All-optical 2 x 2 switching with two independent Yb3+ -doped nonlinear optical fibers with a long-period fiber grating pair

We have demonstrated a new type of all-optical 2 x 2 switch by using two independent Yb3+ -doped nonlinear optical fibers with a long-period fiber grating pair and a 3-dB fiber coupler. A 400-Hz square-wave pulse train at approximately 1549.4 nm was fully switched between the two output ports up to 200 Hz by modulated pump signals at 976 nm with a maximum pump power of approximately 35 mW, where the extinction ratio at approximately 1549.4 nm between the on and the off states was approximately 17.5 dB.     

Characterization of polymer-coated optical fibers using a torsion pendulum

A freely oscillating torsion pendulum has been used to characterize the dynamic mechanical behavior of single polymer-coated optical fibers. The dynamical mechanical spectra of the polymer coatings exhibit a glass transition temperature (T_g), a cryogenic glassy-state relaxation (T_sec), and another cryogenic relaxation that is attributed to water present in the coating (TH₂O). The shear modulus (G′) of the coating was computed from the shear moduli of the composite specimen and the core, assuming that the coating and core deform through the same angle on oscillation. The glassy-state modulus was the same for both thin and thick coatings, although the intensity of the damping peaks, as measured by the logarithmic decrement, increased with coating thickness. Comparison of the dynamic mechanical behavior of a coated optical fiber and of a free film cast from the same reactive components shows that the polymer itself can absorb water at ambient conditions and display a mechanical relaxation at cryogenic temperatures. The T., H₂O and T_sec relaxations are coupled with respect to their intensities. Latent chemical reactivity was found in one coating above its maximum temperature of cure. In this, the temperature of cure determines the glass transition temperature.     

Novel platform for minimizing cell loss on separation process: Droplet-based magnetically activated cell separator

To reduce the problem of cell loss due to adhesion, one of the basic phenomena in microchannel, we proposed the droplet-based magnetically activated cell separator (DMACS). Based on the platform of the DMACS-which consists of permanent magnets, a coverslip with a circle-shaped boundary, and an injection tube-we could collect magnetically (CD45)-labeled (positive) cells with high purity and minimize cell loss due to adhesion. To compare separation efficiency between the MACS and the DMACS, the total number of cells before and after separation with both the separators was counted by flow cytometry. We could find that the number (3241/59 940) of cells lost in the DMACS is much less than that (22 360/59 940) in the MACS while the efficiency of cell separation in the DMACS (96.07%) is almost the same as that in the MACS (96.72%). Practically, with fluorescent images, it was visually confirmed that the statistical data are reliable. From the viability test by using Hoechst 33 342, it was also demonstrated that there was no cell damage on a gas-liquid interface. Conclusively, DMACS will be a powerful tool to separate rare cells and applicable as a separator, key component of lab-on-a-chip.     

Electrochromic device of PEDOT–PANI hybrid system for fast response and high optical contrast

An organic–organic hybrid system composed of the polyaniline (PANI) and poly-(3,4-ethylenedioxythiophene) (PEDOT) with controlled thickness was developed successfully in order to realize synergetic effects in electrochromic (EC) properties such as optical contrast and color-switching rate. From the UV transmittance spectra, we found that the optical contrast (Δ%T) was enhanced up to 6–72% at the wavelength of 580 nm compared with the previous PANI–PEDOT ECDs. Furthermore, the optimized ECD showed an extremely fast response time of less than 160 ms. It is therefore concluded that such a complementary full .cell system of PEDOT–PANI ECD is applicable as an optical device.     

Realization of true-time-delay using cascaded long-period fiber gratings: theory and applications to the optical pulse multiplication and temporal encoder/decoder

This paper proposes and demonstrates a technique for repetition-rate multiplication of an optical pulse train having an arbitrary period or pattern and the optical temporal encoding/decoding for the optical-code-division multiple-access (O-CDMA) system. The technique exploits the difference in the propagation speeds between the core and copropagating cladding modes of a fiber to obtain true-time-delay between the modes traveling in the core mode and the cladding mode, which can be used to achieve pulse multiplication. For the coupling to the cladding mode, long-period fiber gratings (LPGs) were used. A series of cascaded LPGs imprinted in a fiber with a specific separation has been employed to obtain a specific rate of pulse multiplication with a single input pulse. Second, by controlling the separations among the gratings, the temporal encoder/decoder for O-CDMA could be implemented. The principle and the applications of the proposed device are investigated in detail. The effect of the birefringence of fiber and fiber gratings on the system performance in the time and spectral domains is presented. The sensitivity of the cladding modes in a conventional fiber to the perturbations at the cladding has been overcome by replacing the conventional fiber with inner-cladding fiber. The properties and the benefits of using the inner-cladding mode are investigated.     

Application of wind data from automated weather stations to wind resources estimation in Korea

The wind data measured from automated weather stations (AWS) at complex terrain in Korea was used to predict the wind speed at nearby sites that are several kilometers away. The 10-minute averaged wind data was measured at a height of 10 meters. A commercial CFD code, WindSIM, based on the Reynolds averaged Navier-Stokes equation was employed. The results were compared with the data measured using meteorological masts (MM) at heights of 30 to 50 meters installed for this study. The predictions using the AWS data and WindSIM showed good agreements with the measured data. The results are expected to be useful to find out a spot to install a meteorological mast for future wind farm development in complex terrain.     

Phase of acoustic impedance and performance of standing wave thermoacoustic coolers

Investigations on the relations between the phase angle of the acoustic impedance at the driver piston and the system performance of a standing wave thermoacoustic cooler were performed. The system performance measured at a fixed acoustic power showed that the coefficient of performance of the standing wave thermoacoustic cooler increases as the phase angle increases when the stack temperature span is relatively low. The results were consistent with the simulation results obtained from DELTAE, a computer code based on linear thermoacoustic theory. Analysis on the temperature profiles along the stack showed that the cooling efficiency (COP) of the system could be decreased or increased as the phase angle of the acoustic impedance at the driver piston changes depending on the stack temperature spans. This paper was recommended for publication in revised form by Associate Editor Yeon June Kang Insu Paek received the B.S. degree in Mechatronics Engineering from Kangwon National University, Chuncheon, Korea, in 1997, the M.S. degree in Mechanical Engineering from the University of Texas at Austin, USA, in 2000, and the Ph. D. degree in Mechanical Engineering from Purdue University, West Lafayette, USA, in 2005. He worked as a postdoctoral researcher in Purdue University and McGill University in 2006 and 2007. He is currently a faculty member in the Department of Mechatronics Engineering, Kangwon National University, Chuncheon, Korea. His research interests include thermoacoustic cooling and power generation, solar heat driven absorption cooling., and wind power. Luc Mongeau received the B.S. and M.S. degrees in mechanical engineering from the University of Montreal, QC, Canada, in 1984 and 1986, respectively, and the Ph. D. degree in Acoustics from Pennsylvania State University, University Park, USA, in 1990. He is currently a professor in the Department of Mechanical Engineering at McGill University, Montreal, QC, Canada. He has published over 50 archival journal publications on various topics related to acoustics and noise control. His research activities are in the flow and turbomachinery noise areas, as well as in the areas of voice production, and thermoacoustic refrigeration. James E. Braun received the B.S. degree in Mechanical Engineering from the University of Massachusetts, USA, in 1976, and the M.S. and Ph. D. degrees in Mechanical Engineering from the University of Wisconsin, Madison, USA, in 1980 and 1988, respectively. He is currently a professor in the Department of Mechanical Engineering, Purdue University, West Lafayette, USA. Professor Braun’s research combines the use of computer modeling, optimization, and experiments to study and improve the performance of thermal systems. He has published over 140 papers. Professor Braun is currently an associate editor for the international journal of HVAC&R Research. Shin You Kang received the B.S. and M.S. degrees in the Department of Mechanical Design from Seoul National University, Seoul, Korea, in 1982, and 1986, respectively. He then received the Ph.D. in Mechanical Engineering at the same university in 1992. Professor Kang is currently a professor in the Department of Mechatronics Engineering, Kangwon National University, Chuncheon, Korea. His research interests include mechanical structure design, crash analysis, optimal design, computational structure analysis and evaluation.