100G Optical Module Structure

100G optical modules achieve 100 Gbps throughput using multi-lane architectures, advanced modulation, and wavelength multiplexing within compact form factors like QSFP28.

Core Architecture

100G optical modules typically use a lane-based design, where multiple parallel channels aggregate to reach 100 Gbps. The most common configuration is 4×25 Gbps lanes, as seen in QSFP28 modules, where each lane transmits 25 Gbps, combining to a total of 100 Gbps . Some newer modules, like SFP56-DD or SFP112, use 2×50 Gbps lanes to achieve the same aggregate rate . Modules employ hot-pluggable form factors such as QSFP28, CFP, CFP2, and SFP-DD, which define the physical dimensions, electrical interfaces, and connector types . QSFP28 is widely used in data centers due to its high port density, low power consumption, and compact size .

Modulation and Transmission Techniques

100G modules use modulation schemes to encode data efficiently:

• NRZ (Non-Return to Zero): Traditional binary signaling, used in early 100G modules.
• PAM4 (Pulse Amplitude Modulation 4-level): Doubles the data rate per lane by encoding two bits per symbol, reducing the number of required lanes and fibers .
• Coherent modulation: Used in long-haul or high-capacity links for improved signal integrity. Modules can transmit data using parallel optics (multiple fibers, one per lane) or wavelength division multiplexing (WDM), where multiple wavelengths share a single fiber. For example:
• CWDM4: Uses four wavelengths (1270, 1290, 1310, 1330 nm) on a single-mode fiber with uncooled DFB lasers and thin-film filter multiplexers .
• LR4: Uses LAN-WDM with four channels and EML lasers for longer distances, typically more expensive than CWDM4 .
• PSM4: Parallel single-mode fiber with four independent lasers, optimized for medium-distance interconnects .

Optical Components

Key components inside a 100G module include:

• Laser arrays: VCSELs for multimode fiber or DML/EML for single-mode fiber.
• Photodetector arrays: Convert optical signals back to electrical signals.
• MUX/DEMUX devices: Combine or separate multiple wavelengths in WDM modules.
• Electrical interface circuitry: Ensures compliance with IEEE 802.3 standards and supports high-speed signal integrity .

Summary

The 100G optical module architecture combines:

• Multi-lane electrical design (4×25 Gbps or 2×50 Gbps)
• Advanced modulation (NRZ, PAM4, coherent)
• Parallel or WDM optical transmission
• Compact, hot-pluggable form factors (QSFP28, CFP, SFP-DD) This architecture allows scalable, high-density, and cost-effective 100G connectivity for data centers, enterprise networks, and service provider applications .