Biomedical subjects

Jyh-Long Chern

Publications and source records attributed to Jyh-Long Chern.

8 recordsLinked to original sources

PubMed2006

Irradiance formations in hollow straight light pipes with square and circular shapes.

We investigated, both analytically and numerically, the irradiance formation of an asymmetrically located Lambertian light source in hollow straight light pipes with square and circular shapes. The uniform irradiance distribution in a square light pipe and hot-spot localization in a circular light pipe were examined and determined semianalytically. Typical factors of influence, such as light-pipe length, width, and source size, were identified with extensive simulation. When the ratio of light-pipe length and width was less than 0.5, the deviation from uniformity could be more than 20%. But once the source size was large enough (approximately half of the incident port), such that the Lambertian characteristics of the source dominated the irradiance distribution, the uniformity deviation was reduced. Furthermore, a quantity of root-mean-square circular differences was defined in order to identify the shape deformation of the light pipe; it was found that the peak value of the hot spot decreased exponentially with the deformation scale. The influence of nonperfect reflectivity of the pipe wall on irradiance formation was also examined for a square light pipe; when the reflectivity is larger than 90%, the difference in uniformity is less than 10% and uniform irradiance remains, provided that the ratio of light-pipe length and width is larger than 1; even the source is located asymmetrically.

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PubMed2006

Retrieving two-dimensional information of the subwavelength variation from far-field irradiance.

An eigenvalue-problem approach of blind deconvolution is developed to retrieve the information of two-dimensional subwavelength variation from far-field irradiance with an embedded-aperture configuration with three detectors. A reference signal has been implemented to determine the scaling issue, and hence it allows the exact order of magnitude of the retrieved signals to be estimated correctly. It is shown that the subwavelength variations of a two-dimensional aperture can be identified with a precision of better than a 1% error ratio.

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PubMed2006

Optical transfer functions for specific-shaped apertures generated by illumination with a rectangular light pipe.

We investigated the pupil functions of specific-shaped apertures generated by Lambertian illumination with a rectangular light pipe to derive the corresponding optical transfer functions (OTFs) in aberration-free and defocused optical systems. The semianalytical results indicate that the curves of the OTF of the optical system vary with the form of the shaped apertures that are generated by illumination with different geometric structures of light pipes and light sources. It was found that the OTF values of even-peak frequencies decrease when the Lambertian light source decreases. If there are a total of n x n individual apertures within a pupil, then n near-periodical peaks will appear on the OTF curve. It is evident that the values of the OTF remain almost unchanged even when the lengths of the light pipes are different. Furthermore, the geometric structure of the light pipe does not affect the resolution limit of the optical system, and under the condition of a larger defocused coefficient omega(20), the results of the defocused system can coincide with those of the aberration-free systems.

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PubMed2005

No-loss bent light pipe with an equiangular spiral.

Bending a light pipe and maintaining the required volume and size, while at the same time preserving source energy and minimizing bend losses, is the basic criterion for designing a light pipe. An important requirement is the design of a light pipe that is capable of being bent without loss of light and with no limitations on acceptance angle. It is shown that in theory such a light pipe does exist, in a form corresponding to the so-called golden rectangle. Numerical simulations with six different no-loss light pipes with multiple bends are provided as a demonstration.

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PubMed2005

Detection of subwavelength slit-width variation with measurements in the far field by use of an embedded-aperture interferometer configuration.

The dynamic signature of the subwavelength variation of a rectangular aperture has recently been shown to be determinable from far-field irradiance with a precision better than 1 nm [Opt. Lett. 29, 1045 (2004)]. We have proposed, and have theoretically shown, that detection sensitivity can be greatly enhanced with an embedded-aperture Mach-Zehnder interferometer configuration, after parameter optimization. The sensitivity, in terms of derivative intensity of observed subwavelength variations, could be enhanced approximately 2.7 times, compared with the directly detected method. Another method of detection of subwavelength variation from pattern measurement of far-field diffraction has also been proposed. The associated shifting of the dark line of the diffraction pattern had a good linear correlation to subwavelength variation, which was magnified approximately 150 times, and gave good contrast for measurement.

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PubMed2005

Identifying the subwavelength-aperture-width variation in the far field with tunable asymmetrically-embedded-aperture interferometer configuration.

A tunable asymmetrically-embedded-aperture interferometer configuration is proposed to enhance the measurement sensitivity of subwavelength variation. With this configuration, an aperture of reference was posited asymmetrically, relative to the test aperture, that exhibited subwavelength variation. By a shift in the relative position of the reference aperture, the detection sensitivity of measuring the subwavelength variation in the far field can be enhanced to a desired value at any specific detection width. We discuss the underlying mechanism of optimization and address the difference between the embedded-aperture interferometry and tunable asymmetrically-embedded-aperture interferometry with respect to tolerance.

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PubMed2004

Characterization of the signature of subwavelength variation from far-field irradiance.

The dynamic signature of the subwavelength variation of a slit is shown to be determinable from far-field irradiance with a precision of better than 1 nm. One can increase the efficiency of measurement of the subwavelength's signature by adjusting the detection width over which the subwavelength variation is detected. The subwavelength variation of a rectangular aperture was also examined to show the general feasibility.

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PubMed2002

Tilting tolerance analysis of a broadband polarization-preserving beam displacer.

We numerically investigated the performance of an achromatic polarization-preserving beam displacer that was proposed by Galvez [Opt. Lett.26,971(2001)]. First, the four-prism configuration of the Galvez scheme is verified by simulation. We examined the extension of wavelength beyond visible light by considering the corresponding power loss. The degree of polarization is also considered. The tolerance of tilts of reflecting surfaces is comprehensively discussed. It is shown that the second reflector of a four-prism system is the most critical component. Performance of various materials, including plastics, is evaluated. We explain a simplified implementation based on two prisms (the classic Porro configuration), which also improves material performance.

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