In-fibre diffraction grating enables high-efficiency optical wireless communication and time stretch imaging

Optical diffraction elements (ODEs) are key components for innovative applications based on spectral encoding. Two most recent examples are wavelength-controlled laser beam steering for optical wireless communication and wavelength-to-space mapping for photonic time stretch imaging. Most commonly used ODEs are free-space ruled or holographic di?raction gratings, which however suffer from some inherent drawbacks, such as bulky construction, limited diffraction efficiency (up to 75%) due to the inherent zeroth-order reflection, and high coupling loss between free-space diffraction gratings and optical fibres in the system. In this paper, we report the use of a 45° tilted fiber grating (TFG) as a highly efficient, low cost and compact in-fiber diffractive device. Its superior performance in both passive infrared laser beam steering for optical wireless transmission and ultrafast photonic time-stretch imaging is presented with experimental demonstrations. Compared to conventional free-space diffractive devices, the 45° TFG provides significant advantages of high diffraction efficiency (>95%), compactness, low cost and inherent fiber-compatibility and holds great promise in spectral encoded applications.