Speaker
Description
The “all in fiber” phase noise cancellation loop demonstrator makes use of some pigtailed mirrors, beam splitters and photodetectors to sense phase deviations, and an acousto-optic modulator (AOM) to apply proper frequency shift to the reference beam of VIRGO detector’s squeezer. This compensates, to a certain extent, environmental factors affecting the phase of light along its path.
The setup used to employ a bench-top analog RF generator with external frequency modulation capability to drive the AOM. Such instrument has recently been replaced with a direct digital synthesizer, improving system integration and reconfigurability, with the substantial advantage of an overall lower phase noise profile of the modulated RF tone. Moreover, the settling time for frequency steering has also been reduced by almost an order of magnitude with respect to the original circuit, allowing to extend the noise reduction bandwidth to 100 kHz. An ADC bridges the analog and numerical domains, and a specific firmware implements the logic for frequency tuning on an FPGA. The loop compensation, once put in place with an analog PID module and tuned with Ziegler-Nichols method, has been transposed to the digital domain by “emulation”, using Tustin’s bilinear transform to obtain the coefficients of an IIR filter.
The contribution briefly explains the working principle of the optical setup, reports on the ancillary RF electronics, and especially discusses the control strategy and its implementation. Latencies, quantization effects and other limitations are also discussed, highlighting further improvements to be made.
| Minioral | Yes |
|---|---|
| IEEE Member | No |
| Are you a student? | Yes |