Optical deep space communication via relay satellite

The possible use of an optical for high rate data transmission from a deep space vehicle to an Earth-orbiting relay satellite while RF links are envisioned for the relay to Earth link was studied. A preliminary link analysis is presented for initial sizing of optical components and power levels, in terms of achievable data rates and feasible range distances. Modulation formats are restricted to pulsed laser operation, involving bot coded and uncoded schemes. The advantage of an optical link over present RF deep space link capabilities is shown. The problems of acquisition, pointing and tracking with narrow optical beams are presented and discussed. Mathematical models of beam trackers are derived, aiding in the design of such systems for minimizing beam pointing errors. The expected orbital geometry between spacecraft and relay satellite, and its impact on beam pointing dynamics are discussed

Poisson noise channel with dark current: Numerical computation of the optimal input distribution

This paper considers a discrete time-Poisson noise channel which is used to model pulse-amplitude modulated optical communication with a direct-detection receiver. The goal of this paper is to obtain insights into the capacity and the structure of the capacity-achieving distribution for the channel under the amplitude constraint $\mathsf{A}$ and in the presence of dark current $\lambda$. Using recent theoretical progress on the structure of the capacity-achieving distribution, this paper develops a numerical algorithm, based on the gradient ascent and Blahut-Arimoto algorithms, for computing the capacity and the capacity-achieving distribution. The algorithm is used to perform extensive numerical simulations for various regimes of $\mathsf{A}$ and $\lambda$.Comment: Submitted to IEEE ICC 2022. This is a companion paper of: A. Dytso, L. Barletta and S. Shamai Shitz, "Properties of the Support of the Capacity-Achieving Distribution of the Amplitude-Constrained Poisson Noise Channel," in IEEE Transactions on Information Theory, vol. 67, no. 11, pp. 7050-7066, Nov. 202

Silicon Photomultiplier Research and Development Studies for the Large Size Telescope of the Cherenkov Telescope Array

The Cherenkov Telescope Array (CTA) is the the next generation facility of imaging atmospheric Cherenkov telescopes; two sites will cover both hemispheres. CTA will reach unprecedented sensitivity, energy and angular resolution in very-high-energy gamma-ray astronomy. Each CTA array will include four Large Size Telescopes (LSTs), designed to cover the low-energy range of the CTA sensitivity ($\sim$20 GeV to 200 GeV). In the baseline LST design, the focal-plane camera will be instrumented with 265 photodetector clusters; each will include seven photomultiplier tubes (PMTs), with an entrance window of 1.5 inches in diameter. The PMT design is based on mature and reliable technology. Recently, silicon photomultipliers (SiPMs) are emerging as a competitor. Currently, SiPMs have advantages (e.g. lower operating voltage and tolerance to high illumination levels) and disadvantages (e.g. higher capacitance and cross talk rates), but this technology is still young and rapidly evolving. SiPM technology has a strong potential to become superior to the PMT one in terms of photon detection efficiency and price per square mm of detector area. While the advantage of SiPMs has been proven for high-density, small size cameras, it is yet to be demonstrated for large area cameras such as the one of the LST. We are working to develop a SiPM-based module for the LST camera, in view of a possible camera upgrade. We will describe the solutions we are exploring in order to balance a competitive performance with a minimal impact on the overall LST camera design.Comment: 8 pages, 5 figures. In Proceedings of the 34th International Cosmic Ray Conference (ICRC2015), The Hague, The Netherlands. All CTA contributions at arXiv:1508.0589

Space station tracking requirements feasibility study, volume 2

The objective of this feasibility study is to determine analytically the accuracies of various sensors being considered as candidates for Space Station use. Specifically, the studies were performed whether or not the candidate sensors are capable of providing the required accuracy, or if alternate sensor approaches should be investigated. Other topics related to operation in the Space Station environment were considered as directed by NASA-JSC. The following topics are addressed: (1) Space Station GPS; (2) Space Station Radar; (3) Docking Sensors; (4) Space Station Link Analysis; (5) Antenna Switching, Power Control, and AGC Functions for Multiple Access; (6) Multichannel Modems; (7) FTS/EVA Emergency Shutdown; (8) Space Station Information Systems Coding; (9) Wanderer Study; and (10) Optical Communications System Analysis. Brief overviews of the abovementioned topics are given. Wherever applicable, the appropriate appendices provide detailed technical analysis. The report is presented in two volumes. This is Volume 2, containing Appendices K through U

Wavelength Drift in CWDM Systems: Impact and Measurement

The research begins with an investigation of wavelength drift in Coarse Wavelength Division Multiplexing (CWDM) systems, especially in the context of temperature dependent wavelength drift. A simple model was proposed using a typical ‘application’ from ITU-T G.695. OptiSystem was chosen as the simulation platform due to its ease of use, the variety and flexibility of its inbuilt components and similar models simulated on the platform in the past. The research then investigates the measurement of wavelength drift focusing on how to determine an acceptable wavelength accuracy for a CWDM wavelength monitor. The chosen approach arose from observations of the results from a model of how wavelength drift impacts the most important system parameter in CWDM systems, which is error performance. The statistical confidence levels of Bit Error Ratio (BER) measurements taken by typical industry test and measurement equipment was considered and their statistical worst case BER results were calculated. An argument is made equating wavelength drift to an equivalent degradation of a links BER. Using the model developed a minimum wavelength accuracy of 0.1365 nm for the CWDM wavelength monitor was calculated. Following a survey of instruments marketed to the CWDM industry, a set of attributes that are representative of the different types of instruments available was made. These attributes were categorised into parameters and features. Each parameter and feature was considered in the context of a wavelength monitor for use in CWDM systems with a subsequent reclassification of the attributes into ‘essential features’ and ‘key parameters’, hence the attributes of a CWDM wavelength monitor were specified. An in-depth investigation of wavelength measurement operating principles was carried out with the aim of identifying a suitable technology to implement a CWDM wavelength monitor. The ratiometric wavelength measurement operating principle was chosen to implement a proof of principle CWDM wavelength monitor as it offers the best potential to meet the required specification with a least complex solution. The ratiometric wavelength measurement operating principle was discussed in more detail followed by an investigation of the maximum discrimination of the optical filter used in this technique. The limits on the maximum discrimination of the optical filter due to an optical sources wideband noise were then modelled with a proof of principle experiment carried out to validate the model