JDS Uniphase ( JDSU) shares dropped 6% Tuesday after the networking parts maker warned of its latest earnings shortfall.For the fiscal second quarter ended last month, JDS expects to post a 2-cent-a-share loss on $180 million in sales. Analysts had expected a penny-a-share loss on sales of $187 million. Shares of the San Jose optical equipment maker fell 15 cents to $2.63 in premarket trading. JDS blamed a sudden decline in orders from one of its optical and display component customers. The company said that pullback accounted for about $13 million worth of missed sales in the quarter. The company plans to report its second-quarter earnings after the market closes on Jan. 26.