Coupling-enhanced dual ITO layer electro-absorption modulator in silicon photonics

• Published in: Nanophotonics (Berlin, Germany) Vol. 8; no. 9; pp. 1559 - 1566
• Main Authors: Tahersima, Mohammad H., Ma, Zhizhen, Gui, Yaliang, Sun, Shuai, Wang, Hao, Amin, Rubab, Dalir, Hamed, Chen, Ray, Miscuglio, Mario, Sorger, Volker J.
• Format: Journal Article
• Language: English
• Published: Berlin De Gruyter 2019; Walter de Gruyter GmbH
• Subjects: Absorption; Broadband; broadband operation; C band; Co-design; Coupling; Directional couplers; directional coupling; electro-absorption modulators; Electroabsorption modulators; indium tin oxide; Indium tin oxides; Insertion loss; Miniaturization; Modulation; Optical resonance; Optics; Photonics; Silicon
• ISSN: 2192-8606; 2192-8614
• DOI: 10.1515/nanoph-2019-0153

Electro-optic signal modulation provides a key functionality in modern technology and information networks. Photonic integration has not only enabled miniaturizing photonic components, but also provided performance improvements due to co-design addressing both electrical and optical device rules. The millimeter to centimeter footprint of many foundry-ready electro-optic modulators, however, limits density scaling of on-chip photonic systems. To address these limitations, here we experimentally demonstrate a coupling-enhanced electro-absorption modulator by heterogeneously integrating a novel dual-gated indium-tin-oxide phase-shifting tunable absorber placed at a silicon directional coupler region. This concept allows utilizing the normally parasitic Kramers-Kronig relations here in an synergistic way resulting in a strong modulation depth to insertion loss ratio of about 1. Our experimental modulator shows a 2 dB extinction ratio for a just 4 μm short device at 4 V bias. Since no optical resonances are deployed, this device shows spectrally broadband operation as demonstrated here across the entire C-band. In conclusion, we demonstrate a modulator utilizing strong index change from both real and imaginary parts of active material enabling compact and high-performing modulators using semiconductor near-foundry materials.