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.

A highly sensitive curvature sensor based on asymmetrical twin core fiber (TCF) and multimode fiber (MMF) is proposed and experimentally demonstrated. By applying the coupled-mode theory and equivalent refractive index model, we theoretically analyze the uncoupled feature of the TCF and the relationship between peak wavelength and the curvature. Two segments of MMF used as beam splitter and combiner are embedded on the two ends of the TCF, and the extinction ratio of the comb transmission spectrum is about 15 dB. The experimental result shows that the curvature sensitivity of the sensor can be achieved as high as 103.35 nm/m −1 ranging from 0.24 m −1 to 0.6 m −1 , and the strain sensitivity is up to-4.01 pm/µε in the range from 0 µε to 1400 µε. The simultaneous detection of the curvature and strain can be realized. The temperature sensitivity is 0.431 nm/ • C in the range from

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We demonstrate the two-dimensional tunable orbital angular momentum (OAM) generation in a ring-core (vortex) fiber. The LP mode generated by an all fiber fused coupler is coupled into a vortex fiber. Because the vector modes of the LP mode group in the vortex fiber are no longer degenerate, the mode status will change between linearly polarized modes (LPMs) and complex OAM modes periodically during propagation. The generated OAM can be tuned smoothly by filtering the mixed mode with different polarization directions or changing the wavelength at a certain polarization directions. The two-dimensional tuning of OAM from l=-1 to l=+1 is experimentally demonstrated in an all fiber OAM generator.

We propose a new approach to realize switchable mode operation in a few-mode erbium-doped fiber laser. The ring fiber laser structure is constructed with a core-offset splicing between single-mode fiber and dual-mode fiber. Stable operating on the fundamental mode laser and second-order mode laser individually or simultaneously is realized by appropriately adjusting the state of the polarization controller and bending status of the few-mode fiber Bragg grating. The narrow 3 dB linewidth less than 0.02 nm and high optical signal to noise ratio more than 42 dB are obtained for both modes in either separate laser or simultaneous laser operating conditions.

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We experimentally demonstrate a multiwavelength fiber ring laser with tunable orbital angular momentum (OAM) beam output. The laser is embedded with a few-mode fiber Bragg grating and a mode selective coupler (MSC). The mode conversion from LP01 mode to LP11 mode is realized by using the MSC as a mode converter. By rotating a polarizer set at the output end of the MSC, the topological charge of the OAM beam can be tuned from l  =  −1 to l  =  +1 and thus a tunable OAM beam is obtained. By adjusting the polarization controllers (PCs), the laser can operate under single-, dual- and triple-wavelength lasing conditions.