Complex-amplitude modulation by high-carrier-frequency diffractive elements

Complex-amplitude modulation is necessary if we wish to suppress the noise that surrounds the signal in diffractive optics. This is desirable in, e.g., space-invariant optical interconnection. We present a mathematical scheme to synthesize high-carrier-frequency diffractive elements that perform phase and amplitude modulation of the first carrier-grating order without the use of absorption. The amplitude information is encoded in grating-depth variations and in the phase information in pulse-position modulation. Use of rigorous diffraction theory in the design of the local grating structure ensures virtually noise-free reconstruction with efficiencies that are significantly higher than the values one typically obtains, e.g., by conventional holographic recording.