Doctoral College Cyber-Physical Production Systems at TU Wien
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Optical wireless communication is immune against electromagnetic interference and offers a much higher bandwidth and data rate (>2Gbit/s) than WLAN in one direct line-of-sight link. It will be easily possible to have several 10 or even several hundred optical links in a production hall (Figure 1). 

Figure 1: Optical wireless links to be investigated

Especially monolithically integrated optical receivers in silicon technology offer a high bandwidth due to the avoidance of bondpad capacitances between photodiode and amplifier. In addition such photodiode integrated circuits (PDICs) allow for low costs, high reliability and a small footprint and volume. 

It will be the goal in this PhD thesis to investigate the integration of avalanche photodiodes (APDs) in BiCMOS technology, where the combination of the high gain of bipolar amplifiers and the high gain of APDs will allow for considerable increase of the transmission distance towards 100m (Figure 2b). Another optimisation (instead of such a large transmission distance) can be the omittance of an optical receiver lens, the increase of the receiver field-of-view or the omittance of beam forming and focusing (Figure 2a). It also will be investigated whether the direct line-of-sight can be avoided and diffuse links (allowing reflection at walls etc.) are possible (Figure 2c). Especially for diffuse links, the minimisation of amplifier noise and of the so-called excess noise of APDs will be necessary. 

Figure 2: Different possibilities of optical links to be investigated

Furthermore, the emission spectra of light sources used in production halls will be investigated in order to choose the emission wavelength of laser diodes in such a way to obtain a large ratio of signal power to ambient light power. The PhD student will also investigate how optical receivers with a good background light suppression for use in production halls can be realised. With the help of beam steering e.g. by means of a MEMS mirror the optical links can be set up and changed flexibly. In addition blocked line-of-sight links can be repaired by redirecting the optical beam to another transceiver (see Figure 1).

Receiver PDICs with optimised APDs will be designed and fabricated in ASIC foundry BiCMOS technology. Transmitters with appropriate laser diodes guaranteeing eye-safety will be constructed. The performance of the APDs, of the APD-PDICs and of the optical wireless links will be verified experimentally with respect to bandwidth, gain, noise, link setup, transmission distance and ambient light suppression. 

It will be the ultimate goal to achieve a data rate of >2Gbit/s and to reduce the optical input power being necessary to receive a bit by a factor of 100 or even more compared to PIN photodiodes. 

PhD-Student and Supervision

PhD-Student: Dinka Milvancev, M.Sc. 

Dinka is employed at the Institute of Electrodynamics, Microwave and Circuit Engineering (EMCE) at TU Vienna since July 2014, first in the FFG project PHELICITI as a project assistant. Since starting at EMCE, Dinka was able to extend her experience with high-sensitivity optical receivers. In addition, she investigated the possibility of making the receiver switchable between binary and 4-PAM signal detection by circuit simulation and making the layout of the circuit.

During Dinka's final year of undergraduate studies, she was able to participate in an exchange program in Portugal, during which she strengthened her language skills by writing many project reports in English and listening course lectures in English. The exchange program Campus Europae also enabled funding for a 10 month internship which Dinka conducted at the Institute of Telecommunications in Aveiro. During this internship, Dinka finished her Bachelor thesis under the unofficial supervision of Prof. Dr. Luís Nero Alves of University of Aveiro. In her Master thesis, Dinka designed an integrated optical binary receiver for 10 Gb/s data communications for wide dynamic range of input optical power and low noise in 0.35 μm ams SiGe BiCMOS technology, using the Cadence software tools. 

Supervision:

Advisor: Prof. Dr. Horst Zimmermann, Institute of Electrodynamics, Microwave and Circuit Engineering (E354)