Abstract
A schematic diagram of a RoF radio-optic system with vortex signals is presented, in which the radio frequency is determined by the difference between the wavelengths of two lasers. It is assumed that the generation of a vortex signal can be performed through a vortex fiber-optic periodic structure, which can be obtained using a technology similar to the manufacture of long-period fiber Bragg gratings. The parameters of the grating are modeled assuming that the fundamental light-guide mode (LP01) is applied to the specified vortex element, and the higher-order mode (LP11) is reflected. It was found that the distortion of the vortex signal can be reduced by introducing apodization and chirping of this periodic structure. The following optimal parameters have been estimated: the apodization and chirp multiplier functions, at which the distortions of the amplitude and phase of the vortex signal, as well as the appearance of an unwanted angle distortion, will be minimal. It is shown that such gratings can be exploited in addressed sensors systems using the orbital angular momentum (OAM) of a lightwave as a unique sensor address.
Highlights
Interest in optical vortex signals has already shifted from research to a purely practical plane
We have studied a two-frequency radio-photonic scheme designed to generate a radio signal up to the terahertz range, which forms a first-order vortex signal
The orbital angular momentum (OAM) signal generation is proposed to be performed using a vortex optical fiber periodic structure, which can be manufactured similar to the existing technology for the production of long-period Bragg gratings
Summary
Interest in optical vortex signals (or OAM—orbital angular momentum [1,2,3] signals) has already shifted from research to a purely practical plane. To generate OAM signal in the scheme shown, it is proposed to use a directional splitter (circulator) at the output of the lasers and the V-FBG element, which can be obtained, for example, based on the existing method of separate (individual) burning of fingers of long-period FBGs, but with a continuously switched on UV laser and with simultaneous rotation and longitudinal drawing of the optical fiber preform This technology is developing [27] and the details of the implementation of a specific production process will subsequently be worked out and refined.
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