Bandwidth is not infinite, at least not in our restricted media technology enterprise. Cost and innovation are drastically affected today by our ability to interconnect signals of many types over distances no shorter than what we have been used to with coaxial video interconnections. While copper-based interconnection technology has key roles in modern facilities, increasingly optical fiber has important attributes that facilitate technology that traditional wired infrastructures cannot duplicate easily, or at least over practical distances.
From a technology standpoint, we are evolving away from infrastructures in which a single wire (or, more properly, cable) carries a single signal. Most current wiring diagrams show real devices connected by point to point, almost exclusively unidirectional pathways. This is because the signals carried are analog in physical nature, even if signals like SDI and AES digital interconnections are considered.
To make those baseband digital signals work requires sending analog modulation on the bearer, whether coax, paired wiring or fiber-optic cable. As we increasingly embrace IT-based technology, network technology allows us to overcome key aspects of the current interconnection model. First, to fall is the unidirectional nature of baseband interconnections. Second, and particularly affected by optical interconnection methods, more than one signal may be carried on a single cable. In fact, multiple signals can be carried in both directions on a single cable. This has broad implications for the topology of interconnection in single-site operations, as well as in multiple-site operations.
It is important to note that while analog and digital baseband signals occupy significant bandwidth in a cable, optical techniques are not normally amplitude modulation of the light, but rather FM, or more properly pulse modulation of FM. A second important factor is that the “carrier” frequency, i.e. the frequency of the light, is much higher. How high? A typical 1300 nanometer laser is about 230,000GHz. That means a lot of information can be modulated onto one beam.
Using CWDM, you can put about 18 beams in a single fiber, and with DWDM, you can put upwards of 40 and up to 128 wavelengths in a fiber. If you combine the ability to handle high data rates with potentially many video and audio signals in a single data stream, plus DWDM technology, it is easy to see how a single fiber has capacity that is quite astounding.
On my desk I have a short sample of fiber that is now more than 10 years old. One PVC “pipe” carries 864 fibers, each of which can be DWDM modulation. By my simple math, that is 110,592 wavelengths in a bundle that could run short or long distances. That makes any coax look puny.