Subsequent Events	6 Months Ended
Subsequent Events	Mar. 31, 2023
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events Restructuring On April 21, 2023, EMCORE Corporation announced a restructuring program (collectively, the "Restructuring") that includes the strategic shutdown of the Company’s Broadband business segment (including the Company’s cable TV, wireless, sensing, and chips product lines) and the discontinuance of its defense optoelectronics product line (collectively, the "Discontinued Businesses"). On April 19, 2023, the Company’s Board of Directors unanimously approved the Restructuring. Prior to the decision to effect the Restructuring, the Company's Board of Directors performed a thorough review of a number of factors including the competitive landscape, declining revenue and gross profit of the Discontinued Businesses, the current and expected profitability for the Discontinued Businesses, the Company’s cost structure and the Company’s strategic focus on the Company’s Aerospace and Defense business segment, and concluded that the Discontinued Businesses are non-strategic, currently unsustainable and cannot be restructured in a way that will allow the Company to achieve profitable growth and cash preservation. Additionally, the Company engaged in an effort to sell some or all of the Discontinued Businesses but had not been able to consummate any such transaction with a buyer, following several months of discussions with several interested parties, on terms that the Company’s Board of Directors believed were in the best interests of the Company and its shareholders. The Company expects to exit the operations of the Discontinued Businesses by September 30, 2023. As a result of the Restructuring, the Company expects to eliminate approximately 75 positions in the U.S. (primarily in Alhambra, California) and approximately 25 positions in China, collectively representing approximately 22% of the Company’s workforce, and to consolidate facility space by reducing the space used at the Alhambra campus from five to two buildings (including closure of the Company’s indium phosphide wafer fabrication facility in Alhambra), relocating personnel in Concord, California to the operations area from the adjacent office building, and closing the Company’s manufacturing support and engineering center in China, collectively representing an approximately 25% reduction in the aggregate square footage occupied by the Company’s facilities. The actions that are being undertaken by the Company in connection with the Restructuring are expected to result in annualized cost savings of approximately $12 million. At the time of the filing of this Quarterly Report on Form 10-Q, the Company is unable in good faith to make a determination of an estimate of the total amount or range of amounts expected to be incurred by the Company in connection with the Restructuring. However, the Company anticipates that material cash and non-cash charges will be incurred and recorded in the Company's future reporting periods, including, without limitation, one-time employee severance and termination costs related to the Restructuring of approximately $2.1 million (of which the Company expects that approximately $0.5 million will be in non-cash, stock-based compensation expenditures relating to the acceleration of the vesting of outstanding equity awards). The Company expects to recognize substantially all of these charges in the quarter ending June 30, 2023 and that the Restructuring implementation is anticipated to be substantially complete by September 30, 2023. The Company may incur additional expenses in connection with the Restructuring that are not currently contemplated. The charges that the Company expects to incur in connection with the Restructuring are estimates and subject to a number of assumptions, and actual results may differ materially.