Efficiency and Spectral Properties of Integrated Optoelectronic Laser-Diode-Based RF Frequency Mixers

Frequency up/down conversion of optically transmitted RF signals may be useful for a number of microwave-over-fibre applications. In the earlier works [1-2], we have proposed to perform such conversion by means of operating passively Q-switched (self-pulsing) or passively mode locked semiconductor laser diodes (LDs) as integrated optoelectronic frequency mixers, i.e. as a local oscillator and a mixing element integrated within one device. Theoretical calculation proved the feasibility of RF frequency conversion due to parametric effects in such LDs. The calculations considered the input signal applied to a laser as either an electrical signal (optoelectronic scheme) or an RF modulated optical signal (all-optical scheme), the frequency-converted output being in the form of a modulated stream of optical pulses, convenient for further transmission, with an electrical signal as a by-product. In [3], optoelectronic up-conversion has been performed using self-pulsating lasers with subcarrier modulation in optical communications in view. The results of both [1-2] and [3] experimentally demonstrate the feasibility of frequency mixing in GHz range using self-pulsing lasers, but little study has been performed so far of the mixing efficiency, and the spectral properties of the device have been only studied theoretically [2] for the case of mode locked extended-cavity lasers. Here, we investigate, in more detail, the issue of the efficiency of the optoelectronic frequency conversion in dependency of frequency (in different frequency ranges) and intensity of the modulation signal for monolithic cavity Q-switched and mode locked lasers.