Birefringent elastomers with Multiple Stimuli-Responses

Currently, even though birefringent soft materials have attracted considerable attention for many sensors and optical devices, it is still difficult for most of them to achieve multiple responses. Herein, we have designed a multiple-responding birefringent elastomer with high birefringence but low modulus by using 2-phenoxy-ethanoacrylate (PHEA) as monomer and 4-cyano-4'pentylbiphenyl as solvent. The excellent transparency (~90%) exhibited by the designed birefringent elastomer allowed us to observe the change of interference color. The obtained birefringent elastomer not only can be used as a photoelastic strain sensor with high sensitivity and fast response but also show a very sensitive response to heat, particularly in the range of the human body temperature. More interestingly, it shows excellent dielectric properties with a strong correlation between the interference color and the applied electric field, which allows easily writing and erasing the encrypted information. These unique multi-signal response features of our obtained birefringent elastomer shed light on the multiple information encryptions, the anti-counterfeiting, and the multifunctional sensors.

Study on the high birefringence and low confinement loss terahertz fiber based on the combination of double negative curvature and nested claddings

A novel double negative curvature nested fiber structure is designed by adding extra circular cladding tubes to enhance the birefringence and reduce the confinement loss. The fiber structure is composed of eight circular cladding tubes and two semi-elliptical nested tubes. The transmission performances of terahertz fiber, including birefringence, confinement loss, dispersion and effective mode field area, are studied by changing the parameters of cladding tubes. In the frequency range of 1.75 - 2.6 THz, the broad bandwidth of 850 GHz with high birefringence (above 10-4) can be achieved. The confinement loss of y-polarization mode with the frequency of 2.575 THz can be as low as 0.00231 dB/cm. The waveguide dispersion coefficient is between ±0.188 ps/(THz•cm) in the frequency range of 2.0 - 2.475 THz. The maximum effective mode field area of x- polarization mode is 2.618×10-6 m2 at 2.6 THz.

Simultaneous Measurement of pH and Temperature with Phase-Shifted Long-Period Fiber Grating Inscribed on High-Birefringence Fiber by CO2 Laser Pulses

We propose an optical fiber grating sensor capable of simultaneously measuring pH and temperature based on a phase-shifted long-period fiber grating (PS-LPFG) inscribed on high-birefringence fiber (HBF). The PS-LPFG was fabricated on HBF with CO2 laser pulses, and a phase shift π was induced by inserting a grating-free fiber region (GFFR) between two identical LPFGs with a grating period of ˜510 μm. The length of the GFFR was set as half of the grating period to induce a π phase shift. With the spectral characteristics of a π-PS-LPFG exhibiting two split attenuation bands, the PS-LPFG written on HBF, which is referred to as the HB-PS-LPFG, can create two polarization-dependent transmission spectra with dual-resonance dips at different wavelengths according to two orthogonal input polarization states, e.g., linear horizontal polarization (LHP) and linear vertical polarization (LVP). For simultaneous measurement of pH and temperature with the fabricated HB-PS-LPFG as a sensor head, the inter-resonance wavelength separation of the dual-resonance dips in each transmission spectrum obtained for an LHP or LVP input signal was exploited as a sensor indicator. By investigating the wavelength changes of the two sensor indicators, which were induced by pH and temperature variations, linear and independent spectral responses to both pH and temperature variations were experimentally confirmed in a pH range from 1 to 11 and a temperature range from 25 to 65 °C. Owing to the unique pH and temperature responses of the fabricated HB-PS-LPFG, ambient variations in pH and temperature could be simultaneously estimated from the measured wavelength changes and sensitivities of the two sensor indicators.