Modalmetric interferometer under Fingerprint disturbances: The effect of lateral offset between the single‐mode and multimode fiber splice

Abstract

We report on the wavelength and time-domain responses of a lumped or distributed fiber-optic modalmetric interferometer under a very smooth pressure (fingerprint) disturbances in the 1530-1610 nm wavelength range. A simple method to quantify such disturbances is proposed. It is shown that the lateral offset shift of 5.9 mm between RIBEIRO AND BALOD | 151 the single-mode and the multimode fiber splice makes the device even more sensitive. It was measured an electrical signal power enhancements of 3.5 and 7.5 dB for 1 m and 1.65 km multimode fiber link, respectively. K E Y W O R D Sacoustic communications, disturbance sensor, fingerprint, modalmetric fiber-optic interferometer, optoacoustic receiver, security

The effects of scaling and bends in a fiber‐optic modalmetric acoustic detector

“…10,19 However, with L s = 25 cm, where the s-MMF was coiled forming a "figure-of-eight" (see Figure 2), the bends of the fiber may excite other higher-order modes leading to at least three propagating and interfering modes. 10,19,22 Simple calculations already suggest that the lonely increase of L s length is already able to provide an increase of the modalmetric sensitivity by means of the scaling effect. 12 However, the bends imprinted on the s-MMF lead the modalmetric device, presented here as really a multibeam interferometer.…”

“…These devices behave like a multimode (or multibeam in the ray domain), one-arm interferometer and have been used as a distributed disturbance detector operating in the electrical or optical frequency domains. [9][10][11] An optical fiber can be shaped to a surface in which acoustic signals arrive, that is, the s-MMF may be coiled around the perimeter of an extremity or an accessible point of the metallic cable or wall where the acoustic communications take place. Moreover, since a fiber-based device is used for sensing or detection, its sensitivity may be increased when the length of the sensitive fiber is also increased, which is called "scaling" or "amplitude scaling".…”

“…Sensors or detectors based on modal interferometer (modalmetric) in the reflective structure are fabricated by simply splicing a single‐mode fiber (SMF) with a sensitive multimode fiber (s‐MMF) strand. These devices behave like a multimode (or multibeam in the ray domain), one‐arm interferometer and have been used as a distributed disturbance detector operating in the electrical or optical frequency domains 9‐11 …”

Sensitivity of an Opto-Acoustic Detector Based on a Modalmetric Interferometer with the Length of Interacting Fibre

“…The light is launched at the port 1, exits at port 2 of an optical circulator and probes the modalmetric structure itself. A singlemode fibre (SMF) was spliced to a sensitive multi-mode fibre (s-MMF) [8]. The modalmetric interferometer detector operates in the reflective mode (R-MMI).…”

“…For 0-10 V pp range it is also clearly observed the increase of the sensitivity because while for 5 cm s-MMF length, the output exhibit over a half-cycle of an interferometric response, and with 25 cm length an amount of 4.5 cycles is achieved. The sensitivity mechanism of the multimode interference taking place in the s-MMF splice with SMF by excitation with acoustic signals, can be attributed to the induced phase changes of its interfering modes [8]. The mechanism can then be equivalently explained by considering the disturbances as perturbations to the self-image of the input excitation on the output aperture as produced by the multimode interference effect [9].…”