Optical waveguides – With optical coupler – Input/output coupler
Patent
1997-09-23
1999-07-20
Ngo, Hung N.
Optical waveguides
With optical coupler
Input/output coupler
385127, 385 36, 385 38, 385 35, 385 48, G02B 626
Patent
active
059265922
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to confocal imaging systems which use a flexible optical transmission means such as optical fibres as a substitute for the return pinhole, and more particularly but not limited to confocal microscopes constructed using optical fibres.
DESCRIPTION OF THE PRIOR ART
Confocal microscopy can be considered to have originated with the work of Marvin Minsky. His U.S. Pat. No. 3,013,467 describes a system in which light passes through a pinhole, traverses a beamsplitter and is focused by an objective to a spot on or within a specimen. In an epi-illumination embodiment, light returning from the spot region is converged by the same objective lens, reflected by its second encounter with the beamsplitter and passes through a second pinhole to a photo detector. The geometry of the arrangement is such that the focused spot (Gaussian waist volume) is the only volume within the specimen from which the general set of ray paths returning through the lens will retrace their outgoing paths to pass through the second pinhole to the photo detector. Light reflected from above or below this focus which passes through the objective lens will be largely blocked off by the opaque sheet material forming the pinhole surrounding area.
The electrical signal from the photo detector will give a value for the light reflected from the spot. If the specimen is moved the changes in electrical output from the photo detector indicate changes in the level of light return from the material of the specimen along the path of the spot. If the specimen is moved in a two dimensional raster then a two dimensional rastered map of the return light intensity can be build up based on the raster synchronous modulation of the electrical output from the photo detector. This can be displayed on a cathode ray screen or by other means giving an image which is a sharp optical slice, substantially eliminating the contribution of light from above or below the focal plane. Such light normally reduces the contrast and blurs the image in conventional microscopy, particularly from translucent biological specimens, and renders high power microscopic observation of thick tissue sections impossible. The use of an optical fibre in the place of one or more of the pinholes is disclosed in U.S. Pat. No. 5,120,953. In such a fibre confocal microscope, the core of the optic fibre effectively acts as the pinhole, and, when the fibre is single moded, the light leaves the fibre as a single set of concentric expanding wavefronts and the system becomes diffraction limited and maximum resolution is obtained.
The chief advantage of using a fibre to replace the pinhole is that the two sides of the pinhole are effective optically connected by the core of the fibre, but are physically independent and can be independently and separately positioned. The major advantages conferred by this are
(a) the several large and heavy components of the microscope can be located in any convenient position and do not need to be rigidly located with respect to the specimen;
(b) the fibre tip itself can be mechanically scanned to give the raster required to build-up the image data set;
(c) an "in fibre" evanescent wave beamsplitter can be employed.
A disadvantage of existing fibre confocal microscopes is that for these systems there is no direct functional equivalent of opening up the pinhole. Most bulk optic laser scanning confocal microscopes include a function in which the second pinhole can be progressively enlarged. While for the purposes of the highest resolution image, the smallest sized second pinhole is desirable consistent with a reasonable optical signal strength, in practice it is desirable to enlarge and contract the second pinhole as the microscopist examines the object, by the means of operating a continuously variable diaphragm. The diaphragm opens the aperture and collects an increasing fraction of light from the double cone volume on either side of the Gaussian waist region. This increases the strength of the electrical signal but at the e
REFERENCES:
patent: 4427977 (1984-01-01), Carollo et al.
patent: 4978190 (1990-12-01), Veith
patent: 5270537 (1993-12-01), Jacobs
patent: 5579426 (1996-11-01), Li et al.
Delaney Peter
Harris Martin Russell
Ngo Hung N.
Optiscan Pty Ltd
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