Analog photonic link by using DFB lasers operated in the low laser threshold current region and external modulation

In this paper we describe an analog microwave photonic link system used to transmit simultaneously two TV signals. The experimental setup is composed mainly by two distributed feedback (DFB) laser diodes emitting at 1500 nm. When DFB lasers are operated in the low laser threshold current region, relaxation oscillation frequencies are obtained. Relaxation oscillations in the laser intensity can be seen as sidebands on both sides of the main laser line. The optical emissions generated in each laser are combined and amplified by using an Erbium-Doped Fiber Amplifier (EDFA). Next, the amplified optical signal is detected by a fast photo-detector using direct detection method and as result of this photo-detection microwave signals are generated. Microwave signals obtained by this technique are used as electrical carriers to transmit analog TV signals over 30 km of standard optical fiber by using a Mach-Zehnder modulator (MZM). At the end of the optical link the modulated light is photo-detected in order to recover efficiently and successfully the analog TV signals.