Issue link: https://www.e-digitaleditions.com/i/1066130
52 I ICT TODAY 100G-CWDM4 100G-PSM4 400G-FR4 (CWDM) 400GBASE-DR4 (PSM4) Standard CWDM4 MSA 100G PSM4 MSA 100G-Lambda MSA IEEE Reach 2 km 500 m 2 km 500 m Link Budget 8.0 dB 6.2 dB 7.8 dB 6.5 dB Center Wavelength L0: 1270.5 nm L1: 1290.5 nm L2: 1310.5 nm L3: 1330.5 nm L0 - L3: 1310 nm L0: 1270.5 nm L1: 1290.5 nm L2: 1310.5 nm L3: 1330.5 nm L0 - L3: 1311 nm Wavelength Tolerance 13 nm 30 nm 13 nm 13 nm Channel Spacing 7 nm N/A 7 nm N/A Max. TDP 3.0 dB 2.9 dB 3.8 dB 3.5 dB Return Loss per Connector 26 dB 26 dB 38 dB 45 dB TABLE 1: Summary of the 100 Gb and 400 Gb optical transceiver specifications based on CWDM4 and PSM4 architectures. These two broadly classified architectures have opposing effects on the cost of cabling and connectivity required. The parallel optics based architecture requires multiple fibers for transmit and receive directions, thus needing multi-fiber push on connectors (MPOs). The WDM architectures are relatively simpler from a cabling and connectivity perspective, since they only need two fibers and rely on duplex-LC connectors for typical data center installations. By comparing these two architectures with respect to their power budget, total cost of ownership (where the cost of cable, connectivity, and transceiver is considered), and the cost of a link in terms of $/Gb/s, ICT designers, installers, and project managers can gain valuable insight into the cost of deploying 100 Gb and 400 Gb links—vital information for choosing the right optical fiber architecture based on the end-user's migration plans. OPTICAL FIBER ARCHITECTURES When considering the 4-lane parallel singlemode fiber-based architecture, a PSM4 based device is used; each of the four lower speed electrical signals modulate the intensity of a laser, typically emitting around 1300 nm. In a PSM4 device, all four lasers operate at the same center wavelength and, consequently, do not have wavelength diversity. The four optical channels are carrying over independent fiber paths and are multiplexed into a 12-fiber MPO connector. On the receive end, four receive optical fibers carry the optical signals from the other end of the link and are converted back to electrical signals in the optical receiver unit. Devices based on CWDM4 technology for the 4-lane coarse wavelength division multiplexing architecture have lasers operating at different wavelengths. These modulated optical signals with wavelength diversity are multiplexed into a single optical fiber using a multiplexer. At the receive end, the multiple optical channels received are de-multiplexed using a de-multiplexer and then converted back to their native electrical format. Since the CWDM4 devices only need two fibers, one for transmit and one for receive, they use a Duplex-LC connector. Table 1 summarizes the differences between optical transceivers based on these two architectures for both 100 Gb and 400 Gb. In a PSM4 device, all four lasers operate at the same center wavelength and, consequently, do not have wavelength diversity.