Compact silicon-based on-chip wavelength triplexer using directional couplers with double bridged subwavelength gratings

A compact silicon on-chip wavelength triplexer engineered by double bridged subwavelength gratings (BSWGs) is proposed based on cascaded symmetric directional couplers (SDCs). The SDC consists of a pair of symmetric and identical BSWGs with another SWG waveguide implemented in the middle of the SDC section. It functions well provided that the coupling lengths can match even or odd times of beat lengths of the three wavelengths. Relying on deliberately tailoring the structural dimensions of SWGs at different positions of SDC, the two lowest-mode refractive indices and beat lengths can be efficiently tuned, drastically reducing device footprint. The results show a total device length of 42.2 µm, which is ∼ 10 % of its conventional counterpart based on SDCs. An insertion loss (IL) lower than 0.67 dB, reflection loss (RL) below − 21.4 d B , and extinction ratio (ER) as high as 34.5 dB are also obtained in the results. The bandwidths around wavelength bands and fabrication tolerances to dimensional variations are investigated and analyzed. The field evolutions for the three injected wavelength bands are presented.