Ultrabroadband and fabrication-tolerant mode (de)multiplexer using subwavelength structure

Abstract

An ultrabroadband and fabrication-tolerant mode (de)multiplexer [(De)MUX] is proposed and optimized by inserting subwavelength gratings (SWGs) into a three-waveguide coupler (TWC). The coupling strength can be dramatically enhanced, benefitting from both the SWG and TWC structures. The proposed mode (De)MUX is optimized using a three-dimensional, full-vectorial finite difference time domain based band diagram and propagation analyses. The simulated results indicate that the optimal mode (De)MUX is with a compact coupling length of 14.75 µm, a low loss of 0.64 dB, and a low mode crosstalk of $ - 31.7\,\,{\text{dB}}$−31.7dB at the operating wavelength of 1.55 µm. With the mode crosstalk $ \lt - 15.0\,\,{\text{dB}}$<−15.0dB, an ultrabroad bandwidth of 312 nm and a relaxed fabrication tolerance of $ - 42.7\,\,{\text{nm}}$−42.7nm to $ + 36.5\,\,{\text{nm}}$+36.5nm can be achieved. The 3 dB bandwidth is over 320 nm and the insertion loss is less than 1.6 dB for a $ \pm 50 \,\,{\text{nm}}$±50nm width change.