Inverse design of efficient and compact 1 x N wavelength demultiplexer

In this paper, we propose efficient and compact 2D T-junction 1 x N in-plane-incidence wavelength demul-tiplexers by using recently developed objective-first inverse design algorithm. Ultra-high device performance was achieved for the specific designs of 1 x 2, 1 x 4, and 1 x 6 wavelength (de)multiplexers with small footprints 2.80 mu m x 2.80 mu m, 4.60 mu m x 2.80 mu m, 6.95 mu m x 2.80 mu m, respectively. We used two approaches to binarize - epsilon threshold and binarization-cost - to obtain silicon wavelength demultiplexer considering fabrication constraints. For instance, the transmission efficiency of binarization-cost 1 x 2 demultiplexer was -0.30 dB for 1.31 mu m and -0.54 dB at 1.55 mu m while crosstalks at the operating wavelengths are negligibly small, i.e., -17.80 and -15.29 dB, respectively. Moreover, for the binarization-cost 1x4 demultiplexer, the transmission efficiency values were approximately -1.90 dB at 1.31,1.39,1.47, and 1.55 mu m as the crosstalk was approximately -13 dB. Furthermore, the objective-first algorithm was used to employ our demultiplexers as multiplexers, which means the ports that were once used as inputs in demultiplexers are designed to be used as outputs. We envision that the devices are compact, reliable, and T-shaped that is useful for optical communication systems. These rudimentary results are also relevant to the burgeoning field of nanophotonics.