Marko Erman

InP/GaInAsP guided-wave phase modulators based on carrier-induced effects: theory and experiment

An overview of the different contributions due to carrier-induced effects that appear in InP/GaInAsP guided-wave phase modulators is given. The authors review and calculate the band-filling effect in such devices and point out optimized structures. The fabrication of phase modulators and directional coupler switches based on a GaInAsP/InP heterostructure is described. These devices exhibit modulation characteristics in good agreement with the calculations having a phase modulation efficiency as high as 11 degrees /V mm and low optical losses. >

Monolithic integration of a GaInAs p-i-n photodiode and an optical waveguide: modeling and realization using chloride vapor phase epitaxy

A theoretical and experimental study is discussed of a p-i-n GaInAs photodiode integrated with inverted-rib InP or GaInAsP waveguides grown on InP substrate. The coupling efficiency between the waveguide and the photodiode is calculated using the beam-propagation method while the initial condition, i.e. the waveguide eigenmode, is calculated by the finite-difference method. The photodiode absorption is calculated as a function of key design parameters, which are the waveguide dimensions, the wavelength and, in the case of heterostructure waveguide, the composition of the quaternary layer. Two classes of device application are foreseen: monitor photodiode and end line receiver. >

Structural analysis and optical characterization of low GaAs waveguides fabricated by selective epitaxy

Abstract Growth and optical assessment of very low attenuation (1.3 d B /cm for multimode and 1.5 d B /cm for single mode waveguides) GaAs waveguiding structures are reported. They are obtained by selective chloride vapour phase epitaxy. Various prismatic profiles corresponding to different crystallographic orientations and growth conditions are presented. The influence of stripe orientation, width and growth extension on the cross sectional shape of the localized overgrowth is simulated using a Wulff type modelling of the growth morphology. The 1.3 d B /cm loss of these waveguides is the lowest value obtained for homojunction type GaAs waveguides. Their modal properties and their behaviour under polarized light are reported. In particular we demonstrate that TE and TM polarizations are maintained over 8 mm of guiding.

Mach-Zehnder modulators and optical switches on III-V semiconductors

Key components of interferometric structures, i.e., phase modulators and beamsplitters, as well as a Mach-Zehnder modulator are investigated. Inverted rib waveguide phase modulators have been fabricated using vapor phase epitaxy (GaAs and InP homostructures) or a combination of vapor phase epitaxy and metal-organic vapor phase epitaxy (GaAlAs/GaAs double heterostructure). Two different beamsplitters, the three-guide coupler and the etched semitransparent mirror, have been studied both experimentally and theoretically. Experimental results have been obtained by fabricating semitransparent mirrors with the reactive ion etching. Using the three guide coupler, a GaAs homostructure Mach-Zehnder modulator has been realized. The required switching voltage is -14 V for 6-mm-long electrode and a crosstalk of 18 dB has been measured. The use of the semitransparent mirror for Mach-Zehnder interferometers is also discussed. In order to minimize the diffraction losses, the use of higher order waveguides, rather than single-mode waveguide looks promising. >

Extremely high waveguide-optical amplifier coupling efficiencies measured on passive test structures

It is pointed out that extremely high coupling efficiencies can be achieved on passive structures which simulate an integrated waveguide amplifier. The bundle integrated guide (BIG) configuration exhibits a coupling efficiency of 95% per interface, which is in perfect agreement with the theoretical prediction. This coupling efficiency has been determined by measuring 38 monolithically integrated BIG structures.<<ETX>>

Spatially-resolved photoluminescence study of InP: Fe substrates from different suppliers

Abstract This paper reports on the use of spatially-resolved photoluminescence to characterize six InP:Fe substrates from five different suppliers. By means of this technique it is possible to study the macroscopic and microscopic variations of both the photoluminescence yield and the resistivity, which are directly related, as well as to correlate the wafer properties with the growth conditions of the ingot from which the wafer was cut. On a macroscopic scale we found variations of about a factor of ten from supplier to supplier. Across an individual wafer these variations are only on the order of tens of percents. The microscopic variations were found to be less than the macroscopic variations.

Optical and electrooptical analysis of GaAs inverted rib phase modulators grown by vapor phase epitaxy

We present experimental and theoretical analysis of GaAs homojunction Schottky barrier phase modulators. The waveguide structures-inverted rib-were grown using the vapor-phase-epitaxy chloride process. These structures are attractive because perfectly planar devices can be realized. Besides that, single-mode operation and low losses can be achieved. The optical (propagation losses, dispersion curves), electrical (electrical field distribution, breakdown voltages) and electrooptical (modulation efficiency) parameters have been calculated using numerical two-dimensional methods. In order to optimize the modulator, various waveguide structures as well as n+ (i.e., substrate) and n- (i.e., waveguide) dopings have been considered in the modeling. Experimental results fit well with the calculated ones. A modulation efficiency of 2.3° . V-1. mm-1has been measured. For a completely optimized structure, an efficiency of 4° . V-1. mm-1is expected.

Accurate determination of waveguide-fed p-i-n photodiode absorption

Experimental and theoretical determinations of the absorption of a waveguide fed GaInAs photodiode are presented. The absorption is determined as a function of the propagation length using mu -p-i-n diodes regularly spaced along the GaInAs absorbing layer. The detector absorption is as high as 2060 dB/cm. However, for propagation lengths longer than approximately 200 mu m it falls to about 120 dB/cm. The results are analyzed using two different approaches. The first consists in determining the eigenmodes of both the passive waveguide and the detector/waveguide structure. The second is the beam propagation method (BPM). Both methods demonstrate that the absorption curve can be fully explained by the existence of two modes, of which the one with the lowest absorption is induced by the presence of an undoped InP buffer layer. Both eigenmode decomposition and BPM are in quantitative agreement with the experimental data. >

Wafer and epilayer improvement for integrated optics devices on InP: the ESPRIT project 2518

GaxIn1−xAsyP1−y alloys lattice matched to InP substrates are currently used to fabricate optoelectronic and integrated optics devices. To achieve devices with high performances and high fabrication yield, the uniformity and reproducibility of the GaxIn1−xAsyP1−y epitaxial layers (composition, thickness, doping, etc.) have become key parameters. These problems have been addressed in the frame of ESPRIT project 2518 and are presented in this paper. Several aspects have been considered starting from the optimization of InP substrates, the MOVPE growth of uniform GalnAsP layers, the material characterization to the validation of material uniformity on passive optical waveguides. Both scanning photoluminescence analysis and waveguide losses measurements performed on 2 inch wafers with a high lateral resolution have shown that high quality uniform GalnAsP layers can be obtained reproducibly on 2″ InP substrates using a commercially available LP-MOCVD growth process. In particular, more than 60% of 36 mm long, 3μm wide and 100μm spaced rib waveguides exhibit losses below 0.8dBcm−1.

Correlation between photoluminescence and electrical local fluctuations in liquid encapsulated Czochralski semi-insulating GaAs substrates

Abstract We have developed a non-destructive technique, based upon scanning photoluminescence, which is capable of qualifying GaAs semi-insulating substrates used for the fabrication of large scale integrated circuits. The optical results (microscopic fluctuations of the integrated photoluminescence intensity) have been quantitatively correlated with a-posteriori electrical procedure called the dense row pattern procedure which determines the microscopic and macroscopic fluctuations of the MESFETs threshold voltage.