The paper presents an innovative packaging approach to allow highly sensitive in-line Mach–Zehnder interferometer (IMZI) sensor to be used for accurate measurement of curvature and flexural strain specifically in civil engineering. The sensor which consists of two tapers is protected within a polypropylene package to survive in harsh, in-the-field conditions. The package design employs cost effective materials without compromising the curvature and flexural strain sensitivity which are 85.2dBm−1 and 0.0148dB/μϵ. The accuracy of measurement results is further verified by obtaining the flexural modulus for the steel which is in good agreement with theoretical value.