1. Articles from Kenneth K. Y. Wong

    1-16 of 16
    1. Optical coherence tomography with balanced signal strength across the depth for pearl inspection

      Optical coherence tomography with balanced signal strength across the depth for pearl inspection

      Optical coherence tomography (OCT) relies on the reflection of light from structures in different layers to interferometrically reconstruct the volumetric image of the sample. However, light returned from multiple layers suffers from imbalanced attenuation owing to the optical path difference and inhomogeneous tissue absorption. We report an optimization algorithm to improve signal strength in deep tissue for swept-source (SS)-OCT imaging. This algorithm utilizes the attenuation coefficient of consecutive layers within the sample and combines them to compensate for the signal intensity loss from deep tissue. We stacked 170-µm thick cover slides as a standard sample for benchmark testing ...

      Read Full Article
    2. Video-rate centimeter-range optical coherence tomography based on dual optical frequency combs by electro-optic modulators

      Video-rate centimeter-range optical coherence tomography based on dual optical frequency combs by electro-optic modulators

      Imaging speed and range are two important parameters for optical coherence tomography (OCT). A conventional video-rate centimeter-range OCT requires an optical source with hundreds of kHz repetition rate and needs the support of broadband detectors and electronics (>1 GHz). In this paper, a type of video-rate centimeter-range OCT system is proposed and demonstrated based on dual optical frequency combs by leveraging electro-optic modulators. The repetition rate difference between dual combs, i.e. the A-scan rate of dual-comb OCT, can be adjusted within 0~6 MHz. By down-converting the interference signal from optical domain to radio-frequency domain through dual comb beating ...

      Read Full Article
    3. Point-spread function manipulation of the swept-source optical coherence tomography through temporal phase modulation

      Point-spread function manipulation of the swept-source optical coherence tomography through temporal phase modulation

      Recent breakthroughs in microscopy have surpassed Abbe’s spatial diffraction limit, especially in the regime of fluorescence imaging. Microcopy’s depth-imaging relative tomography is, however, still confined to basic imaging quality, which is limited by the Fourier bandwidth. In this paper, we explore the analogy between spatial microscopy and temporal tomography based on the space-time duality, and hence enlighten the advancement of tomography. As a proof-of-principle demonstration, an all-optical manipulation of the point-spread function (PSF) of a swept-source optical coherence tomography (OCT) is performed based on temporal phase modulation. Although the axial resolving power remains the same, much sharper sketch ...

      Read Full Article
    4. Sensitivity enhancement in swept-source optical coherence tomography by parametric balanced detector and amplifier

      Sensitivity enhancement in swept-source optical coherence tomography by parametric balanced detector and amplifier

      We proposed a sensitivity enhancement method of the interference-based signal detection approach and applied it on a swept-source optical coherence tomography (SS-OCT) system through all-fiber optical parametric amplifier (FOPA) and parametric balanced detector (BD). The parametric BD was realized by combining the signal and phase conjugated idler band that was newly-generated through FOPA, and specifically by superimposing these two bands at a photodetector. The sensitivity enhancement by FOPA and parametric BD in SS-OCT were demonstrated experimentally. The results show that SS-OCT with FOPA and SS-OCT with parametric BD can provide more than 9 dB and 12 dB sensitivity improvement, respectively ...

      Read Full Article
    5. Tri-band optical coherence tomography for lipid and vessel spectroscopic imaging

      Tri-band optical coherence tomography for lipid and vessel spectroscopic imaging

      Optical coherence tomography (OCT) has been utilized for various functional imaging applications. One of its highlights comes from spectroscopic imaging, which can simultaneously obtain both morphologic and spectroscopic information. Assisting diagnosis and therapeutic intervention of coronary artery disease is one of the major directions in spectroscopic OCT applications. Previously Tanaka et al. have developed a spectral domain OCT (SDOCT) to image lipid distribution within blood vessel [1]. In the meantime, Fleming et al. have demonstrated optical frequency domain imaging (OFDI) by a 1.3-μm swept source and quadratic discriminant analysis model [2]. However, these systems suffered from burdensome computation ...

      Read Full Article
    6. Tri-band spectroscopic optical coherence tomography based on optical parametric amplification for lipid and vessel visualization

      Tri-band spectroscopic optical coherence tomography based on optical parametric amplification for lipid and vessel visualization

      A tri-band spectroscopic optical coherence tomography (SOCT) system has been implemented for visualization of lipid and blood vessel distribution. The tri-band swept source, which covers output spectrum in 1.3, 1.5, and 1.6μ m wavelength windows, is based on a dual-band Fourier domain mode-locked laser and a fiber optical parametric amplifier. This tri-band SOCT can further differentiate materials, e.g., lipid and artery, qualitatively by contrasting attenuation coefficients difference within any two of these bands. Furthermore, ex vivo imaging of both porcine artery with artificial lipid plaque phantom and mice with coronary artery disease were demonstrated to showcase ...

      Read Full Article
    7. 28 MHz swept source at 1.0 μm for ultrafast quantitative phase imaging

      28 MHz swept source at 1.0 μm for ultrafast quantitative phase imaging

      Emerging high-throughput optical imaging modalities, in particular those providing phase information, necessitate a demanding speed regime (e.g. megahertz sweep rate) for those conventional swept sources; while an effective solution is yet to be demonstrated. We demonstrate a stable breathing laser as inertia-free swept source (BLISS) operating at a wavelength sweep rate of 28 MHz, particularly for the ultrafast interferometric imaging modality at 1.0 μm. Leveraging a tunable dispersion compensation element inside the laser cavity, the wavelength sweep range of BLISS can be tuned from ~10 nm to ~63 nm. It exhibits a good intensity stability, which is quantified ...

      Read Full Article
    8. Simultaneous dual-band optical coherence tomography for endoscopic applications

      Simultaneous dual-band optical coherence tomography for endoscopic applications

      Dual-band optical coherence tomography (OCT) can greatly enhance the imaging contrast with potential applications in functional (spectroscopic) analysis. A new simultaneous dual-band Fourier domain mode-locked swept laser configuration for dual-band OCT is reported. It was based on a custom-designed dual-channel driver to synchronize two different wavelength bands at 1310 and 1550 nm, respectively. Two lasing wavelengths were swept simultaneously from 1260 to 1364.8 nm for the 1310-nm band and from 1500 to 1604 nm for the 1550-nm band at an A-scan rate of 45 kHz. Broadband wavelength-division multiplexing was utilized to couple two wavelength bands into a common catheter ...

      Read Full Article
    9. Breathing laser as an inertia-free swept source for high-quality ultrafast optical bioimaging

      Breathing laser as an inertia-free swept source for high-quality ultrafast optical bioimaging

      We demonstrate an all-fiber breathing laser as inertia-free swept source (BLISS), with an ultra-compact design, for the emerging ultrafast bioimaging modalities. The unique feature of BLISS is its broadband wavelength-swept operation ( ∼ 60     nm ) with superior temporal stability in terms of both long term (0.08 dB over 27 h) and shot-to-shot power variations (2.1%). More importantly, it enables a wavelength sweep rate of > 10     MHz ( ∼ 7 × 10 8     nm / s )—orders-of-magnitude faster than the existing swept sources based on mechanical or electrical tuning techniques. BLISS thus represents a practical and new generation of swept source operating in the unmet ...

      Read Full Article
    10. Broadband fiber-optical parametric amplification for ultrafast time-stretch imaging at 1.0 um

      Broadband fiber-optical parametric amplification for ultrafast time-stretch imaging at 1.0 um

      We demonstrate a broadband all-fiber-optical parametric amplifier for ultrafast time-stretch imaging at 1.0 μm, featured by its compact design, alignment-free, high efficiency, and flexible gain spectrum through fiber nonlinearity- and dispersion-engineering: specifically on a dispersion-stabilized photonic-crystal fiber (PCF) to achieve a net gain over 20 THz (75 nm) and a highest gain of ∼ 6000 (37.5 dB). Another unique feature of the parametric amplifier, over other optical amplifiers, is the coherent generation of a synchronized signal replica (called idler) that can be exploited to offer an extra 3-dB gain by optically superposing the signal and idler. It further enhances ...

      Read Full Article
    11. Parametric spectro-temporal analyzer (PASTA) for real-time optical spectrum observation

      Parametric spectro-temporal analyzer (PASTA) for real-time optical spectrum observation

      Real-time optical spectrum analysis is an essential tool in observing ultrafast phenomena, such as the dynamic monitoring of spectrum evolution. However, conventional method such as optical spectrum analyzers disperse the spectrum in space and allocate it in time sequence by mechanical rotation of a grating, so are incapable of operating at high speed. A more recent method all-optically stretches the spectrum in time domain, but is limited by the allowable input condition. In view of these constraints, here we present a real-time spectrum analyzer called parametric spectro-temporal analyzer (PASTA), which is based on the time-lens focusing mechanism. It achieves a ...

      Read Full Article
    12. Feature Of The Week 3/16/14: The University of Hong Kong Demonstrates MHz A-Line SS-OCT via Optical Time Stretching and Raman Amplification of Pulsed Source

      Feature Of The Week 3/16/14: The University of Hong Kong Demonstrates MHz A-Line SS-OCT via Optical Time Stretching and Raman Amplification of Pulsed Source

      We demonstrate all-optical ultrahigh-speed swept-source optical coherence tomography (OCT) based on amplified optical time-stretch (AOT). Such an inertia-free wavelength-swept mechanism, via group velocity dispersion, enables us to realize OCT with an A-scan rate well above MHz. More importantly, the key significance of AOT-OCT is its simultaneous broadband Raman amplification during the time-stretch process–greatly enhancing the detection sensitivity compared with prior attempts to apply optical time-stretch to OCT. Here, we report on an AOT-OCT system which is operated at an A-scan rate of 7.14 MHz, a superior roll-off performance (>2  mm/dB), a record-high sensitivity of time-stretch-based OCT (>80 ...

      Read Full Article
    13. Wavelet domain compounding for speckle reduction in optical coherence tomography

      Wavelet domain compounding for speckle reduction in optical coherence tomography

      Visibility of optical coherence tomography (OCT) images can be severely degraded by speckle noise. A computationally efficient despeckling approach that strongly reduces the speckle noise is reported. It is based on discrete wavelet transform (DWT), but eliminates the conventional process of threshold estimation. By decomposing an image into different levels, a set of sub-band images are generated, where speckle noise is additive. These sub-band images can be compounded to suppress the additive speckle noise, as DWT coefficients resulting from speckle noise tend to be approximately decorrelated. The final despeckled image is reconstructed by taking the inverse wavelet transform of the ...

      Read Full Article
    14. Speckle reduction of retinal optical coherence tomography based on contourlet shrinkage

      Speckle reduction of retinal optical coherence tomography based on contourlet shrinkage

      Speckle reduction of retinal optical coherence tomography (OCT) images helps the diagnosis of ocular diseases. In this Letter, we present a speckle reduction method based on shrinkage in the contourlet domain for retinal OCT images. The algorithm overcomes the disadvantages of the wavelet shrinkage method, which lacks directionality and anisotropy. The trade-off between speckle reduction and edge preservation is controlled by a single adjustable parameter, which determines the threshold in the contourlet domain. Results show substantial reduction of speckle noise and enhanced visualization of layer structures as demonstrated in the image of the central fovea region of the human retina ...

      Read Full Article
    15. Feature Of The Week 7/29/12: Researchers From The University of Hong Kong Use Optical Parametric Wavelength Conversion for Dual-Wavelength Spectroscopic OCT

      Feature Of The Week 7/29/12: Researchers From The University of Hong Kong Use Optical Parametric Wavelength Conversion for Dual-Wavelength Spectroscopic OCT

      Researchers from the University of Hong Kong recently reported on a high-speed time-multiplexing dual wavelength band swept laser source based on an optical parametric amplifier. A dual-band swept-source optical coherence tomography (OCT) system is implemented to demonstrate the advantage of a second wavelength band for fast spectroscopic OCT (SOCT). The innovative time-multiplexing architecture greatly reduces the complexity of the coupling and detecting configuration in comparison with the previous dual-band swept-source setup. We demonstrate the optical parametric amplification’s characteristics as a dual-band generator and applied the source to firstly achieve the SOCT around 1550 nm.For more information see recent ...

      Read Full Article
    16. Dual-Band Time-Multiplexing Swept-Source Optical Coherence Tomography Based on Optical Parametric Amplification

      Dual-Band Time-Multiplexing Swept-Source Optical Coherence Tomography Based on Optical Parametric Amplification

      We report a high-speed time-multiplexing dual wavelength band swept laser source based on an optical parametric amplifier. A dual-band swept-source optical coherence tomography (OCT) system is implemented to demonstrate the advantage of a second wavelength band for fast spectroscopic OCT (SOCT). The innovative time-multiplexing architecture greatly reduces the complexity of the coupling and detecting configuration in comparison with the previous dual-band swept-source setup. We demonstrate the optical parametric amplification’s characteristics as a dual-band generator and applied the source to firstly achieve the SOCT around 1550 nm.

      Read Full Article
    1-16 of 16
  1. Categories

    1. Applications:

      Art, Cardiology, Dentistry, Dermatology, Developmental Biology, Gastroenterology, Gynecology, Microscopy, NDE/NDT, Neurology, Oncology, Ophthalmology, Other Non-Medical, Otolaryngology, Pulmonology, Urology
    2. Business News:

      Acquisition, Clinical Trials, Funding, Other Business News, Partnership, Patents
    3. Technology:

      Broadband Sources, Probes, Tunable Sources
    4. Miscellaneous:

      Jobs & Studentships, Student Theses, Textbooks
  2. Topics in the News

    1. (15 articles) Kenneth K. Y. Wong
    2. (13 articles) University of Hong Kong
    3. (6 articles) Kevin K. Tsia
    4. (2 articles) Massachusetts General Hospital
    5. (1 articles) Institute of Applied Physics
    6. (1 articles) Ryerson University
    7. (1 articles) Sunnybrook Health Sciences Centre
    8. (1 articles) Cuiru Sun
    9. (1 articles) Victor X. D. Yang
    10. (1 articles) Vivolight
    11. (1 articles) Harvard University
    12. (1 articles) The Chinese University of Hong Kong
    13. (1 articles) University of Miami
    14. (1 articles) VU University Amsterdam
    15. (1 articles) David A. Boas
    16. (1 articles) Brett E. Bouma
    17. (1 articles) Johannes F. de Boer
    18. (1 articles) Frank D. Verbraak
    19. (1 articles) Apollo Medical Optics
  3. Popular Articles

  4. Picture Gallery

    Dual-Band Time-Multiplexing Swept-Source Optical Coherence Tomography Based on Optical Parametric Amplification Feature Of The Week 7/29/12: Researchers From The University of Hong Kong Use Optical Parametric Wavelength Conversion for Dual-Wavelength Spectroscopic OCT Speckle reduction of retinal optical coherence tomography based on contourlet shrinkage Wavelet domain compounding for speckle reduction in optical coherence tomography Feature Of The Week 3/16/14: The University of Hong Kong Demonstrates MHz A-Line SS-OCT via Optical Time Stretching and Raman Amplification of Pulsed Source Parametric spectro-temporal analyzer (PASTA) for real-time optical spectrum observation Broadband fiber-optical parametric amplification for ultrafast time-stretch imaging at 1.0 um Breathing laser as an inertia-free swept source for high-quality ultrafast optical bioimaging Simultaneous dual-band optical coherence tomography for endoscopic applications 28 MHz swept source at 1.0 μm for ultrafast quantitative phase imaging Optical Coherence Tomography: Critical Tool to Manage Expectations after Cataract Extraction Improving the characterization of ex vivo human brain optical properties using high numerical aperture optical coherence tomography by spatially constraining the confocal parameters