Optics: measuring and testing – Shape or surface configuration
Reexamination Certificate
2002-07-18
2004-09-21
Font, Frank G. (Department: 2877)
Optics: measuring and testing
Shape or surface configuration
C356S607000
Reexamination Certificate
active
06795199
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to optical imaging
Relevant Patents
U.S. Pat. No. 5,076,672 All-optical switch apparatus using a nonlinear etalon Tsuda, et al.
U.S. Pat. No. 5,275,168 Time-gated imaging through dense-scattering materials using stimulated Raman amplification, Reintjes, J et al.
U.S. Pat. No. 5,291,267 Optical low-coherence reflectometry using optical amplification Sorin et al
U.S. Pat. No. 5,299,170 Apparatus for measuring pulse width with two photon absorption medium,. Shibata et al
U.S. Pat. No. 5,321,501 Method and apparatus for optical imaging with means for controlling the longitudinal range of the sample, Swanson E. et al.
U.S. Pat. No. 5,418,797 Time gated imaging through scattering material using polarization and stimulated Raman amplification, Bashkansky et al
U.S. Pat. No. 5,489,984 Differential ranging measurement system and method utilizing ultrashort pulses Hariharan, et al.
U.S. Pat. No. 5,491,524 Optical coherence tomography corneal mapping apparatus Hellmuth, T et al
U.S. Pat. No. 5,549,114 Short coherence length, doppler velocimetry system Petersen, C et al.
U.S. Pat. No. 5,530,544 Method and apparatus for measuring the intensity and phase of one or more ultrashort light pulses and for measuring optical properties of materials Trebino, R et al.
U.S. Pat. No. 5,570,182 Method for detection of dental caries and periodontal disease using optical imaging, Nathel; H et al.
U.S. Pat. No. 5,585,913 Ultrashort pulsewidth laser ranging system employing a time gate producing an autocorrelation and method therefore Hariharan, A et al.
U.S. Pat. No. 5,648,866 Optimized achromatic phase-matching system and method Trebino et al.
U.S. Pat. No. 5,862,287 Apparatus and method for delivery of dispersion compensated ultrashort optical pulses with high peak power Stock et al.
U.S. Pat. No. 5,936,732 Apparatus and method for characterizing ultrafast polarization varying optical pulses Smirl et al.
U.S. Pat. No. 5,920,373 Method and apparatus for determining optical characteristics of a cornea Bille, J
U.S. Pat. No. 5,920,390 Fiberoptic interferometer and associated method for analyzing tissue Farahi, et al.
U.S. Pat. No. 5,975,697 Optical mapping apparatus with adjustable depth resolution Podoleanu, A et al.
U.S. Pat. No. 5,994,690 Image enhancement in optical coherence tomography using deconvolution Kulkarni, M et al.
U.S. Pat. No. 6,002,480 Depth-resolved spectroscopic optical coherence tomography Izatt; J. et al
U.S. Pat. No. 6,006,128 Doppler flow imaging using optical coherence tomography Izatt; J. et al
U.S. Pat. No. 6,008,899 Apparatus and method for optical pulse measurement Trebino; R et al.
U.S. Pat. No. 6,023,057 Device for determining the phase errors of electromagnetic waves Gaffard et al.
U.S. Pat. No. 6,053,613 Optical coherence tomography with new interferometer Wei Jay et al.
U.S. Pat. No. 6,095,651 Method and apparatus for improving vision and the resolution of retinal images Williams, D et al
U.S. Pat. No. 6,111,645 Grating based phase control optical delay line Tearney, et al.
U.S. Pat. No. 6,134,003 Method and apparatus for performing optical measurements using a fiber optic imaging guidewire, catheter or endoscope Teamey et al.
U.S. Pat. No. 6,199,986 Rapid, automatic measurement of the eye's wave aberration Williams, D et al
U.S. Pat. No. 6,191,862 Methods and apparatus for high speed longitudinal scanning in imaging systems Swanson; A. et al.
U.S. Pat. No. 6,195,617 B I Autocorrelation of ultrashort electromagnetic pulses Reid et al.
U.S. Pat. No. 6,201,608 Method and apparatus for measuring optical reflectivity and imaging through a scattering medium Mandella et al.,
U.S. Pat. No. 6,226,112 Optical Time-division-multiplex system by Denk, et al.
U.S. Pat. No. 6,249,630 Apparatus and method for delivery of dispersion-compensated ultrashort optical pulses with high peak power Stock et al
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Other Publications
“Imaging Objects Hidden in a Highly Scattering Media Using Femtosecond Second-Harmonic-Generation Cross-Correlation Time Gating”, Yoo et al, Optics Letters, July 1991, pp. 1019-1021. Jenkins & White, fundamental of Optics, McGraw-Hill, 1957
BACKGROUND OF THE INVENTION
It is well known that a Michelson Interferometer enables to make precise distance and incremental displacement measurements by observing the fringes formed by the interference of coherent light waves. The interference between light waves that have traveled along different pathways is limited by the coherence length of the light source. As long as the different pathways differ by less than the coherence length of the source, interference will result in formation of fringes.
Optical Coherent Tomography (OCT) makes use of a Michelson interferometer to image the topography of the layers behind the surface of a tissue by scanning “same-depth” layers. This is achieved by precise balancing of the legs of the interferometer, so that the depth information is obtained by observing the interference fringes when the two legs of the interferometer are within the coherent length of the illuminating light source. Changing the length of one of the paths enables to focus on a layer at a depth that differs by the length changed. However as fringes of equal intensity are obtained with widely differing path lengths, for as long as the interfering light waves are coherent, light sources with short coherence lengths such as superluminescent diodes are used, so as to minimize this ambiguity. This setup greatly facilitates the calibration of the interferometer as no interference fringes are obtained when the path lengths between the two legs of the interferometer differ by more than the coherence length.
However, it is important to realize that the fringes observed with any light source, originate from the interference of light coming from many oscillators which emit light randomly and non-coherently one from the other. Low coherence length sources are limited in resolution by the randomness of the coherence lengths of the different oscillators and the FWHM of the group of fringes is what determines the “path-length difference” resolution and not the FWHM of a single fringe. It is also important to realize that the non-coherence among the various oscillators, also manifests itself in a high uniform background over which the fringe pattern is observed, thus the SNR obtained with low coherence length superluminescent diodes is much worse than the SNR of a fringe pattern obtained with highly coherent sources.
The conventional Optical Coherent Tomography (OCT) technique, (see for example U.S. Pat. No. 5,321,501, Method and apparatus for optical imaging with means for controlling the longitudinal range of the sample, Swanson E. et al.) uses a low coherence light source, to minimize the spread of the fringe pattern and thus increase the “path-length difference” precision.
OCT is constrained by the need to sequentially adjust the depth of the imaged layer by incrementally changing one of the legs of the Michelson interferometer, either mechanically with a retroreflector, by stretching the optical fiber with a piezoelectric motor or by a combination of an acousto-optic deflector, a grating and a mirror (see U.S. Pat. No. 6,111,645 Grating based phase control optical delay line Tearney, et al.). In spite of all the heroic efforts, it takes ~100 microseconds to change the delay, position and balance the interferometer onto a new layer.
OCT is also limited by “speckles”, a background generated by the interference with the coherent multiple back-scattered light, that originates from a spherical volume with a radius equal to the low coherent length of the source.
Ultrafast femtosecond lasers have several important advantages over CW or long-pulse lasers. They permit to achieve high peak power w
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