Tunable orbital angular momentum generation in optical fibers

Abstract

We present a method in this Letter to generate optical vortices with tunable orbital angular momentum (OAM) in optical fibers. The tunable OAM optical vortex is produced by combining different vector modes HE2,meven (HE2,modd) and TE_0,m (TM_0,m) when l=1 or combining HEl+1,meven (HEl+1,modd) and EHl-1,modd (EHl-1,meven) when l>1 with a π/2 phase shift. The vortex can be regarded as a result of overlapping two orthogonal optical vortex beams of equal helicity but opposite chirality with a π/2 phase shift. We have experimentally demonstrated the smooth variation of OAM from l=-1 to l=+1 by adjusting a polarizer at the output end of the fiber.

Wavelength-switchable vortex beams based on a polarization-dependent microknot resonator

“…LP 11 mode is actually the superposition of vector modes, TE 0;1 , TM 0;1 and HE even 2;1 (HE odd 2;1 ). And OAM optical vortex can be obtained by Research Article combining different vector modes HE even 2;1 (HE odd 2;1 ) and TE 0;1 (TM 0;1 ) when l 1, or combining HE even l 1;m (HE odd l 1;m ) and EH even l −1;m (EH odd l −1;m ) when l > 1 with a π∕2 phase shift, where l refers to the azimuthal index and m refers to the radial index [32]. Then a π∕2 phase shift between two vector modes is an indispensable part of generating OAM OVBs.…”

“…The change of the power coupling is observed during the fiber pulling and fusing process, and a different splitting ratio can be obtained by controlling the pulling length. Fiber OAM 1 modes can be obtained by combining vector modes HE even 2;1 (HE odd 2;1 ) and TE 0;1 (TM 0;1 ) with a π∕2 phase shift [32]. By rotating the PC4 on the output of FMF and adjusting the pressure appropriately, a π∕2 phase shift between vector modes can be achieved.…”

Fiber-based mode converter for generating optical vortex beams

“…Free-space optical systems, such as spiral phase plates 10 , cylindrical lens converters 11 , and spatial light modulators (SLM) [7][8][9] , are relatively bulky or expensive. Hence, various fiber-based generation schemes have been investigated, such as acoustic-optic interaction 12 , mechanical stress-induced long-period grating 13,14 , CO 2 laser-inscribed long-period fiber grating 15 , offset splicing 16 or pressure exertion 17 in a single-ring fiber, and the superposition of two orthogonal LP 11 modes with a micro phase difference, because of their superior robustness, low cost, compatibility, and high efficiency. In these previous papers, however, only OAM modes for l = ±1 have been achieved, which makes the development of high-capacity all-fiber communication systems based on OAM modes difficult.…”

Controllable all-fiber generation/conversion of circularly polarized orbital angular momentum beams using long period fiber gratings

“…A beam of light carrying OAM possesses a phase φ(l,ϕ) = exp(ilϕ) in the transverse plane, where ϕ is the azimuth angle and l is the topological charge number. As the unique characteristics of the OAM light beam were found, a number of attempts to generate and manipulate the OAM beams were proposed based on discrete free space optical systems [6][7][8][9][10][11] and optical fiber components [12][13][14][15][16][17][18].…”

“…Recently, OAM modes stably propagating in fiber-based transmission links have also shown the potential applications in optical communication. Such modes have unlimited topological charge and will reduce propagating OAM modes coupling [12][13][14][15][16][17][18][19]. These two sets of modes have a common eigenmode set in fibers, and therefore, the transformation of modal state between LP modes and OAM modes becomes possible.…”