a data diode ...or an "air gap" network (highly secure infra strutures, nuclear facilities, energy grids, etc..) is ...light emitter on one side sends light through a fibre to a photoreceive
https://www.lejournaldesentreprises.com/breve/tekever-va-installer-un-site-de-production-au-parc-des-expositions-de-cahors-2127209