Mini and microspectrometers are in demand now as the need for optical sensing solutions increases. Unfortunately most compact spectrometers have limited resolution. A novel integrated nano-opto-electro-mechanical sensor has been developed that has the potential to enable a high-resolution spectrometer with a micrometer-scale footprint. This invention is unveiled in an article published today in Nature Communications.
According to scientists from Eindhoven University of Technology, this little sensor is just as precise as the lab bench models and is so small it can be incorporated easily and cheaply into a mobile phone and allow real-time measurements of air quality, food freshness, and blood sugar levels.
The sensor developed at Eindhoven uses a “photonic crystal cavity,” a trap of just a few micrometers into which the light falls and cannot escape. This trap is contained in a membrane, into which the captured light generates a tiny electrical current, and that is measured.
To be able to measure a larger frequency range, the researchers placed two of their membranes together, one above the other. The two membranes influence each other: if the distance between them changes slightly, then the light frequency that the sensor is able to detect shifts too. A micro-electromechanical system was incorporated to allow the distance between the membranes to be varied, and the frequency measured. The sensor covers a wavelength range of around 30 nanometers, within which the spectrometer can discern approximately 100,000 frequencies. This precision is made possible by the fact that the researchers can determine the distance between the membranes to just a few tens femtometers.
It is expected to take another five years or more before the micro-spectrometer actually gets into a smartphone because the frequency range covered is currently too small. The team is working on extending the detectable spectrum and also integrating a light source, which will make the sensor independent of external sources.
Image: The blue perforated slab is the upper membrane, with the photonic crystal cavity in the middle. This captures the light of a specific near infrarad frequency and generates a current that is measured (A). If the distance to the red, lower slab is changed, the captured frequency changes. Image courtesy of Eindhoven University of Technology.