We present an innovative approach for fabricating a polarization modulator, which outputs light alternating in time between left- and right-hand circular. The aim is to replace bulky and expensive photoelastic, liquid-crystal, or inorganic-crystal polarization modulators for certain applications. We use a single-mode polymer waveguide, where a controllable amount of birefringence via the electro-optic effect adjusts the output polarization. It has a very small mass, low power consumption, and very compact size. Other desirable attributes are its use of no moving parts, low voltages, and a single high-speed voltage source. The wavelength of operation is adjustable from 700 to 1600 nm. Furthermore, it can operate at arbitrary frequencies up to the GHz range as compared to the KhZ operating frequencies of photoelastic and liquid-crystal modulators. We show how to overcome the problem of different TE an TM mode amplitudes in polymer waveguides and how to ease the fabrication and packaging tolerances. We present some performance data on a polymer waveguide that outputs circularly polarized light.