Laser Selection for 400G to 1.6T Optical Modules: Single Mode vs Multimode Technology

The rapid growth of AI data centers, cloud computing, and high-performance computing is driving optical communication networks from 400G toward 800G and 1.6T. As transmission speeds continue increasing, the selection of optical laser technology has become one of the most important factors affecting optical module performance, cost, power consumption, and scalability.

From VCSEL-based multimode solutions to EML, DML, and silicon photonics-based single-mode solutions, “Made in China” and “Not in China” laser technologies are being talked for different transmission distances and application scenarios.

This article explains the key differences between single-mode and multimode laser technologies and analyzes how laser selection, including the originals impacts the development of 400G, 800G, and 1.6T optical modules.

1. The Evolution of Optical Module Laser Technology

1.1 From 100G to 400G: The Beginning of PAM4 Optical Communication

The transition from 100G to 400G optical modules introduced PAM4 modulation technology, which significantly improved transmission efficiency by transmitting two bits per symbol.

400G optical modules typically use:

• VCSEL for short-distance multimode applications

• DR4 single-mode DFB s

• FR4/LR4 solutions using EML

The industry began moving from traditional NRZ modulation toward PAM4-based high-speed optical transmission.

1.2 800G and 1.6T Drive New Laser Requirements

As AI clusters continue expanding, bandwidth requirements are increasing rapidly in 2026. 800G and 1.6T optical modules require higher-performance lasers with:

• Higher modulation speed

• Lower power consumption

• Better signal integrity

• Higher reliability

Laser selection has become a key technology decision in next-generation optical interconnect architectures.

2. Single Mode vs Multimode Optical Technology

2.1 Multimode Fiber and VCSEL Laser Technology

Multimode optical solutions typically use VCSEL (Vertical Cavity Surface Emitting Laser) technology combined with multimode fiber (MMF). Chinese makers like Sanan® are becoming competitors to Coherent® and Macom®.

VCSEL advantages include:

• Low manufacturing cost

• Low power consumption

• 100Gbps PAM4 / ch, High-speed modulation capability

Suitable for short-distance data center links

Typical applications:

• 100G SR4

• 200G SR4

• 400G SR4/ SR8

• 800G SR8

2.2 Single Mode Fiber and Advanced Laser Technology

Single-mode optical solutions use single-mode fiber (SMF) combined with advanced laser sources such as EML, DML, and silicon photonics lasers. The best Chinese vendor is YuanJie®

Advantages include:

• Longer transmission distance

• Higher bandwidth capability

• Better scalability for future networks

• Lower transmission loss

Typical applications:

• 400G DR4/ FR4/ LR4

• 800G DR8/ FR8/ LR8

• 1.6T DR8/ FR8

Core Differences of VCSEL & DFB/EML

3. Future Trend: Optical Interconnect Moving Toward Higher Integration

The future development of optical modules will not only focus on increasing transmission speed but also improving integration efficiency.

The evolution path is:

• 400G Pluggable Optical Module

• 800G High-Speed Optical Module

• 1.6T Optical Module

• CPO Optical Engine

• Optical I/O Architecture

As AI computing continues expanding, optical technology will gradually move closer to computing chips, requiring more advanced laser solutions.

4. C-LIGHT High-Speed Optical Connectivity Solutions

C-LIGHT provides advanced optical connectivity solutions supporting the evolution from 400G to 1.6T optical networks.

• 400G Optical Transceiver

• 800G Optical Transceiver

• 1.6T Optical Connectivity Solution

• DAC, AOC and AEC ACC Interconnect Products

By combining advanced optical components and high-speed transmission technologies, C-LIGHT supports next-generation AI data center and cloud networking infrastructure.

5.FAQ: 400G to 1.6T Optical Module Laser Selection