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.

Photosensitive Fibers & Fiber Bragg Gratings

As a result of a scientific accident whilst researching the nonlinear effect of intense laser light in optical fibers, a scientist call Kenneth Hill at the Communication Research Center accidently created an in-fiber reflection grating from localized photo-induced refractive index changes. This led to the development of photosensitive fibers and the birth of the fiber Bragg industry. Hill's discovery rapidly paved the way for the development of wavelength-selective reflectors based on Bragg's law, which became the fundamental principle behind the design of fiber Bragg gratings - the primary application of photosensitive fibers.

The demand for FBGs increased rapidly during the growth of the telecommunications industry, and new applications that arose during this time were a strong driver for research and development into FBGs. However the manufacturing capacity of these early devices limited the growth of the industry, and this led to the development of more powerful lasers, higher quality phase masks and optical fibers with greater photosensitivity so that fast FBG inscription speeds could be achieved.

As well as high photosensitivity, fibers used in these applications need to withstand the bend losses which occur when tight bends are formed with the fiber during their deployment, losses resulting from the mode field no longer guiding tightly within the center of the core. Fibercore's highly photosensitive range of specialty singlemode fibers meet both these requirements - increased Germania for enhanced photosensitivity and high NA for low bend-loss - the SM1500(4.2/xxx) fibers are especially suitable for these applications. Fibercore's PS range of intrinisically photosensitive fiber offers a high Germania content with a lower NA and does not require hydrogen loading to encourage absorption into the core.

To find out more, visit Nature Photonics (Nature Photonics/Vol 5/August 2011) and read Dr Andy Gillooly's article on 'Growing Gratings'. Andy is the Senior Sales Engineer at Fibercore Ltd and has a PhD in Fiber Bragg Gratings as well as an industrial background in FBGs and lasers.

'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.

Fibercore to Present at the 'Inertial Sensors & Systems - Symposium Gyro Technology'

Fibercore Ltd, as a world leader in the supply of reduced-cladding, bend-insensitive, polarization maintaining fibers for FOGs, will be presenting a paper at the forthcoming 'Inertial sensors and Systems - Symposium Gyro Technology'.

The recently renamed Inertial Sensors and Systems Conference, formerly the Symposium Gyro Technology, will take place in Karlsruhe, Germany on the 20th and 21st September, where the leading names in the Gyroscope and Sensor industries around the world will come together to discuss Fiber Optic Gyroscopes as well as MEM and Spinning Mass Gyros.

With an average 1 million metres of fiber shipped every month, Fibercore Ltd's Bow-Tie fiber is the most successful and widely-used PM fiber in this marketplace. Dr Andy Gillooly's presentation on 'Ultr-Low Profile, High Birefringence Fibers for Fiber Optic Gyroscopes' will discuss the latest developments and their influence on FOG technology.

OFS-21, 17th-18th May 2011, Ottawa Convention Centre

The OFS-21 Conference, combined with Photonics North, brought a good number of delegates to the Fibercore booth with a particularly strong turn out from Europe.

A wide range of technologies were discussed in the Technical Forums from Fiber Bragg Grating (FBG) sensing techniques using photosensitive fibers such as our PS-range of fiber and our high germania fibers, scattering sensing methods, utilizing Rayleigh, Brillouin and Raman scattering, and polarization sensing techniques using both PM and SM fibers.

The rate of adoption of fiber optic sensors in industry has taken a slow but steady rise with a notable recent acceleration in the acceptance of such techniques for commercial use. As safety becomes a greater issue, companies become liable for any environmental damage and resources become more difficult and costly to extract, these sensor systems start to be viewed as a necessary requirement rather than just academic interest.

Acoustic, vibration, pressure and temperature sensors were all aimed at large industries, particularly the oil and gas, wind energy and security industries.

With OFS-22 based in Beijing, China, between 14th-19th October 2012, it will be exciting to see how some of these technologies have matured and we will hopefully get a strong turn out from the Asian market.

Fibercore to Showcase Specialty Singlemode Fibers for Sensor Manufacturers and Biomedical Applications at OFS-21

OFS-21 Conference, Booth: 39, 17^th – 18^th May 2011, Ottawa Convention Centre, Ottawa, Ontario, Canada

Fibercore, a UK based global market leader in the design and manufacture of specialty optical fibers will showcase its range of singlemode fibers for sensor manufacturers and biomedical applications at OFS-21, which takes place on 17^th and 18^th May 2011, at the Ottawa Convention Centre in Ontario, Canada.

Visitors to booth 39 will learn how Fibercore’s high strength, high Germania, bend-insensitive singlemode fiber and their PS range of photosensitive products are ideally suited for distributed sensing applications including hydrophones and structural health monitoring, as well as ‘downhole’ sensors for oil wells. Also on show will be the company’s erbium-doped fibers, IsoGain™ and MetroGain™, which can be used in the sensors' ASE (Amplified Spontaneous Emission) light sources.

For delegates focused on biomedical applications the booth will feature Fibercore’s new all-silica SM-SC singlemode fibers. For use at shorter near-UV wavelengths these fibers deliver minimal photodarkening and provide a compelling alternative to conventional germanosilicate cored fibers. Meanwhile, specialists in confocal microscopy and optical coherence tomography will be interested in the benefits of the company’s high-performance 125µm HiBi fibers and HB-Z polarizing fiber.

Managing Director of Fibercore, Dr Chris Emslie comments: “OFS is a very natural venue for Fibercore to showcase its products. Fibercore’s Bow-Tie PM fiber, was originally conceived as a sensor fiber and now lies at the heart of most of the Fiber Optic Gyroscopes manufactured in the World today – more than 65,000,000 metres at last count. The innovations in Zing™ single-polarisation fiber, HB-C fused-coupler fiber and our IsoGain™ ASE fibers simply extend and support both FOG and other interferometric fiber sensor technologies. Add-in high-strength, truly bend-insensitive fibers for the growing fields of down-hole and acoustic sensing and OFS 2011 is shaping-up to be a very exciting place to be.”

OFS-21 is celebrating its 21^st International conference since its inception in 1983. The event embraces all research into guided wave optics for instrumentation, sensing and imaging, and its applications in physical, chemical and biological measurement. As a world-renowned and unique technical forum, the conference’s scope extends from relevant theory and fundamental science to the engineering realisation and commercial aspect.

OFS-21 takes place on 17^th and 18^th May at the Ottawa Convention Centre. For more information about the event visit: http://ofs21.org/.

Fibercore To Demonstrate Bow-Tie Fiber Splicing Made Easy At OFC/NFOEC 2011

Booth: 1409, 6th – 10th March 2011, Los Angeles Convention Center, Los Angeles, CA, USA

Fibercore, a UK based global market leader in the design and manufacture of specialty optical fibers, today announced that it will be hosting two presentations at OFC/NFOEC 2011, including a splicing made easy masterclass for its bow-tie polarization-maintaining fiber. The company will also be exhibiting its CATV and FTTx products, as well as providing a market update on the success of its fiber product range.

OFC/NFOEC 2011 is the largest global conference and exposition for optical communications and networking professionals. It takes place between 6th – 10th March 2011 at the Los Angeles Convention Center in Los Angeles, CA, USA.

On Tuesday 8th March at 13:00, Fibercore will present a masterclass entitled ‘Splicing Fibercore's Bow-Tie PM Fiber Quickly and Effectively with the Fujikura ARCMaster PM Splicer’. Fibercore will also be joined in this Masterclass by another industry leader in fiber optic products, Fujikura, who will demonstrate how Fibercore’s wide range of HiBi (Bow Tie) Polarization Maintaining fibers can be spliced with ease.

The following day at 12:00, Fibercore will present ‘Zing™ Polarizing Fiber in the Marketplace’. During this session, Fibercore’s Dr Andy Gillooly will reveal to delegates how Fibercore’s latest polarizing fibers (launched last year) are now successfully being used in various diverse applications from gyroscopes and current sensors through to fiber lasers.

Managing Director of Fibercore, Dr Chris Emslie comments: “OFC is the major international exhibition for the full spectrum of optical fiber technology and applications and Fibercore has supported the event for almost 30 years. This year we will be demonstrating the ease with which our fibers can be spliced and are looking forward to meeting many existing customers and prospects to talk to them about our latest products, particularly the market success of Bow Tie fibers. With well over 1,000,000 metres shipping every month, Bow-Tie is now the most successful and widely-used PM fiber on the Planet.”

The company will also be taking part in the FTTx Resource Center where it will be exhibiting its CATV and FTTx products.

For more information regarding OFC/NFOEC 2011 and to register for the event visit: http://www.ofcnfoec.org/.