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Ultrafast THz optoelectronics: THz-rate electroabsorption modulation in InGaAs/GaAs quantum dots
Prof. Dr. Dmitry Turchinovich
The electroabsorption modulators are widely used in modern high-speed optical communications. Their switching rate, typically in 10-100 GHz range, is fundamentally limited by the RC-constant of the devices.
Quantum dot is the smallest-possible semiconductor element, and its RC-constant is negligible. Here, by applying THz electric field to the quantum dots directly, we demonstrate the THz switching speeds via THz-induced quantum-confined Stark effect (QCSE).
QCSE results from the tilt of confinement potential in an applied field. It leads to a red-shift in ground-state absorption feature (Stark shift), and to an overall absorption quenching due to spatial separation of electron and hole wavefunctions.
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Figure captions
| Fig. 1. | (a) Principle of THz electroabsorption modulation in QDs, and (b) QCSE in a disc-like QD. |
| Fig. 2. | (a) Modulating THz signal. (b) THz electroabsorption modulation of optical probe at 1040 nm wavelength, resonant with the ground-state absorption in QDs. Electroabsorption modulation signal coherently follows the absolute value of THz electric field. Inset: optical spectrum of the probe pulse with and without THz electric field on the QDs. |
| Fig. 3. | Nonlinearity of THz electroabsorption effect on THz field strength. |
| Fig. 4. | Modulation by a THz pulse train, emulating high-bit-rate wireless data-communication channel. Equivalent data rate: 88 Gbit/s. Channel capacity: 0.5 Tbit/s (RZ-OOK). Channel bandwidth: > 3 THz. Inset: amplitude spectrum of a single THz pulse (grey area), of an isolated electroabsorption signal around 0 ps (dashed line), and of a whole pulse train (solid line). These spectra demonstrate the coherence of encoding of a THz signal onto an optical signal. |
References
M. C. Hoffmann, B. S. Monozon, D. A. Livshits, E. U. Rafailov, and D. Turchinovich
"Terahertz electro-absorption effect enabling femtosecond all-optical switching in semiconductor quantum dots"
Appl. Phys. Lett. 97, 231108 (2010)
D.Turchinovich, Encoding an optical signal using a wireless radio-frequency signal, Patent WO2011/015200
Full list of publications is available at: http://www.ultrafast.dk
