Measuring the speed of light in an optical fiber - Integrating Experimentation and Instrumentation
Nasser M. Juma, Anthony D. Edwards, Pi-Jung Chang, Kristan L. Corwin, Brian R. Washburn, N. Sanjay Rebello
Kansas State University, Manhattan, KS 66506 ; USA
Successful experimental physicists must understand the conceptual basis of experiments and the techniques of modern instrumentation, data collection and analysis. Through new capstone projects at Kansas State University, students in an electronics course, Physical Measurements and Instrumentation (PMI), apply their knowledge of electronics, instrumentation and LabVIEW to experiments from previous courses. This allows students to revisit the physics of earlier experiments and to solve real-world problems associated with experimental control and data acquisition. As an example, in the undergraduate Modern Physics Lab (MPL), students measure the speed of light in air with a time-of-flight measurement where pulses of ultraviolet light are reflected across the room in ~ 30 ns. Thus, measurement requires use of a fast photodiode and oscilloscope. This experiment is too fast for standard data acquisition software and hardware such as LabVIEW and NI ELVIS to be used for the measurement. As a solution, students proposed and implemented a much slower and inexpensive experiment using optical fiber. A fiber-coupled laser diode ~1300 nm (Part No. BA5979, Mitsubishi) is directly driven by circuitry on the NI ELVIS board and LabVIEW. The light is then sent through 1 km optical fiber (Corning SMF-28e) and detected by a 200 Hz Infrared Photoreceiver (New Focus, Model 2033). The time between the driving and the detected electronic pulse is determined via NI ELVIS using Virtual Instruments (LabVIEW VIs) which allows the calculation of the speed of light.
This work is supported by the U.S. National Science Foundation under grant DUE-0736897.
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