Fiber Optics and Multimode Optical Loss Testing
Some of you may have read an earlier post of mine whereby I mentioned working on some “firsts” to market of early communications gear that helped AT&T Bell Laboratories qualify chips and network elements. The internet is a grand invention with a limitless memory. Somewhere out in the ether of servers and data storage elements I found pictures of the test equipment that I worked on in the 1980’s.
So what does this Multimode Optical Loss Test Set do?
Well, you are probably aware that the internet is a massive distributed number of networking and memory elements. If you simply send an email to your friend in another state, your input device (a phone, a tablet, or computer) codes that message into digital “bits” and pushes them into the communication network. Somewhere along that network from here to that other state there is most likely a fiber optic cable connecting two of those network elements together. This light cable has your “bits” and everyone else’s data traveling along it as light pulses. Well, even though those fiber optic cables are very long, the bright light pulses entering in on one side gets dim as the photons of light travel down that fiber optic cable to the end where the receiving element is. That cable has a non-ideal property that the longer the cable is, the less light there is at the end… and that property of light loss or attenuation is what is measured with this fiber optic test gear.
If the loss is too great then the receiving side can’t “see” the light pulses and your email, or conversation, or video signal is noisy, distorted, or in the worst case – completely lost.
So…this gear’s purpose in the early days was qualifying the fiber optic cable runs and identifying any that had too much loss and thus couldn’t be used to transmit the data bits from one end to the other reliably.
Speaking of reliability – did you know that the networks were designed to be 99.999% (or “five nines”) reliable? That means the network is designed to down less than one second per day or no more than 5.26 minutes … in a whole year!
For those interested, here is a link that describes a bit of the history of fiber optic communications: https://en.wikipedia.org/wiki/Fiber-optic_communication