The development, construction and space qualification of an IR modulator for f/1 radiation in the 14-16 pm band is described. The modulation is based on the principle of a vibrating Fabry-Perot (FP) interferometer with gap width variations of -Â±Am/8c,-, 2 pm (A-center wavelength) which is considered micromechanical. By connecting two such Fabry-Perot interferometers in series (with two outer CdTe plates in fixed positions and one common vibrating inner CdTe plate for harmonic gap width variation) a modulation effici-ency of about 75% is attained. CdTe is superior to other materials as far as IR absorption (0.2%/cm) within the -20Â°C to +60Â°C temperature range and the 2 to 25 11M wavelength range is concerned. Its modulation efficiency in a single FP interferometer is however too low because of its low refractive index (n = 2.5). The double FP interferometer is designed for small weight, large receiving aperture, small power consumption and high reliability in long-time space operation. The modulator is operated at a selected resonance frequency between 100 Hz and 1 kHz. It can be tuned to other wavelengths in the 2 to 25 pm range.