Generation, Modulation, and Detection of Signals in Microwave Photonic Systems

Doktorsavhandling, 2008

This thesis deals with the use of photonic technology in microwave and millimeter-wave applications. The two major parts of this work have been techniques for transmission and signal generation. The transmission of analog microwave signals over optical fiber is known as radio-over-fiber and utilizes the advantages of the optical fiber in terms of loss, size, weight, cost and immunity to electromagnetic interference. In this thesis, several techniques are presented for generation and modulation of dispersion tolerant millimeter-wave signals, in order to avoid power fading induced by chromatic dispersion. We have demonstrated systems operating with 40 GHz millimeter-wave signals transmitted over optical fiber up to 44 km with 2.5 Gb/s data, including a short range wireless transmission. Furthermore, multiplexed modulation and simultaneous transmission over optical fiber of microwave and millimeter-wave signals are presented, and all-optical demultiplexing using fiber Bragg gratings are successfully demonstrated. Subcarrier modulation can be used in high bit rate optical communication systems in order to send multilevel data in a simple manner, considering the optical link as a "black box" with electrical input and output. A new concept for generating modulated subcarrier signals using binary digital electronics with up to 16-PSK modulation at 2.5 Gsymbols/s is presented. The performance of our in-house fabricated unitraveling-carrier photodiodes (UTC-PD) and a commercial PIN-PD is compared in the context of an analog link requiring high carrier-to-noise ratio and low distortion. We have found that the benefits of using a UTC-PD is mainly its superior spurious-free dynamic range. The generation of millimeter-wave signals is important for applications, where high frequency local oscillators are used, e.g. in antenna arrays. Using nonlinear characteristics or phenomena of photonic technology, millimeter-waves can be generated which have frequencies several times higher than the original electrical signal. Different techniques for harmonic signal generation are presented including harmonic frequency generation using an optical phase modulator, an optoelectronic oscillator, optical four-wave mixing or chirped pulse mixing.