Bandwidth Studies on Multimode Polymer Waveguides for ≥25 Gb/s Optical Interconnects (original) (raw)
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Optical interconnects have attracted considerable attention for use in short-reach communication links within high-performance electronic systems, such as data centers, supercomputers, and data storage systems. Multimode polymer waveguides, in particular, constitute an attractive technology for use in board-level interconnects as they can be cost-effectively integrated onto standard PCBs and allow system assembly with relaxed alignment tolerances. However, their highly multimoded nature raises important concerns about their bandwidth limitations and their potential to support very high on-board data rates. In this paper, we report record error-free (BER < 10 −12) 40 Gb/s data transmission over a 1-m-long multimode polymer spiral waveguide and present thorough studies on the waveguide bandwidth performance. The frequency response of the waveguide is investigated under a wide range of launch conditions and in the presence of input spatial offsets, which are expected to be highly-likely in real-world systems. A robust bandwidth performance is observed with a bandwidth-length product of at least 35 GHz×m for all launch conditions studied. The reported results clearly demonstrate the potential of this technology for use in board-level interconnects, and indicate that data rates of at least 40 Gb/s are feasible over waveguide lengths of 1 m.
40 Gb/s Data Transmission over a 1 m Long Multimode Polymer Spiral Waveguide
We report record error-free data transmission of 40Gb/s over a 1m-long multimode polymer spiral waveguide. The waveguide imposes no significant transmission impairments in the link despite its highly-multimoded nature and long length, demonstrating its potential in high-speed board-level optical interconnections.
Bandwidth and Offset Launch Investigations on a 1.4 m Multimode Polymer Spiral Waveguide
Bandwidth measurements are conducted on a 1.4 m long spiral polymer multimode waveguide for a SMF and 50/125 µm MMF launch and for different input offsets. The waveguide exhibits a bandwidth of at least 30 GHz for all input types, yielding a bandwidth-length product of at least 42 GHz×m, while no impact is observed on the waveguide performance due to the different spatial input offsets. The results indicate that data transmission at data rates even higher than 25 Gb/s can be achieved over such structures, thereby demonstrating the potential of multimode polymer waveguide technologies in short-reach board-level datacommunication links.
Optical interconnects have attracted significant research interest for use in short-reach board-level optical communication links in supercomputers and data centers. Multimode polymer waveguides in particular constitute an attractive technology for on-board optical interconnects, as they provide high bandwidth, offer relaxed alignment tolerances, and can be cost-effectively integrated onto standard printed circuit boards (PCBs). However, the continuing improvements in bandwidth performance of optical sources make it important to investigate approaches to develop high-bandwidth polymer waveguides. In this paper, we present dispersion studies on a graded-index (GI) waveguide in siloxane materials designed to deliver high bandwidth over a range of launch conditions. Bandwidth-length products of >70 and ∼65 GHz×m are observed using a 50/125 μm multimode fibre (MMF) launch for input offsets of ±10 μm without and with the use of a mode mixer (MM), respectively; and enhanced values of >100 GHz×m are found under a 10× microscope objective launch for input offsets of ∼18 × 20 μm 2. The large range of offsets is within the –1 dB alignment tolerances. A theoretical model is developed using the measured refractive index profile of the waveguide, and general agreement is found with experimental bandwidth measurements. The reported results clearly demonstrate the potential of this technology for use in high-speed board-level optical links, and indicate that data transmission of 100 Gb/s over a multimode polymer waveguide is feasible with appropriate refractive index engineering.
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.
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.
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.