Broadband access using wireless-over-fibre technologies

Abstract

This paper describes a number of wireless-over-fibre technologies for broadband access which are being investigated in the Photonics Group at University College London (UCL). In particular, the paper will report the asymmetric Fabry-Perot modulator/detector (AFPM), functioning not only as an optical modulator in the uplink direction, but also as a conventional photodetector in the downlink direction in a single device. Compared to the existing waveguide type electro-absorption modulator, the AFPM is polarisation-insensitive to light, simpler to fabricate and uses only a single optical fibre for both uplink and downlink transmissions, and therefore has the potential to lower the costs of future picocell deployments.Direct modulation of a semiconductor laser is the simplest way to generate modulated optical signals. In the presence of multiple large modulation signals, however, intermodulation or inter-channel distortion can easily be generated in the semiconductor laser and affect other lower power neighbouring channels. A feed-forward linearisation technique for directly modulated semiconductor lasers, capable of operating at frequencies above 5 GHz, has been developed and will be described in detail in this paper. Most modern commercial buildings already have a multimode optical fibre (MMF) infrastructure for carrying the Ethernet data. To provide cost-effective and reliable indoor cellular and wireless local area network (WLAN) coverage without dependence on the radio penetration from outside base-stations, it is highly desirable that the same MMF infrastructure be used to carry these additional services between the equipment room and the remote antenna units around the building.Although not previously regarded as having sufficient bandwidth, it has now been shown that MMF can successfully carry microwave modulated optical signals, including GSM1800 and UMTS cellular radio. Use of MMF for multiservice, multioperator in-building radio coverage has been demonstrated in a collaboration between UCL and the University of Cambridge and will be described in this paper.As the number of cellular and broadband WLAN devices increases, the lower parts of the radio spectrum are becoming more and more congested. To meet the demand for ever higher data transmission rates, other parts of the radio spectrum are being considered for these applications, particularly the millimetre-wave region (30 GHz and above). One of the challenges facing such systems is the generation and delivery of a low phase noise precisely synchronised local oscillator signal. In this paper, a simple optical heterodyne source with two injection locked slave lasers and a more environmentally robust source using an optical injection phase lock loop will be described, together with signal distribution using a bidirectional semiconductor optical amplifier in a coarse wavelength division multiplex fibre ring architecture.Finally it will be argued in the conclusions that future broadband wireless-over-fibre access networks will be required to provide multiservi...

ROF Technology in Intelligent Residential Community

“…Despite the SCM has the disadvantage of the higher nonlinear performance requirements, but the current research still considered it's the first choice for multiplexing and system implementation. ROF system architecture includes the simplex link, the duplex link, the combination of wired and wireless links [4], and the future wavelength division multiplexing passive optical network (PON) links. Figure 1 shows the basic duplex ROF link.…”

TeraHertz Photonics for Wireless Communications

“…The limited propagation distance at THz carrier frequencies allows well-defined microcells and frequency re-use. The architecture illustrated has already been used successfully for lower frequency wireless-over-fibre systems [7]- [10]. Possible applications include high-resolution multimedia services to mobile devices, wireless video distribution, and very high-speed wireless LANs.…”

“…Transmitting baseband data to the antenna units requires complex frequency generation and modulation technology to be placed in the hostile outdoor environment with severe cost implications. The alternative approach of centralised THz wireless signal generation reduces AU functionality to photo-detection and amplification, with the lower data rate uplink requirements met by simple modulation schemes [7], [9], [10]. This approach will now be described in more detail.…”