Project: Ultra-stable High-finesse Optical Reference Cavity

Currently a strong scientific activity aimed at improving the performances of ultra-stable high-finesse optical reference cavities is on-going. Such resonators have demonstrated ultimate performances unmatched by any other resonator type. Frequency stabilities have been demonstrated at the thermal noise limit. This impressive performance is of interest for several applications such as optical atomic clocks, ultra-low phase noise microwave generation, ultra-precise interferometry for distance measurement, coherent optical communication, long-distance ultra-stable optical frequency transfer through optical fibers, optical gyroscopes, earth observation, optical sensing, and spectroscopy. Although these applications have been so far COly academic, several applications will trigger commercial products in the near future. One good example is low phase noise microwave generation where strong interest is present to further improve the radar capabilities thanks to a better local oscillator._x000D__x000D_The resonator consists of a Fabry-Perot optical resonator where two mirrors are optically contacted onto a ultra-low expansion glass spacer. The technology required to build such a resonator is based on three critical building blocks:_x000D_1. Ultra-polished mirror substrates with <1 angstrom rms roughness to reduce light scattering to a minimum level_x000D_2. Highly-reflective mirror coatings with reflectivity above 99.999% and having very low residual absorption_x000D_3. A glass spacer having a coefficient of thermal expansion (CTE) of zero at 5 to 10°K above room temperature_x000D__x000D_The combination of these three building blocks associated with a clever spacer design geometry to reduce the spacer mechanical deformation induced by vibration allows for reaching the thermal noise limit of the length stability of such a resonator. To illustrate this limit, it corresponds to a length fluctuation of 0.2 femtometer over 1 second for a cavity length of 4 cm!_x000D__x000D_One of the major challenges to meet this performance relies on the quality of the deposited layers forming the highly reflective mirrors. Magnetron sputtering as the state-of-the-art deposition technique will be employed and optimized. The company UltraFast Innovations (lead project P) will focus its contribution on enhancing its sputtering technology as well as optical layer design and mirror characterization capabilities to meet the stringent targeted requirements. UltraFast Innovations will transfer its profound know-how in specialty customized optics to the reference cavity mirrors._x000D__x000D_The second consortium P, CSEM, a research institute with relevant activities on cutting edge technologies such as atomic clocks, ultra-stable lasers and LIDARs (Light Detection and Ranging) will select and test several cavity spacer materials by mounting the full cavities that will be fabricated in this project in its laser stabilization facilities. A comparison with a reference cavity will allow for assessing the performance of the fabricated devices. CSEM has, based on a large number of highly educated experts, a strong track record in the development and technology transfer related to atomic clocks and laser systems._x000D__x000D_Worldwide so far only one company (Advanced Thin Films in Boulder, Colorado, USA) offers comparable cavities and mirrors. Therefore this company profits from a dominant position in the market. UltraFast Innovations targets to quickly reach and surpass the quality of presently available ultra-stable high-finesse cavities. Serving the current academic market as well as the growing industrial market is the target of UltraFast Innovations by further pushing its technology level._x000D__x000D_The natural teaming of UltraFast Innovations and CSEM makes an ideal complementary consortium to bring a European company in a position to compete on the quickly growing worldwide market related to optical reference cavities.

Acronym ORCA (Reference Number: 7492)
Duration 01/10/2012 - 31/12/2014
Project Topic Ultra-stable high-finesse optical cavities will be developed. Ultimate performances on the cavity mirrors as well as on the cavity spacers will be targeted through process optimization for mirror coatings as well as spacer material selection.
Project Results
(after finalisation)
For UFI the CO results were:_x000D_1) Processing of complex substrate shapes and rare materials, developing new coating procedure (improvement of internal knowledge base and process skills)_x000D_2) Qualitative analysis of surface roughness requirements and its impact on mirror's specifications (new competence)
Network Eurostars
Call Eurostars Cut-Off 8

Project partner

Number Name Role Country
2 UltraFast Innovations GmbH Coordinator Germany
2 Swiss Center for Electronics and Microtechnology Partner Switzerland