In this paper, we report a novel in-fiber Mach-Zehnder interferometer based directional torsion sensor, in which a section of two-mode fiber is sandwiched between two single mode fibers by over core-offset splicing technique. The variety of fringe visibility demonstrates the strong dependence on offset and fiber length. For the first time the near zero visibility at 0° rotating state is obtained by fine offset-modulation. The experimental results show that, with 0° turning point, the counter-clockwise to the clockwise direction can be recognized by the reversal from peak to dip of fringes. Moreover, a competitive sensitivity of 21.485 dB/(rad/cm) is gained with high linearity and low-temperature crosstalk in the range from −40 rad/m to 40 rad/m. Without any pre-twisting, our fiber torsion sensor is small size, ease of fabrication, cost efficiency and very potential in the applications of industrial and artificial intelligence.

In this paper, a comprehensive passive torsion measurement is performed firstly in a 40-cm-long polarization maintaining fiber-based Sagnac interferometer (PMF-SI), and the non-linear torsion response is found and investigated. Then, a fiber laser torsion sensor (FLTS) with a dual-ring-cavity structure is proposed and experimentally demonstrated, in which the PMF-SI is utilized as the optical filter as well as the sensing unit. In particular, the highly sensitive linear range is adjusted through fine phase modulation, and owing to the flat-top feature of fringes, an ~83.6% sensitivity difference is effectively compressed by the generated lasing. The experimental results show that, without any pre-twisting, the ultra-wide linear response from –175 to 175 rad/m is gained, and the torsion sensitivities are 2.46 and 1.55 nm/rad with high linearity (>0.99) in the clockwise and anti-clockwise directions, respectively. Additionally, a high extinction ratio (>42 dB) and small line-width (~0.14 nm) are obtained in the proposed FLTS, and the corresponding detection limit reaches 0.015 rad/m.

In this paper, an in-line Mach-Zehnder interferometer embedded in a fiber Bragg grating (FBG) is fabricated by a tiny offset-core splicing technique and inserted into a fiber ring laser to effectively improve the detection limit and discrimination of sensing. Through fine power adjustment, the stable operation of dual-wavelength lasing is completed in a single FBG for the first time to our knowledge, and simultaneous measurement of refractive index (RI) and ambient temperature is achieved with high discrimination due to the RI immunity of the FBG. The experimental results indicate that the sensitivities of RI and temperature are $-30.57\mathrm{nm}/\mathrm{RIU}$ and 131.1 pm/°C, respectively, with very low intensity drift. Furthermore, the over 20 times improvement of the RI detection limit is obtained owing to the large extinction ratio ($>30\mathrm{dB}$) and small linewidth ($\le 0.13\mathrm{nm}$).

The polarization-maintaining fiber-based Sagnac loop interferometer (PSLI) is frequently applied in directional torsion measurement, but may suffer from a large temperature cross talk. In this study, a novel method was proposed for fabrication of side-tapered PSLI by a two-step arc-discharge technique at the splicing point. The energy distribution of the taper region was characterized, and comprehensive tests were performed in terms of torsion and temperature. The experimental results showed that, through bias twisting, the measuring areas were effectively gapped and highly sensitive torsion and temperature responses were gained simultaneously. With a small wavelength shift, the torsion sensitivity reached 13.54 dB/rad in the range from − 30 to 30 rad/m. Moreover, the temperature sensitivity was found to be − 1.579 n m / ∘ C , with a near-zero intensity fluctuation. Therefore, the sensor fabricated herein successfully achieves simultaneous measurement of directional torsion and temperature with high sensitivity and ultralow cross talk. The proposed scheme has the merits of practicality, low cost, and ease of operation, and is very promising for multiparameter engineering monitoring.

Metal-free, one-pot tandem reactions of o-(1-alkyn­yl)benzamides proceed smoothly in the presence of Lawesson’s reagent­ leading to 1,3-dihydrobenzo[c]thiophene-imine derivatives in moderate to excellent yields under mild conditions. The method is highly regiospecific for the o-(1-alkynyl)benzothioamide, and only the five-membered-ring product is generated via a 5-exo-dig cyclization involving the sulfur atom.

Metasurface-assisted computational imaging has emerged as a promising route for complex optical field reconstruction. Multi-channel lensless imaging has been proved by leveraging the diverse ingredients of the optical field that can be deliberately manipulated by flat-optics. However, achieving single-shot multi-channel images by a single-cell metasurface is challenging due to the apparent capacity limitation of a single kind of meta-atom. In this work, we introduce an end-to-end inverse design method based on gradient-descent optimization algorithm for multi-channel lensless computational imaging, realizable by a single-cell metasurface. The proposed method directly provides single-cell metasurfaces without the need of complex meta-atom design strategy, which offers high efficiency and eases the fabrication. Particularly, multi-spectral, multi-depth (3D) and polarimetric imaging is demonstrated by a phase-only metasurface across the visible and near-infrared band. Our results prove a viable scheme towards practical metasurface generated lensless image reconstruction, by demonstrating the high-density information coding of single-cell metasurface. The scheme is expected to enable optical storage, optical encryption, holographic display, and full-color and three-dimensional imaging applications.