BUSINESS SEGMENT INFORMATION (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 04, 2015 USD ($) segment	Jun. 28, 2014 USD ($)	Jul. 04, 2015 USD ($)	Jun. 28, 2014 USD ($)
Segment Reporting Information, by Segment
Number of operating segments | segment	3
Sales to external customers	$ 147,977	$ 153,232	$ 304,632	$ 300,122
Segment income	10,071	13,485	23,700	26,011
Photonics
Segment Reporting Information, by Segment
Sales to external customers	61,701	63,466	125,939	122,936
Lasers
Segment Reporting Information, by Segment
Sales to external customers	44,496	47,113	94,355	93,587
Optics
Segment Reporting Information, by Segment
Sales to external customers	41,780	42,653	84,338	83,599
Operating segments
Segment Reporting Information, by Segment
Segment income	21,293	25,537	48,729	49,219
Operating segments | Photonics
Segment Reporting Information, by Segment
Segment income	15,277	14,400	32,429	27,946
Operating segments | Lasers
Segment Reporting Information, by Segment
Segment income	1,041	6,148	6,665	11,728
Operating segments | Optics
Segment Reporting Information, by Segment
Segment income	$ 4,975	$ 4,989	$ 9,635	$ 9,545