Compound Microlens Arrays for High Penetration Depth of Parallel Coherence Tomography
Date Issued
2004
Date
2004
Author(s)
CHUNG, CHEN-FENG
DOI
zh-TW
Abstract
Over the past 14 years a technique called optical coherence tomography (OCT) has been developed for noninvasive cross-section imaging in clinical diagnosis system. OCT uses low-coherence interferometry to produce to en-face and three dimensional image of optical scattering from internal tissue microstructures in a way that is analogous to ultrasonic pulse-echo imaging. In this thesis, we know that parallel OCT in sample arm is demonstrated illuminating with a uniform extended beam and imaged on a two-dimensional array of photodetectors, so it can’t use focal lens in front of the sample. Recently, more and more innovative optical components be manufactured by the fabrication of MEMS (Microelectromechanical System), such as optical-communication system. The objective of this thesis is demonstrated using a 20x20 microlens arrays (in 5 millimeter square) in parallel OCT that compound microlens arrays could enhance both the incident light and collected back scattering efficiency in sample arm. However, there is a trade-off between lateral resolution and focusing depth when conventional optical elements (spherical lenses, mirrors, etc.) are used, because a beam cannot be produced that has simultaneously a long focal length and a narrow lateral width. Whereas high-lateral-resolution imaging requires small spot size by a large numerical aperture, a long focal depth requires a small numerical aperture. When We demonstrated to transform a parallel light beam to an array of narrow parallel light beam by a combination of two different microlens arrays. The size of each narrow parallel light beam is about 60 micrometers, and the penetration depth is about 10 centimeters from 250 micrometers microlens array. The roughness of microlens arrays is about 10-40 nanometers that be useful to avert diffraction.
In the recent years, a parallel detection scheme with a CCD camera has gradually substituted for scanning system of single-point detector. This technique, which employs a two-dimensional array of photodetectors to receive the signal from XY-plane, avoids recording point by point with a fast two-dimensional mechanical scanning system. We called it “parallel OCT or full-field OCT”.
Basing on the optical theory, gray-scale lithography, precision electroforming, and optical plastic material molding technique, several kinds of micro optical component could be developed by the novel Optical-MEMS technology. The 100% fill factor of compound microlens array is designed to enhance the incident light efficiency and increase the penetration depth in OCT system. Moreover, the low cost, simple process and mass production would be its advantages to impact the commercial market.
Subjects
微透鏡組陣列
光學同調斷層掃描
high penetration depth
compound microlens arrays
optcial coherence tomography
Type
thesis
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