Investigation of properties and metrology of Optical detectors

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Cseh Tamás
Department of Broadband Infocommunications and Electromagnetic Theory

These days the optical fiber communication systems are spreading rapidly across the whole world. The reason of this lies within their gorgeous properties like: high stability, extremely fast data transfer rate, low optical fiber attenuation / km, high protection against external noise and interference and last but not least their light weight. However, the implementation of the system might cost a fortune but the investment will be worth while.

The photodetector is one of the key elements of the optical communication systems. The conversion from the optical to the electrical signal is performed by the photodetector itself. Therefore, it is very important to know every single detail and parameter of the photodetector while designing an optical fiber system. The most important ones are the followings: Responsivity, Quantum efficiency, Saturation power, Saturation current and the Bandwidth of the photodiode

The topic of this master thesis is the measurement of the above mentioned parameters of an unknown PIN-diode type photodetector. The first two chapters are about to provide the necessary theoretical knowledge which is important to understand the mechanism and operation of the optical fiber communications systems and photodetectors.

The third and fourth chapters are demonstrating the various measurement structures and measurement processes. The evaluation of the measurement results as well as the control of the measurement processes are done automatically by specific programs written by me for this purpose. The measurement results are organized within chapter five.

In order to achieve more accurate and exact measurement results, specific circuits must be designed. The design process as well as the implementation of the circuits are contained in chapter six and seven. In chapter six a photoreceiver is designed which is matched at the frequency of 1GHz. Appropriate matching of RF devices are extremely important, because by matching, distortions caused by reflexions can be eliminated. Furthermore efficiency and goodness of transfer of the device can be greatly improved. The topic of chapter seven is a Laser transmitter circuit design, which makes the measurement of the monitordiode current possible.


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