Subpicosecond flat-top pulse shaping using a hybrid plasmonic microring-based temporal differentiator

Abstract

Design of a fractional-order photonic temporal differentiator, based on the silicon hybrid plasmonic add-drop microring resonators, is proposed. Because of the strong light confinement in the hybrid plasmonic waveguides, the overall footprint of the differentiator is significantly reduced. The numerical simulation results show that the differentiator can reach considerably wide 3 dB bandwidth of about 2.5 THz (20 nm) with the microring radius of 1.2 μm. It is also shown that the differentiation order and the 3 dB bandwidth of the proposed structure can be tuned in the range of [0.6 1.0] and [1.74 2.5] THz ([14 20] nm), respectively, by modifying the geometrical parameters of the differentiator. Mentioned bandwidth is higher than the previously reported values for microring-based photonic differentiators. Furthermore, the wide bandwidth and the tunable differentiation order of the structure along with its compact footprint make it a promising choice for the processing of ultrashort optical pulses. Generation of short flat-top pulses from input Gaussian pulses is then considered as an example of such applications. It is shown through three-dimensional finite-difference time-domain simulations that the proposed differentiator can be used to generate a flat-top pulse with the flat duration of 330 fs and the FWHM of ∼1  ps, from an ultrashort Gaussian input pulse, with the FWHM of 490 fs.