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A multimodal waveguide for enhanced performance in optical disc read-outResearch Area: III-V Semiconductor Photonic ICs Main Researcher: Frederik Fransoo Optical data storage tries to cope with the strong need for exchangeable super high-density, high-data rate storage memories that can be easily copied and can be produced at low cost. In this search for higher information density, different approaches are being investigated to make read-out of smaller marks possible. As a part of the IST SLAM project, our department investigates a method to improve the resolution, without making the spot size on the disk smaller than the wavelength. The idea is to reconstruct the bit pattern from the complete field profile (including amplitude and phase) of the light response reflected on the disk. Phase and amplitude information are measured by picking up the wave front into different modes of a multimodal waveguide. Once picked up, these modes can be split up by a photonic integrated circuit to be measured by different detectors. By combining the information from these different responses the bit error rate can be improved substantially.
The waveguide scanner. For reasons of clarity the illumination and detection side have been unfolded. The second picture gives the bit error rate as a function of bit size (in lambda/NA units). Response from mode zero, mode one, and an optimized combination 
Bit error rate as a function of bit size (in lambda/NA units). Response from mode zero, mode one, and an optimized combination The last picture gives a view of the mode splitter and shows the measured crosstalk from the zeroth order mode to the output of the first mode, for a range of components with varying MMI width. 
Measured crosstalk from the zeroth order mode to the output of the first mode, for a range of components with varying MMI width. Other people involved: Related Research Projects PhD thesises
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