The National Institute of Standards and Technology (NIST) is conducting market research to identify potential sources for O-band tunable optical filters used in quantum networking research. The requirement includes two line items, each for two filters, with pass bandwidths of 0.15 nm or narrower (Line Item 0001) and 0.25 nm or narrower (Line Item 0002), both covering 1260–1300 nm with low insertion loss and high out-of-band suppression. No budget amount or performance location is specified in this notice. Responses must be submitted via email as soon as possible, preferably before the closing date and time, and questions must be received by May 18, 2026, at 12:00 p.m. ET. This is a sources sought notice only, not a solicitation, and does not obligate the government to award a contract.