Better performances of two-dimensional (2D) grating are required recently, such as polarization independence, high efficiency, wide bandwidth and so forth. In this paper, we propose a 2×2 2D silver cylindrical array grating with excellent polarization-independent high diffraction efficiency (DE) over communication band for beam splitting. The grating was calculated by rigorous coupled wave analysis (RCWA) and can achieve over 24% DE of four first diffraction orders at 1550 nm with nonuniformity of 1.43% in both transverse electric (TE) and transverse magnetic (TM) polarizations, which is a significant improvement over previous reports. The holographic exposure technology, wet chemical development process and electron beam evaporation were used to fabricate the 2D grating. The correctness and accuracy of the calculation are fully verified with the measurement result of fabricated grating. Excellent performances of the 2D splitter we proposed will have great potential for applications in optical communication, semiconductor manufacturing and displacement measurement.

Polarization-independent 2×2 high diffraction efficiency beam splitter based on two-dimensional grating

Newly reflective bi-function beam splitter by SiO2 pencil-like arrays on silver plate

Abstract. We describe a two-port reflective beam splitter with the elimination of the zeroth order based on T-type metal grating. Under the condition of a normal incidence wavelength λ  =  1.550  μm, for transverse electric (TE) polarization, the grating efficiencies of the zeroth and ±first orders can reach 1.35% and 48.28%, respectively. And for transverse magnetic (TM) polarization, efficiencies reach 0.49% and 48.30%, respectively, where energies of the zeroth order are suppressed well for both TE and TM polarizations. Furthermore, the numerical analysis indicates that the grating has a wide incident bandwidth (the efficiencies of over 47% at a bandwidth of 118 nm) as well as an excellent process tolerance in period and duty cycle. The grating performance is also stable with a simple structure so that it has a wide application prospect in optical polarization devices, laser systems, polarization imaging, etc.

Approach for eliminating the zeroth order by T-type grating with polarization loss reduction

A method to eliminate the zeroth order with low polarization-independent loss by a transmission grating

In this paper, we proposed polarization-dependent terahertz reflective beam splitters under normal incidence, in which resonance-domain diffraction gratings with period comparable to incident wavelength are adopted to achieve multi-channel beam separation, appropriate total diffraction efficiency, and good efficiency uniformity. At the frequency of 2.5200 THz (correspondingly the wavelength λ = 118.83 μm), the beam splitters can implement energy output varying from dual- to seven-port. For transverse electric (TE) polarization, the total efficiency of the beam splitters can reach ~ 95% (assuming the values 96.04%, 96.84%, 94.71%, 96.32%, 96.47%, and 95.08%, respectively, when the splitter’s output ports change from two to seven). For transverse magnetic (TM) polarization, under different structural parameters (namely the heights of the grating ridges h1 and h2) from TE polarization, the corresponding values are 96.62%, 95.23%, 92.81%, 93.11%, 92.99%, and 93.19%, respectively. Our results ( Table 2 ) demonstrate that all splitters, irrespective of the number of output ports, can provide appropriate total diffraction efficiency and good uniformity. Through rigorous coupled-wave analysis (RCWA), we derived the fabrication tolerance of the incident wavelength and period, which highlights the reliability of the proposed terahertz beam splitters.

Polarization-sensitive terahertz reflective multi-channel beam separation by cascaded configuration

In this paper, we report a two-layer five-port diffraction grating by a polarization-independent design under normal incidence. To be different from conventional five-port gratings, initially, we design a novel two-layer grating with operation in transmission. Next, we firstly design a polarization-independent grating with five-port splitting output. On the one hand, the accurate grating vector parameters are optimized using rigorous coupled-wave analysis (RCWA) approach. On the other hand, the inherent coupling mechanism happened in the grating region can be well explained by employing simplified modal method (SMM). More importantly, all reported conventional five-port beam splitter gratings were designed based on polarization dependent. Although they could obtain high diffraction efficiency for TE or TM polarization, it requires more complicated and time-consuming fabrication processes in practical grating applications. Thus, this work can open up a possible thought for designing polarization-independent multi-port beam splitter diffraction gratings.

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Bowen Gong

Papers

Polarization-Independent Two-Layer Grating With Five-Port Splitting Output Under Normal Incidence