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. 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.
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.
US-based LGS Innovations, has won a contract from NASA to provide a laser transmitter for a first-of-a-kind space mission. The Herndon, Virginia, company’s photonics technology will be one of the key elements in a high-bandwidth optical communications link that will beam data and high-resolution imagery back to Earth from a craft orbiting around an unusual metal asteroid. A part of what is known is full as NASA’s Deep Space Optical Communications (DSOC) project, the laser transmitter will fly on the mission to the asteroid “Psyche” as a technology demonstration.
For military, FSO is the next frontier for net-centric connectivity, as it can provide low cost, large bandwidth, high speed and secure communications in space and inside the atmosphere. There are size, weight and power (SWAP) advantages as well. Intelligence, Surveillance, and Reconnaissance (ISR) platforms can deploy this technology as they require disseminating large amount of images and videos to the fighting forces, mostly in real time.
That’s why the Defense Department recently awarded a three-year, $45 million grant to a tri-service project for a laser communications system. Thomas and her collaborators have moved past the research equipment and are building a full-up prototype expected to be ready by 2019.
Growing employment of laser free space communication
One major NASA priority is to use lasers to make space communications for both near-Earth and deep-space missions more efficient. Laser wavelengths are 10,000 times shorter than radio waves, allowing data to be transmitted across narrower tighter beams; therefore the energy is not spread out as much as it travels through space.
For example, a typical Ka-Band signal from Mars spreads out so much that the diameter of the energy when it reaches Earth is larger than Earth’s diameter. A typical optical signal, however, will only spread over the equivalent of a small portion of the United States; thus there is less energy wasted. This also leads to reduction in antenna size for both ground and space receivers, which reduces satellite size and mass. “The shorter wavelength also means there is significantly more bandwidth available for an optical signal, while radio systems have to increasingly fight for a very limited bandwidth,” explains NASA.
This technology is capable of providing promising gigabit Ethernet access for high rise network enterprise or bandwidth intensive applications (e.g., medical imaging, HDTV, hospitals for transferring large digital imaging files or telecommunication) or intra campus connections.
FSO technology provides good solution for cellular carriers using 4G technology to cater their large bandwidth and multimedia requirement by providing a back haul connection between cell towers It can provide a back up protection for fiber based system in case of accidental fiber damage. It is believed that FSO technology is the ultimate solution for providing high capacity last mile connectivity up to residential access.
Laser communications could also benefit a class of missions called CubeSats, which are about the size of a shoebox. These missions are becoming more popular and require miniaturized parts, including communications and power systems.
The drawback of the FSO link is that its performance is strongly dependent on atmospheric attenuations. Different atmospheric conditions like snow, fog and rain scatter and absorb the transmitted signal, which leads to attenuation of information signal before receiving at receiver end. As a result of attenuation caused by atmospheric conditions the range and the capacity of wireless channel are degraded thereby restricting the potential of the FSO link by limiting the regions and times.
Laser communications for global internet connectivity
Facebook aims to use a mix of solar-powered aircraft and low-orbit satellites to beam signals carrying the internet to hard-to-reach locations. ‘As part of our Internet.org efforts, we’re working on ways to use drones and satellites to connect the billion people who don’t live in range of existing wireless networks,’ said Mark Zuckerberg.
The drones, flying at 65,000ft (19,800 metres), will be capable of staying in the air for months. ‘Our Connectivity Lab is developing a laser communications system that can beam data from the sky into communities. ‘This will dramatically increase the speed of sending data over long distances.
It is proposed that for sub-urban areas in limited geographical regions, solar-powered high altitude drones will be used to deliver reliable internet connections via FSO links. For places where deployment of drones is uneconomical or impractical (like in low population density areas), LEO and GEO satellites can be used to provide internet access to the ground using FSO.
Freespace laser communications was used to send data reliably between balloons flying on the stratospheric winds in Project Loon. Now loon team is working with AP State FiberNet, a telecom company in Andhra Pradesh, a state in India which is home to more than 53 million people. Less than 20% of residents currently have access to broadband connectivity, so the state government has committed to connecting 12 million households and thousands of government organizations and businesses by 2019 — an initiative called AP Fiber Grid.
AP State FiberNet announced that they’ll be rolling out two thousand FSOC links created by team at X. These FSOC links will form part of the high-bandwidth backbone of their network, giving them a cost effective way to connect rural and remote areas across the state. The links will plug critical gaps to major access points, like cell-towers and WiFi hotspots, that support thousands of people.
World record in free-space optical communications
Researchers at the German Aerospace Center have set a new record in data transmission using laser: 1.72 terabits per second across a distance of 10.45 kilometres, which is equivalent to the transmission of 45 DVDs per second. This means that large parts of the still under-served rural areas in Western Europe could be supplied with broadband Internet services.
We have set ourselves the goal of enabling Internet access at high data rates outside major cities, and want to demonstrate how this is possible using satellites,” explains Christoph Günther, Director of the DLR Institute of Communications and Navigation. Fibre-optic links and other terrestrial systems offer high transmission rates, but are available predominantly in densely populated regions.
Outside of the metropolitan centres a broadband supply via geostationary satellites is possible. Scientists as part of the DLR THRUST (Terabit-throughput optical satellite system technology) project, satellites should be connected to the terrestrial Internet via a laser link. The envisaged data throughput is more than one terabit per second. Communication with the users is then carried out in the Ka-band, a standard radio frequency for satellite communications.
Within the framework of the experiments, a fibre-optic transmission system of the Fraunhofer Heinrich Hertz Institute was employed which operates at wavelengths of around 1550 nanometres and which is suitable for high data rates. This system was integrated into DLR’s newly developed free-space optic transmission system.
NASA’s Lunar Laser Communication Demonstration (LLCD) and Laser Communications Relay Demonstration (LCRD)
NASA’s Laser Communications Relay Demonstration (LCRD) mission has begun integration and testing at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. The LCRD mission continues the legacy of the Lunar Laser Communications Demonstration (LLCD), which flew aboard a moon-orbiting spacecraft in 2013.
LLCD had demonstrated error-free communication from the Moon to the Earth under all conditions, including during broad daylight and even when the Moon was within 3° of the Sun as seen from Earth. It also proved that a space-based laser communications system was viable and that the system could survive both launch and the space environment.
NASA’s Lunar Laser Communication Demonstration (LLCD) used a pulsed laser beam to transmit data from the Moon to Earth at a record-breaking download rate of 622Mb/s. The space laser terminal employed a 0.5W IR laser at 1.55 microns (which is eye-safe as well as invisible to the eye) and 4in (10.7cm) telescope to transmit toward the selected ground terminal. The downlink beam is received by an array of telescopes that are coupled to novel and highly sensitive superconducting nanowire detector arrays that convert the photons in the beam to bits of data.
The Goddard team is now planning a follow-on mission called the Laser Communications Relay Demonstration (LCRD) that proposes to revolutionize the way we send and receive data, video and other information, using lasers to encode and transmit data at rates 10 to 100 times faster than today’s fastest radio-frequency systems, using significantly less mass and power. It will fly as a commercial satellite payload in 2019. It consists of two optical communications terminals in space and will enable real-time forwarding and storage of data up to 1.25 Gbps (coded) / 2.880 Gbps (uncoded).
Mission operators at ground stations in California and Hawaii will test its invisible, near-infrared lasers, beaming data to and from the satellite as they refine the transmission process, study different encoding techniques and perfect tracking systems.While in operation, LCRD will also enable the gathering of information about the longevity and durability of space-based optical systems and their hardware, as well as ensuring the accuracy of the lasers that carry messages to the ground. They also will study the effects of clouds and other disruptions on communications, studying mitigating solutions including relay operations in orbit or backup receiving stations on the ground.
NASA is now planning laser communications from Mars, it is developing new optical communications system, that will reduce the time required to transmit high resolution images from Mars from 90 minutes to few minutes. The new optical communications system that NASA plans to demonstrate in 2016 will even allow the streaming of high-definition video from distances beyond the Moon.
The Deep Space Optical Communications project is developing three key technologies essential for operational deep space optical communications, Spacecraft disturbance isolation platform, Photon counting receiver for spacecraft optical transceiver consisting of radiation-tolerant indium gallium arsenide phosphide (InGaAsP) detector and superconducting photon counting detectors for the Earth-based optical receivers.
The team at Glenn is developing an idea called Integrated Radio and Optical Communications (iROC) to put a laser communications relay satellite in orbit around Mars that could receive data from distant spacecraft and relay their signal back to Earth. The system would use both RF and laser communications, promoting interoperability amongst all of NASA’s assets in space. By integrating both communications systems, iROC could provide services both for new spacecraft using laser communications systems and older spacecraft like Voyager 1 that use RF.
NASA’s up and coming Psyche mission to explore a unique metal asteroid orbiting the Sun between Mars and Jupiter, will also test new communication hardware that uses lasers instead of radio waves. In parallel with a more conventional X-band microwave link, it will send engineering and science data from the Psyche Spacecraft and is said to be the first such laser transmitter to support deep-space, high-bandwidth optical communication.
“Future deep space exploration missions, both manned and unmanned, will require high-bandwidth communications links to ground stations on Earth to support advanced scientific instruments, high-definition video, and high-resolution imagery,” states LGS, adding that its transmitter will enable much faster communication and help improve the efficiency of future solar system exploration missions
Europe’s Global Laser Communications System
The first dedicated laser terminal forming a high-speed optical network in space is now in orbit, after a Proton rocket launch from Kazakhstan on January 29. Part of the future “European Data Relay System” (EDRS), which the European Space Agency (ESA) describes as its “most ambitious telecommunications program to date”, the laser was developed by key partner Tesat Spacecom, an Airbus subsidiary.
The European Space Agency (ESA) and partner Airbus Defence and Space are aiming to build out the European Data Relay System (EDRS) into a global laser communications network by 2020 and hope that the system will become an international standard. Sentinel satellites 1A, 1B, 2A and 2B all have Laser Communication Terminals (LCT) payloads.
ESA and Airbus completed a major test of the EDRS system in late 2014, linking the Sentinel 1A satellite built by Thales Alenia Space with the Airbus-built Alphasat satellite via Laser Communication Terminals (LCTs). The test beamed images from Sentinel 1A, which circles the planet at 700 kilometers in Low Earth Orbit (LEO) to Alphasat 36,000 kilometers up in Geostationary Earth Orbit (GEO) and back to the ground. Tesat boasts it’s point-to-point data transfer covers about 28000 miles with transfer rate of 5 Gigabits per sec.
“[Sentinel 1A] produces around 1.8 terabytes of raw data every single day, and when we process this data it is even three terabytes, more or less, on average we produce everyday. In 2017 we will have seven Sentinels working and roughly seven times the amount of data to download. Four of these Sentinels will have a laser communication terminal and can use EDRS,” he said.
Stefan Klein, head of aviation division General Atomics, Spezialtechnik, said his company is eager to use EDRS laser communications for its Unmanned Aerial Vehicles (UAVs). Today the company’s drones get up to 40 hours of flight without refueling, and require real-time data through secure communications. The company plans to build LCT payloads to leverage EDRS by the end of the decade.
Laser Light Communications’s Optical Satellite Systems
The world’s first optical wave satellite communications has been planned by Laser Light Communications, intending to deploy it in the first quarter of 2017.The company plans on creating a 12-satellite constellation in MEO with an operating system capacity of 4.8 terabytes/sec and satellite-to-satellite optical crosslinks and satellite-to-ground optical up/down links of 200 gigabytes/sec. The company envisions integrating the Optical Satellite System with existing terrestrial and undersea fiber optic levels.
DISA has signed a Cooperative Research and Development Agreement with Laser Light Communications to evaluate the feasibility of the underlying technology and the future potential of the all-optical system for DOD missions.
The laser communications is attractive for defence of its high bandwidth and freedom from issues like spectrum allocation or mutual interference due to satellite spacing. The system is also more secure because enhanced resistance of optical communication systems from interception and jamming.