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Coupled optical resonators are one approach to slowing the propagation of light. An array of more than 100 such resonators has now been demonstrated using a photonic crystal. Such a structure can slow light down to below 1% of its speed in a vacuum.

Photonic circuits are a promising route to developing scalable quantum technologies, if all the necessary components can be built. Using coupled resonator optical waveguides, Takesue et al.present an on-chip single-photon buffer that can delay one photon from a pair for 150 ps while preserving entanglement.

A photonic-crystal platform enables attojoule-energy electro-optic modulators and amplifier-free photoreceivers.

A fingertip-sized on-chip optomechanical device offers a controllable way to shift the frequency of single photons in the telecom band while preserving their quantum information.

High-speed modulation and 4.4 fJ bit⁻¹ data transmission is demonstrated using a photonic-crystal nanocavity laser. Its current threshold of 4.8 µA, modulation current efficiency of 2.0 GHz µA^−0.5 and output power of 2.17 µW may enable on-chip photonic networks in combination with recently developed high-sensitivity receivers.

Using photonic crystal cavities with a buried heterostructure design, scientists demonstrate all-optical RAM at power levels 300 times lower than previous attempts. The 30 nW devices could enable low-power large-scale optical RAM systems for handling high-bit-rate optical signals.

Advanced on-chip photonic networks require integrated nanoscale lasers with low power consumption. Researchers have now demonstrated high-speed modulation of a compact heterostructure photonic crystal laser at room temperature with an unprecedented low required energy of ∼13 fJ per bit transmitted.

The sign of a material's charge carriers is usually reflected in the sign of the 'Hall voltage'. But for a structure inspired by chain mail, altering its geometry inverts the Hall voltage, even if the charge carriers are unchanged.

Integrated nano-optical memories may help overcome the limitations of communication speeds and energy costs in electronic chips. Now, using nanoscale phase-change materials researchers have realized the first multi-bit all-optical non-volatile memories with a very small footprint.

The study explores high transmission in 120-degree bends of photonic crystal waveguides. It reveals that high bend-transmission is primarily influenced by domain-wall configurations and is independent of inversion symmetry (valley-photonic effect).

Large-scale densely integrated optical memory on a single photonic crystal chip is demonstrated. The wavelength-division-multiplexing (WDM) capabilities of nanophotonic memories are exploited for optical addressing. This work may enable optical random-access memories and a large-scale WDM photonic network-on-chip.

Confining light in subwavelength nanowires has posed a challenge to harnessing their potential for integrated photonic devices. Now, it is shown that a high-Q cavity can be achieved by placing a single nanowire into a groove in a photonic crystal resonator.

All-optical switching with a switching energy of 35 fJ and a switching time of 260 fs is reported in a nanoscale integrated optical circuit.

All-optical switching energies as small as 0.42 fJ — two orders of magnitude lower than previously reported — are demonstrated in small photonic crystal cavities incorporating InGaAsP. These devices can switch within a few tens of picoseconds, and may therefore have potential for low-power high-density all-optical processing on a chip.

Using topological singular points, the topological charge of photonic crystals in momentum space is successfully transferred to optical vortex beams in real space.

The performance of components for optical computation has so far been limited by their modest nonlinear responses, reducing their speed while increasing the energy consumed. Here, a microscale, low-loss linear optical logic gate consisting of Si wire is demonstrated, capable of operating at 20 Gbps.