Adaptive two-wave mixing wavelength demodulation of fiber Bragg Grating sensors for monitoring dynamic strains

Qiao Yi*, Sridhar Krishnaswamy

*Corresponding author for this work

Research output: Contribution to conferencePaperpeer-review


A two-wave mixing (TWM) wavelength demodulator using InP:Fe photorefractive crystal (PRC) in the C-band (1530-1570nm) is demonstrated. The system is designed for use with Fiber Bragg Grating (FBG) sensors to monitor dynamic strains such as those induced by acoustic emissions. In this design, the FBG is illuminated with a broadband source, and any strain in the FBG is encoded as a wavelength shift of the light reflected by the FBG. The reflected light from the FBG is spilt into two unbalanced paths and both beams (pump and signal) mix in the PRC. Any wavelength shift of the reflected light is converted into an equivalent phase shift between the pump and signal beams as they travel unbalanced paths. Since TWM is an adaptive process, the two interfering beams are naturally in quadrature and remain in quadrature even in the presence of large quasi-static drift. We demonstrate that FBG demodulation using TWM has the ability to selectively monitor dynamic strains without the need for active compensation of both large quasi-static strains and temperature drift. Since TWM is readily multiplexable, several FBG sensors can be demodulated simultaneously in a single PRC. A multiplexed version of the TWM wavelength demodulator is demonstrated to monitor three FBG sensors simultaneously in a pencil lead breaking transient event.

Original languageEnglish (US)
StatePublished - Dec 1 2005
EventSAMPE Fall Technical Conference - 37th ISTC - Seattle, WA, United States
Duration: Oct 31 2005Nov 3 2005


OtherSAMPE Fall Technical Conference - 37th ISTC
Country/TerritoryUnited States
CitySeattle, WA


  • Fiber Bragg grating
  • Photorefractive
  • Two-wave mixing
  • Wavelength demodulation

ASJC Scopus subject areas

  • Materials Science(all)
  • Mechanics of Materials
  • Mechanical Engineering


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