Abstract: An optical sensor system (such as an oximeter system) for use on a patient in an electrical environment (such as an RF field) includes at least one of the following three subsystems: (A) A light input subsystem includes a first control and display module disposed remotely outside of an electrical field, and input electrical cable connected at one end to the first module and at the other end to an electrically-powered light source disposed closely adjacent but outside of the electrical field. Input fiber optic cable for the transmission of analog optical signals extends from the light source to adjacent a patient in the electrical field. (B) A light output subsystem includes output fiber optic cable for the transmission of analog optical signals extending from adjacent the patient in the electrical field to a light detector disposed closely adjacent but outside of the electrical field.