@article {, title = {Undiscovered issues and solutions for direct detected ϕ-OTDR systems}, journal = {Optical Fiber Technology}, volume = {60}, year = {2020}, month = {12/2020}, pages = {102346}, issn = {1068-5200}, doi = {10.1016/j.yofte.2020.102346}, author = {Adeel, Muhammad and Javier Tejedor and Javier Macias-Guarasa and Zhu, Kun} }