Abdollahzadeh Davani, Hooman (2015)
High-Speed Tunable Short-Wavelength VCSEL for Optical Interconnects.
Technische Universität Darmstadt
Dissertation, Erstveröffentlichung

Kurzbeschreibung (Abstract)

The forecast for serial transmission speed used in data communication systems is a continued exponential increase with time. It is directly scaled in concert with silicon integrated circuits and in response to the human society’s perpetual hunger for massive increases in the bandwidth. This leads to an increase in the data rate of a single transmission channel and at the same time to an efficient usage of the existing transmission medium by using methods such as wavelength devision multiplexing (WDM). The electrical interfaces for a single channel using a bit rate beyond 10 Gbit/s are being standardized for a variety of applications. As a result, the fundamental electro-magnetic limitations of copper wire-based links at a bit rate >10 Gbit/s make fibre-based optics for data communication indispensable for distances >1 m. For shorter distances, problems associated with electrical transmission lines at such high frequencies, e. g. the high power consumption, strong signal attenuation, signal distortions and the electromagnetic interferences, lead to an unstoppable and progressive penetration of the optical communication links into traditional copper interconnect markets [1]. This trend greatly expands the applications of vertical cavity surface emitting lasers (VCSELs), VCSEL arrays and tunable VCSELs as inexpensive, efficient, reliable, readily manufacturable and compact laser light sources for the next generation of fibre-optic, free-space, board-to-board, module-to-module, chip-to-chip and on-chip interconnects and related information systems and networks. This thesis reports the development of a high-speed tunable short-wavelength VCSEL. The goal of our research is developing a device, suitable for optical interconnects. To achieve this goal, the long tradition and experience in fabrication and development of microelectro- mechanical system- (MEMS-) mirrors for the long wavelength VCSELs in the Institute of Microwaves and Photonics of the Technische Universit¨at Darmstadt is combined with the long tradition and experience in design and development of high-speed non-tunable shortwavelength VCSELs at Chalmers University of Technology in G¨oteborg Sweden . The Walter Schottky Institute ofMunich has provided wafers for semiconductor mirrors and the IEIIT-CNR in Torino has supported us with cold-cavity simulations. The developed devices are made of a GaAs based half-VCSEL in combination with a MEMSmirror. They exhibit a maximum amplitude modulation bandwidth of up to 5 GHz, which was the highest achieved amplitude modulation bandwidth among tunable GaAs based VCSELs at the time of publication of our results according to our knowledge. These devices are also the first developed high-speed tunable VCSELs in the short-wavelength range. They exhibit a wide single-mode continuous tuning range of up to 37 nm, which is the highest reported tuning range around 850 nm achieved by VCSELs. Additionally to the results mentioned above, which have been achieved by means of bulkmicromachining of the MEMS-mirror, a surface-micromachining technology has been successfully developed and implemented. Additionally the polarization stability of the devices is achieved by implementing a sub-wavelength grating (SWG). Further characteristics of the devices such as linewidth, far field, tuning speed, relative intensity noise (RIN) and large signal behavior are investigated by means of measurements.

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