This PDF file contains the front matter associated with SPIE Proceedings Volume 11993, including the Title Page, Copyright information, Table of Contents, and Conference Committee listings.

Current CubeSat Laser Communications relies on spacecraft body pointing with thrusters or reaction wheels, resulting in mediocre laser beam pointing accuracy. To increase the laser beam pointing accuracy, active acquisition and tracking of the beam from the counter terminal should be performed. Conventional FSMs (fast steering mirrors) and FPAs (focal plane arrays) are too large to be incorporated into CubeSats, which are inherently constrained by low SWaP (Size, Weight, and Power) limits. In this paper, we present a patent pending method and reference design that implements both acquisition and tracking functions using a MEMS (Micro-Electro-Mechanical-System) FSM and quad detector. Our design fits within 1U (10 cm x 10 cm x 10 cm) with a 6.4 mm diameter MEMS FSM and 1 mm quad detector. Replacing the FPA (that typically performs the acquisition function) enables minimization of SWaP in the laser communication terminal design, which is crucial in CubeSat laser communications. The prototype was designed such that it has an acquisition fieldof-view of 2 deg and tracking field-of-view of 0.5 deg. The acquisition time is measured to be less than 60 seconds, with a probability of acquisition success > 99%.

BridgeComm has worked to advance the capabilities of the Managed Optical Communications Array (MOCA) technology for application to a broad set of use cases and environments. This advancement includes raising technology readiness level to TRL 6 and above and tailoring developments for a specific sets of applications such as optical intersatellite links, space to airborne communications and vehicular communications on the move. The key elements in the design of the optical terminal will be discussed. The ability to steer the beam through a wide field of regard without the use of mechanical gimbals has been demonstrated and will be presented. That design enables the ability to move the optical beam between multiple elements quickly using time division multiple access (TDMA) techniques and support a multitude of end users with a high data rate, dynamically reconfigurable communications network. Analysis of a specific application environment will be reviewed, and data presented.

Mitigation of atmospheric turbulence is a major challenge in optical wireless communication, especially for optical feeder links. In this paper, we present a free space optical (FSO) mode diversity receiver, based on a spatial demultiplexer and a silicon photonic coherent combiner to reduce the atmospheric turbulence deleterious effects. We simulate the spatial light distribution in the ground receiver aperture for a use case consisting of a FSO link from a GEO satellite. We then generate experimentally wavefronts corresponding to the spatial light distribution for that use case with a wavefront emulator, and we compare the collection efficiency of the proposed mode diversity receiver with a FSO single mode fiber (SMF) receiver. The proposed FSO receiver outputs a signal much more stable as the system is resilient to energy redistribution among higher order spatial modes.

A key challenge of photon counting optical communication is delivering light with atmospherically distorted wavefronts from the telescope to detectors efficiently. When using fiber coupled single photon detectors, the efficiency of the transmittance is constrained by the modes supported by the fiber. The number of modes supported by a fiber depends on the size of the core. The larger the core, the more modes supported. However, commercial off the shelf superconducting nanowire single photon detectors (SNSPDs) are currently limited in area, which limits the core size of the fibers that can efficiently couple to the detectors. To increase the amount of light that can be delivered to the detectors, NASA Glenn Research Center is considering many different fiber/detector architectures. This paper compares insertion loss of the fiber device for two different architectures: • a multi-plane light conversion device to split the light from a 30 µm core diameter fiber into 7 separate, 15 μm core diameter few-mode fibers butt-coupled to 7 single-element SNSPDs, and • a 30 μm core diameter multimode fiber butt-coupled to a 16 multi-element, SNSPD array. The measured insertion loss for each fiber device under emulated atmospheric conditions with D/r0 between 2 and 30 is presented. The multi-plane light conversion device shows a consistent ~1 dB loss more than the multimode fiber. Also presented is the measured uneven power splitting of the multiplane light conversion device, especially at lower D/r₀. How this uneven power splitting contributes to system loss called blocking loss is discussed.

The development of space-based, free-space optical (FSO) communication systems is exciting for expanding internet connectivity worldwide. These systems will incorporate dense, low-earth constellations with short intersatellite links. Key to the performance of these satellite constellations are flexible architectures that support higher rates via complex modulation formats, with FSO data links varying between 10-100 Gb/s. However, prior efforts have designed custom modems optimized for each link, severely limiting their flexibility. An alternative is to leverage advances developed by the fiber telecom industry which offer high-rate high-sensitivity digital coherent communication systems while minimizing size, weight, and power (SWAP). These low-SWAP systems rely on commercially available microfabricated integrated coherent receivers (μICRs). Here we present data to help qualify a commercially available μICR for a space application; this data was collected through a series of environmental tests. This work thus expands the reach of coherent systems, allowing for the development of low-SWAP space-based FSO communication systems buttressed with commercially available μICRs. We achieved the space qualification of the μICR by monitoring the component’s bandwidth and electrooptical (EO) transfer function as environmental testing conditions were varied. We selected these environmental conditions to simulate a low-Earth orbit. The environmental testing included: (i) irradiation using a cobalt-60 source up to a total ionizing dose of 100 kilorads, extending qualification to all of the commercial orbits; (ii) thermal cycling with survival temperatures ranging from -40 °C to 70 °C and operational temperatures varying between -5 °C and 65 °C with the part cycled between its survival temperature range twice and its operational range an additional ten times over a 7-day period; (iii) vibration testing to 28 GRMS for 180 seconds on each axis; (iv) shock to a maximum of 1201 g; and (v) thermal vacuum testing at ∼ 6.3 × 10⁻⁶ torr. We observed no degradation in device EO performance after environmental testing.

Interleaving is a well-known technique utilizing temporal diversity to mitigate burst errors in a communications link. Interleaving provides robustness at the physical layer of the network stack, at the expense of an increase in latency. An important parameter used in characterizing interleaver performance is the temporal diversity L, defined as the number of statistically independent fade events experienced by an individual codeword. This temporal diversity L characterizes the interleaver’s ability to whiten a channel so that forward error correction codes designed to mitigate additive white Gaussian noise function effectively. For large values of L, the interleaver is effectively “infinite”, and deeper interleaving produces no additional benefit. As L is decreased, the power penalty grows, and increasingly more average power must be transmitted to ensure error-free decoding at the receiver. Here we investigate interleaver performance in the regime where L is decreasing and the interleaver is not effectively infinite. Our goals are to (1) determine the regime where the interleaver is no longer effectively infinite, and (2) characterize the power penalty as a function of L to understand how the performance degrades as L is reduced. A theoretical model is presented that allows us to investigate interleaver performance in the presence of weak, moderate, and strong turbulence (scintillation indices of 0.2, 0.5, and 1.0, respectively). The model results show a gradual increase in penalty for reduced L for the weak-fading conditions. The moderate and strong fading conditions show similar dependence, with significant penalties over 3 dB developing as L drops below 100, and these penalties grow more rapidly when L drops below 10. We show close agreement to these models with experiments using a fiber-based, optical modem. This optical modem utilizes rate-1/2 coding together with a variable interleaver delay spanning three octaves. The optical data signal is transmitted through a fade emulator that applies the same fade profiles used in the theoretical model. This faded signal is sent to an optical-to-electrical receiver, and then into a digital electronics unit that processes the electrical signal to assess the coded communications performance.

The High Photon Efficiency (HPE) standard is a promising approach for, low Size, Weight and Power (SWaP) optical terminal for space communications. In this paper, we report the creation of a breadboard demonstrator CCSDS compliant HPE source, capable of a Pulse Position Modulation (PPM) order of 256 with an average power of 4W and kW level peak power. The HPE source operates in the optical C-band utilising high bandwidth external intensity modulation and high power optical fibre amplifier technology to enable a range of modulation/data-rates to be accessed. Additional external phase modulation is employed as an active Stimulated Brillouin Scattering (SBS) mitigation to achieve the high output peak power requirements. This laser breadboard utilises a 19” rack enclosure allowing easy integration with a HPE transmitter demonstrator breadboard at TNO to demonstrate the combined modem and laser performance. We present testing results such as electrical to optical efficiency and optical pulse characteristics of the system under a range of modes of Continuous Wave (CW) and pulsed operation. Employing the HPE pulsed laser source, we simulated an optical link and introduce results alongside the road-map toward space qualification.

Several organizations are engaged in the development of deployable optical communication systems for intersatellite and satellite to ground communications supporting commercial and non-commercial objectives. The debate whether to use 1.0 or 1.5 μm continues, although the prevailing view leans toward the latter because of its connection with commercial telecom. Solutions at 1.0 μm, however, enable greater efficiency, which is more appealing for small SWaP constrained systems. To promote an increased interoperability potential, we have explored amplification at both wavelengths using an ErYb-only fiber amplifier and a hybrid Yb/ErYb segmented fiber amplifier configuration. These configurations allow the user to select either wavelength without implementing two independent amplification systems. The work presented here will discuss the difficulties encountered with the former approach, modeling efforts, and recent results with the segmented solution.

Convolutional interleavers are used in many different communications systems to correct for burst errors due to atmospheric fades and scintillation. The interleaver size is related to the channel coherence time and the data rate. Small convolutional interleavers can be implemented in a field programmable gate array (FPGA) block random access memory (BRAM). However, large interleavers exceeding the size of the BRAM on the FPGA are necessary for channels with longer fades and higher data rates. Therefore, an implementation utilizing double data rate (DDR) memory external to the FPGA is necessary. Wide DDR memory data buses can make the use of DDR memory for convolutional interleavers inefficient when individual symbols are written to and read from the memory. DDR memory operational speeds can also limit the data rate of the interleaver. The Consultative Committee for Space Data Systems (CCSDS) Optical Communications High Photon Efficiency (HPE) standard utilizes a convolutional channel symbol interleaver. A previous implementation of the HPE standard utilized BRAM for the convolutional interleaver, but mission requirements for the upcoming Optical Artemis-2 Orion (O2O) communications demonstration dictate the use of an interleaver exceeding the size of the BRAM. An algorithm and method for implementing the convolutional interleaver in the FPGA with DDR memory is described in this paper.

The next generation high bandwidth optical links from earth to space will requirement the development of new high power WDM sources. In this paper G&H present the latest results of their ongoing development of these sources. Namely the development and testing of a 50W optical fibre amplifier that operables across much of C-band is presented as well as a high power wavelength division multiplexer, designed to combine multiple high power amplifiers outputs into a diffraction limited beam.

Fibertek is developing a power efficient, space qualifiable Eight WDM Channel PPM Downlink Tx Seed LAser Module (SAM) with Time Division Multiplexing (TDM) based FWM Mitigation Capability. SAM will be compatible with space qualifiable, high TRL, 8 WDM channel, 50W WDM Amplifier prototype that was delivered in early 2021. SAM together with the WDM Amplifier will meet all the requirements of a spaceflight Deep Space Optical Communication (DSOC) WDM Transmitter (Tx) that can support link distances of 2AU and date rates of 2Gbit/sec. TDM based FWM mitigation is experimentally demonstrated using the high TRL WDM Amplifier at 40W operation with PPM(128+32) format. Fibertek has developed a comprehensive multi gain stage 1.5um WDM fiber amplifier numerical model that accurately quantifies the degradation of WDM PPM signals due to FWM. Comparisons of the simulation to the High power WDM PPM experiments are presented. Using the model system level requirements for the WDM PPM SAM are studied.

The power consumption of the laser systems is an important aspect of optical satellite communication technology. We present an optical amplifier for a WDM optical communication system with a simultaneous multichannel amplification in a single fiber in the 1 μm wavelength range. The desired enhanced wall-plug efficiency of ∼30% can only be achieved through fiber technology. Combining the experiences of in-house manufactured optical fiber components and of laser developments for space applications, an all-fiber amplifier solution was designed. Each of the 10 channels can be efficiently amplified up to a total power level of 100W.

The European H2020-SPACE-ORIONAS project targets the development of optical transceiver and amplifier integrated circuits and modules applicable to high-speed and compact laser communication terminals. This paper presents the most recent project achievements in two areas. Firstly, the fabrication of high-speed electronic-photonic modulator and receiver circuits monolithically integrated in the silicon photonics platform and their assembly in bread-board level photonic modules. Secondly, the assembly, integration and testing of a radiation resistant, high-gain optical fiber preamplifier which exploits hi-rel small form factor fiber optics to shrink the module mass and footprint.

Fibertek has developed a ground based high-power (7 kW) optical communication uplink laser to support NASA’s Jet Propulsion Laboratory’s (JPL) Deep Space Optical Communication (DSOC) program. The uplink laser assembly (ULA) provides a beacon laser and Binary PPM (BPPM) modulation signaling to the DSOC spacecraft terminal. Laser beacons with scalable power (multi-kW) are needed for Earth-to-asteroid, inter-planetary (Mars), and deep-space optical communication uplinks. This paper describes the ULA design, development, and performance verification testing. A single laser system was delivered in 2020 for performance testing and initial integration with the optical uplink telescope system. The full ULA laser was delivered and installed in NASA JPL’s Optical Communications Telescope Laboratory (OCTL) optical ground station facility in 2021. DSOC will fly on the NASA Psyche asteroid mission in 2022 and demonstrate deep space laser communications to earth. The ULA is an automated system with a comprehensive user interface that commands and controls ten (10) individual pulsed Yb fiber lasers. The individual lasers are incoherently combined and propagated to the Psyche satellite. ULA commands and monitors the performance of each individual laser, provides redundancy for high availability, and provides multiple safety interlocks to safeguard equipment and personnel. Each Yb fiber laser is collimated individually with a beam quality of M² < 1.2 at 1064 nm in a pulsed PPM format with 2.7 kW of peak power. This paper describes the DSOC requirements and provides performance verification data.

A high-power Laser Transmitter Assembly (LTA) was developed to support the Deep Space Optical Communications (DSOC) technology demonstration being developed by the Jet Propulsion Laboratory. NASA’s Psyche Mission plans to host the DSOC flight subsystem for testing space-to-ground high-bandwidth laser communications en route to the 16-Psyche asteroid. We review the design, performance, and qualification of the LTA Engineering Model and Flight Model (EM and FM) delivered to JPL. The LTA uses a master-oscillator power amplifier (MOPA) design and delivers up to 4.5 W at 1550 nm, with a highly efficient, cladding-pumped, polarization-maintaining erbium-ytterbium fiber amplifier. The master oscillator generates a range of pulse widths and repetition rates to support modulation formats from 16- to 128-PPM for optical data transmission at <100 Mbps. The LTA was designed for high reliability and radiation hardness, and includes redundant signal and pumping paths to reduce single points of failure, hardware interlocks to ensure safe operation and protection against damage, closed-loop control of optical power, and detailed health and status via telemetry. The LTA EM and FM were subjected to unit-appropriate space qualification testing. We describe the performance testing of the EM and FM, for the characterization of key metrics such as wavelength stability, signal linewidth, optical pulse width, jitter, and extinction ratio, and polarization extinction ratio. The management of optical nonlinearities (selfphase modulation, Brillouin scattering, or pulse-to-pulse energy variation), which could result in an optical link penalty or damage to the LTA, is also detailed, and factors affecting the power efficiency are discussed.

We report on the design, development, and testing of our high-power broadband optical modem supporting NASA’s crewed Artemis-2 mission. The O2O modem will be mounted in the crewed Orion module and provide a broadband 505,000 km bi-directional optical link back to earth while en route to the moon. The full-duplex modem consists of a high-power optical transmitter and receiver optimized for serially-concatenated pulse-position modulation (SCPPM). The transmitter is a master-oscillator power-amplifier optical architecture using efficient cladding-pumped amplification in erbium-ytterbium co-doped fiber. The transmitter outputs up to 1 W at ≈1550 nm (limited for eye safety) and supports 6 different user-rates ranging from 20.39 Mb/s to 260.95 Mb/s using PPM16 and PPM32 modulation formats. The optical receiver supports two user-rates: 10.19 Mb/s and 20.39 Mb/s with both rates employing PPM32. The narrowband receiver filtering is optimized to simultaneously accept four separate wavelength channels to mitigate atmospherics through spatial diversity. A configurable interleaver provides additional protection against atmospherics-based signal fading and a powerful soft-decision error correction scheme enables highly sensitive detection. The measured sensitivities at the two bit-rates are -73.8 and -71.8 dBm, respectively. The architecture was designed for reliable operation in space, featuring automatic hardware interlocks, pump sparing for the amplifiers, and autonomous operation of all internal hardware and software control loops. The protoflight unit (PFU) was put through rigorous environmental testing which included pyroshock, vibration, electromagnetic interference/compatibility, and thermal-vacuum testing. The modem successfully passed all the environmental screening and has been declared at Technology Readiness Level (TRL) 6.

Telecommunication and remote sensing data exchanged between Earth and space has increased dramatically in recent years. Radio frequencies, the medium used for several decades has shown to reach its capacity. Free space optical communications, achieved with laser transmitter devices, is an alternative with better transmission rate and increased security. However, a major drawback of this technology is that laser signal cannot cross through thick clouds, which imply to set up a network of optical ground stations with handover management strategies based on Cloud Optical Depth (COD) observation and Cloud Motion forecasts. Ground-based long-wave infrared observations from a sky imager can be used to estimate COD. However, as a low thin cloud may have similar thermal signature than a high thick cloud, additional Cloud Base Height (CBH) measurement is needed to retrieve accurate COD in any weather situation [1]. The CCSDS currently recommends to use a ceilometer for this purpose [2]. Here, we explore an alternative approach, retrieving CBH directly from a pair of thermal sky imagers and stereoscopic methods. Our CBH retrievals have been compared with the measurement of a reference ceilometer. The results showed a good agreement for a continuous period of acquisition over several days, with a Root Mean Squared Error of 15%. In addition, stereoscopy offers a wider field of view and thus, may increase the forecasting horizon and accuracy, compared to a sky imager+ceilometer configuration [3] [4] [5]. We believe this approach is promising for the cloud monitoring of Optical Ground Stations and should be further investigated.

Optical propagation in a marine environment is important to understand for many applications. In particular, free space optical communication can be significantly impacted by surges and fades in signal strength caused by scintillation. For over ten years, the United States Naval Research Laboratory has maintained a 16 km free space optical link across the Chesapeake Bay at our Lasercom Test Facility. This laboratory has continuously recorded scintillation, as well as environmental parameters. Recently, we have begun a modeling and simulation effort. Fundamental models like the Naval Postgraduate School’s NAVSLaM are used to predict turbulence parameters based on weather measurements. Wave optics simulation, using these parameters, is then used to predict scintillation. These predictions are then compared to measurements. Wave optics simulation requires an underlying model of the spectrum of turbulence. A variety of turbulence spectra have been proposed, including the Kolomogorov, Von Karman, Hill and Marine spectra. In this talk we compare wave optics simulation, using these spectra, to experimental measurements, and examine which spectra best match the data.

The ambition of the High thRoughput Optical Network (HydRON) project of European Space Agency (ESA) is to seamlessly extend terrestrial high-capacity networks into space. The concept aims to empower satellite networks by developing terrestrial networking capabilities and features, in order to interconnect all types of space assets by an “Internet backbone beyond the cloud(s)”. Concretely, HydRON will take advantage of space assets to complement terrestrial high-capacity networks, ultimately enabling the configuration of a worldwide and world-first 3-dimensional optical network interconnecting terrestrial networks with different (orbital) layers in GEO, MEO, LEO, and HAPS. The 3-dimensional optical network capabilities will revolutionize the SatCom sector and its related commercial business. The HydRON project proposal and initial funding were approved at the occasion of the ESA Ministerial Council in November 2019. To prove crucial aspects of HydRON, a subset of key elements of the overall HydRON System (HydRON-S, encompassing the full width of the future implementation) were selected for implementation in the frame of a demonstration system (HydRON-DS), capable to validate all HydRON aspects end-to-end. HydRON-DS represents the initial stage serving the purpose to gradually demonstrate key technologies required to deploy a first (all) optical transport network at terabit-per-second capacity in space and the seamless extension of terrestrial fibre-based networks into space. The HydRON overall architecture is meant to evolve and enable both architecture upscaling and service expansion.

Superconducting nanowire detectors fed by single mode fibres are essential to minimize dark counts in a quantum communication receiver. Efficient coupling of the received light to the single mode fibre is fundamental for the system performance, but it gets deeply affected by the atmospheric turbulence. Adaptive Optics measure and correct for the atmosphere effect on the light optimising the fibre coupling. An Adaptive Optics system is proposed to be installed at the ground station that will receive quantum key distribution from a geostationary satellite. Numerical simulations have been performed for this scenario; the improvement in the fibre coupling have been assessed with and without atmospheric turbulence correction. The present paper encapsulates the simulation framework and main findings, showing the potential for this technology in the quantum communications niche.

This work highlights 10G uncoded OOK communications signals in a lab-based over-the-air demonstration through one of Fibertek’s terminals designed for 1G LEO direct to earth links. Our demonstration not only proves that the 1G terminals are capable of higher data rates without penalty but also validate the pointing stability of the system. The bit error rate tests resulted in a less than 3-dB power penalty compared to back-to-back measurements at 1e-9 which is in line with the theoretical half-angle divergence-to-jitter ratio (w₀/σ) of around 7. This ratio meets the design goals for the terminal. We show that the jitter performance of the terminal meets the design goals of providing optimal performance for error free requirements of 1e-9 and demonstrate that through both direct measurement of the jitter on a PSD and the performance impact on a communications signal.

Blue Cubed has developed Cobalt, a gigabit-per-second class optical crosslink terminal that has been engineered to minimize cost and be easily mass produced. These benefits are realized through the design’s novel, patented self-referenced optical architecture. This approach greatly relaxes manufacturing tolerances and makes the terminal exceptionally robust to environmental loading. Herein the status of terminal development, lessons learned in design validation, and the path towards an on-orbit demonstration are discussed.

The Defense Advanced Research Projects Agency (DARPA) is developing a space-based communication node with the goal to create a reconfigurable, multi-protocol intersatellite optical communications terminal that is low size, weight, power, and cost (SWaP-C), easy to integrate, and will have the ability to connect heterogeneous constellations that operate on different optical intersatellite link (OISL) specifications that otherwise would not be able to communicate.

The Terabyte Infrared Delivery (TBIRD) program will establish an optical communication link from a 6U nanosatellite in low-Earth orbit to a ground station at burst rates up to 200 Gbps. The system is capable of reliable data delivery from a 2-TB storage buffer on the payload to a ground terminal in the presence of atmospheric fading. An overview of the communication architecture for TBIRD is provided as well as results from communications performance testing of the 3U lasercom payload prior to spacecraft integration. Launch is scheduled for mid-year 2022.

The Terabyte InfraRed Delivery (TBIRD) program will establish a communication link from a nanosatellite in low-Earth orbit to a ground station at burst rates up to 200 Gbps. The TBIRD payload is currently in the process of integrating with the 6-U CubeSat host bus and pre-flight testing has been completed. An overview of the pointing, acquisition, and tracking system for TBIRD is provided as well as a summary of results from pre-flight testing. TBIRD relies on the spacecraft bus to implement fine pointing corrections supplied by its quad sensor at a rate of 10 Hz. The measured accuracy of pointing feedback is about 10 μrad RMS per axis. A custom optical assembly was designed for transmitter/receiver alignment stability which was measured to be within 25 μrad two-axis through environmental testing. With TBIRD feedback in the loop, single axis pointing accuracy of the downlink is predicted to be about 30 μrad RMS.

NICT is developing the HICALI (High Speed Communication with Advanced Laser Instrument) payload and an optical ground station to demonstrate 10 Gbps-class optical satellite communication between geostationary orbit and the ground. The HICALI payload is planned to be mounted on the Engineering Test Satellite-9 (ETS-9) which will be launched in 2023. In this paper, we present the status of the HICALI payload and optical ground station development and discuss the initial experiment results using a star (Betelgeus), a planet (Venus) and low-Earth orbit satellite-to-ground optical links.

We develop a software system to automatically identify aircraft in thermal camera imagery to assist with uplink laser safety for deep space optical communications. Ground terminals often transmit a high-powered laser for use as a beacon to assist spacecraft pointing. The wavelengths for these beacons are not eye safe for humans. Previous missions have used spotters and transponder-based aircraft detection (TBAD) as a warning system. However not all aircraft (e.g., low-flying planes, hang gliders) have transponders. For this reason, we take an image-based approach, utilizing data from multiple thermal cameras aligned with the telescope, for detecting lowflying aircraft as part of a multi-tiered system. We use a Kalman filter-based tracking software, which is capable of detecting and tracking aircraft within 20 km of the ground terminal. At these ranges, smaller aircraft are only 1-2 pixels in extent, and any system sensitive enough to detect and track all possible aircraft will also detect and track non-aircraft such as insects and birds. We develop traditional machine learning and neural network classifiers to separate aircraft from non-aircraft, using key distinguishing features based on track statistics. In addition, we develop convolutional and recurrent neural network models that incorporate the time-series history of the tracks. Since we cannot tolerate missed aircraft, we select a decision threshold that yields a true positive rate of 1 (all aircraft are identified), and compare performance of a variety of machine learning classifiers. We demonstrate use in the field, where we correctly identify all aircraft, with a false positive rate around 50% when classification is made using only the initial 45 frames of a track and a false positive rate less than 20% when full system tracks are used.

A plenoptic wavefront sensor is proposed for the measurement of the atmospheric turbulence on satellite-toground optical communications. The design will be based on the outcome of the performance simulations for the specific site Teide Observatory (Spain). The performance of the plenoptic wavefront sensor is compared to a Shack-Hartmann wavefront sensor operating under the same conditions. Scenarios with high signal-to-noise ratio are considered with a main focus on communications with geostationary satellites. The turbulent conditions are modelled taking into account the greatest realistic range (weak and strong turbulence) at Teide Observatory in both daytime and night time. The model is defined for space-to-ground laser communications at 532 nm, 1064 nm, and 1550 nm assuming several apertures for the receiver telescope. This paper presents the numerical simulations and main findings regarding phase retrieval and wavefront sensors behaviour in weak and strong atmospheric turbulence regimes; and demonstrates the outstanding behaviour of the plenoptic camera in strong turbulence conditions.

A fundamental requirement of free-space optical communication is the ability to efficiently couple atmospherically distorted light from a telescope to a detector. A numerical method is presented for modeling fiber-based receiver performance in atmospheric conditions based on phase space optics which does not rely on Monte Carlo methods. This method is employed to analyze the waveguide insertion loss and optimal coupling geometry in atmospheric conditions for step-index fibers, graded-index fibers, and photonic lanterns with and without tilt compensation and central obscurations in the telescope.

This article summarizes the results of a system engineering approach to the design of a Transportable Optical Ground Station (TOGS) intended to be used for quantum key distribution in a number of scenarios. Key requirements are listed and a product breakdown is proposed, identifying parts, which are specific to a particular scenario and others, which are common to many of them, and thus will allow their implementation to be shared. We are proposing the use of Adaptive Optics (AO) for compensation of the effects of the atmospheric turbulence, in order to improve the efficiency of the signal coupling to a Single-Mode Fiber.

Non-Line-of-Sight (NLOS) optical communication systems have attracted a lot of interest the last few years due to their obvious advantages, such as no requirements for optical beam tracking, non-destructive impact of obstacles on performance etc. Utilization of optical carriers in the UV-C band offers additional advantages profiting from the strong optical scattering, very low optical background noise due to ozone absorption in the atmosphere and inherent security since the UV-C radiation is strongly attenuated with distance. So far, the main focus of the demonstrated experiments has been on point-to-point communication systems. In this paper, we report on the implementation and initial performance characteristics of a peer-to-peer network consisting of nodes interconnected through scattered UV-C light. At the transmissions part, each node consists of four properly spatially arranged groups, with four UV-C LEDs per group, emitting at 265 nm. Each LED group is adjusted at a certain elevation angle. Moreover, each node has three receivers based on Photomultiplier Tubes (PMΤs) including a UV-C bandpass optical filter in front of each PMT to further reduce the background noise due to the non-zero responsivity of each PMT in the UV-B band. The modulation scheme adopted in the experiments is the 4-PPM (Pulse Position Modulation). The bit rate at the physical layer is close to 7.80 kbit/s. In the link layer, the rules for communication and collisions avoidance between nodes are also set. The first results for 15 meters distance with focus on the physical layer show that the concept is realistic.

An electro-optics system (TurbNet sensor) composed of a remotely located laser beacon, optical receiver telescope with a CCD camera capturing short-exposure intensity scintillation patterns, and deep neural network (DNN)-based processor implemented on Jetson Xavier Nx embedded AI-computing platform was developed and utilized for real-time sensing of the atmospheric turbulence refractive index structure parameter (2^C_n) over a 7 km propagation path at high temporal resolution.