• Journal of Sensor Science and Technology
• /
• v.9 no.3
• /
• pp.163-170
• /
• 2000

Optical frequency modulated fiber optic interferometric sensor was developed to sense the mechanical quantities, such as displacement, strain, force etc. It has been difficult to distinguish whether the increase of the mechanical quantities or the decrease of the quantities measured by the conventional fiber optic interferometric sensors because their signals only have a sinusoidal wave pattern related to the change of mechanical quantities. In this study, in order to measure the mechanical quantifies with the distinction of the changing direction of the quantities, the fiber of optic Michelson interferometric sensor was simply constructed by the laser light modulated with saw tooth wave pattern. The output signal of the sensor was controlled as the sinusoidal wave. The signal processing was based on the counting of the wave number of the output signal during constant time duration. The strain was determined by the cumulative value of the wave number producted by the gage factor. In order to verify the strain measurement capability of this sensor, the strain increase-decrease test was performed by universal testing machine installed with the aluminum specimen bonded with the fiber optic sensor and electrical strain gage. In the result of the test, the strain from the fiber optic sensor had a good agreement with the values from the electrical strain gage.

• Journal of the Optical Society of Korea
• /
• v.19 no.6
• /
• pp.705-710
• /
• 2015

The fabrication process of thin boron-doped nanocrystalline diamond (B-NCD) microelectrodes on fused silica single mode optical fiber cladding has been investigated. The B-NCD films were deposited on the fibers using Microwave Plasma Assisted Chemical Vapor Deposition (MW PA CVD) at glass substrate temperature of 475 ℃. We have obtained homogenous, continuous and polycrystalline surface morphology with high sp³ content in B-NCD films and mean grain size in the range of 100-250 nm. The films deposited on the glass reference samples exhibit high refractive index (n=2.05 at λ=550 nm) and low extinction coefficient. Furthermore, cyclic voltammograms (CV) were recorded to determine the electrochemical window and reaction reversibility at the B-NCD fiber-based electrode. CV measurements in aqueous media consisting of 5 mM K₃[Fe(CN)₆] in 0.5 M Na₂SO₄ demonstrated a width of the electrochemical window up to 1.03 V and relatively fast kinetics expressed by a redox peak splitting below 500 mV. Moreover, thanks to high-n B-NCD overlay, the coated fibers can be also used for enhancing the sensitivity of long-period gratings (LPGs) induced in the fiber. The LPG is capable of measuring variations in refractive index of the surrounding liquid by tracing the shift in resonance appearing in the transmitted spectrum. Possible combined CV and LPG-based measurements are discussed in this work.

• Korean Journal of Optics and Photonics
• /
• v.19 no.1
• /
• pp.54-59
• /
• 2008

We report on the measurements of absorption spectra from acetylene ($^{12}C_2H_2$) and hydrogen cyanide ($H^{13}C^{14}N$) for wavelength reference in the C-band (conventional band) region using a supercontinuum optical source generated from a mode-locked $Cr^{4+}$:YAG laser. The center wavelength of the mode-locked $Cr^{4+}$:YAG laser was 1510 nm and the pulse duration was 75 fs at 100 MHz repetition rate. The supercontinuum source achieved a flatness of ${\pm}5dB$ over a wavelength range of more than 400 nm, using a 20 m long photonic crystal fiber. The measured absorption spectra from acetylene ($^{12}C_2H_2$) and hydrogen cyanide ($H^{13}C^{14}N$) had more than 50 lines and were analyzed for wavelength standardization.

• Korean Journal of Optics and Photonics
• /
• v.16 no.4
• /
• pp.297-303
• /
• 2005

We present the double resonance optical pumping(DROP) spectra according to the laser power, the polarization combination of lasers, and the alignment of lasers in the transition $5P_{3/2}-4D_{5/2}\;and\;5P_{3/2}-4D_{5/2}$ of $^{87}Rb.$ We observed obviously changing DROP spectrum according to the laser power in the transition $5P_{3/2}-4D_{5/2}$ involved the cycling transition. The laser power effects are attributed to the low optical-pumping-effect in the cycling transition. We observed changing DROP spectrum depending on the polarizations of the lasers. The laser polarization effects are attributed to the changing transition probability according to the polarizations of lasers. We compared the co-propagation with the counter-propagation and the spectral linewidths were 12.2 MHz and 6.9 MHz, respectively.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.26 no.6
• /
• pp.390-402
• /
• 2006

The elastic properties and thickness of mullite environmental barrier coatings grown through chemical vapor deposition (CVD) on silicon carbide substrates were measured using frequency domain photoacoustic microscopy. In this technique, extremely narrow bandwidth surface acoustic waves are generated with an amplitude modulated laser source. A photorefractive crystal based interferometer is used to detect the resulting surface displacement. The complex displacement field is mapped as a function of source-to-receiver distance in order to extract the wavelength of the surface acoustic wave at a given excitation frequency, and the phase velocity is determined. The coatings tested exhibited spatial variations in thickness and mechanical properties. The measured surface wave dispersion curves were used to extract an effective value for the elastic modulus and the coating thickness. Nanoindentation was used to validate the measurements of the effective elastic modulus. The average elastic modulus measured through the coating thickness using nanoindentation is compared to the effective modulus found using the photoacoustic system. Optical microscopy is used to validate the thickness measurements. The results indicate that the photoacoustic microscopy technique can be used to estimate the effective elastic properties in coatings exhibiting spatial inhomogeneities, potentially providing valuable feedback for the optimization of the CVD growth process.

• Journal of Institute of Control, Robotics and Systems
• /
• v.8 no.3
• /
• pp.208-219
• /
• 2002

A novel measurement method to obtain the 6-DOF motions of arbitrary rigid bodies is proposed in this paper. The method adopts a specially fabricated mirror called 3-facet mirror, which looks like a triangular pyramid haying an equilateral cross-sectional shape. The mirror is mounted on the objects to be measured, illuminated by a laser beam having circular profile, and reflects the laser beam in three different directions. Three PSDs(position sensitive detector) detect the three beams reflected by the mirror, respectively. From the signals of the PSDs, we can calculate the 3-dimensional position and orientation of the 3-facet mirror, and thus enabling us to determine the 3-dimensional position and orientation of the objects. In this paper, we model the relationship between the 3-dimensional position and orientation of an object in motion and the outputs of three PSDs. A series of experiments are performed to demonstrate the effectiveness and accuracy of the proposed method. The experimental results show that the proposed sensing system can be an effective means of obtaining 3-dimensional position and orientation of arbitrary objects and provide resonable measurement accuracy.

• Current Optics and Photonics
• /
• v.6 no.1
• /
• pp.44-50
• /
• 2022

An off-axis zone plate is able to focus on a single order while neglecting the zeroth order in a visible imaging system. This allows one to enhance the contrast quality in diffractive images, which is the major advantage of this type of zone plate. However, most previous reflection zone plates are used in focusing X-rays with a small grazing incident angle and are intricately designed with the use of a local grating period. In this study, we suggest the design of an off-axis elliptical zone plate (EZP) that is used to focus a monochromatic light beam with separation between the first and unfocused orders under a large grazing incident angle of 45°. An assumption using the total grating period, which depends on the average and constant grating period, is proposed to calculate the desired distance between the first and zeroth order and to simplify the construction of a novel model off-center EZP. Four diffractive optical elements (DOEs) with different parameters were subsequently fabricated by direct laser lithography and then verified using a performance evaluation system to compare the results from the assumption with the experimental results.

• Bulletin of the Korean Chemical Society
• /
• v.23 no.2
• /
• pp.271-276
• /
• 2002

The energy relaxation dynamics of the lowest excited singlet and triplet states of the Zn(II)porphyrin monomer and its directly linked arrays were comparatively investigated with increasing the number of porphyrin moieties. While the fluorescence decay rates and quantum yields of the porphyrin arrays increased with the increase of porphyrin units, their triplet-triplet (T-T) absorption spectra and decay times remained almost the same. The difference in the trends of energy relaxation dynamics between the excited singlet and triplet states has been discussed in view of the electronic orbital configurations.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.10 no.4
• /
• pp.168-174
• /
• 1985

The wavelength and output power of semiconductor laser is varying sensitively with temperature. It must be stabilized by the aid of some proper stabilization technique in order to use it as a radiative source for heterodyne optical communication, optical metrology, and high resolution spectroscopy. In this paper, the temperature of the thermal chamber was variable from -27$-50^{\circ}C$ to +73$-50^{\circ}C$ and the temperature stability was within ${\pm}2m{\circ}K$ or better.

• Korean Journal of Computational Design and Engineering
• /
• v.14 no.1
• /
• pp.10-17
• /
• 2009

Surface detection and parameter estimation in point cloud is a relevant subject in CAD/CAM, reverse engineering, computer vision, coordinate metrology and digital factory. In this paper we present a software for a fully automatic surface detection and parameter estimation in unordered, incomplete and error-contaminated point cloud with a large number of data points. The software consists of three algorithmic modules each for object identification, point segmentation, and model fitting, which work interactively. Our newly developed algorithms for orthogonal distance fitting(ODF) play a fundamental role in each of the three modules. The ODF algorithms estimate the model parameters by minimizing the square sum of the shortest distances between the model feature and the measurement points. We demonstrate the performance of the software on a variety of point clouds generated by laser radar, computer tomography, and stripe-projection method.