Introduction to Fiber Optics for 10G Network at Home

Fiber optics are becoming cheaper and more affordable for homes nowadays, and they could be a fantastic alternative for RJ-45 10GBase-T Ethernet. Fiber transceivers at the same speed use less power and run cooler. They also don't need to be upgraded like you would need to upgrade an Ethernet cable from Cat5e to Cat6a to now Cat8.

I have worked with fiber network designs at work, at least in theory. But in the last two weeks, I learned even more than I cared for about fiber optics, and here is a quick summary about them before I forget.

• Fiber core size: single-mode fiber (SMF, OS2) vs. multimode fiber (MMF, OM5, OM4, OM3, OM2, OM1).
• Single mode has a smaller core and can run for longer distances. Multimode fibers may be more cost effective once upon a time, but these days single mode fibers are so cheap, they should be the default choice for even short (< 100m) runs.
• Note: the mode type must match with the transceiver as well, so you have to use a single mode fiber with a single mode transceiver.
• Number of strands: simplex (1 fiber) or duplex (2 fibers).
• The transceivers most commonly used for data center applications will use duplex fibers, using one strand for each direction of transmission. Both directions typically use the same wavelength.
• Simplex fibers are more common for Fiber To The Home (FTTH). You have to use a matching (opposite) pair of transceivers at the two ends, e.g. one side is 1330nm-TX/1270nm-RX, and the other side should be 1270nm-TX/1330nm-RX. The two wavelengths traverse on the same fiber strand.
• Connector type: SC (standard connector, larger) vs. LC (lucent connector, smaller).
• For some reason, the LC transceivers are more commonplace, possibly because you can fit a duplex connector into a transceiver with the SFP form factor.
• There are also SC transceivers, but these are less common.
• Again, you have to match the connector with the transceiver.
• Connector contact type: UPC (domed) vs. APC (angled). They refer to how the fiber ending is terminated. The angled type reduces back-reflection.
• You have to match the contact type with the transceiver as well. Inserting APC connector to a UPC transceiver can damage the optics.
• I typically find either SC/APC or LC/UPC to be more common. The other combinations (e.g. SC/UPC or LC/APC) are possible but uncommon.
• Adapters exist but they can cause signal loss. Due to the naming, it can be hard to find the correct adapter by keyword (e.g. "SC/APC female to LC/UPC male" can also give you results for "SC/APC male to LC/UPC female").
• Sometimes SC/APC is written as SC/Angled or simply SCA.

Bend radius: more recently, I became aware about the bend insensitive fibers. They are characterized by having smaller bend radius than the regular fibers (30mm), and they are defined by the standards G.657.A1 (10mm), G.657.A2 or B2 (7.5mm), and G.657.B3 (5mm). This primarily allows installation in tight corners in the home, and the transceivers are agnostic to the bend radius.

FS.com has a custom fiber builder where you can build simplex or duplex fibers with custom core sizes, connector and contact types, and bend radius. They offer white color which is better than bright yellow for home installation. However, their sales representative told me that G.657.A2 with 0.9mm cable diameter has a minimum order quantity (MOQ) of 1KM (this is not on the website). The best they could do with no MOQ is G.657.A1 with a 2.0mm diameter. There appears to be some 0.9mm cables on eBay, but I have not tested them.

So for running between rooms in the home, you would typically use a simplex single-mode LC or SC transceiver, and choose or build a fiber cable with a matching connector. Here are some transceiver options I found:

• LC/UPC single-mode simplex:
• FS.com branded 10GBASE-BX BiDi transceivers. Here you have to buy two separate transceivers with matching opposite TX/RX frequencies.
• Elfcam branded 10G Bidi transceivers, sold as a matching pair.
• Recently, there used to be an Elfcam branded SC/APC single-mode simplex transceiver on Amazon, but it appears to be delisted at the moment. I may have bought the last one?

For running between devices in the rack room, there are more options with the LC duplex single-mode transceivers. I also use a Direct Attached Cable, which is just copper but with both ends hard-wired to SFP+ connector.

The SFP+ connector refers to the plug form factor where the transceiver is inserted into the switch device. It typically determines the speed as well.

• SFP: 1G.
• SFP+: 10G, 25G.
• QSFP (or QSFP28, literally "quad SFP"): 100G.
• QSFP-DD (or QSFP56, literally "double density quad SFP"): 400G, 800G.
• OSFP (literally "octa SFP"): 400G, 800G.

With data centers upgrading from QSFP 100G to QSFP-DD or OSFP 400G or 800G to satisfy the AI computing needs, and with more FTTH deployments, we are seeing more surplus SFP+ 10G transceivers and devices flowing to the consumer market. This could be a good time to upgrade your home network cabling from copper based cable to fiber.