The characteristics of AI03Ga7As/GaAs QW acousto-absorption and acousto-optic modulators using the interaction between Surface Acoustic Wave (SAW) and quantum well (QW) optical waveguide structures are analyzed here theoretically. The QW structures are optimized by maximizing the optical confinement of modal field in the active region and the piezoelectric effect of SAW on QWs. The electric field induced by SAW reduces non-uniformly in depth, which limits in the development of high efficiency modulators, especially for devices with a large number of QWs in the active region. We present the results of the analysis of a range of QW SQW modulators using between one and 25 QWs in the active region. For devices with thin active regions, the QW structures are designed so that at the top surface strong SAW effects can be obtained while for the 25 periods structure, the QWs located at a depth of 2/3 SAW wavelength in order to obtain an uniform SAW induced electric field. The results show that the single and five QW devices are suitable for absorptive modulation and optical modulation respectively while the 25-QW modulators can shorten the modulation interaction length and thus increase modulation bandwidth. The effective index change of these devices are at least 10 times larger than the conventional surface acoustic wave devices. These results make the quantum-well modulators more attractive for the development of acousto-optic device applications.
Electro-optic modulators using the interaction of surface acoutic waves (SAWs) with 111-V semiconductor multiple quantum well structures have gained interests. A SAW induces potential field which provides the phase modulation. In order to improve the phase modulation, an AlGaAs/GaAs asymmetric double quantum well (DQW) optical phase modulator using SAWs is investigated theoretically. The optimization steps of the DQW structure are discussed The optimized phase modulator structure is found to contain a five-period DQW active region Analysis of the modulation characteristics show that by using the asymmetric DQW, the large change of the induced potential at the surface and thus large modification of the QW structure can be utilized. The modification of each QW structure is consistent, although this consistency is not always preserved in typical SAW devices. Consequently, the change of refractive index in each of the five DQWs is almost identical. Besides, the change ofeffective refractive index is 10 times larger here in comparison to a modulator with a five periods single QW as the active region and thus produces a larger phase modulation In addition, a long wavelength and a low SAW power required here increase the size of the SAW transducer and simplify its fabrication.Keywords: double quantum well, electro-optical modulation, surface acoustic wave modulator, acousto-optic device, piezoelectric effect of surface acoustic wave. INTRODUCTIONAcousto-optic devices, such as modulators, beam deflectors, and correlators, based on the interaction with SAWs, have been developed for signal processing applications [1 1 and the SAW technology provides the advantage of optoelectronic integration [2] Recently, electro-optic modulators using the interaction of SAWs with 111-V semiconductor multiple quantum well structures have been demonstrated [2,3].As we have reported [3], SAW induces both a potential and an electric field in the QW device structure which reduce non-uniformly with depth. The induced potential modifies the MQW structure and thus its optical properties A more uniform change of each QW in the MQW structure can be obtained by increasing the SAW wavelength (XsAw) However, the change of the QW properties with the induced potential reduce when XSAW increases, i e. there is a tradeoff between the uniformity and the strength of the variation of the QW properties In order to make use of the large change of the SAW induced potential at the device surface to produce large change of QW properties and to take account of the non-
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