After 30 years in business, there's a Lot More to Fibercore than just Gyro Fibers!

The results of a very recent telephone survey have indicated that many of you only know us for our HB-G Bow-Tie FOG Fibers - and with more than 1,300,000 m of HB800G and HB1500G shipped out of Fibercore House each and every month, the reasons for this impression are very clear indeed. Fibercore's dominant position within the FOG industry certainly confirms both the class-leading performance of our Bow-Tie PM Fiber in any Interferometric sensor (not just gyros) and our unmatched experience in the manufacture of complex Specialty Fiber to tight tolerances and in very high volumes - but we do an awful lot more than just gyro fibers.

A Wider Range of Polyimide Coated Fibers for Harsh Environment Applications
After many years of promise, fiber sensors designed to increase the productivity of oil wells, enhance the efficiency of extraction and even assist the discovery of new reserves are now starting to become accepted by the Industry and are being deployed commercially. Go to our website and you will find an expanded range of SM-P Polyimide Coated Fibers, designed for both 'Down-hole' and other Harsh Environment application. And remember, Fibercore SM-P fibers were originally designed and have evolved over our 30 year history, specifically for sensor application. Not only do they deliver exceptional resistance to bend-induced loss, but the '5.3' and '4.2' variants also offer significant intrinsic photosensitivity, greatly simplifying the inscription of the Fiber Bragg Grating upon which many sensor designs now depend.

Enhanced Efficiency IsoGain™ Erbium Doped Fiber
After the Telecoms crash, many people seem to have dismissed erbium doped fibers as mere commodities, undifferentiated and selected only on the basis of price. But in a high competitive marketplace, even the smallest changes can have a big impact - we have recently made improvements to increase the efficiency of our well-established IsoGain™ I-4 and I-6 fibers and head-to-head evaluations have shown enhanced conversion efficiency for these fibers, reconfirming IsoGain™'s class leading performance. The difference is small, but consistent and meaningful, enabling some users to use less costly pump diodes, or to under-run existing pumps to increase reliability - and confirmed by sales of IsoGain™ into China more than doubling!

Increased Interest in 'RGB' Applications
Whilst volume demand is nowhere near the levels that we see for most sensor fibers, interest in fibers capable of transmitting from the UV through to red, for use in diagnostic probes, continues to grow at a steady pace and R(ed)G(reen)B(lue) fibers will be the subject of a special Product Showcase, delivered by Fibercore's Dr Andy Gillooly at Photonics West in January 2012. The development of these fibers, and the extension of the silica-core technology to PM continues.

So after 30 years of Fibercore, what's new for 2012 - simple:
A wider range of Polyimide-Coated Fibers for Harsh Environments, Enhanced Efficiency IsoGain™ for more reliable and cost-effective EDFAs, SM300/SM400-SC for UV-Green Transmission - and more HB-G Bow-Tie used in more Gyros than ever before!

Dr Chris Emslie
Chief Executive Officer
December 2011

If you would like to know more, visit us at our booth 4926 at the Photonics West 2012 Exhibition in San Francisco during 24-26th January 2012, to discuss your requirements with us, or visit our website at http://www.fibercore.com/

The Fiber Optic Gyroscope

Fibercore Ltd will be presenting at the forthcoming 'Inertial Sensors & Systems - Symposium Gyro Technology' on the 20th September 2011 to discuss the use of reduced clad fibers in Fiber Optic Guroscopes. But what is a Gyroscope and why is a FOG different?

Put simply, a gyroscope is a device that measures rotation. So, by using a gyroscope, you can find out where something is pointing (eg an aircraft) or how level it is (eg a hovering helicopter, a high-speed train carriage, or even a pair of binoculars). This is why gyros are used to help navigate ships, aircraft and even some land vehicles and in systems used for automatically stabilizing things.

To be effective you need one gyro for each degree of freedom (or 'axis') in which the 'platform' can move. Aeroplanes, for example, can move in three dimensions - so need three gyros to cover roll, pitch and yaw.

Traditional gyroscopes have been around for more than 100 years and work on the 'spinning mass' principle. Those of you who had a gyro top as a child, or have played 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 remain upright. Well it is 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.

A FOG achieves the same result, but using polarized light and something called the Sagnac Effect. The Sagnac Effect states that if light travels in both directions around an enclosed optical system, simultaneously, 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. If you analyse this interference, you can find out the degree and the rate of rotation.

In essence, a simple FOG looks a bit like this:

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. As a result, FOGs are tougher, more reliable and demand far less maintenance. In fact one Fibercore customer found that the US Army could use one of their systems for an average 30 times longer before repair, simply by switching from conventional gyros to FOG! Another advantage of FOG is that it is ready to work immediately, whereas a spining-mass gyro can take up to 30 seconds to spin-up and stabilise. 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. Right up until the early 1980s - 30 seconds was a long time!

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.

The fiber used in FOGs needs to preserve polarization because, in order to generate stable interference, two light waves have to have the same orientation - if they crossed at right angles, they wouldn't even know the other one was there! Typically people want to get the longest optical path length into the smallest possible space and this leads to small diameter coils with multiple layers - demanding lots of birefringence (short beat-lengths) to make sure that the micro bending created within these layers does not counteract the stress inside the fiber (see our blogg on 'Bow-Tie Polarization Maintaining Fiber'), high numerical apertures to ensure that the fiber continues to guide strongly in these small coils and reduced coil diameter, to improve lifetime and save space. All of which go a long way to explaining our current development direction of ultra-low profile, ultra-high birefringence Bow-Tie PM Fiber.

If you would like to know more, look out for Dr Andy Gillooly at the Symposium or contact Fibercore Ltd at sales@fibercore.com.

'Bow-Tie' Polarization Maintaining Fiber

... more than 1,000,000 metres shipped by Fibercore Ltd every month.

So what makes it different from standard, telecomunications fibers, and how does it work?

It got its name because it was invented in 1982, so long ago that Fabricators wore bow-ties - because an ordinary tie could too easily have become wrapped around the lathe - OK, so we made this bit up but at least you were listening!

The distinctive cross-section of a bow-tie fiber is created by the two segments of boron-doped glass that flank the core (you may hear these segments being called SAPs or stress-applying parts). As the fiber cools during the drawing process, the boron makes the SAPs contract more than the rest of the fiber, placing the core in tension. This tension stretches the glass structure along the axis running parallel to the stress and compresses it along the axis running perpendicular to it and, in doing so, changes its optical properties. Light moves less easily and more quickly through the stretched structure. In this way, the fast and slow axes are created - the fast running perpendicular and the slow, parallel to the SAPs. This is called birefringence.

A lot of people think that the elliptical shape of the core is caused by stress - it isn't. The core shape is formed in the preform, during the collapse phase of the fabrication process, when the glass is molten and cannot support stress - the birefringence can only start to happen after the glass has solidified.

Birefringence can be a useful thing to have in a fiber because it causes light waves to travel at different speeds, depending on their orientation relative to the SAPs - so if your optical source is polarized, ie if all of the lightwaves it generates have the same orientation, and you line them up to the fast or to the slow axis, then the polarization state of the source will be maintained - and you have a polarization maintaining or 'PM' fiber.

It's as simple as that!

For more information, visit our Technical Resource Center and download the Fibercore PM Fiber Handbook, or contact our Sales Team at sales@fibercore.com.