Abstract: An infrared radiation modulator comprising three parallely arranged interferometer plates, forming two successive slits or cavities therebetween for passing the infrared radiation to be modulated. The width of said slits is periodically varied by the oscillations of the central interferometer plate while the two outer plates remain stationary, a positive variation of the width of one of the slits corresponding at any time to a negative variation of the width of the other slit. A particularly suitable material for the interferometer plates is monocrystalline doped cadmium telluride having a high resistivity and a limited absorption rate for infrared radiation. A very precise alignment of the interferometer plates and an accurate adjustment of the width of the slits therebetween can be achieved by using a wedge-arrangement comprising three radially displaceable wedges disposed at angles of 120.degree.