Next-generation radio telescopes, such as the Square Kilometre Array (SKA) and Next Generation Very Large Array (ngVLA), require precise microwave frequency reference signals to be transmitted over fiber links to each dish to coherently sample astronomical signals. Such telescopes employ phase stabilization systems to suppress the phase noise imparted on the reference signals by environmental perturbations on the links; however, the stabilization systems are bandwidth limited by the round-trip time of light traveling on the fiber links. A phase-locked receiver module (RM) is employed on each dish to suppress residual phase noise outside the round-trip bandwidth. The SKA RM must deliver a 3.96-GHz output signal with 4 MHz of tuning range and <100 fs of timing jitter. We present an RM architecture to meet both requirements. Analytical modeling of the RM predicts 30 fs of output jitter when the reference signal is integrated between 1 Hz and 2.8 GHz. The proposed RM was conceived with best practice electromagnetic compatibility in mind and to meet size, weight, and power requirements for the SKA dish indexer. As the ngVLA reference design also incorporates a round-trip phase stabilization system, this RM may be applicable to future ngVLA design.
Optical phased arrays (OPAs) are a solid-state device able to manipulate the distribution of optical power without the use of mechanical beam steering systems and have potential applications in free-space laser communications, target acquisition and tracking, and interferometry. Here we present a scalable OPA and digital control architecture capable of steering a laser beam at MHz frequencies, and having arbitrary control over the beam wavefront.
We present the preliminary design and experimental results of a 1550 nm solid-state beam pointing system based on an optical phased array (OPA) architecture. OPAs manipulate the distribution of optical power in the far-field by controlling the phase of individual emitters in an array. This allows OPAs to steer the beam in the far field without any mechanical components (e.g., steering mirrors). The beam-steering system presented here uses waveguide electro-optic modulators to actuate the phase of each element in a 7-emitter OPA, enabling kHz bandwidth steering with sub-milliradian pointing precision. The control system used to stabilize and control the phase of each emitter in the OPA exploits a technique called digitally enhanced heterodyne interferometry, allowing the phase of each emitter to be measured simultaneously at a single photodetector, dramatically simplifying the optical system. All digital signal processing is performed using a field-programmable gate-array. Applications of this technology include free-space link acquisition and tracking for satellite-to-satellite laser communications and light detection and ranging (LiDAR).