What does Single mode fibre means? and how is related to the carreir frequency?

Question

I got confused in the relation of single mode fibre, carrier frequency and wavelength of optical source in the transmitter. ur help is appreciated.

And if we have a Laser diode with the specific wave length is it possible to define the carrier frequency from that? If not how should we define it then?
thanks

Answer 1

Single mode fibre (fiber) refers to optical fiber which propagates light in the TEM00 mode. This is generally better for higher bandwidth and longer transmission distances than fiber known as multi-mode. Single mode fiber has a smaller core radius and cladding radius than multi-mode fiber.

In order to be single mode, the Normalized Frequency (V) must be less than or equal to 2.405. V = 2*pi*NA*a/lambda where pi = 3.14, a = radius of core of fiber in micrometers, lambda = wavelength of light in micrometers, and NA = numerical aperature. Single mode fiber has a NA ~ 0.1. The relationship would be:

2*pi*NA*a/lambda < 2.405 ==> a/lambda < 2.405/(6.28 * 0.1)

So that a/lambda < 3.8296. The radius of the core must be less than approximately 4 times the light wavelength in order for it to propagate in single mode. Most commercial single mode fiber propagates light with a wavelength of 1.31 or 1.55 microns which would imply the radius of the fiber core would need to remain below approximately 4.9 to 5.7 microns (diameter under 10 microns).

The carrier frequency would be found from the wavelength and speed of light relationship: c = lambda*frequency
Knowing the wavelength is 1.3 microns would give a carrier frequency of f = c/lambda = 3x10^8 m/s / 1.3x10^-6 m = 230x10^12 Hz but since speed of light is slower in a material like glass in proportion to the material's index of refraction, this frequency is really lower, about 1.5 less for glass = 153 teraHertz would be the frequency of light of wavelength 1.3 microns moving through glass fiber. This is the carrier frequency and explains why optical fiber can transmit information with such a high bandwidth.

Answer 2

single mode mainly means that it can only operate in the principle mode means when the ray passes from the principle axis of the fibre. in single mode fibre only a singlw wave length can transfer which is parallel to the principle axis

Answer 3

SngMod OpFb is Frequency related spec.SngMod OpFb is also WL looped. less load on the TMS.This is way we use to do in field, maybe all changed now.