“…Recently, the application of optical fiber sensors (OFSs) in twist sensing has intensified, due to their advantages of flexibility, light weight, and resistance to electromagnetic interference. Though many different schemes have been proposed, optical fiber twist sensors (OFTSs) can be mainly classified into two types: one interrogated with wavelength (e.g., specially designed fiber gratings [1][2][3][4][5][6][7][8], Sagnac interferometer [9][10][11], helical fiber structure [12][13][14]), and the other with intensity (e.g., Solc filter [15], Lyot filter [16], Mach-Zehnder interferometers [17][18][19]), and fiber gratings [20][21][22][23][24][25][26][27][28][29][30]. Note that for the first type, the wavelength measurement involves the use of expensive and bulky optical spectrum analyzer (OSA) or tunable narrow-linewidth laser, whereas for the second type, intensity measurement only requires an optical power meter (or photodetector), which allows more compact and cost-effective interrogation than the first type.…”