A novel wideband three-layer high-efficiency metal-mirror-based grating is designed and investigated. It consists of an Ag slab and a three-layer rectangular-groove dielectric-grating structure. Both TE and TM polarizations exhibit high efficiency in -1st order with good angular bandwidth and spectral bandwidth. Compared with the reported high-efficiency grating, the efficiency can be improved. Moreover, a wide spectral width of 150 nm and a broad angular width of 5.6 degrees can be shown. The modal method and rigorous coupled-wave analysis are used together to study grating parameters in this optimization.

A three-port surface-relief grating with a connecting layer under the second Bragg condition is put forward and designed for the free space application in this paper. Such grating can function as a beam splitter, which can split the polarized light into the [Formula: see text]2nd order and the [Formula: see text]1st order and the 0th order based on the optimum grating profile parameters. By using rigorous coupled-wave analysis, a highly-efficient polarization-dependent connecting-layer-based grating can be obtained with the optimum different depths and thicknesses with the grating duty cycle of 0.65 and grating period of 1150[Formula: see text]nm. On the basis of the designed grating profile parameters, a modal method can explain the propagating process. Compared with the conventional surface-relief fused-silica grating, the diffraction efficiencies for TE polarization in three orders are improved. Therefore, the novel conception of the grating under the second Bragg condition is significant for further applications such as interferometer with improved efficiency for TE polarization.

The beam-splitting element is described based on the connecting-layer grating to improve the performance. A connecting layer is introduced between the grating region and the substrate. Efficiencies are improved especially for TE polarization. For TE polarization with the grating depth of 0.65 mu m and connecting layer thickness of 0.45 mu m, efficiencies of 49.50% and 49.53% can be diffracted into the -1st and the 0th orders, respectively. For TM polarization with the grating depth of 1.00 mu m and connecting layer thickness of 0.72 mu m, splitting efficiencies of 49.32% and 49.62% can be divided into the two orders.

We design a three-layer rectangular-groove dielectric transmission grating that can be used as a polarization-selective beam splitter. For TE polarization, the grating is equivalent to a high-efficiency grating. For TM polarization, a good splitting ratio can be exhibited with 48.4%/48.8% output. Each thickness of the three grating layers can be approximately calculated by using modal method based on the physical theory of two-beam interference with the chosen duty cycle of 0.41 and period of 690 nm for an operating wavelength of 800 nm. In order to obtain accurate grating layer thickness, the rigorous coupled-wave analysis based on Maxwell's theory is used to calculate the diffraction efficiency. The polarization-selective beam splitter grating reported previously can work only at the special prescribed incident angle or narrow angular width. The three-layer dielectric grating is aimed to obtain the wide incident angular bandwidth.

The novel reflective grating was studied under Littrow incidence as one sort of high-efficiency optical element. A covering layer and a dielectric layer are employed in this structure to achieve higher efficiency and wider bandwidth. For the given wavelength of 1550 nm, by using two-beam-interference theory of modal method, duty cycle and period of grating can be calculated, where the physical essence of high efficiency in the first-order is well explained by the modal method. The other grating parameters are optimized by using rigorous coupled-wave analysis. The optimized grating has an appropriate aspect ratio and shows that diffraction efficiencies of TE and TM polarizations in the first-order are greater than 97%. Compared with the reported surface-relief high-efficiency grating, the diffraction efficiencies of the proposed grating for TE and TM polarizations can be greatly improved.

A three-port polarization-independent beam splitter is described by the grating with a connecting layer between the grating region and the substrate. Such a novel diffractive three-port beam splitter is optimized to achieve high diffraction efficiency with good uniformly. With the optimized grating parameters, efficiencies of 32.03%/32.06% and 32.14%/32.15% can be separated into the +/- 1st and the 0th orders for TE and TM polarizations, respectively. Besides, the usual duty cycle of 0.5 and the aspect ratio of the grating depth to the ridge width of 1.83 facilities the fabrication with reported gratings.

A two-layer three-port output grating with high-efficiency beam splitting is presented in this paper. The grating can split the incident wave into the 0th order and the +/- 1st orders for both TE and TM polarizations at the wavelength of 800 nm. According to the property of the incident angular bandwidth, the efficiency of every diffracted order exceeds 30% within the incident angular bandwidth range of -1.04-3.14. Compared with the conventional reported single-layer three-port grating, the two-layer three-port grating has merits of not only the higher efficiency but also the broader angular bandwidth.

A 50%-50% splitting ratio element is presented by the covering-layer grating. The novel grating introduces a covering layer on the surface-relief grating, which can not only protect the grating surface but also improve the performance of a beam splitter compared with the surface-relief grating. The beam splitter based on fused silica is optimized for the femtosecond laser with high damage threshold. For different incident wavelengths and angles, the 50%-50% splitting ratio element exhibits wideband properties, which are useful compared with most beam splitters operated for certain incident wavelength or angle.

A transmission polarizing beam splitter (PBS) is described and designed by a sandwiched grating with a connecting layer at a central wavelength of 800 nm. The novel grating is analyzed and designed by modal method and rigorous coupled-wave analysis. Compared with the reported surface-relief PBS gratings, the proposed grating extinction ratio, fabrication tolerance and incident spectrum band width can be improved greatly.