Byoung Goo Jeon

Autofocusing method using fluorescence detection for precise two-photon nanofabrication

We propose a method capable of focusing a laser beam on a substrate automatically via fluorescence detection from the resin of a two-photon nanofabrication system. When two-photon absorption (TPA) occurs by focusing the laser beam in the resin, fluorescence is emitted from the focusing region in the visible range. The total pixel number above the threshold value of the fluorescence images obtained by a CCD camera is plotted on a graph in accordance with the focus position. By searching for the position when the total pixel number undergoes an abrupt change in the pre-TPA region, the correct configuration of the focused laser beam can be found. Through focusing tests conducted at four vertices of a 500 μm x 500 μm square placed arbitrarily inside SCR500 resin, the errors of the autofocusing method were found to range from -100 nm to + 200 nm. Moreover, this method does not leave any polymerized marks. To verify the usefulness of the autofocusing method, the fabrication of a pyramid structure consisting of 20 layers was attempted on a coverglass. It was completely fabricated without losing a layer.

Improvement of range precision in laser detection and ranging system by using two Geiger mode avalanche photodiodes

In this paper, the improvement of range precision in a laser detection and ranging (LADAR) system by using two Geiger mode avalanche photodiodes (GmAPDs) is described. The LADAR system is implemented by using two GmAPDs with a beam splitter and applying comparative process to their ends. Then, the timing circuit receives the electrical signals only if each GmAPDs generates electrical signals simultaneously. Though this system decreases the energy of a laser-return pulse scattered from the target, it is effective in reducing the range precision. The experimental results showed that the average value of standard deviation of time of flights was improved from 61 mm to 37 mm when the pulse energy is 0.6 μJ. When the time bin width is 0.5 ns, the single-shot precision error of the LADAR system was also improved from 280 mm to 67 mm.

Simple Wide Range Carrier Frequency Offset Estimator for Coherent Optical OFDM

Coherent optical orthogonal frequency division multiplexing systems have a wide carrier frequency offset (CFO) range due to the frequency inaccuracy of lasers. In this letter, a simple wide range CFO estimator is proposed. In the proposed algorithm, wide estimation range and high accuracy are achieved by using a combination of the Chinese remainder theorem (CRT) for the integer part of CFO and fine estimation for the fractional part of CFO. For the proposed estimator, a training symbol structure consisting of two identical symbols is also suggested. The sizes of subsymbols of the training symbols are relatively prime to apply CRT. Simulations verify the validity of the proposed algorithm. The results indicate that the range of estimator is as large as the sampling frequency.

Precise autofocus method employing normalized fluorescence image size in a two-photon polymerization nanofabrication system.

The autofocus method has been investigated to improve the precise positioning of a substrate surface at the center of the laser focal spot in two-photon polymerization (TPP) nanofabrication. For this purpose, we developed a novel autofocus method using normalized image size, which was calculated with the second momentum radius (SMR) of two-photon induced fluorescence (TPIF). The SMR of TPIF was theoretically analyzed and experimentally compared with the average intensity of TPIF for various input laser powers. The results show that the proposed method enhanced the precision and robustness of autofocus in TPP. Specifically, the experimental creation of ascending voxel arrays demonstrated both the methods immunity to input laser power change, and a high precision of ±0.045  μm. To test the practical feasibility of the proposed autofocus method, 300  μm×260  μm single-layer honey-comb structures were successfully fabricated with precompensation and dynamic compensation using the proposed autofocus method.

Hollow conic beam generator using a cylindrical rod and its performances

By numerical simulations, it has been shown that a conven- tional cylindrical rod can be used as a hollow conic beam generator by illuminating a parallel laser beam inclined to the axis of the rod. Half of the conic beam is formed by the reflection at the surface of the cylindrical rod, and the opposite side of the conic beam by its transmission. We discuss the parameters to determine the size of the conic beam and the effect of the dielectric multilayer coating on the intensity distribution of the conic beam. The line beams of the shapes such as circle, ellipse, parabola, or hyperbola can be generated by this hollow conic beam gen- erator, depending on the position and orientation of the observing plane.

Efficient Chromatic Dispersion Precompensation for Coherent Optical OFDM

To reduce the guard interval, short-cyclic-prefix coherent optical orthogonal frequency division multiplexing (CO-OFDM) divides a band into two subbands and precompensates for chromatic dispersion (CD) with timing offset. Implementation using full band inverse discrete Fourier transformations (IDFTs), however, can excessively increase hardware complexity. We propose an efficient hardware implementation of IDFT with timing offsets for short-cyclic-prefix CO-OFDM. In addition, the residual intersubband CD induced by quantized timing offset is compensated using subcarrier-based phase rotation. By increasing the number of subbands efficiently and compensating for the residual intersubband CD, the transmission performance can be improved. Simulation results show 112-Gb/s single-channel transmission over a 2250-km standard single-mode-fiber with polarization division multiplexing 16 quadrature amplitude modulation (PDM-16 QAM) using 128 DFT with a 16 guard interval.

Novel optical absorbance-based multi-analytes detection module using a tri-chromatic LED, PDs and plastic optical fibers and its application to a palm-sized urine test strip reader

We have designed, fabricated and characterized a new palm-sized urine test strip reader (9.5 × 6.5 × 1.8 cm3) using a novel optical absorbance-based multi-analytes detecting module, consisting of a three-chromatic light-emitting diode (LED) component, photodiodes, and optical waveguide for digital readouts. The instrument is a handheld, simple but powerful in obtaining reliably a numerical analog output compatible with urine-based test strips. The proposed optical module demonstrated the excellent reading out of signal levels of proteins, glucose, blood cells, respectively, in the test urine strip kits, with low fabrication cost, rapidness, precision and reproducibility.

Portable wireless device for hemoglobin level monitoring

The wireless detection of hemoglobin from whole blood with very small volumes is a significant research topic, due to its improving impact on human health in the field. In the present paper, we have fabricated a simple and smart wireless optical device for hemoglobin level monitoring, including the simple optical modules, disposable plastic chip, and wireless near field communication module, for the first time. It has demonstrated a high accuracy performance of 95±2 % and rapid analysis time within 30 seconds using whole blood samples. We have compared with a clinical laboratory instrument and confirmed that it have worked well with a coefficients of determination (R2) of 0.952. Finally, we implemented a near-field communication module in the device for communicating with a smart android tablet. We think that this optical assembly can show great potential as a platform for improving human health through the monitoring of human hemoglobin status in the field.