The optical fibre Sagnac interferometer: an overview of its principles and applications

Abstract

The optical fibre Sagnac interferometer was first demonstrated over 25 years ago. Immediately its potential for gyroscopic measurements became apparent and since the first demonstration substantial research and development investment has evolved a diversity of rotation measuring instruments. The fibre Sagnac interferometer has, however, also ventured into unexpected domains. The fibre loop mirror has become the ubiquitous reflector. Sagnac-based intruder alarms, hydrophones, geophones and current measuring systems have emerged. The Sagnac interferometer has expanded from the rotation measuring instrument into a very versatile sensing tool. Indeed, it is arguably the most successful of optical fibre sensing technologies. In this paper, we review both the principles and applications of the fibre Sagnac interferometer. The background theory highlights the need to understand the conditions for reciprocity within the interferometer network. The applications range from the expected gyroscopes into novel hydrophone arrays and intruder detection systems. The basic interferometer is now well understood and the engineering required to realize useful and effective instruments has been carefully defined. Its versatility though continues to amaze even the most experienced practitioner and doubtless its applications potential will continue to expand.

Role of entanglement in calibrating optical quantum gyroscopes

“…We can construct a second Sagnac interferometer in the xz plane (e =ê y ) to determine the rotation rate ω y , and a third can be added to determine ω x . The use of three such gyroscopes allows a general rotation rate about an arbitrary axis to be determined [34]. We concentrate on the case with two interferometers for clarity, but the generalization to three interferometers will also be discussed below.…”

“…2. The two gyroscopic measurements are equivalent to a single measurement with four gyroscopes simultaneously, with a joint state ρ ≡ ρ 12 ⊗ ρ 34 . In general, the optimal state ρ 12 for 1 and 2 will not be the same as the optimal state ρ 34 for 3 and 4 , since the evolution U 12 of the gyroscopes 1 and 2 is not equal to the evolution U 34 for the gyroscopes 3 and 4 due to the different relative rotation ω.…”

“…A priori there is no reason to choose different probe states for the two orientations 1 + 2 and 3 + 4 during normal operation. However, during the calibration stage of the gyroscopes the rotation ω is a precisely known rotation in an external reference frame, and its value will generally determine different optimal states ρ 12 and ρ 34 . Here we choose ρ 12 = ρ 34 to keep the analysis tractable.…”

“…Here we choose ρ 12 = ρ 34 to keep the analysis tractable. The optimal strategy for different ρ 12 and ρ 34 , as well as the optimal rotation direction ω will be the subject of future work.…”

A new fiber-optic non-contact compact laser-ultrasound scanner for fast non-destructive testing and evaluation of aircraft composites

“…2,5,31,32 A design by this group based on a confocal Fabry-Perot interferometer significantly reduced the influence of the light collection system. Other approaches aimed at minimizing the effects of speckle structure include modifications of a Sagnac interferometer [33][34][35][36][37][38] and interferometer schemes employing photorefractive crystals. 31,[39][40][41] However, the detection sensitivity of all these optical techniques does not approach that of a well-designed, contact piezoelectric transducer.…”