Selecting the right 40G QSFP+ optical module is crucial for optimizing data center network performance, controlling costs, and ensuring smooth upgrades. Below, I’ll introduce common 40G QSFP+ optical module types and provide practical advice on selecting one based on your network needs.
Contents
Basic Concepts and Working Principles
The 40G QSFP+ (Quad Small Form-factor Pluggable) optical module is a high-performance optical transceiver that supports data transmission rates up to 40Gbps. This module achieves high-speed data transmission by simultaneously utilizing multiple channels, each typically operating at 10Gbps, for a combined total bandwidth of 40Gbps.
The module integrates four independent transmit and receive channels, achieving high-speed data transmission through parallel optics technology. Compared to traditional UTP copper cable solutions, the optical transceiver consumes less power (typically 1W or less) and generates less heat, helping to reduce overall data center operating costs.
Comparison of Major 40G QSFP+ Optical Transceiver Types
SR4 Series: High-Density Short-Range Solution
40GBASE-SR4 is the most common short-haul 40G solution, utilizing an 850nm VCSEL (Vertical Cavity Surface-Emitting Laser) array and MPO/MTP connectors. This module implements a high-bandwidth 40G optical link using a 12-fiber ribbon cable, with four fibers dedicated to transmit and four fibers dedicated to receive, and the middle four fibers typically unused
A key advantage of the SR4 module is its support for breakout applications. Using MTP-to-LC breakout cables, a single 40G SR4 module can be connected to four 10G SR optical interfaces, achieving efficient port utilization. This feature makes SR4 ideal for leaf-spine network architectures and high-speed server connectivity.
LR4 Series: Long-Haul Transmission Option
40GBASE-LR4 is designed for longer-haul data transmission, up to 10 kilometers. It utilizes wavelength division multiplexing technology, concentrating four wavelengths near the 1310nm window for transmission over a single single-mode fiber. There are also 20km version 40GBASE-LR4 QSFP+, for instance, QSFPTEK QT-QSFP+-LH4 is equipped with LC duplex connectors, reaching a link up to 20km over OS2 single-mode fiber (SMF).
Unlike SR4, LR4 modules use duplex LC connectors, significantly simplifying fiber management. These modules are typically equipped with DFB (distributed feedback) lasers and consume slightly higher power, typically no more than 3.5W. They are suitable for data center interconnects, campus network backbones, and telecommunications transmission scenarios.
BiDi Series: A Cost-Effective Migration Solution
40G BiDi (bidirectional) optical modules are an innovative solution that uses wavelength division multiplexing technology to enable bidirectional communication over a single multimode fiber using different wavelengths (typically 850nm and 900nm).
The core advantage of BiDi modules is their ability to leverage existing 10G LC cabling infrastructure for 40G network upgrades. This contrasts sharply with SR4 modules, which require the use of MPO/MTP cables, increasing migration costs. For enterprises with significant investments in LC cabling, BiDi offers a highly cost-effective migration path.
Key Factors in Selecting a 40G QSFP+ Optical Module
Transmission Distance Requirements
Determining your link length requirements is the first step in selecting the appropriate module. For short-distance connections (≤150 meters) within a computer room or data center rack, SR4 or BiDi multimode modules are the most economical choice. For medium-distance connections (up to 300 meters), the SR4 eXtended model may be suitable. For longer distances (up to 10 kilometers), the LR4 single-mode module should be selected.
Existing Fiber Infrastructure
It is crucial to evaluate your current fiber cabling resources. If your network primarily uses duplex LC multimode fiber, BiDi modules can seamlessly utilize your existing infrastructure. If you already have or plan to deploy an MPO/MTP cabling system, the SR4 module is a more suitable choice.
Cost Considerations: Total Cost of Ownership
When selecting an optical module, consider not only the initial purchase cost but also the total cost of ownership:
Initial Cost: SR4 modules generally offer a competitive purchase price, but require expensive MPO/MTP cabling.
Cabbing Cost: BiDi modules can reuse existing LC cabling, significantly reducing migration costs.
Power Consumption: Optical transceivers typically consume approximately 1W or less, significantly less than UTP transceivers (approximately 5W), reducing thermal management burdens.
Maintenance Cost: Modules with Digital Diagnostic Monitoring (DOM) functionality can simplify troubleshooting and network maintenance.
Power Consumption and Thermal Management
Power and thermal management in data centers significantly impact operating costs. Selecting low-power optical modules can significantly reduce cooling requirements and associated energy costs. Ensure that the operating temperature range (commercial grade: 0°C to +70°C; industrial grade: -40°C to +85°C) of the selected module meets your environment’s requirements.
Diagnostic and Management Capabilities
Selecting an optical module that supports Digital Diagnostic Monitoring (DOM) can significantly simplify network maintenance. The DOM feature allows administrators to monitor the module’s health in real time, including:
Operating temperature and voltage
Transmitted and received optical power
Bias current
This information helps identify potential fault points before issues impact network performance.
40G Network Deployment and Migration Solutions
Migration Paths from 10G to 40G
When upgrading from a 10G network to 40G, you have two primary options:
Option 1: Using SR4 Modules
This approach requires replacing existing LC cabling with MPO/MTP trunk cables and potentially upgrading fiber cassettes to adapter panels. While providing full 40G performance, the cost and complexity of changing the cabling infrastructure are high.
Option 2: Using BiDi Modules
This approach requires replacing only the optical modules at both ends, allowing the existing duplex LC fiber patch cords and other equipment to be reused without changing the 10G cabling layout. This is a cost-effective and minimally disruptive migration solution.
Structured and Unstructured Cabling Considerations
In unstructured cabling systems (where fiber patch cords connect directly to equipment), both SR4 and BiDi modules can be used for 40G direct connections. In structured cabling systems, SR4 solutions require more component replacement, while BiDi solutions maximize the use of existing infrastructure, significantly reducing upgrade costs and complexity.
Breakout Application Scenario
SR4 modules support splitting a 40G link into four independent 10G links, which is particularly useful for connecting older devices that don’t support 40G. This capability increases network design flexibility and allows for a gradual migration to all-40G networks.
Summary: How to Choose the Right 40G QSFP+ Optical Transceiver
Choosing the right 40G QSFP+ optical module depends on your specific network needs, existing infrastructure, and budget considerations. Here’s a quick guide to selecting the best transceiver:
For short-reach data center connections (≤150 meters) and high-density applications, consider SR4 modules.
For 10G to 40G migrations that leverage existing LC cabling, choose BiDi modules for cost savings and simplified migration.
For long-reach transmission (up to 10 kilometers) and single-mode fiber environments, LR4 modules are the right solution.
Always choose modules that support Digital Diagnostic Monitoring (DOM) to simplify network management and troubleshooting.
Evaluate the total cost of ownership, including cabling, power consumption, and maintenance requirements, rather than just the initial purchase cost of the modules.
By carefully analyzing your network needs and understanding the characteristics of different 40G QSFP+ transceiver types, you can make informed decisions, optimize network performance, and prepare for future expansion.
