Quantum Timing and Sensing
There is a near term, high priority need for next generation timing and sensing solutions for important applications including:
- Autonomonous navigation and inertial sensing (for use in GPS denied environments)
- Gravimetric and magnetic sensing (including earth orbit environmental monitoring and land-based site surveying)
The next generation technology providing these solutions utilizes quantum effects, with a key enabler being the magneto-optical trap based upon the Rubidium atom (Rb-MOT). The Rb-MOT enables “Cold atoms” to be used as ultra-precise atomic clocks and ultra-sensitive sensors for measuring acceleration.1
It is predicted that demand across these and other applications will drive a large increase in the quantum sensing and timing markets. Quantum sensors have a current market size of $260M and are expected to grow to $565M by 2027 (CAGR 16.8%).2
These sensing and timing applications require the quantum technology to be transferred ‘out of the lab’ and to be in a robust form capable of being deployed and operated in remote and harsh environments (land, sea, air or space based).
Wavelength Conversion
Periodically poled lithium niobate (PPLN) is a non-linear optical crystal that can be used to change the wavelength of lasers. For quantum applications, PPLN enables off-the-shelf lasers to be converted to atom- or ion-specific wavelengths that are otherwise difficult to obtain. For Rb atom traps, PPLN enables industry-standard 1560nm telecoms lasers to be converted to the 780nm wavelength needed for Rb cooling. This approach is particularly appealing for operation in harsh environments, such as space, as telecoms lasers are reliable, robust, and rated for thousands of hours of operation.
PPLN waveguides offer the further benefit of very high conversion efficiencies of up to 70%3 and can operate up to the Watt level, enabling rapid cycling of Rb sensing measurements.
UK Investment
Current global investment in quantum technologies is estimated at more than $20bn per year. Within this the UK has committed to investing £1bn over 10 years. This includes Innovate UK (IUK) funded R&D programs investigating the potential for ruggedization of quantum technologies including the enabling systems and components. Covesion has been an active participant in a number of these projects;
- QT Assemble – an underpinning program to develop the UK supply chain for quantum-enabling optical products and systems.
- CASPA – Cold Atom Space Payload. The aim of CASPA was to build a system capable of cold atom trapping Rb atoms autonomously in the space environment. CASPA was the first step to verify the basic concept and gain heritage on the subsystems and overall design of a basic cold atom demonstrator. Covesion supplied the PPLN waveguide chip for integration into the optical subsystem.
- SNORQL – Space-certified Nonlinear Optics for Rugged Quantum Lasers. The aim of SNORQL was to demonstrate Covesion fiber-coupled, PPLN waveguides in a Rb-MOT and perform trials to assess package performance in simulated environmental conditions (thermal, vibration, shock, radiation) for pre-space qualification.
“Current global investment in quantum technologies is estimated at more than $20bn per year. Within this the UK has committed to investing £1bn over 10 years.”
PPLN waveguide performance
Three key criteria need to be met in order to demonstrate that PPLN waveguides are a viable solution for wavelength conversion in harsh environments;
- The waveguide must deliver the required power and conversion efficiency needed by the quantum technology (Rb-MOT)
- Fiber coupled packaging must be available in order to move the technology out of the lab and provide plug and play system integration
- The waveguide package must demonstrate long term reliable operation and be able to withstand the environmental conditions it will be exposed to (thermal, vibration, shock, radiation).
Covesion has taken our standard, off-the-shelf, component waveguide package and tested it against these criteria. It should be highlighted that this fibercoupled module was NOT designed to withstand harsh environments and that this work was therefore undertaken to assess its performance and inform the development needed for ruggedization.
“By exploiting the quantum properties of cooled and trapped Rubidium atoms, ultra-precise gravity measurements can be taken, which have many potential practical applications.” Tristan Valenzuela, Head of Quantum Sensors, STFC RAL Space.
Lifetime and efficiency testing
The Covesion waveguide module has demonstrated high efficiency wavelength conversion for more than 1000 hours of operation. With an overall second harmonic generation (SHG) conversion efficiency of up to 50% the module delivers the Watt level output at 780nm needed in order to enable rapid cycling of Rb-MOT sensing measurements.
A key target of the SNORQL project was to deliver 1W SHG output for minimal pump power as a primary requirement for space-based gravimetric sensing.
Environmental testing
Environmental testing (thermal, vibration, shock, radiation) has been performed to MIL standards (MIL-STD-883K) to assess the robustness of the waveguide module and the need for further ruggedization.
Overall the module performs well despite not being specifically designed for rugged operation. A summary of the results of the testing are shown in the table, the results are split into 4 package properties; mechanical – refers to the module casing; electrical – refers to the internal electrical connections; optical path – refers to the optical beam path from fiber input to fiber output; waveguide chip – refers to the PPLN waveguide chip. For each property a tick signifies that the package has passed the specific environmental test and a ‘D’ signifies that further work is needed and a development path has been identified.
It should be noted that for all tests the PPLN waveguide chip itself passed with no evidence of damage (breakage, cracking etc) and performed SHG with the same efficiency pre- and post-test. This demonstrates that the underpinning PPLN material technology provides a robust solution to operation in harsh environments.
Both the mechanical and electrical properties of the package also survived all tests, showing that the weak point of the package (unsurprisingly) is the optical path. The optical path was degraded in a number of different ways depending on the test exposure. The fiber-pigtails suffered both thermal and radiation damage however this is easily solvable through the use high temperature and radiation hard optical fiber. Optical coupling of the fiber pigtails on the input and output suffered damage during vibration and shock testing. Improvements to the waveguide and fiber support structure are therefore required. A low risk path to achieving these has been identified via engineering re-design and the use of optimized bonding materials.
Summary
Covesion’s approach has been to leverage its internal investment through participation in IUK funded collaborations with UK and European partners in the quantum technology community. This has enabled us to develop a route to market for rugged wavelength conversion modules meeting the demands of applications within harsh and hostile environments. These modules are needed to enable the exploitation of key quantum applications including; next generation atomic clocks, ultra-sensitive accelerometers and gravitometers.
An extensive test and development program has been undertaken to extend the use of PPLN, fiber-coupled waveguide modules to harsh environments including space. Environmental testing has shown that with modest further development our existing waveguide package is suitable for ruggedization and a low risk path has been identified to develop rugged modules suitable for operation in harsh environments including space certification.
“Covesion is keen to partner with organisations who have an interest in further developing and exploiting this technology for use in harsh environments." Corin Gawith, CTO, Covesion
Acknowledgements
Covesion acknowledge the support of Innovate UK, the UK’s national innovation agency.
References
- M. Odstrcil, et al., “Nonlinear ptychographic coherent diffractive imaging,” Optics Express, pp. 20245-20252, 2016.
- Hsiang-Yu Lo, et. al, “All-solid-state continuous-wave laser systems for ionization, cooling and quantum state manipulation of beryllium ions, “Applied Physics B, vol 114, pp. 17-25, 2014.
- Diviya Devani, et al., “Gravity sensing: cold atom trap onboard a 6U CubeSat,” CEAS Space Journal, vol. 12, p. 539–549, 2020.
- Sam A. Berry, et al, “Zn-indiffused diced ridge waveguides in MgO:PPLN generating 1 watt 780 nm SHG at 70% efficiency,” OSA Continuum, vol. 2, no. 12, pp. 3456-3464, 2019.
- Thomas A. Wright, et al, “Two-Way Photonic Interface for Linking the Sr+ Transition at 422 nm to the Telecommunication,” Phys. Rev. Applied, vol. 10, p. 044012, 2018.
