Both 100G CWDM4 (Coarse Wavelength Division Multiplexing 4) and 100G LR4 (Long-Range 4) are optical transceiver modules designed for 100 Gigabit Ethernet (100GbE) applications, but they use different technologies for achieving high-speed data transmission. Here are the key differences between 100G CWDM4 and 100G LR4: 

1. Wavelengths and Multiplexing:

• 100G CWDM4: CWDM4 uses Coarse Wavelength Division Multiplexing, which means that it uses four separate wavelengths for transmitting and receiving data. These wavelengths are typically spaced at intervals of 20nm. CWDM4 is designed to operate over single-mode fiber.

• 100G LR4: LR4, on the other hand, uses a single wavelength for both transmitting and receiving data. The LR4 module operates over four lanes (channels) on a single strand of single-mode fiber, each operating at a different wavelength.

2. Optical Multiplexing and Demultiplexing:

• 100G CWDM4: CWDM4 requires additional optical multiplexing and demultiplexing components to combine and separate the four wavelengths. This increases the complexity of the optical system but allows for the use of fewer fibers.

• 100G LR4: LR4 uses a simpler point-to-point link without the need for wavelength multiplexing/demultiplexing components. Each of the four channels operates independently at a specific wavelength.

3. Fiber Type:

• 100G CWDM4: CWDM4 is typically designed to operate over single-mode fiber (SMF).

• 100G LR4: LR4 is also designed to operate over single-mode fiber.

4. Reach:

• 100G CWDM4: CWDM4 is designed for shorter-reach applications, typically with a reach of around 2 kilometers (km) to 10 km, depending on the specific implementation and the quality of the fiber infrastructure.

• 100G LR4: LR4 is designed for longer-reach applications, with a reach of up to 10 km or more.

5. Use Cases:

• 100G CWDM4: CWDM4 is often used in scenarios where wavelength multiplexing can be beneficial, and shorter reach is acceptable, such as data center interconnects.

• 100G LR4: LR4 is suitable for applications that require longer reach, such as connections between data centers or metro networks.

In summary, the primary differences between 100G CWDM4 and 100G LR4 lie in their wavelength and multiplexing schemes, reach capabilities, and the complexity of the optical systems they require. The choice between the two depends on the specific requirements of the network and the desired reach for the given application.