Nanophotonic technologies for innovative all‐ optical signal processor using photonic crystals and quantum dots

GaAs‐based two‐dimensional photonic crystal (2DPC) slab waveguides (WGs) and InAs quantum dots (QDs) were developed for key photonic device structures in the future. An ultrasmall and ultrafast symmetrical Mach‐Zehnder (SMZ)‐type all‐optical switch (PC‐SMZ) and an optical flip‐flop device (PC‐FF) have been developed based on these nanophotonic structures for an ultrafast digital photonic network. To realize these devices, two important techniques were developed. One is a new simulation method, i.e., topology optimization method of 2DPC WGs with wide/flat bandwidth, high transmittance and low reflectivity. Another is a new selective‐area‐growth method, i.e., metal‐mask molecular beam epitaxy method of InAs QDs. This technique contributes to achieving high‐density and highly uniform InAs QDs in a desired area such as an optical nonlinearity‐induced phase shift arm in the PC‐FF. Furthermore, as a unique site‐controlled QD technique, a nano‐jet probe method is also developed for positioning QDs at the centre ...