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In the field of high-frequency radio interferometer, Atacama Large Millimeter/submillimeter Array (ALMA), its highest receiving frequency reaches 950 GHz. To receive such high frequencies, a higher reference frequency for frequency conversion is required (as much as over 100 GHz). To maintain signal coherency, this reference signal has to be highly stable. To address these issues, we have developed a new method to generate and transmit a reference signal in the form of frequency difference between two coherent light waves. One method to generate two optical signals is producing them from a pair of laser sources using optical phase lock loop for feed back control (Cliche & Shillue (2006)), however, optical phase lock loop also requires a stable laser source. A good alternative method to the optical phase lock scheme is the lithium niobate (LiNbO3) Mach-Zehnder optical modulator which is capable of generating two highly stable optical signals (upper sideband and lower sideband components) by applying a sinusoidal microwave signal to an input laser signal. Compared to the current optical phase lock scheme, the Mach-Zehnder modulator has significant advantages in terms of stability (free from the influence of the input laser stability), robustness to mechanical vibration and acoustic noise, and capability of maintaining polarization state of the input laser. During the signal transmission through the fiber cable, the cable length delay fluctuation is caused together with polarization mode dispersion, which will impact the performance of coherent signal distribution. We have developed the phase stabilizer using the dual difference round-trip phase measurement method with Michelson’s interferometer. The roundtrip phase measurement is performed on each lightwave signal separately. The Round-trip phase measurement method is helpful for successful delay compensation of the microwave signal which is converted from the two coherent optical signals by a photo mixer. The two transmitted optical signals require phase stability better than 10–13 (1sec) in white phase noise in the Allan standard deviation for ALMA project.

Photonic Millimeter-Wave Generation and Distribution Techniques for Millimeter/Sub-Millimeter Wave Radio Interferometer Telescope