Abstract
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 an electro-absorption modulator (EAM) has great potential in reducing them, the additional energy associated with the photocurrent flow will limit the lower-bound of the consumption energy. In this work, a broadband EAM based on an InGaAsP-embedded photonic crystal waveguide is demonstrated, revealing a high modulation bit rate of up to 56 Gbit/s. The air-bridge structure and a device length of 100 μm or less result in a small C ≤ 13 fF while operating with Vpp < 1 V. Particularly, the operation in low reverse voltage for a p-i-n junction, that is, −0.2 V as the minimum value in this study, works effective for the reduction of energy involving the photocurrent. This results in the total electrical energy consumption of <2 fJ/bit, which is lower than that of any waveguide EAMs.
Highlights
Demand has been growing for electrical-to-optical (E-O) converters with ultralow energy consumption towards on-chip photonic systems such as a high-throughput communication link and a large-scale switch system.[1,2] Especially, the construction of such photonic systems over a CMOS layer is a promising way to realize a functional photonic network-on-chip (PhNoC) architecture.[1,3] To compete with future electrical interconnect technologies, the energy consumption for photonic on-chip-com applications has to be less than 10 fJ/bit according to an analysis presented in Ref. 4
The buried heterostructure (BH) formation brings a good overlap between the Photonic crystal (PhC) waveguide, the nonlinear region, and the narrow depletion region, which should lead to the low-voltage operation that cannot be expected with a non-BH device
Our PhC waveguide combined with a BH and lateral p-i-n junction can be of ultra-small size thanks to the strong photon and carrier confinement
Summary
Compact and low-C EAMs have been exploited during the development of high-index-contrast waveguide structures Some of these EAMs are based on a SiGe- and Ge-based waveguide[2,7,8] fabricated on a silicon-on-insulator platform and had a device length of less than 100 μm, resulting in C < 10 fF while maintaining Vpp of a few V. The BH formation brings a good overlap between the PhC waveguide, the nonlinear region, and the narrow depletion region, which should lead to the low-voltage operation that cannot be expected with a non-BH device This results in both low Vpp and low C in a modulation that is applicable to off-chip/on-chip communication. Such an ultralow-energy consumption, as well as high speed broadband operation, and small footprint should be the most important part towards CMOS-integrated electro-optic processors on a chip
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