Diffraction grating

About: Diffraction grating is a research topic. Over the lifetime, 24884 publications have been published within this topic receiving 372437 citations. The topic is also known as: grating.

Total absorption of light by lamellar metallic gratings

Abstract: Lamellar gratings illuminated in conical (off-plane) mounting can achieve with suitable optogeometrical parameters (grating profile, angle of incidence and wavelength) a total absorption of light for any polarization provided there is only the zeroth propagating order. A detailed analysis shows that electromagnetic resonances are involved and their nature strongly depends on the polarization. When the incident electric field is parallel to the cross-section of the grating, the resonance is provoked by the excitation of surface plasmons. For the orthogonal polarization, total absorption occurs for deep gratings only, when the grooves behave like resonant optical cavities. It is possible to reduce the optimal grating height by filling the grooves with a high refractive index material.

Tunable impedance surface

Abstract: A tuneable impedance surface for steering and/or focusing a radio frequency beam. The tunable surface comprises a ground plane; a plurality of elements disposed a distance from the ground plane, the distance being less than a wavelength of the radio frequency beam; and a capacitor arrangement for controllably varying the capacitance of at least selected ones of adjacent elements. A method of tuning the high impedance surface allows the surface to mimic, for example, a parabolic reflector or a diffraction grating.

Enhanced light trapping based on guided mode resonance effect for thin-film silicon solar cells with two filling-factor gratings

Abstract: An approach of enhanced light-trapping in a thin-film silicon solar cell by adding a two-filling-factor asymmetric binary grating on it is proposed for the wavelength of near-infrared. Such a grating-on-thin-film structure forms a guided-mode resonance notch filter to couple energy diffracted from an incident wave to a leakage mode of the guided layer in the solar cell. The resonance wave coupled between two-filling-factor gratings would laterally extend the optical power and induce multiple bounces within the active layer. The resonance effect traps light in the cell enhancing its absorption probability. A dynamic light-trapping behaviour in solar cells is observed. A photon dwelling time is proposed for the first time to quantify the light-trapping effect. Moreover, the light absorption probability is also quantified. As compared the grating-on-thin-film structure with the one of planar silicon thin film, simulation results reveal that it is 3-fold enhancement in the light absorption within a spectral range of 920-1040 nm. Moreover, such an enhancement can be maintained even the incident angle of near-IR broadband light wave varies up to +/-40 degrees.

Highly efficient Er,Yb-doped fiber laser with 188W free-running and>100W tunable output power

Abstract: Efficient high-power operation of an erbium-ytterbium co-doped fiber laser cladding-pumped by two spatially-multiplexed and polarization combined 975 nm diode-stacks is reported. Up to 188 W of continuous-wave output at 1.57 µm was generated with a beam-quality factor (M2) of 1.9 and an overall slope efficiency with respect to launched pump power of 41% (and 43% for output powers Tunable operation was demonstrated by use of an external cavity containing a diffraction grating and a maximum output power of 108 W at 1538 nm was generated for a launched pump power of ~ 336 W. The operating wavelength was tunable from 1531 to 1571 nm, with >100W output power over a tuning range of 36 nm from 1532 nm to 1568 nm.

Long-period gratings in planar optical waveguides

Abstract: We present a theoretical analysis of light propagation in a four-layer planar waveguide that consists of a long-period grating (LPG) having a period of the order of 100 µm. By means of the coupled-mode theory, we show that such a structure is capable of coupling light from the fundamental guided mode to the cladding modes at specific wavelengths (resonance wavelengths) and thus results in sharp rejection bands in the transmission spectrum of the waveguide. Our numerical results show that the resonance wavelengths as well as the transmission spectrum can be significantly changed with the waveguide and grating parameters. A waveguide-based LPG should provide a useful approach to the design of a wide range of integrated-optic devices, including wavelength-tunable filters, switches, and environmental sensors.