Showing papers by "Pang-Chen Sun published in 1998"

Single-shot depth-section imaging through chromatic slit-scan confocal microscopy

Abstract: A chromatic confocal microscope constructed with a white-light source in combination with a diffractive lens provides wavelength-to-depth coding for profile measurements of a three-dimensional sample. We acquired depth-section images nonmechanically and in parallel by incorporating a slit-scan confocal technique into the system. A system using a 100x objective obtained a depth resolution of 0.023 mum comparable with surface profilometers that operate using conventional confocal microscopy. Experimental measurements of a four-phase-level diffractive element and of a machined, metal bearing are presented.

Analysis of Spatial Temporal Converters for All-Optical Communication Links

Abstract: We analyze parallel-to-serial transmitters and serial-to-parallel receivers that use ultrashort optical pulses to increase the bandwidth of a fiber-optic communication link. This method relies on real-time holographic material for conversion of information between spatial and temporal frequencies. The analysis reveals that the temporal output of the pulses will consist of chirped pulses, which has been verified experimentally. When the signal pulses are transmitted along with a reference pulse, the distortions of the received signal, caused by dispersion and other factors in the fiber, are canceled because of the phase-conjugation property of the receiver. This self-referencing scheme simplifies the receiver structure and ensures perfect timing for the serial-to-parallel conversion.

Modeling human eye aberrations and their compensation for high-resolution retinal imaging.

Abstract: We introduced a mathematical eye model using Gullstrand's six-surface eye model modified by clinically measured aspherical data to study human eye aberrations and their compensation for high-resolution retinal imaging. Ray tracing was used to characterize aberrations and point spread functions (PSFs) of the eye model. By using the Zernike polynomial decomposition of the calculated pupil function, we quantified the wavefront aberrations. Based on calculated PSFs, we designed optical inverse filters to reduce the aberrations for a large pupil size and improve the resolution. Spherical aberration and oblique astigmatism were found to be in good agreement with published experimental measurements. Spherical aberration and defocus were the most significant aberrations for on-axis imaging, whereas oblique astigmatism and coma combined with spherical aberration and defocus were most significant for off-axis imaging. The best retinal image resolution occurred at 2- to 3-mm pupil diameter. After aberration correction for an 8-mm diameter pupil, the resolutions for on-axis or 9 degrees off-axis imaging points were very close to diffraction-limited resolutions. Over a limited field of view (FOV), retinal image resolution of the eye model can be greatly improved by aberration correction using aspheric and astigmatic lenses. For imaging large FOVs, space-variant compensation techniques will be required for aberration correction.

Nonvolatile photorefractive spectral holography.

Abstract: We demonstrate nonvolatile storage of femtosecond pulses in a photorefractive LiNbO(3) crystal with recording and readout of spectral holograms at wavelengths of 460 and 920 nm, respectively. No degradation was observed after 24 h of continuous readout. We also show that we can realize the time-lens effect with our system by appropriately setting the ratio of the recording and the reconstruction wavelengths and the spectral resolution of the recording and the reconstruction processes.