Researchers at A*STAR have developed compact silicon photonics sensors than can provide accurate readings of temperature and humidity without being affected by the external environment.
Many machines such as turbines, oil-drills, health monitors and nuclear reactors require internal sensors to monitor physical states such as temperature. Silicon photonics uses structures called waveguides to confine electromagnetic waves to one or two dimensions, so that the wave will change in response to external factors.
Researcher from A*STAR’s Institute of Microelectronics have developed a tiny optical temperature sensor of 120 by 80 mm dimension. It is modeled on a classic experimental design called the Michelson Interferometer.
The device splits light into two beams, which travel through different materials and are then brought back together. The resulting interference pattern gives information about the light and the surrounding temperature.
“Changes in temperature can change the optical properties of some materials,” explains Ji Fang Tao, the lead researcher at A*STAR. “In our sensor, the temperature changes the refractive index of the waveguides. The Michelson Interferometer is a powerful design that allows us to pick up these refractive changes, and therefore work out the temperature changes.”
One of the standout features of the device is that it does not require mirrors, and instead guides light through loops to bring it back to the interference point. The researchers found that it could measure a wide range of temperatures and was 20 times more sensitive to small temperature changes than existing fiber-optic sensors.
Recently the team has also developed a tiny photonic hygrometer that identifies the local dew-point temperature by recognizing the refractive properties of water when droplets condense in the path of the waves. This information can then be combined with the temperature sensor to calculate relative humidity with a very high level of accuracy.
“Silicon photonics and optical microelectromechanical systems (MEMS) are two amazing technologies for sensor development,” Tao says. “Now we can measure temperature, dew-point and humidity with ultrahigh accuracy, the next step is to design on-chip photonic gas sensors.”
Image credits: A*STAR/IEEE