Volume 15 Issue 12, December 2021

The three-dimensional images generated by digital holography are usually limited to a single color. A new technique exploiting frequency combs generates holograms with hundreds of colors at once.

The demonstration of a germanium-based photodiode with a 3 dB bandwidth of 265 GHz and compatibility with silicon photonics and CMOS fabrication offers a cost-effective route to faster channel data rates for optical communications.

The direct generation of femtosecond pulses from an 8-μm quantum cascade laser could prove transformative for sensing and spectroscopy.

For 20 years, nanoscale 3D printing has been based on two-photon absorption, requiring expensive pulsed lasers. Now, via a two-step absorption process, such printing has been demonstrated using a low-cost, low-power continuous-wave laser diode, showing the potential for dramatic cost reductions in 3D nanoprinting.

Measurement of the arrival times of annihilation photons in a detector with greater precision is opening the way to new direct forms of tomographic positron emission imaging that do not require back-projection-based reconstruction techniques.

Progress on Landau level lasers—based on external magnetic field splitting of electronic states—is reviewed, with particular attention paid to the potential for tunable terahertz lasers.

Direct generation of few-cycle high-energy visible pulses is demonstrated via the nonlinear mixing of hollow-core fibre modes. Compression of near-infrared laser pulses by a factor of 40 with no additional dispersion compensation delivers 4.6 fs, 20 μJ pulses (~2 cycles, ~4 GW peak power) centred at around 600 nm.

Dual-comb digital holography based on an interferometer composed of two frequency combs of slightly different repetition frequencies and a lensless camera sensor allows highly frequency-multiplexed holography with high temporal coherence.

Highly efficient upconversion of light by organic semiconductor heterojunction interfaces is demonstrated. This process is enabled by charge separation- and recombination-mediated charge transfer states at the interface.

Multiplexing orbital angular momentum states as independent and orthogonal information carriers for data encryption is realized through disorder-induced synthetic helical dichroism in disordered nanoaggregates.

Visible-spectrum silicon nitride thermo-optic phase modulators based on adiabatic micro-ring resonators with a small device footprint and low power consumption, of potential use for applications like augmented-/virtual-reality goggles, quantum information processing circuits and optogenetics, are presented.

Positron emission imaging without tomographic reconstruction is demonstrated. A Cherenkov radiation detector detects gamma rays produced by positron–electron annihilation. The position of a positron source is determined with a precision of 4.8 mm.

Near-transform-limited 630 fs pulses with 4.5 W of peak power are generated by compensating the dispersion of a quantum cascade laser emitting around 8 μm. Their temporal nature is assessed by a new method called asynchronous upconversion sampling.

By sandwiching a germanium fin between complementary in situ-doped silicon layers, a waveguide-coupled germanium photodiode with a 3-dB bandwidth of 265 GHz, accompanied by high responsivity and low dark current, is realized.

As an alternative to high-resolution fabrication by two-photon absorption, researchers demonstrate a two-step absorption process that employs inexpensive light sources.