title: Adaptive frequency-domain equalization in digital coherent optical receivers.
abstract: We propose a novel frequency-domain adaptive equalizer in digital coherent optical receivers, which can reduce computational complexity of the conventional time-domain adaptive equalizer based on finite-impulse-response (FIR) filters. The proposed equalizer can operate on the input sequence sampled by free-running analog-to-digital converters (ADCs) at the rate of two samples per symbol; therefore, the arbitrary initial sampling phase of ADCs can be adjusted so that the best symbol-spaced sequence is produced. The equalizer can also be configured in the butterfly structure, which enables demultiplexing of polarization tributaries apart from equalization of linear transmission impairments. The performance of the proposed equalization scheme is verified by 40-Gbits/s dual-polarization quadrature phase-shift keying (QPSK) transmission experiments.
authors.affiliation: Department of Electrical Engineering and Information Systems, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan. faruk@ginjo.t.u-tokyo.ac.jp
authors.forename: Md Saifuddin
authors.initials: MS
authors.lastname: Faruk
authors.forename: Kazuro
authors.initials: K
authors.lastname: Kikuchi
mesh_terms: D004868:Equipment Failure; D005336:Fiber Optic Technology / Q000295:instrumentation* / Q000379:methods*; D008962:Models, Theoretical; D012815:Signal Processing, Computer-Assisted / Q000295:instrumentation*; D013685:Telecommunications / Q000295:instrumentation*