Optical Receiver Front-end Design Choices to Enhance Throughput of LiFi

The optical front end (OFE) is a critical part in most Optical Wireless Communication (OWC) systems. It captures the incoming light flux, converts it and amplifies it into an electrical signal. Its photodiode (PD) impedance and transimpedance amplifier (TIA) can be limiting factors to the throughput, determined by the noise levels and the (gain-) bandwidth. This paper starts with a refined model of PD and the TIA, in order to analyze in detail the strength and frequency characteristics of the relevant noise sources. The noise spectral density typically rises at higher frequencies due to the capacitance of PD. This degrades the signal-to-noise ratio (SNR) and limits the useful modulation bandwidth, also depending on which modulation methods, equalization and adaptive power and frequency dependent bit loading is used. To some extent, SNR can be traded for bandwidth by choosing an appropriate PD size. We investigate different optical receiver design strategies, where single PD is segmented into pieces, and connected to one or more TIAs. Numerical analysis on channel quality is carried out to compare between various design strategies