  The performance of laser-based active sensing has been severely limited by
two types of noise: electrical noise, stemming from elements; optical noise,
laser jamming from an eavesdropper and background from environment.
Conventional methods to filter optical noise take advantage of the differences
between signal and noise in time, wavelength, and polarization. However, they
may be limited when the noise and signal share the same information on these
degrees of freedoms (DoFs). In order to overcome this drawback, we
experimentally demonstrate a groundbreaking noise-filtering method by
controlling orbital angular momentum (OAM) to distinguish signal from noise. We
provide a proof-of-principle experiment and discuss the dependence of azimuthal
index of OAM and detection aperture on signal-to-noise ratio (SNR). Our results
suggest that using OAM against noise is an efficient method, offering a new
route to optical sensing immersed in high-level noise.
