Currently, the proliferation of services and applications based on the cloud and the Internet are translating into increasing demand for capacity in data networks. Optical Communications is the only technical field that can address this issue by providing higher performance electro-optical transceivers with enhanced spectral efficiency, power consumption and latency. Many research and implementation efforts are focusing on multicarrier solutions, often referred to as subcarrier multiplexing (SCM), as they are more tolerant to dispersion and allow a higher modulation order per subchannel. In recent years, the most widespread trend has developed SCM subsystems based on digital signal processing (DSP). They can achieve high spectral efficiencies with complicated algorithms, but also present an important drawback: intensive DSP brings about unwanted high-power consumption and high latency. An alternative consists of developing SCM systems based on analogue signal processing (ASP) as it potentially achieves lower power consumption and lower latency. Several advances on the state of the art of ASP based SCM systems are provided in this thesis. Firstly, the implementation of broadband SCM systems based on optical IQ modulators is thoroughly analysed. These optical modulators achieve simultaneously two important features: direct colourless generation of optical single side band signals (OSSB) and partial optical carrier suppression. These features translate into higher tolerance to dispersion and better sensitivities in the receiver. Secondly, the colourless generation of OSSB signals is leveraged to develop SCM systems consisting of several tightly allocated optical channels. This implementation gives rise to low-cost spectrally-efficient wavelength division multiplexing (WDM) configurations. Thirdly, the main weakness of ASP based SCM systems is overcome. These systems have typically consisted of separated subchannels. It is demonstrated that orthogonally overlapping broadband subchannels can be modulated and demodulated without requiring DSP. The concept is proven in real-time all-analogue SCM and WDM/SCM implementations.