  This paper describes the development of a photonic local oscillator (LO)
source based on a 3-stage Mach-Zehnder modulator (MZM) device. The MZM laser
synthesizer demonstrates the feasibility of providing the photonic reference LO
for the Atacama Large Millimeter Array telescope located in Chile. This MZM
approach to generating an LO by radio RF modulation of a monochromatic optical
source provides the merits of wide frequency coverage of 4-130 GHz, tuning
speed of about 0.2 seconds, and residual integrated phase noise performance of
0.3 degrees RMS at 100 GHz.
