FO Technology, Products, News & Tips
19 May 2010
Fiber Optic Technology
What is SBS and Why Should You Care?
SBS is Stimulated Brillouin Scattering. I guess that clears that up, right? Probably not. In the last Olson newsletter, we discussed the fact that optical power densities in the core of an optical fiber are quite high. We also discussed some of the implications of that power density. One implication that we did not discuss is that these high power densities can cause nonlinearities. The SBS nonlinearity, as it's name implies, is caused by light scattering in the glass itself. This scattering can cause the atoms in the glass to vibrate as light passes, much as wind chimes on your porch sway and clang as the wind blows. Click on the picture below to get a simplified simulation of the effect.
As the light travels through the glass in the simulation, it impacts some of the atoms and is scattered. When a light photon hits an atom it moves it slightly. When the light level gets high enough, the atoms move in such a way that they reflect light back towards the source. That's SBS.
Fun Fact: Did you know that light could move objects? Remember the military's 1980's Star Wars program that planned to shoot down incoming missiles with lasers? The most ambitious version had light levels so high that it would actually smash the missile as though it had been hit with a giant sledgehammer! So even if the missile was covered in highly reflective material, it would still be destroyed.
SBS can be seen in optical fiber at optical power levels as low as +5dBm The SBS threshold (the lowest optical power at which the effect occurs) varies a bit at different wavelengths. It is highly affected by the optical line width. An unmodulated DFB laser may have an optical line width of 10MHz. This will trigger SBS around +5dBm. If the laser is modulated, the laser's optical line width will spread out to perhaps 1GHz or more. This raises the SBS threshold significantly.
Olson Technology, Inc. employs advanced SBS suppression in many of it's products, such as the OTOT-1000-FF, 1550nm Direct Modulated Transmitter. This raises the SBS threshold to +16dBm or more. We will announce SBS suppression to +19dBm shortly. That means you can launch those power levels into a long lengths of fiber with no fear of SBS. For more details, read Olson's Application Note on Nonlinearities.
Fiber Optic Products
NeverOff is Introduced
Currently two standard models are defined. The Model 101 can power a 1.5 Watt load for 8 hours or a 3 Watt load for 4 hours. The Model 201 can power a 7 Watt load for 8 hours or a 12.5 Watt load for 4 hours. Customized models can be easily produced to meet your specific requirements.
Fiber Optic News
You will also find archived newsletters at the new and improved Olson Technology web site.
Olson Technology, Inc. and Toner, Incorporated are co-hosting a Fiber 101 Training Session at the AHECTA conference in Minneapolis on 16 June 2010. The course will cover the basics of fiber optics, discuss the key fiber optic components in great detail and cover many aspects of basic and advanced fiber optic system design.
Want to get smarter about fiber optics? Visit our ever expanding Fiber Optic Technology page on the Olson web site for a wealth of knowledge that can help you be successful working with fiber optics.
Fiber Optic Tips
APC vs UPC Optical Connectors
Perhaps the most frequent call we get from distressed customers pertains to APC and UPC or PC connectors. Let's define these terms first. APC stands for Angle Polished Connector. It is the green connector in the picture below. Note that the tip of the white ceramic has an angle on it. This angle prevents backreflections which will seriously degrade the performance of any analog fiber optic system, such as CATV and Satellite. UPC stands for Ultra-Physical Contact and PC stands for Physical Contact. The blue connector in the picture is a UPC connector. You can see that its end looks flat and at zero angle. In fact it has a slightly curves end face so that the fiber cores make contact first. UPC and PC connectors do NOT have well-controlled back reflection performance.
The phone calls that we get fall into two categories;
It's real simple with analog fiber optic links. Go green and you'll be a happy camper. Otherwise you will be blue when you fire up your system.