The future for optical fibers has, for some time, been for diameters smaller than the standard 125µm, fibers like our 80µm reduced-clad PM fibers that we ship over a million metres a month of to FOG manufacturers worldwide. The new HB800G(3.4/60) fiber from Fibercore Ltd is even skinnier with a mere 60µm diameter.
The benefits of these 'ultra-low profile' fibers are that they offer enhanced gyro sensitivity by allowing a longer path-length into a smaller volume, are stronger long-term as the reduced bending stress offers increased lifetime, and they are better for PZT phase-modulators as they offer more stretch for less applied force.
These smaller diameter fibers are more sensitive to microbending and require higher birefringence to overcome microbend induced cross-coupling. The very short 65mm beatlength of the new HB800G(3.4/60) is an indication of how high the birefringence is for this ultra-skinny fiber - the beatlength for our 80µm fibers being around 1.5mm, and less than 2mm for our 125µm fibers.
Andy's presentation discussed the mechanical lifetime of the fiber and the stiffness of the fiber compared to the cladding diameter, as well as the effects of the increasing birefringence on PER. He discussed the PER penalty that has to be paid when the fiber is used in a worse case 'basket weave' fiber wind and showed that the 60µm fiber performs as well as 80µm fiber in small diameter coils. Thermal cycling was also discussed with an illustration of how little the PER performance changes over temperature.
The conclusion: for the smallest diameter, highest birefringent fiber - HB800G(3.4/60) is the answer!