Multiwavelength-channel optical true time delay system implemented by a free-space optics spectral processor

True time delay (TTD) beamforming is critical for wideband phased-array antennas to prevent beam squint and waveform distortion. We present a free-space optical true time delay (OTTD) spectral processor enabling independent, continuously tunable, large-stroke delay control across multiple wavelength channels. A double-pass, self-imaging configuration with a diffraction grating and micro-electro-mechanical system (MEMS) tilting micro-mirrors introduces adjustable optical paths via angular beam steering, providing continuous group delay tuning without additional propagation loss or distortion. The system supports 40 C-band channels spaced at 100 GHz, each independently tuned over a ±0.55 ns range (1.1 ns total) with insertion loss varying between 6 and 8 dB. Optical and electrical characterizations confirm accurate group-delay control, a flat radio frequency (RF) response up to 40 GHz, and a fine delay resolution of ∼0.1 ps. Signal integrity was verified via intensity-modulation direct-detection transmission, achieving error-free performance [bit error rate (BER) <10−9] at 32 Gb/s across the full delay range. Using a time-of-flight technique that, to our knowledge, resolves for the first time the OTTD dynamic transition in the time domain, the measurement identified smooth, millisecond-scale MEMS response times. Combining wide channel bandwidth, large stroke, and fast, low-loss continuous tuning, this scalable OTTD processor is highly promising for broadband microwave photonic beamforming and multibeam next-generation wireless and radar systems.