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Type II fiber Bragg gratings (FBGs) inscribed with femtosecond (fs) laser possess significant potential for high temperature sensing. In this work, we propose and demonstrate a method for fabricating a parallel-integrated ultra-short type II FBG (PI-US-FBG) by using an fs laser point-by-point technology. The PI-US-FBG, featuring by an ultra-short grating length of 80 m, consists of six identical FBGs parallel-inscribed into a fiber core at different radial positions in the same cross section. The fabricated PI-US-FBG exhibits a broadband Gaussian-shape spectrum with a low reflectivity of ~10%, an ultra-low out-of-band insertion loss of 0.01 dB, and a large full width at half maximum bandwidth of 9.4 nm. Moreover, this PI-US-FBG could be used as a high temperature sensor with a wide measurement range from 25 to 1000 C, and an excellent linearity was achieved with a dual-wavelength differential detection. The temperature sensitivity could be increased from 0.00316 to 0.00945 (dB/C) by enlarging the wavelength spacing of the tunable laser. In addition, two cascaded PI-US-FBGs were used to precisely measure the temperature field distribution in a CO2 laser spot with a very high spatial resolution of 100 m. Hence, the proposed PI-US-FBGs could be used for a large-scale fiber sensor network, especially in future distributed temperature measurement with a high spatial resolution.

We inscribe and characterize a series of helical intermediate-period fiber gratings (HIPFGs) on single-mode fiber with pitches from 24 μm to 48 μm. The fabricated HIPFGs have low temperature sensitivity, low torsion sensitivity, and high refractive index sensitivity. A series of separated peaks with low insertion losses and high coupling strengths are observed in the transmission spectra of the HIPFGs. For the HIPFG with grating pitch of 36 μm (HIPFG-3), the peaks located at around 1596 nm and 1603 nm are chosen to evaluate the sensor performance of the fiber gratings. The temperature sensitivities are 6.86 pm/°C and 7.53 pm/°C for peaks around 1596 nm and 1603 nm, respectively. The corresponding values of the torsion sensitivities are 8.67 nm/(rad/mm) and 9.49 nm/(rad/mm) for those two peaks, respectively. In addition, the average refractive index sensitivity of the grating reaches 393.9 nm/RIU in the range of 1.310-1.408. The sensitivity of the HIPFG-3 at the RI of 1.408 is calculated to be 1291 nm/RIU. Therefore, we conclude that the HIPFGs proposed in this paper can be used as a high-sensitivity refractive index sensor which is not sensitive to temperature and torsion.

A highly-sensitive temperature sensor with controllable sensitivity based on Vernier effect by cascading a tunable extrinsic Fabry-Perot interferometer (FPI) and a fixed reflective Lyot filter (RLF) is theoretically investigated and experimentally demonstrated. The temperature sensitivity can be tuned by modulating the cavity length of the extrinsic FPI and online monitoring the envelope of superimposed spectrum with optical spectrum analyzer (OSA). The FPI works as the reference arm to tune the temperature sensitivity of the sensing system, while the RLF with 1-meter polarization maintaining fiber (PMF) acts as the sensing probe. Experimental results prove that by changing the cavity length of the FPI, the sensitivities of −3.82 nm/°C, −8.33 nm/°C and −14.63 nm/°C can be achieved. Compared with the single sensing element, the sensitivities are magnified by 3.78, 8.25 and 14.49 times. The proposed temperature sensor is feasible to be applied practically in scenarios which require different temperature sensitivities in demanded temperature detection ranges.

An effective method, reducing the material volume of the air cavity by asymmetrical tapering fiber, is demonstrated to enhance the sensitivity of the strain sensor dramatically. High-sensitive strain sensors are fabricated through this method that splicing and tapering fiber with arc discharge at the misaligned center of the air cavity. The strain sensitivity of the sensor is measured to be ∼ 41.81 pm/μϵ at a resonant wavelength ∼ 1560 nm ranging from 0 to 500 μϵ. In addition, the experimental results show that the asymmetrical tapered-fiber enables both the material volume to smaller and the wall thickness to thinner, resulting in strain sensitivity higher. The proposed sensors have the advantages of fabricated repeatability, high sensitivity, and compact size, benefiting its practical sensing applications.

Hydrogen is widely used in industrial production and clinical medicine, and as fuel. Hydrogen becomes explosive when the hydrogen-air mixture ranges from 4 to 76 vol%; thus, a rapid hydrogen concentration measurement is particularly important in practical applications. We present a novel fiber optic hydrogen sensor with fast response fabricated from a graphene-Au-Pd sandwich nanofilm and an ultrashort fiber Bragg grating. The response time is only 4.3 s at a 3.5 vol% hydrogen concentration. When the measured hydrogen concentration was increased from 0 to 4.5 vol%, the optical resonance dip in the sensor near 1550 nm shifted by 290 pm. In addition, the sensor has an insertion loss of only -2.22 dB, a spectral contrast of 10.8 dB, and a spectral finesse of 5. Such a flexible, fast-response sensor is expected to be used in the development of hydrogen sensors with low power consumption.

We demonstrate a high-strength strain sensor based on a micro-air-cavity reshaped through repeating arc discharge. The strain sensor has a micro-scale cavity, approximate plane reflection, and large wall thickness, contributing to a broad free spectrum range ~36 nm at 1555 nm, high fringe contrast ~38 dB, and super-high mechanical robustness, respectively. A sensitivity of ~2.39 pm/με and a large measurement range of 0 to 9800 με are achieved for this strain sensor. The strain sensor has a high strength, e.g., the tensile strain applied the sensor is up to 10,000 με until the tested the single-mode fiber is broken into two sections. In addition, it exhibited low thermal sensitivity of less than 1.0 pm/°C reducing the cross-sensitivity between tensile strain and temperature.

Constipation is a functional gastrointestinal disorder and one of the most prevalent conditions encountered in primary care settings. Rhubarb navel dressings have been used for more than 2,000 years in Chinese medicine to treat constipation. However, the effect of topical rhubarb administration has still not been well recognized and this strategy is not yet established as an evidence-based approach.In this study, we performed a prospective multicentric randomized controlled trial to evaluate the efficacy and safety of rhubarb navel plasters for patients with chronic constipation.A total of 374 patients from six teaching hospitals were prospectively included between 09/2016 and 10/2017 in the study based on Rome III criteria. All participants were randomly assigned (1:1) into verum/placebo group and given either Rheum officinale rhubarb powder or a placebo flour stick on the navel for 6 h/day/8 days. Primary outcome measures were the Cleveland Constipation Score (CCS) for the feces condition and Bristol Stool Scale (BSS) for stool consistency and 24 h defecation frequency.The groups demonstrated no statistical differences in demographic data, clinical diagnoses and concomitant medication at baseline. In patients treated with the verum CCS was 5.61 (day 8, 95% CI 5.15-6.07) compared to 8.62 (95% CI 8.07-9.18) in placebo-treated controls (P 0.001). The mean change of CCS at the end of treatment (day 8 versus [vs] day 0) was 6.04 in verum-treated vs 2.73 in placebo-treated controls (P 0.001). Also 24 h defecation frequency (BSS) showed superior results (day 5: 0.84 vs 0.62, 95% CI 0.67-0.80, P 0.001; day 6: 0.82 vs 0.60, 95% CI 0.64-0.78, P 0.01 and day 8: 0.82 vs 0.60, 95% CI 0.64-0.78, P 0.01) and better BSS type classification during treatment than controls (P 0.05). No significant differences in adverse events between both groups became obvious.Rhubarb navel plaster administration over an 8-day-treatment period resulted in significantly improved bowel function as demonstrated by the CCS, 24 h defecating frequency and BSS. Our results suggest that rhubarb navel plasters represent a feasible, safe and efficient application route for the treatment of patients suffering from chronic constipation.

Background There are many cytokines, including TNF-α, TGFβ, PGF, and other factors contributing towards fibrogenesis, that play a role in the control of HBV infection. Among these, TNF-α is the most important cytokine in host immune response to viral infection. This study aimed to determine whether differences in the promoter region of the TNF-α gene may alter the outcomes of HBV infection. Methods Two polymorphisms of tumor necrosis factor-α (TNF-α) gene, -308 G/A (rs1800629) and -863 C/A (rs1800630), were analyzed by DNA sequence in the case–control sample using 171 chronic HBV-infected patients and 227 recovered HBV-infected controls. All subjects were unrelated southern Han Chinese. Results For TNF-α-308, healthy controls compared to HBV infection have a significantly higher allele A and GA genotype frequency. For TNF-α-863, no significant differences in allele or genotype frequencies between the case groups and the control group were observed. Conclusions This study provides evidence of a positive association between HBV clearance and TNF-α-308A.