Optical crosstalk and signal power limitations in simultaneous 2-D multiple-plane WDM optical interconnects

WDM optical interconnects have been proposed as one method of establishing reconfigurable and simultaneous switching for systems with ultra-high (Terabit/s) throughput requirements. Such interconnects can be used to provide either massively parallel data communication among a few ports or local area network support for a large number of processors. The WDM interconnect is realized using a pixel array of multiple-wavelength VCSELs as the transmitter plane and incorporating wavelength-selective photodetectors into each subsequent receiving plane. At each receiving plane, the shortest wavelength signal is detected and the other signals pass through to he detected at the following planes. Optical crosstalk from the detection of non-signal channels and signal power loss from previous detecting planes contribute to system penalties. We have developed a model to investigate the occurrence of these penalties and find that crosstalk from residual power at shorter wavelengths limits the wavelength separation to >20 nm. Even when all residual power is eliminated, unintended signal detection at previous planes limits the wavelength separation to >12 nm. Furthermore, the last channel incurs a power penalty from beam divergence which is minimized with thin substrates, or is eliminated when the detector diameter is at least 20 /spl mu/m greater than the spatial span of the laser array.