Characterization of parallel optical-interconnect waveguides integrated on a printed circuit board (original) (raw)
Related papers
Multimode polymer waveguides are being increasingly considered for use in short-reach board-level optical interconnects as they exhibit favourable optical properties and allow direct integration onto standard PCBs with conventional methods of the electronics industry. Siloxane-based multimode waveguides have been demonstrated with excellent optical transmission performance, while a wide range of passive waveguide components that offer routing flexibility and enable the implementation of complex on-board interconnection architectures has been reported. In recent work, we have demonstrated that these polymer waveguides can exhibit very high bandwidth-length products in excess of 30 GHz×m despite their highly-multimoded nature, while it has been shown that even larger values of > 60 GHz×m can be achieved by adjusting their refractive index profile. Furthermore, the combination of refractive index engineering and launch conditioning schemes can ensure high bandwidth (> 100 GHz×m) and high coupling efficiency (< 1 dB) with standard multimode fibre inputs with relatively large alignment tolerances (~17×15 µm 2). In the work presented here, we investigate the effects of refractive index engineering on the performance of passive waveguide components (crossings, bends) and provide suitable design rules for their on-board use. It is shown that, depending on the interconnection layout and link requirements, appropriate choice of refractive index profile can provide enhanced component performance, ensuring low loss interconnection and adequate link bandwidth. The results highlight the strong potential of this versatile optical technology for the formation of high-performance board-level optical interconnects with high routing flexibility.
Electro-optical circuit boards should provide simple and cost-effective coupling techniques and crosstalk levels of less than −30 dB. A dicing saw was used to create waveguide grooves with a surface roughness of less than 183 nm in a 1.6-mm-thick polymethyl methacrylate polymer (PMMA) substrate. The buried optical waveguides were made from SU-8 in a PMMA substrate covered with a 1-mm PMMA sheet. The propagation loss for a 500 μm × 570 μm straight waveguide was 0.9 dB/cm at 1310 nm. The coupling between parallel waveguides was measured at separation distances from 45 to 595 μm. The crosstalk was less than −40 dB for 65-mm-long waveguides. This fabrication method shows potential for dense optical interconnects with very low crosstalk.
Cost-Effective Multimode Polymer Waveguides for High-Speed On-Board Optical Interconnects
—Cost-effective multimode polymer waveguides, suitable for use in high-speed on-board optical interconnections, are presented. The fundamental light transmission properties of the fabricated waveguides are studied under different launch conditions and in the presence of input misalignments. Low loss (0.04 dB/cm at 850 nm) and low crosstalk 30 dB performance, relaxed alignment tolerances 20 m and high-speed operation at a 10-Gb/s data rate are achieved. No degradation in the high-speed link performance is observed when offset input launches are employed. Moreover, a range of useful waveguide components that add functionality and enable complex on-board topologies are presented. The optical transmission characteristics of the fabricated components are investigated and it is shown that excellent performance is achieved. Excess losses as low as 0.01 dB per wave-guide crossing, the lowest reported value for such components, and bending losses below 1 dB for 90-degree and S-shaped bends are obtained even with multimode fiber launches. Moreover, high-uniformity power splitting and low-loss signal combining are achieved with Y-shaped splitter/combiners while a variable splitting ratio between 30%–75% is demonstrated with the use of multimode couplers. Overall, the devices presented are attractive potential candidates for use in on-board optical links.
Polymer Waveguide Technology for Optical Interconnect Circuits and Components
The goal of this report is to tackle the “interconnection bottleneck” for board-level communications by investigating the high-speed performance of the polymer waveguide and multilevel modulation schemes so as to maximum the data transmission rate. There are two main parts in this report: one is the high-performance studies on the polymer waveguide; the other one is the investigation on advanced modulation schemes. Although the dynamic characteristics of the polymer waveguide have been investigated intensively by Dr. Nikos Bamiedakis in the CPS, the performance of the spiral polymer waveguide is still not fully understood. So the first few chapters of this report are seeking to answer some of the questions such as how much bandwidth the spiral waveguide can support. The importance of this work is to determine if the current waveguide can support high data rate such as 25 Gb/s and beyond (e.g. 100 Gb/s). In addition, very little work has been done on the polymer waveguide using advanced modulations for high speed data transmission. Therefore, the last part of this report presents some studies on advanced modulation schemes based on the polymer waveguide system. Previously, 10 Gb/s data transmission based on the polymer waveguide has been demonstrated by Dr. Nikos and many other research groups. The purpose of this report is to investigate the approaches of increasing the data rate up to 25 Gb/s and beyond using advanced modulation formats.