BUSINESS SEGMENT INFORMATION (Details 2) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Oct. 03, 2015	Sep. 27, 2014	Oct. 03, 2015	Sep. 27, 2014
Segment Reporting Information, by Segment
Sales to external customers	$ 147,560	$ 146,299	$ 452,192	$ 446,421
Segment income	10,465	12,761	34,165	38,772
Photonics
Segment Reporting Information, by Segment
Sales to external customers	60,904	59,757	186,843	182,693
Lasers
Segment Reporting Information, by Segment
Sales to external customers	48,247	44,228	142,602	137,815
Optics
Segment Reporting Information, by Segment
Sales to external customers	38,409	42,314	122,747	125,913
Operating segments
Segment Reporting Information, by Segment
Segment income	21,720	23,627	70,449	72,846
Operating segments | Photonics
Segment Reporting Information, by Segment
Segment income	14,274	12,255	46,703	40,201
Operating segments | Lasers
Segment Reporting Information, by Segment
Segment income	4,278	6,423	10,943	18,151
Operating segments | Optics
Segment Reporting Information, by Segment
Segment income	$ 3,168	$ 4,949	$ 12,803	$ 14,494