Photonic Bandgap Gyro – PHOBAG

The objective of this project is to assess the feasibility of new kind of optical gyro based on an innovative architecture of passive resonant fiber optic gyro (R-FOG) using a hollow-core photonic bandgap fiber (HC-PBF).
The basic principle of an R-FOG is to measure, using an external probe laser, the eigenfrequencies of two counter-propagating modes of a fiber ring cavity, their difference being proportional to the angular velocity of the device (Sagnac effect). While the first proof-of-principle of an R-FOG was made as early as 1983, it has not led to any practical application so far, because Kerr effect puts a strong limitation on the bias stability of this device. A key innovation that has changed things recently is the advent of hollow-core photonic bandgap fibers (HC-PBFs) with relatively low loss, where light propagates mostly in air (>98%), resulting in a strong reduction of Kerr effect (and Brillouin effect as well, although it is not usually the dominant source of bias). A first proof-of-principle HC-PBF R-FOG has been achieved in the United States very recently (2012), but did not reach the medium-performance target. To achieve this goal, we propose to build a new prototype HC-PBF R-FOG with the following significant improvements:
- implementation of an innovative modulation/demodulation scheme designed to optimize the gyro performances (including suppression of the lock-in zone and real time measurement of the scale factor),
- use of a free-space technique to close the fiber cavity in order to reduce coupling losses and improve the finesse of the cavity,
- development a new generation of HC-PBF specially designed for minimizing backscattering and improve gyro performance. In parallel, a new method of splicing a HC-PBF to a conventional fiber will be developed in order to minimize coupling losses, and allow in the future a fully-fibered ring cavity.
A successful project would be a breakthrough in the field of optical gyros. The resulting device would not only be compact, robust and cheap for this class of performance, but also have minimal radiation and magnetic sensitivity (respectively 50 times and 100 times better than a conventional fiber-optic gyro). The objective is to reach medium performance in rotation sensing (random walk around 0.01 deg/sqrt(hr) and bias stability around 0.1 deg/hr), with an ITAR-free product that would not exceed 1 L in volume, 1 kg in mass and 10.000 euros in price. If successful, this project could lead to the development of a cheap and reliable innovative sensor addressing a market in the aerospace field up to 100 million euros per year, with applications such as satellite navigators and attitude and heading reference systems for civilian carriers, which could improve aircraft safety in the future.
Moreover, the developments achieved in the framework of this project could benefit to several other scientific projects having a strong technical overlap with ours, such as the study of magneto-electro-optical effects in molecules with ring cavities or the metrology of Earth rotation rate with giant ring laser gyros, with potential applications in the fields of biophysics, geosciences and photonic bandgap fibers by itself.