Wavelength Division Multiplexing

duplex fiber channel link uses one transmit lane and one receive lane
- requires two fiber strands
parallel fiber uses bundles of lanes
- works at 10 or 25 Gbps to implement 40 or 100 Gbps links
- require 8-20 strands

Wavelength division multiplexing (WDM) is a means of using one or two strands to provision multiple channels.

Bidirectional Wavelength Division Multiplexing

Bidirectional (BiDi) transceivers support transmit and receive signals over the same strand of fiber
- uses WDM to transmit Tx and Rx signals
- uses slightly shifted wavelengths
  - 1,310 nm for Tx, 1,490 nm for Rx
- must be installed in opposite pairs
  - so downstream transceiver uses 1,490 nm for Tx and 1,310 for Rx
Bidirectional wavelength division multiplexing (BWDM) links are documented in Ethernet standards
- 1000BASE-BX and 10GBASE-BX

course wavelength division multiplexing (CWDM) supports up to 16 wavelengths
- typically used to deploy:
  - 4 or 8 bidirectional channels over a single fiber strand
  - or unidirectional channels over dual fiber strands
dense wavelength division multiplexing (DWDM) provisions greater numbers of channels (20, 40, 80, or 160)
- much less spacing between each channel
- requires more precise and expensive lasers
CWDM and DWDM transceivers support multichannel 1 G, 10 G, and 40 G Ethernet links
- transceivers must be installed in opposite pairs