Parity‐time (PT) symmetry breaking offers mode selection capability for facilitating single‐mode oscillation in the optoelectronic oscillator (OEO) loop. However, most OEO implementati

Parity‐time (PT) symmetry breaking offers mode selection capability for facilitating single‐mode oscillation in the optoelectronic oscillator (OEO) loop. However, most OEO implementations depend on discrete devices, which impedes the proliferation due to size, weight, power consumption and cost. Here, we propose and experimentally demonstrate an on-chip tunable PT‐symmetric OEO. A tunable microwave photonic filter, a PT‐symmetric mode‐selective architecture, and two photodetectors are integrated on a silicon‐on‐insulator chip. By exploiting an on‐chip Mach‐Zehnder interferometer to match the gain and loss of two mutually coupled optoelectronic loops, single‐mode oscillation can be obtained. In the experiment, the oscillation frequency of the on-chip tunable PT‐symmetric OEO can be tuned from 0 to 20 GHz. To emulate the integrated case, the OEO loop length is minimized and no extra long fiber is used in the experiment. When the oscillation frequency is 13.67 GHz, the single‐sideband phase noise at 10 kHz offset frequency is −80.96 dBc/Hz and the side mode suppression ratio is 46 dB. The proposed on-chip tunable PT‐symmetric OEO significantly reduces the footprint of the system and enhances mode selection.show less

Electrically connected optical metasurfaces with high efficiencies are crucial for developing spatiotemporal meta-devices with ultrahigh spatial and ultrafast temporal resolutions. Whil

Electrically connected optical metasurfaces with high efficiencies are crucial for developing spatiotemporal meta-devices with ultrahigh spatial and ultrafast temporal resolutions. While efficient metal-insulator-metal (MIM) metasurfaces containing discretized meta-atoms require additional electrodes, Babinet-inspired slot-antenna-based plasmonic metasurfaces are suffering from low efficiencies and limited phase coverage for co-polarized optical fields. Capitalizing on the concepts of conventional MIM and slot-antenna metasurfaces, we design and experimentally demonstrate a new type of optical reflective metasurfaces consisting of mirror-coupled slot antennas. By tuning the dimensions of rectangular-shaped nano-apertures atop a dielectric-coated gold mirror, we achieve efficient phase modulation within a sufficiently large range of 320° and realize functional phase-gradient meta-devices for beam steering and beam splitting in the near-infrared range. The fabricated samples show (22 ± 2)% diffraction efficiency for beam steering and (17 ± 1)% for beam splitting at the wavelength of 790 nm. The considered mirror-coupled slot-antenna configuration, dispensing with auxiliary electrodes, offers an alternative and promising platform for electrically controlled reflective spatiotemporal metasurfaces. show less

The explosion in the amount of information that is being processed is prompting the need for new computing systems beyond existing electronic computers. Photonic computing is emerging a

The explosion in the amount of information that is being processed is prompting the need for new computing systems beyond existing electronic computers. Photonic computing is emerging as an attractive alternative due to performing calculations at the speed of light, the change for massive parallelism, and also extremely low energy consumption. Here, we review the physical implementation of basic optical calculations, such as differentiation and integration, using metamaterials, and introduce the realization of all optical artificial neural networks. We start with concise introductions of the mathematical principles behind such optical computation methods and present the advantages, current problems that need to be overcome, and the potential future directions in the field. We expect that this review will be useful for both novice and experienced researchers in the field of all-optical computing platforms using metamaterials.show less

We realized off-Γ lasing using the Friedrich–Wintgen bound state in the continuum (FW-BIC) in a one-dimensional suspended high-contrast grating (HCG). A clear anticrossing was observed

We realized off-Γ lasing using the Friedrich–Wintgen bound state in the continuum (FW-BIC) in a one-dimensional suspended high-contrast grating (HCG). A clear anticrossing was observed in the band diagram of the HCG corresponding to the coupling between the specific different orders of Bloch modes, and FW-BIC with a high quality factor and large confinement factor was observed near the anticrossing point. Owing to these outstanding characteristics, FW-BIC can serve as a robust and extraordinary cavity mode for realizing low-threshold laser operation and for achieving angle-steering laser beams. The conditions of FW-BIC can be modulated by tuning the geometry related to the coupling modes in the anticrossing, resulting in a tunable lasing direction observed in the measurement. Furthermore, through appropriate design, the emission angle can be controlled precisely within a wide tunable range. Therefore, FW-BICs can be used to realize high-resolution directional lasing within a wide range of emission angles; they can also be applied in 3D sensing for Lidar applications.show less