This letter describes a thermally-actuated reflection mode asymmetric Fabry–Perot modulator that consists of a thin transparent elastomeric film bounded by partially and highly reflecting metallic mirrors. The thickness of the transparent layer determines the intensity of light reflected from the modulator; changes in its thickness modulate the reflectivity. Electrical current flowing through the highly reflecting mirror provides a source of heat for controlling, by thermal expansion, the thickness of the elastomeric film. Modulators with this design show contrast ratios>15 dBand insertion losses<0.3 dB.©1998 American Institute of Physics.