The paper, the method of three-dimensional refractive index measurement in optical fibers. The emphasis is put on experimental technique and instrumentation; however, important theoretical topics are briefly described (e.g., diffraction influence on measurement results). The experimental setup and measurement algorithm are presented in detail. Experimental results include measurement of the following objects: multimode optical fiber; optical fiber splice; and single-mode optical fiber. Sources of errors and accuracy of the method are analyzed. As a conclusion, we discuss the limitations and possible other applications of tomographic microinterferometry.