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Optical sensing

UV holographic inscription
UV laser holographic inscription

Aston Institute of Photonic Technologies (AIPT) has established its world-leading position in advanced optical fibre grating fabrication. Over last 20 years, AIPT has developed and supplied fibre gratings of variety structures and high functions to ~50 worldwide research institutes and industrial companies as key components to research projects and commercial systems.   

Key research areas
  • Design and fabrication of novel structure fibre gratings
  • Multi-parameter sensing using PM, multi-mode and multi-core fibres
  • All-fibre sensing interrogation techniques and systems
  • Optical fibre sensing technology for chemical, bio-medical and food applications 
  • Fibre laser based active sensing techniques and systems 

Possible applications

  •   Up to 80 FBG sensors used to monitor strain condition of a 48m mast in a yacht (MAST project)
  •   Chirped gratings to monitor server condition with strain up to 30000µ (MAST project)
  •   Small angle tilted gratings to form miniature portable in-fibre spectrometer (EMPIRE project)
  •   45°tilted gratings as in-fibre polarisers with polarisation extinction ratio up to 35dB in PM and 50dB in   standard telecom fibres  (US Air Force and Boeing project)
  •   DNA hybridisation sensor using dual-peak long-period gratings (EPSRC)
  •   Optic fibre vector sensors to measure transverse strain with temperature compensation function (EPSRC)
  •   FBGs in passive and active 3-core mid-IR fibres (EPSRC) 

In more details

AIPT has theoretically designed and experimentally demonstrated an advanced allfibre polarisation interference filter formed by a polarisation-maintaining optical fibre cavity structure utilizing two 45° tilted fibre gratings inscribed by a UV laser. These filters can generate modulated transmission of a linear polarisation status. By changing the fibre cavity length, the free spectral range and modulation depth of the filter can be controlled. The filter exhibits a super-high and linear thermal tuning sensitivity of up to 0.6nm/°C, which is almost two orders of magnitude higher than that of normal fibre Bragg gratings. These all-fibre filters are ideal polarisation interference filters for laser and sensor systems enabling high efficiency spectral tuning from a low cost thermal technique. 

Tilted fibre gratings have several other exciting applications. They render the fibre sensitive to twist, enabling rotation or torque to be measured. They can also be used to replace the diffraction grating in a spectrometer, allowing spectroscopic measurements of light guided in a fibre to be made using just the tilted grating, a cylindrical lens and a linear CCD array detector.

2013 saw the start of this 4-year international collaboration, coordinated by Prof. David Webb of the AIPT Prof. David Webb has been instrumental in developing polymer optical fibre grating sensing technology and this project brings together international partners capable of covering all aspects of the sensor production process, from initial polymerisation to final sensor testing. The project aims to realise a mature sensing technology ripe for commercial exploitation, and includes partners who will develop novel applications for the devices as well as companies with specific requirements. 

Integral to the project is the education of a cohort of high-quality PhD students recruited by the partners, through a series of network wide training events. These will cover both the science & technology underpinning the devices as well as a range of transferrable skills that will provide the PhD students with the best possible start to their careers, whether they be in either the academic or industrial sectors. 

The full partners in TRIPOD are Aston University, BAM, the Cyprus University of Technology, the Technical University of Denmark, Ibsen Photonics, Medtronic, Carlos 3rd University Madrid, Marie Skłodowska-Curie University.

Changes to the flight regimes and even the construction of modern aircraft require a rethink of the fuel system to maintain and even enhance passenger safety. SAFUEL (The SAfer FUEL system) is a European Framework 7 project that aims to tackle this issue. AIPT’s contribution is to develop novel sensors to quantify the presence of water in the fuel, which can exist either in the form of free water at the bottom of the fuel tank, or dissolved within the fuel. 

Small quantities of free water are not of themselves a safety issue, however when the water freezes it can block fuel systems leading in exceptional circumstances to catastrophic failures. Free water also promotes the growth of biological contaminants, which can also block fuel pipes and filters. 

AIPT has developed a way of monitoring dissolved water by exploiting the water affinity of poly(methyl methacrylate) based optical fibres containing fibre Bragg grating sensors. These devices have turned out to be very sensitive, exhibiting wavelength shifts of over 1nm for changes in water content below 100 ppm. The level of free water at the bottom of the fuel tank can be monitored using long period grating sensors.

  •   Fibre Bragg and long-period gratings with filter responses from  700nm to 2µm
  •  Chirped gratings with bandwidths from 2nm to 30nm
  •   Tilted fibre gratings with small (0.7° to 20°) and large (~80°)  blazed structures
  •   45° tilted gratings as in-fibre polarisers with polarisation extinction ratios up to 50dB in standard and 35dB in PM fibres
specialfibre
Special grating host fibres