Operating Segments and Geographic Information - Information on Reportable Segments (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jan. 02, 2021 USD ($)	Dec. 28, 2019 USD ($)	Jan. 02, 2021 USD ($) segment	Dec. 28, 2019 USD ($)
Information on reportable segments
Number of broad business categories (in segment) | segment			2
Total net revenue	$ 299.9	$ 313.7	$ 584.6	$ 613.5
Gross profit	$ 180.1	$ 189.5	$ 349.5	$ 363.9
Gross margin (as a percent)	60.10%	60.40%	59.80%	59.30%
Operating income	$ 42.3	$ 45.0	$ 73.6	$ 65.7
Operating margin (as a percent)	14.10%	14.30%	12.60%	10.70%
Other Items
Information on reportable segments
Total net revenue	$ 0.0	$ 0.0	$ 0.0	$ 0.0
Gross profit	(9.2)	(9.7)	(18.6)	(19.2)
Operating income	(24.5)	(22.9)	(53.8)	(54.9)
Network and Service Enablement | Segment Measures
Information on reportable segments
Total net revenue	206.7	234.2	390.2	454.0
Gross profit	$ 130.9	$ 155.6	$ 248.7	$ 296.2
Gross margin (as a percent)	63.30%	66.40%	63.70%	65.20%
Operating income	$ 22.2	$ 37.5	$ 35.5	$ 59.8
Operating margin (as a percent)	10.70%	16.00%	9.10%	13.20%
Network and Service Enablement | Network Enablement | Segment Measures
Information on reportable segments
Total net revenue	$ 180.9	$ 203.0	$ 343.0	$ 401.9
Gross profit	$ 113.3	$ 134.8	$ 216.8	$ 262.8
Gross margin (as a percent)	62.60%	66.40%	63.20%	65.40%
Network and Service Enablement | Service Enablement | Segment Measures
Information on reportable segments
Total net revenue	$ 25.8	$ 31.2	$ 47.2	$ 52.1
Gross profit	$ 17.6	$ 20.8	$ 31.9	$ 33.4
Gross margin (as a percent)	68.20%	66.70%	67.60%	64.10%
Optical Security and Performance Products | Segment Measures
Information on reportable segments
Total net revenue	$ 93.2	$ 79.5	$ 194.4	$ 159.5
Gross profit	$ 58.4	$ 43.6	$ 119.4	$ 86.9
Gross margin (as a percent)	62.70%	54.80%	61.40%	54.50%
Operating income	$ 44.6	$ 30.4	$ 91.9	$ 60.8
Operating margin (as a percent)	47.90%	38.20%	47.30%	38.10%
Product revenue
Information on reportable segments
Total net revenue	$ 262.1	$ 281.9	$ 510.0	$ 546.7
Product revenue | Other Items
Information on reportable segments
Total net revenue	0.0	0.0	0.0	0.0
Product revenue | Network and Service Enablement | Segment Measures
Information on reportable segments
Total net revenue	169.3	202.5	316.2	387.5
Product revenue | Network and Service Enablement | Network Enablement | Segment Measures
Information on reportable segments
Total net revenue	156.4	183.9	295.6	361.2
Product revenue | Network and Service Enablement | Service Enablement | Segment Measures
Information on reportable segments
Total net revenue	12.9	18.6	20.6	26.3
Product revenue | Optical Security and Performance Products | Segment Measures
Information on reportable segments
Total net revenue	92.8	79.4	193.8	159.2
Service revenue
Information on reportable segments
Total net revenue	37.8	31.8	74.6	66.8
Service revenue | Other Items
Information on reportable segments
Total net revenue	0.0	0.0	0.0	0.0
Service revenue | Network and Service Enablement | Segment Measures
Information on reportable segments
Total net revenue	37.4	31.7	74.0	66.5
Service revenue | Network and Service Enablement | Network Enablement | Segment Measures
Information on reportable segments
Total net revenue	24.5	19.1	47.4	40.7
Service revenue | Network and Service Enablement | Service Enablement | Segment Measures
Information on reportable segments
Total net revenue	12.9	12.6	26.6	25.8
Service revenue | Optical Security and Performance Products | Segment Measures
Information on reportable segments
Total net revenue	$ 0.4	$ 0.1	$ 0.6	$ 0.3