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This study presents a theoretical model of a subwavelength grating polarization beam splitter (SWGPBS) using a combination of the theory of thin-film interference and the effective medium theory for guided-mode resonance. The structural parameters of SWGPBSs at oblique incidence calculated by our theoretical models and electromagnetic wave simulation were in good agreement within the range of the predicted approximation error. Feasibility of the oblique incidence SWGPBSs was verified, and the physical limitations of the SWGPBSs were clarified. Because the design procedure of SWGPBSs was simplified with our theoretical analysis, the range of their applications can be expanded to other fields.

A simple measurement technique is proposed for multi-pitched grating inserted in an external cavity diode laser. Measuring grating rotation and variation of multiple resonant wavelengths enables us to estimate grating periods and Littrow angles simultaneously. We experimentally determined that sufficient variation of resonant wavelength (i.e. ∼1.6 nm) could be obtained even with a grating rotation less than 0.05°. The grating periods and Littrow angles of two dual-period holographic gratings were successfully measured with less than 1% error. This technique can be applied to the motionless measurement of multi-pitched gratings, diffractive optics, and metasurfaces in the future.

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