Phase Locking of Semiconductor Lasers for Optical Generation of Millimeter Wave

A novel system design will demonstrate the generation of high frequency (60 GHz) millimeter (MM) waves by means of the beat frequency between two phase locked diode lasers which are offset in frequency by an amount equal to the desired MM wave frequency. Phase locking is key to producing a stable MM wave, but is also costly to implement at such high frequencies. To date, this has required either a high frequency synthesizer, advanced laser structures [1-3], or nonlinear optical effects [4]. The technique proposed here requires phase locking electronics that operate at no more than 5 GHz. No component technology development is required and all components are compatible with monolithic integration. Phase locking at an offset frequency is achieved by phase modulating the first laser and locking one of its sidebands to the second laser. The novelty of the approach resides in sending the light through a phase modulator multiple times in order to generate higher order sidebands far removed from the carrier rather than generating the sidebands directly with a high speed phase modulator. This is how we avoid high frequency electronics/optics. Frequencies up to 200 GHz are possible with off the shelf components; 1000 GHz is anticipated with tunable diode lasers.