Description of Business - Revenue by Product (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Disaggregation of Revenue [Line Items]
Revenue	$ 38,406	$ 23,850	$ 71,832	$ 49,332
Product Concentration Risk
Disaggregation of Revenue [Line Items]
% of Revenue	100.00%	100.00%	100.00%	100.00%
Navigation and Inertial Sensing
Disaggregation of Revenue [Line Items]
Revenue	$ 8,993	$ 8,842	$ 18,195	$ 19,109
Navigation and Inertial Sensing | Product Concentration Risk
Disaggregation of Revenue [Line Items]
% of Revenue	23.00%	37.00%	25.00%	39.00%
Defense Optoelectronics
Disaggregation of Revenue [Line Items]
Revenue	$ 4,141	$ 4,171	$ 8,575	$ 7,608
Defense Optoelectronics | Product Concentration Risk
Disaggregation of Revenue [Line Items]
% of Revenue	11.00%	18.00%	12.00%	15.00%
CATV Lasers and Transmitters
Disaggregation of Revenue [Line Items]
Revenue	$ 21,120	$ 8,782	$ 38,435	$ 18,165
CATV Lasers and Transmitters | Product Concentration Risk
Disaggregation of Revenue [Line Items]
% of Revenue	55.00%	37.00%	54.00%	37.00%
Chip Devices
Disaggregation of Revenue [Line Items]
Revenue	$ 841	$ 1,035	$ 1,584	$ 2,590
Chip Devices | Product Concentration Risk
Disaggregation of Revenue [Line Items]
% of Revenue	2.00%	4.00%	2.00%	5.00%
Other
Disaggregation of Revenue [Line Items]
Revenue	$ 3,311	$ 1,020	$ 5,043	$ 1,860
Other | Product Concentration Risk
Disaggregation of Revenue [Line Items]
% of Revenue	9.00%	4.00%	7.00%	4.00%