Time-sequential color code division multiplexing holographic display with metasurface

Color metasurface holograms are powerful and versatile platforms for modulating the amplitude,phase,polarization,and other properties of light at multiple operating wavelengths.However,the current color metasurface holography can only realize static manipulation.In this study,we propose and demonstrate a multiplexing metasurface technique combined with multiwavelength code-division multiplexing(CDM)to realize dynamic manipulation.Multicolor code references are utilized to record information within a single metasurface and increase the information capacity and security for anticracks.A total of 48 monochrome images consisting of pure color characters and multilevel color video frames were reconstructed in dual polarization channels of the birefringent metasurface to exhibit high information density,and a video was displayed via sequential illumination of the corresponding code patterns to verify the ability of dynamic manipulation.Our approach demonstrates significant application potential in optical data storage,optical encryption,multiwavelengthversatile diffractive optical elements,and stimulated emission depletion microscopy.

Reflection sensitivity of dual-state quantum dot lasers

This work experimentally and theoretically demonstrates the effect of excited state lasing on the reflection sensitivity of dual-state quantum dot lasers,showing that the laser exhibits higher sensitivity to external optical feedback when reaching the excited state lasing threshold.This sensitivity can be degraded by increasing the excited-to-ground-state energy separation,which results in a high excited-to-ground-state threshold ratio.In addition,the occurrence of excited state lasing decreases the damping factor and increases the linewidth enhancement factor,which leads to a low critical feedback level.These findings illuminate a path to fabricate reflectioninsensitive quantum dot lasers for isolator-free photonic integrated circuits.

Dynamic performance and reflection sensitivity of quantum dot distributed feedback lasers with large optical mismatch

This work reports on a high-efficiency In As/Ga As distributed feedback quantum dot laser.The large optical wavelength detuning at room temperature between the lasing peak and the gain peak causes the static,dynamic,and nonlinear intrinsic properties to all improve with temperature,including the lasing efficiency,the modulation dynamics,the linewidth enhancement factor,and consequently the reflection insensitivity.Results reported show an optimum operating temperature at 75°C,highlighting the potential of the large optical mismatch assisted single-frequency laser for the development of uncooled and isolator-free high-speed photonic integrated circuits.

Four-wave mixing in 1.3 μm epitaxial quantum dot lasers directly grown on silicon

This work compares the four-wave mixing(FWM)effect in epitaxial quantum dot(QD)lasers grown on silicon with quantum well(QW)lasers.A comparison of theory and experiment results shows that the measured FWM coefficient is in good agreement with theoretical predictions.The gain in signal power is higher for p-doped QD lasers than for undoped lasers,despite the same FWM coefficient.Owing to the near-zero linewidth enhancement factor,QD lasers exhibit FWM coefficients and conversion efficiency that are more than one order of magnitude higher than those of QW lasers.Thus,this leads to self-mode locking in QD lasers.These findings are useful for developing on-chip sources for photonic integrated circuits on silicon.

Phase characterisation of metalenses

Metalenses have emerged as a new optical element or system in recent years,showing superior performance and abundant applications.However,the phase distribution of a metalens has not been measured directly up to now,hindering further quantitative evaluation of its performance.We have developed an interferometric imaging phase measurement system to measure the phase distribution of a metalens by taking only one photo of the interference pattern.Based on the measured phase distribution,we analyse the negative chromatic aberration effect of monochromatic metalenses and propose a feature size of metalenses.Different sensitivities of the phase response to wavelength between the Pancharatnam-Berry phase-based metalens and propagation phase-reliant metalens are directly observed in the experiment.Furthermore,through phase distribution analysis,it is found that the distance between the measured metalens and the brightest spot of focusing will deviate from the focal length when the metalens has a low nominal numerical aperture,even though the metalens is ideal without any fabrication error.We also use the measured phase distribution to quantitatively characterise the imaging performance of the metalens.Our phase measurement system will help not only designers optimise the designs of metalenses but also fabricants distinguish defects to improve the fabrication process,which will pave the way for metalenses in industrial applications.

Improvement of the chirality near avoided resonance crossing in optical microcavity

Chirality is one of the important phenomena at the vicinity of exceptional point(EP). The conventional understanding is that the chirality is determined by asymmetrical scattering efficiency(?), which reaches to zero only when the resonance approaches EP. Here we study the possibility to enhance the chirality in open systems with a more robust mechanism. By combining chirality with avoided resonance crossing, we show that the chirality and ? can be dramatically modified. Taking a spiral shaped annular cavity as an example, we show that the chirality of optical resonances can be significantly improved when two sets of chiral states approach each other. The imbalance between counterclockwise(CCW) components and clockwise(CW) components has been enhanced by more than an order of magnitude. Our research provides a new route to tailor and control the chirality in open systems.

Uncovering recent progress in nanostructured light-emitters for information and communication technologies

Semiconductor nanostructures with low dimensionality like quantum dots and quantum dashes are one of the best attractive and heuristic solutions for achieving high performance photonic devices.When one or more spatial dimensions of the nanocrystal approach the de Broglie wavelength,nanoscale size effects create a spatial quantization of carriers leading to a complete discretization of energy levels along with additional quantum phenomena like entangled-photon generation or squeezed states of light among others.This article reviews our recent findings and prospects on nanostructure based light emitters where active region is made with quantum-dot and quantum-dash nanostructures.Many applications ranging from silicon-based integrated technologies to quantum information systems rely on the utilization of such laser sources.Here,we link the material and fundamental properties with the device physics.For this purpose,spectral linewidth,polarization anisotropy,optical nonlinearities as well as microwave,dynamic and nonlinear properties are closely examined.The paper focuses on photonic devices grown on native substrates(InP and GaAs)as well as those heterogeneously and epitaxially grown on silicon substrate.This research pipelines the most exciting recent innovation developed around light emitters using nanostructures as gain media and highlights the importance of nanotechnologies on industry and society especially for shaping the future information and communication society.

Emerging opportunities for ultra-high Q whispering gallery mode microcavities

Whispering gallery modes (WGMs) were first discovered for sound waves in the whispering gallery of St Paul’s Cathedral and explained by Rayleigh [1] in 1878. In 1961, Garrett et al.[2] applied the concept of WGMs to optical systems and realized stimulated emissions in Sm2+-doped CaF2 spheres.Since then, WGMs have been widely and intensively studied in a range of micro-sized systems, including microdroplets,microspheres, microtoroids, microdisks, and microtubes.

Phyllotaxis-inspired nanosieves with multiplexed orbital angular momentum

Nanophotonic platforms such as metasurfaces,achieving arbitrary phase profiles within ultrathin thickness,emerge as miniaturized,ultracompact and kaleidoscopic optical vortex generators.However,it is often required to segment or interleave independent sub-array metasurfaces to multiplex optical vortices in a single nano-device,which in turn affects the device’s compactness and channel capacity.Here,inspired by phyllotaxis patterns in pine cones and sunflowers,we theoretically prove and experimentally report that multiple optical vortices can be produced in a single compact phyllotaxis nanosieve,both in free space and on a chip,where one meta-atom may contribute to many vortices simultaneously.The time-resolved dynamics of on-chip interference wavefronts between multiple plasmonic vortices was revealed by ultrafast time-resolved photoemission electron microscopy.Our nature-inspired optical vortex generator would facilitate various vortex-related optical applications,including structured wavefront shaping,free-space and plasmonic vortices,and high-capacity information metaphotonics.