June 1, 2022
… while Airguide Photonics’s development of hollow fibers achieves “record low” propagation losses.
Researchers from the Institute for Network Research at the Japanese National Institute of Information and Communication Technology (NICT) reported the world’s first demonstration of more than 1 petabit per second in a multi-core fiber with a standard diameter of 0.125 mm.
Researchers led by Benjamin J. Putnam is constructing a transmission system that supports a record optical bandwidth exceeding 20 THz using wavelength division multiplexing (WDM) technology. It includes commercially available fiber-optic windows known as C and L-bands, and expands the bandwidth to include the recently studied S-band.
The results of this experiment were adopted as a presentation after the deadline of the International Conference on Laser and Electro-Optics (CLEO) 2022, earlier this month.
Two types of alloy fiber amplifiers, together with Raman amplification with pumps added to a new multi-core pump combiner, allow the transmission of 801 wavelength channels over 20 THz optical bandwidth.
A large number of wavelength channels are transmitted in each core of a quad-core MCF, which has the same sheath diameter as a standard optical fiber. Such fibers are compatible with modern cable technologies and do not require the complex signal processing required to decode signals in multimode fibers, which means that conventional transceiver hardware can be used.
Quad-core MCFs are considered to be the most likely of the new advanced optical fibers for early commercial deployment. This demonstration demonstrates their potential for carrying information and is a significant step towards the implementation of backbone communication systems that support the evolution of information services beyond 5G.
Background
The search for improved data transmission capacity has inspired both the study of new spectral transmission windows and advanced optical fibers using spatial parallelization. In recent years, advanced fibers with the same sheath diameter as standard single-mode optical fibers, but capable of supporting multiple propagation pathways, have been proposed.
NICT set various world records by constructing different transmission systems using new optical fibers and in December 2020 succeeded in the first demonstration of 1 petabit per second transmission in a standard diameter fiber using a 15-mode optical fiber.
However, such fibers require complex MIMO (Multiple-input-multiple-output) digital signal processing to decode signals that are mixed during transmission, and practical implementation is expected to require large-scale development of special integrated circuits.
NICT constructs the latest transmission system using a 4-core MCF with a standard cladding diameter of 0.125 mm, WDM technology and mixed optical amplification systems. The system allows the transmission of 1.02 petabits per second at 51.7 km. Previously, 610 terabits per second were achieved in such a fiber, but only with the help of a part of the S-band.
Hollow fibers show “record” low losses
A study by Southampton’s Airguide Photonics program to develop hollow core fibers with record low propagation losses and outstanding power properties has been published in Nature Photonics.
The study focuses on the transmission of laser beams with a power in kilowatts over a kilometer of fiber length, while maintaining virtually ideal quality single-mode beam. This transmission is impossible in conventional optical fibers because the high intensity of the laser interacts with the glass and quickly compromises the integrity of the beam, which means that power levels in one kilowatt mode can usually be transmitted only a few tens of meters in conventional fibers .
Dr Hans Christian Mulwad of Southampton, who is leading the high-power transmission experiments, said: “The possible technology behind our breakthrough is the development of hollow core fibers with record low propagation losses. Because the laser beam propagates in a hollow core instead of a hard glass core, as in conventional fiber, harmful nonlinear interactions with the glass are virtually eliminated. This allows very high power levels to be transmitted without any detrimental effect on the beam quality.
“In addition, low loss is essential for energy-efficient transmission, which allows most of the power of the laser source to be delivered to the fiber outlet even after a kilometer,” he said.
“Recent breakthroughs have seen that the loss of propagation has been reduced to record lows, comparable to established fibers at near-infrared telecommunications wavelengths and even lower in the visible spectrum. This is one of those low-loss NANFs operating in the near-infrared range that is used in this work. “
“This fiber and arrangement allowed the research team to demonstrate the transmission of a kilowatt single-mode laser beam over a kilometer, with a total power loss of only 20 percent. Mulwad added: “We also performed detailed numerical simulations showing that the fiber can support even higher power levels and longer transmission lengths, highlighting NANF’s superior performance over conventional single-mode power supply fibers.
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