Nortel Networks Corp. of Brampton, Ontario, Canada, has agreed to acquire CoreTek Inc. of Wilmington, Mass., in a stock swap valued at $1.43 billion. The deal, which is expected to be completed in the second quarter of 2000, is subject to approval by CoreTek's shareholders and regulatory agencies. CoreTek produces vertical-cavity surface-emitting lasers and microelectromechanical systems for optical networking solutions. Its next-generation devices, slated for shipment in the fourth quarter, use micromirrors to tune the wavelength of signals in real time, enabling network providers to dynamically monitor and reroute traffic to ease bottlenecks.