Impact of blue filtering on effective modulation bandwidth and wide-angle operation in white LED-based VLC systems

Abstract

This work studies the impact of employing blue filters on the resulting effective modulation bandwidth of visible light communication (VLC) systems using phosphor-coated white light emitting diodes (LEDs) under wide-angle operation. Effective modulation bandwidths are assessed and compared for VLC systems with ideal and non-ideal transmission blue filters at the receiver. Angle tolerance capabilities of the employed filters have also been investigated in the study. Commercially available phosphor-coated white LED and photodetector (PD) models are utilized to obtain realistic results. We show that the choice of the blue filter structure, combined with the white LED and PD, affects the system’s effective modulation bandwidth. We also show that there exists a trade-off between obtaining a relatively large modulation bandwidth and preserving the wide-angle operation of the system. A figure of merit (FOM) is also introduced to represent such a trade-off. Moreover, a simple estimation of the expected effective modulation bandwidth of a VLC system using phosphor-coated white LED is developed as a result of the weighted average of the blue and yellow light responsivity of the filter. A numerical example is also included in which the optical signal to noise ratio (OSNR) is computed in VLC systems with and without the addition of a blue filter. The OSNR shows enhancement when a blue filter with a wide rejection region is inserted in the studied VLC system.