Do you know MUX and DEMUX in WDM?

Wavelength Division Multiplexing(WDM) is one of the most common way of using wavelengths to increase bandwidth by multiplexing various optical carrier signals onto a single optical fiber. It combines a series of optical carrier signals with different wavelengths carrying various information and coupled to the same optical fiber for transmission at the transmitting end. At the receiving end, optical signals of various wavelengths are separated by a demultiplexer. This technique of simultaneously transmitting two or many different wavelengths in the same fiber is called wavelength division multiplexing, or WDM. Depending on the direction of the transmitted signal, WDM can be used for multiplexing or demultiplexing.

MUX

The main function of the combiner MUX is to combine multiple signal wavelengths into one fiber for transmission.  At the transmitting end, the N optical transmitters operate on N different wavelengths respectively, and the N wavelengths are separated by appropriate intervals, which are respectively recorded as λ1, λ2, ... λn. A multiplexer combines these optical wavelengths into a single-mode fiber. Since  optical carrier signals of different wavelengths can be regarded as independent of each other (regardless of fiber nonlinearity), multiplexing transmission of multiple optical signals can be realized in one optical fiber. Through multiplexing, communication carriers can avoid maintaining multiple lines and effectively save operating costs.

DEMUX

The main function of DEMUX is to separate the multiple wavelength signals transmitted in one fiber. In the receiving part, the optical carrier signals of different wavelengths are separated by a Demux and further processed by the optical receiver to restore the original signal. A multiplexer (Demux) is a device that reverses the processing of a multiplexer.

Performance parameters

Multiplexed/demultiplexed devices (MUX/DEMUX) are key components in WDM that affect the performance of the entire system. What are the main performance parameters of the multiplexer/demultiplexer?

Working band

Working bands of the multiplexer/demultiplexer. For example, there is three bands of 1550 wavelength: S-band (short-wavelength 1460~1528nm), C band (conventional band 1530~1565nm), L band (long-wavelength band 1565~1625nm).

Number of channels & channel spacing

The number of channels is the number of channels the device has to send information. This number can range from 4 to 160 with design enhancements adding more channels. The normal channels are 4, 8, 16, 32, 40, 48, etc. Channel spacing is the center-to-center difference in frequency between neighboring channels. It can be used to prevent inter-channel interference.

Insertion loss

Insertion loss is the attenuation caused by the insertion of wavelength division multiplexers (WDM) in an optical transmission system. The attenuation effect of wavelength division multiplexer directly affects the transmission distance of the system. In general, the lower the insertion loss, the less the signal attenuation.

Isolation

Isolation refers to the degree of isolation between individual channel signals. High isolation values can effectively prevent crosstalk between signals and cause distortion of the transmission signal.

Polarization dependent loss（PDL）

Polarization-dependent loss is the maximum deviation in insertion loss across all input polarization states.

In addition to the above, there are of course other performance parameters that affect the multiplexing/demultiplexing devices, such as operating temperature, bandwidth, etc. Generally, a multiplexer and a demultiplexer are combined into a single device allowing the device to process both incoming and outgoing signals. Or a single output of a multiplexer can be connected through a single channel to a single input of a demultiplexer. But mostly is the combined and complex devices for both directions transmission.

HYC Co., Ltd, a leading WDM manufacturer over 19 years, offers a series of WDM/CWDM/DWDM/FWDM/CCWDM modules. You can know more details of WDM MUX/DEMUX at www.hyc-system.com