9 March 2018 All-silicon transparent conducting oxide-integrated electro-optical modulator
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Abstract
An optical modulator is considered one of the most fundamental components in an optical data communication system as it acts as a linking device between the optical and electrical parts of the system. Electro-absorption (i.e. electro-optical) modulation is one popular scheme in designing optical modulators; however, minimizing the device footprint in siliconbased platforms acted as a challenge. Few years ago, “plasmonics” field emerged as a good candidate that could possibly further reduce silicon-based modulators’ footprint. Unfortunately, existence of metals introduced huge propagation losses. Recently, transparent conducting oxides (e.g. indium tin oxide “ITO”) have been intensively used as active media in electro-optical (EO) modulators. They have a metal-like plasmonic behavior with extremely lower losses.

Under no biasing voltage, ITO acts almost as a dielectric. However, by carefully tuning the biasing voltage, the free carrier concentration beneath the ITO surface is changed. This allows a dramatic alteration in the complex permittivity of the ITO reaching an epsilon-near-zero (ENZ) value at some point. At this region, the ITO acts as a metal and a plasmonic mode is present at an ITO-dielectric interface. A heavily doped silicon slab can be used as a contact for the gating voltage to be applied on in order to accumulate free carriers on the ITO surface.

In this work, an all-silicon indium tin oxide-integrated electro-optical modulator is designed. The modulator exhibits superior parameters (e.g. insertion loss and extinction ratio) that outperform the current modulators based on the same technology.
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Mohamed M. Badr, Mohamed Y. Abdelatty, Mohamed A. Swillam, "All-silicon transparent conducting oxide-integrated electro-optical modulator", Proc. SPIE 10535, Integrated Optics: Devices, Materials, and Technologies XXII, 1053520 (9 March 2018); doi: 10.1117/12.2289598; https://doi.org/10.1117/12.2289598
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