Since the first deployments of fiber-optic com- munication systems three decades ago, the capacity carried by a single-mode optical fiber has increased by a staggering 10 000 times. Most of the growth occurred in the first two decades with growth slowing to ten times in the last decade. Over the same three decades, network traffic has increased by a much smaller factor of 100, but with most of the growth occurring in the last few years, when data started dominating network traffic. At the current growth rate, the next factor of 100 in network traffic growth will occur within a decade. The large difference in growth rates between the delivered fiber capacity and the traffic demand is expected to create a capacity shortage within a decade. The first part of the paper recounts the history of traffic and capacity growth and extrapolations for the future. The second part looks into the technological chal- lenges of growing the capacity of single-mode fibers by pre- senting a capacity limit estimate of standard and advanced single-mode optical fibers. The third part presents elementary capacity considerations for transmission over multiple trans- mission modes and how it compares to a single-mode trans- mission. Finally, the last part of the paper discusses fibers supporting multiple spatial modes, including multimode and multicore fibers, and the role of digital processing techniques. Spatial multiplexing in fibers is expected to enable system capacity growth to match traffic growth in the next decades.

https://www.icg.isy.liu.se/courses/optical/Capacity_Trends.pdf

Capacity Trends and Limits of Optical Communication Networks Discussed in this paper are: optical communication network traffic evolution trends, required capacity and challenges to reaching it, and basic limits to capacity.

Since the first deployments of fiber-optic communication systems three decades ago, the capacity carried by a single-mode optical fiber has increased by a staggering 10 000 times. Most of the growth occurred in the first two decades with growth slowing to ten times in the last decade. Over the same three decades, network traffic has increased by a much smaller factor of 100, but with most of the growth occurring in the last few years, when data started dominating network traffic. At the current growth rate, the next factor of 100 in network traffic growth will occur within a decade. The large difference in growth rates between the delivered fiber capacity and the traffic demand is expected to create a capacity shortage within a decade. The first part of the paper recounts the history of traffic and capacity growth and extrapolations for the future. The second part looks into the technological challenges of growing the capacity of single-mode fibers by presenting a capacity limit estimate of standard and advanced single-mode optical fibers. The third part presents elementary capacity considerations for transmission over multiple transmission modes and how it compares to a single-mode transmission. Finally, the last part of the paper discusses fibers supporting multiple spatial modes, including multimode and multicore fibers, and the role of digital processing techniques. Spatial multiplexing in fibers is expected to enable system capacity growth to match traffic growth in the next decades.

Capacity Trends and Limits of Optical Communication Networks

A compact two-mode (de)multiplexer (TM-MUX) based on Si nanowire for mode-division multiplexing is designed. The TM-MUX is composed of two multimode interference (MMI) waveguides and a butterfly-shape tapered phase shifter between two MMI waveguides. Numerical simulations show that the designed device is compact compared with conventional-mode (de)multiplexer and operates as a TM-MUX in the whole C-band. In addition, we show that the designed TM-MUX has relatively good fabrication tolerance.

Design of a Compact Two-Mode Multi/Demultiplexer Consisting of Multimode Interference Waveguides and a Wavelength-Insensitive Phase Shifter for Mode-Division Multiplexing Transmission

We realized mode-division multiplexing(MDM) transmission by using orthogonal LP modes with negligible modal crosstalk, for the first time. A 2×10Gbps MDM transmission was achieved over a 10km two-mode fiber with sufficiently low power penalty.

Demonstration of mode-division multiplexing transmission over 10 km two-mode fiber with mode coupler

We discuss the generation, wavelength-division-multiplexed (WDM) long-haul transmission, and coherent detection of 224-Gb/s polarization-division-multiplexed (PDM) 16-ary quadrature amplitude modulation (16-QAM) at a line rate of 28 Gbaud. We measure a required optical signal-to-noise ratio of 23.4 dB (0.1-nm reference bandwidth; 10-3 bit-error ratio), 3.4-dB off the theoretical limit. Using ultra-large-area fiber, we achieve 2000-km single-channel transmission. We also demonstrate 1200-km WDM transmission on a 50-GHz grid (4-b/s/Hz spectral efficiency), including three passes through a wavelength-selective switch.

Spectrally Efficient Long-Haul WDM Transmission Using 224-Gb/s Polarization-Multiplexed 16-QAM

We demonstrate the record total capacity of 69.1 Tb/s with a spectral efficiency of 6.4 b/s/Hz by employing 21.4-Gbaud 16-QAM modulation, blind digital coherent detection, and 10.8-THz ultra-wideband amplification in the C- and extended L-bands.

M. Fujiwara

Papers

69.1-Tb/s (432 × 171-Gb/s) C- and extended L-band transmission over 240 km Using PDM-16-QAM modulation and digital coherent detection

69.1-Tb/s (432 × 171-Gb/s) C-and extended L-band transmission over 240 km using PDM-16-QAM modulation and digital coherent detection