Introduction to SWDM technology

      ⦁ What is SWDM technology
      SWDM (Short Wavelength Division Multiplexing), that is, short-wave wavelength division multiplexing, drawing on the wavelength division multiplexing (WDM) technology of single-mode optical fiber, expanding the range of wavelengths used in transmission from the 850 nm used in conventional multimode fiber to 850 nm-950 nm, using cost-effective short-wave vertical cavity surface emitting Laser (VCSEL) light source and optimized Wideband Multimode Fiber (WBMMF), supporting four wavelengths on a single multimode fiber to transmit data, reducing the number of fiber cores required to 1/4 of the original.
      ⦁ How SWDM works
      SWDM technology uses operating wavelengths starting from 850 nm and increasing by one wavelength every 30 nm, i.e., 850 nm, 880 nm, 910 nm, and 940 nm. In the shortwave wavelength-division-multiplexing (WDM) module, four VCSELs generate optical signals at four different wavelengths, which are multiplexed onto a single optical fiber, and all the VCSELs and the optical coupling are carried out in the optical module. At the receiving end of the module, the signals are demultiplexed and converted into four electrical signals. By using two optical fibers, one transmitter and one receiver can be used for data transmission as shown in the figure below:

Figure 1  Shortwave wavelength division multiplexing

      ⦁ SWDM Consortium
      The SWDM Alliance is the industry organization that develops SWDM specifications, and its members include Compaq, Finisar, Hisense, Lumentum, OFS, and Prysmian.
      ⦁ SWDM transmission rates
      The SWDM consortium currently publishes two SWDM standards for 40G and 100G (download at https://swdm.org/msa/), which define SWDM optical interfaces for optical transceivers 4 x 10 Gbps and 4 x 25 Gbps. For 40G, the multimode fiber length between two transceivers ranges from 2m to 440m, with a signal rate of 10.3125 Gbps per channel in one direction; for 100G, the multimode fiber length between two transceivers ranges from 2m to 150m, with a signal rate of 25.78125 Gbps per channel in one direction, and the transceivers need to turn on the FEC function.
      ⦁ SWDM transmission distance
      The transmission distances for different rates and fiber types are shown in Table 1.

Table 1 Fiber Transmission Distance

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