Polarization-insensitive one-dimensional guided-mode resonance filter operating at conical mounting.

We report the design and implementation of a one-dimensional guided-mode resonance filter (1D-GMRF) aiming to achieve polarization insensitivity at conical mounting. (The incident plane is aligned neither perpendicularly nor parallelly to the grating bars.) The design guideline indicates that, at conical mounting, polarization insensitivity of the 1D-GMRF can be achieved by optimizing the grating parameters to excite the fundamental TE and the fundamental TM waveguide modes simultaneously. Moreover, it is revealed that, at conical mounting, the polarization-insensitive GMR position in the angle-resolved resonance spectra is azimuthal angle ϕ-dependent. The experimental results demonstrate that polarization insensitivity of the fabricated 1D-GMRF occurs at the resonance wavelength of ∼673 nm for the conical mounting of azimuthal angle ϕ≈30° and incident angle θ≈11.2°, which agree with the simulated results.

Spectral responses of linear grating filters under full-conical incidence.

To completely clarify the spectral responses of linear grating filters (LGFs) under full-conical incidence (where the incident plane is parallel to the linear grating bars), a bandstop LGF is implemented on an HfO2-on-silicon platform, and its spectral responses are comprehensively investigated. The measured spectra agree well with the simulated outcomes. For the TM- (or TE-) polarized wave under full-conical incidence, there exists a pair of resonance bands, whose spectral features differ significantly from each other. One resonance band has a high angular tolerance and is capable of accommodating divergent waves, whereas the other band presents a tunable spectral linewidth and can be used to achieve an ultra-high Q-factor. In particular, it is demonstrated that all of the resonance bands under full-conical incidence are degenerate regardless of what the value of the incident angle is. Our investigations reveal interesting spectral attributes of LGFs under full-conical incidence, which are highly beneficial for developing new filtering devices.

Spatiotemporal summation and correlation mimicked in a four-emitter light-induced artificial synapse.

In the brain, each postsynaptic neuron interconnects many presynaptic neurons and performs functions that are related to summation and recognition as well as correlation. Based on a convolution operation and nonlinear distortion function, we propose a mathematical model to explore the elementary synaptic mechanism. A four-emitter light-induced artificial synapse is implemented on an III-nitride-on-silicon platform to validate the device concept for emulating the synaptic behaviors of a biological synapse with multiple presynaptic inputs. In addition to a progressive increase in the amplitude of successive spatiotemporal excitatory postsynaptic voltages, the differences in the stimulations are remembered for signal recognition. When repetitive stimulations are simultaneously applied and last over a long period of time, resonant spatiotemporal correlation occurs because an association is formed between the presynaptic stimulations. Four resonant spatiotemporal correlations of each triple-stimulation combination are experimentally demonstrated and agree well with the simulation results. The repetitive stimulation combinations with prime number-based periods inherently exhibit the maximum capacity of resonant spatiotemporal correlation. Our work offers a new approach to building artificial synapse networks.