The full exploitation of the advantages that radio frequency, microwave and millimetre-wave technologies bring to broadband telecommunications and other related applications requires a coordinated effort in the development of signal processing techniques suitable for them. This is especially important as novel applications demand the use of increasingly higher-frequency carriers and broadband signals.The traditional approach towards radio frequency (RF) signal processing is illustrated in the upper part of Figure 8.1. Here an RF signal originating from an RF source or coming from an antenna is fed to an RF circuit that performs the signal processing tasks either at the RF signal or at an intermediate frequency band after a down-conversion operation. In any case, the RF circuit is capable of performing the signal processing tasks for which it has been designed only within a specified (often reduced) spectral band. This approach results in poor flexibility since changing the band of the signals to be processed requires the design of a novel RF circuit and possibly the use of different hardware technology. Furthermore, even if the RF carrier is not changed, the nature of the modulating signal might be, thus requiring more bandwidth or sampling speed from the processor. This is especially true in the case where discrete time signal processing has to be carried over the RF signal. This set of drawbacks is often termed in the optical communications technology literature as the electronic bottleneck. Although important it is by no means the only source of degradation, since electromagnetic interference (EMI) and frequency dependent losses can also be sources of major impairments.An interesting approach to overcome the above limitations involves the use of photonics technology and especially fibre and integrated optics devices and circuits to perform the Microwave Photonics: Devices and Applications Edited by Stavros Iezekiel

Gomes, N.; Morant, M.; Alphones, A.; Cabon, B.; Mitchell, J.; Lethien, C.; Csörnyei, M.... (2009). Radio-over-fiber transport for the support of wireless broadband services. Journal of Optical Networking. 8(2):156-178. https://doi.Some of the work carried out within the EU Network of Excellence ISIS on radio over fiber systems for the support of current and emerging wireless networks is reviewed. Direct laser modulation and externally modulated links have been investigated, and demonstrations of single-mode fiber and multimode fiber systems are presented. The wireless networks studied range from PANs (such as ZigBee and UWB) through wireless LANs to wireless MANs (WiMAX) and third generation mobile communications systems. The performance of the radio over fiber transmission is referenced to the specifications of the relevant standard, protocol operation is verified and complete network demonstrations have been implemented.

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Abstract-The feasibility of using multimode fiber as an inexpensive cell feed in broad-band indoor picocellular systems is investigated in this paper. The performance of coded orthogonal frequency-division multiplexing (OFDM) for a variety of multimode fiber profiles, including stepped index and -profile graded index fibers, is assessed. In addition to its ability to perform well in a frequency-selective multipath environment, OFDM is shown to offer good protection against the frequency selectivity of a dispersive multimode fiber. Data rates in excess of 100 Mb/s (without equalization) over a multimode fiber channel are possible, whereas they may be limited to some 20-30 Mb/s using conventional ASK modulation.Index Terms-Broad-band indoor picocellular systems, fiberradio systems, OFDM modulation, optical fiber dispersion.

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A hollow-core fiber with nested anti-resonant node-free cladding tubes suitable for broadband THz guidance with low transmission losses is proposed. It is shown that the tube separation and tube thickness of the inner elements have a significant effect on the confinement loss and effective material loss of these fibers in the THz band. Using TOPAS copolymer, the proposed fiber was optimized for operation at 1 THz and it is predicted from numerical simulations that loss can be reduced to as low as 0.05 dB/m with a 0.6 THz wide dispersion flattened bandwidth.

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