Extending the Frequency Range of Surface Plasmon Polariton Mode with Meta-Material

The frequency range that surface plasmon polariton(SPP) mode exists is mainly limited by the metal material.With high permittivity dielectrics above metal surface, the SPP mode at high frequency has extremely large loss or can be cutoff, which limits the potential applications of SPP in the field of optical interconnection, active SPP devices and so on.To extend the frequency range of SPP mode, the surface mode guided by metal/dielectric multilayers meta-material has been studied based on the theory of electromagnetic field. It is demonstrated that surface mode not only could be supported by the meta-material but also extends the frequency to where conventional metal SPP cannot exist. Meanwhile, the characteristics of this surface mode, such as dispersion relation, frequency range, propagation loss and skin depth in metamaterial and dielectrics, are also studied. It is indicated that, by varying the structure parameters, the meta-material guided SPP mode presents its advantages and flexibility over traditional metal one.

Photon-Counting Spectrometers Based on Superconducting Nanowire Single-Photon Detectors

Optical spectrum analysis provides a wealth of information about the physical world.Throughout the development of optical spectrum analysis,sensitivity has been one of the major topics and has become essential in applications dealing with faint light.Various high-sensitivity optical detection technologies have been applied in optical spectrum analysis to enhance its sensitivity to single-photon level.As an emerging single-photon detection technology,superconducting nanowire single-photon detectors(SNSPDs)have many impressive features such as high detection efficiency,broad operation bandwidth,small timing jitter,and so on,which make them promising for enhancing the performance of optical spectral analysis.Diverse schemes for photon-counting spectrometers based on SNSPDs have been demonstrated.This article reviews these impressive works and prospects for the future development of this technology.Further breakthroughs can be expected in its theories,device performance,applications,and combinations with in-sensor computing,promoting it to be a mature and versatile solution for optical spectrum analysis on ultra-faint light.

Photon counting reconstructive spectrometer combining metasurfaces and superconducting nanowire single-photon detectors

Faint light spectroscopy has many important applications such as fluorescence spectroscopy, lidar, and astronomical observations. However, the long measurement time limits its application to real-time measurement.In this work, a photon counting reconstructive spectrometer combining metasurfaces and superconducting nanowire single-photon detectors is proposed. A prototype device was fabricated on a silicon-on-insulator substrate,and its performance was characterized. Experiment results show that this device supports spectral reconstruction of mono-color lights with a resolution of 2 nm in the wavelength region of 1500–1600 nm. Its detection efficiency is 1.4%–3.2% in this wavelength region. The measurement time required by the photon counting reconstructive spectrometer was also investigated experimentally, showing its potential to be applied in scenarios requiring real-time measurement.

Deep-learning based on-chip rapid spectral imaging with high spatial resolution

Spectral imaging extends the concept of traditional color cameras to capture images across multiple spectral channels and has broad ap-plication prospects.Conventional spectral cameras based on scanning methods suffer from the drawbacks of low acquisition speed and large volume.On-chip computational spectral imaging based on metasur-face filters provides a promising scheme for portable applications,but endures long computation time due to point-by-point iterative spec-tral reconstruction and mosaic effect in the reconstructed spectral im-ages.In this study,on-chip rapid spectral imaging was demonstrated,which eliminated the mosaic effect in the spectral image by deep-learning-based spectral data cube reconstruction.The experimental results show that 4 orders of magnitude faster than the iterative spec-tral reconstruction were achieved,and the fidelity of the spectral re-construction for the standard color plate was over 99%for a standard color board.In particular,video-rate spectral imaging was demon-strated for moving objects and outdoor driving scenes with good per-formance for recognizing metamerism,where the concolorous sky and white cars can be distinguished via their spectra,showing great po-tential for autonomous driving and other practical applications in the field of intelligent perception.

Phonon and photon lasing dynamics in optomechanical cavities

Lasers differ from other light sources in that they are coherent,and their coherence makes them indispensable to both fundamental research and practical application.In optomechanical cavities,photon and phonon lasing is facilitated by the ability of photons and phonons to interact intensively and excite one another coherently.The lasing linewidths of both phonons and photons are critical for practical application.This study investigates the lasing linewidths of photons and phonons from the underlying dynamics in an optomechanical cavity.We find that the linewidths can be accounted for by two distinct physical mechanisms in two regimes,namely the normal regime and the reversed regime,where the intrinsic optical decay rate is either larger or smaller than the intrinsic mechanical decay rate.In the normal regime,an ultra-narrow spectral linewidth of 5.4 kHz for phonon lasing at 6.22 GHz can be achieved regardless of the linewidth of the pump light,while these results are counterintuitively unattainable for photon lasing in the reversed regime.These results pave the way towards harnessing the coherence of both photons and phonons in silicon photonic devices and reshaping their spectra,potentially opening up new technologies in sensing,metrology,spectroscopy,and signal processing,as well as in applications requiring sources that offer an ultra-high degree of coherence.

Photonic-reconfigurable entanglement distribution network based on silicon quantum photonics

The entanglement distribution network connects remote users by sharing entanglement resources,which is essential for realizing quantum internet.We propose a photonic-reconfigurable entanglement distribution network(PR-EDN)based on a silicon quantum photonic chip.The entanglement resources are generated by a quantum light source array based on spontaneous four-wave mixing in silicon waveguides and distributed to different users through time-reversed Hong–Ou–Mandel interference by on-chip Mach–Zehnder interferometers with thermo-optic phase shifters(TOPSs).A chip sample is designed and fabricated,supporting a PR-EDN with3 subnets and 24 users.The network topology of the PR-EDN could be reconfigured in three network states by controlling the quantum interference through the TOPSs,which is demonstrated experimentally.Furthermore,a reconfigurable entanglement-based quantum key distribution network is realized as an application of the PR-EDN.The reconfigurable network topology makes the PR-EDN suitable for future quantum networks requiring complicated network control and management.Moreover,it is also shown that silicon quantum photonic chips have great potential for large-scale PR-EDN,thanks to their capacities for generating and manipulating plenty of entanglement resources.

Phonon lasing enhanced mass sensor with zeptogram resolution under ambient conditions

High-sensitivity mass sensors under ambient conditions are essential in various fields such as biological research,gas sensing and environ-mental monitoring.In the current work,a phonon lasing enhanced mass sensor was proposed based on an optomechanical crystal cav-ity under ambient conditions.The phonon lasing was harnessed to achieve ultra-high resolution since it resulted in an extremely nar-row mechanical linewidth(less than 10 kHz).Masses with different weights were deposited on the cavity,it is predicted that the maxi-mum resolution for mass sensing can be 65±19 zg,which approaches the mass order of a protein and an oligonucleotide.This implies the potential application of the proposed method in the biomedical fields such as oligonucleotide drug delivery area and the Human Proteome Project.

Vortex Smith-Purcell radiation generation with holographic grating

Smith–Purcell radiation(SPR)is the electromagnetic wave generated by free electrons passing above a diffraction grating,and it has played an important role in free-electron light sources and particle accelerators.Orbital angular momentum(OAM)is a new degree of freedom that can significantly promote the capacity of information carried by an electro-magnetic beam.In this paper,we propose an integrable method for generating vortex Smith–Purcell radiation(VSPR),namely,SPR carrying OAM,by having free-electron bunches pass on planar holographic gratings.VSPRs generated by different electron energies,with different topological charges of the OAM,radiation angles,and frequencies are demonstrated numerically.It is also found that,for high-order radiation,the topological charge of the OAM wave will be multiplied by the radiation order.This work introduces a new way to generate SPR with OAM and provides a method to achieve an integratable and tunable free-electron OAM wave source at different frequency regions.

Phonon lasing in a hetero optomechanical crystal cavity

Micro-and nanomechanical resonators have emerged as promising platforms for sensing a broad range of physical properties,such as mass,force,torque,magnetic field,and acceleration.The sensing performance relies critically on the motional mass,mechanical frequency,and linewidth of the mechanical resonator.Herein,we demonstrate a hetero optomechanical crystal(OMC)cavity based on a silicon nanobeam structure.The cavity supports phonon lasing in a fundamental mechanical mode with a frequency of 5.91 GHz,an effective mass of 116 fg,and a mechanical linewidth narrowing in the range from 3.3 MHz to 5.2 kHz,while the optomechanical coupling rate is as high as 1.9 MHz.With this phonon laser,on-chip sensing can be predicted with a resolution of δλ∕λ=1.0×10^(−8).The use of a silicon-based hetero OMC cavity that harnesses phonon lasing could pave the way toward high-precision sensors that allow silicon monolithic integration and offer unprecedented sensitivity for a broad range of physical sensing applications.

Generating heralded single photons with a switchable orbital angular momentum mode

The orbital angular momentum(OAM) carried by photons defines an infinitely dimensional discrete Hilbert space. With OAM modes, high-dimensional quantum states can be achieved for quantum communication and cryptography. Here we demonstrate a heralded single-photon source with a switchable OAM mode, which consists of a heralded single-photon source and an integrated OAM emitter as the mode converter. As the first step, the heralded single-photon source is based on the dispersion-shifted fiber. In this work, the OAM mode(quantized by topological charge l) carried by the heralded single photon(at fixed wavelength of 1555.75 nm) can be switched within the range of l=3–7 while the mode purity is more than 80%.

Nonsuspended optomechanical crystal cavities using As_(2)S_(3) chalcogenide glass

An optomechanical crystal cavity with nonsuspended structure using As_(2)S_(3) material is proposed. The principle of mode confinement in the nonsuspended cavity is analyzed, and two different types of optical and acoustic defect modes are calculated through appropriate design of the cavity structure. An optomechanical coupling rate of 82.3 kHz is obtained in the proposed cavity, and the designed acoustic frequency is 3.44 GHz. The acoustic mode coupling between two nonsuspended optomechanical crystal cavities is also demonstrated, showing that the proposed cavity structure has great potential for realizing further optomechanical applications in multicavity systems.

Programmable unitary operations for orbital angular momentum encoded states

We have proposed and demonstrated a scalable and efficient scheme for programmable unitary operations in orbital angular momentum(OAM)domain.Based on matrix decomposition into diagonal and Fourier factors,arbitrary matrix operators can be implemented only by diagonal matrices alternately acting on orbital angular momentum domain and azimuthal angle domain,which are linked by Fourier transform.With numerical simulations,unitary matrices with dimensionality of 3×3 are designed and discussed for OAM domain.Meanwhile,the parallelism of our proposed scheme is also presented with two 3×3 matrices.Furthermore,as an alternative to verify our proposal,proof of principle experiments have been performed on path domain with the same matrix decomposition method,in which an average fidelity of 0.97 is evaluated through 80 experimental results with dimensionality of 3×3.

Novel optoelectronic characteristics from manipulating general energy-bands by nanostructures

This paper summarizes our research work on optoelectronic devices with nanostructures. It was indi- cated that by manipulating so called ＂general energybands＂ of fundamental particles or quasi-particles, such as photon, phonon, and surface plasmon polariton （SPP）, novel optoelectronic characteristics can be obtained, which results in a series of new functional devices. A silicon based optical switch with an extremely broadband of 24 nm and an ultra-compact （8 μm -17.6μm） footprint was demonstrated with a photonic crystal slow light waveguides. By proposing a nanobeam based hereto optomechanical crystal, a high phonon frequency of 5.66 GHz was realized experimentally. Also, we observed and verified a novel effect of two-surface-plasmon-absorption （TSPA）, and realized diffraction-limit-overcoming photolithography with resolution of-1/11 of the exposure wavelength.

Tunable mechanical-mode coupling based on nanobeam-double optomechanical cavities

Tunable coupled mechanical resonators with nonequilibrium dynamic phenomena have attracted considerable attention in quantum simulations, quantum computations, and non-Hermitian systems. In this study, we propose tunable mechanical-mode coupling based on nanobeam-double optomechanical cavities. The excited optical mode interacts with both symmetric and antisymmetric mechanical supermodes and mediates coupling at a frequency of approximately 4.96 GHz. The mechanical-mode coupling is tuned through both optical spring and gain effects, and the reduced coupled frequency difference in non-Hermitian parameter space is observed. These results benefit research on the microscopic mechanical parity–time symmetry for topology and on-chip high-sensitivity sensors.