MEMS grating modulators enable versatile beam steering functions through the electrostatic actuation of movable ribbons. These modulators operate at ultrahigh frequencies in the hundred kHz range, and their micromirror-free configuration simplifies the fabrication process and reduces costs compared to micromirror-based modulators. However, these modulators are limited in their optical efficiency and aperture. Especially in FSO communication or remote sensing applications, the aperture size and efficiency are crucial factors for improving the detection range and energy efficiency.

In this work, we introduced a tunable sinusoidal grating-based MEMS grating modulator with a large-scale extendable aperture and high optical efficiency. The proposed modulator is constructed with a tunable grating pitch array, in which each pitch is designed with a broadside-constrained continuous ribbon to generate deflection deformation. Owing to the unidirectional equal stiffness of the pitch, its resonant frequency remains constant regardless of variations in its longitudinal dimensions. Consequently, a large-scale aperture can be constructed by extending the pitch length and arranging the pitches in a one-dimensional array. Additionally, a continuous sinusoidal grating profile, rather than a rectangular discrete grating, was adopted to modulate the diffraction intensity with a higher optical efficiency. Owing to the proposed sinusoidal grating structure, the modulator chip can be efficiently fabricated with only a two-layer structure configuration.

For the current embodiment, the implemented continuous sinusoidal grating enables the modulator to have a surface fill factor of over 96% and an optical efficiency of over 90%, corresponding to an optical insertion loss of less than 1 dB. The end-free grating allows scalability along the grating, enabling a large aperture of 30 × 30 mm. Regarding optical modulation performance, an extinction ratio of over 20 dB and a modulation contrast of over 98% is achieved for the 0^th-order beam with normal incidence light. The reported modulator can achieve a dynamic modulation contrast of over 95% within a 250 kHz operating frequency. The proposed modulator also achieves nearly full modulation within an incident angle range of ± 30° and a FOV of 120° under a 3 dB bandwidth.

The reported MEMS grating modulator holds promise for application in high-speed light attenuation and modulating retroreflector free-space optical (MRR-FSO) communication systems. Our device also paves new ways for future high-speed, energy-efficient, and cost-effective communication networks.