Abstract
Optical vortex beams that carry orbital angular momentum (OAM), also known as OAM modes, have attracted considerable interest in recent years as they can comprise an additional degree of freedom for a variety of advanced classical and quantum optical applications. While canonical methods of OAM mode generation are effective, a method that can simultaneously generate and multiplex OAM modes with low loss and over broad spectral range is still in great demand. Here, via novel design of an optical fiber device referred to as a photonic lantern, where the radial mode index ("m") is neglected, for the first time we demonstrate the simultaneous generation and multiplexing of OAM modes with low loss and over the broadest spectral range to date (550 nm). We further confirm the potential of this approach to preserve the quality of studied OAM modes by fusion splicing the end-facet of the fabricated device to a delivery ring-core fiber (RCF).
Highlights
Light beams can have orbital angular momentum (OAM)
3.1 Demonstration of an annular OAM mode MUX To efficiently transmitting the OAM modes of the mode generator into a delivery ring-core fiber (RCF), one should assure high coupling efficiency between the two fiber components. This can be achieved by appropriately designing the OAM mode MUX to perfectly mode match the delivery RCF, i.e. a ring-core mode MUX
To fabricate a ring-core OAM mode MUX, we follow the same procedure as for the aforementioned standard mode selective photonic lantern (MSPL) except for replacing the central core by a core-less fluorinedoped fiber. This fiber has a core diameter of 86 μm and a refractive index contrast of −9 × 10−3 with respect to the background glass in order to form a null intensity profile in the center. This is the key feature of our ring-shaped OAM mode MUX, which leads to exceptionally reliable mode-match, providing low-loss and stable transformation of the OAM modes into the delivery RCF
Summary
Light beams can have orbital angular momentum (OAM). A light beam that has an azimuthally varying phase front given by exp(ilφ) , is referred to as an optical vortex which has an OAM of l per photon where, l = 0, ±1, ±2,... It is possible to use OAM modes to increase the data speeds of free space and optical fiber communications via mode division multiplexing [3,4,5,6] and amplitude multiplexing [7] and enhance the security of quantum cryptography via high-dimensional quantum key distribution [8,9,10]. OAM modes or their superposition, provide a high-dimensional resource for fundamental tests of quantum mechanics such as quantum entanglement [11,12,13,14], and can be used for novel methods of remote sensing [15], high-resolution imaging [16,17] and high-precision optical measurements [18,19]
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