By using a new technique to directly modulate telecommunications-type laser diodes at high speeds with exquisite control of the optical field, researchers from the Optoelectronics Research Centre at the University of Southampton (ORC; Southampton, England), Alcatel-Lucent Bell Labs (Holmdel, NJ), and Eblana Photonics (Dublin, Ireland) are eliminating the need for bulky, expensive, and inefficient external optical modulators for highly advanced modulation formats in fiber-optic communications.1
Currently, external electro-optic modulators must be used for next-generation on-off-keyed 10 Gbit/s systems. In addition, up-and-coming modulation schemes such as 100 Gbit/s coherent systems, which use quadrature amplitude modulation (QAM) or other very complex modulation formats, cannot rely on conventional direct-current-modulated laser-diode schemes.
The researchers optically injection-lock directly modulated laser diodes to allow the very complex in-phase-quadrature (IQ) modulation necessary to, for example, create a 16-level QAM signal.
The technique was demonstrated over a 230 km fiber link with 75 km of standard single-mode fiber in the first and third spans and 80 km of large-effective-area fiber in the second span. The technology is patented by the University of Southampton and licensed to Eblana Photonics.
"The new capability we have demonstrated will be of relevance and could be of significant impact within many scientific and engineering communities that are directly concerned with or exploit laser radiation," says Radin Slavik, a Principal Research Fellow at the ORC.
One potential use of this technology is for coherent combination of high-power lasers.
1. Zhixin Liu et al., Nature Communications (2014); doi: 10.1038/ncomms6911