Japan-based NTT Communications Corp, the international unit of Nippon Telegraph and Telephone Corporation (NTT), has announced what it claims is the ‘world’s first commercial deployment of 100Gbps digital coherent technology upgrade on a trans-pacific route’, thus increasing the capacity of the Pacific Crossing-1 (PC-1) submarine cable system, which links the US and Japan. Digital coherent transmission technology improves spectral efficiency through multi-level modulation, such as phase modulation and polarisation multiplexing, and enhances receiver sensitivity by combining coherent detection and digital signal processing. According to a press release, although the company initially demonstrated 100Gbps optical transmission using the technology on the 20,900km cable system in October 2011, the communications stability was compromised. However, after optimising the cable architecture with optical repeaters and an enhanced fibre-optic layout, the technology was deemed suitable for commercial deployment. The company has also announced its plans to upgrade the Asia Submarine-cable Express (ASE)/Cahaya Malaysia with 100Gbps optical transmission technology by the end of 2014. According to TeleGeography’s Submarine Cable Map, NTT jointly owns four fibre pairs of the 7,500km cable system, with landing points in Singapore, the Philippines, Japan, Malaysia and Hong Kong, in association with Philippines’ largest telco in terms of subscribers PLDT and Singapore-based StarHub.