Gallium arsenide electroabsorption avalanche photodiode (EAP) detectors have been fabricated in n - n(+) GaAs waveguides. Since these EAP detectors respond to wavelengths beyond the normal absorption edge of GaAs, due to the Franz-Keldysh effect, they have been used to detect the below band gap radiation from GaAs lasers and the 1.06-mum radiation from Nd:YAG lasers. The measured absorption and responsivity at these wavelengths suggest a number of applications. These EAP devices have been used to detect analog signals with a distortion less than 6%. Methods for utilizing them in time- and frequency-demultiplexing applications are also described.