1. Articles from Osami Sasaki

    1-15 of 15
    1. External-cavity laser diode using acousto-optic deflector as tunable grating

      External-cavity laser diode using acousto-optic deflector as tunable grating

      In this study, a novel, to the best of our knowledge, external-cavity laser diode (ECLD) without a diffraction grating is proposed and demonstrated. In the proposed configuration, an acousto-optic deflector (AOD) acts not only as a deflector but also as a diffraction grating. Thus, the AOD functions as a wavelength-selective device, which helps improve the overall performance of the ECLD. In fact, the proposed configuration realizes a wide range of wavelength scanning with a simple configuration, highly efficient optical feedback, and a steady optical resonator with a constant cavity length. We confirm that the wavelengths scanned with the proposed ECLD ...

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    2. Acousto-optically tuned external-cavity laser diode for optical coherence tomography with continuous wavelet transform

      Acousto-optically tuned external-cavity laser diode for optical coherence tomography with continuous wavelet transform

      We propose an acousto-optically tuned external-cavity laser diode (ECLD) based on the Littrow configuration to expand the wavelength-scanning range and eliminate mechanical motions. The scanning range and tuning rate of our prototype were 68.85 nm and more than 100 kHz, respectively, without any mode hop. Moreover, we implemented this improved ECLD in an optical coherence tomography imaging system and conducted a measurement of the two-dimensional thickness distribution of a thin glass plate via continuous wavelet transform analysis.

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    3. A simple system of swept source optical coherence tomography for a large imaging depth range

      A simple system of swept source optical coherence tomography for a large imaging depth range

      In swept source optical coherence tomography (SSOCT), the imaging depth range sometimes limits its application, such as the whole eye measurement. The methods of extending depth range usually need to redesign the system or add some additional devices. In this paper, we propose a simple system of SSOCT for a large imaging depth range. The system is the same as the original SSOCT with using the swept source clock signal except for a slice glass in the reference arm. The large depth range is achieved by increasing the number of sampling point in every spectrum and wavenumber calibration. More sampling ...

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    4. Passively Driven Probe Based on Miniaturized Propeller for Intravascular Optical Coherence Tomography

      Passively Driven Probe Based on Miniaturized Propeller for Intravascular Optical Coherence Tomography

      Optical coherent tomography (OCT) has enabled clinical applications ranging from ophthalmology to cardiology that revolutionized in vivo medical diagnostics in the last few decades, and a variety of endoscopic probes have been developed in order to meet the needs of various endoscopic OCT imaging. We propose a passive driven intravascular optical coherent tomography (IV-OCT) probe in this paper. Instead of using any electrically driven scanning device, the probe makes use of the kinetic energy of the fluid that flushes away the blood during the intravascular optical coherence tomography imaging. The probe converts it into the rotational kinetic energy of the ...

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    5. 3-D surface profile measurement using spectral interferometry based on continuous wavelet transform

      3-D surface profile measurement using spectral interferometry based on continuous wavelet transform

      This study proposes a signal analysis technique that uses continuous wavelet transform for signal processing in a spectral domain optical coherence tomography system. Our method enables us to calculate the optical path difference simply by taking advantage of the fact that the product of the phase and wavelength becomes constant. Experimental results obtained using a pair of gauge blocks with a thickness difference of 40 µm confirm that the repetitive measurement accuracy was 65.1 nm. A demonstration of the three-dimensional surface profile measurement indicates that the rms measurement error is 0.17 µm.

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    6. Full-field step profile measurement with sinusoidal wavelength scanning interferometer

      Full-field step profile measurement with sinusoidal wavelength scanning interferometer

      A sinusoidal wavelength scanning interferometer is proposed for 3-D profile measurement. The interference phase-shift signal generated by the sinusoidal wavelength scanning contains information of optical path difference (OPD) covering nm-mm scale structure. The interference phase-shift signal was obtained by the four-step phase shifting method. The sinusoidal wavelength shifting bandwidth of 5.7 nm with a frequency of approximately 180 Hz was performed by the Littman-Metcalf external resonator-type tunable laser with a center of 772.1 nm. The full-field step-height surface profile measurement and 3-D surface measurement were conducted by a CCD image sensor with an accuracy of few tens nm ...

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    7. Low-coherence interferometer using a pulsation laser diode

      Low-coherence interferometer using a pulsation laser diode

      A self-pulsation laser diode interferometer based on spectral-domain optical coherence tomography is proposed. A visible multimode laser diode allows easy optical alignment and an economical, configurable system. A cylindrical lens and acousto-optic deflector used in our system enable rapid and stable scanning. Experimental results confirm that full-field measurement is possible without mechanical scanning devices

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    8. Full-range Fourier domain Doppler optical coherence tomography based on sinusoidal phase modulation

      Full-range Fourier domain Doppler optical coherence tomography based on sinusoidal phase modulation

      A novel full-range Fourier domain Doppler optical coherence tomography (full-range FD-DOCT) using sinusoidal phase modulation for B-M scan is proposed. In this sinusoidal B-M scan, zero optical path difference (OPD) position does not move corresponding to lateral scanning points in contrast to linear B-M scan. Since high phase sensitivity arises around the zero OPD position, the proposed full-range FD-DOCT can achieve easily high velocity sensitivity without mirror image around the zero OPD position. Velocity sensitivity dependent on the OPD and the interval of scanning points is examined, and flow velocity detection capability is verified through Doppler imaging of a flow ...

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    9. Low-coherence interferometry based on continuous wavelet transform

      Low-coherence interferometry based on continuous wavelet transform

      The present paper proposes a low-coherence interferometry system based on continuous wavelet transform, which can simultaneously detect the peak position and frequency of a signal. Although the proposed system is analogous to conventional time-domain optical coherence tomography, it realizes accurate wide-range surface profile measurement because the wavelet transform enables accurate evaluation of the position of the reference mirror. The performance of the proposed system was evaluated through step-height measurement.

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    10. Scattering imaging of skin in Fourier domain optical coherence tomography

      Scattering imaging of skin in Fourier domain optical coherence tomography

      A scattering imaging method for skin tissue in Fourier domain optical coherence tomography is proposed. In this method, parameter F image is obtained from the intensity signal as a function of the depth. Since parameter F contains only the scattering coefficient and its first order derivative, the scattering coefficient image depending on depth can be calculated from the parameter F image. Two-dimensional (2D) scattering coefficient images of palm skin are calculated after extracting the tissue interfaces in the 2D parameter F images.

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    11. Rapid wavelength scanning based on acousto-optically tuned external-cavity laser diode

      Rapid wavelength scanning based on acousto-optically tuned external-cavity laser diode
      High-speed, wide-range wavelength scanning is demonstrated using a laser diode with an antireflection coating and an external cavity employing an acousto-optic deflector. The narrow spectral width of 0.2 nm observed in the experiment indicates the availability of a highly coherent laser beam. The scanning range of 15 nm under rapid modulation is confirmed in the prototype system. A tuning rate of more than 100 kHz is achieved without any mode hops. To the best of our knowledge, no such high-speed wavelength tuning based on an acousto-optical configuration has been demonstrated thus far.
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    12. A new spectral calibration method for Fourier domain optical coherence tomography

      Spectral calibration is important for a Fourier domain optical coherence tomography (FD-OCT) system. A new spectral calibration method for FD-OCT is presented. Through the iterated mapping of spectral interferograms detected by an optical spectrum analyzer and the CCD grating spectrometer, multiple groups of calibration coefficients are obtained. By comparing the effects of these coefficients on improving the amplitude of the axial point spread function (PSF), optimum coefficients are obtained. In this method, no additional calibration laser source is needed, reducing the complexity of the system. The cross-sectional images of a glass plate in milk are acquired, and the experimental results ...

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    13. One-shot parallel complex Fourier-domain optical coherence tomography using a spatial carrier frequency

      We propose a novel method of one-shot parallel complex Fourier-domain optical coherence tomography using a spatial carrier frequency for full range imaging. The spatial carrier frequency is introduced into the 2-D spectral interferogram in the lateral direction by using a tilted reference wavefront. This spatial-carrier-contained 2-D spectral interferogram is recorded with one shot of a 2-D CCD camera, and is Fourier-transformed in the lateral direction to obtain a 2-D complex spectral interferogram by a spatial-carrier technique. A full-range tomogram is reconstructed from the 2-D complex spectral interferogram. The principle of this method is confirmed by cross-sectional imaging of a glass ...

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    14. High-speed full range complex Fourier-domain optical coherence tomography using sinusoidal phase-modulating interferometry

      High-speed full-range complex Fourier domain optical coherence tomography (FDOCT) using sinusoidal phase-modulating interferometry is proposed. A high-rate two-dimensional (2-D) CCD camera is used to record time-sequential sinusoidally phase-modulated 2-D spectral interferograms, from which the complex 2-D spectral interferograms corresponding to each frame of the 2-D CCD camera are extracted by Fourier transform method. By taking inverse Fourier transform of the complex spectral interferograms, full-range B-scan images free of the complex conjugate ambiguity as well as dc and autocorrelation noises are obtained at intervals of the frame period of the 2-D CCD camera. Time-sequential cross-sectional imaging of human skin ex vivo ...

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    15. Dynamic full-range Fourier-domain optical coherence tomography using sinusoidal phase-modulating interferometry

      We propose a technique for dynamic full-range Fourier-domain optical coherence tomography by using sinusoidal phase-modulating interferometry, where both the full-range structural information and depth-resolved dynamic information are obtained. A novel frequency-domain filtering algorithm is proposed to reconstruct a time-dependent complex spectral interferogram from the sinusoidally phase-modulated interferogram detected with a high-rate CCD camera. By taking the amplitude and phase of the inverse Fourier transform of the complex spectral interferogram, a time-dependent full-range cross-sectional image and depth-resolved displacement are obtained. Displacement of a sinusoidally vibrating glass cover slip behind a fixed glass cover slip is measured with subwavelength sensitivity to demonstrate ...

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    1-15 of 15
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    1. (5 articles) Chinese Academy of Sciences
    2. (2 articles) Boston University
    3. (2 articles) Massachusetts General Hospital
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    Rapid wavelength scanning based on acousto-optically tuned external-cavity laser diode Scattering imaging of skin in Fourier domain optical coherence tomography Low-coherence interferometry based on continuous wavelet transform Full-range Fourier domain Doppler optical coherence tomography based on sinusoidal phase modulation Low-coherence interferometer using a pulsation laser diode Full-field step profile measurement with sinusoidal wavelength scanning interferometer A novel algorithm for multiplicative speckle noise reduction in ex vivo human brain OCT images Volumetric characterization of microvasculature in ex vivo human brain samples by serial sectioning optical coherence tomography Depth of focus extension in optical coherence tomography using ultrahigh chromatic dispersion of zinc selenide Retinal changes in bipolar disorder as an endophenotype candidate: Comparison of OCT-detected retinal changes in patients, siblings, and healthy controls Intraoperative optical coherence tomography guided 25G micro-amount trajectory vitrectomy for the treatment of penetrating ocular injury caused by a foreign body in the right eye: A case study Optical coherence tomography angiography reveals paradoxically decreasing choroidal thickness & increasing blood flow in remitting Vogt Koyanagi Harada syndrome