Abstract
In this paper, we investigate the optical modulation characteristics of a resonant tunnelling diode (RTD) oscillator. This preliminary work on the first RTD-PD oscillators with an optical window available from the iBROW project demonstrate that this device can effectively be used to accomplish amplitude and frequency modulation with light injection.

Abstract
In this paper, we further explore the concept of phase-conjugated twin waves (PCTW) for nonlinear cancellation in space-division multiplexed (SDM) systems. Previously, we demonstrated that the PCTW technique can successfully provide nonlinear cancellation in SDM systems. In this paper, we investigate the cases where two and four spatial modes are copropagating in a multimode fiber, considering three link lengths (1000, 3200, and 8000 km). Weak-and strong-coupling regimes are also evaluated. Our numerical simulation results show an average performance improvement > 10 dB after a 1000 km transmission link.

Abstract
Digitized radio-over-fiber (D-RoF) transport schemes are being pointed as viable alternative solutions to their analog counterparts, in order to avoid distortion/dynamic range problems. Here we propose a novel D-RoF architecture that takes advantage of a bandpass sigma-delta modulator at the transmitter which subsequently permits the usage of a simpler/cheaper base station that avoids the employment of a digital to analog converter. The proposed architecture exploits the properties of the digital signal to enable the extraction of an higher carrier frequency through the employment of a bandpass filter. Furthermore, we present a comprehensive analysis regarding the impact of a low-cost electro-optic modulation on the quality of received demodulated signal. Finally, a comparison performance analysis between the conventional D-RoF and the proposed architecture is presented. We conclude that although the proposed architecture performs similarly to conventional D-RoF schemes, it is more competitive for either upgrading installed systems as well as for new deployments. (C) 2014 Optical Society of America

Abstract
Spatial division multiplexing (SDM) is seen as an effective technique to overcome the present limits of fiber capacity and satisfy future bandwidth requirements, by substantially increasing optical transport capacities [1-5]. Similarly to single-mode fiber based modern telecommunication systems, the nonlinear penalties will eventually become the ultimate limiting factor in SDM systems, arising from crosstalk effects in multimode core or few mode fibers, which generate intramodal and intermodal nonlinearities. Here we explore the concept of conjugated twin waves in few mode fibers based SDM optical systems, as a means to overcome these nonlinear impairments and assess the performance of SDM systems for different PCTW configurations and coupling regimes. Our numerical simulation results show that this technique is an effective means to overcome the nonlinear impairments arising in mode division multiplexed systems, improving performance by up to 10 dB, in the strong coupling regime.

Abstract
In this paper we present a comprehensive analysis and a performance assessment on the transmission of digitised RF signals over optical fibre (DRoF). Specifically, a study of the impact of the ADC/DAC quantization, jitter noise and the signal attenuation caused by the sub-sampling technique and DAC frequency roll-off are addressed by means of simulation, considering the transmission of RF signals conveying QAM symbols. Additionally, an experimental evaluation of DRoF links using vertical-cavity surface-emitting lasers (VCSEL) for different optical fibre attenuation levels is also conducted. Finally, a new paradigm of DRoF systems based on well-known sigma-delta modulators (SDM) is also presented. Results show that it is possible to digitally transmit signals through a digital optical-based network and to distribute them wirelessly at the receiver side without the need for local oscillators (LO) and/or frequency up-converters. Results also show that the new sigma-delta-over-fibre concept performs similarly to conventional DRoF schemes, whilst being more competitive for either upgrading installed systems as well as for new deployments.

Abstract
The performance of Resonant Tunnelling Diode (RTD) oscillators with an optical window is evaluated experimentally, in the transmission of advanced modulation formats using electrical and optical modulation, for the first time. Additionally, the impact of phase noise in the transmission performance is also assessed.