# DWDM and other Light Spectrum Wavelengths (Nanometer vs Frequency)

Jun 22nd, 2009

Hi all,

1. What is the range of frequencies that DWDM uses. Is there a defined band of the EM spectrum where all laser/light frequencies can operate at?

2. Why do we mesaure all laser and optical light carriers as NM wavelengthsize, ie 850nn, 1310nm etc etc, and why dont we just use the term freqeuncy in Thz? After all, all other ranges within the spectrum use the primary term of frequency and not wavelength size?

Many thx indeed,

Ken

Is it the same for an optics carrier signal -The freqency and carrier waves are being generated all the time, if data is ready for transmission or not?

Yes the frequency chart you attached earlier are the DWDM frequency/wavelngth and then you modulate with data.

In Ethernet, Fast or Gig but there is no multiplexing involved as in DWDM there are many wavelngth In case of etherent only baseband signal.

For frequency for Ethernet, Fast & gig see the link

http://www.ertyu.org/steven_nikkel/ethernetcables.html

see if this is helpful too

http://www.cisco.com/en/US/docs/internetworking/technology/handbook/Ethernet.html

"A typical human eye will respond to wavelengths from about 380 to 750 nm.[1] In terms of frequency, this corresponds to a band in the vicinity of 790-400 terahertz."

The DWDM frequencies are in the 186 - 192 THz range.

Yes frequency for a particular wavelngth in in THz but two wavelngth are 100Gh apart. Like first two wavelngth in your attachement are 1530.33 and 1529.99 in frequency they are 196THz and 195.9THz so 0.1Thz is equal to 100Ghz.

Te formula you mentioned is to calculate frequency not change in frequency you have to differentiate to get change will lat you know the formula to calculate that 100Ghz soon

Overall Rating: 5 (4 ratings)

## Replies

Ken,

1. DWDM typically refers to lambda or wavelength rather than frequency. DWDM systems primarily use C and/or L band ranges which start around 1500 nm and go higher.

2. Not sure why wavelength is used instead of frequency. Obviously there is a simple conversion from one to the other. Keep in mind that the physical fiber is also rated according to the wavelengths they support and should be chosen based on the lasers employed by the DWDM system.

- Jaie

kfarrington Mon, 06/22/2009 - 07:14

Hi Jaie, and all.

Many thx for the help mate.

Can I just confirm the conversion with your from Nanometer to wavelength? Or do you know of a simpler calulations.

I got this from the following URL:

http://www.powertechnology.com/calculations.asp

Converting wavelength to frequency

Use the following equation to convert wavelength to frequency:

v (Hz) = 2.998 x 10'17 / wavelength (nm).

==============

So example 1 is the color red approx 440 tHz

2.998

x

100000000000000000

=

299800000000000000

/

682 nm

=

439589442815249.26686217008797654

==============

Example 2 is a DWDM wavelength 1539.19nm which is 194.9 Thz

2.998

x

100000000000000000

=

299800000000000000

/

1538.19 nm

=

194904400626710.61442344573817279

==============

Example 3 is the standard 850nm GBIC which equates (I hope) TO 352.7 tHz

2.998

x

100000000000000000

=

299800000000000000

/

850 nm

=

352705882352941.17647058823529412

Many thx indeed,

Ken

Tom Randstrom Mon, 06/22/2009 - 07:38
• Gold, 750 points or more

The wavelengths used by the ONS 15454 MSTP are outlined in data sheet (link below):

The current light frequencies in use were mainly chosen due to the fiber cable's operating characteristics, mainly specific frequency regions with low optical loss. Also, current optical amplifier designs have a limited operating range.

A good book on the subject is "Optical Networks - A Practical Perspective" authored by Rajiv Ramaswami (a Cisco employee) and Kumar Sivarajan.

Hope this helps!

kfarrington Mon, 06/22/2009 - 07:50

Hi there,

Many thx, but sorry to confuse matters.

If you look at the doc

32-wavelength multiplexer, 100-GHz, C band

32-wavelength demultiplexer, 100-GHz, C band

32-channel demultiplexer 100-GHz (for use with 32-WSS), C band

32-channel demultiplexer 100-GHz (for use with 32-WSS), L band

4-wavelength multiplexer/demultiplexer, 100-GHz, C band

If you look here, light in the em spectrum is within the tHz frequency range?

http://en.wikipedia.org/wiki/Visible_light

So I am a little confused?

Many thx,

Ken

viyuan700 Mon, 06/22/2009 - 07:57
• Silver, 250 points or more

Hi Ken,

As in my earlier post this 100GHz is not the frequency of the wavelngth but it is the difference between to wavelngths. Take 2 wavelngth for cisco i.e 1530.3 & 1531.1 and calculate frequency as per your formula you will get difference of 100GHz.

so in wavelngth they are 0.8nm apart but in frequency they are 100GHz apart.

kfarrington Mon, 06/22/2009 - 08:00

ahhhh. Thankyou :)

So wavelengths are typically in the ThZ frequency seperated by 100 gHz of freqeuncy. Is that the correct way to keep it in my head?

Please would you be so kind to confirm.

Many thanaks a big 5s to all who have made it clear :))

Beer in post.

Thx

Ken

viyuan700 Mon, 06/22/2009 - 08:09
• Silver, 250 points or more

Yes frequency for a particular wavelngth in in THz but two wavelngth are 100Gh apart. Like first two wavelngth in your attachement are 1530.33 and 1529.99 in frequency they are 196THz and 195.9THz so 0.1Thz is equal to 100Ghz.

Te formula you mentioned is to calculate frequency not change in frequency you have to differentiate to get change will lat you know the formula to calculate that 100Ghz soon

kfarrington Mon, 06/22/2009 - 08:17

Hi Vishwamurti,

BIG 5 for you mate. Many many thx. That is an excellent and conside response. Excellent.

Many thx indeed for the help,

Ken

viyuan700 Mon, 06/22/2009 - 08:56
• Silver, 250 points or more

Hi Ken,

Thanks for the rating.

As per my previous post formula to calculate the difference between frequency in GHZ you have to go back to your college Math means Differentiation

Î»=c/f (f=Frequency)

when you differentiate

dÎ»=c/f^2*df

When you insert df (difference in frequency)=100GHz

f(frequency)=take any of your frequency e.g 192THz

c(speed of light)=3x10^8meter per second

after calculation you will fine that 100Ghz is equal to 0.8nm as per above formula difference in wavelngth in nm.

kfarrington Mon, 06/22/2009 - 09:21

Thx man. My brain has just "blue-screened" - gonna have to absorb this one carefully :)

Thx so much mate :)

Ken

kfarrington Mon, 06/22/2009 - 09:52

OK, just to take things on a bit of a tangent, if I may.

Lets say in Wireless, the frequency is 2.4 Ghz, and the wireless carrier is always there, and only when data needs to go over the airwaves, data is encoded onto the carrier wave.

Is it the same for an optics carrier signal -The freqency and carrier waves are being generated all the time, if data is ready for transmission or not?

Now, a bit off topic for this section: would it be the same for ethernet?

Lets say I have my PC at home, connected to my ethernet hub. and nothing is being transmitted by my PC or on the wire (theorectically). Is there a constant elctrical signal generating a carrier wave on the wire bewteen my laptop and hub or does a carrier only exist on ethernet when data is ready to be transmitted?

And what are the fequencies of ethernet, fast and gig ethernet?

Sorry if I have diverted from the optical stuff now, as you guys have given me all the awnsers on that side of things :))

Many thx, and kind regards,

Ken

viyuan700 Mon, 06/22/2009 - 11:59
• Silver, 250 points or more

Is it the same for an optics carrier signal -The freqency and carrier waves are being generated all the time, if data is ready for transmission or not?

Yes the frequency chart you attached earlier are the DWDM frequency/wavelngth and then you modulate with data.

In Ethernet, Fast or Gig but there is no multiplexing involved as in DWDM there are many wavelngth In case of etherent only baseband signal.

For frequency for Ethernet, Fast & gig see the link

http://www.ertyu.org/steven_nikkel/ethernetcables.html

see if this is helpful too

http://www.cisco.com/en/US/docs/internetworking/technology/handbook/Ethernet.html

kfarrington Mon, 06/22/2009 - 08:18

Hi Vishwamurti,

BIG 5 for you mate. Many many thx. That is an excellent and conside response. Excellent.

Many thx indeed for the help,

Ken

Tom Randstrom Mon, 06/22/2009 - 08:11
• Gold, 750 points or more

"A typical human eye will respond to wavelengths from about 380 to 750 nm.[1] In terms of frequency, this corresponds to a band in the vicinity of 790-400 terahertz."

The DWDM frequencies are in the 186 - 192 THz range.

kfarrington Mon, 06/22/2009 - 08:15

Many thx indeed Tom!!

BIG 5 for you. Excellent response!

many thx mate

Ken

viyuan700 Mon, 06/22/2009 - 07:52
• Silver, 250 points or more

Hi Ken,

1. For DWDM C& L bands are used and they are C 1530-1565nm L from 1565-1625.

U can see this link to see other bands use

http://en.wikipedia.org/wiki/Fiber-optic_communication

We use only these bands for DWDM as in other range we dont have Optical amplifier which are good as those works in C & L bands.

2. I think you use nm for optical wavlenth as they are easier to speak (my opinion if you see at smaller frequency u say 900MHz, 2.4 Ghz, 5Ghz ) but u have seen in your conversion that how complicated number becomes when you have to tell them in THz. In nm it is number which you can communicate easily like 850nm, 1300 nm, 1530nm etc

You conversion formula is right

C(Speed of light)3X10^8= V (frequency in Hertz)* Lambda in m.

So when u convert m into nm you get that 10^17.

In DWDM bands for fast convertion remember if 2 DWDM wavelngths are

0.8nm apart then in frequency they are 100GHz

0.4nm=50GHz

0.8nm=100GHz

1.6nm-200GHz

If you have spoke to anybody speaking about DWDM bands u will hear that wavelngths are 50G apart or 100G apart.

So i think we jsut use where number are easire to use whether it is frquncy or wavelngth.

kfarrington Mon, 06/22/2009 - 07:56

Hi there, I just posested a reponse about the confusion of ThZ and 100GHz for DWDM. Also, Please look at attachment which I pulled off some DWDMs provider spec sheet?

Many thx to all for the help guys

Ken

Attachment:
Richard.Ednay Mon, 06/29/2009 - 02:18

Hi Ken, note that the 'code' numbers are vendor specific - different vendors may use different codes. The wavelengths and frequencies for DWDM are defined by the ITU-T in their G.694.1 recommendation.

This does allow even closer spacing (down to 12.5GHz) but commercial DWDM systems are usually 50 or 100GHz.

Richard

jbardgett Tue, 06/30/2009 - 11:58

The nm (nanometer) length specification comes from the laser development. Transitions as they are called by folks who founded the laser industry typically refer to the dropping of an electron from one level to another within an atom or molecule in the terms of length. Here is a better explination of the term transition: http://www.rp-photonics.com/laser_transitions.html

Jim ~ optics student at CREOL

kfarrington Wed, 07/01/2009 - 02:47

Hi Jim,

Many many thanks for that gonna have a good read. Thx for the help.

Kind regards,

Ken

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