On-chip low-loss all-optical MoSe2 modulator.

Monolayer transition metal dichalcogenides (TMDCs), like MoS2, MoSe2, WS2, and WSe2, feature direct bandgaps, strong spin-orbit coupling, and exciton-polariton interactions at the atomic scale, which could be harnessed for efficient light emission, valleytronics, and polaritonic lasing, respectively. Nevertheless, to build next-generation photonic devices that make use of these features, it is first essential to model the all-optical control mechanisms in TMDCs. Herein, a simple model is proposed to quantify the performance of a 35-µm-long Si3N4 waveguide-integrated all-optical MoSe2 modulator. Using this model, a switching energy of 14.6 pJ is obtained for a transverse-magnetic (TM) and transverse-electric (TE) polarized pump signals at λ = 480 nm. Moreover, maximal extinction ratios of 20.6 dB and 20.1 dB are achieved for a TM and TE polarized probe signal, respectively, at λ = 500 nm with an ultra-low insertion loss of <0.3 dB. Moreover, the device operates with an ultrafast recovery time of 50 ps, while maintaining a high extinction ratio for practical applications. These findings facilitate modeling and designing novel TMDC-based photonic devices.

Electrical control of all-optical graphene switches.

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.

Low Insertion Loss Plasmon-Enhanced Graphene All-Optical Modulator.

Graphene has emerged as an ultrafast optoelectronic material for all-optical modulators. However, because of its atomic thickness, it absorbs a limited amount of light. For that reason, graphene-based all-optical modulators suffer from either low modulation efficiencies or high switching energies. Through plasmonic means, these modulators can overcome the aforementioned challenges, yet the insertion loss (IL) of plasmon-enhanced modulators can be a major drawback. Herein, we propose a plasmon-enhanced graphene all-optical modulator that can be integrated into the silicon-on-insulator platform. The device performance is quantified by investigating its switching energy, extinction ratio (ER), IL, and operation speed. Theoretically, it achieves ultrafast (<120 fs) and energy-efficient (<0.6 pJ) switching. In addition, it can operate with an ultra-high bandwidth beyond 100 GHz. Simulation results reveal that a high ER of 3.5 dB can be realized for a 12 µm long modulator, yielding a modulation efficiency of ∼0.28 dB/µm. Moreover, it is characterized by a 6.2 dB IL, which is the lowest IL reported for a plasmon-enhanced graphene all-optical modulator.