Optical: systems and elements – Having significant infrared or ultraviolet property – Lens – lens system or component
Reexamination Certificate
1997-01-23
2001-06-19
Chang, Audrey (Department: 2872)
Optical: systems and elements
Having significant infrared or ultraviolet property
Lens, lens system or component
C359S354000, C359S566000, C359S357000, C359S676000
Reexamination Certificate
active
06249374
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates generally to optical systems, and more particularly to a wide field of view infrared zoom lens assembly having a constant F/Number.
BACKGROUND OF THE INVENTION
Infrared or thermal imaging systems typically use a plurality of thermal sensors to detect infrared radiation and produce an image capable of being visualized by the human eye. Thermal imaging systems typically detect thermal radiance differences between various objects in a scene and display these differences in thermal radiance as a visual image of the scene. Thermal imaging systems are often used to detect fires, overheating machinery, planes, vehicles and people, and to control temperature sensitive industrial processes.
The basic components of a thermal imaging system generally include optics for collecting and focusing infrared radiation from a scene, an infrared detector having a plurality of thermal sensors for converting infrared radiation to an electrical signal, and electronics for amplifying and processing the electrical signal into a visual display or for storage in an appropriate medium. A chopper is often included in a thermal imaging system to modulate the infrared radiation and to produce a constant background radiance which provides a reference signal. The electronic processing portion of the thermal imagining system will subtract the reference signal from the total radiance signal to produce a signal with minimum background bias.
Thermal imaging systems may use a variety of infrared detectors. An infrared detector is a device that responds to electromagnetic radiation in the infrared spectrum. Infrared detectors are sometimes classified into two main categories as cooled and uncooled. A cooled infrared detector is an infrared detector that must be operated at cryogenic temperatures, such at the temperature of liquid nitrogen, to obtain the desired sensitivity to variations in infrared radiation. Cooled detectors typically employ thermal sensors having small bandgap semiconductors that generate a change in voltage due to photoelectron interaction. This latter effect is sometimes called the internal photoelectric effect.
Uncooled infrared detectors cannot make use of small bandgap semiconductors because dark current swamps any signal at room temperature. Consequently, uncooled detectors rely on other physical phenomenon and are less sensitive than cooled detectors. However, because uncooled detectors do not require the energy consumption of cooled detectors, they are the preferred choice for portable, low power, applications where the greater sensitivity of cooled detectors is not needed. In a typical uncooled thermal detector, infrared photons are absorbed and the resulting temperature difference of the absorbing element is detected. Thermal detectors include a pyroelectric detector, a thermocouple, or a bolometer.
An infrared window is a frequency region in the infrared spectrum where there is good transmission of electromagnetic radiation through the atmosphere. Typically, infrared detectors sense infrared radiation in the spectral bands from 3 to 5 microns (having an energy of 0.4 to 0.25 eV) and from 8 to 14 microns (having an energy of 0.16 to 0.09 eV). The 3 to 5 micron spectral band is generally termed the “near infrared band” while the 8 to 14 micron spectral band is termed the “far infrared band.” Infrared radiation between the near and far infrared bands cannot normally be detected due to atmospheric absorption of the same.
Infrared radiation is generally focused onto a thermal detector by one or more infrared lenses. Infrared lens assemblies may be classified as zoom or single field of view and as wide or narrow field of view. A wide field of view infrared zoom lens may employ a fixed or a variable aperture stop. A fixed aperture stop allows a infrared zoom lens to maintain a constant F/Number, and thus a constant sensitivity, over the zoom range. Wide field of view infrared zoom lenses having a fixed aperture stop, however, are typically expensive to manufacture due to the number and size of lens elements and to the materials needed to construct the lens elements.
SUMMARY OF THE INVENTION
In accordance with the present invention, a wide field of view infrared zoom lens assembly having a constant F/Number is provided that substantially eliminates or reduces the disadvantages and problems associated with prior infrared detection systems.
In accordance with the present invention, a wide field of view infrared lens assembly is provided with a plurality of components located along an optical axis to focus infrared radiation of an object. A focusing component includes a pair of focusing zoom lenses. The focusing lenses may be formed of a high dispersion, low index material. A collecting component includes at least one collecting lens that may also be formed of high dispersion, low index material. An aperture stop may be located along the optical axis in a fixed location. A diffracting component includes at least one diffractive surface that may be employed to correct color aberrations associated with an infrared waveband. The focusing and collecting components cooperate with the diffractive component to focus infrared radiation of the object onto an image plane of an associated infrared detector.
More specifically, the collecting lens may be located proximate to the image plane. In this embodiment, a second collecting lens may be located between the collecting lens and the focusing component. The aperture stop may be mounted to the second collecting lens.
In accordance with another aspect of the present invention, a diffractive lens incorporating the diffractive surface may be removably mounted in the wide field of view infrared lens assembly. To reduce costs, the diffractive lens may be formed from an inexpensive polymer. The high dispersion, low index material of the focusing and collecting lenses may be chalcogenide glass or other material having infrared transmitting properties that change minimally between the near and far infrared wavebands.
Important technical advantages of the present invention include providing a relatively low cost wide field of view infrared zoom lens assembly having a constant F/Number, and thus a constant sensitivity, over the zoom range. In particular, the location of the aperture stop minimizes the front lens diameter and allows the lens assembly to have a constant, very fast F/Number. Thus, the present invention eliminates the cost associated with large lenses for wide field of view applications.
Another important technical advantage of the present invention includes providing a wide field of view infrared zoom lens assembly operable in the near and far infrared wavebands. Thus, separate wide field of view infrared lens assemblies need not be designed and fabricated for use in the near and far infrared wavebands.
Other technical advantages will be readily apparent to one skilled in the art from the following figures, descriptions, and claims.
REFERENCES:
patent: 3825315 (1974-07-01), Altman et al.
patent: 3846820 (1974-11-01), Lampe et al.
patent: 4007978 (1977-02-01), Holton
patent: 4018608 (1977-04-01), Frazier
patent: 4067641 (1978-01-01), Holton
patent: 4080532 (1978-03-01), Hopper
patent: 4084130 (1978-04-01), Holton
patent: 4085550 (1978-04-01), Graham
patent: 4142207 (1979-02-01), McCormack et al.
patent: 4143269 (1979-03-01), McCormack et al.
patent: 4162402 (1979-07-01), Hopper
patent: 4205227 (1980-05-01), Reed
patent: 4275302 (1981-06-01), Imbert et al.
patent: 4379232 (1983-04-01), Hopper
patent: 4411732 (1983-10-01), Wotherspoon
patent: 4431917 (1984-02-01), Gibbons
patent: 4447291 (1984-05-01), Schulte
patent: 4594507 (1986-06-01), Elliott et al.
patent: 4614957 (1986-09-01), Arch et al.
patent: 4615595 (1986-10-01), Hornbeck
patent: 4621888 (1986-11-01), Crossland et al.
patent: 4639756 (1987-01-01), Rosbeck et al.
patent: 4679891 (1987-07-01), Roberts
patent: 4684812 (1987-08-01), Tew et al.
patent: 4705361 (1987-11-01), Frazier et al.
patent: 4710732 (1987-12-01), Hornbeck
patent: 4751387
Baker & Botts L.L.P.
Chang Audrey
Raytheon Company
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