Networking – How to convert a PON interface to a WAN interface in the home router

Is there a way to convert my router's "PON" interface (for fiber cables, see following picture) to a WAN interface (not LAN)?

It's already a WAN interface; that's literaly what it's there for.

I've bought a media converter (TPLINK MC220L) and a SFP (TL-SM311LM), only to find out that I didn't consider that my fiber port is apparently "Simplex" while the TPLINK device supports only "Duplex" connections.

Not exactly. When the MC220L product page says "Half-Duplex / Full-Duplex mode", that refers to the copper Ethernet port (and is a standard feature for all Ethernet ports, which normally auto-negotiate Full Duplex unless something goes wrong).

The MC220L does not care about whether the optical connection is duplex or 2xsimplex: it's all in the SFP module. It'll take your 2x LC SFP just as well as a 1xSC "Bidirectional" SFP; in fact the former are probably much more common. ("BiDi" 1000BASE-BX SFPs are probably not sold by TP-Link, but can be found at Fiberstore and just about everywhere else.)

Note that with a BiDi module, you have to pay close attention to what wavelength it sends at, vs what wavelength it receives at: e.g. if your router's datasheet says "upstream 1310nm, downstream 1490nm", the other end must have it in reverse.

(Note: This is practically where my knowledge on this topic ends.)

At this point I'm not really sure if I should buy another SFP

Well, yes, your current SFP is unsuitable for several different reasons.

1. It is built for multi-mode fiber; the router expects single-mode fiber.
2. It uses separate fibers to transmit and receive; the router uses a single fiber and transmits/receives on different wavelengths (~frequencies).
3. It transmits/receives at 850nm (common for MM); the router probably expects something like 1300nm/1500nm for transmit/receive.

But the bigger problem is that the router's port is made for a completely different protocol, and as far as a I know, there are no SFP modules for what it wants on the other end. (Or rather it is not enough to just have a matching SFP – you also need a device that sends the correct data format.)

There are several different optical connections which go over a single "duplex" SC connector:

• Ethernet, which provides a point-to-point connection (e.g. 1000BASE-BX for a 'duplex' Gigabit link);
• PON, which provides a one-to-many connection through an optical splitter (e.g. G.984 GPON for a Gigabit link);
• EPON, which is like PON physically but transfers Ethernet-compatible data frames.

Your SFP module (and most BiDi SFPs you'll find) is made for ordinary Ethernet, which uses identical software and hardware on both ends. Your router, however, expects GPON and not Ethernet.

So even if you connect it to an SFP module with the correct physical parameters (1490nm/1310nm, etc.) it won't actually talk to a plain Ethernet device, it needs to be connected to an actual GPON OLT device instead.