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6 October 2003 Fibergyro for educational purpose
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Proceedings Volume 9663, Eighth International Topical Meeting on Education and Training in Optics and Photonics; 966326 (2003) https://doi.org/10.1117/12.2208504
Event: Eighth International Topical Meeting on Education and Training in Optics and Photonics, 2003, Tucson, Arizona, United States
Abstract
We describe an experiment that allows students to measure the Sagnac effect with a fibergyro linked to a rotating plate. The Sagnac signal is compared to an independant measurement that uses an optical encoder. The Sagnac law can be verified and the speed of Earth rotation can be estimated experimentaly.

1.

Introduction

Fibergyros are widely used devices in aircraft industry. Our labwork experiment uses a commercial-type interferometer with all suitable integrated optics: superluminescent laser diode, integrated coupler and electro-optic modulators, 2 km monomode fiber-coil, photodiode. In a first part, with no modulation applied to the electro-optic modulators, the electric Sagnac signal delivered by the photodiode of the rotating fibergyro is transmitted to the laboratory recording station through a free space optical digital link and compared to an independant measurement that uses a classical optical encoder. Then, the Sagnac law can be precisely verified in the range [– 40 rpm, +40 rpm]. In a second part, with modulation applied and using a lock-in amplifier, the speed of Earth rotation can be estimated with a precision limited by the fibergyro sensitivity.

2.

Experiment

2.1

Set-up

Fig.1 shows the set-up of the fibergyro. The conditioning of the signal and the digital transmission through the dedicated optical link from the moving plate to the measurement station will be detailed in the paper.

Fig. 1.

Fibergyro set-up.

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2.2

Verification of Sagnac’s law

The Sagnac signal Sg is recorded with the Lab VIEW software and finally plotted versus the speed of rotation Ω measured independently. Figure 2 shows the front ends of the virtual instrument with Sg and Ω variations.

Fig. 2.

Left: Sagnac signal Sg and independently measured speed of rotation Ω versus time. Right: Sagnac's law Sg(Q).

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2.3

Speed of Earth rotation

In a second part, the extremly tiny useful signal due to the Earth rotation will be extract from noise with a lock-in amplifier and give an estimation of the speed of rotation (Ω ≈ 1.0 revolution per day ±10%), the uncertainty being governed by the electrical signal to noise ratio and the residual non-reciprocity of the interferometer.

© (2003) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Hervé Sauer, Lionel Jacubowiez, Thierry Avignon, Nicolas Dubreuil, and Marc Bondiou "Fibergyro for educational purpose", Proc. SPIE 9663, Eighth International Topical Meeting on Education and Training in Optics and Photonics, 966326 (6 October 2003); https://doi.org/10.1117/12.2208504
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