Optical: systems and elements – Single channel simultaneously to or from plural channels – By partial reflection at beam splitting or combining surface
Reexamination Certificate
2003-02-13
2004-04-06
Mai, Huy (Department: 2873)
Optical: systems and elements
Single channel simultaneously to or from plural channels
By partial reflection at beam splitting or combining surface
C359S618000, C359S619000, C359S631000
Reexamination Certificate
active
06717736
ABSTRACT:
BACKGROUND
This invention relates to optics, and more particularly to catoptric imaging systems.
Imaging systems of varying sorts have existed for thousands of years. Even after such a long period of development, modem imaging systems still have a similar purpose as their ancient counterparts. Imaging systems gather light from an object point and its vicinity and focus this light into an image at an image point and its vicinity. Light can be focused using refraction and this branch of optics is known as dioptrics. Light can also be focused using reflection and this branch of optics is known as catoptrics. Irregardless of the focusing system used typical imaging systems strive to optimize a few important parameters. For example, many imaging systems are designed to optimize resolution, numerical aperture, and shape of the image plane. Resolution of the imaging system is the smallest distance between features in the object space that can be distinguished in the image plane. Therefore resolution determines the level of detail that can be derived from the image. Numerical aperture relates to the amount of available light that the imaging system collects from the object. For most types of detectors, such as photographic film, charge coupled devices, or even the human eye, a larger numerical aperture increases light intensity and typically yields better images. Lastly, the shape of the image plane can be quite important. A flat plane is typically most useful for detection devices like photographic film or charged coupled devices (CCD). Unfortunately, all of these parameters can be degraded by a host of aberrations.
SUMMARY
The present invention features catoptric optical systems that utilize a beam splitter surface and a reflecting surface. Primary focusing can be achieved with the reflecting surface and therefore longitudinal chromatic aberrations are reduced. In preferred embodiments, the beam splitter is positioned relative to the object point, image point, and the reflective surface such that light rays from the object point which are focused to the image point have been both reflected and transmitted by the beam splitter surface. The combination of a reflection and a transmission for each ray of the beams being focused substantially eliminates first-order variations in the beam intensity due to imperfections in the reflective and transmissive properties of the beam splitter for incident angles deviating from a central design angle. Some embodiments of the system may further include refractive elements to reduce additional aberrations.
Furthermore, in some embodiments of the system, light transmission may be enhanced by use of interferometric recombination of light reflected and transmitted by the beam splitter. In such embodiments, rays emerging from an object point are separated into a first set of rays that are transmitted by the beam splitter and a second set of rays that are reflected by the beam splitter. The first set of rays is incident on a first curved reflective surface, and subsequently reflected by the beam splitter to an image point, whereas the second set of rays is incident on a second curved reflective surface, and subsequently transmitted by the beam splitter to the image point. The subsequent reflection of the first set of rays and subsequent transmission of the second set of rays by the beam splitter interferometrically recombines the sets of rays to enhance light intensity at the image point.
Moreover, in additional embodiments, one of the reflective surfaces may be positioned relative to the beamsplitter and the first reflective surface so that the set of rays incident on it focus to a second image point spatially separated from the first image point. Furthermore, such a system may be used in “reverse,” to image a pair of spatially separated object points to a common image point. Both applications may be useful in confocal and/or phase-contrast microscopy.
Also, in any of the embodiments, the reflecting surface(s) may be a “Fresnal” mirror, which is defined herein as a reflecting surface formed by multiple curved facets each having a common center of curvature. Using such reflecting surfaces may increase the numerical aperture and working distance of the catoptric imaging system, which in turn improve lateral resolution and depth resolution.
We now summarize particular aspects and features of the invention.
In general, in one aspect, the invention features an imaging system for imaging an object point to an image point. The system includes i) a beam splitter positioned to receive light rays from the object point and separate each ray into a transmitted portion and a reflected portion, the transmitted portions defining a first set of rays and the reflected portions defining a second set of rays; and ii) a reflecting surface positioned to receive one of the sets of rays from the beam splitter and focus that set of rays towards the image point via the beam splitter, wherein the reflecting surface comprises multiple curved facets each having a common center of curvature.
Embodiments of the imaging system may include any of the following features.
The reflecting surface may be positioned to receive the first set of rays and reflect the first set of rays back to the beam splitter, in which case the beam splitter is positioned to reflect at least a portion of each ray received from the reflecting surface to the image point. Furthermore, the reflecting surface may be substantially concentric with the object point. A center of the reflecting surface may define an object optical axis with the object point, and the beam splitter may be positioned substantially perpendicular to the object optical axis or at an acute angle to the object optical axis (e.g., an acute angle substantially equal to 45 degrees).
Alternatively, the reflecting surface may be positioned to receive the second set of rays and reflect the second set of rays back to the beam splitter, in which case the beam splitter is positioned to transmit at least a portion of each ray received from the reflecting surface to the image point. Furthermore, the reflecting surface may be substantially concentric with the image point. A center of the reflecting surface may define an image optical axis with the image point, and the beam splitter may be positioned substantially perpendicular to the image optical axis or at an acute angle to the image optical axis (e.g., an acute angle substantially equal to 45 degrees).
The imaging system may further include a first optic having an internal surface defining the reflecting surface. For example, the internal surface of the first optic may be curved. The first optic may have a flat surface opposite the internal surface, and the beam splitter may be positioned adjacent the flat surface. Furthermore, the system may include a plano-convex optic having a plano surface adjacent one of the object point and the image point and a convex surface contacting the first optic, wherein the interface between the plano-convex optic and the first optic defines a refracting surface.
More generally, the imaging system may include a refracting surface positioned between the object point and the beam splitter to receive the light rays from the object point. For example, the refracting surface may be substantially concentric with the object point. Alternatively, or in addition, the system may include a refracting surface positioned between the beam splitter and the image point to receive the light rays focused by the reflecting surface. For example, the refracting surface may substantially concentric with the image point. Moreover, there may be more than one refracting surface positioned between the beam splitter and the object point, and/or between the beam splitter and the image point. Also, the space between any two such refracting surfaces may be air.
The system may also include a second optic adjacent the first optic, wherein the beam splitter is positioned at an interface between the first and second reflective optics. Furthermore, the system may include a plano-convex optic having a pla
Fish & Richardson P.C.
Mai Huy
Zetetic Institute
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