An optical waveguide-based absorption modulator is described having a multilayer structure of the conjugated polymer poly(2,5-dimethoxy- p-phenylenevinylene) (PDMeOPV) and polyimide (Dupont PI2566), sufficiently thick to support several modes at the laser wavelengths of 633 and 780 nm. These structures operate as field-effect devices, and the origin of the electro-optical effect is through optical absorption in the red and infrared caused by charge injection into the conjugated polymer layer. The active length of the devices was 1 mm and modulations of up to 5% were measured when 70 V r.m.s. was applied to the electrodes, with the modulation dropping to zero above about 1 kHz, attributed to the long RC time constant of the device. Waveguides were assessed by prism coupling and end-fire coupling. Insertion losses were 24 to 44 dB and optical propagation losses ranged from 8 to 30 dB cm −1, depending on the mode and polarization.