Modulated fabry-perot

A spectrometer for gas detection comprising a Fabry-Perot interferometer including two plane, essentially parallel, mirror surfaces mounted in a frame, the mirrors having a known distance between them, wherein at least one of the mirror surfaces is both partially reflective and partially transparent, where there are at least two actuator units, each including at least one actuator, wherein the first actuator unit is adapted to adjust the distance between the mirrors so as to adjust the filtered wavelength within a specified range and wherein the second actuator unit is adapted to modulate the distance at a chosen frequency in the range of 10-1000 Hz, both thus providing a variation over a range of mirror distances corresponding to a range of filtered wavelengths in the Fabry-Perot interferometer, and wherein the amplitude of the movements of the second actuator modulation is less than the amplitude of the movements made by the first actuator unit;

• wherein at least one of the mirrors is related to the frame through a silicon membrane, at least the second of the actuator units comprising a piezoelectric material on the membrane, thus constituting a bimorph or unimorph actuator unit;
• and
• wherein the second actuator unit is operated at a lower strain than the first actuator unit so as to increase actuator lifetime.