& cplSiteName &

Wavelength Division Multiplexing (WDM)

Light Reading
Beginners' Guides
Light Reading
8/2/2001
50%
50%

Before reading this you may find the following tutorials useful:
Optical Networks, Optical Fiber

As an optical network consists of optical fibers carrying flashes of light from a laser, you can improve the speed of information transfer by increasing the number of laser light flashes per second (increasing the bit-rate). However, a point comes at which the technology of lasers cannot meet the demands of an optical network. Just as with the lone, dirty old man that flashes at passersby in the park — he can only flash so fast. But what if this man were to invite a group of his dirty old friends? Now they could all flash at the same time and vastly increase the amount of information they are transmitting to the innocent people walking by.

In an optical network, you can increase the number of lasers and have them all sending their light down the optical fiber at the same time. However, there is a catch. If the dirty old man and his friends were all wearing the same color of trench coat, then people would not be able to distinguish the different sources of information. So each flasher would need to have his own color of trench coat, to make sure that his information is not confused with that of the others. Similarly, all the different lasers must give out different colors (different wavelengths) of light so that their information can be separated at the other end of the network. The sending of many different wavelengths down the same optical fiber is known as Wavelength Division Multiplexing (WDM).

Modern networks in which individual lasers can transmit at 10 Gigabits per second can now have several different lasers each giving out 10 Gbit/s through the same fiber at the same time. The number of wavelengths is usually a power of 2 for some reason. So WDM systems will use two different wavelengths, or 4, 16, 32, 64, 128, etc. Systems being deployed at present will usually have no more than maybe 32 wavelengths, but technology advancements will continue to make a higher number of wavelengths possible.

Wavelength Division Multiplexing

The act of combining several different wavelengths on the same fiber is known as multiplexing. At the receiving end, these wavelengths need to be separated again, which is known, logically enough, as demultiplexing. Each wavelength will then need its own light detector to convert it back into useful information.

A WDM System

The exact wavelengths of light being used are usually around the 1550 nanometer region, the wavelength region in which optical fiber performs the best (it has very “low loss” or “low attenuation” at this wavelength). Each different wavelength will be separated by a multiple of 0.8nm (sometimes referred to as “100GHz spacing,” which is the frequency separation; or as the “ITU-Grid,” named after the standards body that set the figure). So if you have four wavelengths you may have them at 1549.2nm, 1550nm, 1550.8nm, and 1551.6nm. However, you could also separate each by 1.6nm, or even 2.4nm, as long as it is some multiple of 0.8nm. Newer designs that aim to cram even more wavelengths into an even tighter space, may even have half the regular spacing (0.4nm) or a quarter (0.2nm). There can be problems with wavelengths spreading out (known as dispersion) and affecting neighboring wavelengths; so this and other more complicated issues need to be considered carefully when designing a WDM system.

Key Points

  • Increases capacity of optical fibers
  • Different wavelength lasers each transmitting at same time down same fiber
  • 'Multiplexing' is combining wavelengths; 'demultiplexing' is splitting wavelengths
  • Usually in powers of 2 — 2, 4, 8, 16, 32, 64, 128, etc. wavelengths
  • Wavelengths separated by multiples of 0.8nm (100GHz, ITU-Grid)


Further Reading

Laser Basics, Tunable Lasers, Nonlinear Effects, Optical Amplification
(149)  | 
Comment  | 
Print  | 
Newest First  |  Oldest First  |  Threaded View        ADD A COMMENT
Page 1 / 15   >   >>
rubyliu
50%
50%
rubyliu,
User Rank: Light Beer
5/29/2014 | 4:05:26 AM
re: Wavelength Division Multiplexing (WDM)
In fiber-optic communications, wavelength-division multiplexing (WDM) is a technology which multiplexes a number of optical carrier signals onto a single optical fiber by using different wavelengths (colours) of laser light. This technique enables bidirectional communications over one strand of fiber, as well as multiplication of capacity.@fiberstore.com
zataki
50%
50%
zataki,
User Rank: Light Beer
12/5/2012 | 3:27:28 AM
re: Wavelength Division Multiplexing (WDM)
Another option for this is to have a WDM coupler such as a 1310/1550 coupler. with this device it does not matter what direction the traffic is travelling in. The TX and RX can easily co-exist on the same fiber.
tony33
50%
50%
tony33,
User Rank: Light Beer
12/5/2012 | 1:19:32 AM
re: Wavelength Division Multiplexing (WDM)
test
alvind
50%
50%
alvind,
User Rank: Light Beer
12/5/2012 | 1:12:31 AM
re: Wavelength Division Multiplexing (WDM)
If I send different wavelength lasers from either ends on the same fibre simultaneousely, will it be possible to recover them on the other sides using refraction or something ?
PO
50%
50%
PO,
User Rank: Light Beer
12/5/2012 | 1:12:18 AM
re: Wavelength Division Multiplexing (WDM)
You'll want to look into a device called an optical circulator.

From one website's description, an "optical circulator is a multi-port passive device, which routes one incoming optical signal from port 1 to port 2 and another signal from port 2 to port 3."

Port 2 is the rx/tx multiplex port; port 1 is tx, port 3 is rx.

Is this what you intended?
lightmaniac
50%
50%
lightmaniac,
User Rank: Light Beer
12/4/2012 | 11:04:20 PM
re: Wavelength Division Multiplexing (WDM)
L=C/F is a hyperbola function, so by any means there is no such linear relationship between delta L and delta F. If we apply differential of F on both sides, we can get dL/dF = -c/F^2 = -L^2/c.

This means the channel spacing is around 0.78nm at wavelength of 1530nm, and 0.81nm at wavelength of 1560nm.
dwdm2
50%
50%
dwdm2,
User Rank: Light Beer
12/4/2012 | 10:54:00 PM
re: Wavelength Division Multiplexing (WDM)
Apparently this thread died before I spotted. However, it raised my curiosity enough to jump in even this late.

I tried to do the calculation in the following way. The basic formula that relates the frequency, f, wavelength, l, speed of light, c, and refractive index of propagating medium, n, is

nfl = c ....... (1)

Where, c = 299792.458 THz.nm.

Also, ITU grid frequeny is given by,

f_N = 190.000 + 0.1*N (THz), N = 0, 1, 2, ...
(2)
where, N is a given ITU channel number.

For N=0, the wavelength from Eq. (1) can be found to be,

l = c/f = 1577.855 nm (ITU # 0)... (3)

Eq. (3) produces correct value of wavelengths corresponding to each ITU frequency. For 100 MHz (0.8nm) channel spacing, one then expects to be able to write Eq. (2) in terms of ITU wavelength as

l_N = 1577.855 + 0.8N, N = 0, 1, 2, ....
(4)

However, that is not the case! If you compute the wavelengths using Eq. (4), they do not correspond to the ITU grid wavelenths! In fact if you compute delta-l from the values obtained from Eq. (3), youGÇÖll find that at ITU #1, delta-l = 0.83 and it is only ~ 0.77 at the other edge of C-band. This matches with lightmanicGÇÖs analysis.

Regards,

AR
dwdm2
50%
50%
dwdm2,
User Rank: Light Beer
12/4/2012 | 10:52:54 PM
re: Wavelength Division Multiplexing (WDM)
In fact if one plots the delta-l vs. ITU channel#, it can be expressed as

delta-l = 0.83 - 0.0008*N (nm), N is an ITU channel#.

This shows that, delta-l = 0.8 nm only at ITU# 36.

However, most 100GHz systems have a passband of only +/- 0.1 nm (i.e., 25 GHz). So even 0.75 nm channel spacing is not bad, there is plenty of room.

Can anyone comment on 50 GHz or 25 GHz systems. Is there an ITU definition for these spacing?

Thanks.
debasish71
50%
50%
debasish71,
User Rank: Light Beer
12/4/2012 | 10:49:39 PM
re: Wavelength Division Multiplexing (WDM)
What is the maximum electrical speed that can be transported over the fibre without resorting to WDM?Suppose the signal to be transported over the fibre exceeds that value; how can it be a candidate for WDM? because, it still is a single electical signal, it is not a bunch of signals having varying speeds.. so that each signal can be converted to the optical context by parellel lasers and can be input to a DWM box which can mux them?If DWM is normally the mux of 32 signals, what is this value for DWDM?
Thanks,
dwdm2
50%
50%
dwdm2,
User Rank: Light Beer
12/4/2012 | 10:48:50 PM
re: Wavelength Division Multiplexing (WDM)
debasish71:

What is the maximum electrical speed that can be transported over the fibre without resorting to WDM?
-------

Well, debasish71, fiber does not transport electrical signal. Perhaps someone can/would try to explain if you try to rephrase/ask a question.
Page 1 / 15   >   >>
From The Founder
NFV's promises of automation and virtualization are intriguing, but what really excites service providers is the massive amount of money they could save.
Flash Poll
Live Streaming Video
Charting the CSP's Future
Six different communications service providers join to debate their visions of the future CSP, following a landmark presentation from AT&T on its massive virtualization efforts and a look back on where the telecom industry has been and where it's going from two industry veterans.
Women in Comms Introduction Videos
VMWare VP Brings Women Up With Her

8|16|17   |   6:49   |   (1) comment


It's an art and a science to make mentorship, inclusive leadership, diversity and promotion of high-potential women work, says Honore' LaBourdette, vice president of Global Market Development at VMWare.
LRTV Documentaries
5G Spectrum Wars – The Recap

8|15|17   |   2:22   |   (0) comments


Service provider 3 has filed a lawsuit against Ofcom over 5G spectrum auction in the UK.
LRTV Custom TV
Say What? Facebook Unleashes AI Anarchy – The Recap

8|7|17   |     |   (0) comments


A recap of the week's talking points on Light Reading's sister site, telecoms.com. Facebook AI programmers had a bit of a brain-fade as they allowed one of its AI applications to invent its ...
Women in Comms Introduction Videos
Fujitsu's Women Band Together to Help Girls Do STEM

8|2|17   |   9:35   |   (1) comment


Supporting women both inside and outside of Fujitsu is a top priority of the telecom vendor. Yanbing Li, Fujitsu Network Communication's director of System Software Development & Delivery, shares why it's important, but why there's still a long road ahead.
LRTV Custom TV
If You're Not First, You're Last – The Recap

7|31|17   |   08:18   |   (1) comment


In case you missed it, Amazon's 1% stock increase helped Jeff Bezos dethrone Bill Gates as the richest man in the world. Also, Taiwanese electronics manufacturer
Women in Comms Introduction Videos
AT&T's Tech President Preps Workforce for the Future

7|26|17   |   5:47   |   (10) comments


AT&T is focused on the software-defined network of the future and is reskilling its workforce to get ready too, according to AT&T's President of Technology Development Melissa Arnoldi.
Women in Comms Introduction Videos
Cisco: Mentoring Critical to Attract & Retain Women

7|19|17   |   6:40   |   (1) comment


Liz Centoni, senior vice president and general manager of Cisco's Computing System Product Group, shares why mentoring in all its forms is important for women and what Cisco is doing that's made a difference for women in tech.
LRTV Custom TV
Gigabit LTE With Snapdragon 835

7|12|17   |     |   (1) comment


At an event in Wembley stadium, EE used its live network to demonstrate gigabit LTE using a Sony Xperia XZ Premium smartphone with a Qualcomm Snapdragon 835 chip.
LRTV Custom TV
Implementing Machine Intelligence With Guavus

7|12|17   |     |   (0) comments


Guavus unites big data and machine intelligence, enabling many of the the largest service providers in the world to save money and drive measureable revenue. Learn how applying Machine Intelligence substantially reduces operational costs and in many cases can eliminate subscriber impact, meaning a better subscriber experience and higher NPS.
LRTV Custom TV
Unlocking Customer Experience Insights With Machine Intelligence

7|12|17   |     |   (0) comments


When used to analyze operational data and to drive operational decisions, machine intelligence reduces the number of tasks which require human intervention. Guavus invested in Machine Intelligence early. Learn about the difference between Machine Learning and Machine Intelligence.
Women in Comms Introduction Videos
Verizon VP Talks Network, Career Planning

7|12|17   |   4:49   |   (0) comments


Heidi Hemmer, vice president of Technology, Strategy & Planning at Verizon, shares how bold bets and the future of tech define her career.
Telecom Innovators Video Showcase
Masergy's NFV Journey

7|11|17   |     |   (0) comments


Ray Watson, vice president of global technology at Masergy, discusses the advantages and challenges in entering the still-maturing NFV market for the past three years.
Upcoming Live Events
September 28, 2017, Denver, CO
October 18, 2017, Colorado Convention Center - Denver, CO
November 1, 2017, The Royal Garden Hotel
November 1, 2017, The Montcalm Marble Arch
November 2, 2017, 8 Northumberland Avenue, London, UK
November 30, 2017, The Westin Times Square
All Upcoming Live Events
Infographics
With the mobile ecosystem becoming increasingly vulnerable to security threats, AdaptiveMobile has laid out some of the key considerations for the wireless community.
Hot Topics
Intel CEO Leaves Trump Biz Advisory Board
Dan Jones, Mobile Editor, 8/15/2017
Are Cord-Cutting's Days Numbered?
Alan Breznick, Cable/Video Practice Leader, Light Reading, 8/14/2017
Analyst Nolle: Fundamental Errors Plague NFV
Carol Wilson, Editor-at-large, 8/11/2017
Verizon Video Woes Pile On
Mari Silbey, Senior Editor, Cable/Video, 8/14/2017
Orchestration Startup UBiqube Pivots Away From NFV
Carol Wilson, Editor-at-large, 8/15/2017
Like Us on Facebook
Twitter Feed
Animals with Phones
We Know a Tough Day When We See One Click Here
Live Digital Audio

Understanding the full experience of women in technology requires starting at the collegiate level (or sooner) and studying the technologies women are involved with, company cultures they're part of and personal experiences of individuals.

During this WiC radio show, we will talk with Nicole Engelbert, the director of Research & Analysis for Ovum Technology and a 23-year telecom industry veteran, about her experiences and perspectives on women in tech. Engelbert covers infrastructure, applications and industries for Ovum, but she is also involved in the research firm's higher education team and has helped colleges and universities globally leverage technology as a strategy for improving recruitment, retention and graduation performance.

She will share her unique insight into the collegiate level, where women pursuing engineering and STEM-related degrees is dwindling. Engelbert will also reveal new, original Ovum research on the topics of artificial intelligence, the Internet of Things, security and augmented reality, as well as discuss what each of those technologies might mean for women in our field. As always, we'll also leave plenty of time to answer all your questions live on the air and chat board.