Multi-format all-optical-3R-regeneration technology

Amount of information flowing through the Internet is growing by about 40% per year. In Japan, the monthly average has already reached 3.7Tb/s as of May 20 . Considering the explosive spread of smartphone use now underway, the growth of information flow through the optical network is expected to be greater than ever before. From this background, there is strong demand for faster, power-saving optical transmission system. Until now, due to the very high carrier frequencies of optical signals, using a simple OOK (On-Off Keying) that assigns binary signals to the presence or absence of electric field strength was sufficient for achieving higher speeds. Unfortunately, electrical circuits that perform signal generation are reaching their speed limit. In order to meet the above mentioned requirement, multi-level modulation such as QPSK (Quadrature Phase Shift Keying) and digital coherent technologies are currently being used to put 00Gb/s transmission systems into practical use. However, with optical fiber transmissions exceeding 00Gb/s, power per bit decreases resulting in severe signal degradation due to noise. Optical fiber specific degradation factors such as dispersion and polarization mode dispersion (PMD) also significantly affect signal making reception difficult. For this reason, large-scale optical networks with transmission distances extending several thousand kilometers require 3R repeaters. 3R refers to the three signal regeneration functions (Re-amplification, Reshaping, Re-timing) of an optical repeater. To perform 3R, optical-to-electrical signal conversion, signal processing and electrical-to-optical signal conversion are necessary, but as mentioned previously, limitation in processing speed of the electrical circuits makes regeneration process difficult with speeds exceeding 00Gb/s. If 3R can be achieved without electrical processing (optical 3R), the problem will become easier to resolve, and this viewpoint is the reason 3R regeneration using optical processing technology is attracting attention. Optical processing technology using nonlinear effects such as with an optical fiber has been shown to be capable of switching operations reaching 640Gb/s. Optical signal processing using a similar technology is expected to be applicable to ultra-fast optical 3R. Furthermore, optical 3R regeneration does not perform power-losing OEO conversions, and therefore advantageous from a power-saving point of view. In future optical networks, as services diversify, optical signals are also expected to show diversification, so an optical 3R technology that flexibly responds to different modulation schemes and transmission speeds is desired. This article introduces initiatives aimed at achieving, with optical signal processing, 3R regeneration capable of ultra-fast processing beyond 00Gbit/s and flexibly supporting different modulation formats.