High Speed Ⅲ-Ⅴ Semiconductor Based Electrooptic Modulators
Sep 26, 2011
from 10:00 AM to 11:00 AM
|Where||Faraday Room, Engr. IV 67-124|
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Advisor: Prof. Harold Fetterman
In this talk, InGaAsP/InP quantum well (QW) and In(Ga)As/GaAs quantum dot (QD) material systems have been studied for high frequency applications.
For the QW modulator, both electrooptic (EO) and electroabsorption (EA) effects are observed for the same modulator. For high bias, the modulator performs as an EA modulator. At relatively low bias, the device acts like an EO modulator. These muli-QW structures are limited by material growth. Therefore, our second generation devices are based on new QD materials developed by Prof. Huffacker and Dr. Baolai Liang. The InAs/GaAs QD modulators were designed and fabricated. These modulators show a modulation efficiency, and with a reverse bias at -6V at operation wavelength 1550nm. The insertion loss is 6.5dB/mm, which is dominated by waveguide sidewall scattering. The 3dB-bandwidth for an 800μm-long device is ~10GHz. This is the first high frequency design and measurement on QD modulators. The EO coefficient is measured to be 35pm/V, which is 27 times as large as bulk GaAs. This means that for a 2mm-long Mach Zehnder modulator using push-pull drive, the half wave voltage Vπ can be reduced to less than 2.5V. To further reduce the optical loss, and improve the high frequency performance, the aligned QD chain structures have been designed and fabricated. These QD chain modulators show anisotropic properties along  and [01-1] directions. The 800μm-long modulator has a 3dB-bandwidth of ~12.2GHz. The optical insertion loss reduces to ~4.5dB/mm.
Because of their small size and easy integration with other photonic devices, these semiconductor modulators have great potential in next generation photonic integrated circuits.
Wei Liu is a PhD candidate in the Electrical Engineering department at UCLA. He is a part of Photonic and Millimeter Wave Laboratory headed by Prof Harold Fetterman. He is interested in semiconductor photonic circuits, optical signal processing and THz imaging. He has MS degree and BS degree in Electrical Engineering from Harbin Institute of Technology, Harbin, China.