Multimode PDMS waveguides fabricated using a hot-embossing technique

A novel method for fabricating multimode PDMS waveguides is presented. This process is based on a hot-embossing technique and generates high quality optical waveguides without a substantial residual layer after embossing. Furthermore, the process allows for low-cost fabrication since it relies on a replication technique and additionally only commercially available materials are used. The measured propagation loss is smaller than 0.24dB/cm and can be further reduced by improving the master mould quality

Fully embedded optical and electrical interconnections in flexible foils

This paper presents the development of a technology platform for the full integration of opto-electronic and electronic components, as well as optical interconnections in a flexible foil. A technology is developed to embed ultra thin (20 μ m) VCSEL's and Photodiodes in layers of optical transparent material. These layers are sandwiched in between two Polyimide layers to get a flexible foil with a final stack thickness of 150 μ m. Optical waveguides are structured by photolithography in the optical layers and pluggable mirror components couple the light from the embedded opto-electronics in and out of the waveguides. Besides optical links and optoelectronic components, electrical circuitry is also embedded by means of embedded copper tracks and thinned down Integrated Circuits (20 μ m). Optical connection towards the outer world is realized by U-groove passive alignment coupling of optical fibers with the embedded waveguides

Expanded-beam backside coupling interface for alignment-tolerant packaging of silicon photonics

We demonstrate an alignment-tolerant backside coupling interface in the O-band for silicon photonics by generating an optimized through-substrate (downward) directionality beam from a TE-mode grating coupler and hybrid integrating the chip with backside silicon microlenses to achieve expanded beam collimation. The key advantage of using such an expanded beam interface is an increased coupling tolerance to lateral and longitudinal misalignment. A 34 mu m beam diameter was achieved over a combined substrate thickness of 630 mu m which was then coupled to a thermally expanded core single-mode fiber to investigate the tolerances. A 1-dB fiber-to-microlens lateral alignment tolerance of 14 mu m and an angular alignment tolerance of 1 degrees was measured at a wavelength of 1310 nm. In addition, a large +/- 2.5 mu m 1-dB backside alignment accuracy was measured for the placement of microlens with respect to the grating. The radius of curvature of Si microlens to achieve a collimated beam was 480 mu m, and a 1-dB longitudinal alignment tolerance of 700 mu m was measured for coupling to a single-mode expanded core fiber. The relaxation in alignment tolerances make the demonstrated coupling interface suitable for chip-to-package or chip-to-board couplin

Ball lens embedded through-package via to enable backside coupling between silicon photonics interposer and board-level interconnects

Development of an efficient and densely integrated optical coupling interface for silicon photonics based board-level optical interconnects is one of the key challenges in the domain of 2.5D/3D electro-optic integration. Enabling high-speed on-chip electro-optic conversion and efficient optical transmission across package/board-level short-reach interconnections can help overcome the limitations of a conventional electrical I/O in terms of bandwidth density and power consumption in a high-performance computing environment. In this context, we have demonstrated a novel optical coupling interface to integrate silicon photonics with board-level optical interconnects. We show that by integrating a ball lens in a via drilled in an organic package substrate, the optical beam diffracted from a downward directionality grating on a photonics chip can be coupled to a board-level polymer multimode waveguide with a good alignment tolerance. A key result from the experiment was a 14 chip-to-package 1-dB lateral alignment tolerance for coupling into a polymer waveguide with a cross-section of 20 x 25. An in-depth analysis of loss distribution across several interfaces was done and a -3.4 dB coupling efficiency was measured between the optical interface comprising of output grating, ball lens and polymer waveguide. Furthermore, it is shown that an efficiency better than -2 dB can be achieved by tweaking few parameters in the coupling interface. The fabrication of the optical interfaces and related measurements are reported and verified with simulation results