From computer consultants and food retailers to manufacturers of baseball bats and sonic toothbrushes, America's fastest-growing private companies are a diverse lot. Yet they all sell the right product at the right time. This year the list of the top 500 performers, as published by Inc. magazine, includes five photonics firms that weigh in with growth rates of 663 to 1436 percent from 1993 to 1997. NZ Applied Technologies in Woburn, Mass., outpaced other photonics companies, coming in at No. 188 on the list. The 6-year-old company had sales of $3.3 million last year, much of it owing to its blockbuster product: a variable optical attenuator -- a critical component in the rapidly growing optical telecom networks. With a newly signed contract with Corning Inc., NZ CEO Peter Norris predicts a torrid pace again next year as the company doubles sales. Next on the list, F&S Inc. of Blacksburg, Va., designs and manufactures fiber optic-based instrumentation that is replacing conventional electronic systems measuring strain, temperature and pressure. With a 1240 percent growth rate, the 8-year-old company came in at position 224. Sales in 1997 climbed to $4.7 million, and company spokesman Steve Poland sees opportunities in aerospace, process control and public works. "We expect growth to continue if not accelerate over the next three years," he said. Three years running At E-Tek Dynamics Inc. of San Jose, Calif., the sales charts are off the page. Listed as the 281st fastest-growing company, the manufacturer of erbium-doped fiber amplifiers and WDM components made the list for the third straight year. E-Tek has managed growth of 1022 percent over the past five years and sales of $73 million in 1997, largely based on strong export growth to Europe and the Asia-Pacific region. Pixelvision Technology Inc. in Acton, Mass., made it to the top 500 for the second year in a row. The manufacturer of flat panel monitors has enjoyed 698 percent growth over the last five years despite slipping from 25th to 450th place in the rankings since last year. At 468, Geltech Inc. of Orlando, Fla., had sales of $6 million in 1997. "Our growth is really centered around the growth of laser diodes," said Ed Patton, vice president of sales and marketing. The company makes aspheric lenses and precision-molded optics.