Bridging the Cosmic Divide: Free Space Laser Communications for Satellites, Moon, and Mars

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Communication is the backbone of human progress and exploration, extending its reach from Earth to the farthest corners of our solar system and beyond. As we push the boundaries of our interplanetary ventures, the need for cutting-edge communication technologies becomes paramount. Enter Free Space Laser Communications, a transformative technology that is revolutionizing the way we connect with aircraft, satellites, and even celestial bodies like the Moon and Mars.

The Challenge of Radio Communication

Communicating with spacecraft, especially those beyond Earth’s orbit, is a complex endeavor. The existing methods of deep space communication rely heavily on radio-frequency (RF) signals, which have served us well for decades. However, RF communications have limitations, such as low data rates and narrow bandwidth. Spacecraft typically have relatively weak receivers, necessitating the transmission of strong radio signals from Earth. These signals are not only demanding in terms of power but also require large sensitive radio dishes to capture the spacecraft’s relatively weak replies. This is why NASA’s Deep Space Network (DSN), a collection of specially designed radio telescopes, plays a crucial role in enabling deep-space communication.

Need for Deep Space Optical Communications

As our endeavors in space exploration become increasingly ambitious and our reliance on satellite technologies continues to grow, the limitations of traditional radio-based communication systems are becoming more pronounced. When we return to the Moon and place our first footsteps on Mars, we will want not only scientific data but live video feeds, high-resolution images, and even tweets from the astronauts.  Increased space exploration and the growing capability and thus data output of satellite-borne sensors operated by agencies such as NASA, ESA and JAXA impose greater demands on communication systems to operate at higher data rates and to reach across farther distances into space.  Even the most sophisticated radio network isn’t capable of that level of bandwidth.

To address the growing demands of long-distance communication, a groundbreaking technology has emerged: Free Space Optical Communications (FSOC). Unlike conventional radio waves, FSOC relies on visible and infrared light for data transmission, opening up a new era in space communication.  FSO operates on the Line-of-Sight phenomenon, consisting of a LASER at source and detector at the destination which provides optical wireless communication between them. This contrasts with using solids such as optical fiber cable. “Free space” means air, outer space, vacuum, or something similar.  This innovative technology offers several key advantages that are transforming the way we communicate in space.

One of the most significant advantages of FSOC is its ability to deliver high data rates. With substantially larger bandwidth and higher data transfer speeds, FSOC excels at transmitting large volumes of data quickly and efficiently. This is particularly important for missions that require real-time data exchange and high-resolution imagery, as well as for accommodating the ever-increasing data output from satellite-borne sensors.

Another compelling feature of FSOC is its operation in the license-free spectrum. Unlike traditional radio communication, which often demands the allocation of specific radio spectrum frequencies, FSOC operates in a spectrum that is free from regulatory constraints. This not only simplifies the implementation of FSOC systems but also reduces the bureaucratic hurdles often associated with obtaining the necessary spectrum licenses.

Quick deployability is a hallmark of FSOC systems. These systems are relatively easy to set up, making them ideal for various applications, including temporary communication links and disaster recovery scenarios. In situations where laying fiber optic cables or configuring traditional radio communication may be impractical, FSOC can be rapidly deployed to establish point-to-point communication links, providing a flexible and efficient solution.

Furthermore, FSOC boasts lower power requirements compared to traditional radio frequency (RF) communication technology. This enhanced energy efficiency is a vital factor for resource-constrained missions, where power conservation is of paramount importance. It allows spacecraft and ground stations to transmit and receive data while minimizing the demand on power resources, ultimately extending the lifespan of mission-critical equipment.

In summary, Free Space Optical or Laser communications is creating a new communications revolution, that by using visible and infrared light instead of radio waves for data transmission  is providing  large bandwidth, high data rate, license free spectrum, easy and quick deployability,  low mass and  less power requirement.  It also offers low cost transmission as against radio frequency (RF) communication technology and fiber optics communication. As the technology continues to advance, we can anticipate a future where FSOC plays a pivotal role in enabling seamless and high-speed communication throughout the cosmos.

Applications of FSOC

Both military and civilian users have started planning Laser communication systems from terrestrial short-range systems, to high data rate Aircraft and Satellite communications, unmanned aerial vehicles (UAVs) to high altitude platforms (HAPs), near-space communications for relaying high data rates from moon, and deep space communications from mars.

Revolutionizing Satellite Communication:

Satellites play a pivotal role in modern life, from global communications to Earth observation and weather forecasting. To enhance their capabilities, FSLC has emerged as a game-changer. Traditional radio-frequency communication for satellites has limitations in terms of data transfer rates and bandwidth. FSLC resolves these issues by employing laser-based communication.

Free Space Laser Communications facilitate high-speed data transfer between Earth and satellites in orbit. This technology allows satellites to relay large volumes of data in a fraction of the time compared to traditional methods. It is particularly critical for Earth observation satellites, space telescopes, and scientific missions, enabling rapid transmission of high-resolution images and other data to Earth.

Interplanetary Exploration:

The expansion of our exploration horizons encompasses celestial bodies like the Moon and Mars. FSLC is an indispensable tool for interplanetary communication, especially given the vast distances involved. When astronauts embark on lunar or Martian missions, maintaining real-time communication with Earth is essential.

FSLC comes into play by facilitating high-speed data exchange between spacecraft and mission control on Earth. The low signal latency and high data transfer rates of FSLC make it possible for astronauts to receive immediate instructions, conduct remote experiments, and stay connected to loved ones during their missions. This technology has the potential to transform the way we approach lunar bases and future Martian colonies, ensuring seamless communication even across interplanetary gaps.

Security and Data Transfer Efficiency:

One of the significant advantages of FSLC is its enhanced security. Laser beams used for communication are highly directional, reducing the risk of interference or interception. This is particularly crucial for secure military and sensitive government communications, where data privacy is of utmost importance.

Additionally, FSLC technology enables efficient data transfer, making it ideal for transmitting large datasets, high-definition videos, and other resource-intensive information. The high data transfer rates ensure that critical data reaches its destination swiftly, minimizing delays and latency.

Free Space Optical Technology

Atmospheric conditions pose a significant challenge in free space optical (FSO) communication systems, causing signal attenuation and increasing the bit error ratio (BER). To address these issues, vendors have devised innovative solutions, including multi-beam or multi-path architectures that utilize multiple transmitters and receivers. Some cutting-edge FSO devices incorporate larger fade margins, which reserve additional power to counter environmental factors like rain, smog, and fog. Furthermore, the implementation of strict safety measures maintains an eye-safe environment, with good FSO systems adhering to laser classes 1 or 1M, ensuring safe operation.

One crucial aspect to consider is the impact of atmospheric and fog attenuation, which follows an exponential nature, ultimately limiting the practical range of FSO devices to several kilometers. However, FSO systems operating at a 1550 nm wavelength experience considerably lower optical losses than those employing an 830 nm wavelength, particularly in dense fog conditions. FSO systems utilizing the 1550 nm wavelength can transmit significantly higher power than their 850 nm counterparts, all while remaining safe for human eyes, typically classified under 1M. In addition, some advanced FSO solutions like EC SYSTEM enhance connection reliability in adverse weather conditions through continuous monitoring of link quality, allowing for real-time adjustments of laser diode transmission power via built-in automatic gain control. With developers worldwide successfully addressing the most challenging aspects of the technology, free space optical communications are poised to revolutionize global and extra-global telecommunications landscapes.

 

 

Free Space Optical System

Free space optical communication links necessitate the integration of various essential components, including optical transmitters and receivers, space-ready high-performance steerable telescopes, and mechanisms for precisely locating and stabilizing the narrow optical beams.

These links commonly employ distinct optical channels, including the Transmit, Receive, Acquisition and Tracking (such as a beacon), and Reference (or align) channels. The optical system’s role encompasses transmitting optical data and receiving beacon signals. Transmit and receive channels may feature separate or shared apertures. The beacon signal serves for acquisition and tracking purposes and may be a narrow-band laser signal from a cooperative target or a broader spectrum source, such as celestial reference signals from stars, the Sun-illuminated Earth, or the Moon.

The Transmit Channel extends from the laser transmitter’s output to the optics’ exit aperture. The Receive Channel is responsible for capturing light emerging from the fore-optics and directing it to a photo-detector. The Acquisition and Tracking Channel projects the incoming beacon signal onto the acquisition and tracking detector. The Reference (or align) Channel forms an image of a portion of the transmitted light at the array detector without demanding an extremely high level of image quality.

Laser communications involving airborne and space-borne assets typically require three different optical systems with distinct specifications. These include the flight terminal with telescope apertures typically ranging from 5 to 50 cm in diameter, the ground receiver terminal with apertures ranging from 0.5 to 10 m, and the uplink command or optical beam pointer (e.g., beacon) with aperture diameters typically between 0.5 to 1 m.

Achieving Transmit-Receive Isolation is crucial since the transmit power significantly surpasses the receiver’s sensitivity levels. For transceivers that need to point near the Sun, up to 150 dB isolation of the receive channel from the transmit channel might be necessary. It’s essential to minimize scattering from optical surfaces and incorporate adequate optical isolation at each design stage. Different isolation strategies, such as spatial isolation, spectral isolation (e.g., filtration), temporal isolation (e.g., transmitting and receiving at different times), polarization isolation, aperture sharing, and coding with deep interleaving, can be implemented.

Dedicated Star-Trackers can be added to the optical system as acquisition and tracking beacons. Precise alignment between these sensors and the optical channels within the terminal is critical, especially for achieving sub-micro-radian pointing accuracy. Dedicated star trackers typically feature small apertures, around 6 to 8 cm, but a significantly wider field-of-view spanning a few degrees.

Maintaining Mechanical, Thermal, and Temporal Stability is of utmost importance. The structural integrity and thermal stability of the terminal are critical design parameters. Simultaneously, efforts should be made to minimize the telescope’s mass. Thermal gradients can lead to changes in the optical system’s surface figure, and mismatches in thermal expansion between the optics and the structural components may affect the system’s performance.

 

Reduction in SWap of FSOC system

The ongoing drive to reduce the Size, Weight, and Power (SWaP) of optical communication systems has ushered in a new era of possibilities in the field of telecommunications. Compact and lightweight designs are now capable of being integrated into microsatellites, commonly referred to as CubeSats. This breakthrough empowers these diminutive spaceborne platforms to extend internet connectivity to remote and underserved regions, effectively eliminating the need for costly and logistically challenging cabling infrastructure. In contrast to previous hardware, which relied on large and intricate steering mechanisms mounted on weighty, stable optical benches, along with power-hungry multistage optical amplifiers, current designs have harnessed the potential of fast-steering mirrors (FSMs) and optical closed-loop beacon tracking to achieve a tightly focused optical communications beam within a significantly smaller form factor.

As elaborated by BridgeComm’s Sanford, these innovations translate into substantial reductions in SWaP requirements. Presently, commercially available optical communication systems boast impressive capabilities, with designs supporting data rates ranging from 10 to over 100 Gb/s, all while maintaining a total weight of less than 5 kg and exhibiting remarkable energy efficiency. These designs are versatile enough to fit seamlessly into CubeSats, meeting the needs of not only space-based applications but also mobile commercial and military platforms, terrestrial point-to-point connections, and airborne systems.

The deployment of satellite constellations, often referred to as “constellations in the sky,” is a key strategy for many companies looking to establish global internet coverage. These constellations leverage laser communications for intersatellite links, creating expansive canopies of internet connectivity in the Earth’s orbit. Subsequently, this connectivity can be efficiently directed to terrestrial locations as needed, facilitating comprehensive internet access on a global scale.

 

Transmitters and Receivers

Free Space Optical (FSO) communication has traditionally operated within the 1- to 1.5-µm bands, with a notable emphasis on the 1.55-µm fiber telecom band and the closely related 1.064-µm band. This strategic wavelength selection has allowed FSO systems to leverage components developed by the expansive fiber telecommunications and its subsidiary markets. However, the future holds promising developments in FSO technology, with systems expected to explore new horizons in the 0.8 to 0.9-µm bands, as well as venturing into the visible and ultraviolet (UV) spectrums.

To achieve the highest bandwidth formats, detectors need to be physically compact or even single-spatial-mode, a requirement that imposes unique challenges on FSO receivers due to atmospheric turbulence, which can stem from both natural phenomena and disturbances caused by aircraft traversing the airspace. Adaptive optics, employing deformable mirrors or coherent array concepts, offer a solution by mitigating the effects of turbulence and enabling efficient coupling of light into single-mode detection systems. These single-mode receivers encompass coherent and optically preamplified architectures, both of which have reached a high level of maturity. Additionally, analogous to certain radio frequency systems, non-demodulating transponders have become feasible, relying on single-mode reception and amplification.

Some FSO receivers, such as avalanche photodiode detectors, exhibit relatively low complexity and do not necessitate single-mode reception. While they may be 10 to 20 dB less efficient compared to other receiver types, their performance remains suitable for specific system designs. Lastly, photon-counting detectors, which can be semiconductor-based, rely on photomultiplier tubes or superconducting materials, and they have demonstrated a remarkable 5- to 15-dB improvement in photon efficiency compared to coherent receivers. Importantly, many of these photon-counting detectors do not mandatorily require single spatial mode reception. Currently, some of these advanced detectors demand more intricate support systems like cryogenic refrigeration, which confines their use to terrestrial applications. Nonetheless, there is considerable promise that future developments will render these superlative efficiency photon-counting detectors suitable for use in small aircraft or even spaceborne FSO systems, thereby enhancing the capabilities of FSO communication technology.

One photon-per-bit receiver

Significant progress has been made in advancing receiver sensitivity, a crucial factor in maximizing data throughput with minimal received photons. Improved receiver sensitivity holds the key to extending the reach, achieving higher data rates, and enabling the use of more compact optics or a combination thereof. While free space communication enjoys an extensive optical bandwidth, photon counting receivers with limited detection bandwidth can impose constraints on attainable data rates, particularly in the case of higher-order PPM, which tends to be spectrally inefficient.

Demonstrated advancements in photon counting receivers employing PPM modulation have yielded noteworthy sensitivities, including approximately 1 photon-per-information-bit (PPB) at 14 Mbps and 1.2 PPB at 38 Mbps. NASA’s endeavors have further pushed the boundaries, showcasing the successful application of PPM and photon counting technologies at rates exceeding 100 Mbps, reaching speeds of 622 Mbps with a sensitivity of 3.8 PPB in the Lunar Laser Communication Demonstration (LLCD) and 781 Mbps with a remarkable 0.5 detected PPB sensitivity. It is essential to consider factors like insertion loss and non-ideal quantum efficiency, with the latter result corresponding to an approximate black-box sensitivity of 8 incident PPBs.

As the demands for future space communication systems, encompassing inter-satellite and satellite-to-ground links, surge to speeds of several tens of Gbps and beyond, it is imperative to achieve substantial improvements in existing receiver technology. These improvements need to focus on both data rate and sensitivity enhancements to meet the burgeoning data transmission needs.

Notably, superconducting nanowire-based receiver variants have displayed exceptional performance, boasting a quantum efficiency of up to 90% at data rates of a few hundred Mbps. However, one of the key limitations of such receivers is their requirement for cooling to 2–4 K, and they face challenges in detecting photons at rates in the multiple Gbps range.

The sensitivity of these systems is predominantly determined by the noise figure (NF) of the pre-amplifier, typically at a theoretical level of 3 dB for most amplifiers. Promisingly, phase-sensitive optical amplifiers (PSAs) have surfaced as a technology with an exceptionally low NF of 0 dB, holding the potential to deliver the utmost sensitivity for long-haul Gbps-rate free-space links. Innovative experiments have demonstrated the efficacy of a PSA-based receiver in free-space transmission, achieving a groundbreaking bit-error-free, black-box sensitivity of 1 PPB at an information rate of 10.5 Gbps. This system adopts a straightforward modulation format (quadrature-phase-shift keying, QPSK), standard digital signal processing for signal recovery and forward error correction, and is readily scalable to even higher data rates, promising to address the growing needs of future high-speed FSO communication.

 

Flight optics and pointing, acquisition and tracking systems

The precision of laser communication systems heavily relies on flight optics and the mechanisms used for pointing, acquisition, and tracking. For optimal performance, various strategies and technologies are employed to ensure accurate beam control.

In the context of beam steering, the means to achieve large steering motions involve gimballing the telescope or employing methods like periscopic mirrors or Risley prisms. For small beam adjustments, both these traditional methods and modern alternatives, such as mechanical steering mirrors or solid-state devices located within the small-beam-space behind an afocal telescope, come into play. These mechanisms collectively contribute to fine-tuning the laser beam’s direction and alignment.

Initial beam pointing depends on direction estimates derived from a combination of star trackers, Earth sensors, GPS, and gyros. However, the inherent error margins associated with these sensors are typically larger than the beamwidth delivered by the telescope, often only in the range of tens of microradians. Consequently, the link’s spatial acquisition phase is nearly always essential, allowing the two terminals to precisely locate each other. In this phase, a variety of approaches can be adopted, such as transmitter scanning or broadening and the use of specialized receiver sensors designed to detect signals from a wide field of view, all in accordance with agreed-upon protocols.

Given the extreme narrowness of laser beams, designers must also consider the relative cross-velocity of the two platforms involved in the communication link. This necessitates a “point-ahead” strategy, where the transmitter is directed slightly in front of the receiver. The required angles for point-ahead adjustments vary from approximately 17 urad for geostationary orbit (GEO) to ground links, to around 60 urad for GEO to low Earth orbit (LEO) connections, and up to as much as 500 urad for interplanetary systems. Once the beams are accurately pointed, maintaining their stability within a small fraction of their width is crucial. Active tracking designs, which are based on tracking the incoming beam, demand the use of specialized detectors or conically scanned receivers for motion detection, coupled with mechanisms like fast, small mirrors situated behind the telescope. Alternatively, non-received-beam methods can be employed, including inertial references or actively stabilized platforms, further enhancing the precision and reliability of laser communication systems.

Challenges of FSOC

Despite its promising advantages, Free Space Optical Communications (FSOC) does encounter some challenges that need to be addressed for its widespread adoption and reliable operation in various space communication scenarios.

Accurate beacon positioning plays a pivotal role in the establishment of stable laser communication links within satellite systems. In satellite-to-ground optical communication, the acquisition of the beacon is primarily influenced by two key factors: background noise and atmospheric turbulence. These elements are critical in ensuring the reliable and uninterrupted transmission of data via laser communication technology.

Moreover, when it comes to long-haul optical links traversing through the Earth’s atmosphere, several challenging factors can significantly impact signal quality. These factors include attenuation caused by various atmospheric conditions, such as fog, haze, rain, clouds, scintillation, and the influence of index-of-refraction turbulence (IRT). Additionally, optical links may face disruptions due to link blockages from obscuration. Hamid Hemmati, Director of Engineering for Telecom Infrastructure at Facebook, highlighted these challenges during a presentation at the Milcom conference. He emphasized the uncertainties associated with maintaining satellite-to-ground communication links, particularly when signals must travel through atmospheric disturbances.

Physical Obstructions: The line of sight (LOS) transmission in FSO systems can be temporarily obstructed by flying birds, trees, or tall buildings when they come into the path of the optical beam.

Geometric Losses: Optical beam attenuation, resulting from beam spreading, diminishes the power level of the signal as it travels from the transmitter to the receiver.

Absorption: Suspended water molecules in the terrestrial atmosphere can cause absorption of photons’ power, reducing the power density of the optical beam and directly affecting transmission availability. Carbon dioxide can also contribute to absorption.

Atmospheric Attenuation: One of the primary challenges that FSOC systems face is the impact of atmospheric conditions. Factors such as fog, snow, rain, and turbulence can attenuate optical signals, leading to a degradation in the performance of the communication link. These weather-related variables can obstruct the free-space path, affecting the signal quality and, in turn, the reliability of data transmission.

Scintillation: Temperature variations among different air pockets, often caused by factors like heat rising from the Earth and man-made sources such as heating ducts, can lead to fluctuations in the amplitude of the optical signal. This phenomenon, known as “image dancing,” affects signal stability. Some FSO systems address scintillation using unique multibeam approaches.

Pointing and Tracking Accuracy: Achieving and maintaining precise beam alignment over extended distances is crucial for FSOC systems. Small optical beam divergences, vibrations, and platform movements can lead to pointing inaccuracies. Advanced technologies are required to address these challenges, ensuring that the optical signals are precisely directed and tracked, especially in the presence of factors like wind loads and thermal expansions.

Atmospheric Turbulence: Atmospheric turbulence, stemming from weather-related phenomena such as wind and convection, poses a significant challenge to FSOC communication. The mixing of air parcels with varying temperatures can lead to fluctuations in the density of the air and, consequently, changes in the air’s refractive index. This turbulence can result in beam wander, where the optical beam spot shifts rapidly, or intensity fluctuations, known as scintillation. These disturbances can degrade the quality of optical signal transmission and disrupt data transfer.

Interference from Environmental Factors: In practical scenarios, FSOC communication links may face interference from various environmental factors. Physical obstructions like buildings, trees, and even flying birds can temporarily block the optical beam’s line of sight, causing signal interruptions. Temperature variations in the atmosphere due to factors such as heat from the Earth or man-made sources, like heating ducts, can lead to fluctuations in signal amplitude, resulting in the phenomenon known as “image dancing” at the receiving end. These challenges underscore the need for robust FSOC systems capable of mitigating the effects of these environmental interferences.

Addressing these challenges is essential to ensure that FSOC can fulfill its potential as a reliable and high-speed communication technology for space exploration, satellite communication, and various other applications. Advances in adaptive optics, beam stabilization, and environmental interference mitigation techniques will be crucial in overcoming these hurdles and maximizing the capabilities of FSOC in diverse operational environments.

Developments in FSOC

However, FSOC technology has advanced significantly, with a track record of successful demonstrations, including notable projects like SILEX (the Semiconductor laser Intersatellite Link Experiment), GOLD (the Ground/Orbiter Lasercom Demonstration), and LADEE (NASA’s Lunar Atmosphere and Dust Environment Explorer). Furthermore, FSOC achieved a significant milestone by providing the first operational laser communication service through EDRS (the European Data Relay System), often referred to as the SpaceData Highway. These accomplishments underscore the maturity and reliability of FSOC technology in space-based communications.

NASA developed integrated photonics modem for International Space Station

NASA’s Breakthrough in Integrated Photonics Modem for International Space Station

NASA has achieved a significant milestone in space communication technology by developing its first integrated photonics modem, which is scheduled for testing aboard the International Space Station in 2020. This cutting-edge device, boasting a form factor comparable to a mobile phone, incorporates lasers and switches onto a microchip. Its groundbreaking feature lies in its ability to use lasers to encode and transmit data at rates 10 to 100 times faster than today’s conventional communications equipment.

In a collaborative effort, LGS Innovations, a specialized technology company focused on mission-critical communications research and solutions, has been selected to support the NASA Integrated Laser Communication Relay Demonstration (LCRD) Low-Earth Orbit (LEO) User Modem and Amplifier (ILLUMA) project. As part of this pioneering program, LGS will develop a free-space optical modem set to be deployed on the International Space Station, marking the first demonstration of a fully operational end-to-end optical communications system. Leveraging LGS Innovations’ extensive expertise in free-space laser communications and fiber laser technology, this advancement promises to reshape space communication capabilities.

Integrated photonics, described as integrated circuits that harness light instead of electrons to perform an array of optical functions, represent a transformative leap in technology. Don Cornwell, director of NASA’s Advanced Communications and Navigation Division, leading the modem’s development, highlights that recent advancements in nanostructures, meta-materials, and silicon technologies have vastly expanded the potential applications of these highly integrated optical chips. Furthermore, the possibility of mass-producing them through lithographic processes akin to electronic circuitry holds the promise of substantial cost reduction for photonic devices.

NASA’s mission is not merely to advance technology but to deliver tangible benefits, as Thomas Krainak, NASA’s laser communications lead, explains. The aim is to enhance data exchange within the scientific community, demanding affordable, compact, and lightweight modems. Ultimately, the goal is to develop and demonstrate this technology, making it available to industry and other government agencies, thereby creating an economy of scale that drives costs down significantly.

The Integrated LCRD LEO User Modem and Amplifier (ILLUMA) is set to be installed on the International Space Station in 2020. It will serve as a low-Earth terminal for NASA’s Laser Communications Relay Demonstration (LCRD) mission, highlighting yet another advancement in high-speed, laser-based communications. ILLUMA will not only qualify the technology for flight but also demonstrate a pivotal capability for future spacecraft. Beyond communicating with ground stations, upcoming satellites will require the capacity to communicate with one another, thus expanding the horizon of possibilities for laser-based communication technology. This achievement represents a leap forward in space communication, enabling faster data transfer, higher data rates, and more efficient utilization of resources, including scientific data transfer and ultra-high-definition video streaming to and from space.

 

Space Photonics Received Patent for Free Space Laser Communications in 2017

Space-qualified optics developer Space Photonics Inc. has received its seventh patent in the technology sector that includes free space laser communications. The new patent, titled “Simultaneous Multi-Channel Optical Communications System with Beam Pointing, Switching and Tracking Using Moving,” and the company’s other patents, use specific inventions for very rapid and extremely accurate angular pointing and tracking of free space laser communications beams used for ultrahigh-capacity digital signals commonly used in ground-based internet networks. The technology will provide a much needed boost for emerging global networks using satellites, aircraft and high-altitude balloons.

 

“This patent is by far the most valuable we’ve received. It provides innovative but simple techniques for pointing and tracking laser communications beams sent and received from moving airborne and space borne vehicles. It does this without using heavy gimbals or moving prisms and mirrors commonly used by others with techniques that are much less accurate for laser beam angular tracking and pointing. Using lasers also can replace certain standard radio frequency transceivers used on orbiting satellites,” said Chuck Chalfant, president and CEO. “The patent title can put you to sleep but is descriptive.”

Laser beam technology breakthrough could revolutionise optical communications

In a groundbreaking development, scientists have introduced a new class of laser beams referred to as “spacetime wave packets” that seemingly challenge established laws of light physics. These innovative beams exhibit distinct behaviors in refraction, potentially paving the way for transformative communication technologies. The conventional understanding is that light travels at varying speeds through different materials, slowing down as it passes through denser substances. A classic example illustrating this concept is the way a spoon placed in a glass of water appears bent at the water’s surface. This optical distortion occurs because light moves more slowly through water than air, resulting in the bending of light rays—a phenomenon governed by Snell’s Law.

The implications of this discovery extend significantly to the realm of optical communication technologies. To illustrate, consider a scenario where a plane transmits messages encoded in light to two submarines located at the same depth but varying distances away. Typically, the message would reach the closer submarine first. However, with spacetime wave packets, these light pulses could be meticulously manipulated to reach both submarines simultaneously.

While it may seem that this innovation contradicts fundamental laws of physics, it is important to note that it remains consistent with special relativity. The scientists are not tampering with the oscillations of the light waves themselves; instead, they are controlling the speeds at which the peaks of light pulses travel. This is achieved through the utilization of a spatial light modulator, a device that restructures the energy of each light pulse, intertwining its properties in both space and time. According to Basanta Bhaduri, a co-author of the study, “Space-time refraction defies our expectations derived from Fermat’s principle and offers new opportunities for molding the flow of light and other wave phenomena.” This pioneering research was published in the journal Nature Photonics, opening doors to innovative and transformative possibilities in the field of optical communications.

Recent Breakthroughs

Free space laser communications (FSLC) is an evolving technology poised to redefine communication within the realms of satellites, lunar missions, and Martian exploration. FSLC harnesses the power of laser beams to transmit data across vast distances in space, presenting a game-changing solution with superior data rates and bandwidth when compared to conventional radio frequency (RF) communication systems.

Recent strides in FSLC for applications spanning satellites, lunar missions, and Mars expeditions are truly noteworthy:

1. In 2023, NASA’s Deep Space Optical Communications (DSOC) experiment achieved a remarkable milestone by demonstrating the viability of optical communications for deep space missions. DSOC impressively transmitted data across a record-breaking distance of 4 million kilometers, and it seamlessly beamed high-definition video from the Psyche spacecraft to Earth.
2. The year 2022 saw the European Space Agency (ESA) launching the Laser Communication Relay Demonstration (LCRD) satellite. LCRD serves as a technology demonstrator, diligently assessing the potential of optical communications for inter-satellite links and ground stations’ connectivity to satellites.
3. In 2021, the China National Space Administration (CNSA) introduced the Tianlian-2 01 satellite, which boasts an advanced optical communications system. The Tianlian-2 01 satellite plays a pivotal role in providing optical communications services to Chinese spacecraft currently in orbit.

These breakthroughs are just the tip of the iceberg, with several other FSLC missions on the horizon, including:

• NASA’s Lunar Laser Communication Demonstration (LLCD) mission, slated for launch in 2024, will critically evaluate optical communications for lunar-Earth connectivity.
• The European Space Agency’s (ESA) forthcoming SILEX-NG mission, set for liftoff in 2025, will introduce a laser communication relay satellite capable of delivering optical communications services to ESA’s orbiting spacecraft.
• The US Space Force’s Space-Based Infrastructure (SBI) program is actively developing a network of laser communication relay satellites. This infrastructure will play a pivotal role in providing optical communications services to both US military and civilian spacecraft.

These impressive advancements are gradually solidifying FSLC’s position as a viable communication alternative for satellites, lunar missions, and Mars exploration.

The Path to the Future

Despite these challenges, the free space optical communication field is continuously advancing. Researchers are exploring innovative ways to improve receiver sensitivity, expand data rates, and develop advanced tracking and alignment systems. In 2020, NASA initiated a project to test an integrated photonics modem aboard the International Space Station, demonstrating data transmission rates 10 to 100 times faster than traditional systems.

FSOC is expected to continue shaping the landscape of global and extra-global telecommunications, providing the means for swift and efficient communication over vast distances. As this technology matures and becomes more widely adopted, we can look forward to a future where interplanetary communication is seamless and real-time, even across the cosmos.

 

 

 

 

 

 

 

 

 

 

 

 References and Resources also include:

http://www.albanydailystar.com/science/nasa-develops-integrated-photonics-modem-for-international-space-station-erie-tech-time-15961.html

https://www.photonics.com/a61909/Free-Space_Optical_Communications_Comes_of_Age

https://trs.jpl.nasa.gov/bitstream/handle/2014/38461/03-1910.pdf?sequence=1&isAllowed=y

https://www.photonicsspectra-digital.com/photonicsspectra/january_2020/MobilePagedArticle.action?articleId=1550707#articleId1550707

https://www.nature.com/articles/s41377-020-00389-2