Acquisitions - Pro Forma Information (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Business Acquisition [Line Items]
Revenue	$ 26,698	$ 23,675	$ 78,471	$ 98,561
Cost of revenue	23,198	19,777	68,201	69,849
Gross profit	3,500	3,898	10,270	28,712
Operating expense:
Selling, general, and administrative	6,452	7,800	26,347	22,550
Research and development	5,171	4,513	16,319	13,675
Severance	1,838	0	2,296	1,318
Gain on sale of assets	0	(1,318)	(1,147)	(1,919)
Total operating expense	13,461	10,995	43,815	35,624
Operating loss	(9,961)	(7,097)	(33,545)	(6,912)
Other income (expense):
Interest (expense) income, net	(219)	9	(682)	(14)
Foreign exchange loss	321	(185)	442	(160)
Other income (expense)	31	(349)	184	(349)
Total other income (expense)	133	(525)	(56)	(523)
Loss before income tax expense	(9,828)	(7,622)	(33,601)	(7,435)
Income tax expense	(29)	(27)	(177)	(25)
Net loss	(9,857)	(7,649)	(33,778)	(7,460)
Foreign exchange translation adjustment	(134)	69	(79)	91
Comprehensive loss	$ (9,991)	$ (7,580)	$ (33,857)	$ (7,369)
Net loss per basic share (in dollars per share)	$ (0.18)	$ (0.20)	$ (0.74)	$ (0.20)
Weighted-average number of basic shares outstanding (in shares)	53,926	37,425	45,546	37,197
Net loss per diluted share (in dollars per share)	$ (0.18)	$ (0.20)	$ (0.74)	$ (0.20)
Weighted-average number of diluted shares outstanding (in shares)	53,926	37,425	45,546	37,197
Pro Forma
Business Acquisition [Line Items]
Revenue		$ 31,373		$ 121,655
Cost of revenue		25,775		87,843
Gross profit		5,598		33,812
Operating expense:
Selling, general, and administrative		9,679		27,802
Research and development		5,692		17,212
Severance		0		1,318
Gain on sale of assets		(1,318)		(1,919)
Total operating expense		14,053		44,413
Operating loss		(8,455)		(10,601)
Other income (expense):
Interest (expense) income, net		327		940
Foreign exchange loss		(185)		(160)
Other income (expense)		(315)		(247)
Total other income (expense)		(173)		533
Loss before income tax expense		(8,628)		(10,068)
Income tax expense		(46)		(80)
Net loss		(8,674)		(10,148)
Foreign exchange translation adjustment		69		91
Comprehensive loss		$ (8,605)		$ (10,057)
Net loss per basic share (in dollars per share)		$ (0.23)		$ (0.27)
Weighted-average number of basic shares outstanding (in shares)		37,425		37,197
Net loss per diluted share (in dollars per share)		$ (0.23)		$ (0.27)
Weighted-average number of diluted shares outstanding (in shares)		37,425		37,197
Pro Forma | Pro Forma Adjustments
Business Acquisition [Line Items]
Revenue		$ 0		$ 0
Cost of revenue		171		512
Gross profit		(171)		(512)
Operating expense:
Selling, general, and administrative		(1,026)		(3,077)
Research and development		(264)		(793)
Severance		0		0
Gain on sale of assets		0		0
Total operating expense		(1,290)		(3,870)
Operating loss		1,119		3,358
Other income (expense):
Interest (expense) income, net		318		954
Foreign exchange loss		0		0
Other income (expense)		0		0
Total other income (expense)		318		954
Loss before income tax expense		1,437		4,312
Income tax expense		(6)		(17)
Net loss		1,431		4,295
Foreign exchange translation adjustment		0		0
Comprehensive loss		$ 1,431		$ 4,295
Net loss per basic share (in dollars per share)		$ 0		$ 0
Weighted-average number of basic shares outstanding (in shares)		0		0
Net loss per diluted share (in dollars per share)		$ 0		$ 0
Weighted-average number of diluted shares outstanding (in shares)		0		0
Pro Forma | EMCORE Corporation (excluding EMCORE Chicago)
Business Acquisition [Line Items]
Revenue		$ 23,675		$ 98,561
Cost of revenue		19,777		69,849
Gross profit		3,898		28,712
Operating expense:
Selling, general, and administrative		7,800		22,550
Research and development		4,513		13,675
Severance		0		1,318
Gain on sale of assets		(1,318)		(1,919)
Total operating expense		10,995		35,624
Operating loss		(7,097)		(6,912)
Other income (expense):
Interest (expense) income, net		9		(14)
Foreign exchange loss		(185)		(160)
Other income (expense)		(349)		(349)
Total other income (expense)		(525)		(523)
Loss before income tax expense		(7,622)		(7,435)
Income tax expense		(27)		(25)
Net loss		(7,649)		(7,460)
Foreign exchange translation adjustment		69		91
Comprehensive loss		$ (7,580)		$ (7,369)
Net loss per basic share (in dollars per share)		$ (0.20)		$ (0.20)
Weighted-average number of basic shares outstanding (in shares)		37,425		37,197
Net loss per diluted share (in dollars per share)		$ (0.20)		$ (0.20)
Weighted-average number of diluted shares outstanding (in shares)		37,425		37,197
Pro Forma | EMCORE Chicago
Business Acquisition [Line Items]
Revenue		$ 7,698		$ 23,094
Cost of revenue		5,827		17,482
Gross profit		1,871		5,612
Operating expense:
Selling, general, and administrative		2,905		8,329
Research and development		1,443		4,330
Severance		0		0
Gain on sale of assets		0		0
Total operating expense		4,348		12,659
Operating loss		(2,477)		(7,047)
Other income (expense):
Interest (expense) income, net		0		0
Foreign exchange loss		0		0
Other income (expense)		34		102
Total other income (expense)		34		102
Loss before income tax expense		(2,443)		(6,945)
Income tax expense		(13)		(38)
Net loss		(2,456)		(6,983)
Foreign exchange translation adjustment		0		0
Comprehensive loss		$ (2,456)		$ (6,983)