Polymeric multimode waveguides are of particular interest for optical interconnections in short-reach data links. In some applications, for example in space-borne systems, the use of advanced materials with outstanding performance in extreme environments is required (temperature and radiation). In this paper therefore, we present novel siloxane polymers suitable for these applications. The materials are used to form straight, 90° bent and spiral polymer waveguides by low-cost conventional photolithographic techniques on FR4 substrates. The samples have been tested to investigate their propagation characteristics and demonstrate their potential for high-speed data links. Overall, there is strong evidence that these multimode waveguides can be successfully employed as high-speed short-reach data links. Their excellent thermal properties, their low cost and the simple fabrication process indicate their suitability for a wide range of space applications.
This paper presents an overview of multimode waveguides and waveguide components formed from siloxane polymer
materials which are suitable for use in optical interconnection applications. The components can be cost-effectively
integrated onto conventional PCBs and offer increased functionality in optical transmission. The multimode waveguides
exhibit low loss (0.04 dB/cm at 850 nm) and low crosstalk (< -30 dB) performance, large alignment tolerances and
negligible mode mixing for short waveguide lengths. Error-free data transmission at 10 Gb/s over 1.4 m long waveguides
has been successfully demonstrated. Waveguide crossings exhibit very low excess losses, below 0.01 dB/crossing, and
excellent crosstalk performance. Low loss is obtained for waveguide bends with radii of curvature larger than 8 mm and
6 mm for 90° and S-shaped bends respectively. High-uniformity splitting is achieved with multimode Y-splitters even in
the presence of input misalignments. Y-combiners are shown to benefit from the multimode nature of the waveguides
allowing low loss combining (4 dB for an 8×1 device). A large range of power splitting ratios between 30% and 75% is
achieved with multimode coupler devices. Examples of system applications benefiting from the use of these components
are briefly presented including a terabit capacity optical backplane, a radio-over-fibre multicasting system and a SCM
passive optical network.
In this work the recent interest in waveguides for use in short optical links has motivated a study of the modal noise
dependence on launch conditions in short-reach step-index multimode polymer waveguides. Short optical links,
especially those with several connection interfaces and utilising a restricted launch are likely to be subject to a modal
noise power penalty. We therefore experimentally study the modal noise impact of restricted launches for a short-reach
optical link employing a 50 x 50 μm polymer multimode waveguide. Lens launches resulting in small diameter input
spots are investigated as are restricted launches from an 8 μm core optical fibre. For a launch spot of 10 μm diameter no
impairment is observed for up to 9 dBo of mode selective loss, and for a fibre launch with a dynamic input movement of
6 μm no impairment is seen for up to 8 dBo of mode selective loss.
The most recent impetus for the convergence of photonics and silicon integrated circuit technology has been the looming communications bottleneck associated with chip-to-chip and on-chip high-speed data transfer. Whilst there have been significant separate improvements in the materials and technologies for both integrated optics and integrated electronics, there is now a real commercial interest in putting these pieces together to achieve functional circuits that take advantage of both technologies. It is the purpose of this paper to review the recent developments in both microelectronics and photonics that are causing these fields to merge in the area of on-chip and off-chip data links.
We demonstrate an electro-optic switch and a variable attenuator for
telecommunication applications at λ=1550nm by employing the
ferroelectric and electroclinic properties of an organosiloxane liquid crystal. In the ferroelectric SmC* phase an optical switch has been realised with an extinction ratio of 36dB between crossed polarisers. The switching time was ~200microseconds. In the SmA* phase the analogue nature of the electroclinic effect was employed to obtain a variable attenuator. The maximum attenuation range between crossed polarisers was 35dB for an applied electric field of +-9V/micron. The response time of the device was about 100microseconds, independent of the applied electric field. Both devices where demonstrated in the same 21.5micron thick cell which provided a retardance of λ/2 at λ=1550nm.
The continuous penetration of optical data transport into diverse applications is driving an imperative to find lower cost fabrication routes to high performance waveguides and devices. Strip-loaded waveguides (SLWG) offer a unique opportunity to enable ultra-low cost processing and excellent performance in these applications. In this paper we will show that simple waveguides and devices may be fabricated that have compelling performance metrics. Similarly it is shown that the waveguide design is easily accomplished and that the designs may be rendered with limiting precision using standard process tool-sets. The combination of good design and facile manufacturing practice suggests that, unlike conventional waveguide technology, the SLWG is eminently suited to a wide variety of applications. It will also be shown that the simplicity of the processing offers new opportunities to apply this approach to waveguides in a wide variety of materials and on diverse substrates.
Forward design and rendition of devices with excellent reconciliation of measured performance with the design parameters provides a feasibility proof for the validity and manufacturability of the SLWG. Perhaps contrary to pre-conception it is proven that very low coupling loss with normal, single mode, fibres is readily achieved with waveguides of this type. This has been shown both by simulation and via the measured performance of devices. Processing of the test artifacts was via conventional silica-on-silicon planar waveguide manufacturing processes. However, other processes are shown to offer a strong proposition for much lower cost and a diversification of the utility and applicability of waveguides on many substrates.
The use of optical waveguides as the data link for off-chip and on-chip interconnects is attracting considerable interest. This paper examines the requirements and some possible solutions suitable for FPGA applications.
The Automotive Market offers several opportunities for Dow Corning to leverage the power of silicon-based materials. Dow Corning Photonics Solutions has a number of developments that may be attractive for the emergent photonics needs in automobiles, building on 40 years of experience as a leading Automotive supplier with a strong foundation of expertise and an extensive product offering- from encapsulents and highly reliable resins, adhesives, insulating materials and other products, ensuring that the advantage of silicones are already well-embedded in Automotive systems, modules and components. The recent development of LED encapsulants of exceptional clarity and stability has extended the potential for Dow Corning’s strength in Photonics to be deployed “in-car”. Demonstration of board-level and back-plane solutions utilising siloxane waveguide technology offers new opportunities for systems designers to integrate optical components at low cost on diverse substrates. Coupled with work on simple waveguide technology for sensors and data communications applications this suite of materials and technology offerings is very potent in this sector. The harsh environment under hood and the very extreme thermal range that materials must sustain in vehicles due to both their engine and the climate is an applications specification that defines the siloxane advantage. For these passive optics applications the siloxanes very high clarity at the data-communications wavelengths coupled with extraordinary stability offers significant design advantage.
The future development of Head-Up-Displays for instrumentation and data display will offer yet more opportunities to the siloxanes in Automotive Photonics.
Silicone based polymers possess a unique set of properties that makes them highly suitable for optical applications. In addition to their excellent thermal stability, mechanical properties, and ease of processing, they are highly transparent in the ultraviolet, visible, and selected bands of the near-IR spectra. The loss and absorption characteristics for a variety of silicone based polymers are examined and an example of a recently developed ultra-violet transparent polymer coating that is UV cured illustrates the flexibility of the silicone polymer family to be tailored to meet specific application needs.
Silicone polymeric materials are being developed that will allow the hybrid integration of tunable functionality provided by polymer dispersed liquid crystal, PDLC, and continuous phase liquid crystal materials on planar silica-on-silicon and planar polymer light circuits. The advantages of this approach are ease of integration, the possibility for reduced power consumption, and therefore a reduction of the overall cost for component manufacturing and operation. A successful demonstration of a low loss approach to hybrid integration of polymers and liquid crystals is presented. The challenges for successful integration and acceptance will be discussed. New liquid crystal materials are being developed specifically for this application.
VLSI/ULSI and the evolutions being driven by the International Technology Roadmap for Semiconductors (ITRS) are once again presenting severe challenges to the metal interconnect. Clock skew and other timing delays are becoming application critical design factors. The RC induced delays as well as parasitics (due to the trace density) are causing severe limitations to designs. Unfortunately these issues are very difficult to deal with using conventional computer aided design tools although efforts are being made, notably via DARPA funded programmes. We shall review techniques (and design elements) for on-chip optical communications. Through this we will present a new proposition for optical interconnects integrated upon otherwise conventional CMOS devices. We believe that the illustrated methodologies can be developed to provide very effective optical functionality appropriate to alleviating high-speed communications and timing issues.