MEMS optical filters give Iphone's camera hyperspectral powers

November 28, 2016 // By Julien Happich
Integrating thin electrically-tunable Micro-Opto-Electro-Mechanical (MOEMS) structures within the camera optical stack of an iPhone, researchers from the VTT Technical Research Centre of Finland have created what they believe is the first fully integrated hyperspectral smartphone.

Capacitively tunable MEMS Fabry-Perot Interferometer
made of drilled-out TiO2-Al2O3 λ/4-thin film Bragg

The MOEMS here is a tunable MEMS Fabry-Perot Interferometer (FPI) consisting of atomic-layer deposited TiO2-Al2O3 λ/4-thin film Bragg reflectors, with an air gap formed by sacrificial polymer etching – see figure 1. Metal electrodes are integrated into the mirror membranes to that the air gap height can be tuned by capacitive actuation, influencing the passband wavelength.

The researchers fabricated an iPhone 5s hyperspectral imager (HSI) demonstrator (see figure 2) with a single MEMS FPI tunable filter for the visible-range around 500 nm (with an operation range of 450 to 550nm), but in SPIE proceedings "MEMS FPI-based smartphone hyperspectral imager", they also demonstrated that a tandem-FPI set-up could be used to scan a larger wavelength range.

They reported a configuration of two cascaded FPIs centred at 500 and 650nm (combined with an RGB colour camera), to expand the wavelength tuning range from 400 to 700nm. Although they didn't integrate the cascaded setup inside an iPhone, the mechanical thinness of such MOEMS filters would be easily compatible for smartphone integration within the optical stack, providing OEMs would license VTT's technology.