New research by optical fiber experts at Boston University and optical communications systems experts at the University of Southern California created a new kind of optical fiber stable enough to transmit donut-shaped laser beams called optical vortices, also known as orbital angular momentum (OAM) beams. OAM beams are generating interest not only in communications, but also atom manipulation and optical tweezers.
They packed several colors into each mode and used multiple modes. Unlike in conventional fibers, OAM modes in these specially designed fibers can carry data streams across an optical fiber while remaining separate at the receiving end.
Ramachandran’s OAM fiber had four modes (an optical fiber typically has two), and he and Willner showed that for each OAM mode, they could transmit 400 Gb/s in just a single wavelength of light — or 1.6 Tb/s across 10 wavelengths — over the course of 0.68 miles (1.1 km).
“This is very impressive,” University of Rochester physicist Robert Boyd told Science. “I can imagine a huge commercial market.”
Journal Science - Terabit-Scale Orbital Angular Momentum Mode Division Multiplexing in Fibers
In 2012, the same research team led by USC developed a system of transmitting data using twisted beams of light at ultra-high speeds – up to 2.56 terabits per second through free space. That method didn’t work, however, when it was tried in a standard optical fiber.
ABSTRACT - Internet data traffic capacity is rapidly reaching limits imposed by optical fiber nonlinear effects. Having almost exhausted available degrees of freedom to orthogonally multiplex data, the possibility is now being explored of using spatial modes of fibers to enhance data capacity. We demonstrate the viability of using the orbital angular momentum (OAM) of light to create orthogonal, spatially distinct streams of data-transmitting channels that are multiplexed in a single fiber. Over 1.1 kilometers of a specially designed optical fiber that minimizes mode coupling, we achieved 400-gigabits-per-second data transmission using four angular momentum modes at a single wavelength, and 1.6 terabits per second using two OAM modes over 10 wavelengths. These demonstrations suggest that OAM could provide an additional degree of freedom for data multiplexing in future fiber networks.
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