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Interferometric fiber optic sensors.

Lee BH, Kim YH, Park KS, Eom JB, Kim MJ, Rho BS, Choi HY - Sensors (Basel) (2012)

Bottom Line: Some of the simple to fabricate but exceedingly effective Fabry-Perot interferometers, implemented in both extrinsic and intrinsic structures, are discussed.Also, a wide variety of Mach-Zehnder and Michelson interferometric sensors based on photonic crystal fibers are introduced along with their remarkable sensing performances.Finally, the simultaneous multi-parameter sensing capability of a pair of long period fiber grating (LPG) is presented in two types of structures; one is the Mach-Zehnder interferometer formed in a double cladding fiber and the other is the highly sensitive Sagnac interferometer cascaded with an LPG pair.

View Article: PubMed Central - PubMed

Affiliation: School of Information and Communications, Gwangju Institute of Science and Technology, Buk-gu, Gwangju, Korea. leebh@gist.ac.kr

ABSTRACT
Fiber optic interferometers to sense various physical parameters including temperature, strain, pressure, and refractive index have been widely investigated. They can be categorized into four types: Fabry-Perot, Mach-Zehnder, Michelson, and Sagnac. In this paper, each type of interferometric sensor is reviewed in terms of operating principles, fabrication methods, and application fields. Some specific examples of recently reported interferometeric sensor technologies are presented in detail to show their large potential in practical applications. Some of the simple to fabricate but exceedingly effective Fabry-Perot interferometers, implemented in both extrinsic and intrinsic structures, are discussed. Also, a wide variety of Mach-Zehnder and Michelson interferometric sensors based on photonic crystal fibers are introduced along with their remarkable sensing performances. Finally, the simultaneous multi-parameter sensing capability of a pair of long period fiber grating (LPG) is presented in two types of structures; one is the Mach-Zehnder interferometer formed in a double cladding fiber and the other is the highly sensitive Sagnac interferometer cascaded with an LPG pair.

No MeSH data available.


Related in: MedlinePlus

(a) Fourier spectra of the fabricated FPI fiber sensor measured with liquid (upper inset) and without liquid (lower inset) at the cavity, and (b) the RI of the liquid calculated from the Fourier spectrum and plotted with respect to the labeled RI. A series of liquid solutions of RIs from 1.400 to 1.438 with a step of 0.002 were applied into the cavity [35].
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f3-sensors-12-02467: (a) Fourier spectra of the fabricated FPI fiber sensor measured with liquid (upper inset) and without liquid (lower inset) at the cavity, and (b) the RI of the liquid calculated from the Fourier spectrum and plotted with respect to the labeled RI. A series of liquid solutions of RIs from 1.400 to 1.438 with a step of 0.002 were applied into the cavity [35].

Mentions: Figure 3(a) (see the lower inset) shows that the Fourier spectrum of Figure 2(b) has only one dominant peak corresponding to a half OPD of around 1 mm, the physical length of the cavity. The spectra measured with the series of liquid solutions at the cavity are presented with the upper inset of the figure. With increasing the RI, the Fourier peak is gradually shifted to the longer OPD, which means the optical length of the cavity increases with the RI of the liquid in it. In order to confirm the reproducibility of the sensor, the spectrum of the air cavity was repeatedly measured after every measurements of the liquid cavity. The lower inset of Figure 3(a) is composed of 20 Fourier spectra but looks like a single spectrum, which means the repeatability is excellent. From the Fourier peak variation, the RI of the liquid was calculated and compared with the labeled RI of the liquid as shown in Figure 3(b). We can see the data points are well fitted with a linear curve. However, since the labeled RI was measured at a wavelength of 589 nm, different from our measurement done at 835 nm, there exists a constant offset between two RI data [35]. Measurement in the Fourier domain has the limitation in resolving the Fourier peaks when there are several peaks nearby. Generally, the spatial resolution in the Fourier domain is defined by the bandwidth of a single resolved Fourier peak, which is determined by the spectral bandwidth of a light source. In our experiment, the source bandwidth was about 50 nm and the spatial bandwidth was about 10 μm. However, the FPI sensor based on a PCF lens has only one Fourier peak, which means only one cavity mode is involved, so that the Fourier peak overlap does not occur except near the DC peak. In this case, the accuracy or sensitivity of the sensor are important and given by how accurately the position of a Fourier peak position can be read. Of course, the spectral resolution of the spectrometer is a key factor, but disturbance of the source power and system instability affect the accuracy also. With a cavity length of 1 mm and a spectrometer resolution of 0.05 nm, the RI resolution of 2.6 × 10−5 was calculated [35]. As a result, this extrinsic FPI fiber sensor based on a specialty fiber PCF and a PCF lens is simple but very accurate, so that it should be useful for real time RI measurements of various liquid samples including gasoline, alcohol, and polluted water.


Interferometric fiber optic sensors.

Lee BH, Kim YH, Park KS, Eom JB, Kim MJ, Rho BS, Choi HY - Sensors (Basel) (2012)

(a) Fourier spectra of the fabricated FPI fiber sensor measured with liquid (upper inset) and without liquid (lower inset) at the cavity, and (b) the RI of the liquid calculated from the Fourier spectrum and plotted with respect to the labeled RI. A series of liquid solutions of RIs from 1.400 to 1.438 with a step of 0.002 were applied into the cavity [35].
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3376629&req=5

f3-sensors-12-02467: (a) Fourier spectra of the fabricated FPI fiber sensor measured with liquid (upper inset) and without liquid (lower inset) at the cavity, and (b) the RI of the liquid calculated from the Fourier spectrum and plotted with respect to the labeled RI. A series of liquid solutions of RIs from 1.400 to 1.438 with a step of 0.002 were applied into the cavity [35].
Mentions: Figure 3(a) (see the lower inset) shows that the Fourier spectrum of Figure 2(b) has only one dominant peak corresponding to a half OPD of around 1 mm, the physical length of the cavity. The spectra measured with the series of liquid solutions at the cavity are presented with the upper inset of the figure. With increasing the RI, the Fourier peak is gradually shifted to the longer OPD, which means the optical length of the cavity increases with the RI of the liquid in it. In order to confirm the reproducibility of the sensor, the spectrum of the air cavity was repeatedly measured after every measurements of the liquid cavity. The lower inset of Figure 3(a) is composed of 20 Fourier spectra but looks like a single spectrum, which means the repeatability is excellent. From the Fourier peak variation, the RI of the liquid was calculated and compared with the labeled RI of the liquid as shown in Figure 3(b). We can see the data points are well fitted with a linear curve. However, since the labeled RI was measured at a wavelength of 589 nm, different from our measurement done at 835 nm, there exists a constant offset between two RI data [35]. Measurement in the Fourier domain has the limitation in resolving the Fourier peaks when there are several peaks nearby. Generally, the spatial resolution in the Fourier domain is defined by the bandwidth of a single resolved Fourier peak, which is determined by the spectral bandwidth of a light source. In our experiment, the source bandwidth was about 50 nm and the spatial bandwidth was about 10 μm. However, the FPI sensor based on a PCF lens has only one Fourier peak, which means only one cavity mode is involved, so that the Fourier peak overlap does not occur except near the DC peak. In this case, the accuracy or sensitivity of the sensor are important and given by how accurately the position of a Fourier peak position can be read. Of course, the spectral resolution of the spectrometer is a key factor, but disturbance of the source power and system instability affect the accuracy also. With a cavity length of 1 mm and a spectrometer resolution of 0.05 nm, the RI resolution of 2.6 × 10−5 was calculated [35]. As a result, this extrinsic FPI fiber sensor based on a specialty fiber PCF and a PCF lens is simple but very accurate, so that it should be useful for real time RI measurements of various liquid samples including gasoline, alcohol, and polluted water.

Bottom Line: Some of the simple to fabricate but exceedingly effective Fabry-Perot interferometers, implemented in both extrinsic and intrinsic structures, are discussed.Also, a wide variety of Mach-Zehnder and Michelson interferometric sensors based on photonic crystal fibers are introduced along with their remarkable sensing performances.Finally, the simultaneous multi-parameter sensing capability of a pair of long period fiber grating (LPG) is presented in two types of structures; one is the Mach-Zehnder interferometer formed in a double cladding fiber and the other is the highly sensitive Sagnac interferometer cascaded with an LPG pair.

View Article: PubMed Central - PubMed

Affiliation: School of Information and Communications, Gwangju Institute of Science and Technology, Buk-gu, Gwangju, Korea. leebh@gist.ac.kr

ABSTRACT
Fiber optic interferometers to sense various physical parameters including temperature, strain, pressure, and refractive index have been widely investigated. They can be categorized into four types: Fabry-Perot, Mach-Zehnder, Michelson, and Sagnac. In this paper, each type of interferometric sensor is reviewed in terms of operating principles, fabrication methods, and application fields. Some specific examples of recently reported interferometeric sensor technologies are presented in detail to show their large potential in practical applications. Some of the simple to fabricate but exceedingly effective Fabry-Perot interferometers, implemented in both extrinsic and intrinsic structures, are discussed. Also, a wide variety of Mach-Zehnder and Michelson interferometric sensors based on photonic crystal fibers are introduced along with their remarkable sensing performances. Finally, the simultaneous multi-parameter sensing capability of a pair of long period fiber grating (LPG) is presented in two types of structures; one is the Mach-Zehnder interferometer formed in a double cladding fiber and the other is the highly sensitive Sagnac interferometer cascaded with an LPG pair.

No MeSH data available.


Related in: MedlinePlus