My simple understanding is that one of the advantages of going to fibre (light) is that you transfer things at a lot higher rate than a standard cable using the light frequency. Adjusting the light frequency, theoretically will allow more data to transfer (i.e. UV -vs- IR) per unit time.

Thinking over the frequency spectrum, I seem to recall that light is at a relatively low Hz rate as compared to the higher radio frequencies. Would it be theoretically possible to use something like radio wave frequency (say GHz RF) transmitted over copper wire to increase bandwidth between two points?

On my audio/visual receiver, I notice that I have wired RF input as well as optical input. I understand here that RF input is higher bandwidth.


7 Answers 7


Adjusting the light frequency, theoretically will allow more data to transfer (i.e. UV -vs- IR) per unit time

No this is not true. Please see this question's answer on the Electronics Stack Exchange site. The frequency of the light travelling down the fibre is not relational to the speed of data transmitted as you may think. I know that question I linked is about copper but it might give you some insight. Single Mode fibre for example can run at 100Mbps, 1Gbps and 10Gbps; all at a wavelength of 1310nm. You need to look into symbol rate and encoding methods such as Manchester Encoding, 8b/10b encoding and 64b/66b encoding.

Would it be theoretically possible to use something like radio wave frequency (say GHz RF) transmitted over copper wire to increase bandwidth between two points?

No, this is not true. The speed at which data travels down a copper cable is nearly as fast as a fibre (circa 0.6*c). The electromagnetic wave is propagating around the edge of the copper cable at a rate called the dielectric constant, which is based upon the relationship between the transmission medium (the copper) and the air and plastic coating around it. See the answer to this different question on the Electronics Stack Exchange.


As you delve deeper into the physics of electronics and light, they behave completely counter intuitively.

  • 1
    Actually copper is in fact usually faster (lower delay) than fibre, but that's utterly irrelevant in practice as by the time you've gone enough distance to care you've had to regenerate the signal on the copper many times adding back much more delay than you avoided in the first place.
    – LapTop006
    Commented May 24, 2013 at 15:16

Looking over the frequency spectrum, I notice that light is at a relatively low Hz rate as compared to high frequency.

What spectrum chart were you looking at, because this is not correct. Here's a spectrum chart from Wikipedia:

enter image description here

Notice higher frequencies are to the left, and longer wavelengths are to the right. In fact these are related by the formula

f = c / lambda

where c is the speed of light.

High frequency (HF) is nominally 3 to 30 MHz. The highest practical rf (actually microwave) frequency is around 100-300 GHz.

An 1550 nm optical signal is about 190 terahertz and 850 nm about 350 THz, or 1000 times higher than microwave frequencies.


TL;DR: No, RF is slower than laser transmission.


Frequency is, as you've described, a fundamental aspect of the carrier signal. Within the electromagnetic spectrum, lasers generally operate in or near visible wavelengths, (although there are infrared and ultraviolet lasers too,) and "radio" frequencies (RF) are much LOWER, (ie, well below the infrared.)


Theoretical bandwidth is determined by the frequency at which one can vary the carrier signal. The variation must be very small; If it varied greatly, it wouldn't appear to be a variation at the receiver. The rate at which you can vary the frequency is dependent on the frequency. So for a given percentage of variation, you get a higher frequency of variation when you use a higher carrier frequency. That is to say: a 1% variation of a red laser frequency is a much higher frequency than a 1% variation of a radio frequency.

The actual usable bandwidth -- the number of "bits" one can pour through a communication channel -- is significantly less. But the theoretical bandwidth gives you a hard ceiling which is a good first approximation of the usable bandwidth.

So no, RF is significantly slower than laser transmission.


Understanding what you're trying to accomplish is critical.

For data network purposes (traditional L2/L3 switching/routing), 10G is typically the fastest current deployments are at without LAGs (port bonding/channeling for some vendors). There are some 40G deployments and possibly some 100G deployments out there, but these are expected to run over copper as well as fiber.

Now what we begin to discuss is distance. Fibre can send light farther than copper can send electricity (without regeneration). This means you can send the same speeds the same distances (ultimately) but will need regeneration to do so with copper mediums.

Now we need to examine latency. Latency differences over distances that do not require regeneration for electrical mediums (copper) will be negligible at best if you can even see a difference. Nodes that regenerate electrical signals will increase latency. Therefore, over long distances, copper has higher latency than fiber. The speed at which a signal is sent over a medium is independent of the bandwidth utilized. Put another way, the speed of light is a constant and does not change because you increase the bandwidth being sent over the fiber.

So what is "faster"? Is it bandwidth or is it latency or is it both? If it is strictly bandwidth (the amount of bits which can be transmitted and/or received within a given interval), then for L2/L3 switching/routing fiber and copper are nearly identical or will soon be identical. If it is latency or bandwidth + latency, then fiber is "faster" but only once your distance exceeds the distance limitations of a single run of copper (which then requires regeneration which adds latency).

We can also add another factor to this: is "faster" any or both of the afore-mentioned (typical) measurements plus the ability to multiplex multiple bandwidth channels over a single physical medium? If this is the case, then fiber is the clear winner. It can multiplex 160x10Gbps signals over a single fiber. This means a single fiber can operate at 1.6Tbps. These must be MUX'd and DMUX'd, so this is only applicable in backhaul transport of the data and not in end-user/device implementations.


Here's my non-EE viewpoint.

For reasonable distances, neither speed of light (vs electrical impulse) nor frequency are large considerations. If you were to talk with someone on the phone via an old (non-optical) undersea cable, you wouldn't notice a delay over the phone the way you do when we communicate by bouncing light off satellites in geostationary orbit.

Your major limiting factors are signal fidelity (for lack of a better term), and how quickly you can sense changes in voltage, light levels, etc. Both of these depend on cabling, distance, etc both for copper and fiber. The fact is we can't encode data on the quantum/photon level and even if we could, we couldn't get it there reliably. Even single-model fiberoptic cable isn't really single mode so there is still a minimum signal time due to the optical properties of the cable (at distance it is a lot less over single-mode than multi-mode cable though). Similar considerations occur regarding copper and a major part of cat 5 vs cat 5e vs cat 6 specifications have to do with these issues, namely minimizing the minimum reliable signal timeslice so that more signals can be sent down the cable in a given time.

The one area here where laser over fiber makes a big difference though is in wavelength division multiplexing. Unlike copper, several lasers of different frequencies can send signals down the same fiberoptic path and these can be divided and decoded on the other end.

As the other poster noted, RF is slower than cable or fiber. The big issue is that transmitting a signal over a frequency carrier wave is not as simple as on/off like it is over a physical cable. These are complicated approaches (see https://superuser.com/questions/298568/how-does-wi-fi-modulate-the-electro-magnetic-wave), but the answer is even more there, you can't just send individual bits as single waves.


My non-EE-background stab at an answer is:

I don't believe fiber was initially looked at as a transmission medium purely for bandwidth reasons, but more for the fact that it [light] can travel much longer distances without amplification/regeneration, and the fact that it's immune to factors that electrical transmission mediums are not immune to, like noise for example.

The higher bandwidth rates are a product of engineering done at the PHY level - I'm not sure if you're familiar with WDM technology, but basically it multiplexes light at various wavelengths to increase the total capacity of a single fiber pair - this gives you a higher aggregated bandwidth, but each wavelength still has a max of 10G (disclaimer: I'm not up on optical engineering news so it's possible that you can get higher rates per wavelength).

There are certainly specs for (and maybe even small deployments of) 10G over copper, typically over what's called "direct attach" cables - they're twinax copper cables with SFP's on either side. There are also QSFP's which are 40G capable, but these will typically have one QSFP on one end and break out into 4 10G cables on the other end.


High frequency traders are looking more and more for microwave routes for lower latency. Main advantage is that microwaves are direct paths between two points and can go past lakes and other obsticles easier than fibre which is often routed along roads and facilities like gas lines and sewers etc...

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