Abstract
Presented for the first time, to the best of the authors’ knowledge, is the design of a power smart in-door optical wireless link that provides lossless beam propagation between Transmitter (T) and Receiver (R) for changing link distances. Each T/R unit uses a combination of fixed and variable focal length optics to smartly adjust the laser beam propagation parameters of minimum beam waist size and its location to produce the optimal zero propagation loss coupling condition at the R for that link distance. An Electronically Controlled Variable Focus Lens (ECVFL) is used to form the wide field-of-view search beam and change the beam size at R to form a low loss beam. The T/R unit can also deploy camera optics and thermal energy harvesting electronics to improve link operational smartness and efficiency. To demonstrate the principles of the beam conditioned low loss indoor link, a visible 633 nm laser link using an electro-wetting technology liquid ECVFL is demonstrated for a variable 1 to 4 m link range. Measurements indicate a 53% improvement over an unconditioned laser link at 4 m. Applications for this power efficient wireless link includes mobile computer platform communications and agile server rack interconnections in data centres.
Highlights
It was realized in the late 1970s that diffused Infrared (IR) light much like Radio Frequency (RF) radiation filling a room could be used for wireless data communications [1]
Recent advances in micro-devices, such as laser modules, micro-lenses, Electronically Controlled Variable Focus Lenses (ECVFLs), and Micro-Electro-Mechanical Systems (MEMS) beam directing micro-mirrors, points to the realization of a new higher compactness micro-optics scale optical wireless T and R modules that can be readily adapted for use in a smart indoor low loss application link design
Low cost visible laser pointers have become available with good beam divergence and beam shape properties, these can be exploited for short range indoor optical wireless links such as the one attempted in this paper
Summary
It was realized in the late 1970s that diffused Infrared (IR) light much like Radio Frequency (RF) radiation filling a room could be used for wireless data communications [1]. This indoor optical wireless technique is known as the Diffused Infrared Radiation (DFIR) and is very effective in preventing physical blocking of light to the receiver and tolerant to transmitter/receiver mobility Since this method uses scattered light in room, it is highly power inefficient and limits achievable data rates due to multipath effects. A smart free-space link design was proposed and theoretically analysed for a variety of link ranges varying from short indoor applications to long distance inter-satellite links [9] These smart link designs use Transmitter (T) and Receiver (R) electronically agile beam conditioning lens optics that adjust focus based on specific link distance requirements for a given scenario. Common Transmit (T) and Receive (R) Aperture smart T/R module design
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