Optical vortex beams that carry orbital angular momentum (OAM), also known as OAM modes, have attracted considerable interest in recent years as they can comprise an additional degree of freedom for a variety of advanced classical and quantum optical applications. While canonical methods of OAM mode generation are effective, a method that can simultaneously generate and multiplex OAM modes with low loss and over broad spectral range is still in great demand. Here, via novel design of an optical fiber device referred to as a photonic lantern, where the radial mode index ("m") is neglected, for the first time we demonstrate the simultaneous generation and multiplexing of OAM modes with low loss and over the broadest spectral range to date (550 nm). We further confirm the potential of this approach to preserve the quality of studied OAM modes by fusion splicing the end-facet of the fabricated device to a delivery ring-core fiber (RCF).

Leveraging recent advances in space-division multiplexing, we propose and demonstrate turbulence-resistant free-space optical communication using few-mode (FM) pre-amplified receivers. The rationale for this approach is that a distorted wavefront can be decomposed into a superposition of the fundamental Gaussian mode and high-order modes of a few-mode fiber. We present the noise statistics and the sensitivity of the FM pre-amplified receiver, followed by experimental and numerical comparisons between FM pre-amplified receivers and single-mode (SM) pre-amplified receivers with or without adaptive optics. FM pre-amplified receivers for FSO can achieve high sensitivity, simplicity and reliability.

An order of magnitude improvement in the signal-to-noise ratio (SNR) of a 1550 nm LiDAR receiver was achieved using a few-mode optical preamplifier as compared to a multi-mode avalanche photodiode (APD).

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