In this work we present experimental results on the auto-correlation and cross-correlation properties of the two counterpropagating modes of a monolithic semiconductor ring laser. The ring laser can operate in a bidirectional regime where the two modes have equal power, and also in a unidirectional regime where one of the modes is almost suppressed. Auto-correlation measurements, that are carried out using an unbalanced Mach-Zehnder fiber interferometer, allows to determine the coherence length and linewidth of the ring laser. Cross-correlation measurements are carried out using a modifed interferometric set-up, and they reveal that the two counterpropagating modes are phase-locked.
In this work we demonstrate that the normal photomixing scheme, i.e. one built around a two-mode laser (or a mode-locked laser) as the source, and a fast photodiode acting as the optical mixer of the two modes, can be used also to perform the electrical demodulation of an incoming weak signal at the same frequency.
In particular, we consider a mode spacing c/2L in the range of mm-waves, typically 60GHz for a practical WLAN communication system. With optical powers in the range of mW’s (or 0dBm) for each mode, and an optical power amplifier boosting powers up to 8-10 dBm, the two modes can be photomixed on a high frequency photodiode and obtain an electrical signal with power of about 0dBm at the carrier frequency of 60GHz. Now, if an electrical signal, with a frequency slightly different from 60GHz, is applied to the photodiode output, electrical mixing with the photomixing carrier takes place and demodulation of the weak signal is performed, down to the baseband.
In this work we report on a reliable and low-cost
frequency-response characterization method for high-bandwidth
photodiodes. Using the photomixing technique, we were able to
experimentally characterize the electrical response of commercial
devices up to 60GHz using both DFB and low-cost Fabry-Perot laser