Abstract: A free-space optical (FSO) terminal may include a controller and an alignment sensor. The alignment sensor includes a set of detectors. Each detector generates a signal responsive to receiving electromagnetic radiation at a detection surface. The set of detectors includes an inner set of detectors and an outer set of detectors. The detection surfaces of the inner detectors and the outer detectors may be aligned in a plane. The outer set of detectors surround the inner set of detectors (e.g., in the plane) and have larger detection surfaces than the inner set of detectors. During a tracking mode, the controller is configured to adjust an orientation of the FSO terminal based on signals from the inner set of detectors. During an acquisition mode, the controller is configured to adjust the orientation of the FSO terminal based on signals from the outer set of detectors.

Abstract: Methods and systems are described for free space optical communication. An example device may comprise an optical beam separator configured to separate a first optical path into a receiving (Rx) optical path for signals received from free space and a transmitting (Tx) optical path for signals being transmitted into free space. The example device may comprise at least one positioner coupled to one or more of the Rx optical path or the Tx optical path. The example device may comprise a controller configured to control the at least one positioner to adjust one or more of the Rx optical path or the Tx optical path to facilitate communication with a remote communication device via free space.

Abstract: Embodiments relate to a bidirectional free space optical (FSO) communications system. Specifically, data-encoded FSO beams are transmitted and received between two terminals. A transmit (Tx) direction of a beam transmitted from the first terminal is dithered by a beam steering unit (BSU). As the dithered beam is received by the second terminal, the power levels of the beam are measured. The power levels are then encoded in a data-encoded FSO beam transmitted to the first terminal. This allows the first terminal to decode the received FSO beam and determine the power levels. The power levels allow the first terminal to determine Tx direction misalignments and adjust the Tx direction for the Tx beam sent to the second terminal. This process may be repeated to reduce Tx misalignments and may be performed by both terminals such that each terminal sends power level information to the opposite terminal.

Abstract: A free-space optical (FSO) terminal may include a controller and an alignment sensor. The alignment sensor includes a set of detectors. Each detector generates a signal responsive to receiving electromagnetic radiation at a detection surface. The set of detectors includes an inner set of detectors and an outer set of detectors. The detection surfaces of the inner detectors and the outer detectors may be aligned in a plane. The outer set of detectors surround the inner set of detectors (e.g., in the plane) and have larger detection surfaces than the inner set of detectors. During a tracking mode, the controller is configured to adjust an orientation of the FSO terminal based on signals from the inner set of detectors. During an acquisition mode, the controller is configured to adjust the orientation of the FSO terminal based on signals from the outer set of detectors.

Abstract: A local free space optical (FSO) terminal senses an external environment that includes at least two beacons transmitted from a remote FSO terminal. The local terminal is configured to sense the beacons at a frame rate. Each beacon comprises a pulse train with pulses that are transmitted at a pulse rate. The pulse trains are temporally offset relative to each other so that pulses from at least one of the pulse trains do not fall across frame boundaries during sensing, regardless of a temporal location of the frame boundaries. In addition to detecting the at least two beacons, the local terminal is configured to identity the beacon that contains pulses that do not fall across the frame boundaries, and adjust its orientation based on the identified beacon.

Abstract: Embodiments relate to a free space optical (FSO) communications system with a feed-forward control path. A data-encoded FSO beam is transmitted from a local terminal to a remote terminal. The local terminal directs a propagation direction of the FSO beam by a beam steering unit. To reduce pointing errors between the terminals, the FSO communications system includes a feed-forward control path. The control path includes an inertial measurement unit (IMU) that outputs motion data indicative of motion of the local terminal, for example if the local terminal is mounted to a tower that sways. The control path also includes a controller that receives the motion data from the IMU and generates feed-forward control signals for the beam steering unit. The control signals compensate for an effect of the motion of the local terminal on the propagation direction of the FSO beam.

Abstract: Embodiments relate to a bidirectional free space optical (FSO) communications system. Specifically, data-encoded FSO beams are transmitted and received between two terminals. A transmit (Tx) direction of a beam transmitted from the first terminal is dithered by a beam steering unit (BSU). As the dithered beam is received by the second terminal, the power levels of the beam are measured. The power levels are then encoded in a data-encoded FSO beam transmitted to the first terminal. This allows the first terminal to decode the received FSO beam and determine the power levels. The power levels allow the first terminal to determine Tx direction misalignments and adjust the Tx direction for the Tx beam sent to the second terminal. This process may be repeated to reduce Tx misalignments and may be performed by both terminals such that each terminal sends power level information to the opposite terminal.

Abstract: Embodiments relate to a free space optical (FSO) communications system with a feed-forward control path. A data-encoded FSO beam is transmitted from a local terminal to a remote terminal. The local terminal directs a propagation direction of the FSO beam by a beam steering unit. To reduce pointing errors between the terminals, the FSO communications system includes a feed-forward control path. The control path includes an inertial measurement unit (IMU) that outputs motion data indicative of motion of the local terminal, for example if the local terminal is mounted to a tower that sways. The control path also includes a controller that receives the motion data from the IMU and generates feed-forward control signals for the beam steering unit. The control signals compensate for an effect of the motion of the local terminal on the propagation direction of the FSO beam.

Abstract: Embodiments relate to a bidirectional free space optical (FSO) communications system. Specifically, data-encoded FSO beams are transmitted and received between two terminals. A transmit (Tx) direction of a beam transmitted from the first terminal is dithered by a beam steering unit (BSU). As the dithered beam is received by the second terminal, the power levels of the beam are measured. The power levels are then encoded in a data-encoded FSO beam transmitted to the first terminal. This allows the first terminal to decode the received FSO beam and determine the power levels. The power levels allow the first terminal to determine Tx direction misalignments and adjust the Tx direction for the Tx beam sent to the second terminal. This process may be repeated to reduce Tx misalignments and may be performed by both terminals such that each terminal sends power level information to the opposite terminal.

Abstract: Embodiments relate to a bidirectional free space optical (FSO) communications system. Specifically, data-encoded FSO beams are transmitted and received between two terminals. A transmit (Tx) direction of a beam transmitted from the first terminal is dithered by a beam steering unit (BSU). As the dithered beam is received by the second terminal, the power levels of the beam are measured. The power levels are then encoded in a data-encoded FSO beam transmitted to the first terminal. This allows the first terminal to decode the received FSO beam and determine the power levels. The power levels allow the first terminal to determine Tx direction misalignments and adjust the Tx direction for the Tx beam sent to the second terminal. This process may be repeated to reduce Tx misalignments and may be performed by both terminals such that each terminal sends power level information to the opposite terminal.

Abstract: Exemplary embodiments described herein include a bi-directional Free Space Optical (FSO) communication unit that may be used in a multi-node FSO communication system. The bi-directional FSO unit may include a co-boresighted optical unit such that received and transmitted beams are coincident through a common aperture. Embodiments described herein may be used to correct or accommodate the alignment errors of the received and transmitted beams.

Abstract: Exemplary embodiments described herein include a bi-directional Free Space Optical (FSO) communication unit that may be used in a multi-node FSO communication system. The bi-directional FSO unit may include a co-boresighted optical unit such that received and transmitted beams are coincident through a common aperture. Embodiments described herein may be used to correct or accommodate the alignment errors of the received and transmitted beams.

Abstract: Exemplary embodiments described herein include a bi-directional Free Space Optical (FSO) communication unit that may be used in a multi-node FSO communication system. The bi-directional FSO unit may include a co-boresighted optical unit such that received and transmitted beams are coincident through a common aperture. Embodiments described herein may be used to correct or accommodate the alignment errors of the received and transmitted beams.

Abstract: Exemplary embodiments described herein include a bi-directional Free Space Optical (FSO) communication unit that may be used in a multi-node FSO communication system. The bi-directional FSO unit may include a co-boresighted optical unit such that received and transmitted beams are coincident through a common aperture. Embodiments described herein may be used to correct or accommodate the alignment errors of the received and transmitted beams.

Abstract: A mirror drive mechanism for a tilting mirror is controlled using feedback from one or more interferometric angular sensors. The wavelength of an optical beam is varied as it is fed into an interferometric angular sensor. The wavelength at which the resulting interference pattern is measured to be at a minimum intensity is determined. This wavelength is used to determine a distance quantity representative of the angular position of the mirror.

Abstract: Apparatus and methods are provided for driving a two-axis MEMS mirror using three non-contact actuation elements or electrodes. A differential bi-directional mirror control uses unipolar drive voltages biased at a suitable value. Transformation functions map two-axis tip-tilt commands to three actuation drive signals for selected electrode orientations and sizes.

Abstract: Methods and apparatus are provided for the closed loop attenuation of optical beam power in a multiple-axis free-space-coupled single-mode fiber-optic transmission system. In a specific embodiment involving two tip-tilt mirrors to couple optical power from an input fiber to an output fiber, the four mirror axes arc actuated in such a way as to produce either a static or time-varying set of induced mirror angles that yield a desired time history of optical loss. The attenuation technique uses the DC level of the measured output power to adjust the amplitude of the induced mirror angles.

Abstract: Methods and apparatus are provided for the closed loop attenuation of optical beam power in a multiple-axis free-space-coupled single-mode fiber-optic transmission system. In a specific embodiment involving two tip-tilt mirrors to couple optical power from an input fiber to an output fiber, the four mirror axes are actuated in such a way as to produce either a static or time-varying set of induced mirror angles that yield a desired time history of optical loss. The attenuation technique uses the DC level of the measured output power to adjust the amplitude of the induced mirror angles.

Abstract: Apparatus and methods are provided for driving a two-axis MEMS mirror using three non-contact actuation elements or electrodes. A differential bi-directional mirror control uses unipolar drive voltages biased at a suitable value. Transformation functions map two-axis tip-tilt commands to three actuation drive signals for selected electrode orientations and sizes.

Abstract: Methods and apparatus are provided for detection and control of multiple-axis active alignment for a free-space-coupled single-mode fiber-optic transmission system that automatically optimizes the coupling through the system. In a specific embodiment, a measurement of coupled power is made and error signals are used to control actuation via four axes of beam steering elements to null four generally orthogonal alignment errors (combinations of two lateral errors and two angular errors) of the beam between the input and output fibers. The four alignment errors are detected using a synchronous-detection approach. A feedback control system nulls the four errors.