High-sensitivity and high extinction ratio fiber strain sensor with temperature insensitivity by cascaded MZI and FPI.

Low extinction ratio (ER) and high temperature cross-sensitivity are serious but common problems for most strain sensors based on Vernier effect. In this study, a hybrid cascade strain sensor of a Mach-Zehnder interferometer (MZI) and a Fabry-Perot interferometer (FPI) with high sensitivity and high ER based on Vernier effect is proposed. The two interferometers are separated by a long single-mode fiber (SMF). The MZI is used as the reference arm, which can be flexibly embedded in the SMF. The FPI is used as the sensing arm and the hollow-core fiber (HCF) as the FP cavity to reduce optical loss. Simulation and experiments have proven that this method can significantly increase ER. At the same time, the second reflective face of the FP cavity is indirectly spliced to increase the active length to improve the strain sensitivity. Through the amplification of Vernier effect, the maximum strain sensitivity is -649.18p m/µ ε, and the temperature sensitivity is only 5.76pm/∘C. The magnetic field was measured by combining the sensor with a Terfenol-D (magneto-strictive material) slab to verify the strain performance, and the magnetic field sensitivity is -7.53nm/mT. The sensor has many advantages and has potential applications in the field of strain sensing.

Intensity-symmetric accelerating caustic beams.

We construct and generate symmetric accelerating caustic beams (ACBs) by using 3/2-order phase-only masks with elliptical contour based on optical caustics and diffraction theory. The symmetric ACBs are a type of bimodal accelerating caustic beam with two quasi-constant intensity peaks, very similar to the combination of two face-to-face Airy-like beams judging by appearance. Their fundamental optical morphology and force properties of particles in ACBs are subsequently provided. The unique optical properties of ACBs can be exploited for practical uses, such as accelerating electrons and clearing micrometer-sized particles as a laser micrometer-sized "water pump" instead of a laser micrometer-sized "snowblower" of accelerating Airy beams.

[A new kind of grade system for thoracic pedicle screw placement and its clinical purpose].

OBJECTIVE: To introduce a new kind of grade system for thoracic pedicle screws placement by performing postoperative computerized tomography (CT) scanning and discussion the clinical purpose. METHODS: Four hundred and fifty thoracic pedicle screws were implanted in 64 patients with the assistance of fluoroscopy. Postoperative CT scanning was conducted to determine a grade for each screw: Part A, screw entirely contained within pedicle; Part B(1), violate lateral or upper pedicle but screw tip entirely contained within the vertebral body (VB); Part B(2), violate medial or inferior of pedicle; Part B(3), tip penetrated anterior or lateral VB; Part C, violate pedicle or VB and endangers spinal cord, nerve roots, or great vessels. Based on anatomical morphometry, thoracic vertebral were subdivided into upper (T(1 - 2)), middle (T(3 - 6)), and lower (T(7 - 12)) regions. The mean follow-up period was 25.8 months. RESULTS: The postoperative CT scanning-documented grade were determined: Part A, 367 screws (81.6%); Part B, 78 (17.3%), B(1) 40 (8.1%); Part B(2), 23 (5.1%); Part B(3), 15 (3.4%); Part C, 5 (1.1%). There were not significant difference between upper and lower thoracic that the placement of pedicle screws in part B or C. In part C, 5 pedicle screws were all in the middle thoracic. CONCLUSION: Postoperative CT scanning should be considered as a routine examination for evaluating thoracic pedicle screw placement.