Optics: measuring and testing – Angle measuring or angular axial alignment – With photodetection remote from measured angle
Reexamination Certificate
2002-03-14
2004-07-20
Buczinski, Stephen C. (Department: 3662)
Optics: measuring and testing
Angle measuring or angular axial alignment
With photodetection remote from measured angle
C250S342000, C356S153000
Reexamination Certificate
active
06765663
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates to lasers. Specifically, the present invention relates to bipolar semiconductor laser and quantum cascade laser boresight sources and accompanying systems and methods for aligning and stabilizing components in targeting, imaging, and sensing applications.
2. Description of the Related Art
Boresight sources and accompanying boresight alignment mechanisms are employed in various demanding applications including imaging, chemical analysis, and military targeting, surveillance, and reconnaissance systems. Such systems often require precise alignment of multiple constituent sensor components to ensure accurate handover of sensing function from one sensor to another or to facilitate multi-sensor data integration or fusion.
Precise system component alignment is particularly important in multi-spectral electro-optical systems employing multiple sensors sharing a common aperture. Multi-spectral systems may have different sensor types, such as infrared thermal imagers and visible color television cameras that detect different frequencies of electromagnetic energy.
An exemplary electro-optical system sensor suite includes a laser transceiver, a visible camera, and an infrared imager. The laser transceiver transmits a laser beam toward a scene. The scene reflects the beam, which is detected by the transceiver. The transceiver includes electronics and may include software to measure the round trip delay between transmission and reception of the beam and thereby determine the distance to a specific location within the scene, which may be a target.
The infrared imager detects thermal energy emanating from the scene. Electronics within the infrared imager convert received thermal energy into an image. Similarly, the visible camera receives visible-band electromagnetic energy reflected from the scene and generates a corresponding image. The infrared and visible images may be combined with laser range information to facilitate targeting or sensing. Generally, the center of the received reflected laser beam should coincide with the center or aimpoint of the infrared and visible images for accurate targeting.
The primary non-common path disturbances that cause boresight misalignments between the sensing elements, typically result from shock, vibration, and thermal displacements that warp the structure on which the different sensors are mounted. In some cases, one sensor may be located on a different gimbal with one or more rotational degrees of freedom relative to the other sensor(s). In this case, gimbal bearing runout and gimbal axis non-orthogonality also cause boresight misalignment. Due to their physical size and their complex power/thermal interface requirements, laser transceivers are often located on a different gimbal location than the other sensors. Atmospheric disturbances are common to all sensing elements in a shared-aperture system (ignoring the effects of dispersion in the atmosphere where different wavelengths refract at different angles).
When boresighting a visible or infrared sensor, the sensor is typically aligned with the axis of the range-finding laser beam. A boresight reference source provides a reference beam that is rigidly aligned relative to the range-finding laser and generates a spot on the sensor. The difference between location or the spot on the sensor and the fiducial aimpoint of the sensor represents the amount by which the sensor is misaligned relative to the range-finding laser.
Conventionally, the boresight sources in targeting and sensing systems are blackbody or diode laser sources. A blackbody source emits a beam having a broad spectrum of electromagnetic energy including infrared, visible, and ultraviolet components. The spectral radiance of the blackbody source is determined by temperature of the radiating element, the hotter the element, the more the output spectrum is shifted from the infrared region of the electromagnetic spectrum toward the visible and ultraviolet regions. The reference beam may be physically aligned with the range-finding laser beam and may be directed to create a spot on the detecting surface of an infrared imager, visible camera, and/or other sensor simulating the far-field location of the range-finding laser beam within the scene. The position of each spot corresponds to the aimpoint or preferred center of the infrared and visible camera images, respectively. When the infrared imager or visible camera becomes misaligned, the spot moves on the detecting surface of the infrared imager or visible camera.
To compensate for misalignments when a computer-generated fiducial is used by the system to designate the sensor's aimpoint, software associated with the infrared imager and the visible camera may adjust the stored aimpoint for these sensors to coincide with the energy centers of their respective reference spots or may electronically shift the images that are displayed to an operator. Alternatively, the aimpoint for the infrared imager and visible camera may be adjusted manually via cursor control on a display monitor.
To compensate for misalignments when a particular sensor uses a fixed reticule to designate the aimpoint, software may command a servo mechanism to physically move the sensor line of sight (LOS) such that the reference spot is aligned with reticule aimpoint symbology or cross hairs. Alternatively, the sensor line of sight may be adjusted manually through a control interface, such as a pair of adjustment knobs, which allows the operator to center the reference spot over the reticule aimpoint symbology.
Unfortunately, conventional thermal blackbody boresight sources are often undesirably bulky, relatively dim, highly divergent, not well matched to sensor passbands, require excess operating power, require bulky and expensive collection or projection optics, require undesirably lengthy warm-up times, and emit excess heat. The hot blackbody sources used with visible cameras typically operate between 900 and 1000° C. and must be isolated from critical alignment structures via costly design features to prevent thermal component deformation and associated beam misalignments. The low brightness of blackbody sources and their poor match to specific sensor passbands result in low-contrast spots at the sensor under high ambient lighting conditions, making it difficult or impossible to align the sensor without having to block the scene imagery. The low brightness of blackbody sources may make them unsuitable for use with otherwise desirable high angular resolution sensors, such as low-sensitivity, two-dimensional contiguous photoresistive detectors, called photo-potentiometers or photopots. Photopots are typically less susceptible to problems caused by spot shape nonuniformities than quadrant or quad-cell detectors.
Structural features of the blackbody source may further reduce the source output power. For example, a pinhole may be provided in a light-shield container surrounding the blackbody source to define and limit the size of the spot. The pinhole vignettes much blackbody radiation, making the overall source very inefficient and substantially reducing the optical signal before it reaches the sensors.
The blackbody sources, such as wire-wound ceramic sources as disclosed in U.S. Pat. No. 5,479,025, entitled BORESIGHT THERMAL REFERENCE SOURCE, herein incorporated by reference, produce uncollimated radiation, which must be collimated via expensive optics. To provide adequate signal at the boresight sensors (especially when the primary imaging sensors are themselves used for direct boresighting), a full-aperture optical system may be needed to collect and collimate the blackbody radiation. For example, some sensor suites require a pair of full-aperture reflective off-axis aspheric elements in the collimation system, which are expensive, difficult to align, and may employ expensive full-aperture beamsplitter components.
As an alternative to the blackbody sources, some targeting, imaging, and sensing systems employ one or more semiconductor diode laser
Arnn Edward L.
Byren Robert W.
Buczinski Stephen C.
Gunther John E.
Lenzen, Jr. Glenn H.
Raufer Colin M.
Raytheon Company
LandOfFree
Efficient multiple emitter boresight reference source does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Efficient multiple emitter boresight reference source, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Efficient multiple emitter boresight reference source will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3222707