Segment and Revenue Information - Revenue by Product (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Disaggregation of Revenue [Line Items]
Revenue	$ 23,675	$ 42,658	$ 98,561	$ 114,490
Product Concentration Risk | Revenue, Product and Service Benchmark
Disaggregation of Revenue [Line Items]
Concentration risk, percentage	100.00%	100.00%	100.00%	100.00%
Navigation and Inertial Sensing
Disaggregation of Revenue [Line Items]
Revenue	$ 9,891	$ 9,280	$ 25,651	$ 27,475
Navigation and Inertial Sensing | Product Concentration Risk | Revenue, Product and Service Benchmark
Disaggregation of Revenue [Line Items]
Concentration risk, percentage	42.00%	22.00%	26.00%	24.00%
Defense Optoelectronics
Disaggregation of Revenue [Line Items]
Revenue	$ 3,525	$ 3,047	$ 6,671	$ 11,622
Defense Optoelectronics | Product Concentration Risk | Revenue, Product and Service Benchmark
Disaggregation of Revenue [Line Items]
Concentration risk, percentage	15.00%	7.00%	7.00%	10.00%
CATV Lasers and Transmitters
Disaggregation of Revenue [Line Items]
Revenue	$ 7,006	$ 27,364	$ 56,449	$ 65,799
CATV Lasers and Transmitters | Product Concentration Risk | Revenue, Product and Service Benchmark
Disaggregation of Revenue [Line Items]
Concentration risk, percentage	29.00%	64.00%	57.00%	58.00%
Chip Devices
Disaggregation of Revenue [Line Items]
Revenue	$ 1,353	$ 819	$ 3,534	$ 2,403
Chip Devices | Product Concentration Risk | Revenue, Product and Service Benchmark
Disaggregation of Revenue [Line Items]
Concentration risk, percentage	6.00%	2.00%	4.00%	2.00%
Other Optical Products
Disaggregation of Revenue [Line Items]
Revenue	$ 1,900	$ 2,148	$ 6,256	$ 7,191
Other Optical Products | Product Concentration Risk | Revenue, Product and Service Benchmark
Disaggregation of Revenue [Line Items]
Concentration risk, percentage	8.00%	5.00%	6.00%	6.00%