High-speed optical telemetry system with 310 Mb/s Raman modulators for scientific underwater cable networks

We report recent progress of a novel telemetry transmission system for next generation scientific underwater cable networks. Our proposed system is based on reliable Raman modulation for telemetry transmission. The design concept features: (1) simple undersea Raman-effect transmitters employing reliable optical devices, (2) high capacity wavelength division multiplexing (WDM), (3) flexible and upgradeable optical add-drop multiplexing (OADM), and (4) loop-back transmission robust against cable failures. In our previous work, we experimentally demonstrated the feasibility of our proposed system. In this paper, we investigate methods to improve the modulation speed. The modulation speed in our previous experiment was limited by chromatic dispersion of the modulation fiber. Therefore, we compare several types of fiber having different dispersion values from the points of view of the achievable modulation speed and unwanted nonlinear effects. We have experimentally verified that Raman modulation speed can be successfully improved to up to 310 Mb/s by using highly nonlinear dispersion shifted fiber (HNL-DSF) and field-proven reliable pump LD modules. We believe that the demonstrated Raman-modulated transmission speed of 310 Mb/s is adequate to support a range of sensors and HDTV (high definition television) cameras. For example, 160 observation nodes (8 fiber pairs and 20 waves) with 300 Mb/s Raman modulators can handle 48 Gb/s of data. The proposed transmission system concept using Raman modulation with HNL-DSF is promising for the high speed, highly reliable scientific underwater cable networks of the next generation