A THEORETICAL PERFORMANCE STUDY OF AN EXTERNAL CAVITY FIBER FABRY- PEROT INTERFEROMETER FOR DISPLACEMENT MEASUREMENT

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Arumugam, K. (2015). A THEORETICAL PERFORMANCE STUDY OF AN EXTERNAL CAVITY FIBER FABRY- PEROT INTERFEROMETER FOR DISPLACEMENT MEASUREMENT. Unc Charlotte Electronic Theses And Dissertations.
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Abstract

The objective of this research is to explore a mathematical model developed by Wilkinson and Pratt for the external cavity fiber-based Fabry-Perot interferometer (EFPI) and to create a Michelson interferometer setup to validate a frequency modulation component of this model. A laser diode with nominal wavelength 635 nm is modulated by oscillating the diode current of maximum amplitude 22.62 mA to create correspondingly varying wavelength. Experiments are included to evaluate a rotating vector representation of the modulation harmonics in the signal received at the photodetector as of a cube corner translated by a piezo-electric actuator is displaced. Wavelength modulation as a function of diode current, the coherence length of the laser, and characteristics of the modulation harmonics are evaluated. A real time DAQ system and two lock-in amplifiers are utilized for detecting three side-band harmonics of the signal. For short range displacements this interferometer setup is monitored using a capacitance displacement sensor. The capacitance displacement measurement differed from the Michelson interferometer by 160 nm. The piezoelectric stage actuated with a 15 V Ramp signal produced 2.54 μm displacement of the cube corner. The setup is tested with Ramp signals of 75 V to 1.5 V and with the Ramp periods of 1 to 20 seconds to find the resolution of the interferometer, modulation of the wavelength sensitivity and the coherence length of the laser as 10.53 nm, 1.786 nmA-1 and >1 m respectively. The best quadrature signal achieved corresponded to modulating the laser at amplitude of 18.86 mA at 1 kHz frequency with a path length difference of 6.35 mm. The amplitude comparison of side-band harmonics with Bessel function curves is consistent with a modulation amplitude of 1.28 rad corresponding to amplitude ratios of 0.5 (second and first) , 0.15 (third and second) and 0.06 (third and first) in the first through third Bessel function values.

Details
Author

Arumugam, Kumar

Title

A THEORETICAL PERFORMANCE STUDY OF AN EXTERNAL CAVITY FIBER FABRY- PEROT INTERFEROMETER FOR DISPLACEMENT MEASUREMENT

Physical Description

1 online resource (90 pages) : PDF

Date

2015

Degree Granting Institution

University of North Carolina at Charlotte

Abstract

The objective of this research is to explore a mathematical model developed by Wilkinson and Pratt for the external cavity fiber-based Fabry-Perot interferometer (EFPI) and to create a Michelson interferometer setup to validate a frequency modulation component of this model. A laser diode with nominal wavelength 635 nm is modulated by oscillating the diode current of maximum amplitude 22.62 mA to create correspondingly varying wavelength. Experiments are included to evaluate a rotating vector representation of the modulation harmonics in the signal received at the photodetector as of a cube corner translated by a piezo-electric actuator is displaced. Wavelength modulation as a function of diode current, the coherence length of the laser, and characteristics of the modulation harmonics are evaluated. A real time DAQ system and two lock-in amplifiers are utilized for detecting three side-band harmonics of the signal. For short range displacements this interferometer setup is monitored using a capacitance displacement sensor. The capacitance displacement measurement differed from the Michelson interferometer by 160 nm. The piezoelectric stage actuated with a 15 V Ramp signal produced 2.54 μm displacement of the cube corner. The setup is tested with Ramp signals of 75 V to 1.5 V and with the Ramp periods of 1 to 20 seconds to find the resolution of the interferometer, modulation of the wavelength sensitivity and the coherence length of the laser as 10.53 nm, 1.786 nmA-1 and >1 m respectively. The best quadrature signal achieved corresponded to modulating the laser at amplitude of 18.86 mA at 1 kHz frequency with a path length difference of 6.35 mm. The amplitude comparison of side-band harmonics with Bessel function curves is consistent with a modulation amplitude of 1.28 rad corresponding to amplitude ratios of 0.5 (second and first) , 0.15 (third and second) and 0.06 (third and first) in the first through third Bessel function values.

Genre

masters theses

Subjects--Topics

Mechanical engineering
Optics
Meteorology

Degree

M.S.

Subject Area

Mechanical Engineering

Advisor(s)

Smith, Stuart

Committee Members

Schmitz, Tony
Her, Tsinghua

Degree Note

Thesis (M.S.)--University of North Carolina at Charlotte, 2015.

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Rights Holder Information

Copyright is held by the author unless otherwise indicated.

Identifier

Arumugam_uncc_0694N_10992

Permalink

http://hdl.handle.net/20.500.13093/etd:1049