A continuously variable true-time delay beamformer based on a multichannel chirped fiber grating (MCFG) is demonstrated. The beamformer is capable of wide-band squint-free operation and demonstrates beam steering of a four-element array over /spl plusmn/40/spl deg/. The use of an MCFG provides a significant reduction in the length of the chirped grating required, eliminates spurious signal transmission, and utilizes narrow-band tunable laser sources. In addition, the effect of grating errors on the antenna pattern is examined and the tolerance on performance is presented.

Demonstration of a continuously variable true-time delay beamformer using a multichannel chirped fiber grating

Fabrication and characterization of a guided-mode resonance-based polarizer is presented. This polarizer is made by electron-beam patterning a single layer of amorphous silicon on a glass substrate. The fabricated device has high and low transmittance for transverse-electric and transverse-magnetic polarizations, respectively, over a ~ 40-nm wavelength range for normally incident light. Its experimental extinction ratio is ~ 97:1 at a central wavelength of 1510 nm.

Silicon-Layer Guided-Mode Resonance Polarizer With 40-nm Bandwidth

Mechanically tunable electromagnetic and photonic devices featuring enhanced spectral tunability with minimal mechanical movement are provided. These nano/micro-electromechanically (N/MEMS) tunable elements, including filters and pixels, rely on leaky-mode resonance effects in subwavelength photonic lattices that constitute periodic wavelengths. Such elements can operate in reflection (bandstop) or transmission (bandpass) modes, and can be arranged in one-dimensional or two-dimensional arrays, or operated as single units, and their spectral regions are controlled by the element design. Input electromagnetic radiation illuminates the element and is then filtered, modulated, analyzed or tuned by the element. Mechanical motion alters the structural symmetry, and therefore, the tuning properties, of the nanostructured subwavelength resonance elements. Further, incorporating metals and dielectrics to generate coexisting plasmonic and leaky-mode resonance effects adds to the versatility of the potential applications.

Tunable resonant leaky-mode N/MEMS elements and uses in optical devices

In this letter, a type of guided-mode resonance (GMR) reflection filter incorporating multimode resonance and the Brewster effect is presented. Long-range, low sidebands, and multiple channels are found to be obtainable for a single-layer GMR reflection filter with a TM-polarized plane wave incident at the Brewster angle. Detailed characteristics are calculated using rigorous coupled-wave analysis. In our calculation, for TM-polarized incident wave, we find it sufficiently accurate to calculate the effect index by using the zero-order permittivity e0,TM of the effective media theory, and narrowband multichannel reflectance can be achieved at the Brewster angle by tuning the grating depth.

Guided-mode resonance Brewster filters with multiple channels

The guided mode resonance (GMR) effect is widely used in biosensing due to its advantages of narrow linewidth and high efficiency. However, the optimization of a figure of merit (FOM) has not been considered for most GMR sensors. Aimed at obtaining a higher FOM of GMR sensors, we proposed an effective design method for the optimization of FOM. Combining the analytical model and numerical simulations, the FOM of "grating-waveguide" GMR sensors for the wavelength and angular shift detection schemes were investigated systematically. In contrast with previously reported values, higher FOM values were obtained using this method. For the "waveguide-grating" GMR sensors, a linear relationship between the grating period and groove depth was obtained, which leads to excellent FOM values for both the angular and wavelength resonance. Such higher performance GMR sensors will pave the way to lower detection limits in biosensing.

https://www.mdpi.com/2079-4991/9/6/837/pdf

Guided Mode Resonance Sensors with Optimized Figure of Merit.

The idea of implementing optical filters by coupling evanescent waves from several diffracted orders into multiple leaky waveguide modes is studied theoretically. Using a dielectric thin-film structure consisting of a coupling grating placed between adjacent waveguides, guided-mode resonance filters exhibiting multiple reflection peaks within a specified wavelength range can be obtained. These peaks originate in the resonant waveguide modes that are excited by the diffracted waves dispersed by the grating. It is shown that this device can be used to realize multiwavelength as well as wide-band spectral filters.

Concept of multiorder multimode resonant optical filters

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Concept of multiorder multimode resonant optical filters