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.

We have proposed and experimentally demonstrated a novel optical fiber sensor for simultaneous measurement of high temperature and gas pressure based on a Regenerated Fiber Bragg grating (RFBG) cascaded with a homemade hollow core Bragg fiber (HCBF). The HCBF functions as an anti-resonant reflecting waveguide and acts as a pressure and temperature sensing unit. The sample was fabricated and tested in our lab, exhibiting a high linear pressure and temperature sensitivity of −3.747 nm/MPa and 25.925 pm/°C in a large-dynamic range of 2 MPa and 600 °C, respectively. The RFBG, as a temperature monitor, was integrated to compensate the temperature cross-correspondence of the HCBF. By utilizing a 2 × 2 matrix obtained with the experimental results, simultaneous measurement of temperature and gas pressure can be achieved. Besides, compact size, low cost and high sensitivity make the sensor more competitive in harsh environment application.

A novel cylindrical hybrid plasmonic waveguide is proposed to achieve subwavelength confinement of light. With a metal core surrounded by a silica layer and a silicon layer, the proposed cylindrical hybrid plasmonic waveguide can achieve a ring-structure mode profile at the operating wavelength ($1550\mathrm{nm}$). Most mode power locates in the silica layer with a nanoscale thickness (e.g., 50, 20, or even $5\mathrm{nm}$), which is due to the effects of both a strong discontinuity of the normal component of the electric field at the silicon–silica interface and the exited surface plasmon wave at the silica–metal interface. Cylindrical hybrid plasmonic waveguides with different structure parameters are investigated and a relatively long propagation distance of tens of micrometers (or even hundreds of micrometers) is observed.

In the article, a novel reflective all-fiber integrated sensor for simultaneous gas pressure and temperature sensing has been proposed and demonstrated in experiment. The proposed sensor is fabricated by combining seven core fibers (SCFs), a twin-hole and dual-core fiber (THDCF), a single-mode fiber (SMF) extrinsic Fabry-Perot interferometer (FPI) and a fiber Bragg grating (FBG). The FPI section and FBG section act as a pressure and temperature sensing unit. Especially, the MZI has the effect of filtering the FPI spectrum and is more conducive to the demodulation of the FPI reflected signal. In FPI section, the two SMFs connects with a hollow core capillary (HCC) by the ultraviolet (UV) curing glue. The sensor exhibits a high pressure and temperature sensitivity of 13.10 nm/MPa and 0.20 nm/°C in the range of 0.1-1.2 MPa and 30-90 °C, respectively. The FBG works as a temperature sensor without pressure responding, is fabricated by using the UV laser-based phase mask technology in our lab. By utilizing the dual-wavelength matrix method, both gas pressure and temperature can be measured simultaneously. In sum, with the advantage of compact size, easy fabricated, low cost, high sensitivity, reflection-type and the ability of multi-parameter measurement, our sensor is more competitive in harsh environments.

A thulium-doped fiber laser employing a Sagnac loop mirror made by a 145.5 cm polarization-maintaining fiber is demonstrated, which can operate with stable dual-wavelength lasing or tunable single-wavelength lasing around 1860 nm. Both stable dual-wavelength and tunable single-wavelength lasing are achieved by adjusting a polarization controller in the Sagnac loop mirror. The experimental results show that the output of the reported fiber laser with two different operation modes is rather stable at room temperature.