Ultralow-energy electro-absorption modulator consisting of InGaAsP-embedded photonic-crystal waveguide

Towards realizing highly integrable low-energy optical modulators, the small device capacitance(C) as well as the low driving voltage (Vpp)is demanded for suppressing the charging energy during the dynamic operation. Although anelectro-absorption modulator (EAM) has great potential in reducing them, the additionalenergyassociated with the photocurrent flow will limit the lower-bound of the consumptionenergy. In thiswork, a broadband EAM based on an InGaAsP-embedded photonic crystal waveguide isdemonstrated, revealing a high modulation bit rate of up to 56 Gbit/s. The air-bridgestructure and a device length of 100 μm or less result in a smallC ≤ 13 fF while operating with Vpp < 1V. Particularly, the operation in low reverse voltage for a p-i-n junction, that is, −0.2V as the minimum value in this study, works effective for the reduction of energy involving thephotocurrent.This results in the total electrical energy consumption of <2 fJ/bit, which is lower thanthat of any waveguide EAMs