Young-Geun Han

• Hanyang University

Background Noninvasive monitoring of tear glucose levels can be convenient for patients to manage their diabetes mellitus. However, there are issues with monitoring tear glucose levels, such as the invasiveness of some methods, the miniaturization, inaccuracy, or the high cost of wearable devices. To overcome the issues, we newly designed a sucking...

High-degree time-multiplexed multifocal multiphoton microscopy was expected to provide a facile path to scanningless optical-sectioning and the fast imaging of dynamic three-dimensional biological systems. However, physical constraints on typical time multiplexing devices, arising from diffraction in the free-space propagation of light waves, lead...

Magnetic field sensor using a two-mode microfiber knot resonator with polymeric dispersant EMG nano-particles is investigated. Three different peaks in the proposed TM-MKR have different magnetic field sensitiviity of 0.83, 0.122 and 0.139 nm/G.

A polymer-overlaid two-mode microfiber knot resonator (TM-MKR) was proposed for simultaneous measurement of ambient index and temperature. By optimizing the waist diameter of the microfiber, the ambient index sensitivity of the polymer-overlaid TM-MKR is improved.

A temperature-insensitive in-line Mach-Zehnder interferometer (MZI) based on a thin-core optical fiber is investigated. The temperature sensitivity of the in-line MZI is successfully suppressed which is 750 times lower than that of the conventional MZI.

Transmission characteristics of periodically surface-corrugated long-period gratings (LPGs) inscribed on photonic crystal fibers (PCFs) using a wet-etching technique were experimentally investigated. A conventional wet method was implemented to periodically engrave the silica cladding region of the PCFs resulting in the periodic surface corrugation...

The temperature sensitivity of the free spectral range (FSR) for a polymer-overlaid microfiber Mach-Zehnder interferometer (MZI) is investigated both theoretically and experimentally. The waist diameter of the optical microfiber can be controlled to alter the thermal expansion and optic properties of the polymer-coated MZI. Inserting an optical mic...

A new method for all-fiber weak value amplification (WVA) based on optical attenuation is proposed, and we theoretically and experimentally demonstrated improved sensitivity of the centroid shift of a fiber Bragg grating (FBG) sensor to an external perturbation change. In the proposed WVA method, we figure out that optical attenuation plays an impo...

A highly sensitive relative humidity sensor based on a few-mode microfiber knot resonator (FM-MKR) incorporating a polyvinyl alcohol overlay is investigated. The sensitivity of the proposed FM-MKR to the relative humidity is successfully enhanced by mitigating the difference in effective refractive group indices between the HE11 and HE12 modes. The...

A temperature-insensitive microfiber Mach-Zehnder interferometer (MZI) for absolute strain measurement is investigated theoretically and experimentally depending on the diameter of the microfiber. The thermo-optic quantity of the microfiber MZI is effectively controlled by optimizing the diameter of the microfiber within the MZI incorporating an ex...

A highly sensitive relative humidity (RH) sensor based on a microfiber knot resonator (MKR) with a polyvinyl alcohol (PVA) overlay is investigated. To realize a miniature fiberoptic RH sensing probe, we designed a MKR with a PVA coating. After making a tie using the microfiber with a diameter of 2 μm, the MKR with a loop diameter of 70 μm is realiz...

We propose a humidity sensor using a periodically micro-tapered long-period fiber grating incorporating low index polymer and polyvinyl alcohol (PVA). We effectively suppress sensing uncertainty for measurement of the relative humidity.

A periodically patterned long-period grating on a D-shaped photonic crystal fiber is investigated for simultaneous measurement of temperature and ambient index. The proposed LPG exhibits different temperature and ambient index sensitivities corresponding to two polarization states.

We propose a real-time multi-monitoring interrogation technique based on Fourier domain modelocked fiber laser for simultaneous measurement of radiation dose and multi-point strain. Radiation dose and multipoint strain can be monitored in real-time by measuring the variation of output power and detection time interval of the sensing signals. Since...

A simple technique to effectively enhance the temperature sensitivity of the Mach-Zehnder interferometer (MZI) by using a microfiber with low index polymer coating is theoretically and experimentally investigated. We successfully improve the temperature sensitivity of the polymer-overlaid microfiber MZI to be -6.68 nm/oC around a temperature of 25°...

We propose an in-line modal coupler based on a multicore fiber (MCF) which can be readily fabricated by using the adiabatic tapering method. The intermodal coupling of the in-line modal coupler apparently generated the transmission oscillation of the center core and the multiple side core modes depending on the waist diameter. The reduction of the...

A highly sensitive RH sensor based on the MKR with the PVA overlay is investigated. After making a tie using the microfiber with a diameter of 2 μm, the MRK with a loop diameter of 90 μm is fabricated and coated by using a PVA which can absorb humidity. The optical spectra of the MRK with the PVA overlay are converted to the spatial frequency spect...

Transmission characteristics of long-period fiber gratings (LPFGs) fabricated by periodically etching a conventional single-mode fiber (SMF) are investigated. After coating the SMF with photoresist, the cladding of the SMF is symmetrically and periodically removed by using a wet etching technique resulting in the formation of the LPFG. Tensile stra...

An in-line interferometer based on the intermodal coupling of a multicore fiber (MCF) is proposed and experimentally demonstrated. The in-line interferometer is fabricated by adiabatically tapering the MCF. The intermodal coupling of the in-line interferometer is strongly affected by the waist diameter of the MCF, which changes the evanescent field...

A highly sensitive current sensor based on an optical microfiber loop resonator (MLR) incorporating low index polymer is proposed and experimentally demonstrated. The microfiber with a waist diameter of 2 μm is wrapped around the nichrome wire with low index polymer overlay to realize the MLR as the highly sensitive current sensor. Low index polyme...

We investigated the effects of the thickness and doping concentration in p- and n-type poly-Si layers on the performance of a solar cell based on a carbon fiber in order to improve the energy conversion efficiency of the cell. The short-circuit current density and open-circuit voltage of the carbon fiber-based solar cell were Significantly influenc...

According to the generalization of mobile device use in our life, the complexity and diversity of mobile applications are increased, and thus the importance of application test to find faults and errors quickly and easily before release grows. This paper reviews the current automatic testing methodologies for mobile device applications and their el...

The objective of this study is to provide mobile application developers with a standard testing system and service method. By using this testing service, the developers can test the functional performance and quality of their applications from remote sites through Internet. This service standard helps to test applications quickly, easily, and cheap...

We investigate the propagation characteristics of a pulse laser in a time-of-flight laser range finder (TOF-LRF) system with variations in atmospheric conditions, such as temperature, pressure, relative humidity, and the concentration of $CO_2$ . The measurement error of distance related with the group velocity change in the TOF-LRF system is analy...

We propose a sensing scheme of an erbium-doped fiber (EDF) ring laser for multi-monitoring of radiation dose and strain simultaneously. The EDF and fiber Bragg grating (FBG) are exploited as sensing probes for simultaneous measurement of radiation dose and strain. The output power and the lasing wavelength of the proposed EDF laser are changed by i...

A microfiber-based Mach-Zehnder interferometer (MZI) for measurement of absolute strain is proposed and demonstrated experimentally. The diameter of the microfiber is optimized to induce the negative thermo-optic effect in the microfiber MZI and the temperature sensitivity of the microfiber MZI is successfully suppressed. When the diameter of the m...

A highly sensitive current sensor based on an optical microfiber loop resonator (MLR) incorporating low index polymer is proposed and experimentally demonstrated. The microfiber with a waist diameter of 1 μm is wrapped around the nicrhrome wire with low index polymer coating and the optical MLR is realized. The use of the microfiber and low index p...

A reflective in-line modal interferometer based on a polarization- maintaining photonic crystal fiber (PM-PCF) with two exterior air holes is proposed for simultaneous measurement of chemical vapor and temperature. After fusion-splicing the PM-PCF with a standard single-mode fiber, we collapse all of air holes in the PM-PCF resulting in two types o...

We investigate the effect of a waist diameter of a polarization-maintaining fiber (PMF) on ambient index and temperature sensitivities by configuring a Sagnac loop interferometer. To make the PMF sensitive to external index change, a micro-tapering technique is exploited to fabricate the tapered PMF. The Sagnac loop interfoermeter is fabricated by...

A simple technique for simultaneous measurement of the concentration of ethylene glycol and temperature by using a hybrid Sagnac interferometer is proposed and experimentally demonstrated. The hybrid Sagnac interferometer is configured by inserting a long-period fiber grating (LPFG) and a D-shaped polarization-maintaining fiber (PMF) into a Sagnac...

We investigate an effective technique to alleviate the speckle contrast based on the temporal angular decorrelation induced by multiple beamlets with diverse optical paths. Multiple beamlets with diverse optical paths are generated by using a microlens array incorporating a galvo-mirror at the foci of two spherical lenses. As the multiple beamlets...

The effect of a waist diameter of a microtapered polarization-maintaining fiber (PMF) on the temperature and the ambient index sensitivities is investigated theoretically and experimentally. Stress-induced and geometrical birefringences strongly depend on the waist diameter of the microtapered PMF, which plays a key role in temperature and ambient...

As companies were concerned with developing green logistics and environment, most logistics concerned functions like packaging, loading, storage, transportation and IT studies are active in study. Even if active in research studies, companies still recognized that logistics cost increases as green concepts are applied. For the efficient execution o...

The temperature sensitivity of modal birefringence (dB/dT) of different types of polarization-maintaining fibers with side holes was measured using Sagnac loop interferometer. The thermal expansion coefficient can be varied by controlling the amount of germanium doped in the core region. Using this method dB/dT could be made higher (~10-7/degC) tha...

Transmission characteristics of microtapered long-period fiber gratings (MTLPGs) and their strain and temperature sensitivities with variations in the waist diameters are investigated theoretically and experimentally. Transmission characteristics of MTLPGs strongly depend on the waist diameter of the tapered optical fiber (TOF) because of the modif...

A multiwavelength erbium-doped fiber laser based on a nonlinear amplified loop mirror with a highly-nonlinear photonic crystal fiber was proposed and experimentally investigated. The performance of the nonlinear amplified loop mirror was improved by using a single 3-dB coupler and a highly-nonlinear photonic crystal fiber with a length of 100 m. Th...

In general, optical fiber gratings can be classified as either fiber Bragg gratings (FBGs) or long-period fiber gratings (LPGs) depending on whether the periodic variation in the refractive index is ranged in the submicron or in the hundreds of microns scale [1, 2]. © 2013 Springer Science+Business Media New York. All rights are reserved.

Micro-ridge long-period fiber grating (MRLPFG) inscribed on a photonic crystal fiber was proposed and experimentally demonstrated. Transmission characteristics of the PCF-based MRLPFG with variations in strain and temperature were measured.

A novel fabrication technique of H-shaped highly birefringent (Hi-Bi) microfiber is proposed. The birefringence of fabricated H-shaped microfiber was improved by a factor of 20 higher than that of a conventional birefringent fiber.

We propose a novel scheme for a switchable dual wavelength erbium-doped fiber laser based on a polarization-dependent surface long-period grating. The lasing wavelength was switched in C- and L-band with a response time of 270 μs.

We propose a novel fiber Bragg grating (FBG) sensor interrogation using a Raman-based Fourier-domain mode locking (FDML) fiber laser for a high speed and long distance measurement. A residual Raman pump after the generation of the Raman-based FDML fiber laser is recycled for secondary signal amplification in a 2-m erbium-doped fiber (EDF) to furthe...

After the Uruguay Round, Korean agriculture industry has been protected and reared with government grants. However, until now there has been very minimal development to establish a solid export industry which can make the most of the trade agreements in place. There has been much research on ways to expand agricultural exports in order to respond p...

Transmission characteristics of a surface long-period grating (SLPG) inscribed in a Dshaped photonic crystal fiber (PCF) are investigated, which exhibits strong dependence on TE and TM polarization modes. Advanced Photonics Congress

We demonstrate spectral-domain optical coherence tomography (SD-OCT) with high axial resolution and high image acquisition speed, which is realized by using a broadband coupler based on a photonic crystal fiber (PCF). The PCF-based coupler with broad bandwidth was fabricated by using a fused biconical tapered (FBT) method, and the axial resolution...

A simple and practical scheme for simultaneous measurement of bending and temperature based on a multiwavelength Raman fiber laser incorporating a single sampled fiber Bragg grating (FBG) is investigated. By using a sampled FBG and a Raman gain medium, we generated a multiwavelength Raman fiber laser and then applied it to discriminate between bend...

A hybrid grating based on a surface long-period grating (SLPG) incorporating a fiber Bragg grating (FBG) was proposed, and its optical characteristics were experimentally investigated by changing the external temperature and the ambient refractive index. For the fabrication of the hybrid grating, a FBG was firstly fabricated by using a beam scannin...

We fabricate a small-size embedded optical microfiber coil resonators (OMCRs) with a high Q-factor and investigate the dependence of the transmission characteristics of the OMCRs on the microfiber diameter and the OMCR diameter. Various microfibers with different diameters of 2.0, 2.1, 2.2, and 2.3 µm are fabricated by using a micro-tapering techni...

A reflection-type interferometer based on a polarization-maintaining photonic crystal fiber (PM-PCF) is investigated for simultaneous measurement of chemical vapor and temperature. The PM-PCF with a length of 2.6 cm is fusion-spliced to standard single-mode fiber and airholes of the PM-PCF are fully collapsed allowing the excitation of different co...

We propose a novel refractive index sensor using Sagnac loop interferometers configured by using tapered polarization-maintaining fibers (PMFs) with different tapered diameters. To make the PMF sensitive to external index change, a micro-tapering technique is exploited to fabricate the tapered PMF. The sensitivities of the PMFs to ambient index str...

We propose the temperature-insensitive bending sensor based on a hole-assisted single polarization fiber (SPF). Without fiber grating structures, the SPF-based sensing probe can provide the sensing technique to measure the bending change. If bending is applied to the SPF, two cutoff wavelengths are shifted to shorter wavelengths and the transmissio...

We investigate a new fabrication technique for LPFGs by using a surface imprinting or a micro-tapering technique. Transmission characteristics of surface LPFGs deposited on a D-shaped PCF strongly depend on input polarization states, which makes possible to discriminate ambient index and temperature sensitivities. A micro-ridge LPFG fabricated by a...

We propose a novel fiber Bragg grating (FBG) sensor interrogation system using a Raman-based Fourier domain mode locking (FDML) fiber laser for a high speed and a long distance measurement. To improve transmission efficiency of the sensing probe signal over a long distance of 20-km, the residual pump powers are recycled. The external strain change...

Transmission characteristics of a surface long-period grating (SLPG) inscribed in a D-shaped photonic crystal fiber (PCF) are investigated, which exhibits strong dependence on TE and TM polarization modes.

A hybrid Sagnac interferometer with a locally D-shaped polarization maintaining fiber (PMF) incorporating a fiber Bragg grating (FBG) and a long-period fiber grating (LPFG), is invesitigated for simultaneous measurement of ambient index and temperature.

A long-period fiber grating (LPFG) written in a tapered fiber was proposed and experimentally demonstrated. Strain sensitivity of the proposed LPFG based on a tapered fiber was improved to be -2.99 nm/mϵ.

We investigate a periodically micro-tapered fiber grating for simultaneous measurement of strain and temperature. The fundamental core mode can be coupled to the cladding mode by tapering a single-mode fiber periodically, which results to the resonant wavelength. The coupling strength is directly proportional to the number of micro-tapered regions...

Polarization-dependent in-line Mach–Zehnder interferometer fabricated by using a polarization-maintaining fiber (PMF) depending on input polarization state is investigated for discrimination of temperature and ambient index. Interference is induced by inserting the PMF with a length of 1 cm between two conventional single mode fibers. A core-misali...

A switchable multichannel filter based on a hybrid Sagnac interferometer was proposed and experimentally demonstrated. The hybrid Sagnac interferometer was realized by inserting a sampled fiber Bragg grating (SFBG) into a fiber loop mirror by using a polarization-insensitive 3-dB coupler. By using a beam scanning technique, we fabricated a sampled...

The transmission characteristics of a Sagnac interferometer based on an etched polarization-maintaining photonic crystal fiber (PM-PCF) incorporating an erbium-doped fiber (EDF) are investigated for simultaneous measurement of strain and temperature. After reducing the cladding diameter of the PM-PCF, we fabricated the Sagnac interferometer to indu...

A stably and widely tunable single-longitudinal-mode dual-wavelength erbium-doped fiber (EDF) laser is investigated for the generation of a tunable optical beat frequency. The lasing wavelength spacing is widely controlled in a range from 3.46 to 13.2 nm, which means that the tunable optical beat frequency in a range from 0.43 to 1.66 THz can be ac...

We demonstrate a spectral-domain optical coherence tomography (SD-OCT) using a microfiber coupler with an insertion loss of ~0.5-dB over 900-nm bandwidth. The axial resolution of the SD-OCT is measured to be ~2 um.

We introduce a new configuration for large-core optical transceiver platforms based on asymmetric three- dimensional multimode Y junctions. We developed a simply structured bidirectional waveguide platform without using a wavelength division multiplexing filter or angled mirror. This structure was designed with two different size waveguides by usin...

Polarization-dependent in-line Mach-Zehnder interferometer fabricated by using a polarization-maintaining fiber depending on input polarization state is investigated for discrimination of temperature and ambient index.

A long-distance remote sensing technique using a multiwavelength Raman fiber laser with fiber Bragg gratings (FBGs) embedded in a quartz tube is proposed. A Raman linear cavity for multiwavelength generation was configured by using a long length of single mode fiber and FBGs. To discriminate concurrent sensitivities, such as temperature and strain...

A simple scheme for discrimination of temperature and ambient index based on a D-shaped photonic crystal fiber with surface long-period fiber gratings depending on input polarization state are proposed and experimentally investigated.

A new fabrication of micro-tapered long-period fiber grating based on a micro-tapering technique is proposed for simultaneous measurement of strain and temperature. The transmission characteristics of the periodically tapered long-period fiber gratings with variations in strain and temperature are measured.

We propose the temperature-insensitive bending sensor based on a hole-assisted single polarization fiber (SPF). Without fiber grating structures, the SPF-based sensing probe can provide the sensing technique to measure the bending change. If bending is applied to the SPF, two cutoff wavelengths are shifted to shorter wavelengths and the transmissio...

A hybrid Sagnac interferometer with a D-shaped polarization maintaining fiber (PMF) and a fiber Bragg grating (FBG) is proposed and experimentally demonstrated for simultaneous measurement of ambient index and temperature. Since the core mode of the locally D-shaped PMF is directly interfaced to the external environment, the interference pattern of...

A simple scheme for simultaneous measurement of bending and temperature based on a dualwavelength Raman fiber laser at a long distance of more than 50 km is investigated without additional light sources.

A new fabrication technique of long-period fiber gratings with periodically surface-etched structures is proposed. Transmission characteristics of the periodically surface-etched long-period fiber gratings are improved by changing strain because of variation of coupling strength between the core and the cladding modes. The sensitivities of the peri...

We present a simple fiber-optic confocal method for high-precision thickness measurement of optically transparent and non-transparent objects that require noncontact measurement. The method is based on measurement of confocal backreflection responses from the opposite surfaces of objects, which imposes inessential limitations on the shape, thicknes...

A thermally tunable multiwavelength Raman fiber laser based on a misaligned long-period fiber grating is investigated. The proposed multiwavelength Raman laser has a high thermal tunablity of -0.48 nm/°C.

A hybrid sensing method based on a surface long period grating incorporating a fiber Bragg grating is investigated for simultaneous measurement of external refractive index and temperature.

An in-line tunable Mach-Zehnder interferometer (MZI) based on cascaded micro-ridge long-period fiber gratings (MRLPFGs) is proposed and experimentally demonstrated. The transmission characteristics of the MZI based on cascaded MRLPFGs can be controlled by applying external strain and torsion.

In order to determine home delivery service routes, conditions specified for each parcel such as customer-assigned delivery times and parcel contents should be considered, so the conventional route search algorithms have some limits to be applied for home delivery services. In this study, a multi-purpose route searching algorithm is suggested in or...

The effect of single-wall carbon nanotubes (SWNTs) on nonlinear optical absorption of D-shaped fibers with versatile the remaining length of the cladding region and the interaction length are investigated. The optical absorption based on SWNTs is induced by the energy bandgap in SWNTs. The bandgap energy depends on the tube diameter of SWNTs. After...

We investigate an optical technique for beam shaping and optical amplification of a pulsed laser diode without variation of its original properties, such as repetition rate and pulse duration. The horizontal and longitudinal sizes of the pulsed laser diode are 300 and 2?m, respectively, and its output power is 1.1mW/cm^2. The multimodal and ellipti...

We propose a new type of surface long-period fiber grating (LPFG) with enhanced sensitivities to ambient index and temperature, inscribed in photonic crystal fibers (PCFs). The PCF-based D-shaped fiber is fabricated by using a side-polishing technique and the surface LPFGs are formed by using a spin-coating method with a photoresist (PR) and a stan...

The transmission characteristics of multiply-cascaded phase-shifted long-period fiber gratings (LPFGs) are investigated theoretically and experimentally. By including the phase-shift in the middle of a LPFG, an optical filter, such as a bandpass filter can be realized. A wavelength shift of the passband occurs as the amount of phase shift in the mi...

A tunable multiwavelength erbium-doped fiber laser based on an in-line Mach Zehnder interferometer is proposed and experimentally demonstrated. The in-line Mach Zehnder interferometer is realized by using cascaded long-period fiber gratings. The long-period fiber gratings can couple the guided core mode to several cladding modes. If two identical l...

We developed a broadband optical coupler based on a photonic crystal fiber (PCF), which is very useful for applications to optical coherence tomography (OCT). The PCF-based coupler is fabricated by using a fused biconical tapering (FBT) method. The PCF has six hexagonally-stacked layers of air holes. The PCF-based coupler has a nearly-fiat 50/50 co...

We were experimental demonstrated the transmission characteristic of Sagnac loop mirror based on single polarization fiber (SPF). The interference fringe of Sagnac loop mirror was not revealed at specified wavelength range, because of SPF with cutoff polarization states. The sensitivities of Sagnac loop mirror based on SPF applied strain and temper...

A practical scheme for a tunable multiwavelength Raman ring laser incorporating a two phase-shifted fiber Bragg grating is investigated. The proposed multiwavelength Raman ring laser has a high extinction ratio of ~50 dB and a high tunability of 0.11 nm/V.

A new fabrication technique for corrugated long-period fiber gratings (CLPFGs) with periodic polymer microstructures is proposed. Transmission characteristics of CLPFGs are improved by changing the applied strain because of the control of the coupling strength. The sensitivities of strain, torsion and ambient refractive index were measured.

A broadband optical coupler with a broad bandwidth of 1000 nm based on a photonic crystal fiber (PCF) is investigated. The PCF has 6 layers of air hole structures and a diameter of . The PCF-based coupler is fabricated by using a fused biconical tapering method based on heating and elongation processes. Changing temperature and an elongation length...