1. Articles from Chang-Seok Kim

    1-23 of 23
    1. Linear-in-wavenumber actively-mode-locked wavelength-swept laser

      Linear-in-wavenumber actively-mode-locked wavelength-swept laser

      We report on an akinetic actively-mode-locked wavelength-swept laser (ASL) with a sweep that is highly linear in wavenumber. By tailoring the drive waveform of the intracavity modulator, the wavenumber sweep was further linearized to enable high fidelity frequency-domain interferometric ranging without resampling of the acquired data. Used for catheter-based optical coherence tomography, the ASL showed comparable imaging performance to a state-of-the-art polygon-based wavelength-swept source at a matching sweep rate of 103.6 kHz, a duty cycle of 95%, and a bandwidth of 100 nm, centered at 1330 nm.

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    2. Akinetic swept-source optical coherence tomography based on a pulse-modulated active mode locking fiber laser for human retinal imaging

      Akinetic swept-source optical coherence tomography based on a pulse-modulated active mode locking fiber laser for human retinal imaging

      Optical coherence tomography (OCT) is a noninvasive imaging modality that can provide high-resolution, cross-sectional images of tissues. Especially in retinal imaging, OCT has become one of the most valuable imaging tools for diagnosing eye diseases. Considering the scattering and absorption properties of the eye, the 1000-nm OCT system is preferred for retinal imaging. In this study, we describe the use of an akinetic swept-source OCT system based on a pulse-modulated active mode locking (AML) fiber laser at a 1080-nm wavelength for in-vivo human retinal imaging. The akinetic AML wavelength-swept fiber laser was constructed with polarization-maintaining fiber that has an average ...

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    3. Unfolding displacement measurement method for the aliasing interferometer signal of a wavelength-comb-swept laser

      Unfolding displacement measurement method for the aliasing interferometer signal of a wavelength-comb-swept laser

      We demonstrate an unfolding displacement measurement method to overcome the aliasing problem of wavelength-comb-swept laser (WCSL). Compared to the conventional wavelength-swept laser (WSL), the WCSL exhibits an extended coherence length, owing to the narrowing spectral linewidth of the etalon filter. However, the aliasing interference signal induces an unexpected back-bounced phenomenon during displacement measurement because of the discretely distributed comb-like periodic spectra of the etalon filter. By using the dual-reference interferometry method, the back-bounced displacement measurement can be successfully unfolded to extend the measurement range by two times. In addition, we demonstrate a longer-range surface profiling image over 18 mm within ...

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    4. Optical measurements of paintings and the creation of an artwork database for authenticity

      Optical measurements of paintings and the creation of an artwork database for authenticity

      Paintings have high cultural and commercial value, so that needs to be preserved. Many techniques have been attempted to analyze properties of paintings, including X-ray analysis and optical coherence tomography (OCT) methods, and enable conservation of paintings from forgeries. In this paper, we suggest a simple and accurate optical analysis system to protect them from counterfeit which is comprised of fiber optics reflectance spectroscopy (FORS) and line laser-based topographic analysis. The system is designed to fully cover the whole area of paintings regardless of its size for the accurate analysis. For additional assessments, a line laser-based high resolved OCT was ...

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    5. A Fiber Bragg Grating Sensor Interrogation System Based on a Linearly Wavelength-Swept Thermo-Optic Laser Chip

      A Fiber Bragg Grating Sensor Interrogation System Based on a Linearly Wavelength-Swept Thermo-Optic Laser Chip

      A linearized wavelength-swept thermo-optic laser chip was applied to demonstrate a fiber Bragg grating (FBG) sensor interrogation system. A broad tuning range of 11.8 nm was periodically obtained from the laser chip for a sweep rate of 16 Hz. To measure the linear time response of the reflection signal from the FBG sensor, a programmed driving signal was directly applied to the wavelength-swept laser chip. The linear wavelength response of the applied strain was clearly extracted with an R-squared value of 0.99994. To test the feasibility of the system for dynamic measurements, the dynamic strain was successfully interrogated ...

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    6. Short cavity active mode locking fiber laser for optical sensing and imaging

      Short cavity active mode locking fiber laser for optical sensing and imaging

      We demonstrate a highly linear wavenumber- swept active mode locking (AML) fiber laser for optical sensing and imaging without any wavenumber-space resampling process. In this all-electric AML wavenumber-swept mechanism, a conventional wavelength selection filter is eliminated and, instead, the suitable programmed electric modulation signal is directly applied to the gain medium. Various types of wavenumber (or wavelength) tunings can be implemented because of the filter-less cavity configuration. Therefore, we successfully demonstrate a linearly wavenumber-swept AML fiber laser with 26.5 mW of output power to obtain an in-vivo OCT image at the 100 kHz swept rate.

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    7. Optical Coherence Tomography (OCT) Device For Processing THREE-DIMENSIONAL OCT Data

      Optical Coherence Tomography (OCT) Device For Processing THREE-DIMENSIONAL OCT Data

      The purpose of the present invention is to increase the data processing speed in an SS-OCT and an FD-OCT including the SS-OCT and, in particular, to process large-size data obtained by a receiving unit at a faster speed than the data obtaining speed, reconfigure a tomography image in real time, and provide the reconfigured image to a user. In order to achieve the purpose, according to one embodiment of the present invention, an optical coherence tomography (OCT) is disclosed. The OCT device includes: a light source unit emitting a coherent light; an interferometer unit generating an interference pattern from a ...

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    8. 800-nm-centered swept laser for spectroscopic optical coherence tomography

      800-nm-centered swept laser for spectroscopic optical coherence tomography

      The isosbestic point of oxy- and deoxy-hemoglobin at 800 nm is an important point in biomedical optical spectroscopic imaging. We have developed a novel swept laser centered at 800 nm and demonstrated its performance for spectroscopic optical coherence tomography. The measured −10 dB spectral bandwidth of the swept laser was 40 nm and averaged laser output power per sweep was 4 mW. This swept laser was incorporated into our OCT system and used to measure non-scattering liquid phantoms and blood samples. The measured maximum sensitivity and roll-off rate over a range of image depths were 112 dB and − 1.45 ...

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    9. Simultaneous Dual-Band Wavelength-Swept Fiber Laser Based on Active Mode Locking

      Simultaneous Dual-Band Wavelength-Swept Fiber Laser Based on Active Mode Locking

      We report a simultaneous dual-band wavelength-swept laser based on the active mode locking method. By applying a single modulation signal, synchronized sweeping of two lasing-wavelengths is demonstrated without the use of a mechanical wavelength-selecting filter. Two free spectral ranges are independently controlled with a dual path-length configuration of a laser cavity. The static and dynamic performances of a dual-band wavelength-swept active mode locking fiber laser are characterized in both the time and wavelength regions. Two lasing wavelengths were swept simultaneously from 1263.0 to 1333.3 nm for the 1310 nm band and from 1493 to 1563.3 nm for ...

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    10. Lens-free endoscopy probe for optical coherence tomography

      Lens-free endoscopy probe for optical coherence tomography

      We present an ultrathin fiber-optic endoscopy probe for optical coherence tomography (OCT), which is made of a series of fused optical fibers instead of the conventional scheme based on an objective lens. The large-core fiber with a core diameter of 20 μm was utilized for the probe, while a single-mode fiber of core diameter 8.2 μm mainly delivered the OCT light. Those fibers were spliced with a bridge fiber of an intermediate core size. The guided light was stepwise converted to a beam of a large mode-field diameter to be radiated with a larger depth of focus. We obtained ...

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    11. Optical sensor interrogation system based on FDML wavelength swept laser

      Optical sensor interrogation system based on FDML wavelength swept laser

      Provided is an optical sensor interrogation system. The optical sensor interrogation system includes: a light source unit which matches round-trip time of light and wavelength tunable cycle time of light in a resonator and emits light; a sensing unit which receives an optical signal in which a center wavelength periodically tunes, from the light source unit and tunes the center wavelength of the optical signal according to physical changes applied from the outside; and a signal processing unit which receives the optical signal reflected from the sensing unit, detects data, and images the data. In particular, the light source unit ...

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    12. Spectrally Sampled OCT Imaging Based on 1.7um Continuous-Wave Supercontinuum Source

      Spectrally Sampled OCT Imaging Based on 1.7um Continuous-Wave Supercontinuum Source

      We demonstrate a novel multiwavelength light source around the 1.7um region based on continuous-wave (CW) supercontinuum (SC) generation for the deeper imaging of low-water-absorption sample with a spectrally sampled optical coherence tomography (OCT) system. This self-regulated Gaussian spectrum of CW SC source has an extremely smooth flat width with more than 210-nm full-width at half-maximum bandwidth centered at the 1.7um region, a high output power of 500 mW, and a low temporal instability with less than 0.1 dB for an hour. In order to improve the OCT signal sensitivity without increasing the optical illumination power, a multiwavelength ...

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    13. Double common-path interferometer for flexible optical probe of optical coherence tomography

      Double common-path interferometer for flexible optical probe of optical coherence tomography

      A flexible curled optical cord is useful for a common-path optical coherence tomography (OCT) system because a bending-insensitive arbitrary length can be chosen for the endoscopic imaging probe. However, there has been a critical problem that the partial reflector needs to be placed in between the sample and the objective lens. It limits the structure design of optical probe and leads to a low transverse resolution OCT imaging. Instead of a conventional single common-path interferometer, we propose a novel double common-path interferometer configuration in order to generate an interference signal that is independent of the optical distance between the partial ...

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    14. Post-tuning of Sample Position in Common-path Swept-source Optical Coherence Tomography

      Post-tuning of Sample Position in Common-path Swept-source Optical Coherence Tomography
      Common-path interferometers are widely used for endoscopic optical coherence tomography (OCT) because an arbitrary arm length can be chosen for the endoscopic imaging probe. However, the scheme suffers from the limited range of the sample position distance from the end of the imaging probe because the position between the reference reflector and the sample is limited by the optical path-length difference (OPD) to induce an interference signal. In this study, we developed a novel method for compensating the arbitrary sample position in common-path swept-source OCT by adding an extra Mach-Zehnder interferometer in the post-path of the interfered optical signal. Theoretical ...
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      Mentions: Jae-Seok Park
    15. Fourier Domain Optical Coherence Tomography for Retinal Imaging with 800-nm Swept Source: Real-time Resampling in k-domain

      Fourier Domain Optical Coherence Tomography for Retinal Imaging with 800-nm Swept Source: Real-time Resampling in k-domain
      In this study, we demonstrated Fourier-domain/swept-source optical coherence tomography (FD/SS-OCT) at a center wavelength of 800 nm for in vivo human retinal imaging. A wavelength-swept source was constructed with a semiconductor optical amplifier, a fiber Fabry-Perot tunable filter, isolators, and a fiber coupler in a ring cavity. Our swept source produced a laser output with a tuning range of 42 nm (779 to 821 nm) and an average power of 3.9 mW. The wavelength-swept speed in this configuration with bidirectionality is 2,000 axial scans per second. In addition, we suggested a modified zero-crossing method to achieve ...
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    16. Characterization of wavelength-swept active mode locking fiber laser based on reflective semiconductor optical amplifier

      Characterization of wavelength-swept active mode locking fiber laser based on reflective semiconductor optical amplifier

      The static and dynamic characteristics of a wavelength-swept active mode locking (AML) fiber laser are presented in both the time-region and wavelength-region. This paper shows experimentally that the linewidth of a laser spectrum and the bandwidth of the sweeping wavelength are dependent directly on the length and dispersion of the fiber cavity as well as the modulation frequency and sweeping rate under the mode-locking condition. To achieve a narrower linewidth, a longer length and higher dispersion of the fiber cavity as well as a higher order mode locking condition are required simultaneously. For a broader bandwidth, a lower order of ...

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    17. Calibration and characterization protocol for spectral-domain optical coherence tomography using fiber Bragg gratings

      Calibration and characterization protocol for spectral-domain optical coherence tomography using fiber Bragg gratings
      We present a calibration protocol to obtain the alignment factors of a custom-made spectrometer and the nonlinear fitting function between the measured CCD pixel domain and the wavelength domain to apply to the spectral-domain optical coherence tomography (SD-OCT) using fiber Bragg gratings. We have used five gratings with different center wavelengths covering the broadband source spectral range. All have a narrow spectral bandwidth (0.05 nm) and the same reflectivity (92%) to calibrate and align the custom-made spectrometer. The implemented SD-OCT system following the proposed protocol showed the alignment factors as 44.37 deg incident angle, 53.11 deg diffraction ...
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    18. Flexible Curled Optical Cord for Bending-Insensitive Optical Imaging Delivery

      Flexible Curled Optical Cord for Bending-Insensitive Optical Imaging Delivery

      In the application of optical imaging technologies to the biomedical field, the flexible optical cord is one of the key components used to deliver the reflected optical signal from the internal biological tissue to the biomedical imaging system. However, the conventional optical fibers suffer from a critical wiring limitation, which results in severe power losses under a small bending radius that is less than a few centimeters. In this paper, we demonstrate that holey optical fibers with 18 air holes in cladding have negligible bending loss under a minimum bending radius of 3 mm. Excellent bending insensitivity of the holey ...

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    19. Calibration protocol for Fourier-domain OCT using optical fiber gratings

      Calibration protocol for Fourier-domain OCT using optical fiber gratings
      We present a calibration protocol to get the alignment factors of a custom-made spectrometer and the nonlinear fitting function between the measured CCD pixel domain and the wavelength domain to apply the Fourier-domain optical coherence tomography (FD-OCT) using optical fiber gratings. We have used 5 different center wavelength gratings covered the broadband source spectral range with a narrow spectral bandwidth (<0.05 nm) and the same reflectivity (>92 %) to calibrate and align the custom-made spectrometer. The implemented SD-OCT system following the proposed protocol showed the alignment factors as 44.37o incident angle, 53.11o diffraction angle, and 70.0 mm focal length. The spectral resolution of 0 ...
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    20. Spectrally-sampled OCT for sensitivity improvement from limited optical power

      Spectrally-sampled OCT for sensitivity improvement from limited optical power

      Although high optical illumination power is favored in optical coherence tomography (OCT) for better signal-to-noise ratio, optical power is often limited by a damaged threshold for biomedical living tissues and autocorrelation signals observed in tomograms. In order to improve signal sensitivity without increasing the optical illumination power, a spectrally sampled multi-wavelength light source is proposed for the OCT system. A fiber Sagnac comb filter was used to spectrally sample the output of a continuous spectral light source. Point spread function analysis shows that the spectrally sampled OCT has an almost 50% dynamic range improvement in comparison with a conventional continuous ...

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    21. Multi-wavelength source for the lower exposure intensity of spectral OCT

      There have been several technologies to enable high resolution cross-sectional images of biological tissues in optical coherence tomography (OCT) method. Optical frequency comb (OFC) source has been proposed to overcome the crosstalk problem among the CCD detector pixels of the continuous spectrum of light source. Recently, a passive-type OFC is demonstrated simply placing a Fabry-Perot interferometer filter right after the broadband light source, but it shows a high loss of output light power and limited tenability of channel spacing of multi-wavelength. In this work, we experimentally demonstrate a spectral comparison of a novel multi-wavelength source based on a fiber Sagnac ...

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    22. Curled optical patch cord for bending insensitive biomedical imaging endoscope

      Biomedical optical imaging technologies based on optical fibers have been of great interest because of their superiority over conventional bulk-optic counter part in size and integration. Flexible endoscope is a key component to deliver the reflected optical signal from biological tissue to the optical imaging system, such as Optical Coherence Tomography (OCT) and Fiber Confocal Microscopy (FCM). However, conventional optical fibers for the biomedical imaging endoscope have been suffered from a critical wiring problem of a fiber waveguide, which induces additional loss severely. In this work, we have shown excellent properties of holey optical fibers with low bending loss under ...

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    23. Endoscopic common-path OCT based on sweeping laser source and curled optical patch cord

      Several technical problems have to be overcome before Optical Coherence Tomography (OCT) can be accepted among the established endoscopic imaging modalities. Most of conventional Michelson-based OCT systems need to have two separated paths of the sample and reference arms, which limits the flexibility of endoscopic probe. Recently, common-path interferometer based OCT have been demonstrated to circumvent the mismatch problems of length, polarization, and dispersion between the reference and sample arms, but the interferometric scanning methods have been realized with time-domain PZT or spectral-domain CCD. In this work, we demonstrate a novel Fourier-domain common-path OCT based on sweeping laser source, which ...

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    1-23 of 23
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    1. (22 articles) Chang-Seok Kim
    2. (19 articles) Pusan National University
    3. (12 articles) Myung Yung Jeong
    4. (7 articles) Jae-Seok Park
    5. (7 articles) Tae Joong Eom
    6. (6 articles) UC Irvine
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    Spectrally-sampled OCT for sensitivity improvement from limited optical power Calibration protocol for Fourier-domain OCT using optical fiber gratings Flexible Curled Optical Cord for Bending-Insensitive Optical Imaging Delivery Calibration and characterization protocol for spectral-domain optical coherence tomography using fiber Bragg gratings Characterization of wavelength-swept active mode locking fiber laser based on reflective semiconductor optical amplifier Fourier Domain Optical Coherence Tomography for Retinal Imaging with 800-nm Swept Source: Real-time Resampling in k-domain Double common-path interferometer for flexible optical probe of optical coherence tomography Spectrally Sampled OCT Imaging Based on 1.7um Continuous-Wave Supercontinuum Source NIRS-IVUS for Differentiating Coronary Plaque Rupture, Erosion and Calcified Nodule in Acute Myocardial Infarction Optical Coherence Tomographic Patterns as Predictors of Structural Outcome After Intravitreal Ranibizumab in Diabetic Macula Edema Identification of plaque ruptures using a novel discriminative model comprising biomarkers in patients with acute coronary syndrome Endovascular Cerebral Venous Sinus Imaging with Optical Coherence Tomography