Comment

We posit that inconsistent interpretations of experimental data have led to inaccurate claims on metalens focusing efficiencies. By performing a meta-analysis, we show that extraordinary claims of high focusing efficiency at high numerical apertures are, unfortunately, not yet backed by rigorous simulation or experimental results.

In recent decades, progress in developing better nonlinear materials has not been as rapid as wished. Here I propose that this may be explained by considering the simple view of nonlinear optical phenomena as being determined mostly by the length of interaction time between photons and matter. Tentative routes towards improvements in the efficiency of nonlinear optical phenomena are suggested.

A heat-powered emitter can sometimes exceed the Planck thermal-emission limit. We clarify when such super-Planckian emission is possible, arguing that far-field super-Planckian emission requires a distribution of energy that is not consistent with a unique temperature, and therefore the process should not be called ‘thermal emission’.

The field of flat lens research brings innovative nanophotonic design concepts to the world of macro-optics. However, when evaluating the performance of these lenses a lack of consistency prevents proper comparison of competing technologies. This problem can be solved by using methods developed in industry for conventional lenses.

Low stability of perovskite light-emitting diodes (PeLEDs) is the biggest obstacle to the commercialization of PeLED displays. Here, we cover the current status and challenges in analysing and improving the stability of PeLEDs and suggest some advice that will benefit the community to boost the operational lifetime of PeLEDs.

Jonathan P. Dowling, who died in June, was a pioneer in quantum optics and one of the founders of the US government’s research programme in quantum information.

Unidirectional and topological surface plasmon polaritons are currently attracting substantial interest and intense debate. Realistic material models and energy conservation considerations are essential to correctly understand extreme wave effects in non-reciprocal plasmonics, and to assess their potential for novel devices.

Philip Warren Anderson is one of the founding fathers of modern condensed-matter physics. With his death on 29 March 2020, we have lost one of the most influential physicists of the twentieth century.

The arrival of light-emitting diodes based on new materials is posing challenges for the characterization and comparison of devices in a trusted and consistent manner. Here we provide some advice and guidelines that we hope will benefit the community.

Evgeny Dianov (1936–2019) was a pioneer of fibre-optics research in the former Soviet Union and director of a highly successful research centre in Moscow dedicated to the field.

Father of the semiconductor laser, Nobel Prize laureate and director of the Ioffe Institute in St Petersburg, Zhores Alferov was a much-loved scientist and educator whose research changed the modern world.

Yaron Silberberg of the Weizmann Institute in Israel passed away in April. Here, some of his former students and friends remind us of who Yaron was: a creative researcher and a mentor without ego with major achievements in nonlinear optics, microscopy and quantum physics.

The Shockley–Queisser model is a landmark in photovoltaic device analysis by defining an ideal situation as reference for actual solar cells. However, the model and its implications are easily misunderstood. Thus, we present a guide to help understand and to avoid misinterpreting it.

As a pioneer in the research on ultra-high-quality dielectric microresonators and their applications in nonlinear optics, frequency metrology and laser science, Mikhail Gorodetsky is badly missed.

As the most abundant biopolymer on Earth since it can be found in every plant cell wall, cellulose has emerged as an ideal candidate for the development of renewable and biodegradable photonic materials, substituting conventional pigments.

The 2005 Nobel laureate, Roy Jay Glauber, sadly passed away on 26 December 2018 at the age of 93. He was highly regarded for his work on the quantum theory of coherence, as well as for his contributions to nuclear physics, scattering theory and statistical mechanics.

Victor Georgievich Veselago (1929–2018), a Russian scientist from the Lebedev Physical Institute in Moscow, provided great inspiration and impetus to the field of metamaterials with his theoretical analysis of materials with a negative index of refraction.

Osamu Shimomura’s 90-year life came to an end on 19 October 2018. Throughout his long and exceedingly fruitful career, the Japanese marine biologist and chemist passionately explored the phenomenon of bioluminescence in living organisms, earning a Nobel Prize in the process.

The performance of photodetectors fabricated from emerging semiconductors such as perovskites, quantum dots, two-dimensional materials or organics, for example, can be prone to misinterpretation. This Comment exposes the problems and proposes some guidelines for accurate characterization.

Optical fibre technology transformed telecommunications, leading to the global broadband Internet, and beyond. Charles Kuen Kao is the father of optical fibre communications whose vision changed the world.