What is the difference between grey optics and colored (WDM) optics?

Grey optics transmit on standard wavelengths (typically 1310 or 1550nm), while colored (WDM) optics use specific ITU-standardized wavelengths for multiplexing.

Grey Optics

• Standard wavelengths: 850, 1310, 1550nm
• Uncooled lasers (DFB or Fabry-Perot)
• Wavelength drifts ±10-20nm with temperature
• Cannot be multiplexed on same fiber
• Lower cost, mass produced

Colored (CWDM) Optics

• 18 specific wavelengths: 1271, 1291, ..., 1611nm
• 20nm channel spacing (ITU G.694.2)
• Uncooled lasers within CWDM tolerances
• Can multiplex via passive CWDM mux
• Slightly higher cost

Colored (DWDM) Optics

• Precise wavelengths on ITU grid (typically 100 GHz / 0.8nm)
• Fixed wavelength or tunable
• Cooled DFB lasers (TEC-stabilized)
• Enable 40-96 channels on one fiber
• Higher cost, precision components

Tunable DWDM Modules

• Software-configurable wavelength
• Single SKU covers all C-band channels
• Simplifies sparing (one module vs 96)
• Cost premium over fixed DWDM

Cost Comparison (10G LR class)

Application Guide

• Point-to-point single link: Grey optics
• Fiber-limited metro: CWDM (up to 18 channels)
• Long-haul high-capacity: DWDM
• Growing networks: Tunable DWDM

Integration with Passive Muxes

• CWDM mux: 4, 8, 16 channel typically
• DWDM mux: 8, 16, 32, 40, 48, 96 channel
• Passive muxes work without power
• Add ~2-4 dB insertion loss per side

Practical Deployment

Modern data center interconnect (DCI) often uses tunable DWDM 100G/400G modules directly in switches, eliminating traditional transponder shelves — a major cost reduction.