Electrical control of all-optical graphene switches

Abstract

Graphene has emerged as an ultrafast photonic material for on-chip all-optical switching applications. However, its atomic thickness limits its interaction with guided optical modes, resulting in a high switching energy per bit. Herein, we propose a novel technique to electrically control the switching energy of an all-optical graphene switch on a silicon nitride waveguide. Using this technique, we theoretically demonstrate a 120 µm long all-optical graphene switch with an 8.9 dB extinction ratio, 2.4 dB insertion loss, a switching time of <100 fs, a fall time of <5 ps, and a 235 fJ switching energy at 2.5 V bias, where the applied voltage reduces the switching energy by ∼ 16 × . This technique paves the way for the emergence of ultra-efficient all-optical graphene switches that will meet the energy demands of next-generation photonic computing systems, and it is a promising alternative to lossy plasmon-enhanced devices.

High-Performance All-Optical Modulator Based on Graphene-hBN Heterostructures

“…This result is similar to the experimentally reported electron cooling times for graphene-on-hBN, which were in the range of 200-400 fs in [28]. The switching time of the device is on the order of the electron heating time (< 150 fs) [16]- [18], because this is the time in which a sea of hot electrons is induced following a pump excitation; these electrons fill up the conduction band states leading to Pauli-blocking [67]. Then, the modulator reverts to its steady-state in a timescale of ∼ τ cool , which is < 600 fs in the case that is considered in Fig.…”

Ultra-Efficient DC-gated all-optical graphene switch

“…1a, functions as an open circuit because the applied voltage is DC. As a result, the current (I) is zero, and thus the consumed electrical power (P E ) is zero based on P E = IV G [5]. As explained in Appendix C, the left and right Au/Cr contacts are placed 0.8 µm away from the left and right Si rails, respectively, to ensure that they do not induce an ohmic loss.…”

“…Next-generation telecom and datacom networks require low-energy (<1 pJ/bit) and low-insertion-loss (<5 dB) photonic devices [4], which necessitates the quest for designing devices with alternative structures that satisfy these requirements. It was recently reported that the switching threshold of an alloptical graphene switch can be significantly reduced by applying a few volts bias [5]. Using this method, the chemical potential of graphene is electrostatically increased by the applied DC voltage, which enables a low-energy optical pump signal to fill the remaining conduction band states and saturate the absorption of graphene, hence achieving efficient all-optical switching.…”

“…Electrical control of the saturable absorption threshold in graphene was experimentally reported in [6]. In [5], the studied devices consisted of silicon nitride (Si 3 N 4 ) wire waveguides, which have a relatively large crosssection and low confinement of guided light. Thus, instead of Si 3 N 4 waveguides, we herein propose a novel design of an electrically-biased all-optical graphene switch that is integrated into silicon slot waveguides.…”

“…Si slot waveguides confine and guide the optical mode in a relatively small cross-section, which strongly enhances its interaction with graphene. While several designs of all-optical graphene switches have been proposed in the literature [2,3,5,7], these designs either suffer from high switching thresholds or a high insertion loss, and therefore do not meet the stringent demands of next-generation telecom and datacom networks. To overcome this challenge, we first boost the optical absorption of the graphene switch by integrating it into Si slot waveguides, where the guided optical mode is strongly enhanced and confined.…”