Oral phenylephrine was shown to be ineffective for treating nasal congestion over a year go. This week, the FDA took the first steps toward removing it from pharmacy shelves.
A new and practical approach to the low-noise amplification of weakened optical signals has been unveiled by researchers in Sweden. Drawing from the principles of four-wave mixing, Rasmus Larsson and colleagues at Chalmers University of Technology believe their approach could have promising implications for laser-based communication systems in space.
Until recently, space-based communication systems have largely relied on radio waves to transmit signals. Increasingly, however, these systems are being replaced with optical laser beams. The shorter wavelengths of these signals offer numerous advantages over radio waves. These include higher data transmission rates; lower power requirements; and lower risks of interception.
However, when transmitted across the vast distances of space, even a tightly focused laser beam will spread out significantly by the time its light reaches its destination. This will weaken severely the signal’s strength.
To deal with this loss, receivers must be extremely sensitive to incoming signals. This involves the preamplification of the signal above the level of electronic noise in the receiver. But conventional optical amplifiers are far too noisy to achieve practical space-based communications.
Phase-sensitive amplification
In a 2021 study, Larsson’s team showed how these weak signals can, in theory, be amplified with zero noise using a phase-sensitive optical parametric amplifier (PSA). However, this approach did not solve the problem entirely.
“The PSA should be the ideal preamplifier for optical receivers,” Larsson explains. “However, we don’t see them in practice due to their complex implementation requirements, where several synchronized optical waves of different frequencies are needed to facilitate the amplification.” These cumbersome requirements place significant demands on both transmitter and receiver, which limits their use in space-based communications.
To simplify preamplification, Larsson’s team used four-wave mixing. Here, the interaction between light at three different wavelengths within a nonlinear medium produces light at a fourth wavelength.
In this case, a weakened transmitted signal is mixed with two strong “pump” waves that are generated within the receiver. When the phases of the signal and pump are synchronized inside a doped optical fibre, light at the fourth wavelength interferes constructively with the signal. This boosts the amplitude of the signal without sacrificing low-noise performance.
Auxiliary waves
“This allows us to generate all required auxiliary waves in the receiver, with the transmitter only having to generate the signal wave,” Larsson describes. “This is contrary to the case before where most, if not all waves were generated in the transmitter. The synchronization of the waves further uses the same specific lossless approach we demonstrated in 2021.”
The team says that this new approach offers a practical route to noiseless amplification within an optical receiver. “After optimizing the system, we were able to demonstrate the low-noise performance and a receiver sensitivity of 0.9 photons per bit,” Larsson explains. This amount of light is the minimum needed to reliably decode each bit of data and Larsson adds, “This is the lowest sensitivity achieved to date for any coherent modulation format.”
This unprecedented sensitivity enabled the team to establish optical communication links between a PSA-amplified receiver and a conventional, single-wave transmitter. With a clear route to noiseless preamplification through some further improvements, the researchers are now hopeful that their approach could open up new possibilities across a wide array of applications – especially for laser-based communications in space.
“In this rapidly emerging topic, the PSA we have demonstrated can facilitate much higher data rates than the bandwidth-limited single photon detection technology currently considered.”
This ability would make the team’s PSA ideally suited for communication links between space-based transmitters and ground-based receivers. In turn, astronomers could finally break the notorious “science return bottleneck”. This would remove many current restrictions on the speed and quantity of data that can be transmitted by satellites, probes, and telescopes scattered across the solar system.
The addition of Discover to LabX’s portfolio strengthens its position as a leading voice in science and research media, bringing one of the most recognized science publications into its family.
The Arecibo Observatory’s “uniquely powerful electromagnetic radiation environment” is the most likely initial cause of its destruction and collapse in December 2020. That’s according to a new report by the National Academies of Sciences, Engineering, and Medicine, which states that failure of zinc in the cables that held the telescope’s main platform led to it falling onto the huge 305 m reflector dish – causing catastrophic damage.
While previous studies of the iconic telescope’s collapse had identified the deformation of zinc inside the cable sockets, other reasons were also put forward. They included poor workmanship and the effects of hurricane Maria, which hit the area in 2017. It subjected the telescope’s cables to the highest structural stress they had ever endured since the instrument opened in 1963.
Inspections after the hurricane showed some evidence of cable slippage. Yet these investigations, the report says, failed to note several failure patterns and did not provide plausible explanations for most of them. In addition, photos taken in 2019 gave “a clear indication of major socket deterioration”, but no further investigation followed.
The eight-strong committee, chaired by Roger McCarthy of the US firm McCarthy Engineering, that wrote the report found that move surprising. “The lack of documented concern from the contracted engineers about the inconsequentiality of cable pullouts or the safety factors between Hurricane Maria in 2017 and the failure is alarming,” they say.
Further research
The report concludes that the root cause of the catastrophe was linked to the zinc sockets, which suffered “unprecedented and accelerated long-term creep-induced failure”. Metallic creep – the slow, permanent deformation of a metal – is caused by stress and exacerbated by heat, making components based on the metal to fail. “Each failure involved both the rupture of some of the cable’s wires and a deformation of the socket’s zinc, and is therefore the failure of a cable-socket assembly,” the report notes.
As to the cause of the creep, the committee sees the telescope’s radiation environment as “the only hypothesis that…provides a plausible but unprovable answer”. The committee proposes that the telescope’s powerful transmitters induced electrical currents in the cables and sockets, potentially causing “long-term, low-current electroplasticity” in the zinc. The increased induced plasticity accelerated the natural ongoing creep in the zinc.
The report adds that the collapse of the platform is the first documented zinc-induced creep failure, despite the metal being used in such a way for over a century. The committee now recommends that the National Science Foundation (NSF), which oversees Arecibo, offer the remaining socket and cable sections to the research community for further analysis on the “large-diameter wire connections, the long-term creep behavior of zinc spelter connections, and [the] materials science”.
Meanwhile, the NSF had planned to reopen the telescope site as an educational center later this month but that has now be delayed until next year to coincide with the NSF’s 75th anniversary.
More than 50 papers from India have been recognized with a top-cited paper award for 2024 from IOP Publishing, which publishes Physics World. The prize is given to corresponding authors who have papers published in both IOP Publishing and its partners’ journals from 2021 to 2023 that are in the top 1% of the most cited papers.
“Knowing that the astronomy community has appreciated the published research is excellent,” says Vaidehi. “It has been postulated for a long time that the physics of relativistic jets is governed by the central supermassive black hole and accretion disk, also known as the central engine of an active galaxy. Our work is probably the first to quantify their physical properties, such as the black hole mass and the accretion disk luminosity, for a large sample of active galaxies hosting powerful relativistic jets called blazars.”
Vaidehi explains that getting many citations for the work, which was published in Astrophysical Journal Supplement Series, indicates that the published results “have been helpful to other researchers” and that this broad visibility also increases the chance that other groups will come across the work. “[Citations] are important because they can therefore trigger innovative ideas and follow-up research critical to advancing scientific knowledge,” adds Vaidehi.
Vaidehi says that he often turns to highly cited research “to appreciate the genuine ideas put forward by scientists”, with two recentexamples being what inspired him to work on the central engine problem.
Indeed, Vaidehi says that prizes such as IOP’s highly cited paper award are essential for researchers, especially students. “Highly cited work is crucial not only to win awards but also for the career growth of a researcher. Awards play a significant role in further motivating fellow researchers to achieve even higher goals and highlight the importance of innovation,” he says. “Such awards are definitely a highlight in getting a career promotion. The news of the award may also lead to opportunities. For instance, to be invited to join other researchers working in similar areas, which will provide an ideal platform for future collaboration and research exploration.”
Vaidehi adds that results that are meaningful to broader research areas will likely result in higher citations. “Bringing innovation to the work is the key to success,” he says. “Prestigious awards, high citation counts, and other forms of success and recognition will automatically follow. You will be remembered by the community only for your contribution to its advancement and growth, so be genuine.”
For the full list of top-cited papers from India for 2024, see here.
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