OW1G.4.pdf OFC/NFOEC Technical Digest © 2013 OSA Fabrication of the First High-speed GaAs IQ Electro-optic Modulator Arrays and Applicability Study for Low-Cost Tb/s Direct-Detection Optical OFDM Networks L. Stampoulidis (1) , M. F. O’Keefe (2) , E. Giacoumidis (3) , R. G. Walker (2) , Y. Zhou (2) , N. Cameron (2) , E. Kehayas (1) , I. Tomkos (3) and L. Zimmermann (4) (1) Constelex Technology Enablers Ltd, Athens Inno-Centre, 12 Sorou Str., Marousi 15125, Athens, Greece (2) u2t Photonics Uk Limited, NETPark incubator, Thomas Wright Way, Sedgefield, TS21 3FD, Uk (3)Athens Information of Technology (AIT), Markopoulo Ave, GR – 19002, P.O. Box 68, Peania-Athens, Attica, Greece (4) IHP Microelectronics, Im Technologiepark 25, 15232, Frankfurt (Oder), Germany Author e-mail address: ls@constelex.eu Abstract: We present fabrication of the first GaAs electro-optic IQ modulator arrays for high capacity optical transport. Modulators demonstrate >35 GHz bandwidth with 3V Vp. The applicability study reveals suitability for 440Gb/s OOFDM over 1000 km. OCIS codes: (230.4110); (060.4510); (060.2330) 1. Introduction The implementation of future, practical Optical Transport Systems (OTN) relying on Optical-OFDM (OOFDM) modulation format will require an electro-optic (EO) modulator technology capable to blend high-speed operation, scalability and cost-effectiveness. So far research demonstrations of OOFDM transmission have relied heavily on two different material systems, i.e. LiNbO3 and InP. In this context LiNbO3 and InP Mach-Zehnder and Cartesian (IQ) modulators have been fabricated to allow the generation of advanced modulation formats and have been demonstrated in diverse experimental and theoretical OOFDM transmission experiments [1, 2]. However, these two technologies exhibit different disadvantages that are critical when considering practical high capacity OOFDM systems where device scalability is of prime concern. LiNbO3 devices exhibit a large chip size which makes the integration of arrays difficult whereas InP chips are costly due to the small 2-inch InP wafers. In this paper we demonstrate the fabrication of the first electro-optic IQ modulator array based on the GaAs alternative material system that satisfies the requirements of future OFDM systems and we present an applicability study of the technology in sub-Terabit OOFDM transmission. We demonstrate the fabrication of a GaAs EO Mach- Zehnder Modulator (MZM) with a 3-dB bandwidth of >35 GHz and a Vp as low as 3V. The modulator is used as the building block for the integration of six parallel IQ EO modulator structures in a single photonic GaAs chip. We present basic device characterization including 20 Gb/s QPSK and we demonstrate sub-Terabit OOFDM transmission of 320 Gb/s (QPSK) and 440 Gb/s (16QAM) over 1000km with dual-polarization (DP) single side band (SSB) carrier suppressed (CS) - zero padded (ZP) OOFDM in our OFDM transmission modeling testbed. The high yield process combined with the availability of large 6-inch wafers and potential fabrication in large foundries renders GaAs a promising future-proof technology for scalable and cost-effective OOFDM OTN systems. 2. GaAs IQ modulator arrays GaAs modulators have been fabricated using u 2 t Photonics’ foundry-based fabrication process. Six inch semi- insulating GaAs is used in the processing of the modulators. The epi-layers are grown by Molecular Beam Epitaxy (MBE). Standard i-line steppers are used for optical waveguide and electrode photolithography. Y-branch optical splitters and combiners are used in the design of the high-speed Mach Zehnder as well as in the implementation of the “parent” and “child” MZ interferometer of the IQ modulators. Y-branch splitters and combiners can provide high-extinction ratio devices and insensitivity to wavelength and input optical spot position. This leads to devices with improved temperature stability, high purity sinusoidal transfer functions and higher repeatability [3]. Figure 1a) shows the experimental results from the RF and phase characterization of the GaAs MZM. The device exhibits 35 GHz 3-dB bandwidth with a driving voltage (Vp) of 3V. The measured ER is 20 dB and the dynamic range is 70 dBm. The device was used as the building block for the development of the parallel array of IQ EO modulators. Figures 1c) shows a single fabricated IQ GaAs modulator. The chip size is 40x2mm 2 . The modulator was characterized using a modulation analyzer Figure 1d) shows the constellation diagram obtained for 20 Gb/s QPSK which reveals the suitability of the modulator to generate advanced modulation formats. Finally figure 1e) shows the array die with six parallel IQ GaAs modulators.