Phase error correction of MEMS-based spatial light modulations by computer generated holograms (CGH)

Texas Instruments Phase Light Modulators (TI-PLMs) offer high-speed, polarization-independent phase control. However, residual substrate deformation of MEMS mirror backbone introduces wavefront aberrations that broaden the point spread function (PSF), consequently image quality is degraded. At wavelength of 633 nm for which PLM is designed, an on-axis computer-generated hologram (CGH) can negate the aberration and restore a diffraction-limited PSF with the phase modulation range of 2π. At a wavelength of 1550 nm, however, the phase modulation depth drops to 0.8π which is insufficient for full correction with an on-axis CGH. To address correction of substrate induced wave aberration at 1550nm, we design an off-axis CGH that shifts the corrective phase into the ±1 diffraction orders, preserving the compensation effect under limited modulation depth of MEMS SLMs. Numerical simulations confirm that at 633 nm, the on-axis CGH restores the PSF to diffraction limited, while at 1550 nm, the off-axis CGH sharpens the central lobe, increases peak intensity, and reduces PSF broadening compared to the on-axis case. This approach offers a practical phase correction strategy for MEMS-based PLMs across visible and infrared wavelengths.