A Portuguese engineer pleaded guilty on Monday to conspiring to help an Iranian firm illegally obtain sophisticated U.S. optical lenses and inertial guidance systems that have both commercial and military uses, the U.S. Justice Department said. Joao Pereira da Fonseca, a 55-year-old Portuguese citizen, pleaded guilty to a federal charge of conspiring to help an Iranian firm obtain the technology from two U.S. companies, the department said in a statement. The plea agreement, if approved by the court, calls for a 20-month prison sentence.