Sungbin Jeon

Dual-wavelength digital holography with a single low-coherence light source.

We propose a measurement system using dual-wavelength digital holography and low-coherence interferometry to measure micro- and nanostructure surface heights. To achieve an extended axial step-measurement range and better image quality, a single light-emitting diode generates two distinct light sources by filtering different center wavelengths and narrower bandwidths. The system can measure surface profile with higher step heights and lower speckle noise in a large field-of-view. Using single-source lighting and a simple configuration, the method supports compactly configured and lower-cost surface-topography measurement systems applicable in various fields. Experimental results for a standard step sample verify the systems performance.

Selective Interpolation Method for Two-Step Parallel Phase-Shifting Digital Holography

We propose the reconstruction algorithm for two-step parallel phase-shifting digital holography. Parallel phase-shifting digital holography records a single hologram and numerically extracts the multiple images needed for obtaining the complex amplitude in phase-shifting technique. During the reconstruction process, phase error and degradation of image occur due to the calculation error. The proposed algorithm interpolates into two steps that include the subpixel data to reduce the error, so the quality that a reconstructed image can be enhanced. Both numerical simulation and experiment are conducted to verify the effectiveness of the proposed algorithm.

Improvement of Bit Error Rate in Holographic Data Storage Using the Extended High-Frequency Enhancement Filter

Optimized image restoration is suggested in angular-multiplexing-page-based holographic data storage. To improve the bit error rate (BER), an extended high frequency enhancement filter is recalculated from the point spread function (PSF) and Gaussian mask as the image restoration filter. Using the extended image restoration filter, the proposed system reduces the number of processing steps compared with the image upscaling method and provides better performance in BER and SNR. Numerical simulations and experiments were performed to verify the proposed method. The proposed system exhibited a marked improvement in BER from 0.02 to 0.002 for a Nyquist factor of 1.1, and from 0.006 to 0 for a Nyquist factor of 1.2. Moreover, more than 3 times faster performance in calculation time was achieved compared with image restoration with PSF upscaling owing to the reductions in the number of system process and calculation load.

Quality-enhanced holographic system utilizing quantum-dot-based light source

We presented the digital holography (DH) system with enhanced image quality. While conventional DH uses highcoherence laser for illuminations, the speckle noise included in the image degrades the quality of the reconstructed data. To reduce the noise regards to the light source, lower-coherence light source could be applied in DH system. In this paper, the quantum dot (QD) based wavelength converter is utilized as the light source. Compared with light-emitting diode (LED), QD-based light source could be applied to versatile system, including dual-wavelength DH. Due to the low coherence both temporally and spatially, spatial filtering and collimation is presented. Also, numerical processes including noise reduction and aberration compensation is described to enhance the quality of the image. By experimental verifications, the proposed DH system shows better quality compared with conventional system, which is enough to utilize the quantitative measurement.

Wavelength-multiplexed digital holography for quantitative phase measurement using quantum dot film

We propose an enhanced quantitative three-dimensional measurement system using wavelength-multiplexed digital holography. To simplify the configuration, a dual-peak quantum dot wavelength converter, combined with a blue LED, is adapted as a single low-coherence light source. Rather than a conventional dual-wavelength method, which records and reconstruct the object wave for each wavelength, the proposed system can capture the holograms of two wavelengths simultaneously with fewer acquisitions, simple setup, and low noise. To verify the systems performance, the measurements of the step height sample are presented.

Dual-wavelength off-axis digital holography using a single light-emitting diode

We propose a new low-coherence interferometry system for dual-wavelength off-axis digital holography. By utilizing diffraction gratings, two beams with narrower bandwidths and different center wavelengths could be filtered in a single light-emitting diode. The characteristics of the system are analytically determined to extend the coherence length and field-of-view enough for off-axis configuration. The proposed system enables the fast and accurate measurement of the surface profile with more than a micrometer step height and less noise. The performance of the system is verified by the experimental results of a standard height sample.

Quantitative phase imaging method using dual-wavelength Fourier ptychography

Fourier ptychography (FP) is a technique which enable to obtain a high-resolution complex image with only intensity images. In this research, we propose dual-wavelength FP scheme for step-height measurement.

Numerical speckle simulation model using generalized Harvey-Shack method

We propose the numerical method for simulating speckle from surface. By utilizing generalized Harvey-Shack method, speckle profile reflected from large distance could be obtained and inspected with varying parameters.

Phase-Shifting Digital Holography Using Multilayer Ceramic Capacitors

Multilayer ceramic capacitors for phase shifter in digital holography is tested and implemented. The measurement of displacement profile and 4-step phase-shifting holograms are conducted for verification of the proposed method.

Applications of Digital Holography with a Single Low-Coherence Light Source

To utilize the practical topographic measurement system using digital holography, low-coherence light source is adapted in the system. By filtering methods both spatial and temporal coherence is controlled suited for the object to be measured.