Enhanced fiber Bragg grating sensor demodulation technique using cascade wavelength division multiplex couplers

An enhanced technique for interrogating fiber Bragg grating wavelength shift using cascade wavelength division multiplexer (WDM) couplers was proposed and demonstrated. Three WDM couplers which show a linear filter function over the expected wavelength range are employed and cascaded to track Bragg wavelength shifts. Compared with single WDM demodulator. sharper spectral slope is obtained and considerable linear filter range is kept. The static and dynamic strain sensor demodulation experiments demonstrated that the simple passive technique improves the sensitivity approximately two times and keeps 5nm linear demodulation range based on our devices. The cascade WDM coupler demodulation system has high scan rate which can be used to monitor fast vibration.

Surface plasmon waves generated by nanogrooves through spectral interference

A pure surface plasmon polariton (SPP) model predicted that the SPP excitation in a slit-groove structure at metallodielectric interfaces exhibits an intricate dependence on the groove width P. Lalanne et al. [Phys. Rev. Lett. 95, 263902 (2005); Nat. Phys. 2, 551 (2006)]. In this paper, we present a simple far-field experiment to test and validate this interesting theoretical prediction. The measurement results clearly demonstrate the predicted functional dependence of the SPP coupling efficiency on groove width, in good agreement with the SPP picture.

Investigation of spectral bandwidth of optical parametric amplification

The spectral bandwidth of three-wave-mixing optical parametric amplification has been investigated. A general mathematical model for evaluating the spectral bandwidth of optical parametric amplification is developed with parametric bandwidth and gain bandwidth via three-wave noncollinear interactions. The spectral bandwidth is determined by expanding the wave-vector mismatch in a Taylor series and retaining terms through second order. The model takes into account the effects of crystal length, noncollinear angle, group velocity, group-velocity dispersion and gain coefficient. The relation between parametric bandwidth and gain bandwidth is clearly defined. The model is applied to a BBO OPA, a LBO OPA and a CLBO OPA.

Spectral relationship of photoinduced refractive index and absorption changes in fulgide films

Fulgides are one kind of organic photochromic compound, which are famous for their thermal irreversibility. In this report, from the difference spectra of the absorption A() of one kind of pyrrylfulgide, the spectral refractive index change n() was calculated by the Kramers-Kronig relation (KKR), and a good correlation of theoretically derived values and the experimental values of the n measured by a modified Michelson interferometer was found. Further, it is demonstrated that it was possible to calculate the spectral dependence of diffraction efficiency from the easily accessible absorption changes. This method will be a useful tool for the characterization and optimization of fulgide films. The results show that the diffraction efficiency is high at 488 and 750 nm, where the absorption is very small, so we can realize non-destructive reconstruction.