Acquisitions - Pro Forma Information (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Sep. 30, 2022	Sep. 30, 2021
Business Acquisition [Line Items]
Revenue	$ 124,126	$ 158,444
Cost of revenue	94,408	96,956
Gross profit	29,718	61,488
Operating expense:
Selling, general, and administrative	33,710	24,544
Research and development	18,536	17,448
Severance	1,353	0
Gain on sale of assets	(2,685)	515
Impairment charge	2,956	0
Total operating expense	53,870	42,507
Operating (loss) income	(24,152)	18,981
Other (expense) income:
Interest expense, net	139	(466)
Foreign exchange gain (loss)	(352)	207
Pension income	171	0
Total other (expense) income	(320)	7,234
(Loss) income before income tax benefit (expense)	(24,472)	26,215
Income tax benefit (expense)	139	(572)
Net (loss) income	(24,333)	25,643
Foreign exchange translation adjustment	173	(231)
Pension adjustment	(441)	0
Comprehensive (loss) income	$ (23,719)	$ 25,412
Net (loss) income per basic share (in dollars per share)	$ (0.65)	$ 0.75
Weighted-average number of basic shares outstanding (in shares)	37,269	34,020
Weighted-average number of diluted shares outstanding (in shares)	37,269	35,789
Pro Forma
Business Acquisition [Line Items]
Revenue	$ 149,786
Cost of revenue	114,516
Gross profit	35,270
Operating expense:
Selling, general, and administrative	38,862
Research and development	22,290
Severance	1,353
Gain on sale of assets	(2,685)
Impairment charge	2,956
Total operating expense	62,776
Operating (loss) income	(27,506)
Other (expense) income:
Interest expense, net	(1,199)
Foreign exchange gain (loss)	(352)
Pension income	148
Other income	137
Total other (expense) income	(1,266)
(Loss) income before income tax benefit (expense)	(28,772)
Income tax benefit (expense)	78
Net (loss) income	(28,694)
Foreign exchange translation adjustment	172
Pension adjustment	441
Comprehensive (loss) income	$ (28,081)
Net (loss) income per basic share (in dollars per share)	$ (0.77)
Weighted-average number of basic shares outstanding (in shares)	37,269
Weighted-average number of diluted shares outstanding (in shares)	37,269
Pro Forma | Pro Forma Adjustments
Business Acquisition [Line Items]
Revenue	$ 0
Cost of revenue	683
Gross profit	(683)
Operating expense:
Selling, general, and administrative	(4,102)
Research and development	(1,057)
Severance	0
Gain on sale of assets	0
Impairment charge	0
Total operating expense	(5,159)
Operating (loss) income	4,476
Other (expense) income:
Interest expense, net	(1,060)
Foreign exchange gain (loss)	0
Pension income	0
Other income	0
Total other (expense) income	(1,060)
(Loss) income before income tax benefit (expense)	3,416
Income tax benefit (expense)	(19)
Net (loss) income	3,397
Foreign exchange translation adjustment	0
Pension adjustment	0
Comprehensive (loss) income	$ 3,397
Net (loss) income per basic share (in dollars per share)	$ 0
Weighted-average number of basic shares outstanding (in shares)	0
Weighted-average number of diluted shares outstanding (in shares)	0
Pro Forma | EMCORE (excluding EMCORE Chicago)
Business Acquisition [Line Items]
Revenue	$ 118,029
Cost of revenue	89,486
Gross profit	28,543
Operating expense:
Selling, general, and administrative	33,294
Research and development	18,401
Severance	1,357
Gain on sale of assets	(2,685)
Impairment charge	2,956
Total operating expense	53,323
Operating (loss) income	(24,780)
Other (expense) income:
Interest expense, net	(139)
Foreign exchange gain (loss)	(352)
Pension income	148
Other income	0
Total other (expense) income	(343)
(Loss) income before income tax benefit (expense)	(25,123)
Income tax benefit (expense)	139
Net (loss) income	(24,984)
Foreign exchange translation adjustment	172
Pension adjustment	441
Comprehensive (loss) income	$ (24,371)
Net (loss) income per basic share (in dollars per share)	$ (0.67)
Weighted-average number of basic shares outstanding (in shares)	37,269
Weighted-average number of diluted shares outstanding (in shares)	37,269
Pro Forma | EMCORE Chicago
Business Acquisition [Line Items]
Revenue	$ 31,757
Cost of revenue	24,347
Gross profit	7,410
Operating expense:
Selling, general, and administrative	9,670
Research and development	4,946
Severance	(4)
Gain on sale of assets	0
Impairment charge	0
Total operating expense	14,612
Operating (loss) income	(7,202)
Other (expense) income:
Interest expense, net	0
Foreign exchange gain (loss)	0
Pension income	0
Other income	137
Total other (expense) income	137
(Loss) income before income tax benefit (expense)	(7,065)
Income tax benefit (expense)	(42)
Net (loss) income	(7,107)
Foreign exchange translation adjustment	0
Pension adjustment	0
Comprehensive (loss) income	$ (7,107)