Sandwich structure for polarization-insensitive high-dispersion diffraction grating based on total internal...

Combining a grating structure with a prism can realize a device with high diffraction efficiency, low polarization-dependent loss, and strong dispersion in a wide spectral range, that is, a total internal reflection (TIR) grating. Here, we propose a new, to the best of our knowledge, sandwich structure grism based on the principle of TIR, which includes a prism, a dielectric slab layer, and a grating layer. The prism grating with this structure can reduce the groove depth of the grating by increasing the refractive index of the grating layer, which is beneficial to actual production. In addition, the polarization sensitivity of the prism grating can be regulated by optimizing the thickness and refractive index of the slab layer. The device can achieve high first-order diffraction efficiency in the wavelength range of 1.525 µm to 1.575 µm under Littrow incidence conditions and shows extremely low polarization-dependent loss (PDL), which is about 0.01 dB to 0.09 dB. We made the sandwich grism by processes including interference lithography, ICP etching, and optical bonding. The experimental results show that the diffraction efficiency of -1 order is between 90% and 95%, although it is slightly decreased due to the error in experimental manufacturing, and |PDL| is in line with the theoretical design value. This form of element not only concentrates diffracted energy more effectively but also possesses excellent dispersive capabilities compared to a conventional planar grating, making it suitable for producing high line density gratings with promising applications in modern high-speed telecommunications and high-precision spectroscopy domains.