Hybrid LPG-FBG Based High-Resolution Micro Bending Strain Sensor.

Sensitivity and reliability are essential factors for the practical implementation of a wearable sensor. This study explores the possibility of using a hybrid high-resolution Bragg grating sensor for achieving a fast response to dynamic, continuous motion and Bragg signal pattern monitoring measurement. The wavelength shift pattern for real-time monitoring in picometer units was derived by using femtosecond laser Bragg grating processing on an optical wave path with long-period grating. The possibility of measuring the demodulation system's Bragg signal pattern on the reflection spectrum of the femtosecond laser precision Bragg process and the long-period grating was confirmed. By demonstrating a practical method of wearing the sensor, the application of wearables was also explored. It is possible to present the applicability of sophisticated micro transformation measurement applications in picometer units.

Analysis of Design and Fabrication Parameters for Lensed Optical Fibers as Pertinent Probes for Sensing and Imaging.

A method for adjusting the working distance and spot size of a fiber probe while suppressing or enhancing the back-coupling to the lead-in fiber is presented. As the optical fiber probe, a lensed optical fiber (LOF) was made by splicing a short piece of coreless silica fiber (CSF) on a single-mode fiber and forming a lens at the end of the CSF. By controlling the length of the CSF and the radius of lens curvature, the optical properties of the LOF were adjusted. The evolution of the beam in the LOF was analyzed by using the Gaussian ABCD matrix method. To confirm the idea experimentally, 17 LOF samples were fabricated and analyzed theoretically and also experimentally. The results show that it is feasible in designing the LOF to be more suitable for specific or dedicated applications. Applications in physical sensing and biomedical imaging fields are expected.

Comparison of laser ablation using multidirectional and forward-firing fibers in breast cancer.

BACKGROUND: The aim of this study was to compare the therapeutic effect of laser ablation using the forward-firing fiber and the multidirectional-firing fiber for breast cancer treatment with pathologic results. MATERIAL AND METHODS: An ex vivo study of laser ablation was conducted using normal breast and breast cancer tissue. Each ablated area was demarcated into three zones, and the temperature was measured. Laser ablations using multidirectional and forward-firing types of fiber were compared regarding the shape, diameter and aspect ratio of the ablated lesions. RESULTS: The ablated lesions were classified into three zones: a carbonized zone with complete tissue loss; a coagulated zone with no viable cells; and a non-damaged zone. The shape of the ablated lesion was elliptical using the forward-firing fiber and round using the multidirectional-firing fiber. Compared with normal breast tissue, breast cancer tissue required a more powerful setting for laser ablation to achieve necrosis, and the aspect ratio of the thermal lesion was higher for laser ablation using the multidirectional-firing fiber. CONCLUSIONS: The experimental results on breast tissue have shown that multidirectional-firing fiber is more effective than using forward-firing fibers and that this may prove to be another feasible therapeutic option for management of breast cancer.

High refractive index metamaterials using corrugated metallic slots.

We report on a method for realizing high refractive index metamaterials using corrugated metallic slot structures at terahertz frequencies. The effective refractive index and peak index frequency can be controlled by varying the width of the air gap in the corrugated slot arrays. The phenomenon occurs because of the secondary resonance effect due to the fundamental inductive-capacitive resonance, which generates a red-shift of the fundamental resonance determined by twice the length of the corrugated metallic slots. In addition, multiple gaps in the corrugated slots act as plasmonic hotspots which have the properties of three-dimensional subwavelength confinement due to extremely strong enhancement of the terahertz waves. The versatile characteristics of the structures may have many potential applications in designing compact optical devices incorporating various functionalities and in developing highly sensitive spectroscopic/imaging systems.

4 channel × 10 Gb/s bidirectional optical subassembly using silicon optical bench with precise passive optical alignment.

We demonstrate an advanced structure for optical interconnect consisting of 4 channel × 10 Gb/s bidirectional optical subassembly (BOSA) formed using silicon optical bench (SiOB) with tapered fiber guiding holes (TFGHs) for precise and passive optical alignment of vertical-cavity surface-emitting laser (VCSEL)-to-multi mode fiber (MMF) and MMF-to-photodiode (PD). The co-planar waveguide (CPW) transmission line (Tline) was formed on the backside of silicon substrate to reduce the insertion loss of electrical data signal. The 4 channel VCSEL and PD array are attached at the end of CPW Tline using a flip-chip bonder and solder pad. The 12-channel ribbon fiber is simply inserted into the TFGHs of SiOB and is passively aligned to the VCSEL and PD in which no additional coupling optics are required. The fabricated BOSA shows high coupling efficiency and good performance with the clearly open eye patterns and a very low bit error rate of less than 10-12 order at a data rate of 10 Gb/s with a PRBS pattern of 231-1.

Monopole resonators in planar plasmonic metamaterials.

We first present a new phenomenon: the quarter-wavelength resonance of an electromagnetic field in planar plasmonic metamaterials consisting of asymmetrically coupled air-slot arrays, which is essential for a monopole resonator. The anti-nodal electric field intensity of the quarter-wavelength fundamental mode is formed by strong charge concentrations at the sharp metallic edges of the crossing position of the air-slots, and the nodal point of the electric field intensity naturally occurs at the other end of the air-slot. By tuning the structural asymmetry, the quarter-wavelength resonances were successfully split from the half-wavelength resonance, experimentally and numerically.

Formation of void array inside transparent and absorptive glasses by femtosecond laser irradiation.

We demonstrate self-fabrication of void arrays in a fused silica transparent in the visible and a color-filter borosilicate glass strongly absorptive at 800 nm using tightly focused Ti-sapphire femtosecond laser pulses at 1 kHz without scanning. The period, the size, the number of voids, and the length of the aligned void structure were controlled by changing the laser pulse energy, and the position of the focal point inside two materials. The void arrays were observed by an optical microscope and also estimated by an optical diffraction experiment. The void size and period were smaller in the absorptive glass than in the transparent glass. The submicrometer-sized void was observed by a scanning electron microscope. The smaller and clearer void arrays were formed in the color filter than the fused silica glass. With increasing the laser focal depth, the void-array length increased in the fused silica and decreased in the color filter.

Salt Heat Treatment and Passivation to Improve the Corrosion Resistance of Nitinol (Ni-Ti).

Corrosion of nitinol (NiTi) is a major factor in the failure of implantable materials. Recently, as the importance of corrosion of metals has increased, testing according to international guidelines is essential. The purpose of this study was to evaluate the corrosion resistance of NiTi wire through heat treatment and passivation process. In this study, NiTi wire used two commercially available products and a self-manufactured stent. Experimental consideration was carried out according to ASTM standards. Heat treatment was carried out in an air or a salt furnace, and the corrosion was measured after additional process, such as passivation and scratch tests. As a result, the metal potential was rapidly decreased in the air furnace group. On the other hand, the potential of wires was dramatically increased in the salt furnace group compared to the air furnace group. The dislocation decreased below the acceptance criteria (>600 mV) within 60 s of heat treatment time in the air furnace. Moreover, the potential was dramatically improved, even after only 20 min of passivation treatment (1076 mV, 442% compared to the non-passivated group), and it continued to rise until 180 min. This phenomenon was similarly observed in the group of self-manufactured stents. The potential slightly decreased by the scratch process (93.1%) was significantly reduced by the air furnace process (315 mV, 24.4% of the nontreated group). In the passivated group of the air furnace sample with reduced potential, the potential was restored to the level before the air furnace (scratch stage) (1032 mV). In conclusion, the heat treatment is preferably carried out in a salt furnace rather than an air furnace, and the passivation process can be an advantageous tool to improve corrosion resistance by suppressing the oxidation process.

Femtosecond laser and arc discharge induced microstructuring on optical fiber tip for the multidirectional firing.

Most optical fibers are designed for forward firing i.e. the light is emitted at the distal end along the optical axis of the fiber. In some applications such as the laser surgery and laser scanners, side firing of the optical fiber is required. In this paper, we present the microstructuring of an optical fiber tip using the femtosecond laser and an arc discharging process for the multidirectional firing of the beam. The distal end of the optical fiber with diameter of 125 µm was machined into a conical structure using a femtosecond laser. The surface of the machined tip was exposed to the arc discharge using a fiber splicer. The arc discharge leads to the melting and re-solidification of the fiber tip. This results in a smoothing of laser-induced conical microstructure at the tip of the fiber. We were able to demonstrate the multidirectional (circumferential) emission of the light from the developed fiber tip.

Ultrasound-Guided Laser Ablation Using Multidirectional-Firing Fiber for Papillary Thyroid Carcinoma: An Ex Vivo Study with Evaluation of Tumor Cell Viability.

OBJECTIVE: The objective of this study was to evaluate the viability of tumor cells after laser ablation for papillary thyroid carcinoma and to determine if the laser ablation procedure using multidirectional-firing fiber had a therapeutic effect. BACKGROUND DATA: Many noninvasive techniques have been introduced for the treatment of thyroid cancer. Among them, the laser ablation technique has been proven its therapeutic effect for large benign thyroid nodules. MATERIALS AND METHODS: Three patients who were diagnosed with papillary thyroid carcinoma using fine-needle aspiration cytology were enrolled. All of the selected tumors were >2 cm in size and there was no case of extrathyroidal extension. A laser fiber was inserted into the tumor by means of ultrasound guidance and ablation was performed for 3 min at 7 W of output power. The specimens were stained using hematoxylin and eosin (H&E) and nicotinamide adenine dinucleotide (NADH), and were evaluated by a pathologist. RESULTS: The specimen showed three clearly distinct zones: zone 1, carbonized zone; zone 2, coagulated zone; and zone 3, normal thyroid tissue. No remaining thyroid tissue was visible in zone 1 after staining, because of complete necrosis of the tumor cells. Although thyroid tissue remained in zone 2, no viable tumor cells were detected using NADH staining. CONCLUSIONS: It was found that laser ablation using multidirectional-firing fiber could be an effective treatment technique for papillary thyroid carcinoma. This technique enables not only direct cancer treatment with cell necrosis but also the securement of a tumor safety margin in a similar manner to surgery.

Fabrication of photonic devices directly written within glass using a femtosecond laser.

We present a novel method for three-dimensional optical splitter that have U-grooves, which are used for fiber alignment, within a fused silica glass using near-IR femtosecond laser pulses. The fiber aligned optical splitter has a low insertion loss, less than 4 dB, including an intrinsic splitting loss of 3 dB and excess loss due to the passive alignment of a single-mode fiber. The output field pattern is presented, demonstrating the splitting ratio of the optical splitter is approximately 1:1. Finally, we demonstrate the utility of the femtosecond laser writing of periodic patterns by fabricating the submicron line and dot patterns inside the silica glass, which is applicable to 3-D optical memory.

Comparison of laser ablation using multidirectional and forward-firing fiber in human thyroid gland: experimental study.

The aim of this study is to evaluate the differences between forward-firing and multidirectional lasers and to evaluate the effects of exposure times and power on laser ablation of thyroid tissue. This is an experimental, ex vivo study. The experiments were conducted on 3 thyroid glands using 2 power levels (3 and 5 W) and exposure times (3 and 5 minutes) with forward-firing and multidirectional lasers. The length and width of the demarcated zone were measured to assess the size of thermal effect. NADPH staining was performed to determine tissue viability. Thermal transformation caused by the forward-firing laser produced oval necrotic zones, whereas thermal transformation caused by the multidirectional-firing laser produced clear round necrotic zones, which clearly demarcated in both hematoxylin and eosin staining and NADH staining.

Single-body lensed photonic crystal fibers as side-viewing probes for optical imaging systems.

We report the fabrication and performance of a lensed photonic crystal fiber (PCF) designed as a compact but effective side-viewing optical imaging probe. The lensed-PCF probe was implemented in a single body without using any other fibers or additional optics. The beam expansion region and a focusing ball lens, necessary for a focuser, were simultaneously formed along a small piece of PCF by applying arc discharges. The side-viewing ability was provided by polishing the ball lens with a femtosecond laser to form a total internal reflection surface. The working distance and the transverse resolution of the fabricated single-body lensed-PCF were experimentally measured to be 570 and 6.8 microm, respectively. With the proposed lensed-PCF probe, optical coherence tomography images of an in vitro biological sample were successfully obtained.