Photonic Network Communications, 3:4, 377±381, 2001 # 2001 Kluwer Academic Publishers. Manufactured in The Netherlands. Network Access to 2000 WDM Channels at 2 GHz Granularity with a Single Laser in C-band Ronan O'Dowd,* Sean O'Duill, Neal O'Gorman, Gavin Mulvihill Optoelectronics Research Centre, Department of Electronic and Electrical Engineering, University College Dublin, Ireland E-mail: Ronan.ODowd@ucd.ie Received May 28, 2001 Abstract. As WDM channel spacing continues to decrease in size, and with the application of tunable lasers in DWDM (dense wavelength division multiplexing) systems, we demonstrate the ability of electronically tuned lasers to cope with demanding channel spacing and inevitable low frequency setting error. By ®nding the stable operating points of a single tunable laser at the desired frequencies, using advanced software for feature extraction a look-up table to drive the laser was generated. Once the drive currents to access 2000 channels in a 2 GHz comb are found, and in order to justify their usability in WDM networks, their frequency setting error and Side Mode Suppression Ratio (SMSR) was found. These results open up new possibilities for DWDM access networks while pointing to new potential for management of versatile wavelength re-allocation as well as providing a limit of achievement for channel density and granularity in the optical ®ber network. Keywords: tunable laser transmitters, massive DWDM, granularity 1 Introduction We consider an optical frequency plan that conforms to existing ITUT-G962 frequencies, beginning at 192.1 THz with channel spacing of 2000 MHz, and ending at 196.098 THz. These channels coincide with the current DWDM (dense wavelength division multiplexing) channels at 100GHz and 50GHz channel spacing, Fig. 1. Since there are no agreed recommendations nor speci®cations for a frequency plan as dense as the one proposed, it was decided to adopt the speci®cations as laid out for the ITUT-G692 for WDM channels at 100 and 50 GHz spacing. A desirable frequency setting error would be within 10% of channel spacing although a range of 15% is still realistic. We found 95% within 300MHz of the required frequency. ThetunablelaserusedwasaSG-DBRlaser,devices which were designed for wide tunability [1], but are dif®cult to control. Frequency setting is a dif®cult task to achieve with these devices as the device must be characterized for all four drive currents and the four drive currents that produce at the desired lasing frequency must be found [2]. A previous experiment found 96 WDM channels and demonstrated frequency setting precision with a widely tunable laser [3]. The new2000frequenciesfoundheremustbeveri®edwith a wavelength meter, and measurements such as linewidth and SMSR readings must be taken for each channel. Since the laser linewidth in the present experiment was below 100MHz [3], the channel bandwidth will be set by the signal bandwidth at the external modulator. Hence, these are implications for data rate in the context of access or core network frequency plans. An experiment contemporaneous to the present [4] reported 1000 channels at 10GHz spacing. The result here is 2000 channels at 2000 MHz frequency spacing so that a factor of 10 comparison applies in respect to utilization of ultimate laser capability. These results open up new possibilities for WDMaccessnetworkswhilepointingtonewpotential for management of versatile wavelength re-allocation as well as providing a granularity limit of 1 Gbit/s. for channel density in the core network. 2 Frequency Plan At 2000 MHz channel spacing there is an allowable 0.2 GHz frequency setting error in the core network but some relaxation of this may be contemplated at the *Corresponding author. Optoelectronics Research Centre, Department of Electronic and Electrical Engineering, University College Dublin, Bel®eld, Dublin 4, Ireland.