Display glass for low-loss and high-density optical interconnects in electro-optical circuit boards with eight optical layers

Abstract

Parallel optical interconnects on-board level requires low propagation loss in wavelength range between 850 and 1550 nm to be compatible with datacom and telecom optical engines. For highest integration density tight waveguide bends and a scalable number of optical layers should be manufacturable for 2D interfaces to optical fiber array connectors and photonic assembly I/O's. We developed a glass waveguide panel process for double-sided processing of commercial available display glass by applying a two-step thermal ion-exchange process for low-loss multi-mode graded-index waveguides. Multiple glass waveguide panels can be embedded between electrical layers. The generic concept enables fabrication of high-density integration (HDI) electro-optical circuit boards (EOCB) with high number of optical and electrical layers. Waveguides with high NA of 0.3 for low bend losses could be achieved in glass with propagation loss of 0.05 dB/cm for all key wavelengths. Four of those glass waveguide panels were embedded in an EOCB demonstrator with size of 280 x 233 mm² providing eight optical layers with 96 channels in an area of 2.8 x 1.5 mm². To the best of our knowledge it's the highest number of layers that has ever been demonstrated for an EOCB.

Ball Lens Embedded Through-Package Via To Enable Backside Coupling Between Silicon Photonics Interposer and Board-Level Interconnects

“…Although both polymer and glass based optical interconnects have been demonstrated in the past [32], [33], it is well-known that the polymer waveguide technology provides simplicity, flexibility and low-cost prospect with good optical properties. For the experimental demonstration, the substrate to fabricate the polymer waveguides was chosen to be silicon due to its high flatness and the benefit of spinning on the polymer layers easily.…”

Large Optical Backplane With Embedded Graded-Index Glass Waveguides and Fiber-Flex Termination

“…Electrooptical circuit board (EOCB) and mid-board optical transceiver subassemblies (optical engines) will be the two key enabling elements of this migration. In first step very low-loss optical fiber shuffles can be easily combined with electrical PCBs but with higher optical circuit complexity [4] including multiple optical layers planar waveguide technologies are required which will be embedded as inner PCB layer with up to eight or more optical layers and waveguide pitch of 125 µm or below [5]. A common implementation would be an optical backplane with MTP compliant interfaces, which can be connected directly or via pluggable board-to-board interfaces to the optical engine on a peripheral linecard as schematically shown in Fig.…”