Laser Links Give Aging Supercomputers a Second Wind – IEEE Spectrum

2 Comments

1. March 10, 2016 at 12:36 pm

   Tomi Engdahl says:

   Gigabit Ethernet Through the Air
   http://hackaday.com/2016/03/10/gigabit-ethernet-through-the-air/

   There are a couple of really great things about transmitting data using light as the carrier. It can be focused so that it doesn’t spill all over the neighborhood like radio signals do — giving it both some security against eavesdropping and preventing one signal from stepping on another’s toes. And while you can modulate radio signals up nearly to the carrier frequency, the few gigahertz we normally use for radio just won’t cut it for really high bit rates. Light gets you terahertz.

   The Koruza project is an open-source, “inexpensive” system that aims to transmit 1 Gb/sec over distances around 100 meters, using modulated infrared light.

   1Gbps networking connectivity for locations up to 100m apart, using an eye-safe infrared light beam.
   http://koruza.net/index.html

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2. September 16, 2022 at 10:15 am

   Tomi Engdahl says:

   Free-space optics surpasses traditional technology
   Aug. 16, 2022
   Free-space optics moves from science fiction to a practical technology deserving of a place in wireless access networks.
   https://www.laserfocusworld.com/optics/article/14280255/freespace-optics-surpasses-traditional-technology

   As optical signals move deeper and deeper into access networks, achieving the ambitious performance goals of 5G architectures requires more optics than ever between small cell sites.

   Extending fiber optics deeper into remote communities “is a critical economic driver, promoting competition, increasing connectivity for the rural and underserved, and supporting densification for wireless,” according to Deloitte, a financial and tech consulting firm.1

   But there are cases in which fiber isn’t cost-effective to deploy. For example, a network carrier might need to quickly increase its access network capacity for a big festival, and there is no point in deploying extra fiber. In many remote areas, the customer base is so small, the deployment of fiber won’t produce a return on investment. These situations can be addressed via some kind of wireless access solution.

   Carriers have used fixed microwave links for years to handle these situations. But radio microwave frequencies might not be enough as the world demands greater internet speeds.

   Simply changing over to higher carrier frequencies will limit the reach of microwave links. The radio spectrum is also quite crowded, and carriers might not have the available licensed spectrum to deploy this wireless link. And microwave point-to-point links produce plenty of heat while struggling to deliver capacity beyond a few gigabits per second.

   FSO is often referred to as a futuristic technology for space applications, but can also be used for ground-to-ground links in access networks. FSO can deliver a wireless-access solution for quick deployment and with more bandwidth capacity, security features, and less power consumption than traditional point-to-point microwave links. And since it does not use the RF spectrum, there is no need to secure spectrum licenses.

   Alignment and atmospheric turbulence

   FSO has struggled to break through into practical applications despite these benefits because of certain technical challenges. Communications infrastructure, therefore, focused on more stable transmission alternatives such as optical fiber and RF signals. But research and innovation during the last few decades is removing these technical barriers.

   One obstacle to achieving longer distances with FSO is the quality of the laser signal. Over time, FSO developers have found a solution to this issue in adaptive optics systems. These systems compensate for distortions in the beam by using an active optical element—such as a deformable mirror or liquid crystal—that dynamically changes its structure depending on the shape of the laser beam.

   Another drawback of FSO is aligning the transmitter and receiver units. Laser beams are extremely narrow and if the beam doesn’t hit the receiver lens at just the right angle, the information may be lost. The system requires almost perfect alignment (see Fig. 2), which it must maintain even when there are small changes in the beam trajectory due to wind or atmospheric disturbances.

   FSO systems can handle these alignment issues with fast steering mirror (FSM) technology.

   Safe, private networks

   One understated benefit of FSO is, from a physics perspective, they’re arguably the most secure form of wireless communication available today.

   Point-to-point microwave links transmit a far more directional beam than mobile antennas or WiFi systems, which reduces the potential for security breaches. But even these narrower microwave beams are spread out enough to cover a wide footprint vulnerable to eavesdropping and jamming (see Fig. 3). At a 1 km distance, the beam can expand enough to cover roughly the length of a building, and at 5 km, it could cover an entire city block. Microwave systems have side and back lobes radiating away from the intended direction of transmission that can be intercepted, as well. If an attacker is close enough to the source, even the reflected energy from buildings can be used to intercept signals.

   Laser beams in FSO are so narrow and focused that these issues don’t exist. At 1 km, a typical laser beam only spreads out about 2 m, and at 5 km, only about 5 m. There are no side and back lobes to worry about and no near-zone reflections. The beam is so narrow that intercepting the transmission becomes an enormous challenge. An intruder would need to get within inches of a terminal or the line of sight, making it easier to be discovered. To complicate things further, the intruder’s terminal would also need to be very well aligned to pick up enough of a signal.

   While fiber-optic communications drove the push for smaller and more efficient optical transceivers, this progress also has a beneficial impact on FSO.

   FSO systems can now take advantage of affordable, low-power transceivers to transmit and receive laser signals in the air. For example, a transceiver based on an optical SoC can output a higher power into the FSO system. By using this higher laser power, the FSO does not need to amplify the signal as much before transmitting it, improving its noise profile.

   FSO can deliver a wireless access solution to be deployed quickly and with more bandwidth capacity, security features, and less power consumption than traditional point-to-point microwave links. And since it does not use the RF spectrum, it is unnecessary to secure spectrum licenses.

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