Photonic Reference

ALMA requires unprecented levels of phase stability to achieve coherent interfometry up to THz frequencies. The optoelectronic local oscillator timing reference, distributed as the beatnote between two optical tones, is stable to within 10 fs over 15 km distances.

The development program for the ALMA photonic reference and distribution system developed several key technologies, including:

a tunable (30-122 GHz) photonic millimeter-wave synthesizer for generating the high-stability local oscillator reference signal
round-trip phase correction to maintain low phase drift over long distances of fiber

Millimeter-wave photomixing

Laser frequency synthesis by phase locking

laser freq synthesis.jpg

Round-trip phase correction by optical interferometry

round trip phase correction.jpg

Customized low phase drift Erbium doped fiber amplifiers

fiber amplifier.jpg

Eurocard standardized optoelectronics packaging

eurocard photonic module.jpg

Dense fiber distribution packaging for arrays

photonics rack 1.jpg photonics rack 2.jpg

The National Radio Astronomy Observatory and Green Bank Observatory are facilities of the U.S. National Science Foundation operated under cooperative agreement by Associated Universities, Inc.

Founded in 1956, the NRAO provides state-of-the-art radio telescope facilities for use by the international scientific community. NRAO telescopes are open to all astronomers regardless of institutional or national affiliation. Observing time on NRAO telescopes is available on a competitive basis to qualified scientists after evaluation of research proposals on the basis of scientific merit, the capability of the instruments to do the work, and the availability of the telescope during the requested time. NRAO also provides both formal and informal programs in education and public outreach for teachers, students, the general public, and the media.