The speed of light is 3*10^8 m/s and data transmission rate of optical fiber is ~100 Tb/s, how do we calculate data transmission rate?

Question

How do we calculate data transmission rate? Is there some formulas that is involved?

Fiber optic cables beat copper in this department, and it isn’t even close. Fiber optic cables are made of tiny strands of glass, each about the size of a human hair, and use light pulses. Thus, they can carry a lot of data—up to 60 terabits per second—at speeds just slightly slower than the speed of light. Copper cables, limited by the speed at which electrons travel, can only reach about 10 gigabits per second.

https://blog.tripplite.com/7-reasons-you-should-choose-fiber-optics-over-copper

The standard way to measure data transmission rates is via bandwidth. These days, it is measured in gigabits of data per second (Gbps), or even terabits per second (Tbps). Copper-based transmissions currently max out at 40 Gbps, whereas fiber optics can carry data at close to the speed of light. In fact, the bandwidth limits imposed on fiber are primarily theoretical, but have been tested to be measurable in hundreds of terabits per second.

https://www.cablexpress.com/education/blog/5-reasons-why-it-professionals-choose-fiber-optic-cables-instead-of-copper/

Fiber optic cables transmit data much faster than copper wires do because fiber optics use the speed of light rather than the speed of electrons. Fiber optic Internet connections can range from 5 Mbps to 100 Gbps. This ensures no wasted time or productivity due to a slow Internet connection. Fiber optic cables also enable “symmetric speed,” which means that uploading and downloading speeds are equal.

https://www.fiberplusinc.com/services-offered/benefits-fiber-optic-cables/

I am really intrigued by how did we calculate data transmission rate of optical fiber or any transmission medium. What is the math behind it?

Answer 1

because fiber optics use the speed of light rather than the speed of electrons

A complete nonsense.

Both methods propagate the signal at the speed of light in the particular media used. This can be assumed roughly to be 2/3 of the speed of light in vacuum in either case.

Both methods involve moving the electrons in the media somewhat (way below the speed of light).

Both methods imply that the signal goes over copper media (traces on the PCB) at least from the CPU to the transmitter/receiver circuit, be it optical or electrical.

The reason why optical cables are better in our current technological context (not per se) is that it is easier to make an optical cable that has more or less constant (or at least acceptably variable) properties over the signal bandwidth.

Answer 2

First, the speed at which a signal propagates is irrelevant to bandwidth. Fiber optics, which have the highest bandwidths propagate signals at 2/3 the speed of light, but a 100 year old AM radio, cable of sending only a few thousand bits per second sends those bits at the speed of light. If you send a signal over a radio, it will get there first, then after a delay, a signal will arrive by fiber. The fiber signal will take longer but can contain billions of times more information.

As for your core question, the advantage of fiber comes down to frequency and attenuation. Frequencies greater than about 100-1000 MHz are strongly absorbed in metal cabling. This is why each new generation of USB/HDMI/DP/etc has required more expensive cables while imposing decreasing limits on their length. The higher frequency signals are more attenuated. Glass fibers also have this property, but (depending on the material) they attenuation becomes low around 150 THz and stays low until about 550 THz (this is why glass is clear at all visible wavelengths as well as more in the infrared and UV). Compared to the 0-.001 THz range on a copper cable, the ~500 THz range on fiber gives you millions of times as much bandwidth (depending on the exact fiber type, etc). This if you have millions of times more bandwidth, you can send data millions of times faster (at least in theory).

Answer 3

The article is hot garbage.

There are two things that determine the throughput of a communications medium: bandwidth, and signal to noise ratio. This is formalized in the Shannon-Hartley Theorem as follows:

$$C = W *log_2(1 + SNR)$$ Where \$W\$ represents the bandwidth and \$C\$ is the capacity of the channel.

Note that there is no mention of propagation velocity, which is similar for light in fiber and copper, both being about 2/3 c. Instead, \$W\$ is much, much larger for fiber.

What limits fiber presently is the ability to encode and decode data at each end, which today happens in the electrical (copper and silicon) domain, not so much limited by the fiber itself.

Fiber’s larger bandwidth however allows operating with simpler codings that are more tolerant of SNR and so can achieve higher throughput at longer distances than would be possible with copper.

Answer 4

It is not only about the fibre itself, but also about the light source used to transmit the data and the light detector used to receive data. Any part of the system can and will affect the data rate, so the fiber may not be the limitation. Like with any other data transfer system, as long as the transmission medium itself does not distort the sharp transmitted data pulses too much to be blurry at the receiving end, the data will pass. There is no single formula for that, unfortunately.

Answer 5

Light photons would move at the speed of light 300000000 m/s however transmission thru the fiber would be a bit slower due to the propagation of light between the core and the cladding, so your statement would still be correct. so the answer to the question would be depends on the angle light was launched into the fiber strand. higher the angle longer the traveled distance. i.e a 20degree angle would arrive before a 75 degree. If I understood the question correctly.