Published in IET Optoelectronics Received on 6th March 2007 Revised on 28th October 2007 doi: 10.1049/iet-opt:20070017 ISSN 1751-8768 Use of return-to-zero formats in electrical dispersion compensated optical single sideband transmission systems A.P.S. Ferreira 1,2 T.G. Silveira 1,2,3 P.M.N.P. Monteiro 1,2,3 R.F.G.S. Ribeiro 1,2 1 Optical Communications Group, Instituto de Telecomunicac¸ ~ oes, Campus Universita´ rio de Santiago, Aveiro 3810-193, Portugal 2 Departamento de Electro´nica, Telecomunicac¸ ~ oes e Informa´tica, Universidade de Aveiro, Campus Universita´ rio de Santiago, Aveiro 3810-193, Portugal 3 Nokia Siemens Networks S. A., Rua Irm ~ aos Siemens, no. 1, Amadora 2720-093, Portugal E-mail: aferreira@av.it.pt Abstract: The use of return-to-zero (RZ) formats is proposed to enhance the dispersion tolerance of intensity- modulated carrier-unsuppressed (IM-CUs) optical single sideband (oSSB) systems. The performance of these systems, employing electrical dispersion compensation (EDC), is accessed using unipolar and polar RZ signalling formats, and compared with common non-return-to-zero (NRZ). Simulation results at 10.7 Gb/s reveal that oSSB systems with EDC using both NRZ and unipolar RZ signalling formats are limited to low extinction ratio (ER) values. However, the use of polar RZ allows increased ER and transmission distances, because of higher inter-symbol interference tolerance and the absence of discrete spectral tones. Considering a minimum ER of 9 dB and resort to forward error correction schemes, polar RZ allows single-channel error free transmission over 1400 km of standard single-mode fibre, substantially improving the 980 km obtained for NRZ with ER of 6 dB. Dense wavelength-division multiplexing transmission was also assessed, retrieving improved resilience of IM-CUs oSSB polar RZ. 1 Introduction The fast growth of data exchange has led to an increasing demand for transmission bandwidth. Dense wavelength- division multiplexing (DWDM) core networks answer this requirement offering high-capacity and long-reach transmission. Cost-efficient DWDM networks can be enabled by the use of appropriate advanced modulation formats, such as differential binary phase shift keying [1], differential quadrature phase shift keying [2], duobinary [3], carrier-suppressed return-to-zero (CS-RZ) [4] and optical single sideband (oSSB) [5, 6]. By suppressing one of the signal sidebands, oSSB allows an increase in the channel density of DWDM systems and improved tolerance to group velocity dispersion (GVD). Moreover, oSSB enables the use of efficient electrical dispersion compensation (EDC) after direct detection to further mitigate the effects of GVD. As a stand-alone solution, EDC allows compensation of several thousands ps/nm of GVD per 10 Gb/s channel, avoiding the use of costly dispersion compensating fibre in metro and regional networks [7–12]; in addition, EDC can minimise residual dispersion arising from mismatched optical dispersion compensation. Recent results have demonstrated efficient EDC of optical double sideband (oDSB) signals; however, these schemes require complex and fast electrical processing. On the other hand, EDC can be performed on oSSB systems employing direct detection through simple and low-cost passive dispersive lines, Butterworth filters and adaptive filters [5, 11–13]. 148 IET Optoelectron., 2008, Vol. 2, No. 4, pp. 148–157 & The Institution of Engineering and Technology 2008 doi: 10.1049/iet-opt:20070017 www.ietdl.org