All-Optical Sampling based on Two-Photon Absorption in a Semiconductor Microcavity for High-Speed OTDM P.J.Maguire a and L.P.Barry a , T.Krug b , M.Lynch b , A.L.Bradley b and J.F.Donegan b , H.Folliot c a Research Institute for Networks and Communications Engineering, School of Electronic Engineering, Dublin City University, Dublin 9, IRELAND ; b Semiconductor Optronics Group, Physics Department, Trinity College, Dublin 2, IRELAND ; c Laboratoire de Physique des Solides, INSA, Rennes, FRANCE ABSTRACT Future high-speed optical communications networks operating at data rates in excess of 100Gbit/s per channel will require a sensitive and ultrafast technique for precise optical signal monitoring. 1 The standard way of characterising high-speed optical signals to use a fast photodetector in conjunction with a high-speed oscilloscope. However, this method is limited to a maximum data rate of approximately 40Gbit/s. An alternative is to employ all-optical sampling techniques based on ultrafast optical nonlinearities present in optical fibres, optical crystals and semiconductors. One such nonlinearity is the optical-to-electrical process of Two-Photon Absorption (TPA) in a semiconductor. This paper presents an optical sampling technique based on TPA in a specially designed semiconductor microcavity. By incorporating the microcavity design, we are able to enhance the TPA efficiency to a level that can be used for high-speed optical sampling. Keywords: Optical Communications, Optical Time Division Multiplexing, Hybrid WDM/OTDM, Optical Sampling, Two-Photon Absorption, Microcavity 1. HIGH-SPEED OPTICAL MULTIPLEXING TECHNIQUES Due to the continued growth of the Internet and the introduction of new broadband services such as video- on-demand and mobile telephony, there will be a need to better exploit the enormous bandwidth that optical fibre provides in the network. The conventional method employed by many network providers is to use optical multiplexing techniques to increase the number of carriers per optical fibre. The most common variant, Wave- length Division Multiplexing (WDM), divides up the optical spectrum into a large number of non-overlapping wavelength bands and transmits each individual channel using a different wavelength over a single fibre. To increase capacity in WDM networks, new transmitter/receiver pairing (operating at a different wavelength) can be added, but this is expensive. A second option is to increase the data rate transmitted per channel, but this is limited by the speed of electronics in current integrated circuits. An alternative to multiplexing in the wavelength domain, as in WDM, is to carry out multiplexing in the time domain. Optical Time Division Multiplexing (OTDM) 2 uses short optical pulses to represent data and multiplexes in the time domain by allocating each channel specific bit slots in the overall multiplexed signal. The basic configuration for a bit-interleaved OTDM transmitter is shown in Figure 1. The main component in a bit- interleaved OTDM system is an ultrashort optical pulse source. The optical pulse train generated is at a repetition rate R and is split into N copies by a passive optical coupler, where N corresponds to the number of electrical channels to be multiplexed. Each copy is then modulated by electrical data which is at a data rate R. The resulting output from the modulator is an optical data channel where the electrical data is represented using short optical pulses. The modulated optical signal then passes through a fixed fibre delay length, which delays each channel by 1/RN relative to adjacent channels in the systems. This ensures that the optical data channels arrive at the output at a time corresponding to its allocated bit slot in the overall OTDM signal. The For further information, E-mail:maguirep@eeng.dcu.ie, Ph: +353 (0) 1 700 5884, Fax: +353 (0) 1 700 5508 Opto-Ireland 2005: Optoelectronics, Photonic Devices, and Optical Networks, edited by J. G. McInerney, G. Farrell, D. M. Denieffe, L. P. Barry, H. S. Gamble, P. J. Hughes, A. Moore, Proc. of SPIE Vol. 5825 (SPIE, Bellingham, WA, 2005) · 0277-786X/05/$15 · doi: 10.1117/12.604835 316 Downloaded from SPIE Digital Library on 04 Feb 2010 to 134.226.1.229. Terms of Use: http://spiedl.org/terms