CWDM vs DWDM: Which Wavelength Technology to Choose?

Wavelength Division Multiplexing (WDM) lets multiple data streams travel over one fiber pair by giving each stream its own color of light, and the two mainstream flavors - Coarse WDM (CWDM) and Dense WDM (DWDM) - split the optical spectrum very differently. This article compares CWDM and DWDM on channel spacing, reach, cost and upgrade path, so you can pick the technology that matches the distance and capacity of your link instead of defaulting to whichever is more popular.

Channel Spacing: The Core Difference

CWDM follows ITU-T G.694.2 with channels spaced 20 nm apart, covering 1270-1610 nm - up to 18 channels total (9 in each direction with BiDi pairs). DWDM follows ITU-T G.694.1 with channels packed 100 GHz (~0.8 nm) or 50 GHz apart inside the C-band (and L-band) around 1550 nm, fitting 40, 88, 96 or even 160 channels onto one fiber.

Reach and the Water Peak Problem

• CWDM - up to about 70 km unamplified; between 40 and 70 km the usable channel count shrinks because the 1370-1430 nm range sits in the fiber water peak where loss reaches ~1.0 dB/km versus ~0.25 dB/km in the 1550 nm region.
• DWDM - up to 80 km unamplified and 1000+ km with amplification (EDFA, Raman), because all channels live in the low-loss 1550 nm window where erbium-doped amplifiers work best.

Cost and Deployment Reality

CWDM wins on cost and simplicity for short links and limited capacity: uncooled lasers, passive mux/demux, no amplifier planning. DWDM costs more per mux and per transceiver but buys capacity headroom - adding channels later only requires new transceivers if the mux was sized correctly. As one CTO put it, the shift is rarely a preference for DWDM over CWDM; it is capacity and distance catching up with you earlier than expected. For links where growth is likely, starting with DWDM avoids a forklift upgrade.

Comparison at a Glance

Related Reading on This Site

See DWDM basics for the dense side and the CWDM/DWDM mux principle guide for the hardware view.

原文链接：https://smartoptics.com/knowledgebank-post/cwdm-dwdm-explained/