Researchers demonstrate the ability to multiplex and transfer data between twisted beams of light with different amounts of orbital angular momentum — a development that provides new opportunities for increasing the data capacity of free-space optical communications links.

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Terabit free-space data transmission employing orbital angular momentum multiplexing

This Review summarizes the simultaneous transmission of several independent spatial channels of light along optical fibres to expand the data-carrying capacity of optical communications. Recent results achieved in both multicore and multimode optical fibres are documented.

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Space-division multiplexing in optical fibres

Orbital angular momentum (OAM), which describes the “phase twist” (helical phase pattern) of light beams, has recently gained interest due to its potential applications in many diverse areas. Particularly promising is the use of OAM for optical communications since: (i) coaxially propagating OAM beams with different azimuthal OAM states are mutually orthogonal, (ii) inter-beam crosstalk can be minimized, and (iii) the beams can be efficiently multiplexed and demultiplexed. As a result, multiple OAM states could be used as different carriers for multiplexing and transmitting multiple data streams, thereby potentially increasing the system capacity. In this paper, we review recent progress in OAM beam generation/detection, multiplexing/demultiplexing, and its potential applications in different scenarios including free-space optical communications, fiber-optic communications, and RF communications. Technical challenges and perspectives of OAM beams are also discussed.

Optical communications using orbital angular momentum beams

Differential-phase-shift keying (DPSK) has recently been used to reach record distances in long-haul lightwave communication systems. This paper will review theoretical, as well as implementation, aspects of DPSK, and discuss experimental results.

Optical phase-shift-keyed transmission

We report simultaneous transmission of six spatial and polarization modes, each carrying 40 Gb/s quadrature-phase-shift-keyed channels over 96 km of a low-differential group delay few-mode fiber. The channels are successfully recovered by offline DSP based on coherent detection and multiple-input multiple-output processing. A penalty of ;28 dB.

Mode-Division Multiplexing Over 96 km of Few-Mode Fiber Using Coherent 6 $\,\times\,$ 6 MIMO Processing

An efficient single frequency distributed feedback (DFB) Brillouin fiber laser producing 22mW of Stokes output, using 81mW of pump from a semiconductor DFB laser, is shown. The laser operated for a pump frequency detuning >1GHz.

Highly Efficient Distributed Feedback Brillouin Fiber Laser

This paper describes the enabling fiber and amplifier technologies for ultra-long reach unrepeatered transmission submarine cable systems. The key enabling technologies include the large-area ultra-low attenuation fibers, high-efficient Remote Optically Pumped Amplifier (ROPA), and second order pumped distributed Raman amplification. The benefits of the technologies are illustrated, and their physical limiting factors for unrepeatered transmission are discussed. We then present the design and experimental demonstrations of ultra-long reach total capacity of 400 Gb/s (4 × 100 Gb/s) unrepeatered transmission links with real-time signal processing. The unrepeatered transmissions are achieved by using commercially available large-area ultra-low attenuation fibers and transceiver modules. This 4 × 100 Gb/s unrepeatered transmission over 557 km fiber is demonstrated with single fiber configuration. TeraWave SCUBA150 fibers with an effective area of 153 μm2 and an average attenuation of 0.153 dB/km at 1550 nm, and forward and backward ROPAs with second-order Raman pumping schemes are employed in this demonstration. Long-term real-time error free transmission results are also reported. In addition, we report the experimental demonstration of real-time transmission of 4 × 100 Gb/s unrepeatered link over 578 km fiber by employing an additional dedicated pump fiber path.

Ultra-Long Reach 4 × 100 Gb/s Unrepeatered Transmissions With Real-Time Signal Processing Using Large A eff Ultra-Low Loss Fiber

We report the transmission of 3×112-Gb/s DP-16QAM at 20 GHz channel spacing over 35×80-km spans of ultra-large effective area fiber (ULAF), with interchannel nonlinearity compensation at a coherent receiver

3×112-Gb/s DP-16QAM transmission over 35×80 km of ULAF with interchannel nonlinearity compensation

PROBLEM TO BE SOLVED: To provide, in a best condition, amplification for multichannel transmissions carried by multicore fiber spans.SOLUTION: An optical transmission and amplification system includes a multichannel transmission span with one multicore transmission fiber having a plurality of individual transmission cores. A first, tapered multicore coupler provides connectivity between the plurality of transmission cores of the multicore fiber and a plurality of corresponding individual transmission leads. A fiber amplifier is provided having a plurality of individual cores including at least one pump core and a plurality of amplifier cores. A second tapered multicore coupler provides connectivity between the amplifier cores of the fiber amplifier and a respective plurality of amplifier leads, and between the at least one pump core and respective pump leads.SELECTED DRAWING: Figure 1

Multicore fibers for transmission and amplification, and schemes for launching pump light to amplifier cores

PROBLEM TO BE SOLVED: To provide technique and a device for low loss connection to multi-core fiber.SOLUTION: An optical fiber coupler is composed of a plurality of coupler fibers 61 each having a separate core 62. Each coupler fiber is composed of: a core area having first refraction index; a pedestal area that surrounds the core area and has second refraction index smaller than the first refraction index; and a clad area that surrounds the pedestal area and has third refraction index smaller than the second refraction index. Each coupler fiber has a mode field diameter corresponding to the mode field diameter of each input fiber. A plurality of coupler fibers are bundled at one end with a block 63 that is terminated at an output end face 64 having a core structure corresponding to a multi-fiber core, melted, and made into a tapered shape. Each core has a mode field diameter corresponding to the mode field diameter of each core of multi-core fiber whose core is connected with the output end face.SELECTED DRAWING: Figure 4

Benyuan Zhu

Papers

Highly Efficient Distributed Feedback Brillouin Fiber Laser

Ultra-Long Reach 4 × 100 Gb/s Unrepeatered Transmissions With Real-Time Signal Processing Using Large A eff Ultra-Low Loss Fiber

3×112-Gb/s DP-16QAM transmission over 35×80 km of ULAF with interchannel nonlinearity compensation

Multicore fibers for transmission and amplification, and schemes for launching pump light to amplifier cores

Technique and device for low loss connection to multi-core fiber