A Highly Accurate All-Fiber MMZI Current Sensor

Earlier reported micro-Mach-Zehnder interferometer (MMZI) sensors, fabricated by concatenation of tapered fibers, considered the interference between LP01 and LP02 modes only for generating the fringe pattern. However, the experimental studies evidenced aperiodic and nonsinusoidal spectral response, which may be attributed to the occurrence of interference among higher order cladding and LP01 and LP02 modes enroute the interference region. In order to accommodate the effect of interference among the higher order cladding modes, a perturbation term has been inserted in the expression for free spectral range and formula for shift in the fringes, due to rise in temperature of the fiber, in this paper. Furthermore, three samples of in-house fabricated MMZIs, placed over a direct current carrying power resistor, senses the temperature produced due to emanation of Joule's heat and resulted into shift in the output fringe pattern. The effect of change in temperature/current is displayed as shift in the output spectrum, recorded on an optical spectrum analyzer, in accordance with the amended equations. The fabricated sample demonstrates the higher current sensitivity 1.76 nm/A
²
with the regression/correlation coefficient (R
²
) value 0.99.