Optical filtering device

Details Optical filtering device Optical filtering device

1996-11-07

2001-03-20

Moskowitz, Nelson (Department: 3662)

Optical: systems and elements

Holographic system or element

Using a hologram as an optical element

C359S890000, C356S310000, C356S330000

Reexamination Certificate

active

06204941

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an optical filtering device. More particularly, although not exclusively, it relates to a device suitable for selectively reducing the intensity of unwanted radiation in an optical system, such as that arising from a high intensity monochromatic localised source.
2. Discussion of Prior Art
Dazzle produced by high intensity radiation sources is a common problem in optical systems such as imaging devices. United Kingdom Patent No. 1,115,864 describes a gas cell used to protect a radiation detector against damage from high intensity radiation. The pressure of gas in the cell is such that, at sufficiently high radiation intensity, the gas breaks down into a plasma which scatters and attenuates unwanted radiation. However, such an arrangement provides no improvement in imaging performance in the presence of a dazzling source. It merely provides protection against damage. There is for example a need for a device capable of selectively blocking radiation from a high intensity source, while allowing other radiation from a scene containing such a source to be collected for use in imaging. Optical apparatus having a need for such a device includes television and film cameras, binoculars, night sights, flying helmets, safety goggles and optical instruments incorporating sensitive detectors.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an optical filtering device.
The present invention provides an optical filtering device including dispersing means arranged to provide spatial dispersion as a function of wavelength without substantial angular dispersion, and a stop arranged to provide capability for blocking at least one wavelength interval from at least one direction of radiation incident on the device.
The invention provides the advantage that a radiation wavelength interval from a scene location may be blocked while radiation of other wavelengths from the same scene location remains unblocked. For example, high intensity monochromatic radiation from a localised source such as a laser may be blocked to avoid dazzle or damage.
The invention may include means for forming an image from spatially dispersed radiation from the dispersing means and from which the said at least one wavelength interval has been blocked by the stop. This provides an imaging device capable of removing for example monochromatic sources of dazzle or damage from an imaged scene while retaining capability for producing images of such sources at unblocked wavelengths. An observer may then “look past” a source of dazzling radiation.
The dispersing means may comprise a first dispersing element and a second dispersing element arranged to counteract angular dispersion introduced by the first.
The dispersing elements may be prisms, and may be arranged in combination with reflecting means to define a folded light path.
Alternatively, the dispersing elements may be diffraction gratings arranged in combination with a subsidiary stop to inhibit unwanted radiation reaching the image forming means.
The stop may be an electronically controlled spatial light modulator such as a liquid crystal device arranged for selective addressing of individual pixels. The invention may include image forming means arranged to provide feedback control over obscuration introduced by the stop, as appropriate for selective attenuation of radiation from a monochromatic source producing dazzle in an imaged scene.
The invention may include means for producing an intermediate focus in an optical path between first and second dispersing elements of the dispersing means.


REFERENCES:
patent: 3620597 (1971-11-01), Schwartz et al.
patent: 3623795 (1971-11-01), Taylor et al.
patent: 3751133 (1973-08-01), Nishino
patent: 4007989 (1977-02-01), Wajda
patent: 4497540 (1985-02-01), Breckinridge et al.
patent: 4660975 (1987-04-01), Aughton
patent: 4790654 (1988-12-01), Clarke
patent: 5090807 (1992-02-01), Tai
patent: 5208674 (1993-05-01), Setchell
patent: 5315423 (1994-05-01), Hong
patent: 5442438 (1995-08-01), Batchelder et al.
PARPA—US Army Advanced Laser Protection Program, Mar. 1989, pp. 1-99.

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