Width (μm)Line fit slope (dB/cm)Propagation Loss, α(w) (dB/cm) ± ± ± ± ± ± Experimental Study of Bend and Propagation Loss in Curved Polymer Channel Waveguides for High Bit-Rate Optical Interconnections Ioannis Papakonstantinou, David R. Selviah and F. Aníbal Férnandez Department of Electrical and Electronic Engineering, University College London, UK Photoreceiver μmμm μmμm μmμm Bend Radius R (mm) Normalized waveguide loss P norm1 (dBm) – Raw experimental data, P bend has coupling loss due to Fresnel reflections and scattering at the end waveguide surfaces. This loss is calibrated out by subtracting the power of a straight waveguide P str1 to give the normalized power P norm1 as: After this calibration the remaining loss is simply due to the bend and can be subdivided into the following components: Transition loss between straight – curved and curved – straight waveguide segments Pure bend loss due to the leaky nature of bend modes DC EXPERIMENTS μmμm μmμm μmμm Bend loss P bend (dBm) Bend Radius R (mm) – P norm1, is the combination of bend P bend, and propagation loss due to material absorption and scattering of light from the waveguide side walls. Propagation loss is calibrated out by subtracting a line, across all bend radii, fitted only at large R as:, where l bend and l cal are the lengths of the bend and the calibration straight waveguide correspondingly. AC EXPERIMENTS CONCLUSIONS CW experiments on curved waveguides showed that overall loss in the system reached a minimum between 17.5mm < R < 21mm and increased again for larger radii. Propagation loss at 850nm was found to be 0.09 dB/cm, 0.08 dB/cm and 0.07 dB/cm for the 50μm, 75μm and 100μm waveguides respectively. Narrower waveguides appear to have less propagation loss probably due to weaker scattering at the waveguide side walls. Bend loss is higher for wider waveguides. This is due to the transition loss at the first straight – bend waveguides interface. Bend loss minimizes after R > 15mm where it seems to saturate. For w = 50μm bend loss <0.25 dB for w = 75μm <0.4 dB and for w = 100μm <0.7 dB. AC experiments at 2.5 Gbit/s showed that lateral misalignment of the photodetector results to BER degradation. This can be seen from the shift of the BER versus received optical power curves for the waveguides with respect to the same curve of the system without any waveguide. There is seem to be no significant difference between the results of a bend and a straight waveguide to within the accuracy of our measurements. ACKNOWELEDGEMENTS This work was supported by the UK Department of Trade and Industry (DTI) and the Engineering and Physical Sciences Research Council (EPSRC), LINK Information Storage and Displays Storlite grant GR/S28136/01 and through a EPSRC DTA. We would like to thank Steve Thompson, Dave Milward, Richard Pitwon and Ken Hopkins, Xyratex Technology Ltd. for additional sponsorship of the first author and general support. Special thanks to Navin Suyal, Exxelis Ltd. for preparation of the wafers and Kai Wang and Frank Tooley for useful discussions. – The aim of these experiments is to assess how possible misalignments in our system affect the BER. – A 62.5/125μm graded index fibre was positioned on a sub-micron motorised stage and butt-coupled to the waveguides of the wafer. The other end of the fibre was connected to the receiver. – Tuneable attenuator held the initial power at the receiver for all waveguides constant at - 15 dBm. – BER as well as optical power was recorded as the fibre was laterally misaligned with respect to the waveguide facet for both directions of movement. + - Output Input Power at the receiver (dBm) BER (+) Direction (-) Direction Power at the receiver (dBm)