Polarization-based real-time diffraction efficiency measurement of reflection volume holographic gratings

Holographic gratings play a crucial role in various applications, including spectroscopy, displays, security holograms, and sensing technologies. Real-time monitoring of the diffraction efficiency of these gratings is essential for improving fabrication processes and performance optimization. For many applications, such as displays and sensing, reflection volume holographic gratings (RVHGs) are preferred over transmission gratings due to their high wavelength selectivity. Existing real-time diffraction efficiency measurement setups typically rely on the Bragg degenerate method, which requires two lasers, resulting in increased cost and bulkiness. Also, it requires precise wavelength tuning and alignment, making the system more complex. Therefore, we propose a polarization-based novel, to the best of our knowledge, setup that performs real-time measurement of the diffraction efficiency of RVHGs with a single laser source. In this approach, the probe beam, having a different polarization state than the recording beams, provides real-time measurements, demonstrating a simplified method for the characterization and optimization of RVHGs. Furthermore, the refractive index modulation and polymerization rates are calculated for RVHGs recorded in photopolymer film, which are essential for determining grating quality and optical performance. Application of the proposed method is demonstrated in the optimization of holographic couplers required for the holographic waveguide-based near-eye augmented reality displays.