We propose a kind of novel low-loss Terahertz (THz) waveguide, a polymer tube with a cross section of ring structure. Low-loss property of the polymer tube for THz guiding is achieved due to the effect of the air core inside the polymer tube which traps a large part of mode power and, at the same time, enlarges the mode area of the fundamental mode. Both the polymer tube and a solid polymer fiber are comparatively investigated, considering effective indexes, mode area, power fraction, relative absorption loss and mode profile. Simulation results show that the proposed polymer tube exhibits better loss property and confinement property than the solid polymer fiber. As an example, we finally show the experimentally measured property of a Polytetrafluoroethylene (PTFE) tube.

A highly birefringent elliptical-hole terahertz (THz) fiber with a squeezed lattice is proposed. This THz fiber is formed through regular linear deformation of a circular porous fiber by squeezing it in one direction, which may be fabricated with the existing fabrication technology. By numerical analysis we show that, with a moderate amount of deformation, the proposed THz fiber can exhibit high birefringence on a level of ${10}^{-2}$ over a wide THz frequency range. And the THz fiber guiding loss caused by material absorption can be reduced effectively, since a dominant fraction of modal power is distributed in the airholes inside the dielectric material.

A fiber-optic vector magnetic field sensor based on a large-core-offset Mach–Zehnder interferometer (MZI) infiltrated by magnetic fluid (MF) is proposed and demonstrated in this paper. By large-core-offset fusion splicing of a short single-mode fiber (SMF) between a lead-in SMF and a coupling multi-mode fiber, the MZI with a sub-millimeter length is formed, which is then sealed in an MF-infiltrated glass capillary. Through the MF’s refractive index modulation by external magnetic field, the phase of the light passing through the MZI is altered. As a result, the transmission spectrum can be monitored for the magnetic field measurement. Furthermore, from the axial-asymmetry of the large-core-offset MZI structure, the proposed sensor possesses vectorial magnetic-field-sensing ability. Experiments show that the MF-infiltrated large-core-offset MZI vector magnetic-field sensor can achieve a high wavelength sensitivity of 96.68 pm/Oe in a magnetic field range of 50–130 Oe.

A white light non-scanning correlation interrogation system was proposed and built to interrogate absolute length of the air cavity of fiber-optic compound Fabry–Perot pressure sensors for the extraction of pressure value. By carefully choosing thickness range and tilt angle of the optical wedge used for cavity length matching, correlation interferometric signal of the basal cavity can be naturally filtered out. Based on peak positioning by Fourier transform, bandpass filtering in frequency domain, inverse Fourier transform back to time domain, envelope fitting and zero fringe finding through a gravity center method, cavity length can be determined with an accuracy of 0.04%. The system was used for the interrogation of a fiber-optic compound Fabry–Perot pressure sensor under different pressures. For a pressure range of 0.1~2.9 Mpa, the linear relationship between the air cavity length and the gas pressure imposed was successfully extracted.