Electrically tunable Fabry-Perot interferometer, comprising - a substrate, - a first mirror on the substrate, - a second, movable mirror, - the second mirror has a movable optical area and a movable area surrounding the optical area, - a Fabry-Perot cavity between the first and second mirrors (102-106; 112-116), - the first and second mirror have electrodes (110a, 110b, 106, 112) for electrical control of the distance between the mirrors (102-106, 112-116), - the surrounding area and the optical area of the second mirror have a gap between two layers of the mirror (112,116), and mirror layers (112,116) at the opposite sides of the gap are connected with anchoring through the gap, wherein the gap (104,114) has a vacuum or the gap includes air or other gas which is transparent at the operational wavelength range of the interferometer, characterised in that - the electrodes of the first and second mirrors (102-106, 112-116) extend to the optical area, and - the implementation of the mirror anchoring is such that the stiffness of the surrounding area is lower than the stiffness of the optical area, whereby the movable mirror is arranged to bend more at the surrounding area than at the optical area on activation of the electrodes (106,112) with a control voltage, wherein the difference in mirror stiffness between the optical area and the surrounding area is based on the density of anchors in the gap of the second, movable mirror being higher at the optical area than at the surrounding area, the distribution pattern of the anchors, the form of the anchors and/or width of the anchors, and wherein the movable mirror comprises etching holes through which the sacrificial layer was etched to release the movable mirror. - a substrate, - a first mirror on the substrate, - a second, movable mirror, - the second mirror has a movable optical area and a movable area surrounding the optical area, - a Fabry-Perot cavity between the first and second mirrors (102-106; 112-116), - the first and second mirror have electrodes (110a, 110b, 106, 112) for electrical control of the distance between the mirrors (102-106, 112-116), - the surrounding area and the optical area of the second mirror have a gap between two layers of the mirror (112,116), and mirror layers (112,116) at the opposite sides of the gap are connected with anchoring through the gap, wherein the gap (104,114) has a vacuum or the gap includes air or other gas which is transparent at the operational wavelength range of the interferometer, - the electrodes of the first and second mirrors (102-106, 112-116) extend to the optical area, and - the implementation of the mirror anchoring is such that the stiffness of the surrounding area is lower than the stiffness of the optical area, whereby the movable mirror is arranged to bend more at the surrounding area than at the optical area on activation of the electrodes (106,112) with a control voltage, wherein the difference in mirror stiffness between the optical area and the surrounding area is based on the density of anchors in the gap of the second, movable mirror being higher at the optical area than at the surrounding area, the distribution pattern of the anchors, the form of the anchors and/or width of the anchors, and wherein the movable mirror comprises etching holes through which the sacrificial layer was etched to release the movable mirror.