We report a type of single-hole core photonic crystal fiber for low-loss polarization-maintaining terahertz (THz) wave guidance. Simulation results show that high birefringence at a level of 10 − 2 can be obtained by a design of minor position adjustment of the central air hole. Low effective material loss can be achieved because of the introduced central air hole. The strategy of the central air hole movements is also applicable for the three-hole core THz photonic crystal fibers. Other transmission characteristics including single-mode condition, power fraction, confinement loss, and dispersion were discussed in detail. It is quite clear that the proposal facilitates the fabrication process due to the simple structure.
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.
Measurements of birefringence induced in K9 and fused silica specimens by cracks produced by 1064 nm Nd∶YAG laser have been presented. The Birefringence data is converted into the units of stress, thus permitting the estimation of residual stress near crack. The intensity of residual stress in K9 glass is larger than that in fused silica under the same condition. The similarity of residual stress distribution along the y-axis reveals that the nature of shock wave transmission in optical materials under 1064 nm laser irradiation is the same with each other. The value of residual stress can be influenced by laser parameters and characterization of optical material. Simulation based on a theoretical model giving the residual stress field around a crack is developed for comparison with experiment results. The probability of initial damage and the direction of the energy dissipation in cracks determine the residual stress distribution. The thermal stress coupling enlarges the asymmetry of residual stress distribution. Residual stress in optical material has a strong effect on fracture and should be taken into account in any formulation that involves the enhanced damage resistance of optical components used in laser induced damage experiments.