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26 February 2020 Low voltage 12 GHz silicon optical electro-absorption modulator (EAM) using a Schottky diode for optical interconnectors in the C-band
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Proceedings Volume 11285, Silicon Photonics XV; 112851L (2020)
Event: SPIE OPTO, 2020, San Francisco, California, United States
A silicon optical electro-absorption modulator (EAM) operating at a high speed and low voltage was achieved by using a Schottky diode in the C-band (1530 nm ~ 1570 nm). The optical modulation is demonstrated by the intensity change of guiding light due to the free-carrier absorption in the semiconductor to change its absorption coefficient, not conventional interference effects. The proposed EAM has lateral metal-semiconductor (MS) junctions that aid in maximizing the free carrier injection and extraction by a Schottky contact on the rib waveguide center. The rib waveguide structure of the modulator on the standard 220-nm silicon-on-insulator (SOI) platform has an etch depth of 80 nm and a width of 450 nm for the single-mode operation. The center of the rib waveguide is lightly doped with 1015 cm-3 indium, where light is mostly confined. The sides are heavily doped with 1020 cm-3 indium to contribute to the optical absorption change in the center. The depletion width in the middle region was drastically changed by a Schottky contact with bias. This design allowed a high overlap between the optical mode and carrier density variations in the center of the waveguide. To achieve a high speed operation, the travelling-wave type electrodes were designed to allow copropagation of electrical and optical signals along the waveguide. The measured results demonstrated a broad operational wavelength range of 40 nm with a uniform 3.9 dB modulation depth for a compact 25 μm modulation length with 1 Vpp driving voltage. The travelling-wave type electrodes enabled the modulator operating up to 26 GHz with 12 GHz of 3-dB electrooptic bandwidth, experimentally.
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Uiseok Jeong, Kwangwoong Kim, Kyungwoon Lee, Jinsik Kim, and Jung Ho Park "Low voltage 12 GHz silicon optical electro-absorption modulator (EAM) using a Schottky diode for optical interconnectors in the C-band", Proc. SPIE 11285, Silicon Photonics XV, 112851L (26 February 2020);

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