Fabrication and Characterization of Infrared Optical Fibre

Lead Research Organisation: University of Southampton
Department Name: Optoelectronics Research Centre

Abstract

I produce infrared fibre from Gallium Lanthanum Sulphide based glasses (GLS), using both preform and crucible drawing.
This glass has a crystallization temperature close to its fibre drawing temperature. When it crystallizes, it rapidly loses its light transmitting properties as well as its mechanical qualities. Therefore, it must be drawn into fibre rapidly, before crystallization has time to negatively impact the glass.

In order to address this issue, past work has deemed necessary to add oxygen to the composition of the glass. This enables to facilitate drawing at the cost of sacrificing part of the transmission window of the resulting fibre.

In this work, we are questioning that assumption. This will enable us to produce GLS fibre with an uncompromised transmission window. We aim to achieve this goal thanks to systematic enhancements of the method for traditional preform drawing, as well as developing a novel crucible drawing method.

If we are successful, GLS will become a considerably stronger competitor as infrared fibre, benefiting both from its uniquely positioned transmission window, ranging from 500 nm to 16Mu m (from the visible to long-wavelength infrared), as well as its remarkable mechanical strength. In particular, it would find very well-suited applications in thermal imaging and chemical sensing.

Publications

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Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/N509747/1 01/10/2016 30/09/2021
1950276 Studentship EP/N509747/1 01/04/2017 30/09/2020 Bruno Moog
 
Description The aim of this work is to explore the feasibility of fabricating oxygen-free Gallium Lanthanum Sulfide (GLS) infrared optical fibre. This particular glass possesses a uniquely located transmission window ranging from 500 nm to 16µm, with applications in thermal imaging and chemical sensing. This glass is particularly difficult to make into optical fibre, due to its crystallization temperature being close to its fibre drawing temperature. The formation of any crystals compromises the overall transmission of the glass as well as its mechanical properties. As such, past work has deemed it necessary to add a small percentage s of oxide to the composition of this glass for the purpose of fibre drawing. And while this does facilitate the drawing process significantly, the transmission window is sacrificed towards the infrared, with a hard cut-off at around 5µm.

Optical fibre may be fabricated in one of three ways.
1) It can be drawn from a uniform rod of glass suspended into a cylindrical furnace. As the glass is slowly fed into the top and softened, it is pulled out of the bottom of the furnace, it stretches and forms coreless fibre.
2) It can be drawn from a structured rod of glass, typically made of two different compositions, one enveloping the other in a core/clad structure. The process is the same, but the resulting fibre possesses significantly lower optical losses than coreless fibre.
3) And finally, it can be drawn from a molten state a crucible at the bottom of which a hole was previously made. The crucible is heated in a similar cylindrical furnace, and as the glass softens, it is pushed out of the hole via the application of pressure, forming optical fibre. This method has been demonstrated to produce the best optical fibre, as it reduces the number of potential sources of contamination, as well as improves the surface quality of the resulting fibre.

In order to achieve the goal of oxygen-free GLS fibre, several innovations have been made and are currently being perfected:
- Crucible drawing has been implemented successfully for the first time at the ORC. It has been demonstrated that it can be used to produce ultra-thin coreless fibre (<50µm), which can then be made into an optical bundle for imaging.
- The available equipment for fibre drawing has been modified to enable better control of the experimental parameters, in particular regarding the structure of the silica furnace and the application of gaseous purge to it.
- Rod casting has been successfully tested, in order to quickly fabricate glass rods from bulk material. It is currently being modified in an attempt to produce core/clad preforms.
- Lathe turning of glass ingots into rods is now routinely performed in order to make coreless fibre. This enables to quickly test the feasibility of fibre fabrication from novel glass compositions.
- In-house rod polishing is now an integral part of the fibre fabrication process, minimizing surface imperfections that would otherwise promote crystallization.
- A new fibre coating method has been successfully tested, and should further facilitate fibre fabrication as it does not require the use of a coating dye that needs to be aligned, slowing down the fibre drawing process and increasing the risk of breaking the fibre. As such, this improved coating method does not slow or complicate the fibre drawing process.
Exploitation Route This work will produce novel optical fibre with applications in chemical sensing and thermal imaging.
Sectors Aerospace, Defence and Marine,Digital/Communication/Information Technologies (including Software),Electronics,Environment

URL http://chalcogenide.net