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.

We report on fabricating high-fill-factor plano-convex spherical and square micro-lens arrays on fused silica glass surface using CO2 laser assisted reshaping technique. Initially, periodic micro-pillars have been encoded on the glass surface by means of a femtosecond laser beam. Afterwards, the micro-pillars are polished several times by irradiating a CO2 laser beam on top of the micro-pillars. Consequently, spherical micro-lens array with micro-lens size of 50 um x 50 um and square micro-lens array with micro-lens size of 100 um x 100 um are formed on fused silica glass surface. We also study the intensity distribution of light passed through the spherical micro-lens array engraved glass sample. The simulation result shows that, the focal length of the spherical micro-lens array is 35 um. Furthermore, we investigate the optical properties of the micro-lens array engraved glass samples. The proposed CO2 laser based reshaping technique is simple and fast that shows promises in fabrication arrays of smooth micro-lenses in various transparent materials

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.

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.

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.

We propose a new method for precisely fabricating a lensed fiber with a desired focal length by first cleaving a coreless silica fiber using an ultrafast femtosecond laser without thermal effects and subsequently shaping the radius of curvature at the optical-fiber end using a CO₂ laser. The precisely cleaved segment of the coreless silica fiber obtained with the femtosecond laser is attached to a long single-mode fiber. The beam-exposure time and laser power of the CO₂ laser are adjusted to melt the coreless-fiber end to yield a uniform, consistent, and precise radius of curvature, thereby realizing a lensed optical fiber. The precision of the radius of curvature in this case is greater than those obtained with the conventional arc discharge method with thermal treatment requiring fairly complex processes and yielding relatively low fabrication accuracy. In our study, we observe a difference between the measured and calculated focal lengths of the fabricated lens, possibly because the exact value of the mode field diameter is uncertain. On the other hand, the beam size measured using the knife-edge method matches closely with the theoretical size. Our findings confirm the feasibility of fabricating lensed optical fibers for fiber-based biosensing using CO₂ and femtosecond lasers.