Single-step holographic grayscale lithography of Fabry-Perot filter arrays

Multispectral filter arrays underpin compact spectral imaging but are typically fabricated through complex, multi-step photolithography. Here, we demonstrate a single-step holographic grayscale lithography method using a spatial light modulator (SLM) to directly write Fabry–Perot filter arrays. A phase-retrieval algorithm computes holograms that project grayscale intensity patterns into photoresist, enabling cavity thicknesses from 600 to 1300 nm across a single exposure. Transmission spectra are modeled using transfer-matrix simulations with Monte Carlo sampling to capture thickness variations, and experimental spectra are fitted via Tikhonov-regularized inversion, showing good agreement between theory and experiment (R² ≈ 0.95). We show that speckle-like noise, typically detrimental in projection systems, can instead be exploited as a design parameter to broaden Fabry–Perot resonances in a controllable manner. We show that the method can achieve lateral resolutions down to 1-2.5 μm depending on resolution criteria, representing the highest reported for holographic projection lithography and comparable to many commercial direct-write techniques. This approach consolidates multiple fabrication steps into one, offering a scalable and tunable route toward integrated multispectral filter arrays compatible with CMOS imaging technology.