Record-fast terahertz electro-absorption modulation in quantum dots supports switching rates of at least 3 THz

In an effort led by DTU Fotonik, a group of researchers from 5 different European universities and companies demonstrated a record-fast THz-rate electro-absorption modulator. Such an ultrafast electro-absorption modulator will have a primary application in the wireless data communication systems capable of supporting Terabit-per-second (Tbit/s) data rates.

Application of THz electro-absorption modulator in an ultra-high-speed wireless data communication system. Measurements on an emulated communication channel with the data rate of 88 Gbit/s, and capacity of 0.5 Tbit/s
In an effort lead by DTU Fotonik, a group of researchers from 5 different European universities and companies demonstrated a record-fast THz-rate electro-absorption modulator. Such an ultrafast electro-absorption modulator will have a primary application in the wireless data communication systems capable of supporting Terabit-per-second (Tbit/s) data rates.
Semiconductor quantum dots were used as the switching medium, in which the optical absorption strength was changed by the ultrafast THz signals incident form a free space. Quantum dots (QDs) are the smallest-possible semiconductor elements, only consisting of 10s of thousands of individual atoms, and they can only accomodate up to 2 electron-hole pairs in the lowest energy state. It is this tiny size of the QDs, that allowed the researchers to achieve the unprecedented fast speeds at which the optical absorption in the QDs could be manipulated.
In the experiment, recently described in an article in Applied Physics Letters [1], the researchers managed to encode a THz signal with the spectrum covering the range of 0.2 – 3 THz, onto an optical signal with the wavelength of 1040 nm resonant with the quantum dot absorption. The full 3 THz bandiwdth of a THz signal was encoded onto an optical signal, with individual encoded temporal features being as fast as only 460 fs. It was demonstrated, that such an electro-absorption modulator can be used as a receiver for the THz-range wireless data links supporting the data rates of at least 0.5 Tbit/s.
This project was led by assoc. prof. Dmitry Turchinovich (DTU Fotonik). Matthias Hoffmann (Univ. Hamburg), Boris Monozon (Marine Tech. Univ., St. Petersburg), Daniil Livshits (Innolume GmbH), and Edik Rafailov (Univ. Dundee) participated in the project.
This work is based on DTU Fotonik’s invention (D.Turchinovich, patent pending PCT/DK2010/050200, 05 August 2009), and a DKK 750,000 grant from the Danish Proof of Concept Foundation was recently awarded to Dmitry Turchinovich for further development of this device.
For more information please contact assoc. prof. Dmitry Turchinovich (dmtu@fotonik.dtu.dk)
[1] M.C.Hoffmann, B.S.Monozon, D.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).

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