Relating the chirp parameter to the number of quantum wells in GaAs/AlGaAs waveguide modulators

IEEE J. Quantum Electron.

1998

Abstract-An AlGaAs-GaAs asymmetric double-quantum-well (DQW) optical phase modulator using surface acoustic waves is investigated theoretically. The optimization steps of the DQW structure, which so far have not been reported in detail, are discussed here. The optimized phase modulator structure is found to contain a five-period QDW active region. A surface acoustic wave induces a potential field which provides the phase modulation. 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 quantum-well (QW) structure can be utilized. The modification of each QW structure is consistent, although this consistency is not always preserved in typical surface acoustic wave devices. Consequently, the change of refractive index in each of the five DQW's is almost identical. Besides, the change of effective refractive index is ten times larger here in comparison to a modulator with a five-period single QW as the active region and thus produces a larger phase modulation. In addition, a long wavelength and a low surface acoustic wave power required here simplify the fabrication of surface acoustic wave transducer and the acoustooptic phase modulator.Index Terms-Acoustooptic device, double quantum well, electrooptical modulation, piezoelectric effect of surface acoustic waves, surface acoustic wave modulator.

Section: Resultsmentioning

confidence: 99%

“…A typical electrooptical phase modulator requires [20]. High-performance phase modulators also require a low , which is a measure of the insertion loss of the device, where is defined as with the SAW effect.…”

Section: Modulator Characteristicsmentioning

confidence: 99%

Asymmetric double-quantum-well phase modulator using surface acoustic waves

IEEE J. Quantum Electron.

1998

“…Typical electro-optical ͑refractive index͒ and electroabsorptive types of modulator require a large than 10 and a less than 1 chirp parameters of Ͼ10 and Ͻ1, respectively. 22 The optical confinement factor ⌫ is determined using ⌫ϭ ͐ the core region of the waveguide device ͑z ͒*͑ z ͒dz ͐ the entire cover range of a guiding field ͑z ͒*͑ z ͒dz , ͑10͒…”

Section: Modulator Performancementioning

confidence: 99%

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

Li²,

Journal of Applied Physics

1998

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.

“…Equation (11) shows that can be considered as a measure of the phase modulation strength to intensity modulation strength due to an applied electric field. A useful phase modulator requires chirp parameter 10 [24].…”

Section: Modulation Characteristicsmentioning

confidence: 99%

AlGaAs-GaAs quantum-well electrooptic phase modulator with disorder delineated optical confinement

IEEE J. Quantum Electron.

1998

Abstract-Waveguide phase modulators, with 0.5-and 1-m quantum-well (QW) active regions which are defined by impurityinduced disordering are investigated theoretically. By controlling the extent of the interdiffusion in the lateral claddings, the refractive index difference between the core and claddings is used to provide single-mode operation. Strong optical confinement, which is required to produce single-mode high-efficiency modulation, requires the peak impurity concentration to be at the center of the QW active region. Moreover, the annealing time needs to be optimized so that single mode can be maintained at the desired bias field. A low dopant concentration is also expected to minimize the destruction of the modulator structure. The results show that since the core/cladding interface is graded, the width of the metal contact is important. A comparison of modulation efficiency for active layer thicknesses of 0.5 and 1.0 m shows that the 0.5-m one is a more efficient structure and its absorption loss can be reduced by increasing the applied field from 50 to 100 kV/cm.