A. Stano

Monolithic integrated InGaAlAs/InP ridge waveguide photodiodes for 1.55 μm operation grown by molecular beam epitaxy

The monolithic integration of a low loss InGaAlAs ridge waveguide with a low leakage InGaAs photodiode is demonstrated. The structure has been grown by molecular beam epitaxy on an n+‐InP substrate, using an InGaAlAs layer with a band gap of 1.29 μm, suitable for waveguiding at 1.55 μm wavelength. Absorption of the guided light is provided by leaky coupling from the InGaAlAs guiding layer into the higher index InGaAs absorbing region containing a p/n junction. The devices showed external quantum efficiencies as high as 20% for operation at 1.55 μm wavelength. This is the first demonstration of a monolithic integrated waveguide device in the InGaAlAs/InP material system.

Loss analysis and interference effect in semiconductor integrated waveguide turning mirrors

Semiconductor integrated waveguide turning mirrors (IWTM) are investigated using the beam propagation method. A mirror is fabricated and modeled along with realistic geometries in the presence of offset and roughness of the mirror surface. An interference effect between waves reflected at different surfaces in the device is evidenced, that has strong impact on the device performance in the case of weakly-confining structures. A widely-accepted fabrication approach is criticized in view of this effect. A solution is outlined that minimizes the losses due to either technological limitations or interference.

BUTTERFLY BISTABILITY IN AN INGAAS/INP MULTIPLE-QUANTUM WELL WAVEGUIDE WITH DISTRIBUTED FEEDBACK

We report the experimental observation of butterfly bistability in an InGaAs/InP multiple‐quantum well waveguide with a distributed feedback grating, under cw operation and at sub‐milliwatt input power. Plasma effects on the excitonic optical properties in multiple‐quantum well structures are the basis of the observed bistability. Insight provided by a simple coupled‐mode description of the device and by many‐body theory of the field‐matter interaction is used both for device design and for interpretation of the results. In particular, the unconventional shape of the hysteresis is due to increased optical absorption at high injected optical power.

Nonlinear contradirectional coupler

Results of room-temperature experiments with a multiple-quantum-well, nonlinear, contradirectional coupler are reported. A power-dependent, contradirectional coupling condition is demonstrated, inducing an optically controlled switching of optical signals, with a switching energy of 1 pJ.

High-resolution depth monitoring of reactive ion etching of InP/InGaAs(P) MQWs using reflectance measurements

Small-dimension photonic devices for telecommunications applications have recently attracted increasing interest along with the development of dry etching techniques. Extremely accurate control of etching depth is often needed for the fabrication of these devices containing multiple quantum well (MQW) structures. The excellent anisotropy, reasonable etching rates and excellent compatibility with resist masks of reactive ion etching (RIE) permit this technique to be used for fabrication of such devices. A drawback of the technique is that it is difficult to control etched depth with an accuracy of the order of the QW dimension. Laser interferometry (reflectometry) (LIR) is a powerful method for in situ monitoring of MQW structure etching. End-point detection (EPD) with very high depth resolution is obtained by appropriately combining the operating parameters of RIE and of LIR acquisition. In this paper we discuss the use of LIR at 670 nm to monitor the etching of InP/InGaAs(P) MQW structures by RIE and we report the real-time monitoring for etching of a 0.5 nm thick InGaAsP layer embedded between InP layers which is, to the best of our knowledge, the highest resolution ever reported for this technique. In the MQW etching process, the use of LIR combined with RIE successfully detects all stack layers with a resolution better than the well/barrier thicknesses. This capability permits etching to be monitored with well thickness as small as 3 nm in the case of InP/InGaAs layers. For structures having well/barrier layers with similar composition and hence a small refractive index difference, such as two layers with y = 0.57 and y = 0.84 respectively, monitoring of the etching of MQW with well thicknesses as small as 5 nm is demonstrated. The technique illustrated in the paper also proved to be useful as a simple method of analysing structure layers: the sequence and the uniformity of the QWs can be characterized with very high resolution.

InGaAs-InP superlattice electroabsorption waveguide modulator

An electroabsorption waveguide modulator with an extinction ratio for TE-polarized light at 1550 nm of more than 20 dB for a voltage swing of less than 3 V, and low insertion losses has been realized, which exploits the Wannier-Stark effect in an InGaAs-InP short period superlattice, grown by chemical beam epitaxy. Even for a fixed voltage swing of 2.6 V, a good transmission contrast has been obtained in a wide wavelength range.<<ETX>>

REFRACTIVE INDICES OF INGAALAS GROWN BY MOLECULAR BEAM EPITAXY

The accurate determination of the refractive indices of InGaAlAs, grown by molecular beam epitaxy, is reported for the first time. The method used, modal, cutoff spectroscopy, is applied to InGaAlAs/InP single heterostructure waveguides, with compositions corresponding to band‐gap wavelengths in the range of 1.02–1.12 μm. The refractive indices are determined at different wavelengths between 1.1 and 1.6 μm, with an accuracy better than 10−3.

Growth of In. 53Ga. 47as layers on InP substrates for I.R. detectors by MBE

Abstract The increasing interest in the 1.3–1.55 μm region for optical fibre communications assignes to In . 53 Ga . 47 As a prominent role for detectors operating at these wavelengths. In this contribute we mainly discuss the origin of several kinds of morphological defects on this material and the technical solutions used to reduce the defect density to less than 1×10 4 / cm 2 . Using chemical etching techniques combined with transmission cathodoluminescence and optical microscope observations, we show that there is no relation between single dislocations in the substrate and morphological defects in the layer. Most of defects originate at the interface between the substrate and the layer, and are strongly dependent on the substrate cleaning procedures. Moreover we discuss the influence of growth conditions (growth rate, substrate temperatures and As pressure) on the evolution of these defects. Hall measurements on InGaAs single layers give a residual doping concentration as low as n = 1.10 14 cm −3 and a mobility (at n = 2 10 15 cm −3 ) as high as 10000 cm 2 ·V −1 ·sec −1 at room temperature. InGaAs PIN detectors were fabbricated, and dark currents as low as 3 nA at 10V were obtained over 65 μm mesa diameter.

Optically multistable operation of a waveguide device based on the Wannier–Stark effect in an InGaAs/InP superlattice

An optically multistable device in waveguide configuration has been fabricated, which is based on the Wannier–Stark effect in an InGaAs/InP superlattice. It implements a waveguided version of the self‐electro‐optic effect device and it operates at room temperature at a wavelength of 1.55 μm.

High-efficiency coupling between semiconductor waveguides and single-mode optical fibers

Some experimental aspects of the problem of efficient coupling between semiconductor waveguides and single-mode optical fibers are examined. Waveguides based on different InP/InGaAsP structures (single- and double-heterostructures, multi-quantum-well structures (MQW) with different degrees of dilution) have been fabricated, as well as modified single- mode fibers (i.e. with flat or lensed, straight or tapered ends). Coupling efficiency measurements between these structures have been performed, and the results are presented and discussed; the lowest coupling loss, about 0.5 dB, was obtained with a conveniently tapered fiber and a moderately diluted MQW structure (MD-MQW).