Recently, NTT Corporation (NTT), a leading global technology service provider, successfully demonstrated a technology that can increase transmission capacity and reduce the power consumption of the C-band (near 1550 nm wavelength) optical communication platform by 67%. To demonstrate this capacity expansion and power consumption reduction, NTT used a multicore fiber and multicore amplification system, which uses a core structure of 12 cores densely arranged in the fiber for amplification.
As part of its Innovative Optical and Wireless Network (IOWN) initiative, NTT aims to deploy this technology by 2030, which will have a space-division multiplexing transmission line with more than 10 channels. This is a revolutionary communication infrastructure that aims to achieve a smarter world by applying cutting-edge research fields including photonics and advanced computing.
How do optical amplifiers increase transmission capacity and reduce power consumption? Traditional optical amplifiers use core pumping, which is usually to inject pump light into the core unit to amplify the signal light propagating in the core; while optical amplifiers use cladding pumping, which applies pump light to the entire cross-section of the fiber, amplifying all signal light propagating in multiple cores within the cross-section. The amplifying fiber maximizes the area ratio of the core and the cladding by reducing and increasing the outer diameter (cladding diameter) and core diameter of the fiber, while maintaining the same multicore arrangement (core number and core spacing) as the fiber transmission line.
Therefore, researchers can make the most of the pump light. Since reducing the cladding diameter is to increase the area ratio of the amplifying fiber core, the cladding diameter does not match the connection point between the transmission line fiber and the amplifying fiber, and some pump light is lost. In addition, both traditional and proposed techniques produce pump light that is not used for optical amplification but is removed after fiber propagation. By using a conical structure and a reflector, NTT successfully reduced the pump light loss and residual pump light, further improving the optical amplification efficiency.
