And if those solar cells stop pointing at the Sun, the satellite dies – so I guess we play a pretty important part in ensuring the success of ESA missions! Satellite manufacturers often ask for long lengths of continuous fiber, sometimes up to 5,200 m lengths of HB1500G variants – this is because the fiber is used in the very accurate FOGs used in satellites launched by the European Space Agency (ESA) that make sure that the solar cells are always pointing at the Sun. The optical fiber in a FOG enables a very long optical path length to be confined into a small volume and so magnify the small phase shift caused by the Sagnac Effect – and the longer the path length, the more accurate the FOG.
Right up until the early 1980s – 30 seconds was a long time!
30 seconds might not seem that much – but those of you old enough to remember the Cold War, will also remember that we would only have had three minutes to wait from detection to destruction. Another advantage of FOG is that it is ready to work immediately, whereas a spinning-mass gyro can take up to 30 seconds to spin-up and stabilize. In fact one Fibercore customer fo und that the military could use one of their systems for an average 30 times longer before repair, simply by switching from conventional gyros to FOG. As a result, FOGs are tougher, more reliable and demand far less maintenance. The true benefit of FOG over a traditional, spinning-mass gyro is that it has no moving parts – no moving parts means nothing to wear out and nothing to service. In essence, a simple FOG looks a bit like this: If you analyze this interference, you can find out the degree and the rate of rotation. The Sagnac Effect states that if light travels simultaneously in both directions around an enclosed optical system and the optical system experiences a rotation, the light will undergo a Doppler-Shift (remember how police sirens change pitch as the car speeds past you?…same thing) with the result that the two beams will recombine out-of phase, creating interference. Those of you who had a gyro top as a child, or have pl ayed with one of those wrist-strengthening balls will recall that when you spin the rotor, the gyro gets a mind of its own and wants to remai n upright? Well it’s the force that the gyro exerts trying to right itself (aka ‘gyro torque’) that can be used to determine how far you have tried to rotate it.Ī FOG achieves the same result, but using polarized light and something called the Sagnac Effect. Traditional gyroscopes have been around for more than 100 years and work on the ‘spinning mass’ principle. Aircraft, for example, can move in three dimensions – so need three gyros to co ver roll, pitch and yaw. To be effectiv e, you need one gyro for e ach degree of freed om (or ‘axis’) in which the ‘platf orm’ can move. This is why gyros are used to help navigate ships, aircraft and even some land vehicles and in systems used for automatically stabilizing things. a hovering helicopter, a high-speed train carriage or even a pair of binoculars). So, by using a gyroscope, you can find out where somethi ng is pointing (e.g. Put simply, a gyroscope is a device that measures rotation. What are the key PM fiber design elements ? What makes a fiber optic gyroscope bette r?ĥ. Last time you learned about our BIG Product, Bow-Tie PM Fiber – this month, it’s the turn of the BIG Applic ation. Five Minute Fiber Expert 4 - Th e Fiber Optic Gyroscope (FOG)