Chromatic dispersion is a phenomenon that is an important factor in optical fibre communications. It is the result of the different colors, or wavelengths, in a light beam arriving at their destination at slightly different times.

In multimode optic fibre links we have a similar problem.  Different wavelengths of light propagate at different speeds.  This material dispersion causes the light to break up and the carrier signal is lost due to this disruption.  This is why multimode optical fibre links can not travel as far as single mode fibre links.  Single mode use a single wavelength and not the full visible spectrum to transmit a signal to they do not suffer from the chromatic dispersion problem.


Chromatic dispersion is the term given to the phenomenon by which different spectral components of a pulse travel at different velocities.  To understand the effect of chromatic dispersion, we must understand the significance of the propagation constant β.  We will restrict our discussion to single mode fiber since in the case of multimode fiber, the effects of intermodal dispersion usually overshadow those of chromatic dispersion.  So the propagation constant β in our discussions will be that associated with the fundamental mode of the fiber.

Chromatic dispersion arises for two reasons.

1./ The first reason is that the refractive index of silica, the material used to make optical fiber, is frequency dependent. Thus different frequency components travel at different speeds in silica.  This component of chromatic dispersion is called material dispersion.

2./ Although material dispersion is the principle component of chromatic dispersion for most fibers, there is a second component, called waveguide dispersion.

A high-speed pulse contains a spectrum of l components. Lecture

To understand the physical origin of waveguide dispersion, we need to know that the light energy of a mode propagates partly in the core and partly in the cladding. Also that the effective index of a mode lies between the refractive indices of the cladding and the core.  The actual value of the effective index between these two limits depends on the proportion of of power that is contained in the cladding and the core.  If most of the power is contained in the core, the effective index is closer to the core refractive index; if most of it propagates in the cladding, the effective index is closer to the cladding refractive index.

The power distribution of a mode between the core and cladding of the fiber is itself a function of the wavelength.  More accurately, the longer the wavelength, the more power in the cladding.  Thus, even in the absence of material dispersion – so that the refractive indices of the core and cladding are independent of wavelength – if the wavelength changes, this power distribution changes, causing the effective index or propagation constant β of the mode to change.  This is the physical explanation for waveguide dispersion.

SM Fiber How

Therefore, the colour of light is the biggest hurtle to overcome.  The perception of colour is heavily influenced by the media and how light interacts with the media.


Fosco Connect. (2018). What is Chromatic Dispersion ? (material dispersion and waveguide dispersion). Fosco Connect. Retrieved on December 22, 2018 from,

About the Author:

Michael Martin has more than 35 years of experience in systems design for broadband networks, optical fibre, wireless and digital communications technologies.

He is a Senior Executive with IBM Canada’s GTS Network Services Group. Over the past 13 years with IBM, he has worked in the GBS Global Center of Competency for Energy and Utilities and the GTS Global Center of Excellence for Energy and Utilities. He was previously a founding partner and President of MICAN Communications and before that was President of Comlink Systems Limited and Ensat Broadcast Services, Inc., both divisions of Cygnal Technologies Corporation (CYN: TSX).

Martin currently serves on the Board of Directors for TeraGo Inc (TGO: TSX) and previously served on the Board of Directors for Avante Logixx Inc. (XX: TSX.V). 

He serves as a Member, SCC ISO-IEC JTC 1/SC-41 – Internet of Things and related technologies, ISO – International Organization for Standardization, and as a member of the NIST SP 500-325 Fog Computing Conceptual Model, National Institute of Standards and Technology.

He served on the Board of Governors of the University of Ontario Institute of Technology (UOIT) and on the Board of Advisers of five different Colleges in Ontario.  For 16 years he served on the Board of the Society of Motion Picture and Television Engineers (SMPTE), Toronto Section. 

He holds three master’s degrees, in business (MBA), communication (MA), and education (MEd). As well, he has diplomas and certifications in business, computer programming, internetworking, project management, media, photography, and communication technology.