Optical: systems and elements – Single channel simultaneously to or from plural channels – By partial reflection at beam splitting or combining surface
Reexamination Certificate
1999-06-01
2001-01-23
Epps, Georgia (Department: 2873)
Optical: systems and elements
Single channel simultaneously to or from plural channels
By partial reflection at beam splitting or combining surface
C359S629000, C359S401000, C359S365000
Reexamination Certificate
active
06178047
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to optical devices, and, more particularly, to an all-reflective optical de-rotation device that separately processes two beams and tends to negate the effects of bearing imperfections.
In one type of optical system, an optical train directs a beam into a detector. The detector converts the beam energy into electrical signals, which are processed for viewing or analysis. All or some of the optical train may be supported on a gimbal structure to permit it to be pointed at portions of a scene that are of interest. As the gimbal articulates to change the pointing direction, the beam rotates so that the image on the detector rotates.
This rotation of the image is undesirable, as it greatly complicates the image analysis. To overcome this problem, a de-rotation device is included in the optical train. The de-rotation device compensates for the rotation of the beam resulting from articulation of the gimbal. De-rotation devices have typically incorporated a de-rotation segment utilizing prisms and/or planar mirrors and, where the beam is to be imaged, an imaging segment utilizing lenses and mirrors. These conventional devices, while operable, are heavy and complex.
An improved all-reflective re-imaging de-rotation optical device, comprising two planar beam-folding mirrors and an off-axis powered-mirror set, is disclosed in U.S. Pat. No. 5,078,502. The powered-mirror set reimages the beam to form an intermediate image at one of the mirrors, which is the third mirror in the five-mirror embodiment of the '502 patent.
While operable in many applications, the optical device of the '502 patent has some limitations in other applications. Some advanced optical systems utilize and must process two optical beams, each of which requires de-rotation. For example, the two beams may include an imaged, relatively low-energy visible and/or infrared beam that is the image of the scene, and a non-imaged, relatively high-energy near-infrared laser beam that provides ranging, designating, and/or targeting functions. The present inventor has observed that the optical device of the '502 patent is not suitable for processing both of these beams through the same optical train, because the relatively high-energy beam may damage the mirror at which the intermediate reimage is formed.
There is a need for an improved de-rotation optical device which is suitable for processing two different types of beams. The present invention fulfills this need, and further provides related advantages.
SUMMARY OF THE INVENTION
The present invention provides an all-reflective de-rotation optical system that is operable with two input beams. The two input beams are processed separately with two different internal optical paths, so that a higher energy beam cannot damage the imaging mirrors used with a lower-energy beam. No powered refractive components are used in the optical system, which is consequently operable over a wide range of wavelengths. In most applications, the optical system must rotate about an optical reference axis, and is supported on bearings for that purpose. In one embodiment, the optical system is such that the responses to bearing imperfections of the two beam processing arrays are the same, avoiding line-of-sight errors that would otherwise arise from the bearing imperfections.
In accordance with the invention, an all-reflective optical system comprises an entrance region coincident with an optical reference axis, an exit region coincident with the optical reference axis, and a dichroic beam splitter assembly coincident with the optical reference axis. The dichroic beam splitter assembly includes an entrance dichroic beam splitter positioned to receive radiation passing through the entrance region, and an exit dichroic beam splitter positioned to direct radiation through the exit region. The optical system further comprises a first beam processing array having a first array input beam of a first wavelength range reflected from the entrance dichroic beam splitter and a first array output beam of the first wavelength range directed to the exit dichroic beam splitter so as to be reflected through the exit region, and a second beam processing array having a second array input beam of a second wavelength range transmitted through the entrance dichroic beam splitter and a second array output beam of the second wavelength range transmitted through the exit dichroic beam splitter to the exit region.
Preferably, the entrance region comprises an entrance aperture, and the exit region comprises an exit aperture. The dichroic beam splitter assembly may be reflective of a first wavelength range in the visible and/or the infrared, and transmissive of a second wavelength range in the infrared, or may be of some other functional characteristic. The first beam processing array comprises an odd number of powered mirrors, preferably five mirrors. The second beam processing array comprises an odd number of flat mirrors, preferably three flat mirrors.
In one form, the dichroic beam splitter, the first beam processing array, and the second beam processing array together comprise a single optical unit rotatable about the optical reference axis. A bearing set supports the single optical unit for rotation about the optical reference axis. Preferably, the second beam processing array and the first beam processing array are circumferentially angularly displaced by about 90 degrees about the optical reference axis. This arrangement of the two beam processing arrays has important advantages, because the assembly is insensitive to differential line of sight errors between the two beam processing arrays that would otherwise be introduced by bearing imperfections. That is, all systems mounted on bearings are subject to wobbling effects due to the imperfections that are present in bearings, regardless of the care taken to minimize bearing imperfections. In the present case, the problems resulting from bearing imperfections would be expected to be exacerbated because there are two beams being processed in the optical system along two substantially different beam paths. The 90-degree circumferential displacement of the two beam processing arrays has been found to negate the differential errors, minimizing line-of-sight (boresighting) errors that would be otherwise expected.
The present optical system is entirely reflective using mirrors, and has no powered refractive components such as lenses. (In this art, an optical system is considered to be “all-reflective” even if some non-powered refractive elements, such as windows, dichroic beam splitters, and spectral filters, are present.) This permits the optical system to be operable over a wide range of wavelengths such as, for example, both visible and infrared wavelength ranges. Refractive optics generally cannot be used in broadband applications, because the powered lenses have wavelength-dependent focal lengths and aberrations. The focal plane location of a refractive imaging system varies as a function of the wavelength of the radiation, complicating or degrading the imaging process.
Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. The scope of the invention is not, however, limited to this preferred embodiment.
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Alkov Leonard A.
Epps Georgia
Lenzen, Jr. Glenn H.
Raufer Colin M.
Raytheon Company
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