• Journal of the Korean Institute of Telematics and Electronics
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• v.23 no.6
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• pp.961-967
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• 1986

A technique of optical image synthesis with an extended incoherent source is presented and compared with the coherent method. A holographic diffraction grating is fabricated by using Michelson interferometer, and by equalizing the 8th-order to the 2nd-order diffraction efficiency, complex amplitude addition and subtracdtion of optical images are simultaneously realized. The experiment shows that the quality of synthesized optical images in the incoherent method is improved in comparison with that of the coherent method by suppressing the coherent artifact noise.

• The Journal of Pediatrics of Korean Medicine
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• v.17 no.2
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• pp.55-74
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• 2003

Objective : The purpose of this study was to investigate the back shape and self-conscious symptoms of the students in S High school using the phase-shifting scanning grating projection Moire interferometer and Questionnaire investigations. Methods : In this study the subjects consisted of 317 pupils[168 boys(53%), 149girls(47%)] attending S high school in Sungnamsi, Kyoungkido in 2002. Their ages ranged from sixteen to eighteen. With the phase-shifting scanning grating projection moire interferometer, the posterior views of the body were taken to see if there are correlation of remainder value of the height spot of left & right shoulder blade and gluteal region in Moire topography. And using questionnaire investigation, we investigated the self-conscious symptoms. Results : 1. In questionnaire investigation, we observed that the ratios of self-conscious symptoms of girls are more than that of boys. The ratios of headache, neck pain, lower back pain, digestive symptom were more than 70% in boys and girls. 2. In Moire topography, more frequent findings of scapular region were observed that left scapular area were higher than right(in boys 69.3%, 60%, 100%, aged 16,17,18, in girls 66.8%, 40.5%, 58.8% aged 16,17,18). 3. More frequent findings of gluteal region were observed that left scapular area were higher than right(in boys 75.2%, 60%, 36.4% aged 16,17,18, in girls 61.1%, 46.8%, 64.7% aged 16,17,18) 4. More frequent findings of reminder value of the vertical lines of cervical and buttock region in Moire topography were observed that the vertical lines of cervical region were inclined to left than the vertical lines of buttock(in boys 73.3%, 92.2%, 100% aged 16,17,18, in girls 72.2%, 77.2%, 73.5% aged 16,17,18) Conclusion : From these results, we found that the self-conscious symptoms were more than in girls than boys; the ratio of headache, neck pain, Lower back pain, digestive symptom was more than the others; the back shape of high school students were not balanced in scapular and buttock region; necks were inclined to left than buttock.

• Korean Journal of Optics and Photonics
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• v.8 no.4
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• pp.333-339
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• 1997

We fabricated a sensor head which consists of spliced different-diameter fiber gratings for discrimination between strain and temperature. Because the fibers were drawn from the same preform, their temperature characteristics were the same but not for strain sensitivities which are inversely proportional to fibers cross-sectional areas. In measurement range of 0-1500$\mu$strain and 20-10$0^{\circ}C$, we could obtain, by using the matrix calculation, the unknown physical quantities within 10% of calculation error compared with the micrometer and thermocouple values. To improve the strain measurement accuracy, we suggest a new, novel method which deploys an unbalanced fiber Mach-Zehnder interferometer. This new signal processing technique converts the strain information to interference signal amplitude variation, temperature-independently. we obtained measurement accuracy nearly 80 times better than that obtainable with the conventional optical spectrum analyzer usage.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.289-290
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• 2006

In general, atomic force microscope (AFM) used for metrological purpose has measuring range less than a few hundred micrometers. We design and fabricate an AFM with long measuring range of $200mm{\times}200mm$ in X and Y axes. The whole stage system is composed of surface plate, global stage, microstage. By combining global stage and microstage, the fine and long movement can be provided. We measure the position of the stage and angular motions of the stage by laser interferometer. A piezoresistive type cantilever is used for compact and long term stability and a flexure structure with PZT and capacitive sensor is used for Z axis feedback control. Since the system is composed of various actuators and sensors, a real time control program is required for the implementation of AFM. Therefore, in this work, we designed a multi-axis control program using a FPGA module, which has various functions such as interferometer signal converting, PID control and data acquisition with triggering. The control program achieves a loop rate more than 500 kHz and will be applied for the measurement of grating pitch and step height.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.11
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• pp.75-82
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• 2004

A metrological atomic force microscope (M-AFM) was developed fur the length measurements of nanometer range, through the modification of a commercial AFM. To eliminate nonlinearity and crosstalk of the PZT tube scanner of the commercial AFM, a two-axis flexure hinge scanner employing built-in capacitive sensors is used for X-Y motion instead of PZT tube scanner. Then two-dimensional displacement of the scanner is measured using two-axis heterodyne laser interferometer to ensure the meter-traceability. Through the measurements of several specimens, we could verify the elimination of nonlinearity and crosstalk. The uncertainty of length measurements was estimated according to the Guide to the Expression of Uncertainty in Measurement. Among several sources of uncertainty, the primary one is the drift of laser interferometer output, which occurs mainly from the variation of refractive index of air and the thermal stability. The Abbe error, which is proportional to the measured length, is another primary uncertainty source coming from the parasitic motion of the scanner. The expanded uncertainty (k =2) of length measurements using the M-AFM is √(4.26)$^2$+(2.84${\times}$10$^{-4}$ ${\times}$L)$^2$(nm), where f is the measured length in nm. We also measured the pitch of one-dimensional grating and compared the results with those obtained by optical diffractometry. The relative difference between these results is less than 0.01 %.

• Korean Journal of Optics and Photonics
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• v.23 no.4
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• pp.135-142
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• 2012

We have developed a measurement method of the refractive index profile of an optical fiber by using diffraction phase microscopy. In the microscope system, the reference light was extracted directly from the probe light that passed through the sample by means of pinhole filtering with a diffraction grating. The spatial interference pattern produced by the probe light and the reference light was processed to generate the phase image of the sample fiber. The index profile was obtained by the inverse Abel transform of the phase profile. In order to remove the background phase that originated from the index difference between the cladding and the surrounding medium, the background phase was calculated from the phase data of the cladding to make a core phase profile that can be directly transformed to the index profile of the core without the full phase image that includes the entire cladding part.

• Korean Journal of Optics and Photonics
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• v.28 no.3
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• pp.108-115
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• 2017

We report the assembly procedure and performance evaluation of a visible and near-infrared spectrometer in the wavelength region of 400-900 nm, which is later to be combined with fore-optics (a telescope) to form a f/2.5 imaging spectrometer with a field of view of ${\pm}7.68^{\circ}$. The detector at the final image plane is a $640{\times}480$ charge-coupled device with a $24{\mu}m$ pixel size. The spectrometer is in an Offner relay configuration consisting of two concentric, spherical mirrors, the secondary of which is replaced by a convex grating mirror. A double-pass test method with an interferometer is often applied in the assembly process of precision optics, but was excluded from our study due to a large residual wavefront error (WFE) in optical design of 210 nm ($0.35{\lambda}$ at 600 nm) root-mean-square (RMS). This results in a single-path test method with a Shack-Hartmann sensor. The final assembly was tested to have a RMS WFE increase of less than 90 nm over the entire field of view, a keystone of 0.08 pixels, a smile of 1.13 pixels and a spectral resolution of 4.32 nm. During the procedure, we confirmed the validity of using a Shack-Hartmann wavefront sensor to monitor alignment in the assembly of an Offner-like spectrometer.