Ultra-Stable micro-wave/THzr Oscillator – OSMOTUS

The principle is a conversion of the stability of optical carriers. The optical resonators are among the world best resonators for dimensional stability. A few dual frequency dual polarization lasers (large tunability or compactness for industrial applications) are being built. The amplitude noise is stabilized to a few 1e-9/sqrt(Hz) @ 10 Hz in order to mitigate amplitude to phase conversion. Specific photo mixing elements are constructed. Phase noise performance will be assessed.

To come:
- two dual frequency dual polarization lasers tunable from GHz to THz,
- a dual frequency dual polarization laser focused on industrial needs,
- two benches for laser frequency stabilization,
- two AM/PM mitigation systems,
- high bandwidth photomixing elements specific to low phase noise measurement,
phase noise characterization

The OSMOTUS project will realize a microwave/THz (10 GHz – 1 THz) oscillator with a very low phase noise (below -150 dB rad2/Hz at an offset frequency 10 kHz from the carrier for an operation at 20 GHz). The oscillator is tunable by steps of 1.5 GHz, with additional adjustments of 10 MHz.

In the recent years the laboratories involved in ultimate frequency metrology obtained the best short term (below 100 s) stabilities for oscillators with the main frequency in the optical frequency range, with km-scale cavities of interferometric gravitational wave detectors on the 10 Hz-10 kHz offset frequency range, and with 10-cm or 30-cm rigid optical frequency reference cavities in the 0.01 Hz – 10 Hz offset frequency range.

We propose a setup to transfer this exceptional stability from the optical domain to the microwave/THz frequency range for the carrier. The linewidth could be as low as 1 mHz on a 1s timescale. We aim at a 1 mHz linewidth for a carrier in the 20 GHz range, and 100 mHz for a carrier in the THz range (tentative 10 mHz), for integration time larger than 10 ms, at least one or two order of magnitude better than the world best oscillators, with a potential to reach a 2 mHz linewidth.

In the 20 to 100 GHz range, this performance meets strong needs for the industrial partner for the improvement of the discrimination of low level radar echoes from low observability and slow movement objects by radar systems. Above 100 GHz, the oscillator will be used for cold molecules spectroscopy, high performances telecommunication applications. These oscillators could be either on a laser carrier or not. Other applications could range from THz imaging security systems to radiometry of the atmosphere of the earth and planets.

The project gathers a unique expertise in optical metrology at ultimate levels, in ultra-low phase noise measurements and in photomixing semiconductors for THz systems.