A simple fiberoptic differential temperature probe that utilizes the change of absorption of light in undoped GaAs in the vicinity of its bandgap as a temperature sensing mechanism is described. The probe is similar to that described by Kyuma et al.¹ but uses a different scheme of modulation, measures differential temperature, and is an improvement in accuracy by a factor of two. Prior to reporting on details of the probe that was constructed, the paper briefly discusses temperature sensing based on semiconductor bandgap behavior. This is followed by a report on initial experiments, which demonstrated the desired temperature response but also revealed the disturbing problem of changes in probe output caused by temperature induced mechanical misalignments. To attempt to remedy this problem, frequency division multiplexing was used, in which the output of one LED, of wavelength 0.88 pm was used as the actual temperature sensing mechanism, while changes in the transmitted radiation from another LED, of wavelength 1.27 μm, were used to correct the measured output for the mechanical misalignment. The 0.88 PM LED was amplitude modulated at 100 Hz; the 1.27 μm LED at 3 kHz. Although predicted minimum temperature difference for this system is 1.8 x 10-3°C, our margin of error with the signal generators used to modulate the LEDs that were available to us was ± 0.5°C. Indications are that this figure would be reduced considerably with signal generators of greater frequency stability.

Date Published: 23 March 1988
PDF: 8 pages
Proc. SPIE 0838, Fiber Optic and Laser Sensors V, (23 March 1988); doi: 10.1117/12.942511

Published in SPIE Proceedings Vol. 0838:
Fiber Optic and Laser Sensors V
Ramon P. DePaula; Eric Udd, Editor(s)