Dynamic Phase-Error Compensation for High-Resolution InP Arrayed-Waveguide Grating Using Electro-optic Effect W. Jiang, . K. Fontaine, F. M. Soares, J. H. Baek, K. Okamoto, and . J. B. Yoo D partm nt of Electrical and Comput r Engin ering, University of California, Davis, CA 95616, USA -mail: yoo@ece.ucdavis.edu F. Olsson, S. Lourdudoss Department of Microelectronics and Information Technology, Royal Institute of Technology, Sweden Abstract: We demonstrate for the first time the phase-error compensation for a 20-GHz-spacing InP AWG with electro- optic phase shifters placed on 42 arrayed waveguides. The experiment results show successful phase control and 6-dB reduction of crosstalk. -naPEs - -1f118 PEs ••• '1f13 PEs en -20 8 . 'E -40 l\l BCB 5.1 InP substJate • .-. . ... : .. . .. ... ". ..- . • .. rIJ .....; .. · ".:.. -. · ., -.. . . -.. . .... if • I ' • -60 1549.5 1550 1550.5 Wavelength (nm) W Fig. I: (a) Design layout of the InP AWG with EO pha e hifter on arrayed waveguides, (b) cro s section of the waveguide for the EO phase shifter, and (c) simulated AWG transmission with phase errors (PEs) of different nns values. The arrayed-waveguide grating (AWG) is a viable technology on silica [I], silicon-on-insulator (SOl) [2], and InP [3] platforms for optical communications and signal processing. While ilica-based AWGs are commercially deployed today, InP-based A WGs are attractive because of their potentials for monolithic integration with active components on a compact platform. However, high-re olution InP AWG are challenging to realize due to their high ensitivity to fabrication tolerance and wafer nonuniformity. Recently, we have demonstrated 20-GHz- [3] and 10-GHz-spacing [4] AWGs in InP with the crosstalk level of -15 dB and -10 dB, respectively. The primary factor limiting the performance of high-resolution A WGs i the large pha e error accumulated over the long phase anns due to variation in the waveguide geometry (width and thickness) and material compositions. Several phase-error compensation techniques, such as using thin film heaters [5], a-Si films [6], phase compensating plates [7], and UV-trimming [8], have been demonstrated for silica AWGs. This paper reports a dynamic scheme of phase-error compensation by electro-optically inducing a phase shift on each arrayed arm after fabrication of a 20-GHz-channel-spacing InP AWG. Fig. I(a) shows a design layout of a 20-GHz-spaced 5 x 12 AWG [3] with a box geometry realized by InP/lnGaAsP (1.15 Q) buried-hetero waveguide. It consists of 5 input waveguides, 12 output waveguides, 42 array arms with a path length difference LlL of 359.5 J..lm between the adjacent arms, and 42 electro-optic (EO) phase shifters. Fig. 1(b) hows the cross section view of the waveguide with a p-i-n doping profile for EO phase shifters. Fig. I(c) shows different simulated AWG responses with phase error averaging to zero ( olid), n/18 (dashed line), and nl3 (dotted line) root-mean-square (I'm) values. Achieving crosstalk level below -15 dB requires phase errors below nl3 rms, which means that less than 0.02% rms deviations in optical path lengths accumulated over the total path length (-12 mm) can be tolerated. First, we characterize the phase error on each arrayed arm by measuring the impulse response of the AWG similar to the procedure described in [9]. The impulse response of the AWG can be thought of a measurement where the AWG is probed by a short (I ps Or below) optical pulse. The pulse is injected into One of the input armS of the AWG. The pulse will split onto all the array arms, with intensity in each arm directly related to the amount of diffraction in the free propagation region. The pulse travels through each arm and recombines in the output free propagation region to create a pulse train. Small changes in path length differences, or the AWG phase errors, will appear as phase differences of the 53 MF2 2:00 PM – 2:15 PM 978-1-4244-1932-6/08/$25.00 ©2008 IEEE Authorized licensed use limited to: Univ of Calif Davis. Downloaded on March 28, 2009 at 15:14 from IEEE Xplore. Restrictions apply.