Segment and Revenue Information - Revenue by Product (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2022	Mar. 31, 2021
Disaggregation of Revenue [Line Items]
Revenue	$ 32,650	$ 38,406	$ 74,886	$ 71,832
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	$ 7,615	$ 8,993	$ 15,760	$ 18,195
Navigation and Inertial Sensing | Product Concentration Risk | Revenue, Product and Service Benchmark
Disaggregation of Revenue [Line Items]
Concentration risk, percentage	23.00%	23.00%	21.00%	25.00%
Defense Optoelectronics
Disaggregation of Revenue [Line Items]
Revenue	$ 1,391	$ 4,141	$ 3,146	$ 8,575
Defense Optoelectronics | Product Concentration Risk | Revenue, Product and Service Benchmark
Disaggregation of Revenue [Line Items]
Concentration risk, percentage	4.00%	11.00%	4.00%	12.00%
CATV Lasers and Transmitters
Disaggregation of Revenue [Line Items]
Revenue	$ 20,984	$ 21,120	$ 49,443	$ 38,435
CATV Lasers and Transmitters | Product Concentration Risk | Revenue, Product and Service Benchmark
Disaggregation of Revenue [Line Items]
Concentration risk, percentage	64.00%	55.00%	66.00%	54.00%
Chip Devices
Disaggregation of Revenue [Line Items]
Revenue	$ 1,113	$ 841	$ 2,181	$ 1,584
Chip Devices | Product Concentration Risk | Revenue, Product and Service Benchmark
Disaggregation of Revenue [Line Items]
Concentration risk, percentage	3.00%	2.00%	3.00%	2.00%
Other Optical Products
Disaggregation of Revenue [Line Items]
Revenue	$ 1,547	$ 3,311	$ 4,356	$ 5,043
Other Optical Products | Product Concentration Risk | Revenue, Product and Service Benchmark
Disaggregation of Revenue [Line Items]
Concentration risk, percentage	5.00%	9.00%	6.00%	7.00%