LAN-WDM: Enabling High-Speed Ethernet over Optical Fiber

LAN-WDM (Local Area Network Wavelength Division Multiplexing) uses closely spaced
wavelengths, primarily in the 1310 nm O-band, to transmit multiple optical channels
over a single single-mode fiber. It has been particularly important in high-speed Ethernet
transceivers used for data centers and short- to medium-reach data center interconnects (DCI).

What Is LAN-WDM?

LAN-WDM is a wavelength plan designed for high-speed optical communication. Instead of transmitting
an entire data stream on one optical wavelength, the data is divided among multiple optical channels.
The wavelengths are then combined for transmission through a single fiber and separated at the
receiving end.

A commonly used LAN-WDM four-wavelength grid has center wavelengths near:

• 1295.56 nm
• 1300.05 nm
• 1304.58 nm
• 1309.14 nm

These wavelengths are nominally separated by approximately 800 GHz. The closely
spaced channels allow high-speed Ethernet signals to be carried over a single strand of
single-mode fiber.

How LAN-WDM Works

A typical LAN-WDM optical link consists of several basic components:

1. Optical transmitters: Multiple lasers generate signals at different wavelengths.
2. Optical multiplexer: The individual wavelengths are combined into one optical signal.
3. Single-mode fiber: The multiplexed signal travels through the fiber.
4. Optical demultiplexer: The individual wavelengths are separated at the receiver.
5. Optical receivers: Photodetectors convert the individual optical channels back
   into electrical signals.

This architecture allows a high aggregate data rate to be transmitted without requiring a separate
fiber for every optical channel.

Why Use the 1310 nm O-Band?

LAN-WDM operates near the 1310 nm O-band, where standard single-mode fiber has
relatively low chromatic dispersion. This makes the wavelength region particularly attractive for
high-speed, short- and medium-reach links where dispersion can otherwise limit transmission
performance.

The O-band is especially useful for data-center applications because it allows high-speed
intensity-modulated and directly detected (IM/DD) optical systems to operate without the complexity
of long-haul coherent transmission.

LAN-WDM and High-Speed Ethernet

LAN-WDM became particularly important with the introduction of 100GBASE-LR4,
which uses four wavelengths around 1310 nm. Similar four-wavelength architectures have been used
for higher-speed Ethernet generations.

For example, 400G optical modules can use four optical wavelengths, with each wavelength carrying
approximately 100 Gb/s. More recent 800G designs use several different optical architectures,
including four-wavelength and eight-wavelength implementations, depending on reach and application.

The important point is that not all 800G or future 1.6T transceivers use LAN-WDM.
Current designs may use single-wavelength, four-wavelength, eight-wavelength, or other architectures
depending on the required reach, fiber type, power budget, and cost. :contentReference[oaicite:1]{index=1}

LAN-WDM vs. CWDM and DWDM

CWDM uses widely separated wavelengths and relatively simple optical components. DWDM uses much
tighter wavelength spacing and can support many channels over a broad optical spectrum.
LAN-WDM occupies a different niche: it provides a small number of closely spaced wavelengths
optimized for compact, high-speed Ethernet transceivers.

LAN-WDM in Data Center Interconnects

LAN-WDM is particularly useful for data center interconnect (DCI) applications,
where large amounts of Ethernet traffic must be transported between switches, buildings, and
nearby data centers.

LAN-WDM technology has been incorporated into optical modules such as:

• 100G LR4
• 400G LR4
• 400G LR8
• 800G FR8 and other emerging multi-wavelength architectures

Modern 800G transceiver designs illustrate the increasing variety of approaches. For example,
current products include four-wavelength 2×FR4 architectures as well as eight-channel LAN-WDM
implementations.

Advantages of LAN-WDM

• High fiber utilization: Multiple optical channels can share a single fiber.
• Low chromatic dispersion: Operation near 1310 nm is well suited to high-speed
  short- and medium-reach transmission.
• Compact transceivers: Multiple optical channels can be integrated into a
  pluggable module.
• Scalability: Multiple wavelengths allow Ethernet capacity to increase without
  requiring a separate fiber for every channel.
• Cost efficiency: LAN-WDM systems can be considerably simpler than full
  long-haul DWDM systems.

The Future of LAN-WDM

As data-center and AI networking speeds continue to increase, optical transceivers are evolving
rapidly. However, there is no single optical architecture for every application.

Higher-speed systems are using a combination of approaches, including single-wavelength
transmission, LAN-WDM, CWDM, parallel optics, and coherent technology. The appropriate
solution depends on reach, power consumption, fiber count, optical budget, and transceiver cost.

LAN-WDM will therefore remain an important technology for high-speed Ethernet, particularly where
multiple wavelengths provide an efficient way to increase capacity over single-mode fiber without
the complexity of a full DWDM transport system.

Conclusion

LAN-WDM is an important optical technology for high-speed Ethernet and data-center
networking. By combining closely spaced wavelengths around the 1310 nm O-band, it allows
multiple high-speed optical channels to share a single fiber while taking advantage of the
O-band’s relatively low chromatic dispersion.

From 100G and 400G Ethernet to today’s 800G optical modules, LAN-WDM has helped enable the rapid
increase in optical bandwidth required by cloud computing, AI, and hyperscale data centers.
As Ethernet continues toward 1.6T and beyond, LAN-WDM will remain one of several important
optical architectures used to scale network capacity.