What is SWDM Shortwave Wavelength Division Multiplexing


In 2015, the SWDM Alliance was formed by a group of transceiver, fiber and system vendors to develop a multi-source agreement (MSA) for SWDM transceivers. As OM5 permits the use of a much wider wavelength range, it is now desirable to reduce fiber count by transmitting multiple VCSEL wavelengths in the same multimode fiber.

The potential wavelength grids { λ1 , λ2 , λ3 and λ4 } are designed as {850 nm, 880 nm, 910 nm and 940 nm}, with a spacing of 30 nm. New SWDM- based QSFP multimode transceivers, including 40G-SWDM4, 100G-SWDM4 and 100G-SWDM2, have already been demonstrated by a few vendors.

SWDM advantages for duplex MMF connectivity

WDM offers users an alternate solution for 40Gbps and higher connectivity over duplex MMF. Some of the many advantages of SWDM are:

  • Reach – up to 440m for 40G and 150m for 100G (200m by using OM5 fiber)
  • Power Dissipation – As low as 1.5W (Power varies depending on data rate and module design.)
  • Ability to easily tap for network security appliances
  • Full DDM – including Tx power monitoring
  • Operational and measurement simplicity – single Tx and Rx ports

Reach – 40G SWDM can operate up to 240, 350, and 440 meters on OM3, OM4, and OM5, respectively. These reaches are suited to the physical sizes of data centers originally designed for 10G and now upgrading to higher data rates.

Power Dissipation – SWDM uses a 4x WDM optical architecture that matches the 4x electrical interface, and is therefore capable of lower power dissipation comparable to SR4 modules. For 40G, this means power dissipation as low as 1.5W per QSFP+ module is possible, and therefore SWDM QSFP+ modules can be readily inserted into system ports architected for standard 40G SR4. Other duplex solutions requiring higher power, sometimes up to 3.5W, may not be readily useable in system ports designed for lower power modules such as 40G SR4.

Ability to easily tap for network security appliances – SWDM has a simple Tx and Rx port, making it straightforward to tap using a simple optical power coupler for network security appliances.

Full DDM – All five digital diagnostics functions can be supported with SWDM: temperature, voltage, bias current, Rx power, and Tx power.

Operational simplicity – Data center technicians are comfortable with individual Tx and Rx fibers. WDM is already a familiar concept in the data center. However, bi-directional solutions require technicians to connect together fibers where both sides are transmitting light, which is counter-intuitive. This complexity is not present in the SWDM solution. Additionally, SWDM solutions can use optical test equipment that runs at standard per-lane data rates.