Table 1.

The main functions of each module in orbital angular momentum (OAM) on-off keying transmission system.

Module name	Function
On-off keying control signal generator	Convert the user data into bit sequence, and select which branch works according to the bit 1 or 0.
High-voltage power supply	Provide the high voltage in the cyclotron.
Cyclotron	Generate the vortex microwave photons by the vortex electrons.
Mode selector	Select the vortex microwave photons with mode 1, then feed the plane wave into the waveguide combiner.
Plane wave signal source	Generate the sine signal for the plane wave.
Power amplifier	Enhance the energy of the plane wave.
Waveguide converter	Convert the plane wave from the rectangular to circular waveguide.
Waveguide receiver	Receive the electromagnetic wave from the free space.
OAM detection device	Transfer the OAM mode from the received microwave photons to the electrons, then detect the OAM mode by the diffraction pattern of the vortex electrons.
Camera	Record the diffraction pattern of vortex electrons on the fluorescent screen.
Information sequence identifier	Recover the user data by distinguishing the diffraction pattern recorded by the camera.