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I'm new to networking, sorry if my question sounds dumb. Let's say we want to transmit a sequence of 10101010 via fiber optics. We see that fiber optics has a lot of tiny optical fibers as the picture below shows: enter image description here

so does each tiny fiber transmit one bit? in our example, 10101010 needs 8 tiny fibers to transmit?

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No on your picture you have a fiber optic cable that embed several optic fiber strands

This cable goes in a split box where each strand is connected to a separate connector.

optical fiber split box

Most network devices will use 2 strands, one for transmit (TX) and one for receive (RX) to connect to a another device which will use the same strands but with TX and RX crossed.

When you send a stream of bit it is encoded and modulated into a stream of light impulses that goes one after each other on the same fiber strand.

Now there's more elaborated cases, like explained in @Zac67 answer:

  • you can use a single strand for both TX and RX , using different wave length (usually referred as "colors")
  • you can multiplex connection for several devices on the same strand, using once again different colors. This need an intermediate equipment

  • on the other side, you can also split the signal among several links, but this is not done by simply putting each bite on separate line, there's very elaborated encoding to do this.

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Generally, network connections use serial signaling, so bits are serialized onto the fiber. In order to recover the senders's bit and byte clocks on the receiver side, a line code like 8b10b or 64b66b is required.

For Ethernet, some high-speed variants (10+ Gbit/s) use four or more lanes to spread bandwidth across multiple carriers. For short-range multi-mode fiber that usually means multiple fiber strands per direction, and for long-range single-mode fiber it's usually done with a single strand and multiple wavelengths/colors (wavelength-division multiplex WDM).

Also, you can run multiple, independent links over a single fiber pair using WDM as well.

On the other hand, up to 50 Gbit/s can be sent using a single lane or carrier. 100 Gbit/s lanes are currently under development (e.g. 100GBASE-LR).

Additionally, when fiber strands are scarce, there are various bidirectional variants that use a different wavelength for each direction (wavelength-division duplex WDD). You can e.g. use 1000BASE-BX10 for a 1 Gbit/s link over 10 km using just a single strand.

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