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title: "The Impact of the Length of Fluorescent Fiber Concentrators on the Performance of VLC Receivers"
date: 2021-10-01T19:10:59+01:00
draft: false
category: paper
excerpt: "IEEE Photonics Technology Letters, first-authored by Wajahat Ali: how the length of a fluorescent fiber concentrator trades collected signal against bandwidth, tested at 16 cm, 30 cm and 1 m."
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::publication[8]

Published in IEEE Photonics Technology Letters with Dr Wajahat Ali as first author.
It is more work using ~wave:fluorescent fibers~, following on from the [wide field-of-view fiber receiver](/posts/fluorescent-fiber-wide-fov-receiver/).

## Abstract

Fluorophore doped plastic optical fibers can be used to create optical concentrators in receivers for visible light communications, that also act as wide field of view filters.
Increasing the length of these fibers allows them to collect more of the signal from the transmitter, however, it can also reduce the bandwidth of the fiber.
Results are presented from 3 different lengths of fiber which show that the best length of a fluorescent fiber depends upon the data rate.
However, a simple calculation results in a length that is a good choice for a range of OOK data rates.

## Key Findings

Fluorophore-doped optical elements make wide field-of-view VLC receivers that concentrate light from the transmitter while filtering out ambient light.
Both the fluorophore's lifetime and the transit time of photons along the concentrator limit the receiver's bandwidth.
Fibers of 16 cm, 30 cm and 1 m were characterised, and the best length depends on the required data rate.
For higher rates, a fiber whose maximum transit time matches the fluorophore lifetime beats one sized by equating 3 dB bandwidths.
For SCSF-81J fiber that length is 30 cm, at which self-absorption in the fiber is insignificant.
It also fits hosts such as laptops, and several fibers can be connected to one SiPM to cut the irradiance needed further.
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