They are complicated, but standardised and commoditised. Ubiquiti, for example, sells an ONT (fibre modem) in a SFP form factor for US$39 [1], or a little standalone unit with an Ethernet port for US$49 [2].

1. https://store.ui.com/us/en/category/fiber-gpon/products/uf-i...

2. https://store.ui.com/us/en/category/fiber-gpon/products/wave...

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direwolf20 3 hours ago | parent [-]

For comparison: you can bring your own DOCSIS modem to a cable network, even though all the houses on the street are connected to the same cable and you could jam it, or send a voltage spike to break everyone's modem.

	▲	perching_aix 2 hours ago \| parent [-]
		Not very familiar with DOCSIS and cable; the story I'm getting from my nearest friendly LLM is that while you could bring your cable modem, it'd have to be a pre-approved model, and that the firmware and configuration would be under ISP control, unlike with DSL modems. Is that wrong?