Free-Space Laser Communications XXXVII

Kepler presents the results of its on-orbit Space Development Agency (SDA)-compatible optical inter-satellite link (OISL) testing, between two TESAT SCOT80 optical terminals onboard Kepler Communications low Earth orbit (LEO) satellites, compatible with v2.1.2 of the SDA Optical Communications Standard. Since June 2024, Kepler has closed OISLs across thousands of kilometers lasting several hours and is continually shortening link acquisition times. We describe optical communications terminal (OCT) commissioning, self-test procedures, validation of the OCT / star tracker interface, Moon calibration, and successful link acquisition. We show example OCT telemetry including the pointing, acquisition, and tracking state machine, dynamic attitude knowledge error, the corrections by the fine-steering mirror to maintain the link, and received power on the tracking sensors. Kepler plans further demonstrations of SDA-compatible links including space-to-ground and space-to-air. Kepler’s SDA-compatible optical space data relay constellation is launching in 2025, providing gigabit, sub-second connectivity anywhere in LEO.

Free-space optical communication systems are becoming more and more prominently used in a number of application scenarios, such as satellite communications, Quantum Key Distribution, as well as optical time- and frequency transfer. The Optical Satellite Links department at German Aerospace Center’s Institute of Communications and Navigation has been performing research in free-space optical communications for more than two decades. The department runs research & development programs in order to advance optical communication technology and to perform system demonstrations with end-to-end character. In this paper, recent results in the fields of atmospheric turbulence characterization and mitigation, optical communication terminals, Optical Ground Stations, Quantum Communication Systems and of more fundamental developments will be presented. This includes an overview about the department’s Optical Ground Stations including its adaptive system, results for satellite-to-ground measurement campaigns and flight campaigns.

This paper details the progress in laser communication activities of Tesat-Spacecom. Besides the EDRS program (European Data Relay System) update of in-orbit laser communication terminal (LCT) performance, with more than 87.014 data relay links executed (status May 2024), we report on the successful inter-satellite operation of the SDA compatible SCOT80 LCTs on Kepler S/Cs and share recent results. In addition, we present the status on our access terminal SCOT30, targeting the small LEO user segment. Our intradyne development activities have been continued and the algorithms have been further optimized for the atmospheric turbulent channel. We will share the latest lab measurements and achieved improvements.

In recent years, space-based laser communications have become crucial in the industrial and commercial sectors due to their higher throughput compared to traditional RF communications. This is possible through free-space optical communications, which allow greater data transmission rates and discretion, and do not require frequency allocation. The Keraunos project, supported by the French Agency for Defense Innovation, focuses on advancing a Low Earth Orbit (LEO) to ground optical link. This presentation covers the development and performance of an Optical Ground Station (OGS) with an 800 mm telescope designed for high data rates, low elevation angles, and atmospheric turbulence. Initial results from a commercial OCT on a LEO Cubesat by Unseenlabs validate the optical communication links with the OGS.

The Integrated LCRD Low Earth Orbit (LEO) User Modem and Amplifier Terminal (ILLUMA-T) Payload mounted on the International Space Station (ISS) was the first space-based payload to communicate optically with NASA’s Laser Communications Relay Demonstration (LCRD). A 6-month long Experiments Program on ILLUMA-T concluded in June 2024. The Experiments Program was designed to characterize the terminal point, acquisition, and track systems and understand end-to-end relay communication performance. We present key experimental results from the mission.

The Integrated LCRD Low-Earth Orbit User Modem and Amplifier Terminal (ILLUMA-T) optical communications payload operated on the International Space Station (ISS) for 8 months, concluding in June 2024. ILLUMA-T made the ISS the first space-based user to communicate with NASA’s Laser Communications Relay Demonstration (LCRD). Often optical and radio frequency communications systems have outages while they are pointing close to the Sun, where unwanted incident and scattered solar energy significantly reduces or prohibits operations. This paper presents optical scattering modeling predictions, pre-launch laboratory testing results, and on-orbit measurements of solar scatter at angles ranging from 3 to 25 degrees.

It is becoming crowded in space. With an ever-increasing number of satellites orbiting the Earth and ever-increasing resolution of the instruments, the competition for RF bandwidth to offload the data of these satellites intensifies. The CubeCAT laser communication terminal (LCT) has been designed by TNO, AAC Hyperion and partners to overcome this problem and allows for direct-to-Earth optical links, with a terminal of only 1 U, a weight of 1.0 kg and a power consumption of 15 W. Given its size and weight and power, this is the fastest DTE LCT demonstrated in space. In the paper, we report on the IOD measurements, both downlink and uplink, the performance of both space LCT and ground OGS, and pinpoint the relations between the atmospheric losses and turbulence, pointing performance, received optical power, fading and the resulting bit error rate performance. Moreover, we plan to perform additional tests on the use of (higher) datarates, interoperability tests and transmitter diversity tests and share the latest results. The paper shall report on insights, learnings & recommendations for the design of (future) LCTs for small satellites.

A pair of 6U cubesats was recently launched into low-earth orbit to demonstrate optical crosslink capability for this class of small vehicles. For this mission, each satellite incorporates a 2U lasercom system consisting of a 2W Yb fiber amplifier transmitter, three optical detectors and a fast-steering mirror to enable bi-directional communications and independent steering of the transmitter from the vehicle. Data transmission from 50 - 300 Mbps are planned over a range of 500 – 1500 km.

JAXA's new optical data relay system, "LUCAS," was launched in November 2020. It successfully acquired and tracked with the optical ground station and completed the checkout phase without any issues. So far, LUCAS has conducted experiments such as measuring the effects of atmospheric turbulence. The latest operational status of LUCAS will be explained.

Optical phased arrays (OPA) offer the promise of all electronic beam steering, adaptive optic compensation, aperture scaling, and reduced moving parts. Historically, optical phased arrays have found applications in directed energy, LIDAR, and down-link free-space optical communication ground receivers. However, optical phased arrays for space to space (S2S) crosslinks have not received as much attention and present some unique challenges. This talk will describe an architecture that seeks to address the following challenges for S2S optical communications: 1) the OPA requires beam agility on both the TX and RX with point-ahead capability, 2) the OPA should reduce the number of mechanisms to be competitive, and 3) the OPA should provide a path to lower Size, Weight, and Power (SWAP).

This study demonstrates a phase noise compensation system for free-space optical communication (FSO) using a stabilized 1535 nm laser over a 1.3 km atmospheric path. The laser frequency is shifted by 40 MHz with an Acousto-Optic Modulator (AOM) and transmitted using Pointing, Acquisition, and Tracking (PAT) technology. A beam transmitted from site A to site B and back is amplified using an Erbium-Doped Fiber Amplifier (EDFA). Phase noise compensation is achieved by locking the beating signal of the recirculated beam and the reference beam at site A to a local oscillator, resulting in a 20 dBc/Hz reduction in phase noise at a 10 Hz offset frequency and a 2 Hz beat frequency linewidth. The Signal-to-Noise Ratio (SNR) of the beating signal is 30 dB, confirming effective phase compensation. These results highlight the potential application of this phase noise compensation method in future coherence communication systems, improving phase stability and feasibility for advanced FSO systems and inter-satellite communication.

This paper offers an overview of the design, ground testing, mass production, and space demonstration of a laser communication terminal (LCT) developed by Laserlink. The terminal is designed for LEO communication constellation, considers the SWaP, the efficiency and cost requirements of mass production, and provides a maximum of 100Gbps communication ability up to 2000km. The weight of the LCT is around 7kg, of which the optical head part is less than 4kg. The optical head installed outside the satellite has an envelope size of 200mm*200mm*120mm, which can meet the needs of high-density stacking of flat-panel satellites. After deployment in orbit, the terminal can achieve the rotation angle of ±180° in azimuth and -80°~+30° in pitch directions, the single terminal can support inter-satellite link, space-to-ground link, and LEO-to-MEO/GEO link establishment.

The talk will concentrate on the most recent work performed under ESA Optical and Quantum Communication – Scylight programme. The paper will present latest update on the flagship mission HydRON (High thRoughput Optical Network) with a focus on LEO satellites network connectivity. It will also introduce newly initiated ESA activities for satellite Quantum Information Network (QIN) definition and development.

Fibertek has developed a lunar orbiter-based optical communications terminal for NASA Artemis, lunar orbiter, small satellite science mission. The terminal is designed specifically for lunar and Heliophysics missions out to 1 AU and includes multi-waveform OOK/PPM capability (2 Gbps, 800Mbps) with compatible modes with the NASA O2O ground stations. The terminal is ultra-low SWaP-C, relative to other lunar and extended-range terminals, with traceability towards supporting NASA Moon to Mars Initiatives. The terminal maintained the modularity of Fibertek’s CubeSat terminals to enable the extension of the capability of this terminal to > 100Gbps operations in support of next-generation modems. The paper will describe the engineering model terminal and link budget performance modeling results for high-speed lunar optical coms.

Space-based Adaptive Communications Node (Space-BACN) is developing a low-cost, reconfigurable optical intersatellite communications terminal that supports multiple protocols and optically interconnects satellite constellations. Space-BACN terminal is modular with independently developed optical and modem modules. We describe the architecture and implementation considerations for a lasercom terminal controller, key to successful integration and on-orbit operations

We developed an optical communication system based on folded mirror for nano-sat. Nano-sat is too small to have big mirrors; therefore, it is challenging to have a wide bandwidth communication system over thousands of km. We overcome this challenge by using a folded mirror and compensating for misalignments with electronic components.

This paper compares theoretical downlink and uplink Bit Error Rate (BER) predictions with three sets of the BERs measurements derived from National Institute of Information and Communications Technology’s and German Aerospace Center’s experiments using the Optical Inter-orbit Communications Engineering Test Satellite. The theoretical estimates and data are in reasonable agreement. The key to getting the good agreement is the use of the satellite slew rate in the refractive index structure parameter vertical profile model. It has a major effect of the resulting BER profile. The authors believe this is the first paper reporting any such comparisons.

In the underwater wireless optical communication (UWOC) system, strong optical scattering caused by impurity particles in the water leads to the rapid divergence of the beam. This results in a significant decrease in the received light power when using a restricted-size aperture. The challenge is overcome by utilizing a new structured optical beam called a "pin-like beam". In this study, we built a 5Gbit/s UWOC system in tap water to compare the propagation performance of four beams: Gaussian, zero-order Bessel, pin-like, and pin-like vortex+2 beams. The experimental results showed that the pin-like and pin-like vortex+2 beams have an auto-focusing property, maintaining a narrow beam characteristic over a range after the auto-focus position. Additionally, the results indicated that the proposed pin-like and pin-like vortex+2 beams have lower power loss compared to the Gaussian and zero-order Bessel beams when using a size-limited receiver aperture.

Traditional C-band free-space laser communication relies on erbium doped fiber amplifiers (EDFAs). EDFAs have several drawbacks, most notably, they have a high cost, size, weight and power (c-SWaP). In addition to this, EDFAs have an inherent inefficiency, requiring two stages to go from electrical-power in to amplified optical-power out. In comparison, using a photonic integrated circuit (PIC) semiconductor optical amplifier (SOA) will provide a smaller c-SWaP and direct electrical-power input to optical-power out. Here, we evaluate a new-to-market C-band Freedom Photonics aura PIC SOA as a promising alternative to an EDFA for laser communication applications. We demonstrate optimal operation settings and make a direct comparison to the traditional EDFA approach.

This paper reports on preliminary prototype development and evaluation of space-grade WDM-based HPA/LNA modules for small LEO satellite constellations. We have developed these modules to ensure reliability, tolerance for space environments, and compliance with SWaP constraints for small satellite platforms including CubeSats. These modules optically amplify WDM optical signals using up to four wavelengths. Both modules occupy less than 0.5U. The HPA module delivers an output power of over 2W, and the LNA module can amplify optical signals of -50 dBm/ch. Our evaluation confirms the fundamental performance of each module including output power, optical gain, noise figure, and gain flatness.

Increasing demand of high-speed connectivity has challenged the future technologies (5G/B5G) in terms of large bandwidth, ultralow latency, massive coverage, reliable connectivity and rapid deployment. Free space optical (FSO) communication addresses these challenges in a cost effective way due to its unlicensed spectrum, high data-rate and long range. To develop a low-cost indoor FSO link, we present high-speed transceivers based on laser diode and photodiode. The transceiver link has achieved signal transmission up to 65 MHz providing minimum data rate of 130 Mbps using NRZ modulation. Link measurements are performed in an indoor campus environment by employing an optical assembly consisting plano-convex lenses, to achieve a range of 50 meters. An experimental demonstration of a square wave transmission up to 1 MHz is presented along with 53% improved quality of retrieved signal. Moreover, OSNR (13.6 dB) and BER (〖10〗^(-9)) parameters are studied to enhance the performance of future FSO networks.

This study developed an intensity-modulated optical communication system for high-speed, secure data transmission over a 1.3 km atmospheric path. Intensity-modulated optical communication in Free-space Optical Communication (FSO) offers advantages due to its simple configuration and low power consumption compared to other optical communication technologies. Using Pointing, Acquisition, and Tracking (PAT) technology and AM noise suppression, the system achieved high coupling efficiency and effectively reduced Relative Intensity Noise (RIN). Light at a wavelength of 1550 nm was transmitted towards the receiver and successfully coupled to the fiber located at the receiver using Fast Steering Mirrors (FSM) and Position Sensing Detectors (PSD). After fiber coupling, the coupled light was inputted into a Semiconductor Optical Amplifier (SOA), where the modulated current effectively suppressed AM noise. RIN was significantly reduced by -35 dB at 10 Hz, ensuring reliable data transmission with low error rates.

Optical Pin Beams (OPBs) are a promising candidate for realizing turbulence-resilient long-distance free-space optical communication links spanning hundreds of kilometers. In this work, we introduce an unified theoretical model to describe the propagation of OPBs and present comprehensive simulation results based on many realizations and link budget analyses for varying turbulence strengths. For reference, we compare the performance of the OPBs to weakly diverging and focusing Gaussian beams. For a 100 km long air-to-air link,10 km above sea level, our simulation results show that OPBs offer an improved link budget of up to 8.6 dB and enhanced beam wander statistics of up to 3 dB compared to the considered Gaussian beams. Additionally, we identified a quadratic relationship between the transmitter aperture diameter and the maximum achievable distances, which is crucial in deciding the suitability of OPBs for a given application scenario.

This project is developing an optical communication payload for 3U CubeSats, designed to operate within their size, weight, and power constraints. The transmitter laser, combining a Distributed Feedback Laser Diode (DFB LD) with an Erbium-Doped Fiber Amplifier (EDFA), achieves a 500 mW output. Our goal is to construct and validate a space optical communication transmitter module for nano-satellites and verify the space-to-ground optical communication downlink. We are developing a ground station system with a 1.2-meter telescope and a calculated link budget of 5.4 dB, expected to achieve a data transmission rate of up to 8 Mbps. The satellite is scheduled for launch in 2026.

A method to compute LEO/MEO satellite orbital parameters based on measurements of the optical Doppler shift is presented. Compared to previous radio frequency methods, the orders of magnitude increase in the optical Doppler shift is theorized to result in better precision for orbital velocity and position. A candidate system based on an example LEO space-to-ground free space optical communication receiver is presented with a discussion of the major design drivers. Next steps in realizing a bench-top system implementation are presented and the path-forward to a full system demonstration on-orbit outlined. Applications of this work extend to Space Situational Awareness and provide a secondary, passive, GPS/GNSS-agnostic method of spacecraft orbit determination.

Optical wireless communications (OWC) offer high-bandwidth, covert and jam-resistant datalinks that can complement RF communications, particularly for small unmanned aerial system (sUAS) operation in RF contested environments – like the battlefields in Ukraine. OWC characteristics are enabled by compact beam-forming possible in the optical domain which can provide extremely directional datalinks. However, it is challenging to deploy OWC onto sUAS because the precision beam-control required is at odds with their size, weight and power plus cost (SWAP+C) constraints. Compact OWC systems for sUAS must provide stabilized steering of the datalink, ideally, in any direction. In this paper, we present and compare three panoramic steering systems that we developed for sUAS OWC. Each system utilizes a different panoramic steering element in between the same OWC back-end and 2-axis fine steering mirror (FSM) front-end. The implementations use: 1) direct-drive DC motor above the FSM, 2) gear-coupled DC motor below the FSM and 3) piezo-driven rotator below the FSM. We compare each system’s line-of-sight control including speed, accuracy, repeatability, and jitter measured in flight on a sUAS.

An important aspect of all-optical coherent satellite communication technology in space is the efficient amplification of ultra-low optical power levels with the constraint of limited power consumption of the employed laser systems. We present an all-fiber amplifier design for the use in WDM optical communication infrastructures operating at 1µm wavelengths. The system is capable of amplifying simultaneously 10 seed channels from input powers of 10-50nW per channel up to the mW power level range by combining advanced fiber-optical technology at 1 µm for an enhanced electro-optical wall-plug efficiency and specialized fiber components for a required mixed-polarization operation.

The growing need for high-capacity free-space optical communication links have placed high demands on the performance of adaptive optics (AO) systems. A key challenge lies in mitigating temporal error, this imposes severe time constraints on the response of deformable mirrors (DM). Recent advancements at ALPAO in the realm of input shaping techniques have yielded promising results, effectively eliminating oscillations and reducing overshoot from 60 to less than 5%. Both, rise time and settling time have been diminished to below 50µs, representing an improvement of one order of magnitude compared to the unshaped case. The solution found is compatible with real-time computing constraints and can be integrated in the DM drive electronics or in separate processing unit. The ALPAO Core Engine (ACE) software is used to quantify the impact of the proposed input shaping algorithm on the overall performance of an AO closed-loop system. Error transfer functions (ETF) measured on an experimental setup comprising an ALPAO Shack Hartmann wave front sensor, an ALPAO RTC and finally an ALPAO DM will be presented.

In this paper, we present the development of an ultra-compact booster RC-EDFA suitable for CubeSat LCTs. The device dimensions are 42x30x15 mm (LxWxH) and it weighs only 32.6 grams. The RC-EDFA delivers a saturated output power of 100 mW over a wavelength range of 1530 to 1570 nm with a Noise Figure of 5 dB (at 1550 nm) and a >20% optical-to-optical efficiency. It features optical isolation and power monitoring for both input and output and optical pumping with redundancy. We have performed gamma irradiation on several different RC-EDFs and achieved a radiation induced gain drop of < 0.8 dB at 20 krad total irradiation dose (TID).

Optically transmitting data through dynamically changing channels is a difficult challenge. Here, we offer a potential solution using the rank of the 4×4 coherence matrix for partially coherent light in which the polarization and spatial degrees-of-freedom (DoFs) are relevant. We show experimentally that the coherence rank is invariant to channels that stochastically change bit-to-bit and even couple DoFs, suggesting that the coherence rank could serve as robust encoder in optical communications.

Quantum Cascade Lasers (QCLs) provide compact high output power in the mid-wave and long-wave infrared regions (MWIR & LWIR). The novel cascaded design of the QCL active region can produce multiple photons with a single electron. This laser technology is suitable for spectroscopy, gas detection, free space optical communication, and target illumination. We describe the different packaging configurations (from single laser chips inside a high-heat load package to multi laser bars in a packaged array) and different fabrication techniques (high reflection coating, etc.) that increases the performance of QCL devices and allows them to be used for Air Force applications.

For free-space optical communications through the atmosphere there is a trade-off to be explored between the "correct many modes" approach of adaptive optics and the "detect many modes" approach of modal diversity receivers. We present a numerical analysis of modal coupling into the Laguerre-Gaussian (LG) basis for an optical signal through varying strengths of Kolmogorov turbulence after different orders of adaptive optics phase correction. Mapping the LG mode coupling efficiency under different orders of Zernike correction shows concentration in the zero azimuthal modes, informing system trade-offs of which spatial modes to emphasize in the receiver.

A new technique aims to reduce turbulence effects using beam shaping. Initially, a turbulence-impacted vortex beam was shaped by passing a collimated Gaussian beam through a rotating Pseudo Random Phase Plate (PRPP) and a Vortex Phase Plate (VPP), forming Laguerre-Gaussian modes. The scintillation index was measured with a CCD. Comparative studies examined collimated, diverging, and converging beams at five points, using four LG modes and a Gaussian beam.

Universal internet connectivity is an enabler for economic development. Free-Space Optical-Communications (FSOC) can help alleviate infrastructure challenges posed by fiber optical connections. We will present a low-complexity SFP driven, 4x4 multi-aperture diversity transceiver, for mitigating turbulence and tracking errors that does not require Digital Signal Processing or complex electro-optical components. We experimentally verify our system using a bench-top turbulent channel emulator with a CN^2 = 10^−12 and greenwood frequency of 300 Hz. We demonstrate our multi-aperture diversity transceiver can successfully avoid turbulence induced deep-fades for a 1 Gbps NRZ Ethernet encoded signal. This work strongly indicates that FSOC in turbulent links can be achieved using low-complexity diversity transceivers built from commercially available components.

Adaptive Optics (AO) is widely used to correct atmospheric disturbances, particularly in astronomy. However, Free-Space Optical (FSO) communications face major challenges such as high apparent winds, scintillation, and rapidly changing turbulence conditions. Thus, in the field of optical communications in Geostationary Orbit (GEO) or Low Earth Orbit (LEO), a significant portion of the error budget to be corrected lies in temporal and scintillation errors. To mitigate these errors, the use of predictive controllers is emerging as a promising solution. In this context, we compare the performance of the integrator to state-of-the-art predictive controllers. We explore a Linear Quadratic Gaussian (LQG) controller based on Kalman filtering, already successfully proven in astronomical applications [1], as well as a reinforcement learning algorithm showing very promising results in predictive control.[2] This study proposes a comparison based on full end-to-end simulations (developed in Python), and a fair assessment of the relative performance of these controllers under realistic conditions. We account for atmospheric scintillation and use a turbulence model with TURANDOT[3] for case stu

Optical ground-to-satellite adaptive optics pre-compensation techniques, based on the downlink correction, suffer from anisoplanatism, due to the point-ahead angle (PAA) between the downlink and the uplink. Hence, the received uplink signal at the satellite and the link capacity are impaired. To reduce this pre-compensation phase error and improve the communication link quality, we proposed to estimate the phase at PAA using an MMSE estimator based on the downlink phase and log-amplitude measurements and statistical priors. This method was shown theoretically to greatly reduce the pre-compensation phase error and therefore, improve the statistics of the received signal onboard the satellite. In this work, we present an experiment designed to validate both the estimator performance on-sky, using Shack-Hartmann phase and amplitude measurements from double stars, and its feasibility using Cn2 profile reconstruction, which is essential to retrieve to compute the phase estimator. We present here the experiment design and data processing pipeline validated on numerical simulation, including the retrieval of the atmospheric Cn2 profile.

We devise a high-fidelity multi-stage coherent beam combination scheme for photon-starved signals and successfully test it in numerical simulations for deep-space optical communication from the recently launched PSYCHE probe with state-of-the-art SCPPM information encoding.

Honeywell, in partnership with the University of Waterloo Institute for Quantum Computing (IQC), is developing the primary Optical Quantum Ground Station (OQGS) for Canada’s Quantum Encryption and Science Satellite (QEYSSat) at the Canadian Space Agency (CSA) headquarters in Longueuil, Quebec. As QKD progresses through technical demonstrations like QEYSSat and into adoption customers will need a new class of quantum-enabled optical ground stations that are automated, deployable, and ready to integrate with customer networks. Leveraging the design work from OQGS, Honeywell is developing a new generation of deployable optical quantum ground stations based on the successful High Altitude LiDAR Atmospheric Sensing (HALAS) product platform: a shipping-container sized optical instrument for atmospheric metrology that shares many system functions with an optical ground station.

In support of NASA Glenn Research Center’s Quantum Metrology laboratory (NQML) and Real Time Optical Receiver project (RealTOR) a wide bandwidth source of weak coherent pulses has been implemented with a mode locked c-band laser in combination with a home built pulse picker. For component characterization in both of these projects there is a need for a laser source which exhibits short pulses O(1ps) as well as a variable repetition rate and mean photon number per pulse. The setup that has been implemented is operable over a wide bandwidth from approximately 4MHz to 1.4GHz, and variable mean photon number per pulse. The system implements a novel feedback mechanism using a superconducting nanowire single photon detector and high resolution time tagger to reoptimize its extinction ratio via photon arrival times of the weak coherent pulses. This feedback allows for frequency domain studies to be performed with automatic control. The system design as well as characterization data of its performance are presented here.

We report recent progress on technology developments at the NASA Glenn Research Center using photonic lanterns for coherent optical communications applications. In particular, the development of a spatial mode-diversity optical receiver using a 7-channel photonic lantern combined with a photonic integrated circuit (PIC). The PIC is designed for compatibility with the NASA Laser Communication Relay Demonstration’s (LCRD) differential phase-shift keying signaling format. The PIC design, characterization, and packaging efforts are discussed, and receiver performance in combination with the photonic lantern under conditions of emulated atmospheric turbulence are presented. Additionally, we report on the development of a 19-channel photonic lantern and provide updates on efforts to use the photonic lantern as a wavefront sensing device. The photonic lantern insertion loss, and spatial-mode transfer characteristics are detailed, as well as the development of a predictive framework in which the intensities in the 19 single-mode output channels are used to reconstruct the wavefront of the light entering the multi-mode input side of the lantern.

We present a balanced InGaAs photoreceiver, i.e. a matched pair of photodiodes followed by a differential Silicon CMOS TIA, with automatic gain control mode that supports coherent and direct detection optical communication links with a symbol rate up to 25 Gbaud and aggregate data rate up to 100 Gbps. These devices were subjected to 662 keV Gamma rays from Cesium-137 for a total ionizing dose of 15 krad-Si, 30 krad-Si, and 50 krad-Si. The same devices were subsequently subjected to 100 MeV Protons for a fluence of 1E10 /cm^2, 5E10 /cm^2, and 1E11 /cm^2, respectively. During the radiation runs, the TIAs were biased and their drive currents and RF output noise spectra were continuously recorded. The in-situ data was complemented by detailed analog and digital characterization of these devices before and after each radiation run. We did not observe any significant impact on these devices due to either Gamma or Proton radiation.

Modulatable retroreflectors are important components for free-space laser communications, primarily being used for long range applications. This work explores the development of a new modulatable optical retroreflector platform using Silicon photonics. This new platform makes use of the Van-Atta retroreflector architecture which has seen great success in the field of RF communication. This platform makes use of cutting foundry process from AIM Photonics, utilizing fast electro-optic phase modulators to modulate the retroreflectivity of the array. The 2.5D geometry of the array allows for very low SWaP requirements, making it suitable for a variety of applications.

With a more pressing demand for higher throughput in LEO-to-ground, FSOC offers a tailored solution with additional benefits such as more secure data transfer and no frequency allocation requirements. Cailabs' TILBA-ATMO, utilizing Multi-Plane Light Conversion (MPLC) technology, offers efficient turbulence mitigation for atmospheric communication. Here, a 45-mode system designed for Optical Ground Stations is demonstrated in a 5 km ground-to-ground link in different turbulence conditions. An in-depth study of the performances as a function of the different turbulence parameters is also conducted on an in-house designed turbulence emulation bench which copies a LEO-to-ground optical link.

We experimentally demonstrate that varying reference wavefronts yield different performances in dynamic wavefront correction by adaptive optics under strong turbulence conditions. We found a corresponding theory to explain these differences by introducing a new definition of temporal coherence that takes multiple parameters into consideration including not only the strength and direction of turbulence but also the shape of the wavefront. Using numerical modeling, the theory is validated by experimental results. Based on this theory, we can optimize the reference wavefront under different turbulence conditions to improve the performance of adaptive optics and these findings can be important for further stabilizing optical propagation through a strongly turbulent atmosphere.

This presentation addresses the critical need for high-power optical amplifiers in the C-band for optical feeder links in laser communications, in the context of the challenge of scaling up the power delivered by Erbium-Doped Fiber Amplifiers (EDFAs). It showcases the use of Multi-Plane Light Conversion (MPLC) technology for Coherent Beam Combination (CBC), achieving an 85% combining efficiency. Key results include the demonstration of 6-channels CBC with 10 W per channel, phase-locking via Frequency Dithering, and power scalability up to 6 x 20 W with stable performance. The session will delve into the experimental setup and performance analysis, emphasizing MPLC's potential to enable high-power optical feeder links for laser communications.

As the number of nanosatellite launches increases rapidly, optical laser-based (intersatellite) communication systems are integrated for various applications. With the ongoing miniaturization of space systems, new picosatellite platforms require equivalent laser systems. This paper presents a high-level system design of a miniaturized laser communication terminal and a methodology for creating such systems for small platforms. The research develops a tool to assess optical intersatellite link systems and mission design. The system architecture is created aiming to balance the SWaP constraints of the optical communication system and the platform requirements. The study aims to provide a framework for designing laser communication systems for picosatellites. As the development of miniaturized space systems and the need for inter-satellite communication grow, a tool for assessing these systems is essential, enabling the full potential of miniaturized space systems.

Free space optical (FSO) receivers based on spatial demultiplexers offer significant advantages to mitigate atmospheric turbulence for FSO communications. We evaluate the performance of a photonic lantern (PL) based receiver for this application. A modal decomposition approach is presented to assess the PL coupling efficiency. We validate the numerical approach with an experimental characterization of the PL. We compare the PL receiver to a commercial spatial demultiplexer with a simulation of received optical wavefront in a FSO communication scenario. The PL receiver is then associated to a thin film lithium niobate (TFLN) photonic integrated circuit (PIC) coherent combiner to form a compact FSO receiver. The PL and TFLN PIC receiver shows a higher collection efficiency than standard FSO receiver and a strong robustness to phase and intensity perturbation.

Laser-based visible light communication (VLC) system has been receiving increasing research attention for many emerging applications, such as LiFi, Industrial IoT and underwater wireless optical communications (UWOC). Benefiting from the development of large modulation bandwidth InGaN-based laser diodes, laser-based VLC data link with multiple tens of Gbps has been achieved. The recent progress in design, fabrication and characterization of single laser-based VLC system exceeding 30 Gbps and WDM VLC system reaching 100 Gbps will be presented.

Beyond the development and proliferation of a low-Earth-orbit (LEO) constellation based on optical intersatellite links, the Space Development Agency (SDA) intends to explore ground station architectures for use in space-to-ground free space optical communication (FSOC) links. For more demanding SWaP constrained tactical platforms, ground receivers based on free-space coupled low noise, large area avalanche photodiodes (APD) provide increased tolerance to atmospheric impacts while also relaxing pointing requirements relative to single-mode and multi-mode fiber-coupled receivers. When used in tandem with a high speed single-mode fiber (SMF) output electrical-to-optical (EO) converter, this APD-based receiver architecture can more seamlessly integrate with SMF input SDA Optical Communication Terminal (OCT) compatible modems. In this work, we characterize the performance of an APD-based OEO receiver integrated with the U.S. Naval Research Laboratory’s (NRL) SDA OCT reference modem.

Congestion of the RF spectrum has driven the development and proliferation of free space optical communication (FSOC) technology across multiple application platforms including terrestrial, air-to-ground, and space-based telecommunication network architectures. For atmospheric FSOC links, large area avalanche photodiodes (APD) are advantageous for a number of reasons. Owing to their internal gain mechanism, APDs provide superior performance compared to PIN detectors. Advances in heterostucture design and device fabrication have also led to improved APD noise performance relative to those developed in decades past. A large active area allows for: 1) improved tolerance to atmospheric turbulence impacts such as beam wander, break-up, and expansion, and 2) an enhanced field-of-view relative to fiber-coupled receiver architectures that are constrained to the numerical aperture of the coupling fiber. A common system design tradeoff, however, for implementation of large area APDs is given by the inverse relationship between active area and bandwidth. Here, we present performance results of low noise, 100µm active diameter APDs capable of data rates beyond 2.5Gbps.

Temporal-frequency spectra are produced from irradiance measurements of a laser beam after propagation along a 16 km path on the Chesapeake Bay. DC-coupled detectors of 3 coaxial receivers of diameter 12, 25 and 50mm were continuously recorded at 2 kHz. These high-speed raw data supplemented the usual turbulence parameters recorded at the laser test bed. A scalable automated process was developed for extracting salient features of the power spectra such as slopes and knee frequencies. The relevance of these key features will be discussed in relation to the inertial and dissipation regions of turbulence.

In this paper we describe the implementation of Optical to Orion’s synchronous two-way ranging scheme based on the uplink and downlink communication waveforms. We outline the architecture of the Time of Flight capture system, as well as the hardware and software necessary to extract range and range-rate information from the downlink and uplink signals. We also describe a novel calibration scheme that enables highly accurate compensation of the delays within the ground station without the need to directly measure individual path lengths. Finally, we present the results of laboratory measurements of the time of flight system using ground support equipment, including measurements of the full system through various runs of single mode fiber ranging from 1m to 15 km.

Free space optical communication (FSO) is strongly affected by atmospheric effects such as scattering and optical turbulence. To predict availability and performance of terrestrial and ground to space systems, forecasts of these effects are needed. Unfortunately, global measurements of optical loss and scintillation are not available. So, it is not even possible to make predictions based on historical records. However, there have been many measurement campaigns that have produced data that connects optical turbulence parameters such as Cn2 to scintillation, as well as models that show reasonable agreement with experiment. Similarly, optical scattering loss can be related to rain rate and visibility. Thus, numerical weather prediction (NWP) systems may offer a way to predict FSO system performance globally. The Naval Research Laboratory’s (NRL) Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS) represents a state-of-the-art NW. Recently COAMPS has added forecasts of Cn2 to its capabilities. In this work we comp

This research investigates the performance of laser communication systems using beams carrying Orbital Angular Momentum (OAM) as they propagate through diffuse media, such as fog. Foggy environments, characterized by scattering and attenuation, often degrade the quality of optical signals, leading to significant power loss and increased transmission errors. To address these challenges, the study explores the impact of varying wavelengths and different OAM modes on the overall communication system. The findings suggest that by carefully selecting the appropriate wavelengths and OAM modes, it is possible to significantly improve the reliability of optical communication systems under adverse environmental conditions.

Laser beams with Orbital Angular Momentum (OAM) are revolutionizing optical communication systems, especially for next generation 6G networks. These beams encode information spatially, making precise detection crucial. This research presents methods for determining Bessel-Gauss beam OAM by analysing diffraction patterns through various apertures. By using different aperture shapes to sample the Bessel-Gauss beams and examining the resulting far-field diffraction patterns, we can accurately determine the topological charge of the incoming beam.

Reducing the size, weight, power consumption and cost of optical communication systems is critical to mass adoption of wireless laser communications for satellite applications. For the ground segment, deployment and commissioning speed are additional barriers to adoption. Archangel Lightworks is developing the TERRA-M, a small (30cm aperture), deployable, optical ground terminal for proliferated space-ground lasercom. This paper presents initial test results from the prototype TERRA-M demonstration campaign in the UK, including results of rapid deployment & commissioning tests, pointing acquisition and tracking, link budget validation.

US Naval Research Laboratory has been developing a lasercom facility for communications to satellites in low earth orbit. The system uses four transmitters mounted evenly around a central receive aperture. This transmitter configuration has advantages in spatial diversity and maintaining eyesafe levels at smaller apertures with increased total power at the spacecraft. One challenge of the system is aligning the transmitters. With tight beam divergence, using a camera to define an aimpoint in the laboratory and then aligning all transmitters and the receive telescope to the same star was insufficient. Instead, NRL developed a method to use transmitter reflections from a cloud deck to perform in situ alignment and motion calibration. This paper describes the alignment procedure and results.

To improve the performance of the outdoor free-space optical (FSO) communication system, operated in a strong turbulence regime, we propose the application of adaptive LDPC coding techniques over the L-band. The experimental results over an outdoor 1.5 km FSO link, established at the University of Arizona campus, indicate that the proposed adaptive coding scheme significantly outperforms the adaptive optics-based FSO communication system operated in either in C- or L-band.

In this work, for the first time, we experimentally demonstrate mode division multiplexing-based bidirectional free space optical communication in real-time using commercial transponders. As proof of concept, via bidirectional pairs of Hermite-Gaussian modes (HG00, HG01, and HG10), using Telecom-Infra-Project-compliant Phoenix commercial 400G open transponders, 400 Gb/s data signals (56 Gbaud, DP-16QAM) are bidirectionally transmitted error free, i.e., with less than 1e-2 pre-FEC BERs, over approximately 1-m.

This study explores the performance of Bessel-Gaussian and Ince-Gaussian beams for free-space optical communication. We investigate the efficiency of data transmission over varied distances under mild turbulence conditions using their distinct spatial structures, such as circular symmetry in Bessel-Gaussian beams and elliptical symmetry in Ince-Gaussian beams. Using a novel numerical iterative approach, we examine how these complex structured beams encode and decode data, attempting to determine which beam type improves transmission efficiency. The results help to optimize optical wireless communication systems and have implications for advanced applications like high-resolution imaging.

This work details laser control techniques for the Finisar S7500 CW tunable laser. Specifically we demonstrate how to accurately set and tune the output frequency for different ITU channels without a wavemeter for reference.

Space-BACN is developing a low-cost, reconfigurable optical intersatellite communications terminal that will interconnect satellite constellations. The terminal design will be mechanically gimballed providing hemispherical field of regard coverage. This work describes novel alternate optical beam steering based terminal design, expected performance and realizable interconnectivity between proliferated low-earth orbit satellite constellations

US Naval Research Lab (NRL) has, since early 2023, been operating an optical communication interoperability testbed for the Space Development Agency’s (SDA) Tranche 1 program. This testbed measures pointing, acquisition, and tracking capabilities, as well as data transfer performance. The testbed has been used to test optical communication terminals (OCT) from four different vendors as well the modem for a ground station. These OCTs are tested both against a government reference modem and each other to ensure compatibility between all the vendor implementations of the SDA OCT standard. Throughout the course of this testing numerous issues have been found, both in interoperability as well as general operability, which would have been difficult or impossible to resolve once the terminals were on orbit. This work will discuss how these issues are detected, the resolution process between NRL, SDA, and the OCT vendor, and the general process of optical interoperability testing.

The National Aeronautics and Space Administration (NASA) Deep Space Optical Communications (DSOC) Project implemented by the Jet Propulsion Laboratory (JPL), has completed weekly optical link demonstrations from Nov. 2023 – July 2024, following the Psyche spacecraft launch in October 2023. The flight laser transceiver, hosted by NASA’s Psyche spacecraft, along with optical ground stations located in Southern California were used. Over this period, downlink data-rates of 6.25 – 267 Mb/s were achieved over deep space distances of 0.2 – 2.7 astronomical units (AU), or 30 – 400 million Km. Optical link acquisition, tracking and pointing was initiated with a modulated uplink laser assembly that also delivered communications at a fixed rate of 1.8 kb/s over distances of 0.2 – 3 AU. Pre-recorded ultra-high-definition video and imagery along with Psyche mission engineering data was returned over the downlink. In this paper we will provide a system level overview of the DSOC technology demonstration.

The Deep Space Optical Communication (DSOC) project is conducting an ongoing technology demonstration of free-space optical communications over an approximate range of 0.05 to 3.0 AU concurrently with NASA’s Psyche mission, which launched on October 13, 2023 and hosts the DSOC flight transceiver (FLT). The DSOC Ground Laser Transmitter (GLT), located at the Jet Propulsion Laboratory’s Optical Communication Telescope Laboratory (OCTL), provides a high-power (up to 5 kW on-sky) optical uplink beacon that serves as a line-of-sight FLT downlink pointing reference and delivers low rate (1.8 Kbps) uplink command data to the FLT. This paper presents an overview of the GLT subsystems, concept of operations, and results from the first phase of DSOC operations including analysis of the beacon pointing and the performance of the laser safety subsystem.

The Deep Space Optical Communications (DSOC) project has recently successfully completed its first year of operations. The downlink flight laser transmitter operated for over 120 hrs on a weekly cadence demonstrating data rates up to 267 Mbps at near range and 8 Mbps at 2.5 AU. The uplink laser assembly provided a beacon reference for the flight terminal with over 2 kW average power and an uplink data rate of 1.8 kbps at 1064 nm over the entire range. Trends and performance data will be reported on for both systems.

NASA’s Deep Space Optical Communications (DSOC) Project, implemented by the Jet Propulsion Laboratory (JPL), has successfully completed the first year of its technology demonstration, delivering high-rate optical downlinks for the first time from deep space over spacecraft distances ranging from 0.1 to 3 astronomical units (AU). The heart of the flight terminal is an essentially free-floating 22 cm telescope and photon-counting camera, mounted on a platform that is steered by Lorentz-force actuators. The hardware also includes a 4 Watt transmit laser and associated electronics. The instrument software and firmware algorithms detect and track a modulated optical uplink beacon, decode data modulated on that beacon signal, point the downlink laser, and encode pulse position modulated (PPM) data for the optical downlink. These hardware elements are described, along with the firmware and software signal processing algorithms. The concept of operations for the flight terminal is also described.

The Deep Space Optical Communication (DSOC) project has concluded its first year of operations, demonstrating high-photon-efficiency downlinks from 163 kbps to 267 Mbps at ranges from 0.1 to 2.7 AU. Here we report on the performance of the primary Ground Laser Receiver (GLR), installed at the Palomar Observatory 5m Hale telescope, as well as the secondary receiver, installed at Jet Propulsion Laboratory’s Optical Communication Telescope Laboratory (OCTL) sharing the 1m aperture with the Ground Laser Transmitter (GLT). We discuss lessons learned from operations, and present results from decoding with the combined (arrayed) counts from multiple receivers.

NASA’s Deep Space Optical Communications (DSOC) Project, implemented by the Jet Propulsion Laboratory (JPL), has successfully completed the first year of its technology demonstration, delivering high-rate optical downlinks for the first time from deep space over spacecraft distances ranging from 0.1 to 2.8 astronomical units (AU). The precise downlink laser pointing required for high-rate data delivery relies upon the utilization of an uplink optical beacon as a reference signal for flight terminal platform stabilization and microradian-level point-ahead control. The DSOC flight system acquisition, tracking, and pointing architecture and algorithms are described here, followed by a summary of operational performance results to date, as well as future avenues for improvement.

The RF/Optical hybrid ground station (RFO) is a technology demonstration deployed at the Deep Space Network (DSN) site in Goldstone, California. As a pathfinder demonstration, RFO has demonstrated the first simultaneous, co-located radiofrequency and optical communications with a spacecraft in deep space. As the demand for larger data volumes from planetary and exploration missions continues to grow and the DSN's capacity becomes increasingly constrained, hybrid RF/ Optical ground stations emerge as a potential solution. This architecture combines the advantages of optical communications, offering high data rates, with the reliability and weather resilience of RF communications, thereby ensuring the maintenance of mission-critical communications links. This paper provides a description of the RFO system architecture and design. The results of data downlink demonstrations from the Deep Space Optical Communications (DSOC) payload on the Psyche spacecraft are presented, achieving optical data rates of up to 15 Mbps from a distance of 0.12 astronomical units (AU).

The Deep Space Optical Communication (DSOC) project has demonstrated free-space optical communication using three ground telescopes in Southern California. Through a separate NASA program, we have developed a scalable architecture and algorithms for arraying together multiple independent ground stations, allowing for cooperative reception of standards-compliant High Photon Efficiency signals. By coordinating operational plans across the three ground stations, we have taken concurrent recordings of the digitized single-photon-detected signal using high temporal resolution time to digital converters (TDCs). We subsequently combined these recordings using a post-processing software-based realization of our array algorithms to show that we can achieve essentially perfect combining even over the 100-200+ km baselines in our array. We provide analysis on the quality of temporal synchronization across a wide range of signal format and power conditions, as well as analysis on the statistical correlation of the fading processes between the three stations.

Explosive growth in digital technologies has created a radio interferometry renaissance, leading to breakthroughs including the first images of black holes with the Event Horizon Telescope (EHT). I will describe how advances in laser communications are enabling a new mission -- the Black Hole Explorer (BHEX) -- that will extend the EHT to space. BHEX will produce the sharpest images in the history of astronomy, revealing the bright and narrow "photon ring" that is predicted to exist in images of black holes, produced from light that has orbited the black hole before escaping. I will present the motivation for BHEX, the pathway to launch within the next decade, and other science opportunities that are enabled by the emergence of laser communications for space science.

The satellite mission EAGLE-1 represents an important step towards a future pan-European ultra-secure quantum key distribution (QKD) network. The public-private partnership behind the mission consist of a consortium of universities, research institutes, and space companies partially funded by ESA, the European Commission, and supported by national delegations. This unique combination of academic partners and industrial space companies facilitates a swift knowledge transfer from basic research to commercial application. Within the consortium, Tesat-Spacecom (TESAT) is responsible for developing and integrating the payload assembly of the low-earth orbit EAGLE-1 satellite. In addition, TESAT provides the SCOT80 laser communication terminal with minor adaptations for the mission. Here, we report on the status, technical aspects and TESATs contribution to the satellite-to-ground prepare-and-measure QKD mission.

Free-space optical communication links can experience signal power fluctuations due to channel effects such as turbulence and pointing jitter. Systems can ensure reliable, error-free communication over fading channels by using physical-layer techniques such as forward error correction with codeword interleaving and link-layer techniques such as erasure coding or ARQ. In this work, Shannon capacity analysis is used to compare the fundamental performance of different coding architectures in a variety of link conditions. For systems using coherent receivers we find that, in channels with benign to moderate fade statistics, there can be a ~3 dB link budget advantage to using physical-layer interleaving instead of deferring fade mitigation to the link layer. On the other hand, in very strong fluctuations or when system robustness is paramount, it can be advantageous to use link layer codes.

The ability to efficiently generate high modulation extinction ratio (ER) waveforms is important for many free-space optical applications such as those employing high-sensitivity low-duty cycle waveforms like M-ary pulse-position modulation (M-PPM). Here, we report on a simple and efficient technique using a directly modulated laser (DML) and a high-contrast narrow-band transmissive multiple-phase-shift fiber Bragg grating (FBG) filter. The FBG features low insertion loss < 0.5 dB, steep transition edges with a 3 dB bandwidth of 4.2 GHz and 40 dB bandwidth of 8.5 GHz, and deep out-of-band rejection > 60 dB. When used with a commercial DFB laser with fast chirp factor of 0.42 GHz/mA, waveforms with high ER may be generated with low modulation current < 20 mA, voltage < 1 V, and power < 20 mW. Performance and characterization of the DML, FBG, and DML-FBG generating high-ER > 30 dB waveforms at 2.88 GHz are presented.

Scintillation mitigation is a key aspect of communication performance for lasercom links. Scintillation is most often associated with turbulent channels, but can also be caused by residual pointing and tracking dynamics. In high-performance terminals on quiet platforms, robust line-of-sight stabilization can minimize jitter to a small fraction of a beamwidth, so that fading due to pointing and tracking is small enough to be compensated with link margin. However, scintillation mitigation techniques can potentially enable lower cost terminal designs and facilitate hosts with larger base disturbances. Here, we investigate the use of interleaving to mitigate fading induced by pointing and tracking losses. The results can guide system designers in selecting when interleaving is an appropriate tool for mitigating pointing and tracking dynamics in a lasercom link.

The SDA OCT Standard v.3.1.0 defines a 2500 Mbaud NRZ on-off keyed (OOK) waveform for space-space link connectivity between SDA pLEO satellites separated by up to 5500 km. For longer range 20,000 km MEO-LEO links, the new SDA OCT Standard v.4.0.0 specifies a burst mode OOK waveform for closing these links at lower data rates. The burst mode waveform uses the same clock/slot rate as specified in v.3.1.0 thereby enabling backward compatibility with previous versions of SDA optical terminals. The data rate is then set by the duty cycle of the bursts. Manchester-coded data, along with forward error correction, consistent with v.3.1.0, aids with clock and data recovery. Forward and return link modes, BM12 and BM16, with a 1/12 and 1/16 duty rate, provide user rates near 50 Mbps and 40 Mbps, respectively. A baseline transceiver design incorporating a laser, modulator, fiber amplifier, and updated SDA reference modem (COMET) will be presented.

The Integrated LCRD LEO User Modem and Amplifier Terminal (ILLUMA-T) payload was the first space-based user terminal to demonstrate successful two-way optical communications with a ground terminal via NASA’s Laser Communications Relay Demonstration (LCRD). In order to acquire the link, the ILLUMA-T optical module open loop points a wide beacon at the LCRD acquisition sensor. The initial pointing of the beacon is based on real-time ISS position and attitude information and precalculated LCRD ephemeris. This paper examines the on-orbit pointing performance of ILLUMA-T during the mission.

OSIRIS4CubeSat, the smallest commercially available laser communication terminal, was launched as part of the PIXL-1 mission to demonstrate optical direct-to-Earth links within a 0.3-unit space of a three-unit CubeSat. This work focuses on the commissioning phase, particularly the performance of the active fine pointing and tracking mechanism. This mechanism corrects pointing inaccuracies from the satellite’s attitude determination and control system within a 1-degree radius. The design and validation of a closed-loop acquisition and tracking system are presented, which adapts to changing beacon power levels via adaptive gain control. Evaluations of satellite passes, with telemetry from the deployed CubeSat, show superior performance meeting the link budget's pointing requirements. Using the developed control-loop logic, OSIRIS4CubeSat achieves a mean tracking error of 71 µrad, with a 3σ deviation of 140 µrad, even at low power levels of 119 pW. These results validate OSIRIS4CubeSat's capability to enable high-speed data transmission from low Earth orbit to Earth at rates up to 100 Mbit/s.

Free space optical (FSO) communications require robust pointing, acquisition, and tracking (PAT) schemes to maintain a link especially in terrestrial environments and while operating on-the-move. We have previously developed a PAT scheme that nests multiple control loops to achieve coarse and fine pointing and fine beam tracking. The terrestrial and maritime environments pose unique PAT challenges that have led this scheme to typically require experienced link operator personnel to maintain the link. We have worked recently to reduce operator burden with automated transition between the nested control loops. We will present architecture and results of our updated control scheme as demonstrated on a 7 km link across the Chesapeake Bay, MD with a static node on a tripod and a mobile node mounted on a test vehicle. The test results show the capability to automatically recover the link after line-of-sight blockages and vehicle impulse effects while driving.

A critical aspect of a lasercom terminal is its ability to align with a distant companion terminal. Typically, an active pointing, acquisition, and tracking (PAT) system is employed for this purpose. Such systems often require notable size, weight, and power (SWaP), and a pickoff of received power that could otherwise be used by the communication channel. The technical challenges of PAT are further compounded by platform jitter/motion and turbulence. Here, we explore passive tracking with a multi-spatial mode receiver. Multimode reception allows for greater coupling efficiency and increased tolerance to misalignment compared to single mode receivers. Additionally, tilted incident wavefronts couple, in unique ways, to the spatial modes of the multimode receiver and modal power distribution can be used to recover the incident tilt angle. Analytic and experimental results for coupling efficiency and incident angle recovery are discussed.

Lasercom acquisition scans can be broadly categorized as beacon-based or synthesized (“beaconless”). For the same transmitter power, and in the absence of pointing jitter, beacon-based scans can operate at longer ranges than the equivalent synthesized scan, but with longer scan times needed to ensure illumination of the remote terminal. Here, we use numerical simulations to investigate the effect of pointing jitter on lasercom acquisition, and to compare and contrast beacon-based vs. synthesized scans.

We present the initial results from testing of the Low-Cost Optical Terminal (LCOT) at NASA-Goddard Space Flight Center (GSFC). LCOT is designed to be a single modular design that can be quickly reconfigured to support different laser communications missions. LCOT is built around a 70cm commercially available telescope designed with optical and quantum communications in mind. We have installed a state-of-the-art adaptive optics system, novel high-power laser amplifiers, and other innovative subsystems developed by our team to facilitate laser communications. We have conducted tests of our LCOT system against operational space terminals, demonstrating our ability to receive a downlink and transmit an uplink. We show and give analysis of the results of these tests. We will also detail our plans for the future of the LCOT facility.

NASA’s Orion Artemis II Optical Communications System (O2O) will provide operational laser communications between the ground and lunar orbit for the Artemis II crewed mission. In this work we describe a 40W ground-based laser transmitter for the O2O system. The uplink transmitter operates in the optical C-band and uses an energy-efficient 32-PPM modulation format. Four individual 10W channels, each containing both the communications and the 7kHz modulated beacon signal required for acquisition are time-aligned and then combined in the far field. The transmitter delivers data at 10 Mbits/s and 20 Mbits/s channel rates, corresponding to the 250 MHz and 500 MHz slot rates respectively.

In this paper, G&H present work on the development of extremely high-power optical fibre amplifiers in the 1.5µm window for Tbit/s satellite links that will enable next generation optical satellite communications. The EPOS development project focuses on developing a 100W optical amplifier for space and a 1000W amplifier system for ground use. Within this paper, a range of experimental and simulation results are presented which include, FWM crosstalk, and gain flatness under WDM operation, nonlinear polarization rotation under intensity modulation and power limits of ErYb fibres induced by parasitic lasing at 1µm

Optical ground station testbeds were developed at NICT. These include new optical ground station with 2-meter telescope, small optical ground stations, and a transportable optical ground station. Last year, we held discussions on the use of these testbeds, and we started activities to establish guidelines for their use. In this presentation, we will introduce the details of the testbeds and present their current envisioned applications.

Optical links suffer from distortions when propagating through the atmosphere. Ground-based adaptive optics can be used to mitigate these distortions for both the receiver (post-compensation) and the transmitter (pre-compensation). We present the highly automated pre- and post-compensation adaptive optics system (AUDE) installed at the European Space Agency Optical Ground Station (Observatorio del Teide, Tenerife), a summary of the initial test campaign with geo-stationary Alphasat, and an overview of the planned upcoming testing.

In the realm of Free-Space Optical (FSO) communication systems, the transmission of data via satellite in Geostationary Earth Orbit (GEO) presents unique challenges, particularly in mitigating atmospheric turbulence-induced distortions. We here present the validation of a woofer-tweeter adaptive optics system tailored for a GEO downlink application with sub-microradian pointing requirements in strong turbulent environments. The validation process employs a hybrid approach utilizing results obtained from the experimental setup and its numerical twin in ACEsim (ALPAO Core Engine Simulator). During closed-loop operation, this data is applied to (1) the WFS images to mimic scintillation and (2) to the corrector commands to mimic the atmospheric input phase. This laboratory validation serves as a crucial step towards demonstrating the feasibility and efficacy of adaptive optics technology in GEO downlink applications. The AO system was tested on-sky at the French Optical Ground Station in France in 2024. Latest performance results will be reported.

The rising demand for optical and quantum communication necessitates more optical ground stations (OGS) in ground-based networks. To achieve efficient data reception, standardized adaptive optics systems (AOS) are needed to counter atmospheric turbulence. This paper discusses the development of a Generic Adaptive Optics Module (GAOM) aimed at Free-Space Optical Communication (FSOC). The GAOM project focuses on creating a versatile platform for managing optical laser and quantum communication signals while compensating for atmospheric disturbances to enhance single-mode (SM) fiber coupling. The upcoming tests at ESA’s IZN-1 Tenerife station aim to validate this flexible design for various OGS configurations. Key design features of GAOM include modularity and scalability, ensuring adaptability to different use cases and OGS sizes. The presentation outlines GAOM's core design concepts, AOS architecture, and target performance levels, aiming to significantly enhance OGS efficiency and support the growing demand for advanced optical and quantum communication systems.

To maximize the duration of optical downlinks with Low-Earth Orbit satellites, it is crucial to ensure the coupling in the ground terminal even at low elevations. Adaptive optics systems are designed to correct the wavefront deformation induced by the atmospheric turbulence. However, at low elevations, amplitude fluctuations (or scintillation) are challenging this correction. Here we propose an AO system design robust to scintillation, with a focus on the wavefront sensor subsystem: from the wavefront analysis with a Shack-Hartmann Wavefront Sensor to the reconstruction. We then present a simulation of the whole AO system robust to strong perturbations and scintillation which shows remarkable results in terms of coupling efficiency in a single mode fiber. Finally the gain in performance is interpreted thanks to a detailed AO error budget.

Recent work has shown that calculations of scintillation using wave optic simulation provides a much closer match to experiment than analytic approaches, such as extended Rytov theory. However, link budgets using analytic theories can be calculated much faster than those using wave optic simulation. Although there has been progress in speeding up these calculations using graphics processing units, it would still be convenient to have a low complexity solution for quick calculations with limited computing resources. In this work we pre-calculate wave optic simulations for uniform horizontal links using dimensionless parameters that allow application to a wide variety of cases. We develop approximations to the pre-calculated values that allow quick computation, and then extend these calculations to links in moderate slant paths.