The multiple-pass optical cell is an important tool for laser absorption spectroscopy (TDLAS) and its many applications. For most practical applications, such astrace-gas detection, a compact and robust design is es-sential. Here LD-PD INC multi-passcell design based on a pair of cylindrical mirrors, witha particular focus on achieving very long optical paths. We demonstrate a path-length of 40 m in a cell with 40 mm diameter mirrors spaced 88.9 mm apart - a 3-foldincrease over the previously reported longest path-lengthobtained with this type of cell conﬁguration. We char-acterize the mechanical stability of the cell and describethe practical conditions necessary to achieve very longpath-lengths. Also we have our cell with Single mode fiber Coupled and Coated with wide bandwidth HR Coating. Our cell compact with Low insertion loss.