Operating Segments and Geographic Information - Summary of Reportable Segments (Details) $ in Millions	3 Months Ended								12 Months Ended
	Jun. 27, 2020 USD ($)	Mar. 28, 2020 USD ($)	Dec. 28, 2019 USD ($)	Sep. 28, 2019 USD ($)	Jun. 29, 2019 USD ($)	Mar. 30, 2019 USD ($)	Dec. 29, 2018 USD ($)	Sep. 29, 2018 USD ($)	Jun. 27, 2020 USD ($) segment	Jun. 29, 2019 USD ($)	Jun. 30, 2018 USD ($)
Information on reportable segments
Number of broad business categories (segment) | segment									2
Net revenue	$ 266.6	$ 256.2	$ 313.7	$ 299.8	$ 289.7	$ 265.2	$ 306.9	$ 268.5	$ 1,136.3	$ 1,130.3	$ 875.7
Gross profit	$ 154.6	$ 146.8	$ 189.5	$ 174.4	$ 169.5	$ 153.5	$ 178.0	$ 150.4	$ 665.3	$ 651.4	$ 488.4
Gross margin (percent)									58.50%	57.60%	55.80%
Operating income									$ 118.1	$ 67.4	$ 1.9
Operating margin (percent)									10.40%	6.00%	0.20%
Other Items
Information on reportable segments
Net revenue									$ 0.0	$ 0.0	$ 0.0
Gross profit									(38.9)	(38.7)	(43.7)
Operating income									(92.8)	(130.2)	(119.9)
Network and Service Enablement | Segment Measures
Information on reportable segments
Net revenue									849.4	841.2	657.6
Gross profit									$ 551.2	$ 544.3	$ 416.9
Gross margin (percent)									64.90%	64.70%	63.40%
Operating income									$ 108.8	$ 99.6	$ 43.6
Operating margin (percent)									12.80%	11.80%	6.60%
Network and Service Enablement | Network Enablement | Segment Measures
Information on reportable segments
Net revenue									$ 746.7	$ 737.8	$ 539.1
Gross profit									$ 482.4	$ 473.3	$ 334.3
Gross margin (percent)									64.60%	64.20%	62.00%
Network and Service Enablement | Service Enablement | Segment Measures
Information on reportable segments
Net revenue									$ 102.7	$ 103.4	$ 118.5
Gross profit									$ 68.8	$ 71.0	$ 82.6
Gross margin (percent)									67.00%	68.70%	69.70%
Optical Security and Performance Products | Segment Measures
Information on reportable segments
Net revenue									$ 286.9	$ 289.1	$ 218.1
Gross profit									$ 153.0	$ 145.8	$ 115.2
Gross margin (percent)									53.30%	50.40%	52.80%
Operating income									$ 102.1	$ 98.0	$ 78.2
Operating margin (percent)									35.60%	33.90%	35.90%
Product
Information on reportable segments
Net revenue									$ 1,005.2	$ 1,004.2	$ 772.5
Product | Other Items
Information on reportable segments
Net revenue									0.0	0.0	0.0
Product | Network and Service Enablement | Segment Measures
Information on reportable segments
Net revenue									719.0	715.9	556.4
Product | Network and Service Enablement | Network Enablement | Segment Measures
Information on reportable segments
Net revenue									669.1	666.2	497.1
Product | Network and Service Enablement | Service Enablement | Segment Measures
Information on reportable segments
Net revenue									49.9	49.7	59.3
Product | Optical Security and Performance Products | Segment Measures
Information on reportable segments
Net revenue									286.2	288.3	216.0
Service
Information on reportable segments
Net revenue									131.1	126.1	103.2
Service | Other Items
Information on reportable segments
Net revenue									0.0	0.0	0.0
Service | Network and Service Enablement | Segment Measures
Information on reportable segments
Net revenue									130.4	125.3	101.2
Service | Network and Service Enablement | Network Enablement | Segment Measures
Information on reportable segments
Net revenue									77.6	71.6	42.0
Service | Network and Service Enablement | Service Enablement | Segment Measures
Information on reportable segments
Net revenue									52.8	53.7	59.2
Service | Optical Security and Performance Products | Segment Measures
Information on reportable segments
Net revenue									$ 0.7	$ 0.8	$ 2.1