The fabrication of an eccentric three-core fiber and its application as a twist sensor

The fabrication and application for twist sensing of an eccentric three-core fiber were demonstrated. The fiber was made by stack-and-draw technique, in which silica rods and core canes were put in a tube and drawn on a fiber drawing tower. Three cores formed a Mach-Zehnder interferometer, where the lights transmitted in the three cores interfered with each other, resulted in the formation of envelopes on spectrum. Because two of the cores were off axis, phase differences among the cores varied with twist due to different stretches on each core, which caused shift of the spectral envelopes of the interference signal. Wide range twist measurement can be realized with relatively high sensitivity by tracking lower dips of the envelopes. Experimental results revealed that the dips shift quadratically with twist angle, which means that the sensitivity increases with twist. The compensation of temperature influence was also implemented by inscribing a Bragg grating on one of the cores with femtosecond laser. Because the fiber can be mass-produced, it is suitable for twist sensing in practical application for its low cost

Electrically Sensing Characteristics of the Sagnac Interferometer Embedded With a Liquid Crystal-Infiltrated Photonic Crystal Fiber

The electrically sensing characteristics of a liquid-crystal (LC)-infiltrated polarization-maintaining photonic crystal fiber (PCF) have been studied. The small holes on the end face of the fiber collapse and two large holes remain open by controlling discharging-time, -current, and -position of a fiber splicer, then LC is selectively infiltrated into the two large holes, which can not only save LC but also make the welding between the LC-infiltrated polarization-maintaining PCF and single-mode fiber much easier. A new method to weld the two fibers is proposed by filling and volatilizing ethanol to make LC a few millimeters away from the end face which can improve the sensing system stability and prevent the discharge of a fiber splicer from destroying LC molecules. A Sagnac interferometer is set up by embedding the LC-infiltrated polarization-maintaining PCF in a fiber loop and then its electroresponse characteristics are studied. The refractive-index distribution of the LC-infiltrated polarization-maintaining PCF varies with electric voltage due to the variable index of LC, which makes it possible to detect voltage. Three voltage ranges are discussed by the different dips and the sensitivity is improved with voltage increasing. The high sensitivity is up to 3.49 nm/V with the tuning range of 7 nm as voltage changes from 149.67 to 151.61 V. The Sagnac interferometer embedded with an LC-infiltrated polarization-maintaining PCF can be utilized as a voltage sensor, electro-optical modulator, or filter

Electrically Tuning Characteristics of LC Selectively Infiltrated PCF Sagnac Interferometer

A photonic crystal fiber was selectively infiltrated only two of the air holes near the core with liquid crystal. The selective infiltration caused geometric asymmetry and created high birefringence. Because of the geometric asymmetry, the response to varying electric field is concerned with electric field direction. A Sagnac interferometer was set to investigate the electric tuning characteristics of the selectively infiltrated photonic crystal fiber. The effective refractive-indices of the fiber varies with electric field due to reorientation of liquid crystal molecules. The highest sensitivity was 1.12 nm/V (504 nm/kV/mm) with tuning range of 7 nm when electric field direction was parallel to the connecting line of infiltrated holes. The response time of the selectively infiltrated photonic crystal fiber was studied. The device can be utilized as voltage sensors, electro-optical modulators and filters

Cascaded Sagnac loops embedded with two polarization maintaining photonic crystal fibers for highly-sensitive strain measurement

A strain sensor based on cascaded Sagnac loops with two PMPCFs has been experimentally demonstrated. Air holes distributed on the cross section of PMPCF go through the whole fiber which make the special fiber more sensitive to ambient force compared with conventional optical fiber. The lengths of the two PMPCFs are close, but not the same, to form envelopes on the total output spectrum and then obtain high resolution to the detected parameter by Vernier effect. The influences of the difference in length of the two PMPCFS on spectral envelopes are discussed. As the length of the PMPCF in reference loop increases, free spectrum range of the cascaded Sagnac loops (or envelope period) and magnification decrease. The sensitivities of this strain sensor are calculated by tracking upper- and lower-envelope. Results reveal that its average sensitivity is up to 45.15 pm/με and the corresponding resolution is 0.44 με as strain varies from 0 to 2000 με. Compared with a single Sagnac loop, the sensitivity magnification is about 28.94. The sensing characteristics of a conventional PMF are studied to compare with the PMPCF. Moreover, reversibility has also been proved to possess low error rate. In short, the fiber strain sensor possesses high sensitivity and great reversibility

Sagnac mirror loop with two polarization maintaining fibers for twist measurement by tracking adjacent dips with tunable measurement range

The transmission characteristics of Sagnac fiber loop interferometer which consists two sections of polarization-maintaining fiber (PMF) spliced at different offset angles were analyzed. Based on the simulation results, an application for twist measurement where PMFs were spliced at different offset angles was designed. When the lengths of two PMFs are equal, a clear spectrum can be obtained for twist or torsion sensing. A phenomenon that the dips would split or merge with twist angle alteration can be used for sensing. Measurement range and sensitivity can be adjusted by changing the PMFs offset angle. The sensitivity was improved by calculating the distance between two adjacent dips, being 0.73 nm/° or 8.37 nm/(rad/m) when the offset angle was 75°

A review of microstructured optical fibers for sensing applications

Microstructured optical fibers, including not only photonic crystal fibers but also new types of fiber with different configurations on the cross section, are elaborately designed and they usually have special application purposes among which sensing is one of the most common. In this review we first summarize fabrication methods and transmission mechanisms of microstructured fibers. And then application examples using fibers with special and novel microstructures in strain/pressure/bending/twist, temperature, flow rate, electric/magnetic field, humidity, gas, refractive index and chemical/biochemical analyte sensing based on various principles are introduced. Finally, state of the art and developing trends as well as challenges faced by sensing technology based on microstructured optical fibers were discussed

Zwitterionic Nanoparticles Constructed with Well-Defined Reduction-Responsive Shell and pH-Sensitive Core for “Spatiotemporally Pinpointed” Drug Delivery

Enabling nanocarriers to complete the sophisticated journey from the initial injection site to the targeted tumor cells and achieve “spatiotemporally pinpointed” drug release intracellularly is a challenging task in anticancer drug delivery. Herein, versatile shell-cross-linked nanoparticles (SCNPs) were prepared by one-step assembly of triblock zwitterionic copolymers, polycarboxybetaine methacrylate-<i>block</i>-poly­(<i>N</i>-(2-(2-pyridyl disulde) ethyl methacrylamide-<i>block</i>-poly­(2-(diisopropylamino) ethyl methacrylate) (PCB-<i>b</i>-PDS-<i>b</i>-PDPA, termed as PCSSD), which was well-defined via reversible additive fragment transfer (RAFT) polymerization, followed by functionalization with Arg-Gly-Asp (RGD). Thus, the RGD-PCSSD SCNPs cooperatively combine the ultra pH-sensitive PDPA core for efficient drug loading and pH-responsive drug release, the disulfide-cross-linked PDS shell that prevents premature drug release, the zwitterionic PCB corona to stabilize the SCNPs and prolong its systemic circulation, the RGD ligand for active tumor targeting and receptor-mediated endocytosis. Doxorubicin (DOX) was loaded as a model medicine (termed as RGD-PCSSD/DOX SCNPs). The dual-sensitivity studies showed that the pH-sensitivity of PDPA core could be adjusted by the shell-cross-linking density, accompanied by better control over premature drug release. Furthermore, results obtained by flow cytometry and fluorescence microscopy analysis demonstrated that once the RGD-PCSS₁₀D/DOX SCNPs were internalized into tumor cells via receptor-mediated endocytosis, boost drug release was observed with considerable cytotoxicity in vitro. The results of ex vivo imaging studies further confirmed the successful drug delivery from the injection site to the tumor tissue. In summary, the well-constructed RGD-PCSS₁₀D/DOX SCNPs with cooperative multifunctionality showed great potential as novel nanocarriers for tumor targeted anticancer drug delivery

Integrin-Targeted Zwitterionic Polymeric Nanoparticles with Acid-Induced Disassembly Property for Enhanced Drug Accumulation and Release in Tumor

Reasonably structural design of nanoparticles (NPs) to combine functions of prolonged systemic circulation, enhanced tumor targeting and specific intracellular drug release is crucial for antitumor drug delivery. Combining advantages of Arg-Gly-Asp (RGD) for active tumor targeting, zwitterionic polycarboxybetaine methacrylate (PCB) for prolonged systemic circulation, poly­(2-(diisopropylamino) ethyl methacrylate) (PDPA) for acid-triggered intracellular release, novel RGD-PCB-<i>b</i>-PDPA (RGD-PCD) block copolymers were prepared via reversible addition–fragmentation chain transfer (RAFT) polymerization and followed by functionalization with RGD. Doxorubicine (DOX) was encapsulated within the RGD-PCD NPs as model medicine (RGD-PCD/DOX NPs). With ultra pH-sensitivity of PDPA, the drug release was restrained at pH 7.4 for only 24% within 36 h, which was increased to 60% at pH 6.0 within 24 h, and released more rapidly at pH 5.0 for 100% within 5 h, indicating that the RGD-PCD/DOX NPs were able to turn drug release “off” at neutral pH (e.g., systemic circulation) whereas “on” under acidic conditions (e.g., inside endo/lysosomes). Furthermore, the results of fluorescence microscopy and flow cytometry analysis demonstrated improved internalization of RGD-PCD/DOX NPs in HepG2 cells via integrin-mediated endocytosis with rapid DOX release intracellularly. Consequently, the RGD-PCD/DOX NPs showed considerable cytotoxicity against HepG2 and HeLa cells in comparison with free DOX. Importantly, the RGD-PCD/DOX NPs exhibited little protein adsorption property with excellent serum stability, which led to prolonged systemic circulation and enhanced tumor accumulation in tumor-bearing nude mice. Therefore, this multifunctional RGD-PCD NPs, which represented the flexible design approach, showed great potential for the development of novel nanocarriers in tumor-targeted drug delivery