IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 21, NO. 19, OCTOBER 1, 2009 1357 2 2 InP Optical Switching Matrix Based on Carrier-Induced Effects for 1.55- m Applications Malek Zegaoui, Nargess Choueib, Joseph Harari, Didier Decoster, Vincent Magnin, Xavier Wallart, and Jean Chazelas Abstract—This letter demonstrates a 2 2 low optical crosstalk and low power consumption switching matrix device based on carrier-induced effects on an InP substrate. The matrix device comprises two digital optical switches (DOSs) with a wide multi- mode Y-junction associated with a sinusoidal passive integrated optical circuit with an optimized X-crossing. The passive structure was designed using a two-dimensional beam propagation method (BPM) and the entire InP–InGaAsP–InP DOS was designed using a semivectorial three-dimensional BPM. The fabricated 2 2 InP switching matrix heterostructure with m exhibits optical crosstalk as low as 30.5 dB for drive current of 52 mA at 1.55- m wavelength. Maximum crosstalk change of 4 dB is measured under optical polarization variation. Index Terms—Adiabatic transitions, carrier-induced effects, digital optical switch (DOS), InP–InGaAsP–InP waveguides, low crosstalk, optical switching matrix. I. INTRODUCTION H IGH speed, low crosstalk, low power consumption, low sensitivity to polarization, low insertion loss, and low noise optical switching matrixes are basic device requirements for true time delay generation in microwave photonics systems. It is highly desirable to realize high order matrixes on a single chip in order to minimize insertion loss and lower the cost for high port count connections. Pioneering works on switching ma- trixes based on carrier effects are due to Sarma and Flint [1]. Electrically variable optical couplers [1], [2] and digital optical switches (DOSs) [3] have demonstrated maximum ON–OFF ratio close to 20 dB. Recently, Sandy et al. [4] reported the fabri- cation of reconfigurable waveguide DOS devices, with which they obtained a switching ratio of 25 dB at drive current of less than 20 mA. Moreover, we have previously reported [5] that DOSs designed with specific electrodes on n -InP/i-InGaAsP/i- InP/p -InP heterostructure, whose quaternary bandgap compo- sition is m, exhibit crosstalk as low as 38.5 dB at switching current of 33 mA. Since solid state integrated optical Manuscript received April 14, 2009; revised June 16, 2009. First published July 14, 2009; current version published September 11, 2009. This work was supported by the European Union, by the French Government, and by the Re- gional Council. M. Zegaoui, N. Choueib, J. Harari, D. Decoster, V. Magnin, and X. Wallart are with the Institut d’Electronique de Microélectronique et de Nanotechnologie (IEMN) – UMR CNRS 8520 – DHS – USTL, BP 60069, 59652 Villeneuve d’Ascq Cedex, France (e-mail: malek.zegaoui@iemn.univ-lille1.fr). J. Chazelas is with Thales Airborn Systems, 78851 Elancourt, France, and also with Institut d’Electronique, de Microélectronique et de Nanotechnologie (IEMN) – UMR CNRS 8520 – DHS – USTL, BP 60069, 59652 Villeneuve d’Ascq Cedex, France (e-mail: jean.chazelas@fr.thalesgroup.com). Digital Object Identifier 10.1109/LPT.2009.2026484 Fig. 1. Cross-section schematic of the mesa waveguide p-i-n diode. high order matrixes are usually constructed by 1 2 or 2 2 switching elements [6]–[8], this letter focuses on 2 2 basic switching elements based on InP. It is noted that most prob- lems which arise from high order matrixes can be studied ac- curately based on that matrix size. The switches are fabricated on a 2-in-diameter substrate in compliance with our available technology. In this letter, we present a 2 2 switching matrix device based on the original shape multimodal switching zone DOS combined with a sinusoidal passive waveguide. The fab- ricated matrix device exhibits low optical crosstalk ( 30.5 dB at 52 mA drive current) with low sensitivity to optical polariza- tion. II. DESIGN AND FABRICATION Two-dimensional beam propagation method (2D-BPM) device simulations were carried out in a waveguide structure as illustrated in Fig. 1. This structure is based on a p-i-n double heterojunction InP–InGaAsP–InP waveguide grown by molec- ular beam epitaxy on n InP substrate. The structure comprises a 0.3- m nonintentionally doped (n.i.d.) InP buffer layer, a 0.3- m n.i.d. InGaAsP core waveguide layer with m, a 1.50- m-thick n.i.d. InP upper cladding layer, a 0.2- mp InP, and a 0.3- mp InGaAsP ( m) quaternary top layers to form the p-i-n structure of the active region (Fig. 1). These values were deduced from computer simulations to define a single-mode ridge waveguide structure. The structure of the previously optimized DOS is composed of a Y-junction which was based on a mathematical S-bend curve, on which excellent splitting ratios were demonstrated [9]. The structure of the InP-DOS included in the 2 2 matrix device was optimized using a three-dimensional BPM. The schematic diagram of the InP multimodal active zone DOS structure is shown in Fig. 2. The right part of Fig. 2 shows the cross section of the gap between the two active waveguides 1041-1135/$26.00 © 2009 IEEE