A more flattering light

A groundbreaking form of ‘flat’ optical fibre has been developed and patented by Southampton University. It promises to be far more flexible and efficient than existing integrated opto-electronic systems.

A groundbreaking form of ‘flat’ optical fibre has been developed and patented by Southampton University. It promises to be far more flexible and efficient than existing integrated opto-electronic systems, which couple rigid, glass-based substrates with lengths of optical fibre.

Although these are advanced, they are rather limited, according to Dr Corin Gawith, the project’s leader from the university’s Optoelectronics Research Centre.

‘Advances in integrated optoelectronics have allowed us to combine many components and shrink them right down,’ he said. ‘At the moment these things are traditionally based on silicon so you end up with structures etched on to glass, which is very rigid and stable. To get light to and from these “light chips” you need to add optical fibres — and the problem with this is that the losses at the chips are much too high.’

This is particularly bad where the fibre and the circuit are joined, as a portion of the light is lost at each junction. Gawith said while this is not so much of a problem with single devices on a branch of fibre, if you want to perform multiple functions over large distances more information can be lost.

Gawith’s team has filed a patent for the development of a new form of optical fibre that etches the electronic circuits into the fibre itself. Whereas conventional optical fibre is only a few hundred microns across and moves light from one place to another, the team aims to develop a fibre that combines the flexibility of fibre with the functionality of an integrated optical chip.

‘We are trying to come up with a platform that combines the advantages of the fibre processing itself — which is a very mature, high-quality technology — but with the chips themselves in the actual fibre, eliminating additional components,’ said Gawith.

One of the main advantages of this new optical fibre is that it would have extremely low light losses over large distances. Different optical circuits could also be introduced at any number of points along its length.

One possible application would be in measuring water quality. Instead of needing 50 different sensors connected via bundles of optical fibres along the length of a river, the sensors could be written into the fibre itself, which would simplify the entire process and make it far more resilient, said Gawith.

‘We are really breaking the mould with this and it should allow us to do much more versatile work while eliminating unnecessary processing steps,’ he added.

The team has been experimenting with how the optical fibre is constructed, or ‘drawn’. Normally optical fibre production begins with a pure silica tube into which different types of soot are deposited.

This tube is then heated and collapsed, leaving a hair-like rod behind. To produce these new flat fibres, the team is applying a vacuum to the tube, which makes it collapse into a larger rectangular shape.

The flat fibres will also be combined with another patented technology developed by the same team. The fibres will benefit from a technique known as direct UV writing — more commonly used with polymers — that uses an ultraviolet beam to ‘write’ patterns on to silica substrates. This can then be used to draw circuits into the optical fibres.

The research centre has a spin-out called Stratophase, which uses this technology to make miniaturised chips for liquid and biological sensors.

‘These new fibres will be able to eliminate processing steps and losses over distances, while at the same time allowing far more versatility,’ said Gawith. ‘It really is putting the best of two worlds into one.’

The team has been carrying out experiments introducing simple functions such as light-splitters and Bragg Gratings into the fibres, but Gawith said it will require a couple of years more research before a product with commercial potential will be ready.

‘The experiments have been extremely positive but it is still early days,’ he said.