Doublet Metalens with Simultaneous Chromatic and Monochromatic Correction in the Mid-Infrared.

Metalenses provide a powerful paradigm for mid-infrared (MIR) imaging and detection while keeping the optical system compact. However, the design of MIR metalenses simultaneously correcting chromatic aberration and off-axis monochromatic aberration remains challenging. Here, we propose an MIR doublet metalens composed of a silicon aperture metalens and a silicon focusing metalens separated by a fused silica substrate. By performing ray-tracing optimization and particle-swarm optimization, we optimized the required phase profiles as well as the sizes and spatial distributions of silicon nanopillars of the doublet metalens. Simulation results showed that the MIR doublet metalens simultaneously achieved chromatic and off-axis monochromatic aberration reduction, realizing a continuous 400 nm bandwidth and 20° field-of-view (FOV). Thanks to its planar configuration, this metalens is suitable for integration with CMOS image sensor to achieve MIR imaging and detection, which has potential application in troubleshooting and intelligent inspection of power grids. This work may facilitate the practical application of metalens-integrated micro/nanosensors in intelligent energy.

Tailoring the emission polarization with metasurface-based emitters designed on a plasmonic ridge waveguide.

Because of low propagation losses and flexible communication paths, inter-chip optical communications based on plasmonic emitters and receivers can overcome the obstacle of the inherent ohmic loss in metallic nanostructures. To increase the communication capacity and integration density in inter-chip optical communications, we propose to tailor the polarization states of the free-radiation fields from the emitters in both the spectral domain and spatial domain by designing the phased and polarized arrangement of subwavelength metallic nanogroove antennas on a two-dimensional plasmonic ridge waveguide. Herein, the utilization of the two-dimensional plasmonic waveguide with tight field confinements considerably decreases the crosstalk to nearby plasmonic devices in plasmonic circuits and chips. In the spectral domain, three different polarization states of the free-radiation fields from the same emitter are experimentally realized at three specific wavelengths. In the spatial domain, the different polarization states as well as the gear polarization states are experimentally demonstrated. Moreover, the separation of the adjacent polarization-tailoring plasmonic emitters is only 5% of that in dielectric emitters because of the ultra-compact size (<0.6λ2) of metasurface-based plasmonic emitters.

Configurable Integration of On-Chip Quantum Dot Lasers and Subwavelength Plasmonic Waveguides.

The integration of on-chip dielectric lasers and subwavelength plasmonic waveguides has attracted enormous attention because of the combination of both the advantages of the high performances of the small dielectric lasers and the subwavelength plasmonic waveguides. However, the configurable integration is still a challenge owing to the complexity of the hybrid structures and the damageability of the gain media in the multistep micro/nanofabrications. By employing the dark-field optical imaging technique with a position uncertainty of about 21 nm and combining the high-resolution electron beam lithography, the small colloidal quantum dot (CQD) lasers without any damages are accurately aligned with the silver nanowires. As a result, the integration of the CQD lasers and the silver nanowires can be flexibly configured on chips. In the experiment, the tangential coupling, radial coupling, and complex coupling between the high-performance CQD lasers and the subwavelength silver nanowires are demonstrated. Because of the subwavelength field confinements of the silver nanowires, the deep-subwavelength coherent sources (multimode, one-color single-mode, or two-color single-mode) with a mode area of only 0.008λ2 are output from these hybrid structures. This configurable on-chip integration with high flexibility and controllability will greatly facilitate the developments of the complex functional hybrid photonic-plasmonic circuits.

Polarization-independent and high-efficiency dielectric metasurfaces for visible light.

Dielectric metasurfaces are capable of completely manipulating the phase, amplitude, and polarization of light with high spatial resolutions. The emerging design based on high-index and low-loss dielectrics has led to the realization of novel metasurfaces with high transmissions, but these devices usually operate at the limited bandwidth, and are sensitive to the incident polarization. Here, we report the realization of the polarization-independent and high-efficiency silicon metasurfaces spanning the visible wavelengths about 200 nm. The fabricated computer-generated meta-holograms exhibit a 90% diffraction efficiency, which are verified by gradient metasurfaces with measured efficiencies up to 93% at 670 nm, and exceeding 75% at the wavelengths from 600 to 800 nm for the two orthogonally polarized incidences. These dielectric metasurfaces effectively decouple the phase modulation from the polarization states and frequencies for visible light, which hold great potential for novel flat optical devices operating over a broad spectrum.