Abstract: An optical interface coupler for coupling a flow cell to an optical absorption analyzer. The flow cell and analyzer are operable to transmit light through a fluid flowing through a chamber within the cell and analyze the transmitted light for determining certain optical properties of the fluid. The cell includes a first port through which light from a first fiber optic cable is transmitted to the chamber and a second port through which transmitted light is received and transmitted to a second fiber optic cable connected to the optical absorption analyzer. The optical interface coupler comprises a housing and a lens. The housing is releasably attachable to the cell at one of the first and second ports and defines an optical pathway therein. A cable port is in the housing for receiving one of the first and second fiber optic cables, and is in optical communication with the optical pathway.