Document Type : Original Research Paper

Authors

• Morteza Janfaza ¹
• Hamed Moradi ²

¹ Department of Electrical Engineering, Faculty of Engineering, University of Saravan, Saravan, Iran.

² Faculty of New Science and Technology, University of Tehran, Tehran, Iran.

Abstract

Background and Objectives: The domain of optical fiber acoustic sensors (OFAS) has witnessed considerable progress, with a specific emphasis on enhancing their sensitivity. Among the approaches explored, optical phase shift detection and the implementation of tapered single-mode fibers (SMFs) have garnered particular attention. This study evaluates the sensitivity characteristics of interferometric fiber optic acoustic sensors possessing bare SMF, tapered SMF, and standard SMF, all configured within a Michelson interferometer.
Methods: To achieve an efficient hardware implementation, the arctangent is calculated using the Coordinate Rotation Digital Computer (CORDIC) algorithm. CORDIC algorithm computes trigonometric functions through an iterative process of vector rotation. Its principal advantage lies in its reliance on elementary operations—specifically, additions, bit shifts, and table look-ups—which renders it a divider-free and highly area-efficient solution for nonlinear function evaluation.
Results: This work employs a Michelson interferometer configuration, which is illuminated by a 10 mW, 1550 nm Distributed Feedback Laser Diode (DFB-LD). The sensor probe integrates three distinct 1 cm lengths of standard, tapered (30 μm diameter), and bare single-mode fiber. This fiber assembly is embedded in a low-refractive-index polymer gel medium and mounted rigidly onto a metal plate. A piezoelectric phase modulator in the reference arm is driven by a 33 kHz signal, while acoustic stimuli are generated by a speaker, enabling a comparative performance analysis with a co-located commercial microphone. The findings indicate that bare SMF offers enhanced detectability for acoustic disturbances relative to its tapered and standard counterparts. The sensor is capable of resolving acoustic signals across 500 Hz to 4500 Hz.
Conclusion: The demodulated output of an OFAS is presented, confirming the system's ability to isolate acoustic signals from environmental drift. The acoustic sensitivity of three fiber configurations—standard SMF, tapered SMF (30 µm diameter), and bare SMF—was experimentally investigated. Findings demonstrate that the bare SMF exhibits significantly greater sensitivity than its tapered and standard counterparts. This enhanced response was corroborated by a strong correlation between the fiber sensor's output and the signal from a reference standard microphone.

Keywords

• Optical Fiber Acoustic Sensor
• Bare SMF
• Tapered SMF
• Phase Shift

Main Subjects

• Micro Sensors

Open Access

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Shahid Rajaee Teacher Training University