Multifunctional Diffractive Optical Element for Microcavity Mode Control

The precise control of spatial modes in photonic devices underpins various applications, including data communications with mode multiplexing [1], photonic computing, mode-selective lasers, and nonlinear frequency conversion. However, achieving mode-selective excitation often relies on bulky, expensive phase-only Spatial Light Modulators (SLMs) that are not ideal for compact architectures. In contrast, diffractive optical elements (DOEs) offer a simpler, robust, and more compact alternative as shown in Figure 1 (a), and can be fabricated using mature, cost-effective two-level photolithography. In our previous work [2], we demonstrated mode-selective excitation of a two-dimensional grating-coupled microcavity, known as a Cavity Resonator Integrated Grating Filter (CRIGF) [3], using a phase-only SLM in combination with a focusing lens. Although this setup verified the principle of mode selection, the SLM approach is not ideal for integration.