Surface acoustic wave-induced birefringent multiple quantum well modulators for optical system applications

Date of Completion

January 1998


Engineering, Electronics and Electrical|Physics, Optics|Engineering, Materials Science




This dissertation presents the first verification of Surface Acoustic Wave (SAW) induced QCSE in the InGaAs-GaAs Multiple Quantum Wells. This work also describes novel strain induced birefringent optical modulators in which the optical modulation is achieved by field dependent birefringence in strained MQW layers. ^ The device design, fabrication, testing results are also presented. In our study, field dependent birefringence is obtained by straining the MQW layers using two types of Surface Acoustic Waves (SAW) transducers: interdigital and resonator transducers at 119 MHz and 180 MHz respectively. The modulator operates under normal incidence. The induced birefringence by SAW which is as large as 0.02 or 0.05 obtained for a small input SAW power of 1 watt or 0.5 watt when using an interdigital or a resonator transducer respectively, the equivalent induced perpendicular electric field is 2.8 × 10 4 V/cm or 6 × 104 V/cm respectively. A tuning range of 10 nm has been achieved experimentally for the input SAW power of about 0.5 watts by using the resonator transducer. ^ SAW technology also provides a convenience and cost effectiveness in device fabrication in which the conventional top and bottom contacts now can be replaced by a SAW transducer. ^ The devices have been fabricated using lattice matched InGaAs(well)/GaAs(barrier) MQWs on GaAs substrate employing a typical interdigital transducer and a transversly-coupled resonator transducer with different aperture width to compare the effects on induced electric fields and birefringence for 1.01 m m operating wavelength. Devices employing lattice matched InGaAsP-InGaAsP Fabry-Perot MQWs and InGaAsP-InGaAsP MQWs on InP substrate for 1.55 m m operating wavelength have also been fabricated for the surface normal and in-line waveguide configurations respectively to investigate the birefringence due to the reverse DC bias. ^ Computations of refractive index change, absorption coefficient and birefringence for each type of device configurations are computed and compared with the experimental results. SAW induced birefringence of ∼ 0.05 in the presence of the induced perpendicular electric field E z (5.78 × 104 V/cm) can be easily obtained for the input SAW power of 0.5 watt, while the DC bias induced birefringence of ∼ 0.01 has to be achieved for Ez = 30 × 104 V/cm. ^