Precision mechanical sensors are a fundamental part of modern technologies and are used to stabilise aeroplanes, predict earthquakes, deploy life-saving airbags, monitor the integrity of bridges, and even time computer processes. Despite being used almost universally, their precision is generally limited by the electronic circuits used to monitor them. The EU-funded cQOM project has been working on using light instead of electronics to monitor these sensors to significantly enhance precision and reliability.
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Senior PhD student Ryan Schilling, who was part of the cQOM Marie Curie network, explains that the atoms that compose everything around us are not at rest, but constantly vibrating due to their temperature. These thermal vibrations fundamentally limit the precision of any measurement. For example, an accelerometer that measures the rate at which an objects speed is changing, is being constantly agitated by its warm environment. This thermal agitation can be thought of as a type of noise that limits how precisely acceleration can be measured.
Compounding the problem, electronics used to measure the accelerometers motion are also thermally disturbed, causing electrons to move through the circuit even when no signal is present, he adds. The environmental noise fundamentally limits both the mechanical sensor and the circuit used to measure it. Since we are stuck with a warm planet, and rather like it that way, scientists must find methods to circumvent this noise.
Solutions cold light particles and isolated mechanical systems
The network of researchers in the cQOM project researched and applied optomechanics to address these problems by using light to measure mechanical sensors that are strongly isolated from the thermal environment. The use of laser light rather than electrical circuits to gauge movement in this ultrasensitive part could transform the microelectronics and sensor industries, says cQOM project coordinator Tobias Kippenberg.
Particles of light hold the solution because not only are they cold, but they have no temperature whatsoever. This means that there is no thermal noise in light, and this makes it far superior to electronics in making precision measurements. Unlike the atoms that compose a mechanical or electronic system, photons the particles of light carry no kinetic energy and cannot be thermally excited, explains Schilling.
Scientists in the cQOM network also looked at finding ways to minimise energy leakage in sensors. Optomechanics aims to minimise environmental thermal energy from leaking into the mechanical object. This concept works both ways: a mechanical system that loses energy slowly also gains energy slowly. Using optomechanics, the researchers found ways to design a device that it is more isolated from the environment and less disturbed by temperature. The end result is a device that can measure lower levels of noise.
New components for the future of precision sensing
The network of cQOM researchers used its findings to develop new structures for the future of precision sensing, such as tiny photonic circuits for new applications. Thanks to these advances in cavity optomechanics, motion sensors could be more sensitive in future.
The cQOM research unearthed new ways to interconnect optical fields in the optical fibres that keep us connected in a virtual world, paving the way for a quantum revolution. The new optical system can be used to convert electricity into optical signals and vice versa. In this way, the technology could function as an intermediary in networks based on radio waves and electricity.
At the very heart of cQOM was the training of PhD students within the Marie Curie ITN programme, providing young researchers aspiring to enter the field with the tools and skills to maintain the excellence and leading European role in this area. cQOM has also been a catalyst for other EU-funded projects, also coordinated by Kippenberg at EPFL. These projects are developing technologies that control atoms, ions and molecules with light.
Optomechanical Technologies (OMT) focuses on how to use cavity optomechanics to develop devices with new functionalities, taking research concepts to market. OMT also aims to train a new generation of scientists and technology leaders to join the competitive ranks of academia and industry.
Many of the researchers from the cQOM project are working in an even bigger team in the EU-funded Hybrid Optomechanical Technologies (HOT) project to exploit the interactions of light and mechanical systems in developing a new generation of light sensitive devices.
These research projects are keeping Europe at the top of the game in an international playing field where countries such as the US are also investing significantly to advance communication technologies, Kippenberg concludes.