circuit boards|
|Fiber fly-overs are deployed for on-board optical interconnects in combination with on-board optical engines in different products such as high-performance switches for data centers. Polymer waveguides are a promising next step technology solution for integrated board-level optical connectivity to increase the interconnection density; their drawback is the high optical loss at key optical wavelengths around 1310 nm and 1550 nm where promising low-cost silicon photonic transceivers will operate. Glass waveguides fabricated by silver ion-exchange in glass panels have attracted significant interest as a cost-effective candidate due to their very low optical loss at key wavelengths and efficient coupling to optical fiber. The glass waveguide technology and board integration of glass waveguides have been demonstrated for multimode waveguides. Still, the performance of glass waveguides can be optimized by adjusting the refractive index profile for the specific requirements of complex circuits with small pitch, high-number of crossings and tight bends. Low insertion and cross-talk losses are important requirements. For off board communication a reliable connector solution is required for multi-fiber interconnection. The graded refractive index profile of ion-exchanged glass waveguides can be adjusted by glass composition and process parameters during the two-step thermal ion-exchange (salt melt composition, process time, and temperature for each diffusion step) to produce different waveguide core sizes and numerical apertures (NA). The difference in refractive index profile has a strong influence on the optical beam propagation in different waveguide structures such as s-bends, 90 degree arc bends, waveguide crossings, and waveguide arrays with small pitch like 125 μm. By controlling the waveguide process parameters the optical loss and cross talk characteristics can be optimized. Waveguides have been fabricated with optical loss of 0.05 dB/cm. For off-board interconnects, the optical fiber connector is a necessary component; it should be pluggable, low-loss, reliable, and cost-effective. We developed an optical connector concept for the interconnection of electro-optical circuit boards to multimode fiber ribbon cables. Our concept is based on an expanded-beam connector. The expanded beam connector is installed on the edge of the glass waveguide panel by adhesive bonding. The lens array of the expended beam connector collimates the beam emitted by the glass waveguides, and it allows mating to a fiber ribbon cable having an MXC® connector. We developed the assembly process to align the expanded beam connector in front of the waveguide array, and installed connectors on both ends of an array of 17-cm-long waveguides. To assess the connector loss, we measured the optical loss before and after installation of the connectors: we found that the loss introduced by each expanded-beam connector is less than 1 dB.|
Corning Research & Development Corporation
Corning, New York