The proof-of-concept demonstration of a microfiber-based flexural disc accelerometer is presented. The reduced microfiber size and bending radii give rise to high device compactness and responsivity. A flexural disc accelerometer manufactured from a 10 mm long microfiber showed a performance of ∼2:2 rad=g, with the responsivity expected to increase proportionally with the microfiber length. © 2011 Optical Society of America OCIS codes: 060.2370, 120.0280, 120.3180, 280.4788. Accelerometers . In-fiber designs are highly compact, but are limited by low responsivity. Although designs based on compliant cylinders/mandrels and weighted reflective diaphragm showed some positive attributes, notably very high sensitivity ∼10 4 rad=g [4], they also exhibit small operating bandwidth that is typically below 1 kHz. Flexural disc designs exhibit poor responsivity in small packages. Previously, as much as 75 m of SMF-28 has been used in flexural disc designs for the purpose of high responsivity [9]. Still, the flexural disc designs have operating bandwidths higher than most configurations, e.g. a few kHz. For portable applications where weight and size requirements are stringent, flexural discs face a serious design problem. In this Letter, we present a solution with a microfiberbased, centrally-supported flexural disc accelerometer that has the potential to achieve higher compactness and higher responsivity than conventional flexural discs that use telecom single-mode optical fibers or even bendinsensitive fiber (BIF). The phase-demodulation is performed by a differential technique on the intensity. Microfibers used in sensors and devices have diameters in the region of 1-3 μm, meaning that small bend radii can be achieved [12] without inducing significant polarization dependent loss and depolarization of light. Therefore, high device compactness is feasible without deterioration in expected performance. A smaller disc size also implies a higher fundamental resonance frequency, thus higher operating bandwidth. Since microfibers have reduced width, longer lengths are possible on a disc of the same size, leading to a larger response to strain and hence higher responsivity.The operating principle of the flexural disc accelerometer utilizes axial acceleration, which causes extensive strain in one fiber spiral and compressive strain in another, providing a push-pull enhancement and effectively doubles the accelerometer's response while providing common-mode rejection of pressure and temperature variations. Equations (1) and (2) are used to predict the phase (ϕ) responsivity to acceleration (A) of a centrally-supported flexural disc [9]. The stress-optic effect of microfibers are assumed to be the same as bulk silica and approximately equal to doped silica fibers [13]. Equation (1) calculates the length change due to the strain ε (expressed in terms of pressure changes ΔP due to acceleration) experienced by a ring of microfiber at radial distance r from the disc center. Equation (2) gives the sensor responsivity (rad=g) by app...

The optimization of resonantly enhanced Faraday rotation in microfiber loop resonators with linear birefringence is presented. For a sufficiently large birefringence-induced resonance separation, the evolution of differential phase between the two orthogonal polarizations can lead to efficient Faraday rotation when the loop circumference is a quarter of the polarization beat length and the roundtrip phase of the eigenmode in the fast axis is 3π/2 plus an integer multiple of 2π. This study provides the groundwork for fabricating microfiber loop resonator based current sensors that can operate efficiently despite the presence of birefringence.

A flexible technique to periodically perturb the evolution of differential phase in birefringent optical microfiber is proposed. This conceptual demonstration offers a simple yet effective solution to rectify non-ideal microfiber coil sensor heads for high-performance current sensing. Introduction:The rise of optical microfiber technology [1] has opened up a new lineage of current sensing. Optical current sensors employing optical microfibers (OM) based on the Faraday Effect have shown their potential for ultra-fast current detection in ultra-small geometries [2][3][4]. However, as with conventional current sensors, the problem of birefringence [5,6] still persists. Spun optical microfiber was previously proposed and demonstrated [7]. It offered improvements in the current responsivity at the expense of increased fabrication time and resources. In this Letter, we propose a post-fabrication technique to achieve the same goal, but with considerably lower fabrication complexity.Background theory: Optical microfiber coil (MC) based current sensors that exploit the Faraday Effect consist of an OM wrapped around the current-carrying conductor. The Faraday-induced rotation of the plane of polarized light is linearly proportional to the current flow. The change in the polarization azimuth is then translated into an intensity modulation that provides a measure of current. For the ideal case where there is no intrinsic birefringence in the MC, the angle of Faraday rotation (θideal) is related to the Verdet constant (V) of the OM, the magnetic flux density (B), and the interaction length (L) of the OM. Assuming a uniform magnetic field, θideal can be expressed in terms of the magnetic permeability of free-space (μ0), the relative permeability of the OM (μr), the current flow (I), the radius of the fiber coil (r), and the number of OM turns (N):

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Current sensing based on the Faraday effect in optical fibres is a wellestablished area in the landscape of sensor technologies. However, the optical behaviour that sets an upper limit on the detection bandwidth is often overlooked. The underlying mechanisms are explored in this reported analysis to raise awareness about their impact on the measurement results. The findings show that the Faraday effect cancellation and pulse broadening grow with increasing signal frequency, which result in suppression and distortion of the optical response. A correction factor is proposed for alternating and pulsed signals when using the simplified equation, to maintain an accurate measure of the peak current.