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