SOUTH PORTLAND, Maine — Fairchild Semiconductor International has completed its acquisition of QT Optoelectronics Inc. and plans to make additional purchases to further its position in the $6 billion optoelectronics market, the company reported today. QTO’s, which designs and produces optocouplers, light-emitting diodes (LEDs), lamps and displays and infrared components, is based in Sunnyvale, Calif., but its primary engineering and manufacturing operations are in Kuala Lumpur, Malaysia, and Wuxi, China. The company also maintains a wafer fab and die preparation facility in Singapore.