Fabrication and characterisation of 45º and Ex 45º
: tilted fibre gratings and their applications in fibre lasers and sensors

  • Chengbo Mou

Student thesis: Doctoral ThesisDoctor of Philosophy


In this thesis, I present the studies on fabrication, spectral and polarisation characterisation of fibre gratings with tilted structures at 45º and > 45º (namely 45º-
TFGs and ex 45º-TFGs throughout this thesis) and a range of novel applications with these two types of grating. One of the major contributions made in this thesis is the systematic investigation of
the grating structures, inscription analysis and spectral and polarisation properties of both types of TFGs. I have inscribed 45º-TFGs in standard telecom and polarisation maintaining (PM) fibres. Two wavelength regions of interest have been explored
including 1.55 µm and 1.06 µm. Detailed analysis on fabrication and characterisation of 45º-TFGs on PM fibres have also been carried out for the first time. For ex 45º-
TFGs, fabrication has been investigated only on low-cost standard telecom fibre.
Furthermore, thermal responses have been measured and analysed showing that both types of TFG have low responsivity to temperature change. More importantly, their refractive index (RI) responses have been characterised to verify the high responsivity to surrounding medium. Based on the unique polarisation properties, both types of TFG have been applied in
fibre laser systems to improve the laser performance, which forms another major contribution of the research presented in this thesis. The integration of a 45º-TFG to
the Erbium doped fibre laser (EDFL) enables single polarisation laser output at a single wavelength. When combing with ex 45º-TFGs, the EDFL can be transformed
to a multi-wavelength switchable laser with single polarisation output. Furthermore, by utilising the polarisation property of the TFGs, a 45º-TFG based mode locked fibre laser is implemented. This laser can produce laser pulses at femtosecond scale and is
the first application of TFG in the field of nonlinear optics.
Another important contribution from the studies is the development of TFG based
passive and active optical sensor systems. An ex 45º-TFG has been successfully developed into a liquid level sensor showing high sensitivity to water based solvents. Strain and twist sensors have been demonstrated via a fibre laser system using both 45°- and ex 45º-TFG with capability identifying not just the twist rate but also the
direction. The sensor systems have shown the added advantage of low cost signal demodulation. In addition, load sensor applications have been demonstrated using the
45º-TFG based single polarisation EDFL and the experimental results show good agreement with the theoretical simulation.
Date of Award7 Sept 2012
Original languageEnglish
SupervisorLin Zhang (Supervisor)


  • fibre bragg grating
  • tilted fibre grating
  • fibre laser
  • optical sensor
  • fibre sensor

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