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
Round-trip phase correction by optical interferometry
Customized low phase drift Erbium doped fiber amplifiers
Eurocard standardized optoelectronics packaging
Dense fiber distribution packaging for arrays
