Classification of Fiber Optic Interferometer Sensors

Fiber optic interferometer sensors are primarily classified into Fabry-Perot, Mach-Zehnder, Michelson, and Sagnac types, each with unique configurations and sensing capabilities.1. Fabry-Perot Interfe...

Classification of Fiber Optic Interferometer Sensors

Fiber optic interferometer sensors are primarily classified into Fabry-Perot, Mach-Zehnder, Michelson, and Sagnac types, each with unique configurations and sensing capabilities.

1. Fabry-Perot Interferometer (FPI)

Fabry-Perot interferometers consist of two parallel reflecting surfaces forming an optical cavity, where interference occurs due to multiple reflections between the surfaces. FPIs are further classified into:

  • Extrinsic FPI: The cavity is external to the fiber, allowing easy access for measuring refractive index or liquids. It offers high finesse and simple fabrication.
  • Intrinsic FPI: The cavity is formed within the fiber itself, often requiring precise micro-machining. This design is compact and suitable for high-sensitivity applications. FPIs are widely used for temperature, strain, pressure, and refractive index sensing due to their high resolution and sensitivity .

2. Mach-Zehnder Interferometer (MZI)

Mach-Zehnder interferometers split light into two separate paths, with one path interacting with the measurand. The recombination of the beams produces interference patterns that encode changes in optical path difference. MZIs can be implemented using photonic crystal fibers or double-cladding fibers and are suitable for multi-parameter sensing, including strain, temperature, and refractive index . They are valued for compactness, high coupling efficiency, and stability.

3. Michelson Interferometer

Michelson interferometers use a single beam splitter to divide light into a reference and sensing beam. The reference beam reflects off a fixed mirror, while the sensing beam reflects off a movable or perturbed mirror. The interference pattern provides information about displacement, strain, or vibration. Michelson designs are simple and widely used in precision measurement applications .

4. Sagnac Interferometer

Sagnac interferometers rely on counter-propagating light beams in a fiber loop. The phase difference between clockwise and counterclockwise beams is sensitive to rotation, strain, and temperature. Sagnac interferometers are often combined with long-period fiber gratings (LPGs) for enhanced sensitivity and multi-parameter sensing . They are particularly robust against environmental noise and suitable for rotation sensing and gyroscopes.

Summary of Key Features

InterferometerConfigurationMeasurand SensitivityAdvantages
Fabry-PerotParallel mirrors (intrinsic/extrinsic)Strain, temperature, pressure, RIHigh resolution, simple fabrication (extrinsic), compact (intrinsic)
Mach-ZehnderTwo separate pathsStrain, temperature, RIMulti-parameter sensing, compact, high stability
MichelsonSingle beam splitter, reference & sensing mirrorsDisplacement, strain, vibrationSimple, precise, widely used
SagnacFiber loop, counter-propagating beamsRotation, strain, temperatureRobust, high sensitivity, suitable for gyroscopes

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