ERK'2016, Portorož, A:69-72 69 Influence of Fibre Chromatic Dispersion on the Performance of Analogue Optical Links for an Opto-electronic Oscillator within a 5G Network Structure Mehmet Alp Ilgaz 1 , Eszter Udvary 2 , Bostjan Batagelj 1 1 Radiation and Optics Laboratory, Faculty of Electrical Engineering, University of Ljubljana, Slovenia 2 Dep. of Broadband Inf. and Electromagnetic Theory, Budapest University of Technology and Economics, Hungary E-pošta: mehmet.ilgaz@fe.uni-lj.si Abstract. Analogue optical links are widely used in radio-frequency, micro-wave and millimetre-wave signal range applications. One of parameters that affect the performance of an analogue optical link is the chromatic dispersion. Chromatic dispersion affects the signal transmission over the fibre-optic line and in some cases it can destroy the signal shape on the link. In this paper we will give a brief introduction to the opto-electronic oscillator, the analogue optical links and the modulation techniques. Then we will describe the chromatic dispersion and its effect on the analogue optical links. The next step shows the measurements that were made up to 13 GHz for analogue optical links of a length up to 70 km. The final part is composed of the summary and a brief discussion of the results. Index terms- Fibre-optic line, chromatic dispersion, external modulation, opto-electronic oscillator. 1 Introduction The opto-electronic oscillator (OEO), which was invented by Yao and Maleki [1-2], is a new type of oscillator that can be used to produce a high-frequency signal in the radio-frequency (RF), micro-wave (µW) and millimetre-wave (mm-W) ranges. Due to its many advantages we intend to use an OEO in a 5G network structure with the help of radio-over-fibre (RoF) technology. Figure 1 shows how we can implement the idea of an OEO to distribute the signals between the central station and the base station. As shown in Figure 1, our idea for using the OEO in 5G has two analogue optical links. One of them is internal, located in the oscillator itself to complete the opto-electronic feedback given as L1. The second analogue optical link is external for the optical connection between the laser in the central station and the photodiode in the base station given as L2 in Figure 1. Both of these analogue links must be sufficiently long to satisfy the system requirements. The external optical link must be long enough to overcome the physical distance between the central station and the base stations, which can be in different ranges. The internal optical link must be long enough to bring enough delay and oscillator quality to generate a low-phase-noise signal. The OEO consists of the electrical and optical parts [3], which provides an electrical and an optical output signal at the same time [4]. The optical output is connected to the electrical part by analogue optical links. The opto-electrical conversion is, in both cases, made with a photodetector. This signal generated by the OEO is transmitted via a separate optical fibre link (known as an oscillator link) to the base station, as shown in Figure 1. At the base station, the optical signal is converted to the electrical domain on the photodiode, creating a RF signal that is suitable for the frequency up- and down-conversion of the data signal in the mixers. Figure 1. OEO implemented in the central station and connected to the base station with an analogue optical link. 2 Basics of Analogue Optical Links In today’s fibre-optics technology, analogue optical links are used for a variety of applications in the RF, µW and mm-W range signals. It is widely used in different areas such as cable television signal distribution [5], RoF technology [6-7], OEO [8-9], local area networks, remote antenna beam steering [10] etc. In [11], the advantages of optical fibre are described over coaxial cables in GSM applications such as cellular remote antenna feeding. The analogue optical link can be summarized as a combination of components, such as a semiconductor laser diode, optical modulator, fibre-optic line and photodiode, which are linked together. Generally, a distributed feedback (DFB) laser or a Fabry-Perot laser can be used in the optical link. In general, the DFB laser is integrated with an external modulator due to its advantages [12]. In the literature, there have been a number of methods to generate RF, µW and mm-W