Colin J R Sheppard

Summary

Affiliation: National University of Singapore
Country: Singapore

Publications

  1. ncbi Fundamentals of superresolution
    Colin J R Sheppard
    Division of Bioengineering, National University of Singapore, 9 Engineering Drive 1, Singapore 117576, Singapore
    Micron 38:165-9. 2007
  2. ncbi Beam duality, with application to generalized Bessel-Gaussian, and Hermite- and Laguerre- Gaussian beams
    Colin J R Sheppard
    Division of Bioengineering, National University of Singapore, 7 Engineering Drive 1, Singapore 117574
    Opt Express 17:3690-7. 2009
  3. ncbi Zernike expansion of separable functions of cartesian coordinates
    Colin J R Sheppard
    Division of Bioengineering, National University of Singapore, 9 Engineering Drive 1, Singapore 117576, Singapore
    Appl Opt 43:3963-6. 2004
  4. ncbi Orthogonal aberration functions for high-aperture optical systems
    Colin J R Sheppard
    Division of Bioengineering, Department of Diagnostic Radiology, National University of Singapore, Singapore 117576
    J Opt Soc Am A Opt Image Sci Vis 21:832-8. 2004
  5. ncbi Defocused transfer function for a partially coherent microscope and application to phase retrieval
    Colin J R Sheppard
    Division of Bioengineering and Department of Diagnostic Radiology, National University of Singapore, Singapore 117576
    J Opt Soc Am A Opt Image Sci Vis 21:828-31. 2004
  6. ncbi Fresnel diffraction by a circular aperture with off-axis illumination and its use in deconvolution of microscope images
    Colin J R Sheppard
    Physical Optics Laboratory, School of Physics, University of Sydney, Sydney, NSW 2006, Australia
    J Opt Soc Am A Opt Image Sci Vis 21:540-5. 2004
  7. doi Reconstruction in interferometric synthetic aperture microscopy: comparison with optical coherence tomography and digital holographic microscopy
    Colin J R Sheppard
    Optical Bioimaging Laboratory, Division of Bioengineering, National University of Singapore, Singapore
    J Opt Soc Am A Opt Image Sci Vis 29:244-50. 2012
  8. doi Partial polarization in three dimensions
    Colin J R Sheppard
    Optical Bioimaging Laboratory, Division of Bioengineering, National University of Singapore, Singapore
    J Opt Soc Am A Opt Image Sci Vis 28:2655-9. 2011
  9. doi Binary phase filters with a maximally-flat response
    Colin J R Sheppard
    Optical Bioimaging Laboratory, Division of Bioengineering, National University of Singapore, Singapore 117574
    Opt Lett 36:1386-8. 2011
  10. ncbi The divided aperture technique for microscopy through scattering media
    Colin J Sheppard
    Division of Bioengineering, National University of Singapore, Singapore
    Opt Express 16:17031-8. 2008

Collaborators

Detail Information

Publications52

  1. ncbi Fundamentals of superresolution
    Colin J R Sheppard
    Division of Bioengineering, National University of Singapore, 9 Engineering Drive 1, Singapore 117576, Singapore
    Micron 38:165-9. 2007
    ..The fundamental principles behind superresolution are discussed, and different schemes classified. Different definitions for localization of a wave are discussed...
  2. ncbi Beam duality, with application to generalized Bessel-Gaussian, and Hermite- and Laguerre- Gaussian beams
    Colin J R Sheppard
    Division of Bioengineering, National University of Singapore, 7 Engineering Drive 1, Singapore 117574
    Opt Express 17:3690-7. 2009
    ..Duality is considered within the framework of hypergeometric beams in Cartesian and polar coordinates. The connection with the "modified Laguerre-Gauss" beam is discussed...
  3. ncbi Zernike expansion of separable functions of cartesian coordinates
    Colin J R Sheppard
    Division of Bioengineering, National University of Singapore, 9 Engineering Drive 1, Singapore 117576, Singapore
    Appl Opt 43:3963-6. 2004
    ..The expansion can also be applied to cylindrical aberrations over a circular pupil. A product of two such series can thus be used to expand an arbitrary separable function of two Cartesian coordinates...
  4. ncbi Orthogonal aberration functions for high-aperture optical systems
    Colin J R Sheppard
    Division of Bioengineering, Department of Diagnostic Radiology, National University of Singapore, Singapore 117576
    J Opt Soc Am A Opt Image Sci Vis 21:832-8. 2004
    ..This weighting can also be used to account empirically for Fresnel reflection losses in the optical system. The functions can be expressed in an analytic form. Expressions are given for 24 low-order aberrations...
  5. ncbi Defocused transfer function for a partially coherent microscope and application to phase retrieval
    Colin J R Sheppard
    Division of Bioengineering and Department of Diagnostic Radiology, National University of Singapore, Singapore 117576
    J Opt Soc Am A Opt Image Sci Vis 21:828-31. 2004
    ..For weak defocus, this can be expressed analytically. Use of this transfer function for phase restoration (quantitative phase retrieval) from images of weak mixed phase-amplitude objects is discussed...
  6. ncbi Fresnel diffraction by a circular aperture with off-axis illumination and its use in deconvolution of microscope images
    Colin J R Sheppard
    Physical Optics Laboratory, School of Physics, University of Sydney, Sydney, NSW 2006, Australia
    J Opt Soc Am A Opt Image Sci Vis 21:540-5. 2004
    ..The predictions are compared with exact calculations of the Rayleigh-Sommerfeld diffraction integral. Limitations for application in deconvolution of microscope images formed with objectives of finite tube length are discussed...
  7. doi Reconstruction in interferometric synthetic aperture microscopy: comparison with optical coherence tomography and digital holographic microscopy
    Colin J R Sheppard
    Optical Bioimaging Laboratory, Division of Bioengineering, National University of Singapore, Singapore
    J Opt Soc Am A Opt Image Sci Vis 29:244-50. 2012
    ..The spatial frequency response is developed based on the three-dimensional coherent transfer function approach and compared with that in optical coherence tomography and digital holographic microscopy...
  8. doi Partial polarization in three dimensions
    Colin J R Sheppard
    Optical Bioimaging Laboratory, Division of Bioengineering, National University of Singapore, Singapore
    J Opt Soc Am A Opt Image Sci Vis 28:2655-9. 2011
    ..These expressions are applied to the Huynen decomposition and allow interrelations between different parameters to be developed...
  9. doi Binary phase filters with a maximally-flat response
    Colin J R Sheppard
    Optical Bioimaging Laboratory, Division of Bioengineering, National University of Singapore, Singapore 117574
    Opt Lett 36:1386-8. 2011
    ..Solutions are obtained by direct algebraic manipulation, and numerical results are given for filters of up to five elements. Their application for increasing depth of focus is described...
  10. ncbi The divided aperture technique for microscopy through scattering media
    Colin J Sheppard
    Division of Bioengineering, National University of Singapore, Singapore
    Opt Express 16:17031-8. 2008
    ..As the width is increased, the resolution degrades. The efficiency of singly-scattered light rejection is not improved with increased width...
  11. ncbi Image formation in low-coherence and confocal interference microscopes
    Colin J R Sheppard
    Physical Optics Laboratory, School of Physics, University of Sydney, New South Wales 2006, Australia
    Appl Opt 43:1493-502. 2004
    ..The behavior of the interference term in the presence of aberrations also exhibits some differences: Aberrations can be compensated in CPM, but not in OCT...
  12. ncbi Performance parameters for focusing of radial polarization
    Colin J R Sheppard
    Division of Bioengineering, National University of Singapore, Singapore
    Opt Lett 33:497-9. 2008
    ..Performance parameters are presented for high-aperture radially polarized focusing systems. These can be used for comparing the focusing performance of different optical systems, including the effect of pupil filters...
  13. doi Transport-of-intensity approach to differential interference contrast (TI-DIC) microscopy for quantitative phase imaging
    Shan Shan Kou
    Optical Bioimaging Laboratory, Division of Bioengineering, National University of Singapore, 7 Engineering Drive 1, Singapore 117576, Singapore
    Opt Lett 35:447-9. 2010
    ..Numerically solving for the propagation of light in a series of through-focus DIC images allows linear phase information in a single slice to be completely determined and restored from DIC intensity values...
  14. doi A complete and computationally efficient numerical model of aplanatic solid immersion lens scanning microscope
    Rui Chen
    Department of Electrical and Computer Engineering, National University of Singapore, Singapore, 117576
    Opt Express 21:14316-30. 2013
    ....
  15. doi Image formation in holographic tomography: high-aperture imaging conditions
    Shan Shan Kou
    Optical Bioimaging Laboratory, Division of Bioengineering, National University of Singapore, 7 Engineering Drive 1, Singapore 117576, Singapore
    Appl Opt 48:H168-75. 2009
    ..The derived coherent transfer functions offer quantitative insights into the image formation of a diffractive tomography system...
  16. doi Polarization conversion in confocal microscopy with radially polarized illumination
    Wai Teng Tang
    Computation and Systems Biology, Singapore MIT Alliance, National University of Singapore, Singapore
    Opt Lett 34:2147-9. 2009
    ....
  17. ncbi Modeling phase functions in biological tissue
    Wei Gong
    Division of Bioengineering, National University of Singapore, Singapore
    Opt Lett 33:1599-601. 2008
    ..The derived phase functions show good agreement with the experimental results. Implications for microscopic tissue diagnosis are discussed...
  18. doi Edge enhancement for in-phase focal modulation microscope
    Ke Si
    Graduate School for Integrative Sciences and Engineering, National University of Singapore, 10 Medical Drive, Singapore 117597, Singapore
    Appl Opt 48:6290-5. 2009
    ..4% and 58.9% for a thick edge and a thin edge, respectively. Signal level is also discussed, and the results show that, to obtain high transverse resolution with IPFMM, the normalized detector pinhole radius should not exceed 2.8...
  19. ncbi Focal modulation microscopy
    NanGuang Chen
    Division of Bioengineering, National University of Singapore, Singapore
    Opt Express 16:18764-9. 2008
    ..Our method has been validated with animal tissue and an imaging depth around 600 microns has been demonstrated...
  20. ncbi Optimization of axial resolution in a confocal microscope with D-shaped apertures
    Wei Gong
    Division of Bioengineering, National University of Singapore, Singapore 117576
    Appl Opt 48:3998-4002. 2009
    ..The optimum width of a divider that separates the D-shaped apertures to give the maximum axial resolution for a given pinhole size is investigated, and the magnitude of the signal level is explored...
  21. doi Focal modulation microscopy: a theoretical study
    Shau Poh Chong
    Division of Bioengineering, National University of Singapore, 9 Engineering Drive 1, EA 03 12, Singapore 129789
    Opt Lett 35:1804-6. 2010
    ..The scalar diffraction theory is combined with Monte Carlo simulation to evaluate the signal-to-background ratio at various depths. The performance of confocal microscopy with a similar optical setup is also evaluated for comparison...
  22. doi Phase-space representation of partially coherent imaging systems using the Cohen class distribution
    Shalin B Mehta
    Optical Bioimaging Laboratory, Division of Bioengineering, National University of Singapore, Block E3A, 7 10, 7 Engineering Drive 1, Singapore 118431
    Opt Lett 35:348-50. 2010
    ..It uses only the requisite number of dimensions and leads to an efficient algorithm for calculating images. Computed partially coherent images of a double slit and a two-dimensional sinusoidal spoke are presented...
  23. doi Sample-less calibration of the differential interference contrast microscope
    Shalin B Mehta
    1Optical Bioimaging Lab, Division of Bioengineering, National University of Singapore, Block E3A, 7 10, 7 Engineering Drive 1, Singapore 117574
    Appl Opt 49:2954-68. 2010
    ..The method presented is accurate, relies on simple image analysis, and does not require a specimen. We provide a succinct and accurate description of properties of Nomarski prisms to explain the rationale behind the method...
  24. doi Focal modulation microscopy with annular apertures: a numerical study
    Wei Gong
    Division of Bioengineering, National University of Singapore, Singapore, Singapore
    J Biophotonics 3:476-84. 2010
    ..The capability of background rejection is also investigated, showing AFMM has the potential to further increase the imaging penetration depth. Finally, an optimal configuration of AFMM is elaborated...
  25. ncbi Filter performance parameters for high-aperture focusing
    Colin J R Sheppard
    Department of Diagnostic Radiology, National University of Singapore
    Opt Lett 32:1653-5. 2007
    ..These measures can be used to investigate focusing properties of different types of focusing systems, including those with apodizers and superresolving masks...
  26. ncbi Image formation in holographic tomography
    Shan Shan Kou
    Optical Bioimaging Laboratory, Division of Bioengineering, National University of Singapore, Singapore
    Opt Lett 33:2362-4. 2008
    ..Rotating of the sample, on the contrary, has more symmetry in spatial frequency coverage but has a single point of singularity. The 3D transfer function derived can be used for 3D image reconstruction...
  27. doi Divided-aperture technique for fluorescence confocal microscopy through scattering media
    Wei Gong
    Division of Bioengineering, National University of Singapore, Singapore 117574
    Appl Opt 49:752-7. 2010
    ..For a given detector size, an optimum value of the divider strip width is given to obtain the best axial resolution or transverse resolution. The integrated intensity and signal-to-background ratio are also discussed...
  28. doi Motion detection using extended fractional Fourier transform and digital speckle photography
    Basanta Bhaduri
    1Department of Mechanical Engineering, National University of Singapore, 9 Engineering Drive 1, Singapore
    Opt Express 18:11396-405. 2010
    ..The dynamic range and sensitivity of the measurement can be varied readily by altering the position of the mirror/s used in the optical setup. Theoretical analysis and experiment results are presented...
  29. ncbi Improved expressions for performance parameters for complex filters
    Colin J R Sheppard
    Division of Bioengineering, National University of Singapore
    Opt Lett 32:1713-5. 2007
    ..These expressions can be used to predict the behavior of filters that give a small axial shift in the focal intensity maximum and also predict the changes in gain for different observation planes...
  30. doi Optical double-image cryptography based on diffractive imaging with a laterally-translated phase grating
    Wen Chen
    Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore 117576, Singapore
    Appl Opt 50:5750-7. 2011
    ..In addition, security and advantages of the proposed method are analyzed. Feasibility and effectiveness of the proposed method are demonstrated by numerical simulation results...
  31. ncbi Filter performance parameters for vectorial high-aperture wave fields
    Colin J R Sheppard
    Department of Diagnostic Radiology and Division of Bioengineering, National University of Singapore, Singapore
    Opt Lett 33:476-8. 2008
    ..We generalize these parameters to the full vectorial case for an aplanatic optical system illuminated by a plane-polarized wave. The behavior of different optical systems is compared...
  32. doi Improved spatial resolution in fluorescence focal modulation microscopy
    Wei Gong
    Division of Bioengineering, National University of Singapore, Singapore 117576, Singapore
    Opt Lett 34:3508-10. 2009
    ..4%. When applied to saturable fluorescence, the half-width at half-maximum is improved by 33.6%, 50.0%, and 62.9%, at demodulation frequencies 2omega, 4omega, and 8omega, respectively...
  33. doi Complete modeling of subsurface microscopy system based on aplanatic solid immersion lens
    Rui Chen
    Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117576
    J Opt Soc Am A Opt Image Sci Vis 29:2350-9. 2012
    ..For extended scatterers, two types of illuminations-focusing light illumination and plane wave direct illumination-are used to image the scatterers, and observations are explained using interaction of the incident light with the sample...
  34. ncbi Investigation of the point spread function of surface plasmon-coupled emission microscopy
    Wai Teng Tang
    Computation and Systems Biology, Singapore MIT Alliance, National University of Singapore, 4 Engineering Drive 3, Singapore 117576, Singapore
    Opt Express 15:4634-46. 2007
    ..This result is due to the highly polarized and anisotropic emission caused by the metal layer...
  35. doi Quantitative phase restoration by direct inversion using the optical transfer function
    Shan Shan Kou
    Optical Bioimaging Laboratory, Division of Bioengineering, National University of Singapore NUS, 7 Engineering Drive 1, 117576, Singapore
    Opt Lett 36:2671-3. 2011
    ..The proposed method is especially suitable for application to weak phase objects, such as live and unstained biological samples but, surprisingly, has also been shown to work with comparatively strong phase objects...
  36. doi Considerations of aperture configuration in focal modulation microscopy from the standpoint of modulation depth
    Guangjun Gao
    Division of Bioengineering, National University of Singapore, Singapore 117576
    J Opt Soc Am A Opt Image Sci Vis 28:496-501. 2011
    ..In summary, the annular configuration is superior to the fan- and stripe-shaped configurations in modulation depth and spatial resolution...
  37. ncbi Lommel pulses: an analytic form for localized waves of the focus wave mode type with bandlimited spectrum
    Colin J R Sheppard
    Division of Bioengineering, National University of Singapore, 9 Engineering Drive 1, Singapore
    Opt Express 16:150-60. 2008
    ..In particular, a free-space version of "backward light" pulse is considered, which moves in the opposite direction with respect to all its spectral constituents...
  38. doi Second harmonic scattering from small particles using Discrete Dipole Approximation
    Naveen K Balla
    Computation and Systems Biology Program, Singapore MIT Alliance, E4 04 10, 4 Engineering Drive 3, National University of Singapore, 117576 Singapore
    Opt Express 18:21603-11. 2010
    ..We show here that DDA can be used to efficiently model second harmonic scattering by small particles. Our results are compared with experimental data and other computational methods...
  39. doi Resolution of aplanatic solid immersion lens based microscopy
    Rui Chen
    Department of Electrical and Computer Engineering, National University of Singapore, Singapore
    J Opt Soc Am A Opt Image Sci Vis 29:1059-70. 2012
    ..The observations are explained explicitly through a detailed analysis of the dyadic Green's function. A new resolution criterion is also proposed, which provides a very accurate estimate of the resolution limits...
  40. ncbi Fractal model of light scattering in biological tissue and cells
    Colin J R Sheppard
    Division of Bioengineering, National University of Singapore, Singapore
    Opt Lett 32:142-4. 2007
    ..Compared with an alternative previously published model [Opt. Lett.30, 3051 (2005)], the range of allowable power laws is extended into the subfractal regime...
  41. doi Polarization effects in 4Pi microscopy
    Colin J R Sheppard
    Division of Bioengineering, National University of Singapore, 9 Engineering Drive 1, Singapore 117576, Singapore Department of Biological Sciences, National University of Singapore, 14 Science Drive 4, Singapore 117543, Singapore NUS Graduate School for Integrative Sciences and Engineering, National University of Singapore, Singapore 117456, Singapore
    Micron 42:353-9. 2011
    ..The electric energy density at the focus for a given power input can be increased using electric dipole polarization, which is relevant for atomic physics experiments such as laser trapping and cooling. ..
  42. ncbi Recent advances in optical microscopy methods for subcellular imaging of thick biological tissues
    NanGuang Chen
    Department of Biomedical Engineering, National University of Singapore, Singapore
    Crit Rev Biomed Eng 41:393-403. 2013
    ..Focal modulation microscopy has demonstrated an imaging depth comparable to those of multiphoton microscopy and optical coherence microscopy, near-real-time image acquisition, and capability with a multiple contrast mechanism. ..
  43. doi Multipole theory for tight focusing of polarized light, including radially polarized and other special cases
    Thanh Xuan Hoang
    Department of Electrical and Computer Engineering, National University of Singapore, Singapore
    J Opt Soc Am A Opt Image Sci Vis 29:32-43. 2012
    ..The method is also convenient for calculation of fields scattered by particles and calculation of optical trapping forces...
  44. doi Optical color-image encryption and synthesis using coherent diffractive imaging in the Fresnel domain
    Wen Chen
    Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore 117576, Singapore
    Opt Express 20:3853-65. 2012
    ..Compared with conventional interference methods, coherent diffractive imaging approach may open up a new research perspective or can provide an effective alternative for optical color-image encryption and synthesis...
  45. doi Surface-plasmon-coupled emission microscopy with a spiral phase plate
    Wai Teng Tang
    Computation and Systems Biology, Singapore MIT Alliance, National University of Singapore, 4 Engineering Drive 3, Singapore 117576, Singapore
    Opt Lett 35:517-9. 2010
    ..The optical performance of the system is characterized and compared with previous publications. This technique provides more than twofold lateral resolution enhancement...
  46. ncbi Simple spatial phase modulator for focal modulation microscopy
    Chee Howe Wong
    Department of Electrical and Computer Engineering, National University of Singapore, Singapore
    Appl Opt 48:3237-42. 2009
    ..We have designed a simple spatial phase modulator based on a tilting glass plate that provides superb modulation stability. Image quality has been improved remarkably after integrating such a modulator into a FMM system...
  47. ncbi Quantitative phase-gradient imaging at high resolution with asymmetric illumination-based differential phase contrast
    Shalin B Mehta
    Optical Bioimaging Lab, National University of Singapore, Graduate School for Integrative Sciences and Engineering, Department of Biological Sciences, Singapore
    Opt Lett 34:1924-6. 2009
    ..It is amenable to transfer-function engineering, simultaneous fluorescence imaging, and automated live cell imaging...
  48. ncbi Partially coherent image formation in differential interference contrast (DIC) microscope
    Shalin B Mehta
    Optical Bioimaging Lab, Division of Bioengineering, National University of Singapore, 7 Engineering Drive 1, Blk E3A 04 15, Singapore
    Opt Express 16:19462-79. 2008
    ..Approximations for weak or slowly varying specimens are also given. These improved models should be of great value in designing phase retrieval algorithms for DIC...
  49. ncbi Straightness measurements with a reflection confocal optical system-an experimental study
    Kiyofumi Matsuda
    Department of Physical Optics, School of Physics, University of Sydney, New South Wales, Australia
    Appl Opt 41:3966-70. 2002
    ..We demonstrate straightness measurements using reflection confocal optics and show these measurements to be in good agreement with the theory...
  50. ncbi Ultra long high resolution beam by multi-zone rotationally symmetrical complex pupil filter
    Yingshun Xu
    Division of Bioengineering, National University of Singapore, 7 Engineering Drive 1, 117574, Singapore
    Opt Express 15:6409-13. 2007
    ..The scalar diffraction theory is used to optimize the zone parameters. Simulation results show that extended DoF of the beam is increased by 16 times while the spot size at the beam waist is reduced to 0.7 times...
  51. doi Optical image encryption based on diffractive imaging
    Wen Chen
    Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore 117576
    Opt Lett 35:3817-9. 2010
    ..The proposed method can provide a new strategy instead of conventional interference methods, and it may open up a new research perspective for optical image encryption...
  52. ncbi Tight focusing of radially polarized Gaussian and Bessel-Gauss beams
    Elijah Y S Yew
    Division of Bioengineering, National University of Singapore, Singapore
    Opt Lett 32:3417-9. 2007
    ..The ratio of the axial component to the transverse component is also the greatest for the uniform pupil function. On the other hand, the Bessel-Gauss beam benefits the most from the use of an annulus...