Self-pulsating laser diode for the generation of multiple RF data channels in hybrid radio/fiber systems

摘要

Future mobile networks, capable of delivering broadband services, are likely to use high frequency microwave signals as the access medium (15-60 GHz). These high capacity microwave access networks will employ an architecture in which signals are generated at a central location, and then distributed to remote base stations using optical fibre, before being transmitted over small areas using microwave antennas. On the transmission side of these networks it is necessary to generate the microwave optical data signals using a semiconductor laser diodes. The simplest technique available to generate such signals involves direct modulation of the laser. However, the limited bandwidth of laser diodes means that we are normally unable to generate high frequency RF carriers (> 10 GHz) in this manner. One way to overcome this limited bandwidth is to employ external optical injection into the laser diode as this can greatly increase the intrinsic modulation bandwidth of the laser. In addition, at high injection levels the laser can start to self-pulsate at frequencies that are suitable for RF transmission, thus making the device useful for the generation of microwave optical signals in hybrid radio/fiber networks. In this paper we characterize the self-pulsation in the laser under external injection, and demonstrate how the injection-locked commercial laser maybe used in a hybrid radio/fiber system for the distribution of multiple carrier RF data signals.