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Electro optic modulators being key for many signal processing systems must adhere to requirements given by both electrical and optical constraints. Distinguishing between charge driven (CD) and field driven (FD) designs, we answer the question of whether fundamental performance benefits can be claimed of modulators based on emerging electro-optic materials. Following primary metrics, we compare the performance of emerging electro-optic and electro-absorption modulators such as graphene, transparent conductive oxides, and Si, based on charge injection with that of the ‘legacy’ FD modulators, such as those based on lithium niobate and quantum confined Stark effect. We show that for rather fundamental reasons and when considering energy and speed only, FD modulators always outperform CD ones in the conventional wavelength scale photonic waveguides. However, for waveguides featuring a sub-wavelength optical mode, such as those assisted by plasmonics, the emerging CD devices are indeed highly competitive especially for applications where component-density on-chip is a factor.

 

Abstract With success of silicon photonics having mature to foundry-readiness, the intrinsic limitations of the weak electro-optic effects in Silicon limit further device development. To overcome this, heterogeneous integration of emerging electrooptic materials into Si or SiN platforms are a promising path to deliver <1fJ/bit device-level efficiency, 50+Ghz fast switching, and <10's um^2 compact footprints. Graphene's Pauli blocking enables intriguing opportunities for device performance to include broadband absorption, unity-strong index modulation, low contact resistance. Similarly, ITO has shown ENZ behavior, and tunability for EOMs or EAMs. Here we review recent modulator advances all heterogeneously integrated on Si or SiN such as a) a DBR-enabled photonic 60 GHz graphene EAM, b) a hybrid plasmon graphene EAM of 100aJ/bit efficiency, d) the first ITO- based MZI showing a VpL = 0.52 V-mm, and e) a plasmonic ITO MZI with a record low VpL = 11 V- um. We conclude by discussing modulator scaling laws for a roadmap to achieve 10's aJ/bit devices.