Design of task-specific optical systems using broadband diffractive neural networks

摘要

Diffractive neural-network-based design of a spectral filter. Physically fabricated diffractive filter design shown in ( ). The diffractive layers are 3D printed over a surface that is larger than their active (i.e., beam-modulating) area to avoid bending of the layers. These extra regions do not modulate the light and are covered by aluminium, preventing stray light into the system. The active area of the first diffractive layer is 1 × 1 cm, while the other layers have active areas of 5 × 5 cm. Physical layout of the spectral filters with three diffractive layers and an output aperture (2 × 2 mm). Schematic of the optical set-up. Red lines indicate the optical path of the femtosecond pulses generated by a Ti:sapphire laser at 780 nm wavelength, which was used as the pump for the THz emitter and detector. Blue lines depict the optical path of the THz pulse (peak frequency ~ 200 GHz, observable bandwidth ~ 5 THz) that is modulated and spectrally filtered by the designed diffractive neural networks. Photograph of the experimental set-up.