Speaker
Description
The "all in fiber" phase noise cancellation loop demonstrator designed as a possible candidate for reducing the phase noise of the Virgo squeezer makes use of a benchtop analog RF generator with external frequency modulation command. Substitution of such a bulky instrument with a direct digital synthesizer (DDS) is under investigation, with the aim of improving system integration and reconfigurability, and with the substantial advantage of overall lower phase noise of the modulated RF tone. Frequency tuning capability is obtained by using AD9914 chip, which in the proposed setup allows a minimum granularity of 0.6 Hz, however limited by the actual resolution of the employed ADC module. A FPGA is then used deal with A/D conversion via SPI protocol and proper processing of the correction signal coming from the optical configuration. The settling time for frequency steering is also reduced by almost an order of magnitude w.r.t. its analog counterpart, and, again, the bottleneck is given by the ADC’s acquisition rate, which provides further margin for improvement.
