OAM Beams Generation Technology in Optical Fiber: A Review

High-Security OFDM-OAM Optical Transmission Scheme Based on Quad-Wing Ultra-Chaotic Encryption

“…In Eq. ( 1): denotes the OAM topological charge number.denotes the number of spin angular momentum modes.denotes the radial distance to the central axis.is the angular coordinate.is the transmission distance.denotes the Rayleigh distance.denotes the wave number.denotes the radius of the bundle.denotes the concatenated Laguerre polynomial.denotes the spiral phase factor.When when denotes zero-order Gaussian light.Through the Laguerre Gauss formula we can learn that normal electromagnetic waves carrying normal data information can be generated by Gaussian light from the OAM beam,according to the azimuthal angle change,adding the corresponding phase rotation,making the electromagnetic waves originally sent in the same phase in a plane distorted to form an electromagnetic vortex wave [21].the orbital angular momentum characteristics of the OAM beam are jointly determined,as shown in Figure 2,when the The light intensity and phase distribution at the light source when the beam intensity is distributed as 1 outer ring. A conceptual diagram of OAM beam modulation/demodulation is shown in Figure 3.In optical communications,OAM can be considered as an additional degree of freedom,and multiplexing of OAM beams carrying information provides another dimension for improving the capacity and spectral efficiency of the communication link.Capacity and spectral efficiency can be further improved through the use of higher order phase modulation [22].As shown in Figure 3,Gaussian beams are modulated by adding spiral phase conversion to OAM beams through a spatial optical phase modulator,and as they propagate,the intensity of these OAM beams takes on a 'doughnut' shape in the CCD detection plane,consisting of a bright circle with no intensity in the centre.modulator,which can be converted back to a planar phase front by removing the azimuthal phase term exp(i ℓ u)from the OAM beam using a spiral phase mask with the opposite end of the modulation.This beam has a bright high intensity point in the centre and finally the original Gaussian beam is restored by means of spatial filtering.…”

Numerical study of microstructured fiber with concentric dual rings for supporting orbital angular momentum mode propagation

“…HE even 2,1 and HE odd 2,1 can be stably propagated in the form of OAM mode, but TE 0,1 and TM 0,1 have a big refractive index difference, which indicates the generated OAM mode cannot be transmitted stably. For l = ±1, equation ( 1) can be expressed as [16] OAM…”

Structured Light Laser Based on Intra-Cavity Modulation

“…The generation of structured light fields in fibres is principally derived from the excitation and extraction of eigenmodes in dual-mode, four-mode, and other few-mode fibres (FMF). Generally, structured light fields can be generated by mode selection coupling [91], Bragg gratings [92], long-period fibre gratings (LPFG) [93,94], and so on. However, the aforementioned fibre devices always operate in a narrow band and have a high loss in the generation.…”