The Wide Field of View Cherenkov Telescope (WFCT) is mainly constituted by optical reflector and focal-plane photomultiplier (PMT) array camera. In order to avoid loss of Cherenkov signal resulting from the dead area between circular PMT tubes and invalid fringe of each PMT, the light concentrator used as front window of PMT is considered to improve detective efficiency. Basing on the edge-ray principle and features of WFCT, several light concentrators are designed and simulated with ZEMAX. The result shows that the hollow hexahedral compound parabolic concentrator (hex-CPC) has good performance in collecting light. Moreover, the samples of the hollow hexahedral CPC have been manufactured and tested.
We have developed an observable sensitive fiber nonlinear polarization sensing method based on the whispering gallery
mode (WGM). The spectral position of the WGM excited by evanescence field shifts in response to the refractive index
change of the fiber’s dielectric caused by nonlinear polarization interaction with incident light field or surrounded
electromagnetic filed. Theoretical resonance spectral shift equation was derived and calculation showed that a sensitivity
of approximately 0.0172∼0.0196 RIU (refractive index unit) per nm at least was achieved due to the extremely high <i>Q</i>
factor associated with the WGM.
Whispering gallery modes (WGM) in a cylindrical micro-cavity of a silica optical fiber are excited with a tapered fiber
of ~7μm in diameter by evanescence field, and the WGM spectra of the cylindrical micro-cavity with different
diameters (300μm, 400μm and 500μm) are measured. The resonant positions and their separations of the spectra are
assigned precisely by an asymptotic formula. Considering the fiber dispersion and the errors induced from it, the values
of the resonant position and its separation achieved from assignment within the experimental spectra range (1290~1320 nm)
match well with a theoretical calculation and a measured accuracy of the refractive index of the micro-cavity can be
as high as 10<sup>-5</sup>, which indicates that a dispersion sensor can be formed by measuring the dispersive features of WGM in a