A type of high-birefringent terahertz (THz) photonic crystal fiber (PCF) with all circle air holes is proposed. The characteristics including birefringence, dispersion, and confinement loss are numerically analyzed in detail by using the finite element methods. Simulation results show that the proposed THz PCFs exhibit high birefringence on the level of 10−2 in the frequency range of 2 to 4 THz, which is realized by the minor position adjustment of air holes in the first ring of the cladding. We believe that the proposed THz PCFs can be fabricated without complications due to their simple structure. In addition, two porous-core THz PCFs are proposed and the birefringence property is investigated.
High–purity fused silica irradiated by UV laser in vacuum with different laser pulse parameters were
studied experimentally. The defects induced by UV laser are investigated by UV absorption, fluorescence
spectra and the structural modifications in the glass matrix are characterized by Raman spectra. Results show
that, for laser fluence below the laser–induced damage threshold (LIDT), irradiation results in the formation of
an absorption band and four defect–related fluorescence (FL) bands, and the intensities of absorption band and
FL bands were increased with laser power and/or number of laser pulses. The optical properties of these point
defects were discussed in detail. Analyzed these spectra, it indicates that the presence of different centers whose
spectral features are modulated by structural disorder typical of the glass matrix.