Spatial filter

About: Spatial filter is a research topic. Over the lifetime, 6170 publications have been published within this topic receiving 100451 citations.

Narrowband tunable photonic notch filter.

Abstract: We propose a technique for realization of a high-contrast, tunable, low-insertion-loss notch filter using polarization selectivity of whispering-gallery-mode resonators. We demonstrate a 10 MHz filter with 5.5 dB insertion loss and 45.5 dB of in-band rejection. The measured rejection value is limited by the finite (3 kHz) linewidth of our laser. We show that the filter can potentially have tunable bandwidth without significant rejection modification.

Coherent optical pattern recognition

Abstract: Pattern-recognition systems, techniques, and applications using coherent optical systems are reviewed. Many optical pattern-recognition system architectures exist that include time-domain optical correlators and the optical joint transform correlators and refinements in the original optical matched spatial filter synthesis processor. Advanced optical pattern-recognition systems are also described such as hybrid optical/digital processors and diffraction-pattern sampling systems using specially shaped Fourier plane detector arrays. The optical space-variant pattern-recognition systems described are examples of the growing repertoire of operations now achievable in optical computers.

High-power, in-phase-mode operation from resonant phase-locked arrays of antiguided diode lasers

Abstract: A resonant phase‐locked array of antiguides is demonstrated for the first time. A 10/11 element AlGaAs/GaAs antiguided array is grown by two‐step metalorganic chemical vapor deposition. Longitudinally, the structure consists of two noncollinear sets of antiguides separated by a half‐Talbot distance, an ensemble that acts as a spatial filter. Out‐of‐phase‐mode operation is suppressed both by this diffractive‐type spatial filter and by large interelement loss. Resonant in‐phase‐mode operation is a result of the interelement spacing corresponding to one leaky‐wave half wavelength in the lateral direction. Near the in‐phase‐mode resonance, array modes adjacent to the in‐phase‐mode are discriminated against because they have large radiation losses in the antiguided structure and significant edge diffraction losses in the spatial filter. Stable, diffraction‐limited in‐phase‐mode beam patterns are achieved to 10 times threshold and 450 mW output power.

Spatial filtering using dielectric photonic crystals at beam-type excitation

Abstract: Spatial filtering is demonstrated at beam-type excitations by utilizing finite thickness slabs of two-dimensional dielectric photonic crystals (PCs) showing exotic Fabry–Perot resonances that are preserved over a wide range of variation of the incidence angle. Bandstop and dual-bandpass filtering effects are illustrated theoretically and the corresponding filters are validated in the microwave experiments by using square-lattice PCs. It is shown that the basic transmission features that were observed earlier for a plane-wave illumination are also recognizable at beam-type excitations. The proposed spatial filtering mechanism exhibits directional beaming. The desired widths and the locations of the passbands and stopbands are attainable in the angle domain with a proper choice of the operating frequency for the given excitation characteristics.

Terahertz active spatial filtering through optically tunable hyperbolic metamaterials

Abstract: We theoretically consider infrared-driven hyperbolic metamaterials able to spatially filtering terahertz radiation. The metamaterial is a slab made of alternating semiconductor and dielectric layers whose homogenized uniaxial response, at terahertz frequencies, shows principal permittivities of different signs. The gap provided by metamaterial hyperbolic dispersion allows the slab to stop spatial frequencies within a bandwidth tunable by changing the infrared radiation intensity. We numerically prove the device functionality by resorting to full wave simulation coupled to the dynamics of charge carries photoexcited by infrared radiation in semiconductor layers.