This PDF file contains the front matter associated with SPIE Proceedings Volume 12413, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

Since launch in May 2022, NASA's TeraByte Infrared Delivery (TBIRD) program has successfully demonstrated 100-Gbps and 200-Gbps laser communication downlinks from a 6U CubeSat in low-Earth orbit to a ground station. The TBIRD system operates during 5-minute passes over the ground station and has demonstrated an error-free downlink transfer of > 1 Terabyte (TB) in a single pass. This paper presents an overview of the architecture, link operations, and system performance results to date.

The National Aeronautics and Space Administration’s (NASA) Laser Communications Relay Demonstration (LCRD) mission began its two-year Experiment Program in June 2022. This experimental phase includes long-term measurement of the effects of the atmosphere (turbulence, weather) on the performance and availability of lasercom. Furthermore, various future operational scenarios including robotic and exploration missions and various network service configurations are being emulated. In addition to experiments and demonstrations proposed by the LCRD Investigator Team, NASA enables individuals and groups from government agencies, academia, and industry to propose experiments under the LCRD Guest Experimenters Program. This conference paper provides highlights of the early LCRD experiments and a preview of the future experiments, including relaying data to and from the Integrated LCRD Low- Earth Orbit (LEO) User Modem and Amplifier Terminal (ILLUMA-T) on the International Space Station. The LCRD geosynchronous payload includes two laser communications terminals interconnected via an onboard electronic switch, and can relay information between two optical ground stations located in California and Hawaii. LCRD is a joint project involving NASA Goddard Space Flight Center (GSFC), the NASA Jet Propulsion Laboratory (JPL), and Massachusetts Institute of Technology Lincoln Laboratory (MIT LL).

Since launch in May 2022, the TeraByte Infrared Delivery (TBIRD) payload on a 6U CubeSat has successfully demonstrated 100/200 Gbps laser communications and has transferred >1 TB in a pass from low Earth orbit to ground. To support the narrow downlink beam needed for high rate communications, the payload provides pointing feedback to the host spacecraft to precisely track the ground station throughout the 5-minute pass. This paper presents the on-orbit results of the pointing and tracking system for TBIRD, including initial acquisition and closed-loop tracking performance of 20-35 μrad RMS per axis. Results from on-orbit characterization of the transmit beam are also presented. Measurements of Tx/Rx alignment show stability within 20 μrad, ensuring that tracking on the uplink accurately points the downlink.

Free-Space Optical Communications have gained increasing attention throughout the last years. It is intended to use optical links in a large number of application scenarios, such as communications or navigation. The Optical Satellite Links department at the German Aerospace Center's Institute of Communications and Navigation looks back to a heritage in free-space optical communication systems research of more than two decades. The researched topics include applications such as optical communications from the satellites to Earth and between satellites, development of optical ground stations, design of optimized adaptive optics systems, quantum key distribution systems, technologies for optical time-transfer and ranging, among others. This paper will give an overview of recent research activities carried out in the Optical Satellite Links department, and will give an outlook to future developments which are planned.

Rapid increases in global broadband demand are driving advanced commercial Low Earth Orbit (LEO) satellite communications systems that can deliver global broadband capacity at terrestrial level costs and performance. Flight demonstration programs such as the Defense Advanced Research Projects Agency (DARPA) “Blackjack” program are exploring the utility of Optical Inter-Satellite Links (OISLs) for these new LEO systems. For global communications, LEO systems, such as that being developed by Telesat, provide unprecedented broadband capabilities. Telesat’s new LEO system, Telesat Lightspeed, will deliver very low latency, fiber-like mesh connectivity via OISLs, increasing the capabilities for data dissemination and delivery across the globe. The ability for a User Terminal (UT) to opt to reach back without the need for anchor relay stations through multiple OISL hops between communication satellites, provides secure and resilient connectivity. Global (including the polar) connectivity, at fiber-like speeds, provides a dramatic change to high-capacity data distribution and dissemination while delivering robust reliable and trusted information. This paper will provide an architectural overview of the Telesat Lightspeed mesh network interfaces, including OISL spacecraft-to-spacecraft relay connectivity, as well as the integration of User Terminals, landing stations, satellite operations centers, and network operations centers. Satellites operating in both polar and inclined orbit planes and cutting-edge technologies, including phased array antennas, onboard data processing and OISLs, enable pole-to-pole global coverage, along with the ability to concentrate capacity in areas where it is most needed to maximize network efficiency and achieve superior unit cost economics. We identify and address challenges associated with operating OISLs including acquisition, tracking, tasking, efficient data routing, and managing network data. Lastly, we present enabling standards and technologies that enhance network flexibility, interoperability and identify areas of future capability development.

Space-based VLBI imaging can dramatically improve state-of-the-art astronomical radio-imaging resolution by enabling significantly longer baseline distances and eliminating atmospheric-attenuation constraints on RF carrier imaging wavelength. However, smaller space-based apertures and sensitivity constraints impose challenging recorded-data downlink-rate requirements, potentially to 256 Gbit/s. Laser communications is a promising option for realizing such highrate long-distance downlinks with modest power and aperture demands. Here, we present a scalable lasercom architecture that can enable high-rate long-distance downlinks needed for enhanced space-based VLBI imaging from geosynchronous orbit (GEO).

We present the transmission of continuous variable quantum key distribution (CV-QKD) qubits, ultra-high capacity of multi-tera bits over atmospheric and inter-satellite channels via the C-band. With the aid of advanced modulation formats and modern photonic technologies, we argue that multi-satellite jumps are both feasible and realizable. Photonic transceivers utilizing photonic integrated circuits in Silicon and InP technology of electro-absorption modulation lasers are presented. It is shown that optical amplification techniques, booster power amplifiers, and highly sensitive optical preamplifiers can compensate for exceedingly high attenuation of links between optical ground stations and satellites with all optical routing and link distances of 12,000 to 45,000 km. The digital signal processing algorithms in coherent receivers for ultra-high capacity and ultra-low power quantum bit systems are demonstrated to play a critical role in system performance. We specifically provide a Nyquist-equivalent sampling theorem that studies the quantum bit error rate based on both the Nyquist sampling theorem and the Heisenberg uncertainty principle. Furthermore, the Nyquist pulse shaping method and constellation probability shaping are used to maximize tera-bit transmission over spatial channels.

NASA’s Artemis II mission includes an optical communication payload, affectionately known on board as “OpCom,” which is part of NASA’s Orion Artemis II Optical Communications (O2O) demonstration. We describe the OpCom system architecture and operations concept.

The DARPA Space-Based Adaptive Communications Node (Space-BACN) optical terminal will be a low-cost reconfigurable optical intersatellite link (OISL) terminal capable of supporting up to 100 Gbps low-earth-orbit (LEO) links. Space-BACN will enable data transport between heterogenous commercial and government LEO constellations. Key to realizing a flexible transport layer is a robust command and control mechanism to dynamically negotiate service level agreements for cross-constellation OISL access. Here, we describe the development of the hybrid adaptive management schema (HAMS) for coordinating OISL access between network operation centers for different LEO constellations. Cybersecurity by design and other system considerations are also presented.

This paper details the progress in the laser communication activities of Tesat-Spacecom. The EDRS program, the European Data Relay System, a private public partnership program between the European Space Agency ESA and Airbus Defence and Space ADS, is running flawlessly, until now (Oct 2022) 75.000 data relay links have been executed. We report on the performance of the systems in space and detail on other laser comms related activities of TESAT. Especially the delivery and launch of the first optimized LCTs (Laser Communication Terminals) for LEO data relay, the Smart LCTs. In addition, the delivery of Cubesat LCTs have to be mentioned, and the development, qualification and delivery of the ConLCTs for the SDA Tranche 0 program. Furthermore, TESATs involvement in Quantum Key Distribution (QKD) and Precision Navigation and Timing (PNT) programs will be detailed.

The DARPA Space-Based Adaptive Communications Node (Space-BACN) optical terminal will be a low-cost reconfigurable optical intersatellite link (OISL) terminal capable of supporting up to 100 Gbps low-earth-orbit (LEO) links. Rapid and reliable pointing, acquisition, and tracking (PAT) is critical to OISL performance, especially in cross-plane LEO links, where contacts can be short. The Space-BACN optical terminal will demonstrate a novel reconfigurable acquisition implementation, which can be dynamically configured to operate in one of three acquisition modes: in-band, out-of-band, and synthesized beacon. Here, we review the features, implementation, performance analysis, and verification approaches for each of the three acquisition modes.

The Integrated LCRD Low-Earth Orbit User Modem and Amplifier Terminal (ILLUMA-T) payload will be launched to the International Space Station (ISS) in 2023. ILLUMA-T is an optical communications payload that will make the ISS the first space-based user to communicate with NASA’s Laser Communications Relay Demonstration (LCRD). The system will support all-optical forward links up to 150 Mbps and return links up to 1 Gbps. The payload recently underwent system level Thermal VACuum (TVAC) functional testing at MIT Lincoln Laboratory. We present an overview of the payload’s TVAC functional tests and results.

Fibertek is developing a power efficient, space qualifiable Eight WDM Channel PPM Downlink Tx Seed LAser Module (SAM) with 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 DSOC WDM Transmitter. 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. The physics model is used to quantify FWM-PEV for all 2 and 3 overlapping wavelength configurations of PPM orders 256-16. Results are used as inputs to a PPM statistics model that calculates the PEV statistics for all the PPM orders and WDM channels. The significant Improvements of the PEV statistics with the TDM based FWM mitigation using 2 or 3 wavelength subslots are quantified.

Space optical communications have attracted growing attention as space data traffic volumes continue to increase, and as part of ongoing efforts to develop high-speed optical space networks, Nikon and JAXA have been developing a singletransverse- mode 10 W polarization-maintaining Er/Yb-codoped fiber (EYDF) amplifier for modulated continuous-wave signals. We have finished developing the engineering model (EM) and plan to demonstrate this amplifier as a part of optical communication system on the International Space Station in 2024. The EM amplifier has a three-stage backward pumping structure with radiation-hardened EYDF. It also includes pump laser diodes, and power monitoring photodiodes to avoid parasitic lasing, both of which have been confirmed to have adequate radiation tolerance, as well as a control driver circuits. The overall dimensions are 300 mm × 380 mm × 76 mm, and it weighs 6.3 kg. The EM amplifier achieved optical output power of 10 W at pumping power of 34 W in total under standard temperature and pressure conditions (STP: room temperature, 1 atm) with a −3 dBm signal input. The total wall-plug efficiency reached 10.1%. The amplifier achieved an operating time of 2000 hours at 10 W under STP. We conducted a mechanical vibration test and an operating thermal vacuum test to ensure the reliability of the amplifier as a space component. At the upper and lower end of the operation temperature range, ±0 and +50 °C, the output power and polarization extinction ratio (PER) were >10 W and >16 dB, respectively, without any degradation of the amplification gain or PER.

Satellite free-space optical communication offers higher data rates, lower power consumption and mass savings compared to traditional RF and microwave technologies that are currently more widely deployed. Data rates are quickly increasing; with higher data throughputs enabled if higher power optical amplifiers are available. In this paper submission, G&H discuss initial scoping work performed in project EPOS (Extremely Powerful Optical Sources), a European Space Agency (ESA) funded development programme to significantly increase the optical power available from C-Band optical amplifiers. The project will develop a 100W amplifier for spaceborne use and a 1000W combined amplifier source for ground that will be enabling components in Tbit/s links.

High-power solid-state lasers are desirable in directed-energy applications due to their high power output and scalability. The power transmission effectiveness of 1.06-micron high-power lasers in the atmosphere at low altitudes is impacted by a variety of atmospheric effects. We use a novel low-altitude atmospheric propagation model to evaluate power transmission for 1.06-micron high power lasers under various simulated weather conditions by estimating focal irradiance on a metal surface. We introduce a novel adaptive optics framework to improve low-altitude atmospheric propagation performance for high power lasers and validate performance using computer simulations.

Optical wireless communication (OWC) promises high-speed data transmission of multiple Gb/s per user and aggregate capacities beyond Tb/s. To achieve such data rates in an eye-safe environment, we envisage an array of arrays of optical emitters, with each emitter addressing a small atto-cell. To realise this vision, each array emitter must provide uniform illumination of the desired atto-cell while minimising interference to adjacent cells. Vertical Cavity Surface Emitting Laser (VCSEL) is an attractive optical emitter for such a design due to their high modulation bandwidth (BW), circular beam waist, low cost and commercial availability of low cost arrays in the near-infrared spectrum. However, available arrays are typically multi-mode devices developed for data communications, often exhibiting a doughnut-shaped beam profile. If used with a simple lens arrangement, the resulting illumination shows non-uniform SNR over the intended atto-cell area and interference into adjacent cells. In this work, a 5×5 VCSEL-array-based OWC multi-beam transmitter using microlens arrays is designed to homogenise each VCSEL output beam intensity at the receiver plane. The performance of the proposed transmitter is verified in simulation and experiments, demonstrating a beam intensity uniformity of up to 90% over a 1 m² square area and 25.5 mW/m² uniform irradience distribution for each atto-cell area. We demonstrate the data transmission capability of a single array element achieving an 8 Gb/s data rate for a single channel using OOK modulation and Decision Feedback Equalization (DFE) with a Silicon Photomultiplier (SiPM) over a 3-metre free space link.

In free-space optical (FSO) communications, increasing the peak power of a transmission beam is important to extend the communication range. In fiber-optic communications, transmission losses are compensated by an optical fiber amplifier in the transmission path. On the other hand, in space optical communications, fiber amplifiers cannot be used on the transmission path, so it is important to achieve high transmission power output. However, high power output from fiber amplifiers is limited by stimulated Brillouin scattering (SBS) due to fiber nonlinearity. One solution to this limitation is coherent beam combining (CBC), which spatially combines multiple laser beams in the far field. In general, to configure the CBC, the phase of each beam is detected by photodetectors and feedbacked to the transmission phase of each beam, resulting in a complex and large optical system. Therefore, a frequency dither signal is applied to each beam, and the phases of multiple beams are detected simultaneously by a single photodetector. Each beam is separated by its dither frequency. Typically, a plane-wave local beam is combined on all transmitted beams to obtain heterodyne beat signals. Therefore, to achieve higher peak power, the number of beams is increased, so the size of the optical system for emitting and combining the local beam is larger. We propose a configuration in which the local beam is combined into one of the transmitted beams and photoelectrically converted by a single photodetector with the other transmitted beams simultaneously. This can simplify the optical system by removing the optical components for emitting and combining the local beams. In this paper, we explain the proposed configuration and measurement results in detail and show their effectiveness.

In this work, we introduce the concept of a hemispherical retro-modulator for the realization of passive free-space optical communication links. The hemispherical retro-modulator is implemented with a high-refractive-index glass (S-LAH79) hemisphere on a semi-insulating-InP (SI-InP) layer, whose thickness dictates the effectiveness of both retroreflection and modulation. A voltage is applied across transparent indium tin oxide (ITO) and gold (Au) films on either side of the SIInP layer to bring about the desired modulation. The overall device is designed to enable low divergence on the retroreflected beam, as defined by a small divergence angle, and deep modulation on the retroreflected beam, as a result of electroabsorption in the SI-InP layer. To this end, the device is analysed with a ray-based model for retroflection and a unified Franz-Keldysh/Einstein model for modulation in the SI-InP layer. The theoretical results show strong agreement with the experimental results from our prototype. Moreover, the results show effective retroflection and deep modulation—with an applied electric field of 2.167 kV/cm yielding modulation depths of 13%, 34%, and 50% for our 980-nm photons and SI-InP layer thicknesses of 200, 600, and 1,000 μm, respectively. From this, we deem the SI-InP layer thickness of 600 μm to be optimal given its combined capabilities for retroflection and modulation. Ultimately, the introduced hemispherical retro-modulator is shown to be an effective element for future realizations of passive freespace optical communication links.

We demonstrate high-speed data transmission with beam-steering using an as-fabricated silica optical phased array (OPA) chip. In this OPA, a constant optical path difference was built up in arrayed waveguide grating (AWG) delay lines for allocation of sequential phase delay, which enabled the beam-steering following the wavelength variation. Our designed and fabricated 1x101 silica OPA showed a beam steering of 15.4° by wavelength tuning of 30.37 nm. Using the fabricated silica OPA, 25 Gbps data transmission over a free-space range of 5 m distance was experimentally demonstrated employing an appropriate cylindrical lens, dense wavelength-division multiplexing (DWDM) tunable transceiver, and fiber collimator as a receiver. The experimental results showed that free-space data transmission through the silica OPA was successfully achieved with error-free performances regardless of the beam-steering angle.

We present concept design of an innovative, compact, non-mechanical optical beam steering antenna with a liquid crystal beam shaper optimized for lean platforms. Laser communication terminals in air and space-borne platforms must fulfil the low-SWaP (size, weight, and power) design philosophy which is often a challenging task when utilizing mechanical steerers like prisms, MEMS fast steering mirrors, lenslet arrays, gimbal movers etc. We introduce the approach of a compact photonics integrated circuit consisting of power division network, optical phase array antennas and liquid crystal on silicon structure to form a laser transmitting module for a CubeSat. An Erbium Doped Fiber Amplifier provide adequate optical power output that can facilitate a baseline free-space communication link margin at 1550nm. The design parameters were tuned to achieve to minimal divergence and adequate beam steering angle, higher EIRP, high beam switching speed and tolerance of space environmental conditions. Applications are numerous and not limited to optical communication terminals on drones, aircrafts, and satellites; automotive LiDAR systems, medical and scientific instrumentation devices are also promising areas of rapid adoption and integration.

Free-space optical communication systems always require a precise focusing on the receiver to maximize the fiber coupling efficiency. Unfortunately, atmospheric turbulence causes scintillation at the receiver. Ground to ground receivers over short distances (up to 500m) have usually small aperture (about 50mm). In this case the main aberration is tip/tilt and its correction is of fundamental importance for high bandwidth data transmission. We present a new concept of Fast Steering Prism (FSP) for the correction of tilt, suitable for optical communication and optical tracking. The system consists in the use of a novel design of a tunable prism with a variable angle based on the usage of piezoelectric actuators. A system with a FSP has the advantage to be more compact and simpler with respect to the one with a fast-steering mirror. The entire setup has been tested in a 200m outdoor transmission with promising results.

The National Aeronautics and Space Administration (NASA) Glenn Research Center (GRC) has developed a photon-counting optical ground receiver for pulse-position modulated signals. The real-time receiver system includes a fiber interconnect, superconducting nanowire single-photon detectors (SNSPDs), and a real-time field programmable gate array (FPGA) based receiver. The fiber interconnect and SNSPDs are implemented with two different configurations. In the first, a 7-channel few-mode fiber photonic lantern couples the light from the telescope to 7 single-pixel few-mode fiber coupled SNSPDs. In the second configuration, a few-mode fiber couples light to a 16-pixel monolithic SNSPD array. The real-time FPGA-based receiver performs combining of up to 16 SNSPD channels, symbol timing recovery, demodulation, and decoding. The system is scalable with data rates ranging from 20 Mbps to 267 Mbps. It is compliant with the Consultative Committee for Space Data Systems (CCSDS) Optical Communications Coding and Synchronization Standard. This standard will be used in NASA deep space and other low photon flux missions, such as in the Orion Artemis-2 Optical Communications System (O2O) demonstration, planned for the first crewed flight of Orion. This paper describes the scalable real-time optical receiver system and presents characterization test results.

The Deep Space Optical Communication (DSOC) project will conduct its technology demonstration concurrently with NASA’s Psyche mission, which hosts the DSOC flight transceiver (FLT) on its spacecraft and will operate it over an approximate range of 0.05 to 3.0 AU. The DSOC Ground Laser Transmitter (GLT), located at the Jet Propulsion Laboratory’s Optical Communication Telescope Laboratory (OCTL) near Wrightwood, CA, has been developed to provide a high-power 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. In this paper we present an overview of the completed GLT and its subsystems: (i) the multi-beam Uplink Laser Assembly (ULA) capable of transmitting up to 7 kW of average power, (ii) the Uplink Data Formatter that modulates the ULA, (iii) the GLT Optics Assembly that manages the ULA high power output beams and couples them to the OCTL telescope, (iv) the Uplink Laser Safety Assembly that automatically avoids hazardous laser irradiation by shuttering the laser output, and (v) the custom-developed Monitor and Control software used to test and operate the entire system. We discuss various implementation and operational challenges, and review results from key system performance verification and operational tests, indicating the readiness of the Ground Laser Transmitter station to fulfill the DSOC technology demonstration objectives.

The Deep Space Optical Communication (DSOC) project will conduct its technology demonstration concurrently with NASA’s Psyche mission, which hosts the DSOC flight transceiver (FLT) on its spacecraft. The DSOC Ground Laser Receiver (GLR) has been developed by the Jet Propulsion Laboratory and installed at the Palomar Observatory 5m Hale telescope in order to receive the optical downlink signal from the FLT, and is capable of processing discrete downlink data rates from 56 kbps to 265 Mbps over the course of the mission spanning an approximate range of 0.06 to 2.7 AU. In this paper we review the architecture of the completed GLR and its subsystems: (i) the GLR Optics Assembly (GLROA) that acquires the downlink signal and couples it to (ii) the GLR Detector Assembly (GDA) that features a superconducting nanowire single photon counting detector (SNSPD) array, (iii) the GLR Signal Processing Assembly (GSPA) that demodulates and decodes the pulse-position-modulated downlink waveform, and (iv) the GLR Monitor and Control software that is used to interface with the Hale telescope and operate the entire system. We discuss GLR operations in response to planned DSOC downlink activities, and present key results from end-to-end performance tests conducted with FLT hardware, as well as operational readiness test results that demonstrate Ground Laser Receiver station readiness to meet DSOC objectives.

The Australian National University (ANU) Optical Communications Ground Station (OCGS) is currently under development at Mt. Stromlo Observatory in Canberra, Australia. The OCGS will be compatible with a range of wavelengths, coding schemes, and techniques to cover satellites in Low Earth Orbit to Lunar and deep-space, and provide a platform for quantum communication from satellites. We have conducted a feasibility study and preliminary design review for the development of an instrument to support the CCSDS high photon efficiency (HPE) standard so the OCGS can support future lunar missions featuring optical communication terminals. The development of lunar communication capabilities in Australia offers site diversity and increased visibility, allowing for improved optical link availability during missions. We present the preliminary design for the transmitter and receiver which will integrate on the 70 cm telescope in the OCGS. A lab prototype of the transmitter has been built to demonstrate the generation of a pulse position modulation (PPM) waveform which is compatible with the CCSDS high photon efficiency (HPE) standard. The transmitter is made up of four 15 cm apertures which is mounted by a piggyback to the telescope. Each can operate as an independent channel with fine steering control through a fast steering mirror. The apertures are separated by characteristic atmospheric turbulence length r₀ to minimise fading at the spacecraft. The receiver is installed at the Nasmyth port of the 70 cm telescope. The receiver features a fast steering mirror to maximise coupling into a multimode fibre. The signal is split with a photonic lantern and sent to several superconducting nanowire single photon detectors (SNSPD).

NASA is planning a bi-directional space-to-ground optical-communications detailed test object ive (DTO), from the crewed Orion spacecraft scheduled to fly on Artemis II. A space terminal element (STE) developed by MIT, Lincoln Laboratory, and NASA Goddard Space Flight Center (GSFC) is planned for flight on -board the Orion spacecraft. NASA GSFC will implement an Optical-to-Orion ground segment (O2O GS). One of the ground terminals (GT) servicing the O2O GS is planned at the Optical Communications Telescope Laboratory (OCTL) located at JPL’s Table Mountain Facility, near Wrightwood, CA, while the other GT will be co-located with the O2O GS at the White Sands Complex (WSC), New Mexico. A functional description and development status of O2OGT TMF is pres ented in this paper. It is designed to support high photon efficiency (HPE) uplink and downlink signaling. The instrumentation of the O2OGT TMF will include (i) an optical assembly (OA) for interfacing laser signals to and from the OCTL telescope (ii) a beacon laser assembly (BLA) for transmitting modulated beacon lasers; (iii) an uplink laser assembly (ULA) for transmitting 10-20 Mb/s data to the STE (iv) a superconducting nanowire single photon detector (SNSPD) array for detecting the communications downlink (v) a ground signal processing assembly (GSPA) for processing the detected signal and extracting downlinked information codewords, as well as, measuring time of flight range and range rate (vi) a monitor and control (M&C) assembly for gathering and exchanging GT telemetry and (vii) a user gateway (UG) computer for interfacing user data to and from the O2O GS. Existing atmospheric channel monitor (ACM) at TMF will be used to gather and store weather and atmospheric data. The downlink will be received at discrete data-rates between 20 Mb/s and 260 Mb/s.

In this paper we present a comparative study of the losses associated with fiber-coupled single-photon detectors in two different configurations, each with the goal of receiving a pulsed-position modulated signal with a maximum data rate of 267 Mbps. First, we consider a 7x1 few-mode-fiber (FMF) photonic lantern coupled to seven individual superconducting nanowire single photon detectors (SNSPDs). In the second configuration we assess a single FMF coupled to a 16-channel monolithic SNSPD array. In each case we measure and compare combined fiber coupling, SNSPD blocking, and system efficiency losses under emulated atmospheric turbulence conditions. We address subsystem impact on link performance and analyze feasibility for future NASA lunar and deep-space optical communications missions.

This paper provides the status of ongoing work at NASA-Goddard Space Flight Center (GSFC) to build a low-cost flexible ground terminal for optical communication. For laser communication to be cost-effective for future missions, a global network of flexible optical terminals must be put in place. There is a need for a single ground terminal design capable of supporting multiple missions ranging from LEO to lunar distances. NASA’s Low-Cost Optical Terminal (LCOT) has a single modular design that can be quickly reconfigured to support different laser communications missions. The LCOT prototype uses a 70cm commercially available telescope designed with optical and quantum communications in mind. This telescope is currently being integrated with a state-of-the-art adaptive optics system, and novel high-power laser amplifier demonstrate its utility as an optical communications receiver by receiving a downlink from the recently launched Laser Communication Relay Demonstration (LCRD). LCOT uses commercially available components wherever possible, and where commercial options are not available, the LCOT team works with vendors to create commercial options. This paper discusses the development progress for the blueprint of NASA’s future global ground terminal network.

We report on the demonstration of a bidirectional free-space link over 18 km as part of the European-Union project “VERTIGO” that investigates technologies for the optical GEO-satellite feeder link. Two different terminals were deployed: a single-aperture “satellite” terminal and a 4-aperture “ground” terminal. Using SFP+ transceivers with OOK modulation at 10 Gbit/s, real-time bit error rates (BER) were measured for each aperture in both directions using an FPGA platform. In both directions, diversity signals at the receiver were processed digitally for combining. We report on the achieved performance improvement compared to a single aperture.

We present the status of ongoing work at NASA’s Goddard Space Flight Center (GSFC) to build a prototype, low-costof- production, flexibly-configured ground terminal for space optical communication. For laser telecommunication to be cost effective for future missions, a wide-spread global network of operationally responsive optical terminals should be established. There has been a decades-old need for a single modular open systems approach (MOSA) ground terminal architecture capable of supporting multiple space missions ranging from LEO to Lunar distances with 2-way laser communications. At the heart of LCOT’s design concept is the Free-Space Optical Subsytem (FSOS). The major subassemblies of LCOT/FSOS that address most optical comms configurations are : (1) Single 700mm F/12 Nasmyth folded Rx R-C Telescope, (2) Four independent 150mm diameter high-power all-reflective Tx beam directors (XOA), (3) Non-coherent direct detection Rx bench on starboard side of telescope (SOB), and (4) Coherent (possibly Quantum) optical communications bench on port side (POB). The Low-Cost Optical Terminal (LCOT) research and development (R&D) prototype is designed to be a generalized system that can be quickly field-reconfigured to support a wide variety of laser communications missions past, present, and future.

We present the initial laboratory test results of the adaptive optics (AO) subassembly for the Low-Cost Optical Terminal (LCOT), a flexible communications ground terminal developed by Goddard Space Flight Center. LCOT will receive first light in 2023 testing. This terminal includes a 700mm commercial telescope, 1550nm receive instruments, and uplink transmit systems. Demodulating coherent formats requires AO to correct turbulence effects and allow coupling into single-mode fiber. General Atomics delivered the system to Goddard in September 2021, where engineers have evaluated performance. We describe laboratory testing, turbulence phase plate design, results, and AO field testing plans when installed on LCOT.

Laser communication offers orders of magnitude higher throughput than RF with greater stealth and no frequency allocation. However, lasercom becomes truly competitive beyond 10 Gbps. At this data rate, fibered components, requiring SMF coupling, and thus turbulence mitigation become necessary. Cailabs develops an industrial product line of optical ground stations (OGS) based on its turbulence mitigation product. A pilot OGS has been assembled at Cailabs. Several telescopes, from 20 cm to 80 cm, are tested to evaluate, and qualify the system. This paper presents the latest results on OGS. Roadmap will also be presented with LEO-to-Ground link planned in 2023.

Space-to-ground laser communication is booming thanks to high throughput, stealth communication without frequency allocation. However, lasercom becomes really competitive beyond 10 Gbps. At this rate, fiber components, requiring SMF coupling, and thus turbulence mitigation become necessary. Based on Cailabs' core technology, Multi-Plane Light Conversion (MPLC) followed by photonic integrated chip, Cailabs develops a turbulence mitigation product entirely dedicated to lasercom. Previous work showed proof of concept for the 8-mode version. In this article we investigate last results obtained with the system including 100 Gbps communication and present the new 45-modes turbulence mitigation version.

The Terabyte Infrared Delivery (TBIRD) technology demonstration commenced operations in June 2022 following the spacecraft launch in late May 2022. The Jet Propulsion Laboratory (JPL), Optical Communications Telescope Laboratory (OCTL), 1-meter diameter telescope was instrumented to serve as the ground station for TBIRD. The instrumentation was a combination of lasers and modem electronics supplied by the Massachusetts Institute of Technology Lincoln Laboratory (MITLL) along with optics, sensors, and an existing adaptive optics (AO) system. The AO was embedded in an existing Optical Ground Station (OGS-1) setup supporting NASA’s Laser Communications Relay Demonstration (LCRD). The transmitting and receiving optics for TBIRD were “threaded” around the OGS-1 optics without breaking configuration, and facilitated easy switching between LCRD and TBIRD operations with a few motorized actuators. In this paper we describe (i) the design and deployment of the ground station; (ii) the concept of operations and (iii) demonstration results.

For optical links through deep turbulence, closed-loop adaptive optics (AO) can facilitate more efficient communication schemes, such as those based on coherent detection and optically pre-amplified receivers. Perturbation-based wavefront correction algorithms, such as stochastic parallel gradient descent (SPGD), are promising candidates for low size, weight, and power consumption (SWaP) alternatives to conventional AO based on direct wavefront sensing. However, limited actuator bandwidth combined with poor convergence rate can constrain the effective AO refresh rate, and degrade the performance when multiple atmospheric modes need correction. Here, we derive and test a new, generalized, non-stochastic, modal wavefront correction algorithm that utilizes either time- or frequency-division to correct multiple modes simultaneously. Using an end-to-end AO simulation, we show the new approach can relax the actuator bandwidth requirement by up to a factor of 8 in comparison to SPGD. Finally, we describe a hardware testbed that is being used to validate the developed approaches.

Free space optical links between the ground and space can be severely degraded by atmospheric turbulence, resulting in bit errors and signal fades. Adaptive optics (AO) allows partial correction of the phase aberrations induced by atmospheric turbulence, in turn allowing larger apertures and higher bandwidth for the optical link. We present FAST (Fourier domain Adaptive optics Simulation Tool), employing a semi-analytical approach using an analytical Fourier domain AO model. FAST can characterise the distribution of received flux between 10 and 200 times faster than full wave-optical simulations, and can be applied both to downlink and uplink precompensated beams.

We propose a new MMSE method relying on phase and log-amplitude on-axis measurements and statistical priors to estimate the pre-compensation phase at point-ahead angle of a ground to geostationnary satellite telecom link suffering from anisoplanatism. This method shows to reduce the tip and tilt residual phase variance down to 49% and therefore brings a gain on the link margin up to 15 dB. It also shows to improve the fade statistics, reducing the number and mean duration of fades.

Long distance imaging and free space optical communications are largely affected by atmospheric turbulence. To attenuate turbulence effects, Adaptive Optics (AO) has been the main answer and, in the case of large FOV Multi Conjugate AO (MCAO) using two deformable mirrors (DM) has been proven to be an effective solution. We present a study and some preliminary results on the use of a stack of Adaptive Lenses (AL) in a MCAO setup with the main advantage of compactness end easiness of installation.

In this presentation we show Monte Carlo computer simulations of a satellite to ground optical channel, both in downlink and uplink, and analyze the importance of an Adaptive Optics (AO) system in mitigating atmospheric turbulence effects. Finally, the results of the numerical model will be compared with results from analytical models.

We present a dual-heater control approach for narrowband, fiber Bragg gratings (FBGs) that allows both dynamic wavelength stabilization of the devices over a wide temperature range and flexible tunability of the setpoint. The control technique is applied to athermally-packaged FBGs operating in the 1.55-µm band with 3-dB bandwidths of approximately 5 GHz. The devices are actively stabilized within approximately ±7 pm (±0.9 GHz) of wave- length accuracy over a wide temperature range of 0°C to +50°C, and the setpoint is tunable over approximately 280 pm (35 GHz). A custom-designed, pulse-width modulation (PWM) heater controller is applied in two locations to the FBGs to compensate and reduce the native temperature dependence of the athermal FBG package, as well as to provide tunability of the setpoint. A temperature sensor bonded to each FBG measures the local temperature, and a feed-forward control loop adjusts the PWM signal based on the ambient case temperature, to hold the wavelength at the desired setpoint. Two different resistive heaters are bonded to opposite ends of the FBG devices, to evaluate different stabilization and tuning responses. One heater approach provides expanded thermal tunability, while the other provides improved temperature stability. An embedded processor is used to generate two different PWM, heater-control signals, which are applied to the different resistive heaters to achieve this dual-control technique. Calibration polynomials for the temperature stabilization are derived for different tuning setpoint offsets and verified with testing.

The leap to 100 Gbps data transmission rates has relied on coherent communication technology that use dual-polarization modulation formats. While several complex modulation formats use polarization to increase data rate, it can be an unwanted degree of freedom in free space links that baseline single-polarization modulation formats. In links that are signal-to-noise ratio (SNR) limited; have receivers with limited processing resources; or rely on polarization for duplex through a shared aperture; single polarization links may be preferable. Often times, a system of polarization-maintaining (PM) fibers and PM amplifiers preserve single-polarization signals from degradation as they propagate; however, these systems can be challenging to implement due to tight tolerances on components and PMfiber splices. In this paper we present a method for recovering single-polarization signals from arbitrary polarization received signals using integrated dual-polarization coherent receivers. This removes the reliance on PM fiber components while maintaining single polarization receiver performance. The algorithm uses the received signal on both polarization channels to reconstruct the initial single-polarization coherent waveform. This is accomplished by implementing a polarization rotation and polarizing filter in digital signal processing (DSP). A feature of this method is it combines the signal energy in each of the receiver’s polarization channels while rejecting the noise energy in the polarization that is orthogonal to the signal polarization. This preserves SNR while simplifying subsequent DSP steps by eliminating the unwanted polarization mode. Perhaps most importantly, our algorithm is deterministic and can be added to established DSP processes without requiring significant processing.

In this work we describe the development, characterization, and integration of a 16-channel, 400-μm diameter active area, double-ended read-out NbTiN superconducting nanowire single-photon detector (SNSPD) array and the supporting electronics used in an RF/Optical hybrid telescope for deep-space laser communications. This is the first fielddemonstration of a multi-channel, co-wound, double-ended read-out SNSPD array. With the number and complexity of future space exploration missions expected to increase, NASA is investigating ways to augment the information capacity of the Deep Space Network (DSN) global array of RF receivers used to track and communicate with these spacecrafts. Optical communication offers a path toward increasing the overall bandwidth of the DSN while allowing for higher data throughput for the same size weight and power (SWAP) transmitter on the spacecraft. NASA’s RF/Optical Hybrid (RFO) program proposes using a segmented, 8-10-meter equivalent aperture primary mirror mounted on existing 34- meter diameter beam waveguide (BWG) RF antennas to couple light into photon counting detectors for pulse position modulation (PPM) and on-off keying (OOK) data formats. JPL has deployed a pathfinder hybrid telescope on a DSN BWG antenna in Goldstone, California. The pathfinder couples light from a 1.2-meter effective diameter, 7-hexagonalsegment mirror assembly to a 400-μm core graded-index multimode fiber. This fiber is then routed to a cryostat and coupled to an SNSPD array through free-space optics. Coupling from a large diameter fiber to an SNSPD array while maintaining a small number of readout channels from the cryostat presents some unique challenges for the SNSPD array and receiver design.

HydRON (High thRoughput Optical Network) is a project of the European Space Agency (ESA) initiated in 2019. HydRON ambitions to extend high-capacity terrestrial networks into space, seamlessly and by interconnecting all kind of space assets across different orbits and terrestrial networks (i.e., 3-dimensional optical network). The targeted capacity performance is orders of magnitude greater compared to today’s satcom systems (terabit/sec in contrast to gigabit/sec). This paper will present an overview of the HydRON-DS concept, including a summary of the technical baseline and associated programmatics submitted for approval at the ESA Ministerial Council in 2022.

The optical turbulence in the Earth’s atmosphere is a major limitation to free-space optical communications. It is therefore critical that we are able to model and forecast realistic atmospheric optical turbulence conditions for site selection, instrument development, instrument performance validation and network switching. Here, we present global maps of optical turbulence strength and associated parameters (Fried parameter, isoplanatic angle, coherence time and Rytov variance), from a turbulence forecasting tool. These maps can be used by the community to understand the expected performance of free-space optical systems anywhere in the world, day and night. These maps also demonstrate that optical turbulence can be modelled and visualised in the same manner as other aspects of the Earth’s weather system such as wind, rain or temperature, opening the door for more advanced turbulence forecasting functionality. We show global averages, examples of temporal sequences and more detailed analysis from some example sites.

Characterisation and mitigation of atmospheric turbulence is critical for free space optical communication that relies on adaptive optics such as high bit rate coherent modulation or quantum key distribution. Turbulence profiling, i.e. measuring turbulence at different altitudes, provides more detail than typical seeing monitors and supports sophisticated AO and the possibility to forecast conditions. We present the implementation of a Ring-Image Next Generation Scintillation Sensor (RINGSS) instrument that profiles turbulence with a novel approach of defocused ring images introduced by A. Tokovinin (2021)1 . RINGSS is exceptionally low-cost, small, and fully automated, requiring significantly simpler equipment than previous turbulence profilers. We have demonstrated preliminary results that demonstrate the capability of this instrument for measurements of seeing and a low resolution turbulence profile. Future work is outlined that includes cross-calibration with a Stereo-SCIDAR instrument recently commissioned on the ANU 2.3m telescope at Siding Spring Observatory and plans for deployment at prospective optical ground station sites for an Australia-New Zealand optical network.

It is well-known that closed-loop deformable mirrors (DMs), liquid-crystal light valves, as well as MEMS SLMs, can compensate for piston errors. However, most aberrated beams additionally possess local tilt errors. Classes of MEMS-based SLMs exist that can provide “true wavefront reversal”: tilt and piston error correction, but require three actuators to service each optical pixel, with tilt/piston-stroke tradeoffs. True wavefront reversal has also been demonstrated if a corner cube is attached to each piston element of a DM, which is not amenable to large arrays. We propose a compact MEMS-based SLM, augmented with a metasurface-based retroreflector array, providing true wavefront reversal (phase conjugation). Application to free-space optical (FSO) links, targeting, compensated imaging and long lasers will be described.

We present the 24-hour Shack-Hartmann Image Motion Monitor (24hSHIMM), the first truly continuous, 24-hour optical turbulence monitor. Atmospheric optical turbulence is a significant limitation for free-space optical communications and other technologies. Knowledge of the turbulence conditions allows for the selection of favourable sites for optical ground stations. It also enhances operations though providing data for assimilation into turbulence forecasting models and real-time monitoring of conditions. The 24hSHIMM uses a Shack-Hartmann wavefront sensor to measure a low-resolution vertical optical turbulence profile, from which the coherence length, angle and Rytov variance are calculated. Additionally a vertical wind speed profile from meteorological forecast data is used to calculate the coherence time. Due to its portability, the instrument can operate in a wide variety of locations, even urban, to provide continuous information about the atmospheric turbulence. To demonstrate this, we show parameters recorded at the astronomical observatory in La Palma for a continuous 36-hour period. With its wide array of capabilities, the 24hSHIMM offers strong support for future research in free-space optics.

Atmospheric optical turbulence causes signal loses in laser propagation. Here we present vertical measurements of optical turbulence taken in London’s financial district. Additionally, we demonstrate a method of modelling atmospheric states in simulation from the measured data. From this we derive the predicted system performance of an optical downlink from a satellite in low Earth orbit (LEO) to ground in the atmospheric conditions observed on the night. We also present the improvements in performance with the addition of adaptive optics at the receiver end.

Understanding the vertical distribution of atmospheric optical turbulence is essential for the global-scale implementation of free-space optical communications (FSOC). Maintaining communications with satellites in low-Earth orbit (LEO) requires tracking over changing elevation angles. Decreasing elevation angles in optical communication links due to a satellite’s orbit attributes to significant signal losses due to increased propagation lengths and strong turbulence. Here we present the variance in atmospheric optical turbulence measurements in the form of scintillation index and Fried parameter measured on the Island of La Palma. These measurements are taken between elevation angles of 90° and 0° with reference measurements being taken concurrently at zenith to remove temporal variations. The results are compared with the existing theory.

Optical propagation in a marine environment is important to understand for many applications. In this work we compare measurements of the distribution function to simulation. Measurements were conducted on the Naval Research Laboratory’s Chesapeake Bay Lasercom Testbed. The experimental data is compared to wave optics simulations, which also produces a distribution function. The dependence of the distribution function on turbulence and aperture size is studied.

Atmospheric emulators based on spatial light modulators offer the ability to test atmospheric propagation effects on a laser communication component’s performance in the laboratory setting. To create a high-fidelity atmospheric emulator, details of the optical design are key. This paper discusses the optical design choices and refinements that enabled the creation of a system that was verified to recreate multi-layer turbulence with high fidelity up to D/r₀ =50. Optical design choices that affect the fidelity discussed in this paper include the characteristics of the input laser, the spatial light modulator, the holograms, the image relay optical components, and the spatial filter. Also included in this paper is a comparison of the chosen folded optical layout to an alternative angled layout.

For the next-generation wireless back-haul network, free space optical (FSO) communications are considered in non-terrestrial networks. The fading issues for the atmospheric turbulence and the misalignment become important to achieve high received power for seamless and high data rate communications. The spatial diversity technique could be the solution to mitigate these fading issues in FSO systems with a few meters of distance between transmitters larger than the coherence length. However, the distant arrangement of the transmitters causes additional alignment errors in the misalignment detection process in the pointing, acquisition, and tracking (PAT) systems, which increases the pointing loss. Therefore, the increased pointing errors should be considered to obtain desired diversity gain. In this work, we develop a statistical misalignment model due to multiple beam transmissions and analyze the transmission performance for the spatial diversity based vertical FSO links. The proposed misalignment model is investigated by the log-normal atmospheric fading channels, the distant arrangement of transmitters, and the centroid algorithm in the PAT systems. The increased alignment error in the misalignment process for multiple beam transmissions is experimentally demonstrated. The spatial diversity based FSO systems require larger beam width to compensate for the increased pointing error. The simulation results show that the system optimization with the misalignment model can increase achievable diversity gain as the number of channels increases. The proposed scheme provides an enhanced link budget to design seamless FSO based mobile back-haul networks.

Free-space optical (FSO) communication has attracted significant interest recently. This technology can potentially complement or be an integral part of next-generation networks. FSO links provide several advantages compared to conventional radio frequency links, including higher data rates, license-free spectrum, and power efficiency. Furthermore, they could be used to access users in remote areas where optical fiber communications are unavailable. Here, we present a simulation framework for modeling, designing, and analyzing classical and quantum communication systems over terrestrial and satellite free-space optical links. We address different FSO use cases in terrestrial, ground-to-satellite, satellite-to-ground, and inter-satellite links using direct- and coherent detection schemes. For the FSO channel modeling, we discuss two methods. The first approach considers atmospheric scintillation, pointing errors, the Doppler effect, attenuation due to the beam diffraction, and scintillation-induced divergence. The second method captures the wavefront of the optical beam using the phase screens technique, which provides a more detailed description of the signal propagation. Additionally, we provide essential details about system-level simulations to analyze and optimize the entire link performance. Finally, we discuss the simulation environment for designing quantum-key distribution (QKD) systems as an FSO use case. Using this simulation framework, we investigate the performance of several different FSO application examples: a terrestrial link with spatial diversity receivers, inter-satellite communication from low Earth to geostationary orbit, and a polarization-encoded BB84 with decoy states QKD over a satellite downlink.

The design and testing of a free-space optical communication system requires assessment of the impact of random fluctuations in received power from a laser beam transmitted over an atmospheric channel. A number of methods for generating fading power vectors for in-lab emulation of an atmospheric channel have previously been reported. These techniques include spectral shaping and filtering of a signal from a normally distributed pseudo-random number generator, full wave optics simulations with random phase screens, and pre-recorded measurements from experimental free-space links. In this work, a statistical analysis of atmospheric fading is presented with the goal of producing a practical engineering model suitable for generating synthetic fade vectors in real-time for long-duration receiver testing with channel interleaving. Specifically, a parametric model is developed for turbulence-induced fade on space-to-ground links with large-aperture receivers, including aperture-averaging and the effects of aperture size on the instantaneous coupling efficiency for mode-limited receivers. In particular, we analyze the probability density function and temporal power spectrum for fluctuations of the coupling efficiency for few-mode fibers in a range of turbulence conditions.

The atmospheric effects on the propagation of light have been a matter of interest in fields like astronomy, meteorology, and optical communications where phase variations of wavefront have a significant impact in detection systems. The effects of the optical turbulence on the laser beam change from one region to another, this is linked to the atmospheric characteristics of the area (relative humidity, atmospheric pressure, wind, and temperature). Our research center is in a region with harsh atmospheric conditions for optical propagation. For this reason, it is important to measure and replicate these conditions in the laboratory environment. In this work, we present the results of our laboratory experimental setup to characterize infrared beam at 1064-nm using a turbulence chamber designed by our team. In our experimental setup, the transversal windspeed is varied in the turbulence generator chamber, and the beam centroid is measured after 4-m propagation path for different wavelengths and different optical powers. The beam is analyzed before and after the turbulence generation chamber. In this paper, we report our initial results in developing a laboratory experimental setup to emulate Middle East atmospheric conditions and compensate for these effects using an adaptive optics system.

JAXA and NICT have started the collaborative research for cislunar optical communications. NICT is responsible for research and development some of key technologies for cislunar optical communication systems utilizing GEO relay satellite. NICT has especially focused on research and development of a large-aperture optical antenna, high-sensitivity optical communication system applying adaptive optics and HDR method, which is based on binary phase shift keying scheme, onboard the GEO relay satellite. In this paper, we will present the overview of collaborative research and key technologies for cislunar optical communication systems. We will also describe the current status of our research and development activities.

For enabling and realizing long-haul Quantum Key Distribution (QKD), satellite communication infrastructure is exploited to deliver symmetric encryption keys to ground segments. In this direction the European Quantum Communication Infrastructure (Euro-QCI) initiative, supported by the European Space Agency (ESA), aims to build a secure quantum communication network that will span across the EU. In this framework, ESA has selected three observatories in Greece to support European activities in optical communications and QKD systems. In this study, a QKD feasibility analysis between a LEO satellite constellation (100 satellites) and the three selected Optical Ground Stations (OGSs) in Greece, using an entangled based QKD protocol is presented. This contribution focuses on the performance evaluation and the applicability validation of an entanglement-based QKD system in a pragmatic regional segment of Euro-QCI. The time varying atmospheric channel is modeled taking into account the joint cloud coverage of the OGSs, the turbulence, the pointing errors and the solar background radiance. The performance of the regional entangled-based QKD system is validated in terms of annual availability as well as the number of shared distilled key bits between the ground stations per year.

The optical inter-satellite communication system with high-speed, small size and low power consumption is required because of increase of data capacity for observation satellites. Optical coherent technology has promising potential not only high sensitivity of communication systems but also high immunity against the back ground light for communication between satellites as well as between satellite and ground station. To realize a high-speed and small optical terminal, we have developed a coherent optical receiver that integrates optical angular sensor for spatial beam tracking in wavelength of 1.5 μm. The angular sensor is segmented photodiodes and it can detects the direction of arrival beam from a counterpart satellite by calculating the center of gravity of each output. The coherent optical frontend is a free-space optical 90-degree hybrid. By inputting the output light from coherent optical frontend to the segmented photodiodes, both orthogonal detection of communication signals and angle detection are achieved. The integrated coherent receiver is a size of 100 cm2. As a demonstration of coherent angle detection, we compared the results of simulation and actual measurement for angle detection using segmented photodiodes, and verified the validity of the design. We demonstrated orthogonal detection with this receiver by measuring the heterodyne beat output from the segmented photodiodes with cut-off frequency of 3.5 GHz, which corresponds to frequency difference between local and signal light. Applying this optical receiver to laser communication terminal, since it is not necessary to branch the received optical power to the capture and tracking sensor, the transmitted optical power required for communication can be reduced.

Robust laser beam pointing, acquisition and tracking capabilities are key to enable the next generation of laser communication applications. This paper highlights key elements of the design concept, performance simulations and test results of Lighthouse, a wavelength-agnostic and externally mountable high-power beacon for use in optical ground stations, developed by Airbus Netherlands. During the optical communications link, the beacon operates in a static stare-mode, which offers fast and reliable acquisition and re-acquisition capabilities. Lighthouse also offers the capability of automated co-alignment with the telescope system on which it is hosted, by making use of a highly accurate and rotating retroreflector. Uplink beam propagation simulations show that using multiple Lighthouse units in a single optical ground station allow for the effective mitigation of adverse turbulence effects by leveraging the multi-beam effect. A factory test campaign characterizes the performance of the beacon including time traces of the laser output power, the beam quality and the pointing stability. The turbulence simulation results and test results feed into a comprehensive link budget for various mission scenarios. The validation of the multi-mission concept is planned in frame of the TELEO GEO in-orbit demonstration in Q3 2023.

This conference presentation was prepared for the Free-Space Laser Communications XXXV conference at SPIE LASE, 2023.

We report the results of gamma radiation testing of the performance of 1064 nm packaged butterfly single mode DFB lasers (QD Laser QLD1061) for satellite and space applications. Both passive and active tests were conducted, with measurements of output power, optical signal-to-noise-ratio (OSNR), output spectra, and polarization extinction ratio (PER) as a function of dose rates and total radiation exposure. No significant changes in laser behavior were observed for total doses up to 100 kRad.