[Observation of the therapeutic effect on acute ankle sprain treated with surrounding needling and cold compression].

OBJECTIVE: To observe the difference in the therapeutic effect on acute ankle sprain treated with the combination of surrounding needling and cold compression in comparison of the conventional cold compression. METHODS: The patients with acute ankle sprain were randomly divided into control group (33 cases) and observation group (35 cases). In the first 3 days of treatment, the conventional cold compression was used in the control group, while the surrounding needling technique of acupuncture was combined with cold compression in the observation group. Separately, along the distal-lateral side of the leg, and the lateral sides of the heel and the dorsal part of the foot, 3 or 4 needles were inserted in each part，total 9 to 12 needles, toward the center of swelling and pain site, and distributed in a fan shape. The needles were retained for 30 min and the acupuncture therapy was delivered once daily. Since the 4th day of treatment, the hot compress and the static stretching exercise of the ankle joint were adopted in the two groups, once daily for 1 week. The visual analogue scale (VAS) score for ankle pain and ankle swelling degree were compared between the two groups before and after 3-day treatment, as well as the score of American orthopedic foot and ankle society (AOFAS) ankle-hindfoot scale was evaluated. RESULTS: After 3-day treatment, VAS score was decreased in both groups (P<0.01), and the score in the observation group was lower than that of the control group (P<0.01). Ankle swelling degree was relieved in both groups (P<0.01), and there was no significant difference between the two groups. After 1 week of treatment, the scores of AOFAS ankle-hindfoot scale were improved in both groups (P<0.01), and the score in the observation group was higher than the control group (P<0.05). CONCLUSION: Either the combined therapy of surrounding needling and cold compression or the conventional cold compression can effectively relieve pain and swelling induced by acute ankle sprain. The therapeutic effect of the combined therapy is superior to the conventional cold compression for the motor function improvement of ankle joint.

Polarimetric fiber laser for relative humidity sensing based on graphene oxide-coated D-shaped fiber and beat frequency demodulation.

We first propose and demonstrate a polarimetric fiber laser system for relative humidity (RH) sensing based on the beat frequency demodulation. A graphene oxide-coated D-shaped fiber (GDF) with a low insertion loss of 0.8 dB was embedded into a laser cavity to form an RH sensing probe. The output of the fiber laser could generate mode splitting between two orthogonal polarization modes due to birefringence of the GDF device. Hence, two types of beat signals, i.e., longitudinal mode beat frequency (LMBF) and polarization mode beat frequency (PMBF) could be generated synchronously. The experimental results indicated that the LMBFs of the fiber laser had almost no response to the ambient humidity, and the PMBFs of the fiber laser were very sensitive to the various RH levels. There was a good linear relationship between the PMBF and RH changes in the range of 30% to 98%. This fiber-optic RH sensor exhibited a sensitivity of 34.7 kHz/RH% with a high quality of fit (R2>0.997) during the ambient RH increase and decrease. Moreover, the average response and recovery times of the fiber-optic RH sensor were measured to be about 64.2 ms and 97.8 ms, respectively. Due to its long stability, reversibility, quick response time and low temperature cross-sensitivity (i.e., 0.12 RH%/°C), the proposed fiber-optic RH sensor could offer attractive applications in many fields, such as biology, chemical processing and food processing, etc.

Simultaneous measurement of torsion and strain at high temperature by using a highly birefringent cladding fiber Bragg grating.

We demonstrate the fabrication of a new highly birefringent cladding fiber Bragg grating (Hi-Bi CFBG) consisting of a pair of sawtooth stressors near the fiber core by using a femtosecond laser direct writing technology. The unique sawtooth structure serves as in-fiber stressor and also generates Bragg resonance due to its periodicity. After optimization of laser pulse energy, the Hi-Bi CFBG with a high birefringence of 2.2 × 10-4 and a low peak reflectivity of ∼ -24.5 dB (corresponding to ∼ 0.3%) was successfully fabricated in a conventional single-mode fiber (SMF). And then, a wavelength-division-multiplexed Hi-Bi CFBGs array and an identical Hi-Bi CFBGs array were successfully constructed. Moreover, a simultaneous measurement of torsion and strain at high temperature of 700 °C was realized by using the fabricated Hi-Bi CFBG, in which the torsion can be deduced by monitoring the reflection difference between the two polarization peaks and strain can be detected by measuring polarization peak wavelength. A high torsion sensitivity of up to 80.02 dB/(deg/mm) and a strain sensitivity of 1.06 pm/µÉ› were achieved. As such, the proposed Hi-Bi CFBG can be used as a mechanical sensor in many areas, especially in structural health monitoring at extreme conditions.

A Nondestructive Measurement Method of Optical Fiber Young's Modulus Based on OFDR.

A nondestructive measurement method based on an Optical frequency domain reflectometry (OFDR) was demonstrated to achieve Young's modulus of an optical fiber. Such a method can be used to measure, not only the averaged Young's modulus within the measured fiber length, but also Young's modulus distribution along the optical fiber axis. Moreover, the standard deviation of the measured Young's modulus is calculated to analyze the measurement error. Young's modulus distribution of the coated and uncoated single mode fiber (SMF) samples was successfully measured along the optical fiber axis. The average Young's modulus of the coated and uncoated SMF samples was 13.75 ± 0.14, and 71.63 ± 0.43 Gpa, respectively, within the measured fiber length of 500 mm. The measured Young's modulus distribution along the optical fiber axis could be used to analyze the damage degree of the fiber, which is very useful to nondestructively estimate the service life of optical fiber sensors immersed into smart engineer structures.

Femtosecond laser line-by-line inscription of apodized fiber Bragg gratings.

The reflection spectra of conventional fiber Bragg gratings (FBGs) with uniform index modulation profiles typically have strong sidelobes, which hamper the performance of FBG-based optical filters, fiber lasers, and sensors. Here, we propose and demonstrate a femtosecond laser line-by-line (LbL) scanning technique for fabricating apodized FBGs with suppressed sidelobes. This approach can flexibly achieve various apodized modulation profiles via precise control over the length and/or transverse position of each laser-inscribed index modification track. We theoretically and experimentally studied the influences of the apodization function on the side-mode suppression ratio (SMSR) in the fabricated apodized FBG, and the results show that a maximum SMSR of 20.6 dB was achieved in a Gaussian-apodized FBG. Subsequently, we used this method to fabricate various apodized FBGs, and the SMSRs in these FBGs were reduced effectively. Specifically, a dense-wavelength-division-multiplexed Gaussian-apodized FBG array with a wavelength interval of 1.50 nm was successfully fabricated, and the SMSR in such an array is 14 dB. Moreover, a Gaussian-apodized phase-shifted FBG and chirped FBG were also demonstrated with a high SMSR of 14 and 16 dB, respectively. Therefore, such an apodization method based on a modified femtosecond laser LbL scanning technique is an effective and flexible way to fabricate various FBGs with high SMSRs, which is promising to improve the performance of optical filters, fiber lasers, and sensors.

Temperature-insensitive directional transverse load sensor based on dual side-hole fiber Bragg grating.

We propose and demonstrate a temperature-insensitive directional transverse load sensor based on a fiber Bragg grating (FBG) inscribed in a section of dual side-hole fiber (DSHF). The application of transverse load results in an effective change in the refractive index and, consequently, changes in the DSHF birefringence. The directional transverse load response of the fabricated DSH-FBG was studied by monitoring the wavelength separations with transverse load applied in different direction with 15° increments. The load sensitivity exhibited two maxima and two minima in a polar coordinate system, achieving a maximum value of 699 pm/(N/mm) for transverse load applied along the slow axis and a minimum value of 285 pm/(N/mm) for transverse load applied along the fast axis. Subsequently, a finite element analysis (FEA) was conducted to simulate the resulting strain distribution of the DSHF with applied directional transverse load. The temperature response of the DSH-FBG transverse load sensor was also tested, yielding a low sensitivity of 1.5 × 10-2 pm/°C. Hence, the compact size, directional transverse load sensitivity, and temperature insensitivity of this device make it suitable for intelligent transverse load monitoring.

Highly sensitive hydrogen sensor based on an in-fiber Mach-Zehnder interferometer with polymer infiltration and Pt-loaded WO3 coating.

A highly sensitive fiberized hydrogen sensor based upon Mach-Zehnder interference (MZI) is experimentally demonstrated. The hydrogen sensor consists of an MZI realized by creating an air cavity inside the core of a half-pitch graded-index fiber (GIF) by use of femtosecond laser micromachining. Thermosensitive polymer was filled into the air cavity and cured by UV illumination. Subsequently, the external surface of the polymer-filled MZI was coated with Pt-loaded tungsten trioxide (WO3). The exothermic reaction occurs as Pt-loaded WO3 contacts the target of the sensing, i.e. hydrogen in the atmosphere, which leads to a significant local temperature rise on the external surface of the coated MZI sensor. The sensor exhibits a maximum sensitivity up to -1948.68 nm/% (vol %), when the hydrogen concentration increases from 0% to 0.8% at room temperature. Moreover, the sensor exhibits a rapid rising response time (hydrogen concentration increasing) of ∼38 s and falling response time (hydrogen concentration decreasing) of ∼15 s, respectively. Thanks to its small size, strong robustness, high accuracy and repeatability, the proposed in-fiber MZI hydrogen sensor will be a promising tool for hydrogen leakage tracing in many areas, such as safety production and hydrogen medical treatment.

Highly sensitive gas refractive index sensor based on hollow-core photonic bandgap fiber.

A highly sensitive gas refractive index (RI) sensor based on hollow-core photonic bandgap fiber (HC-PBF) and Fourier transform white-light interferometry was experimentally demonstrated. HC-PBFs with lower loss than hollow silica tubes render a longer air cavity for the Fabry-Perot interferometers (FPIs) without a great deal of compromise to the fringe visibility of interference. Fourier transform phase demodulation method was employed in the experiment and a directly proportional relationship between the phase sensitivity and cavity length was demonstrated. For a cavity length of ∼24.9 mm, the sensor's gas RI sensitivity reaches up to 50775.54 µm/RIU in an air RI range from 1.000 to 1.030. Considering the cavity length demodulation resolution of 0.06 µm achieved by this method, the sensor can detect gas RI change with a resolution of 10-6 RIU, which can meet the sensing demand for almost all the gases. Moreover, the gas RI sensitivity and measurement range can be improved further by lengthening the HC-PBF. The high sensitivity, large dynamic range and good linearity of the proposed sensor make it a good candidate for biosensing, monitoring of modern chemical industry or gas laser systems.

[Acupuncture for dysarthria: systematic review].

OBJECTIVE: To systematically evaluate the clinical efficacy of acupuncture for dysarthria, and to explore the rules of acupoints selection for dysarthria. METHODS: The clinical randomized control trial literature regarding acupuncture for dysarthria published before January of 2018 were searched in databases, including CNKI, Wanfang, VIP, CBM, PubMed, Ebsco, Science Direct and Cochrane Library. The information of included studies was extract and the quality was assessed. The Meta analysis was performed by using RevMan 5.3 software. The frequency of acupoints was calculated by using Excel software to analyzed the rules of acupoints selection. RESULTS: Totally 21 papers were included, involving 1651 patients. The pooled effects of clinical efficacy: heterogeneity test P =0.74, I 2=0%, OR =6.36, 95% CI: 4.55, 8.88, Z =10.84 (P<0.01), indicating the efficacy in the treatment group was significantly higher than that in the control group. The pooled effects of the symptom score in Frenchay scale: heterogeneity test P =0.56, I 2=0%, WMD =3.20, 95% CI: 1.38, 5.02, Z =3.45 (P<0.01), indicating the efficacy in the treatment group was significantly higher than that in the control group. The acupoints with frequency of more than 5 times were Fengchi (GB 20), Yuye (EX-HN 13), Jinjin (EX-HN 12), Lianquan (CV 23), Baihui (GV 20), tongue-three needles and Yamen (GV15). The meridians with frequency of more than 5 times were the extra channels, governor vessel, gallbladder channel, conception vessel and stomach channel. CONCLUSION: The clinical efficacy of acupuncture combined with speech training/regular treatment is significantly superior to that of control group (speech training, medication, regular treatment); acupuncture is safe and effective for dysarthria; the majority of selected acupoint is local acupoints around tongue, throat and neck, as well as extra points and empirical points. However, high-quality randomized controlled trials with large sample sizes are still needed to provide further evidence.

In-Fiber Collimator-Based Fabry-Perot Interferometer with Enhanced Vibration Sensitivity.

A simple vibration sensor is proposed and demonstrated based on an optical fiber Fabry-Perot interferometer (FPI) with an in-fiber collimator. The device was fabricated by splicing a quarter-pitch graded index fiber (GIF) with a section of a hollow-core fiber (HCF) interposed between single mode fibers (SMFs). The static displacement sensitivity of the FPI with an in-fiber collimator was 5.17 × 10-4 µm-1, whereas the maximum static displacement sensitivity of the device without collimator was 1.73 × 10-4 µm-1. Moreover, the vibration sensitivity of the FPI with the collimator was 60.22 mV/g at 100 Hz, which was significantly higher than the sensitivity of the FPI without collimator (11.09 mV/g at 100 Hz). The proposed FPI with an in-fiber collimator also exhibited a vibration sensitivity nearly one order of magnitude higher than the device without the collimator at frequencies ranging from 40 to 200 Hz. This low-cost FPI sensor is highly-sensitive, robust and easy to fabricate. It could potentially be used for vibration monitoring in remote and harsh environments.

Measurement of high pressure and high temperature using a dual-cavity Fabry-Perot interferometer created in cascade hollow-core fibers.

A compact dual-cavity Fabry-Perot interferometer (DC-FPI) sensor is proposed and demonstrated based on a hollow-core photonic bandgap fiber (HC-PBF) spliced with a hollow-core fiber (HCF). The HC-PBF, which has low transmission loss, was used as the first FPI cavity and also acted as a bridge between the lead-in single-mode fiber and the HCF. The HCF was used as the second FPI cavity and also acted as a micro gas inlet into the first FPI cavity. A DC-FPI sensor with different cavity lengths of 226 and 634 µm in the first FPI and the second FPI was created. Both gas pressures ranging from 0-10 MPa and temperatures ranging from 100-800°C were measured using the DC-FPI sensors together with a fast Fourier transform and phase-demodulation algorithm. Experimental results showed that the first FPI cavity was gas pressure sensitive but temperature insensitive, while the second FPI cavity was temperature sensitive but gas pressure insensitive. A high gas pressure sensitivity of 1.336 µm/MPa and a temperature sensitivity of 17 nm/°C were achieved in the DC-FPI sensor. Moreover, the cross sensitivity between the gas pressure and temperature was calculated to be ∼-15 Pa/°C and ∼0.3°C/MPa. The proposed DC-FPI sensors provide a promising candidate for the simultaneous measurement of high pressures and high temperatures at some precise locations.

Suppression of parasitic interference in a fiber-tip Fabry-Perot interferometer for high-pressure measurements.

We demonstrate a novel design and fabrication process for fiber-tip Fabry-Perot interferometric (FTFPI) pressure sensors which eliminates fringe envelopes in the reflection spectrum. The outer facet reflectivity and thickness of the FTFPI silica diaphragm were reduced through orthogonal rough-polishing of the fiber end facet. A silica FTFPI sample with a diaphragm thickness of ~10.7 µm was produced and tested under hydraulic pressures ranging from 0 to 30 MPa. The proposed sensor achieved a pressure sensitivity of -284 pm/MPa at 1555 nm and could be a valuable new tool for high pressure measurements.

Antiresonant Reflecting Guidance and Mach-Zender Interference in Cascaded Hollow-Core Fibers for Multi-Parameter Sensing.

We propose and demonstrate a cascaded hollow-core fiber (HCF) device for multi-parameter sensing based on the combination of antiresonant reflecting guidance (ARRG) and Mach-Zender interference (MZI). The device was fabricated by splicing two sections of HCF together. Two sets of fringes, which have different free spectral ranges, were generated from ARRG and MZI, respectively, and were aliasing in the transmission spectrum. The two sets of fringes were then separated using a band pass filter and a Gaussian fitting technique. The wavelengths at two transmission loss dips formed by ARRG and MZI exhibit a temperature sensitivity of 14.1 and 28.5 pm/°C, and a strain sensitivity of 0.4 and -0.8 pm/µÎµ, respectively. By using a crossing matrix with differences sensitivities, the cross-sensitivity between temperature and strain can be solved. The gas pressure response of the cascaded HCF device was also tested up to 300 °C, and linear relationships between the gas pressure sensitivities and temperature were found, which can be used in gas pressure application in various temperatures. Moreover, the proposed cascaded HCF sensor is compact, low cost, and simple for fabrication, and hence offers a promising way for the simultaneous measurement of multiple parameters, such as temperature, strain, and gas pressure.

Sapphire fiber Bragg gratings inscribed with a femtosecond laser line-by-line scanning technique.

We propose and demonstrate the fabrication of single-crystal sapphire fiber Bragg gratings (SFBGs) using a femtosecond laser line-by-line scanning technique. This approach provides a robust method for producing SFBGs at various Bragg wavelengths with an acceptable reflectivity. The spectrum characteristics of the SFBGs with various fiber diameters, track lengths, and grating pitch quantities were investigated. An SFBG with a reflectivity of 6.3% was obtained via optimization of fabrication parameters. Additionally, a serial array consisting of five SFBGs at different wavelengths was successfully constructed. The high-temperature response of these SFBGs was tested and the experimental results showed the SFBGs could withstand a high temperature of 1612°C. Moreover, a temperature sensitivity of 36.5 pm/°C was achieved in the high-temperature region. Such SFBGs could be developed for promising high-temperature sensors in aero engines.

Two-dimensional vector bending sensor based on seven-core fiber Bragg gratings.

We demonstrated a two-dimensional vector-bending sensor by use of fiber Bragg gratings (FBGs) inscribed in a homogeneous seven-core fiber. Seven FBGs were simultaneously inscribed in each of all seven cores using a modified Talbot interferometer and a lens scanning method. The vector bending response of six outer-core FBGs was investigated at all 360° directions with a step size of 15°. The bending sensitivities of the six outer-core FBGs display six perfect '8'-shaped patterns in a polar-coordinate system. That is, they exhibit strong bending-direction dependence with a maximum sensitivity of 59.47 pm/m-1. The orientation and amplitude of the vector bending can be reconstructed using measured Bragg wavelength shifts of any two off-diagonal outer-core FBGs. So, the six outer-core FBGs have 12 combinations for bend reconstruction, which can be averaged across multiple reconstructions to develop an accurate two-dimensional vector bending sensor. The average relative error was lower than 4.5% for reconstructed amplitude and less than 2.8% for reconstructed orientation angle θ. Moreover, the seven-core FBGs offer several advantages such as a compact structure, fabrication flexibility, and the temperature compensating ability of central-core FBG.

[Electroacupuncture Relieves Visceral Hypersensitivity by Down-regulating Mast Cell Number，PAR-2/TRPV 1 Signaling, etc. in Colonic Tissue of Rats with Irritable Bowel Syndrome].

OBJECTIVE: To observe the effect of electroacupuncture (EA) stimulation of "Shangjuxu" (ST 37, Lower Confluent point) and "Tianshu" (ST 25, Front-Mu point) on visceral pain and expression of colonic tryptase(Try), proteinase-activated receptor 2(PAR-2)，transient receptor potential channel vanilloid subfamily member 1 (TPRV 1)，substance P (SP) and calcitonin gene-related peptide (CGRP) in rats with irritable bowel syndrome (IBS), so as to explore its mechanisms underlying improvement of IBS. METHODS: Forty male Sprague Dawley rats were equally randomized into normal control (control), model, medication and EA groups (n＝10 in each). The IBS model was established by chronic acute combining stress (CACS, water deprivation, fasting, tail clamping, forced swimming in ice water, restraint, etc.) for 21 days. Rats of the medication group were treated by gavage of Pinaverium Bromide (1 mg/mL, 15 mg/kg), once daily for 14 d. EA (10 Hz/50 Hz, 0.2－0.3 mA) was applied to bilateral ST 37 and ST 25 for 30 min, once daily for 14 d. The muscular withdrawal reflex (AWR) of both abdomen and buttock was detected by colorectal distension (CRD) with a water-filled balloon for examining the visceral hypersensitivity. The number of mast cells in the colonic tissue was counted after toluidine blue stain. The immunoactivity of colonic Try was determined by immunochemistry and the expression of colonic PAR-2, TRVP 1, SP and CGRP proteins detected by Western blot. RESULTS: After modeling, the body weight was significantly decreased in IBS rats of the model, medication and EA groups compared with their own individual pre-treatment and with the control group (P<0.01), and markedly higher in both medication and EA groups than in the model group (P<0.05, P<0.01). The intra-colonic volume thresholds for inducing abdominal and hip AWR were significantly lower in the model group than in the normal control group (P<0.01), and obviously higher in both medication and EA groups than in the model group (P<0.05，P<0.01). The AWR scores of intra-colorectal balloon at volumes of 0.5, 1.0 and 1.5 mL of water were significantly higher in the model group than in the control group (P<0.01), and considerably lower in the EA and medication groups than in the model group (P<0.01). The number of colonic MC and the expression levels of colonic Try, PAR-2, TRPV 1, SP and CGRP proteins were significantly higher in the model group than in the control group (P<0.01), and obviously decreased in both medication and EA groups relevant to the model group (P<0.01). Comparison between the medication and EA groups showed that the decreased expression levels of colonic PAR-2, TRPV 1, SP and CGRP proteins were significantly lower in the EA group than in the medication group (P<0.05), but no significant differences were found between the two groups in intra-colonic volumes for inducing AWR, AWR scores, body weight, and colonic MC number and Try immunoactivity levels (P>0.05)．. CONCLUSION: EA of ST 37 and ST 25 can relieve visceral hypersensitivity in IBS rats, which may be associated with its effects in down-regulating the number of MC and the expression of PAR-2, TRVP 1, SP, CGRP and Try proteins in the colonic tissue.

[Effect of Catgut Implantation on Spatial Learning-memory Ability, Expression of Hippocampal Protein Kinase C Interacting Protein 1 and GluR 2 and Ca2+ Content in Rats with Chronic Ischemic Cognitive Impairment].

OBJECTIVE: To observe the effect of catgut embedment at "Baihui" (GV 20), "Dazhui" (GV 14), etc. on learning-memory ability, expression of hippocampal protein kinase C interacting protein 1 (PICK 1) and glutamate receptor 2 (GluR 2) proteins and level of calcium ions, so as to explore its mechanism underlying improvement of vascular cognitive impairment. METHODS: A total of 56 male SD rats were randomly divided into sham operation, model, catgut embedment and medication groups (n=14 in each). The chronic ischemic cognitive impairment model was established by permanent occlusion of bilate-ral common carotid arteries. The catgut embedment was applied to GV 20, GV 14, "Shenshu" (BL 23) and "Xuanzhong" (GB 39), once a week, for 4 weeks. Rats of the medication group received intraperitoneal injection of monosialate tetrahexose ganglioside sodium (GM-1, 0.33 mg/kg), once daily for 4 weeks. The rats' learning-memory ability was detected by Morris water maze tasks, pathological changes of hippocampal Nissl's bodies were tested by Nissl staining. The expression levels of PICK 1 and GluR 2 proteins in the hippocampus were detected by Western bolt (WB), and the concentration of calcium ions in the hippocampus tissue was measured by Bicinchoninic acid (BCA) assay. RESULTS: After modeling, the mean escape latencies of place navigation test were significantly increased while the crossing times of target platform quadrant of space probing test notably decreased in the model, catgut embedment and medication groups compared with their own individual pre-modeling (P<0.01). Following the treatment, the increased mean escape latencies and decreased crossing times were markedly reversed in both catgut embedment and medication groups relevant to the model group (P<0.01, P<0.05). Nissl staining showed that after mode-ling, a smaller amount of Nissl bodies with dispersing arrangement, reduction in cellular volume, and loss of large amount of cells with vague structure, and hyperchromatic nuclear pyknosis were found in the hippocampus tissue, which was relatively milder in both catgut embedment and medication groups. The hippocampal PICK 1 protein expression and the calcium ion concentration were obviously higher in the model group than in the sham operation group (P<0.01), and significantly lower in both embedment and medication groups than in the model group (P<0.01, P<0.05), while hippocampal GluR 2 protein expression was obviously lower in the model group than in the sham operation group (P<0.01), and markedly higher in both embedment and medication groups than in the model group (P<0.05, P<0.01). No significant differences were found between the embedment and medication groups in the abovementioned indexes (P>0.05). CONCLUSION: Catgut implantation at GV 20 etc. can effectively improve the learning-memory ability in rats with chronic ischemic cognitive impairment, which may be related to its effects in down-regulating the expression of PICK 1 and calcium ion concentration and up-regulating the expression of AMPA receptor subunit GluR 2 protein in the hippocampus.

Diaphragm-free gas-pressure sensor probe based on hollow-core photonic bandgap fiber.

A diaphragm-free probe-type gas-pressure sensor is proposed and experimentally demonstrated based on a hollow-core photonic bandgap fiber (HC-PBF) with a quartz capillary. The section of the HC-PBF acts as a Fabry-Perot cavity, and the quartz capillary acts as a microfluidic channel for a gas inlet. An inner diameter of the quartz capillary (∼2 µm) smaller than the HC-PBF (∼10.9 µm) ensures a mirror reflection and a microfluidic channel simultaneously. The sensor probe has a minimal size (∼125 µm) and can function at gas pressures as high as 8 MPa. A higher pressure test is limited by our gas-pressure generation devices. Excellent stability of the sensor is observed in a long timescale, and repeatability of the sensor is confirmed by tests of six different samples. Compared with conventional optical fiber gas-pressure sensors, the proposed sensor involves a simple fabrication process and can acquire probe measurements with high sensitivity (∼4.17 nm/MPa), excellent linearity (0.9999), fast response, and no hysteresis. The proposed sensor can also function at temperatures as high as 800°C, which is beneficial for high pressure measurements in extreme conditions. Moreover, the fast response of the sensor is attractive for dynamic pressure measurements, which needs further study and characterization.

Novel fabrication technique for phase-shifted fiber Bragg gratings using a variable-velocity scanning beam and a shielded phase mask.

A new method is proposed and demonstrated for fabricating phase-shifted fiber Bragg gratings (FBGs) using a variable-velocity scanning UV laser beam in combination with a shielded phase mask. The transmission properties of phase-shifted FBGs were analyzed based on coupled-mode theory and a transfer matrix method. The grating is divided into three parts to allow for easier analysis of FBG properties. These segments included a uniform FBG1 and FBG2 which were separated by a shielded section. A novel phase-shifted FBG was fabricated using this method, in which the refractive indices of FBG1 and FBG2 were different. Transmission properties of these phase-shifted FBGs were simulated numerically using MATLAB, and the experimental results and simulated results are in good agreement. In addition to the length and effective refractive index of the shielded section, the phase shift value of a phase-shifted FBG was also found to be dependent on the lengths and effective refractive indices of FBG1 and FBG2. Moreover, we predicted that changing the scanning velocity for fabricating FBG2 would adjust phase shift value, which exhibits a positive linear relationship with the scanning velocity. These results can provide guidelines for fabricating any phase shift value FBGs. This technique is simple, convenient, and may be developed further for use in fabricating novel tunable fiber filters or DFB fiber lasers.

Beat frequency tuning in dual-polarization distributed feedback fiber laser using side polishing technique.

We propose and demonstrate a method for tuning the beat frequency of a dual-polarization distributed feedback (DFB) fiber laser via fiber side polishing. This process can significantly alter the birefringence in DFB fiber lasers. Beat frequency evolutions in DFB fiber lasers were investigated, and the experimental results showed that the beat frequency tuning was dependent on polished thickness, roughness, and direction. The abrasive paper with a grain size of 1.8 µm was adopted to fine-tune the beat frequency. It was found that the beat frequency of DFB fiber lasers shifted toward higher frequencies with increasing polished thickness. However, the beat frequency shifted toward lower frequencies using a secondary side polishing process in the direction orthogonal to the first polished surface. As a result, the beat frequency of the DFB fiber laser was tuned in a wide frequency range from 475.5 MHz to 2080.4 MHz, which corresponds to a birefringence change of 1.2 × 10-5. Side-polished DFB fiber lasers could provide a novel approach to frequency division multiplexing for a large number of fiber laser sensors.