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

    photomixer.jpg

    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

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