Environmental monitoring is essential in order to deal efficiently, safely, and effectively with resources, such as petroleum, natural gas, cultivated land, and others. To this end, various green technologies have been developed.1 However, understanding and prediction of environmental changes remain challenges. Thus, unexpected changes that cause or become an ecological or human-health threat need to be monitored in the temporal and spatial domains.2 Monitoring technologies have been focused on analysis of the chemical and physical properties of environments.3 Electrochemical sensors have been developed as monitoring sensors in various studies according to analytes4-6 or sensing principles.7-9 They have some advantages such as low-power operation, high selectivity, and the linear relationship between output signals and analyte concentration.10 Electrochemical sensors generally contain the electrodes coated with a catalyst that promotes either oxidation or reduction of certain chemical species.11 Even though they contain such high-selectivity catalysts, the study of catalyst species with high durability under extreme conditions of harsh environments remains challenging.12 Other types of electronic sensors, for example electromechanical sensors13 and thermoelectric sensors,14 have also been studied as monitoring sensors in harsh environments. A micro-electro-mechanical sensor has been extensively studied owing to its small size15 and low production cost.16 However, those sensors have a short life-time in harsh environments due to the failure resulting from creep and plastic deformation, corrosion, and electrical disturbance.17 Especially as environmental monitoring sensors are required to be running for long periods in harsh conditions, it is necessary to develop sensors that are durable in harsh environments for long operation times. The optical fiber sensor (OFS) is a promising sensor for harsh environments. Compared with the electronic sensors, the OFS uses optical cables that have low heat loss and high data bandwidth over electric cables.18 This allows connectivity over hundreds of thousands of kilometers via massive optical cables. Massive information technology resources are connected continent-to-continent19 thanks to submarine cables laid around the world as shown in Fig. 1.20 Optical fiber cables offer reliability even underneath the ocean for long durations, as optical fiber has unique characteristics such as immunity to electromagnetic interferences and chemical corrosion, and low heat loss.21 This indicates that the OFS can also generate and transmit measurement data with high sensitivity even in harsh ambient conditions, such as in downholes for oil recovery22 and in nuclear power plants.23 Moreover, the OFS is compatible with existing fiber-optic communication systems, which means environmental monitoring using the OFS can be remotely operated in a network operating system.24 The light weight, small size, and high flexibility of optical fibers play an important role in environmental monitoring sensors as well.