Segment Data and Related Information - Revenue by Product (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation of Revenue [Line Items]
Revenue	$ 42,658	$ 27,266	$ 114,490	$ 76,598
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	$ 9,280	$ 9,861	$ 27,475	$ 28,970
Navigation and Inertial Sensing | Product Concentration Risk | Revenue, Product and Service Benchmark
Disaggregation of Revenue [Line Items]
Concentration Risk, Percentage	22.00%	36.00%	24.00%	38.00%
Defense Optoelectronics
Disaggregation of Revenue [Line Items]
Revenue	$ 3,047	$ 4,164	$ 11,622	$ 11,772
Defense Optoelectronics | Product Concentration Risk | Revenue, Product and Service Benchmark
Disaggregation of Revenue [Line Items]
Concentration Risk, Percentage	7.00%	16.00%	10.00%	15.00%
CATV Lasers and Transmitters
Disaggregation of Revenue [Line Items]
Revenue	$ 27,364	$ 10,905	$ 65,799	$ 29,070
CATV Lasers and Transmitters | Product Concentration Risk | Revenue, Product and Service Benchmark
Disaggregation of Revenue [Line Items]
Concentration Risk, Percentage	64.00%	40.00%	57.00%	38.00%
Chip Devices
Disaggregation of Revenue [Line Items]
Revenue	$ 819	$ 1,443	$ 2,403	$ 4,033
Chip Devices | Product Concentration Risk | Revenue, Product and Service Benchmark
Disaggregation of Revenue [Line Items]
Concentration Risk, Percentage	2.00%	5.00%	2.00%	5.00%
Other
Disaggregation of Revenue [Line Items]
Revenue	$ 2,148	$ 893	$ 7,191	$ 2,753
Other | Product Concentration Risk | Revenue, Product and Service Benchmark
Disaggregation of Revenue [Line Items]
Concentration Risk, Percentage	5.00%	3.00%	6.00%	4.00%