A passive mux (short for multiplexer) in most networks consist of a mux and demux optical component.
The mux combines, or multiplexes, wavelengths on to a fiber. The demux on the other end of the connection splits, or de-multiplexes, the connections. Passive mux and demux components do not require power, simply acting as mirrors to direct light on or off a single fiber.
Standard Duplex Transceiver – One fiber for Transmit, One for Receive, one connection over a fiber pair.
Point-to-Point
Point-to-Point applications combine 4 or more WDM channels onto a fiber pair. These applications consist of a Mux/Demux on each end of the connection. WDM transceivers connect to the appropriate Tx and Rx port on each passive device.
Standard Duplex Transceiver – One fiber for Transmit, One for Receive, one connection over a fiber pair.
Single Fiber Muxes
Single Fiber Muxes are also used for point to point applications, but are able to connect standard duplex transceivers over a single fiber. Single fiber muxes take advantage of a key technical consideration in WDM networking. Each WDM transceiver may transmit at a given center wavelength, but it can receive signals across the full WDM spectrum. In the example below, the 1591 channel on the top mux is receiving the Tx from the 1611 channel on the bottom mux and vice versa.
The resulting limitation is that using a single fiber mux, 16 WDM wavelengths to connect 8 channels.
Multipoint – Optical add/drop muxes (OADMs) offer solutions for multi-point fiber deployments.
Add/Drop muxes filter up to four WDM wavelengths off of a WDM link, making them accessible to a switch or switches at the drop point. Add/Drop Muxes also allow the same wavelength to be added back into the fiber connection from the drop point. This allows redundancy in the connect to allow each point to be connected, even if one link goes down.
Not to be confused with Add/Drop muxes are the other type of OADM, Add or Drop. Add or Drop muxes filter off or on to a WDM link a single wavelength. The most common type of application a fiber drop to the customer premises.
