Free tools Windows power users keep installed
One-click scans. No signup required.
Coarse wavelength division multiplexing (CWDM) lets multiple optical channels share a fiber by sending each on a different wavelength. Under the current ITU-T grid, those channels are spaced 20 nm apart, with nominal center wavelengths from 1271 nm to 1611 nm. “Coarse” refers to this relatively wide spacing compared with dense wavelength division multiplexing (DWDM), not to a different kind of fiber.
How CWDM works
A CWDM system assigns separate wavelengths to optical channels traveling along the same fiber. A multiplexer combines the channels at the transmitting end; a demultiplexer separates them at the receiving end. In this way, one optical path can carry multiple clients, services, or protocols without assigning each a separate fiber.
As an Amazon Associate I earn from qualifying purchases.
The ITU-T overview describes CWDM use in metropolitan-area transport networks and discusses multichannel interfaces and mux/demux connections. It also gives examples of 4-, 8-, 12-, and 16-wavelength applications, including unidirectional and bidirectional arrangements over a single fiber. These are examples, not a guarantee that a particular link or device supports every configuration. ITU-T G.695 overview
The ITU-T CWDM wavelength grid
ITU-T Recommendation G.694.2 defines the CWDM wavelength grid. Its current edition is the December 2003 edition, which is listed as in force; the earlier June 2002 edition is superseded. The recommendation specifies 20 nm spacing and nominal center wavelengths from 1271 nm through 1611 nm. ITU-T G.694.2
#1 Best Overall
- 40GBASE-LR4 QSFP+ to LC Optical 40G Ethernet transceiver module, SingleMode, 4 CWDM lanes in 1310nm window Muxed inside module, Duplex LC connector, DDM, 10km, 40G Ethernet rate only
- Wide Compatibility - Juniper JNP-QSFP-40G-LR4 and other Open Switches. Compliant to the IEEE 802.3ba standard, SFF 8436 and QSFP Multisource Agreement
- Easy to Use - Easy installation, plug and play, fully hot-pluggable. Widely used in fiber switches, routers, NIC, server or other fiber optic equipments with 40Gb QSFP+ ports
- Superior DDM Function - DDM allows you to monitor the critical information concerning the status of the transmitted and received signals of the transceivers in real-time to find out some potential problems
- 10Gtek is a manufacturer of transceiver, customized service is available
| Grid characteristic | Value |
|---|---|
| Channel spacing | 20 nm |
| First nominal center wavelength | 1271 nm |
| Last nominal center wavelength | 1611 nm |
| Grid positions across the stated range | 18, counted from the endpoints at 20 nm intervals |
The 2003 edition shifted the nominal grid by 1 nm from the earlier edition to align with industry practice while maintaining symmetrical nominal central wavelength deviations. The 18 positions describe the standard grid; they do not mean a deployed link uses all of them. The recommendation defines wavelengths, not the reach or throughput of a particular system.
Why the spacing is called “coarse”
CWDM channels are farther apart than DWDM channels. The ITU links this wider spacing to relaxed transmitter wavelength-selection tolerances and wide-passband filters, and identifies uncooled lasers as part of the rationale for cost-effective CWDM applications. These are design characteristics, not a promise that every CWDM installation costs less than every DWDM installation. ITU-T G.694.2
Rank #2
- 【QSFP+ 40G】 Cisco QSFP-40G-UNIV 40Gigabit Ethernet, coding as Cisco QSFP-40G-UNIV also compatible
- 【40GBASE-UNIV】40G QSFP+ transceiver module, 40Gbps, single mode and multimode 4 CWDM 1310nm 2km/150m SMF/MMF , LC duplex connector, Hot Pluggable, support DOM
- 【How 40G UNIV works】SMF with transmission distances of up to 150m on MMF (OM3) and 2km,on SMF. The module converts 4 inputs channels (ch) of 10Gb/s electrical data to 4 CWDMNoptical signals, and multiplexes them into a single channel for 40Gb/s optical transmission.Reversely, on the receiver side, the module optically de-multiplexes a 40Gb/s input into 4CWDM channels signals, and converts them to 4 channel output electrical data
- 【Protocols】Compliant with QDR/DDR Infiniband data ratesUp to 150m transmission on OM3 multimode fiber (MMF) or 2km transmission on single mode fiber (SMF), IEEE 802.3ba, MSA Compliant
- 【3 Warranty】30-Days Free-returned, 65-Days Free-replacement 5-Years Free-maintenance
Actual cost, capacity, and reach depend on the optical interfaces, equipment, and application. The wavelength-grid recommendation does not establish a universal distance or aggregate data rate.
The Tool Desk
Outbyte PC Repair FREEClear out junk files and repair common Windows errorsFree Scan →Outbyte Driver Updater FREEFix the driver behind crashes, sound loss and screen glitchesFind Drivers →What to check when considering CWDM
The grid alone is not enough to determine whether a CWDM system will work for a particular link. Check the requirements for the intended application and the specifications of the equipment at both ends.
Rank #3
- 100% Guaranteed Compatibility in all OEM applications
- Fully compliant with the multi-sourcing agreement (MSA) which enables them to work in all MSA compliant platforms
- OC-3/STM-1 1510nm CWDM SFP Transceiver for Cisco
- Wavelength plan: Confirm that the transmitters and mux/demux support the same channel wavelengths.
- Channel count and services: Match the available channels to the clients, protocols, and services the link needs to carry.
- Optical interfaces: Verify transmitter wavelength tolerances and filter passbands against the system requirements.
- Physical link: Check the link budget and required reach for the actual fiber path and interfaces; G.694.2 does not settle these values.
- Hardware fit: For a CWDM mux/demux, confirm channel count, wavelength plan, connectors, fiber type, and compatibility with the intended application.
ITU-T discusses vendor interoperability at the interface level, but that should not be read as a guarantee that arbitrary commercial products or link designs are compatible. ITU-T G.695 overview
Quick Recap
Best Value
- 40GBASE-LR4 QSFP+ to LC Optical 40G Ethernet transceiver module, SingleMode, 4 CWDM lanes in 1310nm window Muxed inside module, Duplex LC connector, DDM, 10km, 40G Ethernet rate only
- Wide Compatibility - Intel E40GQSFPLR and other Open Switches. Compliant to the IEEE 802.3ba standard, SFF 8436 and QSFP Multisource Agreement
- Easy to Use - Easy installation, plug and play, fully hot-pluggable. Widely used in fiber switches, routers, NIC, server or other fiber optic equipments with 40Gb QSFP+ ports
- Superior DDM Function - DDM allows you to monitor the critical information concerning the status of the transmitted and received signals of the transceivers in real-time to find out some potential problems
- 10Gtek is a manufacturer of transceiver, customized service is available
Rank #4
- 【Dual SFP+ Slots | Fiber-to-Fiber 10G OEO Repeater】Long-Distance Optical Extension Equipped with 2 hot-pluggable SFP+ slots to work as a 10G fiber repeater for fiber-to-fiber transmission up to 80km. It extends backbone links for MAN, SAN and data center networks, operating reliably at -40°C to 80°C (-40°F ~ 176°F) in industrial harsh environments. Full LED indicators display real-time port connection status for easy inspection.
- 【1x Gigabit RJ45 Port | Fiber-to-Copper Media Converter】Dual-Purpose All-in-One Unit When matching one SFP+ fiber port with the RJ45 copper port, it converts 1Gbps fiber signal to Ethernet copper signal, supporting transmission up to 120km over single-mode fiber. This dual-design eliminates the need to buy two separate converters, cutting hardware costs for surveillance, campus and factory LAN deployments.
- 【Professional 3R Signal Regeneration Function】Ultra-Low Latency Stable Transmission Integrated complete 3R functions (Regeneration, Reshaping, Re-timing) to recover attenuated long-distance optical signals without distortion, delivering transparent forwarding with ultra-low latency. It supports hot-swap SFP+ modules, ideal for continuous 24/7 core network operation without shutdown during maintenance.
- 【Rich Optical Test & Rate Switch Features】Flexible Wavelength Compatibility Supports 1310nm/1550nm, CWDM and DWDM optical modules with built-in DDM digital diagnostic for real-time optical power monitoring. It provides loopback test for fast on-site fault troubleshooting and jumbo frame support. The 4-digit DIP switch lets you switch between 1.25G and 10G fiber rates to match diverse network devices.
- 【Industrial-Grade Rugged Protection & Full Certifications】Dual Mount for All Scenarios Compact IP40 dustproof aluminum housing supports DIN-Rail and wall mounting. It adopts 12~48VDC dual redundant power input with overload auto-reset, reverse polarity defense and 6KV lightning surge protection compliant with IEC61000 EMC standards. With >200,000 hrs MTBF, max 8W low power consumption and CE/FCC/RoHS/ISO9001 certifications, widely used in telecom rooms, data centers, highway monitoring and lab testing projects.
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
