Bae Systems Information and Electronic Systems Integration Inc.

Other

Robert T Carlson

David A Haessig, Jr

Dennis P Bowler

Dale A Rickard

Mark C Janelle

Daniel J Creeden

Michael J Powers

Ian B Murray

Martin F Ryba

Amod V Dandawate

Steven G Santee

Clifford D Caseley

David C Donarski

Forrest C Vatter

Stuart M Lopata

An optical bench utilizing narrowband optical filters on precision rotary stages that can provide custom tuning of the operational frequencies of the optical bench while maintaining the ability to switch between narrowband and wideband operation thereof. The precision rotary filters may further provide dynamic reconfiguration of the optical bench to alternate frequencies for intersystem compatibility, the enablement of additional self-test capabilities, and easing the manufacturing tolerances thereof.

Frequency and bandwidth agile optical bench

A continuously adjustable optical beam splitter includes a circular to linear polarization converter, a polarization rotator, and a polarization beam splitter that apportions light between two outputs. The polarization converter can include a quarter wave plate. The polarization rotator can include a mechanically rotated half wave plate or an electronically controlled liquid crystal variable retarder. The light source can be astronomical, reflected LIDAR light, or a laser beam from a remote laser communication node. Also disclosed is a free space laser communication terminal that implements the disclosed optical beam splitter, wherein the optical beam splitter diverts substantially all received laser light to an alignment channel during initial alignment, and then during message communication diverts more than 90%, and in embodiments up to 98%, of the received light to a communication channel, while alignment is maintained by continuing to divert the remaining laser light to the alignment channel.

Continuously variable optical beam splitter

A co-boresight refractive beam director for a full duplex laser communication terminal includes a chromatic beam steering element, such as a two or three prism Risley prism assembly, and a dispersion compensation mechanism (DCM) inserted in either the transmit or receive path. The DCM adjusts a beam direction of either the transmit or receive laser beam to compensate for a pointing difference introduced by the beam steering element due to a difference between the transmit and receive wavelengths. The DCM can include a tip/tilt mirror and actuator, which can be a commercially available FSM assembly. The beam steering element can be temperature stabilized. Position feedback sensors can increase DCM speed and accuracy. The pointing difference can be calculated and/or interpolated from a pre-established look-up table or fitted curve relating pointing differences to transmit and receive frequencies and the pointing direction of the beam steering element.

Refractive laser communication beam director with dispersion compensation

A laser communication architecture provides precise optical alignment between terminals without requiring dedicated beacon lasers or dedicated beacon wavelength optics. Instead, the same lasers and optics are used for both alignment and communication. A beacon modulation is applied to alignment beacons transmitted at or near communication wavelengths so as to differentiate them from communication beams. The beacon modulation can include phase and/or amplitude variation of a high frequency modulation, and/or 'ping-pong' toggling of the beacon wavelength. In some full duplex red/blue embodiments, ping-pong modulation is implemented by alternated red/blue tuning of the transmit laser or by switching between separate red and blue transmit lasers, for example using a 2&#xd7;1 laser switch, while maintaining constant beacon amplitude, thereby avoiding optical amplifier dynamic response issues. During communication, embodiments maintain optical alignment by diverting a percentage of received communication light to the tracking sensor.

Full duplex laser communication terminal architecture without dedicated beacon laser

A full duplex dual red/blue wavelength communication architecture and method provides enhanced network configuration flexibility by enabling terminal switching between red and blue configurations, thereby enabling wavelength reconfiguration within the network on command while the terminal is in the field, airborne, or on orbit. A transmit laser module includes separate 'red' and 'blue' linear polarized lasers, or a single linear polarized laser tunable from red to blue. The transmit/receive diplexer uses a linear polarized beam splitter and a waveplate to transition the output beam between left and right circular polarization without affecting precision pointing, or co-boresight transmit/receive alignment. Waveplate polarization can be switched by physical rotation, or electrically using a liquid crystal variable retarder (LCVR). Red and blue bandpass filters can be selected in the receiver and/or transmitter by physical manipulation, optical switches, DWDM 3-port filters, and/or LCVRs. Two-laser embodiments can include a retroreflector for receiver optics self-calibration.

Full duplex laser communication terminal architecture with reconfigurable wavelengths

A Cassegrain telescope design consists of a silicon primary mirror bonded into a silicon-carbide (SiC) telescope metering tube. A secondary mirror is bonded directly to the telescope window. The window sits in a SiC bezel that is bonded to the SiC telescope tube. A graphite snout is bonded to the rear of the primary mirror and extends forward into the telescope. The snout incorporates a field stop that blocks stray light and sources outside the acquisition field of view (FOV). A lens cell threads into the snout and holds two lenses that collimate the light exiting that end of the telescope.

Athermal cassegrain telescope

A lasercom coefficient of thermal expansion (CTE)-matched optical bench, with optional star-tracker capability, that includes a Transmitter (TX) fiber collimator creating a Gaussian beam from a singlemode (SM) or polarization maintaining (PM) fiber; a tiltball directly bonded to the optical bench, the tiltball performing centration of a TX beam with a telescope optical axis; a TX beam diverger creating a wide beam for acquisition, and a narrow beam for tracking and communications; a Point-Ahead Mechanism/mirror; a polarization diplexer cube or dichroic filter(s) separating TX and Receiver (RX) beams of opposite polarization and/or different wavelengths, wherein the polarization or dichroic and anti-reflective coatings are compatible with the adjunct star tracker; a fast-steering mechanism and mirror having a common-path to TX and RX; a RX optical passband filter; the RX optical passband filter having a flipper mechanism allowing for selecting the passband of the star-tracker or the RX passband.

Space lasercom optical bench

A flexible TOF processing block having power measurement circuitry comprising separate modules that can be modified using parameterizable registers, without complete reconstruction, allows development to continue while the overall design is optimized.

Flexible design for a tunable optical filter (TOF) processing block

A nutation controller and methods of use correct for the small, fixed offset inherent in laser communication systems referred to as pointing bias error, thereby removing the pointing bias error and allowing for more robust and rapid laser communications between distant platforms.

Pointing control with fiber nutation

The Quad Cell permits measurement of four quadrant signal powers simultaneously, metrics which are equal when the laser spot is at the desired zero location, at the center of the cell, the origin of the cells' axes. A control action acts upon the Quad Cell signals to move the laser spot toward the origin of the axes bisecting the four quadrants of the cell, moving the laser spot to the origin to achieve a null in the difference between these four signal levels.

Acquisition and pointing device, system, and method using quad cell

A disclosed apparatus and method verify whether a hot spot within a scene is a valid laser-com signal, and further identify laser-com signals of interest. An extended Kalman filter (EKF) is applied to a received signal or beacon to detect whether it is modulated according to a square wave or other expected amplitude modulation pattern. Embodiments further determine whether the modulation frequency matches a signal or beacon of interest. In embodiments, a plurality of indexed EKF's are 'tuned' to different modulation frequencies, and are used to identify a beacon's modulation frequency index. Where each EKF is required to compute amplitude and phase partial derivatives of the observation vector, the amplitude partials can be calculated according to the expected modulation pattern, and the phase partials can be calculated using a truncated Fourier or step-wise approximation of the expected modulation pattern. Embodiments further assume a time-invariant covariance matrix.

Apparatus and method for rapid identification of laser communication beacons

A disclosed apparatus and method detect light source 'hotspots' and recognize laser communication signals within a scene, while minimizing repeat consideration of previously detected light sources. Local maxima are identified in pixel frames from a focal plane array (FPA), and compared with a table of previous detections. FPA frames can be used directly for hotspot detection, or successive FPA frames can be subtracted for edge detection. Most recent detection frame numbers, coordinates, signal values, and/or other information can be updated in the table upon repeat detection of a hotspot. Source identifying information can be included in the table for entries that are identified as laser communication signals. Source identifying features can be evaluated so that only signals of interest are saved in the table. Hotspots that remain undetected after a designated number of frames can be deleted from the table.

Apparatus and method for rapid identification of candidate laser communication beacons

An apparatus and method for tracking a laser communication signal of interest incident on a focal plane array (FPA) identifies a plurality of 'hotspots' in a scene of interest, and aligns a hotspot that is a signal of interest (SOI) or beacon component thereof with the FPA. Hotspot centroids can be estimated within a fraction of an FPA pixel by considering squares of four pixels and comparing their signal amplitudes. A multi-spot calculation is used to improve the position estimates of all of the hotspots by applying a Kalman filter to the hotspot position data and assuming that the relative hotspots positions are fixed. The calculation is periodically repeated to enable tracking of the SOI. Amplitude variability of the hotspots is accommodated by weighting the hotspot contributions according to their intensities. In embodiments, estimation error of the SOI centroid is less than a smallest dimension of the FPA pixels.

A laser communication system its integrated microradian-accuracy Acquisition and Tracking Sensor (ATS) to perform a celestial navigation fix to determine the attitude of the laser communications payload, including the integrated ATS and the co-boresighted laser beam, prior to establishing a laser communication link with a second vehicle such as a high-altitude aircraft or satellite. The laser communication system may use a legacy platform INS to initially point its narrow FOV ATS at one or more stars to obtain the vehicle's attitude therefrom. Then the precision payload attitude determined with the ATS star tracker fix is used to point the co-boresighted laser beam to establish a laser communications link with the second vehicle.

Celestial navigation using laser communication system

In the method for processing a signal light from free-space by amplifying said signal for free-space optical communications, wherein the improvement includes the steps of (a) pre-amplifying said signal light with low noise; and (b) coupling said signal light into a multimode filter which reduces coupling losses compared to single mode filters.

Growing community of inventors

Bedford, NH, United States of America

Robert T Carlson