Tilted fiber grating accelerometer incorporating an abrupt biconical taper for cladding to core recoupling

Abstract

We demonstrate a compact power-referenced fiber-optic accelerometer using a weakly tilted fiber Bragg grating (TFBG) combined with an abrupt biconical taper. The electric-arc-heating induced taper is located a short distance upstream from the TFBG and functions as a bridge to recouple the TFBG-excited lower-order cladding modes back into the fiber core. This recoupling is extremely sensitive to microbending. We avoid complex wavelength interrogation by simply monitoring power change in reflection, which we show to be proportional to acceleration. In addition, the Bragg resonance is virtually unaffected by fiber bending and can be used as a power reference to cancel out any light source fluctuations. The proposed sensing configuration provides a constant linear response (nonlinearity < 1%) over a vibration frequency range from DC to 250 Hz. The upper vibration frequency limit of measurement is determined by mechanical resonance, and can be tuned by varying the sensor length. The tip-reflection sensing feature enables the sensor head to be made small enough (20~100 mm in length and 2 mm in diameter) for embedded detection. The polymer-tube-package makes the sensor sufficiently stiff for in-field acceleration measurement.

Distributed fiber-optic laser-ultrasound generation based on ghost-mode of tilted fiber Bragg gratings

“…1(a), is based on the ghost mode of a tilted fiber Bragg grating (TFBG) [8][9][10]. Besides the Bragg reflection of the core mode, a TFBG can convert the forward-propagating core mode to a number of back-propagating cladding modes at wavelengths determined by the effective refractive indices of the corresponding cladding modes, as illustrated in Fig.…”

Tilted fiber Bragg grating in graded-index multimode fiber and its sensing characteristics

“…Tilted fiber Bragg grating (TFBG) have been extensively investigated in recent years due to its unique properties in the field of sensing [1][2][3][4][5][6][7][8][9][10][11][12]. Bragg gratings in multimode fibers (MMFs) have also attracted much attention.…”

“…Another commonly-used method is to re-couple the backward cladding mode into the lead-in single mode fiber via core-offset coupling [4,5], employing a short section of the multimode fiber [6,7] or an optical fiber taper [8]. The structure is relatively complex and not flexible enough for the applications that require the small size of the sensor.…”

Polarization-maintaining fiber-optic-grating vector vibroscope

“…Whenever working with cladding modes however, a suitable coupling mechanism must be provided to reintroduce the cladding mode light into the upstream core in order to allow remote interrogation with low loss. Any fiber discontinuity can be used for this purpose, as we have shown in [6][7][8][9]. In the new vectorial vibration sensing mechanism presented here, we avoid the uncertainties associated with the reproducibility and spectral quality of tilted gratings in multimode fiber by simply writing a conventional FBG in a short piece of PM-fiber spliced to standard single-mode fiber (Fig.…”

“…The gap distance between the splice and the grating center was 7 mm. The fiber length downstream from the grating should be carefully selected as it works as the inertial mass, which dominates the sensor resonance frequency and amplitude-frequency response [9]. Meanwhile, care must be taken to eliminate reflections from the end face of the PM fiber tip, since such reflections will return part of broadband light to the interrogation system and reduce the dynamic range of the measurement.…”