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We report the formation of fluorescence patterns inside gold-doped glass medium by femtosecond-laser fabrication. Strong fluorescence images appeared from the irradiated multi-layered region after low temperature annealing. We removed the images by exposing the glass to an electric furnace or a CO 2 laser beam for high temperature annealing. The method was also applied to recording, reading, and erasing of fluorescence data by a femtosecond laser, a 405-nm laser diode, and a CO 2 laser respectively.

Laser ablation with femtosecond lasers is highly promising for microfabrication of materials. Also, the high peak power of femtosecond lasers could induce a multiphoton absorption to ablate transparent materials. Similar results have also been were obtained in the case of optical fibers. In this paper, we present our experimental results of femtosecond laser microstructuring of optical fiber and its applications to microelectronic components and fiber optic devices. Finally, we directly produced micro holes with femtosecond laser pulses in a single step by moving an optical fiber in a preprogrammed structure. When water was introduced into a hole drilled from the bottom surface of the optical fiber, the effects of blocking and redeposition of ablated material were greatly reduced and the aspect ratio of the depth of the hole was increased. We have presented circular and rectangular-shaped holes in optical fiber.

We have fabricated broadband long-period gratings (LPGs) on hollow optical fibers (HOFs) by 15 corrugating slots with various widths by point-by-point exposure of a Ti:sapphire femotosecond laser. The corrugated LPGs showed unique broadband rejection whose FWHM extended to 190 nm with a low insertion loss of less than 1 dB. The maximum coupling strength was 8.5 dB, which is a significant improvement in comparison with previous HOF acousto-optic tunable filters (AOTFs). The center wavelength and coupling strength of the resonant peak could be systematically controlled by modulating the width of the corrugation.

We report the spectroscopic properties of femtosecond laser-irradiated sodium-alumino-borate glass doped with silver and gold ions. We precipitated gold and silver nanoparticles by laser irradiation and annealing at 400°C for 30 min. The irradiation and annealing treatment produced different absorption and emission characteristics in Au3+ doped and Au3+, Ag+ codoped glasses, and the possible mechanisms of the observed results are discussed. The size of the nanoparticles was estimated by TEM and absorption band analysis.

We have investigated spectral properties of the periodic arrays of aluminum rods and holes on papers using the terahertz time-domain spectroscopy. The size of a rod(hole) is $600{\mu}m{\times}100{\mu}m$ and the spacing is $300{\mu}m$ . The samples were fabricated by a femtosecond laser micromachining system. The periodic arrays of aluminum rods exhibit high reflection around 0.25 THz when the polarization of the THz pulse is parallel to the long axis of the rod, whereas the periodic arrays of holes exhibit high transmission around 0.25 THz when the polarization of the THz pulse is perpendicular to the long axis of the hole.

We report the changes in the refractive index and the spectral features in undoped and Ag-doped sodium-alumino-borate glasses irradiated by using a femtosecond laser and post-annealed by using an electric furnace and a carbon dioxide laser. We fabricated a grating structure inside the glass and measured di raction e ciency of the grating as a function of the annealing temperature and the duration time to estimate the refractive-index change. Color centers created by using the femtosecond laser irradiation were more easily removed by using a carbon-dioxide-laser annealing than a furnace annealing. The precipitation of silver nanoparticles with a high-temperature annealing process was investigated by observing the changes in the absorption and the photoluminescence and by measuring the residual refractive index.

A polypropylene (PP) film was ablated using a femtosecond laser with a center wavelength of 785 nm, a pulse width of 184 fs and a repetition rate of 1 kHz. Increments of both the pulse energy and the shot number of pulses lead to co-occurrence of photochemical and thermal effect, demonstrated by the spatial expansion of rim on the surface of PP. The shapes of the laser-ablated PP films were imaged by a scanning electron microscope (SEM) and measured by a 3D optical measurement system (NanoFocus). And, the gas and water vapor transmission rate, mechanical properties of PP film micropatterned by fs laser pulses was characterized. Our results demonstrate that a femtosecond pulsed laser is an efficient tool for breathable packaging films in modifying the flow of air and gas, where the micropatterns are specifically tailored in size, location and number of which is easily controlled by laser processing conditions.

Precise micropatterning of polypropylene film, which is highly transparent in the wavelength range over 250 nm has been demonstrated by 355 nm nano/picosecond laser and 785 nm femtosecond laser. Increments of both the pulse energy and the shot number of pulses lead to cooccurrence of photochemical and thermal effects, demonstrated by the spatial expansion of rim on the surface of PP. The shapes of the laser-ablated polypropylene films were imaged by optical microscope and measured by a 3D optical measurement system. And, the ablation depth and width of polypropylene film ablated by femtosecond laser at various pulse energy and pulse number were characterized. Our results demonstrate that a femtosecond pulsed laser is an efficient tool for fabricating micropatterns of polypropylene films, where the micropatterns are specifically tailored in size, location and number easily controlled by laser processing conditions.

We fabricated micro-lens array on fused silica glass using femtosecond and CO2 laser. We micro-machined periodic micro-grooves on the glass surface with femtosecond laser, and polished the patterned surface with CO2 laser. We confirmed that curvature was formed on the surface by heat from the CO2 laser beam as the surface roughness was removed. Depending on the fabricated pattern size, we could fabricate micro-lens array with controlling sizes. Using such this laser fabrication technique, we have demonstrated micro-lens array with various dimension.

We observed enhanced terahertz (THz) transmission by implementing visible excitation in bi-layer graphene transferred on a metal slit which was designed for funneling THz field.

We demonstrate the design and simulation of a focused intense light beam by means of multi-layer Fresnel zone plate fabricated on the surface of and inside the core of a multi-mode optical fiber. We investigate both single layer and multi-layer Fresnel zone plate engraved intense light beam. Besides, we analyze various optical properties of the intense light beam including focusing characteristics, intensity, and beam profile at the near field and far field. Increase in the number of Fresnel zone plate layers inside the core of the optical fiber causes the increase in the intensity and focusing sharpness at the focal point of the focused intense light beam. In addition, we propose suitable fabrication technologies for forming Fresnel zone plate in the core of multi-mode optical fiber. Furthermore, we explore the potential application areas of the proposed intense light beam. We strongly believe that, the designed intense light beam would find numerous applications in a diverse field of science and technology.

This paper demonstrates the characterization of femtosecond laser filamentation in soda-lime glass. We achieved femtosecond pulse filamentation of variable height and width by focusing the femtosecond laser beam in different layers inside the sample glass. The dielectric medium immediately before the target position increases the effective numerical aperture of the objective lens that causes the elongation of focal length of the laser beam in a tiny focal spot with high power density. As a result, high aspect ratio voids are engraved inside the glass samples. Furthermore, we investigate the characteristics of the fabricated voids and their dependence on the irradiation conditions of the laser beam and associated optical setup. The height and width of the voids are controlled by varying the laser power, numerical aperture & magnification of the objective lens, and width of the dielectric medium before laser focusing position. Using high power femtosecond laser pulse filaments, we fabricated very long voids inside the glass sample, which undergoes cleaving process with uniform mechanical pressure for smooth cutting of the glass substrate.

Using tightly focused femtosecond laser pulses, we produce an optical waveguide and optical devices in transparent materials. This technique has the potential to generate not only channel waveguides, but also three-dimensional optical devices. In this paper, an optical splitter and U-grooves, which are used for fiber alignment, are simultaneously fabricated in a fused silica glass using near-IR femtosecond laser pulses. The fiber aligned optical splitter has a low insertion loss, less than 4㏈, including an intrinsic splitting loss of 3㏈ and excess loss due to the passive alignment of a single-mode fiber. Finally, we demonstrate the utility of the femtosecond laser writing technique by fabricating gratings at the surface and inside the silica glass.

We report a novel process to directly inscribe a Fresnel zone plate (FZP) lens on the cleaved facet of a hard clad polymer fiber using a femtosecond pulsed laser. The FZPs are designed by adopting modal analysis and free-space diffraction, which are experimentally implemented by locally ablating silica glass using femtosecond laser pulses. A good agreement between the design and fabricated FZP lens is obtained with an exceptionally long focal length over 600 m, which can have a strong potential in all-fiber beam shaping technology and optical interconnections.

This paper investigates applications of femtosecond lasers for the micromachining of transparent materials and fabrication of optical devices. We show commercial micromachining examples of transparent materials which have been fabricated for various applications. Near infrared femtosecond laser processing is an attractive method to fabricate three-dimensional optical waveguides into various transparent materials. Focused femtosecond laser pulses induce a permanent refractive-index change only near the focal point. We also demonstrate a Y coupler with the splitting ratio of 1:1 written by femtosecond laser pulses into a fused silica glass. The minimum propagation loss of 0.8 ㏈/㎝ awl the refractive-index change of 0.006-0.01 at the wavelength of 1550 ㎚ were achieved by optimization of the laser fluence.

An optical gain flattened and improved double-pass two-stage EDFA is proposed using microbending long-period fiber grating (LPFG) filters. This type of filter, based on mechanically induced microbends, has desirable characteristics for gain flattening in an EDFA. As such, it is shown that the incorporation a filter in a reflective EDFA can increase the optical gain, plus the optimum position of the filter is obtained as a function of the pump wavelength and power. Accordingly, when using microbending LPFG filters in the second stage of a double-pass two-stage EDFA, an improved flat gain is obtained with a gain improvement of 2.8 dB and gain flatness of less than 1 dB over a 33-nm wavelength range.

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. (C) 2017 Optical Society of America

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. (C) 2014 Optical Society of America

In this article, we report the development of plano-convex cylindrical micro-lens array on the surface of fused silica glass using laser processing technology. Initially, femtosecond laser pulses are irradiated on the target fused silica glass substrate to pattern periodic micro-grooves. Afterwards, laser beam from CO2 laser source is applied several times on the previously micro-patterned fused silica glass surface, the purpose of which is to polish the micro-patterned glass surface. As a consequence, periodic plano-convex cylindrical micro-lens array is evolved on the glass surface. The micro-lens array shows great consistency in size and shape throughout the sample area. We also investigate various optical properties of the micro-lenses evolved glass substrates including the diffraction pattern and diffraction efficiency of light. The glass sample comprising cylindrical micro-lens array can diffract light with moderate diffraction efficiency. We strongly believe that, it is possible to engineer cylindrical micro-lens array on the surface of a variety of transparent materials including glasses and polymers over a large area.

This paper expresses maskless formation of Fresnel zone plate (FZP) lens on fused silica glass surface using femtosecond laser lithography technology. The FZP lens consists of a series of concentric rings that has been encoded on a glass surface using femtosecond laser irradiation followed by chemical etching and stripping. To compare the performance of the FZP lens with traditional laser induced FZP, we also fabricated FZP on the surface of and inside fused silica glass using femtosecond laser direct writing. In all the cases, the FZP lenses have a focal length of 50 mm. In addition, we fabricated a 25-mm focal length FZP lens by means of femtosecond laser lithography. Compared to traditional femtosecond laser direct writing, femtosecond laser lithography technique offers smooth patterning of materials. Consequently, femtosecond laser lithography engraved FZP lens yields considerably higher diffraction efficiency. Besides, we investigated the diffraction pattern of the fabricated FZP lenses. Using these FZP lenses, we are able to observe microletters encoded on an aluminum coated poly-methylmethacrylate surface indicating excellent focusing and imaging capability of the FZP lenses. The proposed maskless technology is simple compared to other lithography techniques, representing great potential for small-scale manufacturing of similar kinds of optical/photonics devices.

A compact intrinsic fiber Mach-Zehnder interferometer (MZI) is proposed and experimentally demonstrated by incorporating a micro air-cavity ablated by femtosecond laser irradiation. A short cavity of length ~ 10 mum along the single-mode fiber core provided two optical paths: one propagating through the air and the other guided along the ring-shaped silica cladding. A spectral analysis confirmed MZI in a good agreement with experimental results. Temperature-dependent spectral shifts were measured and analyzed.

We present a compact all-fiber zone plate lens directly ablated on the surface of a mode-expanded hybrid fiber end by using a high precision femtosecond laser processing technique. To achieve a sufficiently large beam size and focusing efficiency, a segment of a coreless silica fiber having a 200-mu m diameter was adapted. Focusing properties of the zone plate lens were experimentally investigated and compared with numerical simulations.

A novel low-cost fiber in-line-type bidirectional optical subassembly using a tilted fiber Bragg grating has been developed for fiber-to-the-home applications. We successfully realized a low-cost subassembly by reducing the number of components and simplifying the packaging process. The extinction ratio of 14.8 dB, receiver minimum sensitivity of -26.5 dBm at a bit-error rate of 10-12 and frequency response of 2.7 GHz were experimentally obtained. The electrical crosstalk between transmitter and receiver part was less than -86 dB up to 2.5 GHz.

We propose a new in-line wavelength measurement technique based on one-dimensional fiber end-surface grating for monitoring signals in coarse wavelength-division multiplexing. The fiber end-surface grating was fabricated with femtosecond laser pulses by inscribing microstructure on the cleaved surface of a thermally expanded core fiber and the diffracted beam patterns from the fiber end-surface grating were experimentally analyzed according to the wavelength of input light

A novel packaging process using a femtosecond laser has been developed for passive alignment of planar lightwave circuit devices. With only one step of micromachining, optical splitter and U-grooves for fiber aligning are simultaneously defined on fused silica glass. 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. Finally, the output field pattern is presented, demonstrating the splitting ratio of the optical splitter is approximately 1 : 1.

We present a novel method for three-dimensional optical memory and microchannel embedded in fused silica glass. Three-dimensional dot patterning with a femtosecond laser pulse and observation with optical microscope are performed. Dot patterns are created by use of a 0.42 N.A. objective to focus 100 fs laser pulses inside the material. We demonstrate data storage with $2{\mu}m$ dot pitch and $7{\mu}m$ layer spacing $(36 Gbit/cm^3)$ . A three-dimensional microchannel acting as microfluidic and microoptical components is directly fabricated inside a silica glass. The optical micrographs of the microchannel are obtained by a digital camera of a microscope.

Using tightly focused femtosecond laser pulses, we produce an optical waveguide and devices in transparent materials. This technique has the potential to generate not only channel waveguides, but also three-dimensional optical devices. In this paper, an optical splitter and U-grooves, which are used for fiber alignment, are simultaneously fabricated in 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. Finally, we present an output field pattern, demonstrating that the splitting ratio of the optical splitter becomes approximately 1:1.

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.

We demonstrate optically isotropic filters in the terahertz (THz) frequency range using structurally anisotropic metamaterials. The proposed metamaterials with two-dimensional arrangements of anisotropic H-shaped apertures show polarization-independent transmission due to the combined effects of the dipole resonances of resonators and antennas. Our results may offer the potential for the design and realization of versatile THz devices and systems.

The optical gain and noise figure improved double-pass two-stage EDFA using a mirror, circulator, and gain-flattening filters is proposed. By double passing the pump light and removing the ASE propagating into the input part, the signal gain of 5 ㏈ and noise figure of 2.1 ㏈ are improved compared to the conventional single- and double-pass EDFA With gain-fattening filters in the second stage of EDFA, we obtain an improved flat gain with a gain flatness less than 1 ㏈ over 33-nm wavelength range at the 980-nm pump power of 86 ㎽.

We investigate subwavelength confinement of terahertz electromagnetic surface modes in a three-dimensional region with coupled slot structures. Two-dimensional resonance focusing on a subwavelength slot converts to three-dimensional subwavelength confinement, due to sharp edge confinement effect on asymmetric plasmonic structure, at the center position of the slot structures which consists of two or more slots. We also report on the polarization independent confinement of terahertz electromagnetic surface modes beyond diffraction limit. The structure which consists of radially arranged subwavelength slots located at a same center position shows the polarization-independent terahertz three-dimensional subwavelength confinement.

We report on the splitting of the resonant transmission mode, due to the symmetry breaking of the structural shape, in a coupled slit structure. The finding demonstrates the important role of the shape symmetry in designing a plasmonic structure for high-efficiency transmission modulation and supports possibilities of developing new terahertz devices.

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 investigated the characteristics of THz radiation from a n-type InAs wafer with a triangular array of air holes under optical excitation. The periodic array of air holes was introduced by a femtosecond laser machining technique. We observed the power enhancement of THz radiation from the InAs surface surrounded by the air holes in a frequency range.

The effects of laser drilling through silicon substrate formed by femtosecond laser on n-type MOSFET device characteristics are investigated. The tested MOSFET device structures are fabricated using the commercial 130-nm process. Through via holes and laser scanning line affect the device characteristics, such as drain current and threshold voltage, depending on the distance between the location of the drilling. The device degradation and variation along with a distance from the holes or the line are examined and the device characteristic variation is analyzed to determine the reliability of MOSFET devices against laser drilling damage.

We report the controlled precipitation of PbS quantum dots (QDs) in glasses using multiple irradiation of the femtosecond laser pulses followed by thermal treatment. Upon the irradiation of femtosecond laser, PbS QDs were found to preferentially precipitate in the irradiated area after thermal treatment. Photoluminescence spectra showed PbS QDs in the irradiated area emitted at the long wavelength side, and transmission electron microscope images also confirmed that PbS QDs formed in the irradiated area were larger than those formed in the nonirradiated area. This controlled precipitation of PbS QDs can lead to the development of advanced optical materials.

We report huge field accumulations in rectangular aperture arrays on thin metal film by using shape resonance in THz frequency region. A large far-field transmittance enhancement is observed in the samples of various widths ranging from 10 μm to 1.8 μm which corresponds to only an order of λ/100. Theoretical calculations based on vector diffraction theory indicates 230 times field enhancement in the near-field for the 1.8 μm rectangular aperture.

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.

Micro air cavity fiber Mach-Zehnder interferometer (MZI) was experimentally demonstrated by femtosecond laser micromachining process followed by optimal fusion-splicing. Two optical paths were provided by the cavity to result in a characteristic, wide spacing MZI spectra.

We demonstrated a compact zone plate lens on the end facet of hard polymer clad fiber (HPCF). Femto-second laser inscription technique was developed and the focusing properties of the lens were investigated.

The characteristics of femtosecond laser ablation of AlN and Al 2 O 3 for precision microfabrication are studied experimentally. Specifically, the process characteristics during femtosecond laser drilling of microholes with sub-100 µm diameter are investigated for varying laser parameters and beam path designs for trepanning. The accumulation of sub-micrometer size particles within th e hole is prevented using a blower and vent system. Through process optimization the microdrilling with good hole quality is achieved. Keywords: Ultrashort laser ablation, Al 2 O 3 , AlN, Ceramics, Microdrilling 1. INTRODUCTION Ceramics are widely used in many industrial areas such as automobile engine, break linin g, heat exchanger, electrical insulator, electronic substrate for radio frequency devices, and so on. Ceramics are extremely hard, can resist high temperature (1600~1700 °C) and have considerably lower wear than metals. The ceramic substrates mainly used for electronic circuits include alumina (Al

We report on the fabrication and performance of a lensed photonic crystal fiber (PCF) designed as a compact but effective side-viewing optical imaging probe. The lensed-P CF 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 as a focuser, were simultaneously formed along a small piece of PCF by using arc discharges. The side-viewing ability was endowed by polishing the ball lens with a femto-second laser to form a TIR (total inte rnal reflection) surface. The working distance and the transverse resolution of the fabricated single-body lensed-PCF were experimentally measured to be ~570 P m and 6.8 P m, respectively. With the proposed lensed-PCF probe, OCT images of an in vitro biological sample were successfully obtained Keywords: Photonic crystal fiber, lensed-PCF, side-viewing probe, optical coherence tomography. 1. INTRODUCTION Lensed fiber technologies for optical free-space coupling have been primarily de veloped for the optical power coupling between optical devices in fiber communications and fiber sensor systems. Lensed fibers are attractive alternatives for bulk optic interconnections owing to their compactness, small size, flexible design parameters, and simple fabrication process. To this end, various types of lensed fibers have been reported for optical free-space forward interconnections, including those based on a graded index lensed fiber

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.

We demonstrate a synchronized femtosecond laser pulse switching system for a rapid patterning, which is applicable to fabricate periodic photonic band gap structures. Also, we show the utility of the femtosecond laser writing of periodic patterns by fabricating the submicron patterns inside a transparent material, which is great potential for future application.