Electro-optic and electro-absorptive modulations of AlGaAs/GaAs quantum well using surface acoustic wave

Abstract

Effects of lattice mismatch due to partially relaxed buffer layers in InGaAs/AlGaAs strain balanced quantum well modulators Appl.The surface acoustic wave produced electron absorptive and electro-optic modulation in AlGaAs/ GaAs quantum well structures are theoretically analyzed. The quantum well structures are optimized by maximizing the optical confinement of the modal field in the active region and the piezoelectric effect of surface acoustic wave on the quantum wells. The effect of penetration depth of the surface acoustic wave on the number ͑1-25 periods͒ of quantum wells, serving as the active region, is being studied. For 1-5 period structures, the quantum wells are designed on the top surface so that a strong piezoelectric effect can be obtained. For the 25-period structure, the quantum wells locate at a depth of two-thirds the acoustic-wave wavelength in order to obtain a uniform surface acoustic-wave-induced electric field. The results show that the single and five quantum well devices are suitable for absorptive modulation and optical modulation, respectively, while a general advantage of the 25-period quantum well modulator can shorten the modulation interaction length and increase the modulation bandwidth. The effective index change of these devices are at least ten times larger than the conventional surface acoustic wave devices. These results make the surface acoustic wave quantum well modulators more attractive for the development of acousto-optic device applications.

Interdiffusion induced modification of surface-acoustic-wave AlGaAs-GaAs quantum-well modulators

“…However, since the gradient of the SAW-induced potential reduces, the absorption spectra of the five QW's do not coincide. This results in the fourth QW dominating at the optimized 0.864 m [10]. In order to obtain a more uniform gradient of the SAW-induced potential, is increased to 10 m. The gradient of the potential therefore becomes more uniform in the top region 2000 nm), as shown by dotted-dashed line in Fig.…”

“…This can be studied by using a multilayer planar waveguide model using the transfer matrix method [5]. From this calculation, the mode field profiles and the propagation constants are obtained for the determination of the effective absorption coefficient and effective refractive index , respectively [10]. This enables the performance of the absorption modulator to be analyzed.…”

“…The important performance characteristics include the effective index change , effective absorption change taking into account the optical confinement in well regions only [19], contrast ratio (CR), optical confinement factor, chirp parameter and absorption loss . Details of these parameters can be found in [10]. The adjustment of and the modification of quantum-confined Stark shift (QCSS) due to interdiffusion are also used to examine the performance of the modulator.…”

“…Due to the piezoelectric effect, the SAW induces both a potential and an electric field in the QW structure that reduces nonuniformly with depth [10]. The induced potential modifies the MQW structure and, thus, its optical properties.…”

“…Recently, EA modulators using the interaction of SAW's with multiple-quantum-well (MQW) structures have been shown to have some interesting properties [9], [10]. Due to the piezoelectric effect, the SAW induces both a potential and an electric field in the QW structure that reduces nonuniformly with depth [10].…”