Abstract
An encapsulated rectangular-groove fused-silica grating as a highly efficient two-port beam splitter is presented, which
is designed at a central wavelength of 1550nm under Littrow mounting. The design method of such a high-efficiency
two-port beam splitter grating is mainly based on the simplified modal method with consideration of two beam
interference of the modes excited by the incident wave. Meanwhile, this encapsulated grating can be considered
equivalent to an effective Fabry-Perot-resonator, therefore, Fabry-Perot interference of grating modes inside the grating
area also plays an innegligible role in achieving high efficiency and equality in the diffracted zeroth and minus-first
orders, which also should be considered in the design. The rigorous coupled-wave analysis(RCWA) is used to verify the
design method and optimize grating profile. Numerical simulations show that, the RCWA results agree well with the
design conditions derived from modal method. And with the optimum grating profile, high total efficiency(99.78%) and
equal intensity of the diffracted zeroth and minus-first orders can be obtained at the wavelength of 1550nm. Moreover,
the designed encapsulated beam splitter can work well over the C+L band and within 21° angular range. The
encapsulated grating can exhibit higher diffraction efficiency, intensity equality and less reflection loss than
conventional rectangular-groove grating.
