Optical Microwave Mixing By FM/AM Conversion With Different Interferometers

Mixing microwave frequencies with optical devices has many applications in communication systems with fiber-optic links, to upconvert or downconvert the RF signal frequency for transmission or receiver processing respectively. Generally, mixing is achieved by the use of optical intensity modulators (laser diodes or external optical modulators) in different configurations : one modulator working in a non-linear regime or two cascaded modulators biased at quadrature [l, 21. We study here another technique using a frequency modulated semiconductor 1 aser and an interferometer to convert frequency modulation into intensity modulation [3]. We investigate two specific interferometers, a Mach-Zehnder and a Fabry-Perot. The performances of these two systems are compared in terms of conversion Loss, bandwidth .... Experimental results that demonstrate the validity of the theoretical analysis are reported with a Michelson interferometer.