Surfactant-mediated molecular beam epitaxy of strained layer semiconductor heterostructures

The chirp parameter of a multiple-quantum-well (MQW) electroabsorption modulator was measured with accuracy for several operating wavelengths in the 1.5 /spl mu/m window. It varied strongly with applied bias. Effective chirp parameter, defined as the ratio of phase change to transmission change between modulator on and off states, is about zero, or even negative. However, experimental transmission length on standard fiber at 10 Gb/s NRZ is much smaller than what is expected for such a low chirp parameter. It is demonstrated that the effective chirp parameter should not be computed from changes between on and off states, but from the average of the chirp parameter values in a 3 dB region of the most transparent states of the modulator. This simple rule allows us to predict transmission performances based on measurements of the chirp parameter, and can be used to optimize optical components without actually experimenting on a transmission system. The effective chirp parameter of the MQW electroabsorption modulator is found positive. This should be intrinsic to red-shift electroabsorption effects, such as the quantum confined Stark effect. >

On the transmission performances and the chirp parameter of a multiple-quantum-well electroabsorption modulator

Optical on-off modulators require low insertion loss, high contrast ratio (CR), small drive power and large bandwidth or bit-rate. A systematic approach to optimize the total performance of these modulators based on the quantum-confined Stark effect is presented here. The approach consists of minimizing the power/bandwidth ratio while satisfying a given CR and insertion loss. Our design consists of a large-core multimode passive waveguide with a thin buried active layer. The passive waveguide is designed to yield a high coupling efficiency to conventional single-mode fibers. The quantum well material structure is designed to maximize Delta alpha / Delta F/sup 2/, while maintaining a sufficiently large Delta alpha / alpha /sub 0/, where Delta alpha is the absorption change, alpha /sub 0/ is the residual absorption at zero bias, and Delta F is the swing of the applied electric field. Our theoretical model shows that i) wider quantum wells give larger Delta alpha / Delta F/sup 2/, and ii) the bandwidth/power ratio as high as 4 GHz/mW can be achieved simultaneously with small insertion loss, For example, with a drive voltage of 3 V, an RC limited bandwidth as high as 60 GHz is predicted, while a contrast ratio of 20 dB and a total insertion loss of 4.5 dB may also be obtained. >

Theoretical design optimization of multiple-quantum-well electroabsorption waveguide modulators

Conventional high-speed (>10 GHz) external modulators at 1.55 mu m exist in various types and on several kinds of substrate material. Only electroabsorption modulators on InP have so far demonstrated polarization-independent operation at high speeds. In this paper, the properties of two strained multiple quantum well (MQW) modulators are reviewed in the context of optical fibre communications in terms of loss, drive voltage, bandwidth (>40 GHz), eye diagram, bit error rate measurements and optical power handling capacity. An effective modulation polarization sensitivity of 0.6 dB is reported. The two components differ mainly in their saturation optical power levels. A new power saturation mechanism is proposed to explain the nonlinearity of the InGaAs/lnAIAs modulator.

https://iopscience.iop.org/article/10.1088/0268-1242/10/7/001/pdf

Electroabsorption modulators for high-bit-rate optical communications: a comparison of strained InGaAs/InAIAs and InGaAsP/InGaAsP MQW

Three MQW electroabsorption modulator structures made of 7, 13 and 20 wells are reported. The bandwidth is shown to increase linearly with intrinsic region thickness up to 40 GHz, with negligible penalty on the drive voltage which remains at less than 2 V. It is suggested that 100 GHz bandwidth should be reached with low drive voltage.

Experimental optimisation of MQW electroabsorption modulators with up to 40 GHz bandwidths

The authors present optical waveguide modulation results obtained using Wannier-Stark localization in InGaAs-InAlAs superlattices grown by molecular beam epitaxy on InP substrates. It is shown that the results are in good agreement with a previously reported wavefunction model. The authors experimentally investigate the modulation behavior as a function of the electroabsorptive superlattice thickness. For this purpose the authors introduce the extinction ratio per unit waveguide length and per unit electric field as a relevant figure of merit that is broadly applicable to any electroabsorptive superlattice modulator. It is shown that inhomogeneous broadening imposes an optimum thickness for the electroabsorptive superlattice. >

Optimization of optical waveguide modulators based on Wannier-Stark localization: an experimental study

The authors present an optical waveguide modulator structure based on Wannier-Stark localization in a InGaAs-InAlAs superlattice. Optical waveguide transmission below the superlattice bandgap displays expected F/sup -1/ oscillatory behavior leading to various modulation schemes. An 11 dB extinction ratio was obtained by applying a 0.7 V drive voltage to a 100 mu m long waveguide device operating at 1.55 mu m under a transverse-electric (TE)-polarization mode. On-state attenuation was 5 dB. Lower open-state attenuation (3 dB) can be obtained simultaneously with a higher extinction ratio (13 dB) but in that case a larger drive voltage (1.6 V) is needed. >

Wannier-Stark localization in a 1.55 mu m InGaAs/InAlAs superlattice waveguide modulator structure

An InGaAs/InAlAs p-i-n double heterostructure was grown on n-type InP substrate by MBE (molecular beam epitaxy). This structure was optimized for optical waveguide modulation based on Wannier-Stark localization. The intrinsic region contains a strongly coupled superlattice. The superlattice PL (photoluminescence) linewidth is 2.4 meV at 10 K, indicating very high material quality. Under reverse bias, Wannier-Stark localization was observed on photocurrent spectra up to room temperature. Both fundamental and oblique transitions are very sharp with strong excitonic behaviors. Optical waveguide modulation performances were characterized on a 100- mu m-long device operating under TE polarization mode. The performances obtained at phonon energy below the superlattice bandgap are illustrated. Although the structure was optimized for modulation, laser emission was observed under forward bias. >

P. Voisin

Papers

Optimization of optical waveguide modulators based on Wannier-Stark localization: an experimental study

Wannier-Stark localization in a 1.55 mu m InGaAs/InAlAs superlattice waveguide modulator structure

Laser-modulator compatibility in an InGaAs/InAlAs superlattice structure