Fiber optic interferometers to sense various physical parameters including temperature, strain, pressure, and refractive index have been widely investigated. They can be categorized into four types: Fabry-Perot, Mach-Zehnder, Michelson, and Sagnac. In this paper, each type of interferometric sensor is reviewed in terms of operating principles, fabrication methods, and application fields. Some specific examples of recently reported interferometeric sensor technologies are presented in detail to show their large potential in practical applications. Some of the simple to fabricate but exceedingly effective Fabry-Perot interferometers, implemented in both extrinsic and intrinsic structures, are discussed. Also, a wide variety of Mach-Zehnder and Michelson interferometric sensors based on photonic crystal fibers are introduced along with their remarkable sensing performances. Finally, the simultaneous multi-parameter sensing capability of a pair of long period fiber grating (LPG) is presented in two types of structures; one is the Mach-Zehnder interferometer formed in a double cladding fiber and the other is the highly sensitive Sagnac interferometer cascaded with an LPG pair.

Fiber couplers made with photonic crystal fibers (PCF) are reported. Two types of PCF were fabricated by means of stacking a group of silica tubes around a silica rod and drawing them. The fiber couplers were made by use of the fused biconical tapered method. With a fiber that had five hexagonally stacked layers of air holes, a 33/67 coupling ratio was obtained, and with a one-layer four-hole fiber, a 48/52 coupling ratio was obtained. The fabrication processes and the characteristics of the PCFs and the PCF couplers are presented.

This paper proposes an optical method which allows determination of the organic compound concentration in water by measurement of the UV (ultraviolet) absorption at a wavelength of 250 nm~300 nm. The UV absorbance was analyzed by means of a multiple linear regression model for estimation of the total organic carbon contents in water, which showed a close correlation with the UV absorbance, demonstrating a high adjusted coefficient of determination, 0.997. The comparison of the TOC (total organic carbon) concentrations for real samples (tab water, sea, and river) calculated from the UV absorbance spectra, and those measured by a conventional TOC analyzer indicates that the higher the TOC value the better the agreement. This UV absorbance method can be easily configured for real-time monitoring water pollution, and built into a compact system applicable to industry areas.

We have experimentally implemented a multiplexible but compact fiber sensor system suitable for multipoint sensing of hydrogen gas leakage. By making dual cavities along an optical fiber and coating a palladium film only at the end of the fiber tip, the measurement errors induced by the optical source power fluctuation and the mechanical perturbation in the lead fiber could be compensated. By adjusting the length of the dual-cavity, the capability of multiplexing several hydrogen sensors could be achieved. The experiment results showed that the response speed of the sensor was increasing with temperature, but at a low temperature the response amplitude became large.

Background: Accurate identification of tumor sites and boundaries is of paramount importance during minimally invasive surgery. Although laparoscopic resection is being increasingly and widely performed for early gastric and colorectal cancers, the detection of tumors located inside the stomach and intestine is difficult owing to the lack of tactile sensation. Here, we propose the application of an indocyanine green (ICG)-loaded alginate hydrogel system as a fluorescence surgical marker for precise laparoscopic operations.Methods: A physical complex of ICG and human serum albumin (HSA) was mixed with sodium alginate to form an injectable hydrogel system. Calcium carbonate and D-gluconic acid (GA) were added to the gel to control its strength and gelation time, respectively. The optimal conditions for the preparation of injectable hydrogels were determined by analyzing the fluorescence spectra and sol-gel transition time of the prepared samples at various concentrations and compositions. Next, the aqueous solutions of ICG, ICG-HSA, and ICG-HSA-loaded alginate were subcutaneously injected into nude mice (three mice per group), and nearinfrared (NIR) fluorescence images of the mice (λ ex. =780 nm, λ em. =845 nm) were obtained at different points in time for 8 days. Then, fluorescence intensities at the injection sites, target-to-background ratio, and areas of ICG fluorescence were analyzed. Finally, the potential utility of ICG-HSA-loaded alginate hydrogel as a surgical marker was evaluated in a porcine model. The ICG-HSA-loaded alginate solution was injected into three sites in the submucosal space of the porcine stomach via a catheter. A fluorescent laparoscopic system was installed on the abdomen of the pig 3 days post-injection, and the fluorescence signal generated from the fluorescence surgical marker located inside the stomach was evaluated using the fluorescence laparoscope system (λ ex. =785 nm, λ em. =805 nm). Results:The optimal concentration of ICG-HSA complex was determined to be 30 μM, and maximum fluorescence intensity of the complex was obtained at a 1:1 mole ratio of HSA to ICG. The subcutaneous injection of ICG or ICG-HSA solution in mice resulted in the rapid spread of the fluorescence signal around the injection site in 3 h, and a weak fluorescence was detected at the injection site 24 h post-injection. In contrast, the fluorescence detection time was effectively prolonged up to 96 h post-injection in the case of ICG-HSA-loaded alginate gel, while diffusion of the injected ICG from the injection site was effectively prevented. In the laparoscopic operation, injection sites of the hydrogel in porcine stomach could be accurately detected in real time even after 3 days.Conclusions: This alginate hydrogel system may be potentially useful as an effective surgical marker in terms of accuracy and persistence for laparoscopic operation.

We demonstrated a three-dimensional (3D) dental scanning apparatus based on structured illumination. A liquid lens was used for tuning focus and a piezomotor stage was used for the shift of structured light. A simple algorithm, which detects intensity modulation, was used to perform optical sectioning with structured illumination. We reconstructed a 3D point cloud, which represents the 3D coordinates of the digitized surface of a dental gypsum cast by piling up sectioned images. We performed 3D registration of an individual 3D point cloud, which includes alignment and merging the 3D point clouds to exhibit a 3D model of the dental cast.

role in development of atherosclerosis as well as atheroma plaque destabilization and rupture, which in turn leads frequently to thrombo-occlusive complications including strokes and myocardial infarction, macrophages may be a valuable therapeutic target. Indeed, previous studies support targeting macrophages as a promising strategy for atherosclerosis treatment (2). Recent studies have shown that the majority of macrophages in atherosclerotic lesions originate from

We review the research on specialty fiber couplers with emphasis placed on the characteristics that make them attractive for biomedical imaging, optical communications, and sensing applications. The fabrication of fiber couplers has been carried out with, in addition to conventional single mode fiber, various specialty fibers such as photonic crystal fiber, double clad fiber, and hole-assisted fiber with a Ge-doped core. For the fiber coupler fabrication, the side polishing and the fused biconical tapered methods have been developed. These specialty fiber couplers have been applied to optical coherence tomography, fluorescence spectroscopy, fiber sensors, and optical communication systems. This review aims to provide a detailed statement on the recent progress and novel applications of specialty fiber couplers.