# modulating light

#### aac9876

Joined Dec 9, 2006
124
one of the companies on my stock watch list makes products that modulate
light waves for electronics uses. Optical nubiate. etc or something.
Light cant be measured by frequency right.?? How could you read little
bits of modulated light waves. ?? Would it be similar to radio freq. ??

#### Tube Tech

Joined Jan 11, 2007
46
Probably modulating light for use on fiber optics. On-Off, not AM or FM or quadrature shift.

#### hgmjr

Joined Jan 28, 2005
9,029
I believe that some of the old laser based distance measuring equipment had a light modulator that could modulate the intensity of the aggregate laser beam.

hgmjr

#### thingmaker3

Joined May 16, 2005
5,084
I once maintained some fax machines which "modulated" the laser beam with a varying degree of partial blockage.

#### Papabravo

Joined Feb 24, 2006
16,479
Since light is the same kind of electromagnetic radiation as radio waves it certainly can be "measured in frequency". It follows the the same relationship as radio waves, namely:
Rich (BB code):
c = f * lambda

where c is the speed of light, approximately 3e8 meters/second
and f is the frequency in Hertz
and lambda is the wavelength in meters

#### Dave

Joined Nov 17, 2003
6,970
Indeed so, visible light occupies the portion of the electromagnetic spectrum between ~450 and 750THz.

Dave

#### Papabravo

Joined Feb 24, 2006
16,479
And wavelengths of 400 nanometers to 700 nanometers

#### bloguetronica

Joined Apr 27, 2007
1,453
The beauty of using light, is that you can use several wavelengths in one cable, and they won't interfere, since they can be separated by simple optics.

#### thingmaker3

Joined May 16, 2005
5,084
Thus we have "multimode" fiber!

#### Dennis Atwood

Joined May 26, 2007
8
i thought multimode cable transmitted light at the same wavelength, but in several different reflection angles within the cable

#### thingmaker3

Joined May 16, 2005
5,084
Yes. Multiple propagation modes allow effective transmission at different simultaneous wavelengths. As an example, we can transmit at 850u while recieving at 1300u. (Assumes we are using the expensive cards.)

In common practice, only one wavelength is used, and xmt/rcv are on different fibers. This uses affordable cards.