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Time and frequency

Optical reference cavity for space applications

Patented design providing high level of insensitivity to vibrations

Optical reference cavitySensitive laser systems within satellites in orbit need to be able to function in the harsh environment of space.  Optical reference cavities are exceptionally high-quality optical resonators which can be used as frequency references for laser systems. They comprise two highly reflective mirrors which are optically contacted to an ultra-low-expansion glass spacer so they form a standing wave cavity for light waves. Optical cavities are a major component of optical clocks and are used to provide a dramatic improvement in short-term laser frequency stability.

NPL has patented a cubic cavity design and mounting arrangement which make the optical cavity stability highly insensitive to vibrations. It is uniquely robust, and its optical path length is stable to less than the diameter of an atomic nucleus. This means it can reduce the spectral linewidth of commercial laser systems from several MHz to below 1 Hz. This creates an ultra-stable laser which can be used either as a stand-alone frequency reference or as a sub-component of an optical atomic clock.

The optical cubic cavity is one of the European Space Agency’s (ESA) approaches to attaining a narrow linewidth laser in space, and our cavity has the lowest known passive sensitivity to vibration for portable systems.

Optical reference cavityIt is ideal for use in space applications, for example:

  • Development and deployment of future satellite based optical clocks for the next generation of earth orbit-based time and navigation facilities
  • Next-generation of gravity mapping from space, such as detecting changes in glacial movement as a marker for climate change
  • Inter-satellite data relay services
  • Spaced based science and fundamental physics missions

NPL has a world-leading capability in this field and is working to increase the technology readiness level for space operation. Customers and collaborators include the European Space Agency and satellite systems large scale integrators and manufacturers.

The NPL optical cavity work is part of a wider research activity into compact optical and microwave clocks

Technical details

  • Simple symmetric design (50 mm cube) with tetrahedral support
  • Passive acceleration sensitivities along three orthogonal axes: < 2.5 × 10–11 g–1
  • Design has been granted US patent US20130229713A1

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