Dispersive Fourier transform imaging is a powerful technique in achieving ultrafast imaging of wide areas. However, system power efficiency is often limited by dispersive components. Here, we demonstrate that a gap-plasmon metasurface (GPM) based blazed grating can be used in dispersive imaging applications to achieve higher power efficiency than conventional gratings. A sub-wavelength GPM-based grating at telecommunication wavelengths has been designed and fabricated. 75.6% power efficiency with ∼0.4°/10 nm spatial dispersion has been measured for TE polarized waves at normal incidence. The fabricated device has been tested in a wide area real-time dispersive imaging system and <300 μm spatial resolution has been demonstrated experimentally.
Subwavelength high-contrast gratings (sub-λ HCGs) were pursued to design mid-IR optical devices based on wavefront engineering. Unlike metallic counterparts, dielectric and semiconductors offer low-loss operation over a wide spectral range. Silicon gratings on sapphire substrate are proposed here as the device platform due to their transparency at near-IR to mid-IR wavelengths. The proposed generic methodology manipulates the wavefront of the reflected wave based on the phase and magnitude of reflectivity for unit cells with different dimensions. To demonstrate the capability of generating an arbitrary wavefront profile, several design examples are shown: (1) a reflective mirror with ∼100% power efficiency and broad bandwidth of >1 μm as reflectivity >90%; (2) a blazed grating with a reflection peak automatically aligned with its 1st diffraction order at 19.5°; (3) a focusing mirror with a focal length of 35 μm and diffraction-limited focus; (4) a sinusoidal phase profile with a periodicity of 8860 nm.
We have developed a multitone modulated continuous wave (MTCW) Lidar system made of a CW laser with multiple fixed RF tones for a high precision range finding and velocimetry. In this paper, the MTCW Lidar system has been studied analytically and numerically. A proof-of-concept experiment by employing 1550-nm light source and multiple radio-frequency (RF) tone modulations ranging from 50 MHz to 6 GHz has been performed to demonstrate proof of principle for range finding with <1-cm range resolution. We also provide sine fitting algorithms on the measured RF tones to extract the range information in a single shot RF measurement and demonstrate the ways to improve the resolution beyond the actual RF bandwidth.
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