We introduce and experimentally demonstrate a fiber-connectorized optical system based on the use of a fiber-loop mirror (FLM) to study both the optical transmissivity and the optical phase retardation of a material. Our approach to investigating the optical transmissivity of a test sample is by initially adjusting the optical powers at both FLM output ports to the extremum. A reference and the test sample are then placed one by one at one of the FLM output ports. For the optical phase retardation measurement, we propose placing a test sample inside the FLM and analyzing the ratio of the normalized optical powers from the two FLM output ports in order to eliminate the effect of unwanted optical losses. Our experimental proof of concept using three known zero-order wave plates as our test samples shows promising results that agree very well with our theoretical analysis. Key features include robustness, low optical loss, low polarization dependent loss, and ease of implementation.