
113 - Low profile thermal cell optical clock based on acetylene-filled hollow core fibre for future ground & space PNT
DESCRIPTION
GNSSs now provide a ubiquitous dependency for modern technology, critical national infrastructure and business logistics, particularly in the realms of positioning, navigation and timing (PNT). There is a clearly identified need for alternative high-accuracy, resilient holdover clocks techniques to be available, whether ground or space-based, should problems arise with 24/7 delivery of GNSS signals resulting from outages due to intentional jamming, space clock failures or space weather interference. Future resilient PNT systems will need to maintain improved accuracies over longer fly-wheeling intervals than is currently possible with the current deployed clock systems. This can be achieved by use of robust optical clocks offering improved accuracies with lower Size, Weight and Power (SWaP), compared to the conventional microwave clocks such as active hydrogen masers in the ground segment, and passive masers and RAFS used in space.
One example is thermal cell optical clocks based on a single laser wavelength operating at 1542 nm in the optical band. Frequency servocontrol to narrow-linewidth Doppler-free absorptions in molecular acetylene offers the potential for low-profile, robust and resilient compact systems for both space and ground deployment.
Typical components of this clock would be a low pressure acetylene reference enclosed either within a sealed compact cell or within a sealed coiled hollow core fibre (HCF) cell, a narrow linewidth Distributed Feedback laser with its frequency pre-stabilised by means of a ultra-low-expansion cubic cavity, the generation of Doppler-free saturated absorption signals in molecular acetylene to provide the frequency references, and an octave-spanning frequency comb for the optical to microwave down-conversion to provide standard timing outputs.
The objective of this activity is to demonstrate the feasibility and the performance of the reference stage (physics package) of a thermal cell optical clock.
The tasks to be performed shall include:
- Thermal cell acetylene-based optical clocks can be used in ground and space infrastructure when high frequency stability is important and can provide extended fly-wheel holdover periods at a reduced cost and lower SWaP. The main tasks envisaged are:
- Hollow core fibre (HCF) cell filling with low pressure acetylene, pressure optimisation and sealing in robust anti-resonant HCF designs
- HCF cell evacuation and sealing for use as a laser pre-stabiliser
- Evaluation of acetylene Doppler-free signal frequency stability and drift performance within 10cm x 10mm diameter silica cells in comparison to acetylene-filled anti-resonant few-metre HCF cells
- Preliminary system evaluation against conventional standards (e.g. masers, Cs 5071, cold atom optical standards)
- SWaP design optimisation
The main outputs of the activity will consist of:
- Hardware and Software prototype
- Frequency and frequency drift performance evaluation report in silica cells and HCFs
- SWaP design optimisation report