Throughput of Optical WDM with Wide LED Spectra and Imperfect Color-detecting Filters

Abstract

Plastic optical fiber (POF) is considered as an attractive candidate for next-generation networks, for fiber-to the-home or for fronthaul of wireless access points in offices. Inside such spaces, visible light communication (VLC) can be an attractive interference-free communication approach. Such system can offer high data rates with potential cost reduction compared to existing techniques. Wavelength division multiplexing (WDM) can not only increase the link capacity, but also offers the ability to share the POF media with multiple services. In VLC systems, WDM can increase capacity. However, the use of narrow emitters and narrow bandpass filters to demultiplex the WDM signals are relative costly components in such systems. This work focuses on inexpensive light emitting diodes (LEDs), to accelerate mass-market applications, and we explore the potential for relaxing the wavelength filters at the detector. In these scenarios, multiple-input multiple-output (MIMO) technology can efficiently suppress interference or automatically fall back to common signalling if the crosstalk is so large that parallel channels would be insufficiently independent. We calculate the MIMO crosstalk channel coefficients due to relatively wide LED spectra. We derive analytical expressions for the maximum achievable rate of the system and we conclude that relatively large amount of crosstalk can be tolerated without jeopardizing performance, provided that dedicated signal processing is used. We show that without such signal processing, the choice of optical filters is very critical.