Optical: systems and elements – Having significant infrared or ultraviolet property
Reexamination Certificate
1994-11-16
2001-01-30
Schuberg, Darren (Department: 2872)
Optical: systems and elements
Having significant infrared or ultraviolet property
C359S359000, C250S226000, C427S154000
Reexamination Certificate
active
06181468
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates to infrared windows and, more particularly, to fabrication of composite infrared windows by direct bonding.
2. Discussion
Conventional infrared (IR) windows for airborne applications lack high-speed sand and rain impact durability and, as a result, experience cumulative surface and subsurface damage which results in large optical transmittance loss. Repair or replacement of the IR window is expensive and time consuming.
Conventional IR windows rely primarily on two approaches to harden an outer surface thereof against high-speed rain and sand impact. In a first approach, a protective coating, for example boron phosphide (BP) or gallium phosphide (GaP), is deposited on top of an IR substrate. Although the protective coating substantially improves the durability of the IR window, cumulative damage still occurs both in the protective coating as well as in the IR substrate. Repair of IR windows fabricated according to the first approach is expensive and time consuming due to the difficulty of removing the protective coating completely and the need to repolish and recoat the IR substrate.
According to a second approach, a protective layer is bonded to an IR substrate using an adhesive to form the IR window. For example, a chalocogenide glass bonds a diamond film to a zinc sulfide (ZnS) substrate. Alternately, an organic polymer adhesive bonds a diamond film to a germanium (Ge) substrate. However, the intermediate bonding layer must satisfy stringent optical, thermal and mechanical requirements. Furthermore, it is difficult to remove the bonding material completely when replacement of the protective layer is required due to high-speed rain and sand impact. In addition, chalcogenide glasses are extremely toxic and difficult to handle during fabrication.
Therefore, an IR window which provides improved high-speed sand and rain impact durability and which can be repaired easily and at low cost would be desirable.
SUMMARY OF THE INVENTION
A method of fabricating an infrared (IR) window which has high optical transmittance at IR frequencies includes the steps of providing a protective layer having a high IR transmittance and an IR substrate having a high IR transmittance. An inner surface of the protective layer and an outer surface of the IR substrate are contacted without adhesive therebetween. The protective layer and the IR substrate are annealed at a bonding temperature.
According to another feature of the invention, particles are removed from at least one of the inner surface of the protective layer and the outer surface of the IR substrate to ensure good bonding.
According to still another feature of the invention, an anti-reflection coating is applied to an outer surface of the protective layer and an anti-reflective coating is applied to an inner surface of the IR substrate.
According to still another feature of the invention, the IR window is installed as a shield for an IR sensor used in a harsh environment. The IR window and IR sensor can be mounted on an aircraft.
According to yet: another feature of the invention, the protective layer is replaced when cumulative surface damage has occurred. The IR window is removed from the aircraft. The protective layer and the IR substrate are debonded by heating the IR window above the bonding temperature. The protective layer and the IR substrate are separated. A new protective layer is provided. An inner surface of the new protective layer and an outer surface of the IR substrate are contacted at ambient temperature without adhesive therebetween. The new protective layer and the IR substrate are then annealed at a bonding temperature.
According to yet another feature of the invention, an infrared (IR) window according to the invention has a high transmittance at IR frequencies and includes a protective IR-transparent layer directly bonded to an IR-transparent substrate without adhesive therebetween.
According to another feature of the invention, particulates are removed from at least one of an inner surface of the protective IR-transparent layer and an outer surface of the IR-transparent before the IR transparent layer and the IR-transparent substrate are connected together.
Still other objects, features and advantages will be readily apparent.
REFERENCES:
patent: 4311743 (1982-01-01), Kasper et al.
patent: 4778731 (1988-10-01), Kraatz et al.
patent: 5007689 (1991-04-01), Kelly et al.
patent: 5067781 (1991-11-01), Montanari et al.
patent: 5120602 (1992-06-01), Tustison et al.
patent: 5194985 (1993-03-01), Hilton, Sr.
patent: 5441803 (1995-08-01), Meissner
Askinazi Joel
Feng Tom
Lenzen, Jr. Glenn H.
Raytheon Company
Schuberg Darren
Schubert William C.
LandOfFree
Composite infrared windows fabricated by direct bonding does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Composite infrared windows fabricated by direct bonding, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Composite infrared windows fabricated by direct bonding will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2462151