Abstract: An optical detector system provides beam positioning data to an optical tracking system to facilitate optical communications. The optical detector system comprises a plurality of optical photodetectors. For example, a two-by-two array may be used. Incoming light passes through one or more optical elements, such as a lens and a dispersive optical element. A first portion of the beam entering the optical elements is directed into a first spot having a first area on the array. A second portion of the beam entering the optical elements is dispersed to form a second spot having a second area on the array that is larger than the first area. This combination of first portion and second portion of the beam incident on the array provides unambiguous information in the output of the photodetectors that is indicative of a position of the incoming beam with respect to the array.

Abstract: An optical detector system provides output to an optical tracking system to facilitate optical communications by tracking a beam of incoming light using a fast-steering mirror (FSM). The optical detector system comprises an array of optical photodetectors, such array comprising one or more quad cells. The incoming light passes through one or more optical elements to generate a specified beam shape, such as a bar or cross, on the array. The resulting output from the array is highly responsive to changes in position of the reshaped beam on the array. As a result, noise equivalent angle (NEA) of the optical detector system representing pointing error is substantially reduced. A reduction in NEA facilitates more precise alignment, allowing incoming light to be aligned to a smaller area. For example, the incoming light may be aligned to a single mode optical fiber connected to a receiver system.

Abstract: Light is modulated at a source to encode data. An additional tracking signal is imposed on the light using polarization modulation (PM). PM modulates one or more values of polarization rotation or polarization ellipticity of the light. These values may be dithered within constraints to provide a specified modulation index at the optical receiver, without impairing the encoded data. At the optical receiver, a polarization analyzer is used to recover the tracking signal, converting the polarization modulation to amplitude modulation. For example, after the light passes through the analyzer, an array of optical photodetectors detects the changes in apparent intensity resulting in the interaction between the light and the analyzer that correspond to the tracking signal. Due to a high modulation index, the recovered signal exhibits a high signal to noise ratio (SNR). The high SNR improves a noise equivalent angle, improving tracking performance.

Abstract: A method and system to optimally choose antenna collocation sites in a geographic region for one or more cellular carriers based on a quantified relative measure of site desirability, considering variables such as terrain elevation, ground clutter, RF propagation coverage, proximity to fiber, existing antenna mounting structure load capacity, and market.