An array of high-speed optical switches is needed for the optical tapped delay line (OTDL) multiplexer to digitally encode the input optical pulse stream.  Electroabsorption modulators based on InGaAs/InAlAs multiple-quantum-wells (MQWs) are being developed to fill this role.  We have fabricated a waveguide device with an MQW region that modulates the input light passing through the waveguide.  The modulation is accomplished by changing the absorption in the MQW region with an applied electric field.  The applied field redshifts the bandedge of the MQW region, thus shifting the absorption in the waveguide.  For input light with a wavelength of 1550 nm, the waveguide exhibits low attenuation of the optical power with zero applied bias; with a 2-V reverse bias, the attenuation is 10 dB.  Thus, the device acts as an optical switch when the electrical bias is switched between 0 and -2 V.  Figure 1 shows an array of three 500-mm long by 4-mm wide waveguide modulators with metal contact pads.  Light is coupled into and out of one waveguide through two lensed fibers, and the metal contact pads allow an electric field to be placed across the MQW region. An important property of these devices is the ability to modulate at high frequencies, as shown in Figure 2.  The initial 500-mm long modulators have a bandwidth of 6 GHz, and are capacitance limited.  Thus, by reducing the length to 250 mm, a bandwidth of 12 GHz (suitible for 10-Gb/s operation) should be achieved.