Joseph Beals

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 (plusmn20 mum) 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 waveguide 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.

Low-Cost PCB-Integrated 10-Gb/s Optical Transceiver Built With a Novel Integration Method

A novel integration method for the production of cost-effective optoelectronic printed circuit boards (OE PCBs) is presented. The proposed integration method allows fabrication of OE PCBs with manufacturing processes common to the electronics industry while enabling direct attachment of electronic components onto the board with solder reflow processes as well as board assembly with automated pick-and-place tools. The OE PCB design is based on the use of polymer multimode waveguides, end-fired optical coupling schemes, and simple electro-optic connectors, eliminating the need for additional optical components in the optical layer, such as micro-mirrors and micro-lenses. A proof-of-concept low-cost optical transceiver produced with the proposed integration method is presented. This transceiver is fabricated on a low-cost FR4 substrate, comprises a polymer Y-splitter together with the electronic circuitry of the transmitter and receiver modules and achieves error-free 10-Gb/s bidirectional data transmission. Theoretical studies on the optical coupling efficiencies and alignment tolerances achieved with the employed end-fired coupling schemes are presented while experimental results on the optical transmission characteristics, frequency response, and data transmission performance of the integrated optical links are reported. The demonstrated optoelectronic unit can be used as a front-end optical network unit in short-reach datacommunication links.

Optical transceiver integrated on PCB using electro-optic connectors compatible with pick-and-place assembly technology

An optical transceiver formed onto a conventional low-cost printed circuit board with integrated optical waveguides is presented. The transceiver incorporates an optical multimode polymer Y-splitter formed directly on a low-cost singlelayered FR4 substrate enabling duplex transmission along a single optical fibre. The transmitter and receiver assemblies are mounted onto the board using methods common to conventional PCB manufacturing. Simple through-board connectors, compatible with pick-and-place assembly technology, are used to interface the electrical and optical layers of the board. This approach allows end-fired optical coupling between the active devices and optical waveguides on the board. The demonstrated transceiver, intended as a board-level optical network unit, achieves error-free data transmission for both Tx and Rx modules at 10 Gb/s.

Terabit capacity passive polymer optical backplane

A novel, low-loss, low-crosstalk optical backplane with scalable architecture using a planar array of multimode polymer waveguides is presented. Passive strict non-blocking interconnection of 10-cards is enabled via 100 waveguides each capable of 10 Gb/s operation.

Low Loss and Low Crosstalk Multimode Polymer Waveguide Crossings for High-Speed Optical Interconnects

Multimode polymer waveguide crossings exhibiting the lowest reported excess loss of 0.006 dB/crossing and crosstalk values as low as -30 dB are presented. Their potential for use in high-speed dense optical interconnection architectures is demonstrated.

Modal noise investigation in multimode polymer waveguides

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.

Multimode siloxane polymer components for optical interconnects

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.

Photon-like solutions of Maxwell's equations in dispersive media

The first realistically photon-like Schrödinger solution of Maxwells classical equations in dispersive media is presented. Classical modes of transverse electric or transverse magnetic fields with angular frequency ω propagating along an axis are shown to be able to be enveloped with counter-rotating helical modulations which have a different angular frequency Ω. These helical rotations, called distributed spin rotations, propagate at the group velocity. The formation of a completely closed packet of electromagnetic energy requires that the axial fields and transverse fields have a common axial length of envelope. This forces Ω to take quantized values in terms of ω with Ω related to the Schrödinger frequencies of a harmonic oscillator. The spin rotations permit flexible transverse confinement allowing for localization of the photon wave-packet over different spatial areas. It is argued that the energy of this packet is not related to its volume but depends on the quantized helical frequency Ω. Such photon-like packets possess classical phase and group velocities in keeping with experimental evidence. A single photon-like packet does not disperse in dispersive media. Incrementing or decrementing the rate of helical rotation promotes or demotes the packet energy in keeping with standard photon theory. The model offers explanations for self-interference and entanglement.

Electro-optic integration of liquid crystal cladding switch with multimode passive polymer waveguides on PCB

Optical switching functionality is demonstrated in PCB integrated multimode passive polymer waveguides using a localised liquid-crystal cladding structure. Waveguide switching contrast of 15 dB is achieved with only 0.5 dB of on-state excess loss.

Polymer-based board-level optical interconnects

This paper provides an overview of the rationale behind the significant interest in polymer-based on-board optical links together with a brief review of recently reported work addressing certain challenges in this field. Polymer-based optical links have garnered considerable research attention due to their important functional attributes and compelling cost-benefit advantages in on-board optoelectronic systems as they can be cost-effectively integrated on conventional printed circuit boards. To date, significant work on the polymer materials, their fabrication process and their integration on standard board substrates have enabled the demonstration of numerous high-speed on-board optical links. However, to be deployed in real-world systems, these optoelectronic printed circuit boards (OE PCBs) must also be cost-effective. Here, recent advances in the integration process focusing on simple direct end-fire coupling schemes and the use of low-cost FR4 PCB substrates are presented. Performance of two proof-of-principle 10 Gb/s systems based on this integration method are summarised while work in realising more complex yet compact planar optical components is outlined.