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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 20, Iss. 10 — May. 7, 2012
  • pp: 11109–11120
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All-fiber Mach-Zehnder interferometers for sensing applications

Lecheng Li, Li Xia, Zhenhai Xie, and Deming Liu  »View Author Affiliations


Optics Express, Vol. 20, Issue 10, pp. 11109-11120 (2012)
http://dx.doi.org/10.1364/OE.20.011109


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Abstract

We propose and demonstrate a thinned fiber based Mach-Zehnder interferometer for multi-purpose sensing applications. The sensor head is formed by all-fiber in-line singlemode-multimode-thinned-singlemode (SMTS) fiber structure, only using the splicing method. The principle of operation relies on the effect that the thinned fiber cladding modes interference with the core mode by employing a multimode fiber as a mode coupler. Experimental results showed that the liquid refractive index information can be simultaneously provided from measuring the sensitivity of the liquid level. A 9.00 mm long thinned fiber sensor at a wavelength of 1538.7228 nm exhibits a water level sensitivity of −175.8 pm/mm, and refractive index sensitivity as high as −1868.42 (pm/mm)/RIU, respectively. The measuring method is novel, for the first time to our knowledge. In addition, it also demonstrates that by monitoring the wavelength shift, the sensor at a wavelength of 1566.4785 nm exhibits a refractive index sensitivity of −25.2935 nm/RIU, temperature sensitivity of 0.0615 nm/°C, and axial strain sensitivity of −2.99 pm/με, respectively. Moreover, the sensor fabrication process is very simple and cost effective.

© 2012 OSA

1. Introduction

Optical fiber sensors have attracted great attentions in the applications of biological, chemical and environmental industries, including the measurements of the liquid level, refractive index (RI), temperature and strain. Compared to the other techniques that based on the mechanical and electrical methods, the optical fiber sensors have many advantages, such as electromagnetic immunity, resistance to erosion, high sensitivity and capability of remote sensing. In the past years, several types of fiber optical sensors have been developed. For example, the sensors based on the long period fiber gratings [1

1. A. P. Zhang, L. Y. Shao, J. F. Ding, and S. He, “Sandwiched long-period gratings for simultaneous measurement of refractive index and temperature,” IEEE Photon. Technol. Lett. 17(11), 2397–2399 (2005). [CrossRef]

3

3. P. L. Swart, “Long-period grating Michelson refractometric sensor,” Meas. Sci. Technol. 15(8), 1576–1580 (2004). [CrossRef]

] and fiber Bragg gratings [4

4. A. Iadicicco, S. Campopiano, A. Cutolo, M. Giordano, and A. Cusano, “Nonuniform thinned fiber bragg gratings for simultaneous refractive index and temperature measurements,” IEEE Photon. Technol. Lett. 17(7), 1495–1497 (2005). [CrossRef]

,5

5. P. Lu and Q. Chen, “Fiber Bragg grating sensor for simultaneous measurement of flow rate and direction,” Meas. Sci. Technol. 19(12), 125302–125309 (2008). [CrossRef]

] have been widely reported. These sensors possess advantages such as absolute response parameter, large dynamic range and high sensitivities. However, they have large cross sensitivities and the fabrication requires the expensive ultraviolet light laser, phase masks, etc. Sensors based on all fiber interferometer have also been typically used [6

6. Y. J. Rao, “Recent progress in fiber optic extrinsic Fabry-Perot interferometric sensors,” Opt. Fiber Technol. 12(3), 227–237 (2006). [CrossRef]

8

8. Y. J. Rao, M. Deng, T. Zhu, and H. Li, “In-line Fabry-Perot Etalons based on hollow-core photonic bandgap fibers for high temperature applications,” J. Lightwave Technol. 27(19), 4360–4365 (2009). [CrossRef]

], owing to high sensitivity, simple fabrication process and un-limited measuring of wavelength range. Such as the in-line Fabry-Perot interferometer sensor based on the endlessly photonic crystal fiber [9

9. Y. J. Rao, T. Zhu, X. C. Yang, and D. W. Duan, “In-line fiber-optic etalon formed by hollow-core photonic crystal fiber,” Opt. Lett. 32(18), 2662–2664 (2007). [CrossRef] [PubMed]

], but it still requires expensive photonic crystal fiber. Furthermore, the sensor head is very fragile.

Recently, sensors based on all-fiber Mach-Zehnder interferometer (MZI) have received considerable attention [10

10. H. Y. Choi, M. J. Kim, and B. H. Lee, “All-fiber Mach-Zehnder type interferometers formed in photonic crystal fiber,” Opt. Express 15(9), 5711–5720 (2007). [CrossRef] [PubMed]

13

13. Z. Tian, S. S. H. Yam, J. Barnes, W. Bock, P. Greig, J. M. Fraser, H. P. Loock, and R. D. Oleschuk, “Refractive index sensing with Mach-Zehnder interferometer based on concatenating two single-mode fiber tapers,” IEEE Photon. Technol. Lett. 20(8), 626–628 (2008). [CrossRef]

], they are compact and robust. Linh et al. presented a multimode-singlemode-multimode (MSM) fiber structure based MZI sensor for high temperature measurement [14

14. L. V. Nguyen, D. Hwang, S. Moon, D. S. Moon, and Y. Chung, “High temperature fiber sensor with high sensitivity based on core diameter mismatch,” Opt. Express 16(15), 11369–11375 (2008). [CrossRef] [PubMed]

], but the lengths of the MMFs should be perfectly controlled. Wu Q, et al. reported a high sensitivity singlemode-multimode-singlemode (SMS) fiber structure based refract-meter [15

15. Q. Wu, Y. Semenova, P. Wang, and G. Farrell, “High sensitivity SMS fiber structure based refractometer--analysis and experiment,” Opt. Express 19(9), 7937–7944 (2011). [CrossRef] [PubMed]

]. Nevertheless, the sensors based on the etching process have to use poison chemicals in the fabrication process and the diameter of the exposed core is hard to be controlled.

2. Schematic diagram and properties of the sensor

In order to improve the effect of the MMF in the structure, experimental results based on the singlemode-thinned-singlemode (STS) fiber structure and the SMTS fiber structure are shown in Figs. 2(a)
Fig. 2 Measured transmission spectrum of the (a) singlemode-thinned-singlemode (STS), and (b) singlemode-multimode-thinned-singlemode (SMTS) fiber structure.
and 2(b), respectively. The length of the TF in both cases is kept at 48.38mm. Compared to the STS, the interference fringe visibility of the SMTS is improved by several times. It is accredited to the mode field diameter of the MMF being much larger than SMF, thus, the power of the light injected to the cladding mode of the TF is dramatically enhanced. Moreover, the cladding modes of the TF could be excited due to the using of MMF, which is different from the STS structure in [16

16. J. Canning and A. L. G. Carter, “Modal interferometer for in situ measurements of induced core index change in optical fibers,” Opt. Lett. 22(8), 561–563 (1997). [CrossRef] [PubMed]

] that the core modes LP01 and LP11 were excited through the mode field mismatch between two SMFs and the thinned fiber.

Additionally, we also have researched the influence of the MMF length to the sensor performance during our experiment. Theoretically, the length of the MMF determines the transverse field distribution at the interface MMF-TF and influences the coupling strengths of MMF core modes to the TF cladding / core modes [14

14. L. V. Nguyen, D. Hwang, S. Moon, D. S. Moon, and Y. Chung, “High temperature fiber sensor with high sensitivity based on core diameter mismatch,” Opt. Express 16(15), 11369–11375 (2008). [CrossRef] [PubMed]

]. However, when this length is long enough, such as it is above several centimeters, we find that this influence on the interference fringe is very slight through our experiments. It can be seen from Fig. 3
Fig. 3 Measured transmission spectrum with the sensor TF in the air at different lengths of MMF and in the index matching oil of LMMF = 22cm.
with a sensor TF length of 18.02mm in the air, the length of the MMF is changed as 22cm, 32cm and 40cm, respectively. It is due to the fact that the interference spectrum is mainly formed by the TF cladding modes interfering with the TF core mode. The interference between the eigenmodes in the MMF core has very large FSR [15

15. Q. Wu, Y. Semenova, P. Wang, and G. Farrell, “High sensitivity SMS fiber structure based refractometer--analysis and experiment,” Opt. Express 19(9), 7937–7944 (2011). [CrossRef] [PubMed]

], and it may not fall into the measured transmission spectra range. Thus, it only modifies the envelope of the interference when the length of the MMF increases. From Refs. [15

15. Q. Wu, Y. Semenova, P. Wang, and G. Farrell, “High sensitivity SMS fiber structure based refractometer--analysis and experiment,” Opt. Express 19(9), 7937–7944 (2011). [CrossRef] [PubMed]

,23

23. S. M. Nalawade and H. V. Thakur, “Photonic crystal fiber strain-independent temperature sensing based on modal interferometer,” IEEE Photon. Technol. Lett. 23(21), 1600–1602 (2011). [CrossRef]

], we also can obtain that the length of the MMF has no significant influence on the sensor sensitivity

Sensors with TF length of L = 4.62mm, 9.00mm, 27.42mm and 54.54mm SMTS fiber structure are fabricated, and the transmission spectra are shown in Fig. 4
Fig. 4 Measured transmission spectrum of the SMTS sensor with different TF lengths.
. It can be seen that the FSR will decrease as the interferometer length L increases, and the interference fringe of the sensor is not uniform but looks like having several frequency components in the interference fringe periods.

In order to analyze the number and power distribution of the interference modes, the wavelength spectra in Fig. 4 are Fourier transformed [24

24. H. Y. Choi, G. Mudhana, K. S. Park, U. C. Paek, and B. H. Lee, “Cross-talk free and ultra-compact fiber optic sensor for simultaneous measurement of temperature and refractive index,” Opt. Express 18(1), 141–149 (2010). [CrossRef] [PubMed]

] to get the spatial frequency spectra in Fig. 5
Fig. 5 Spatial frequency of the SMTS sensor with different TF lengths.
. The dominant intensity peak at zero relates to the core modes. The powers are primarily distributed in the core mode and the low-order cladding mode as the length varies. It means that the mode coupling of different length mainly occurs between the core mode and the low-order cladding mode. The multiple minor intensity peaks in the inset of Fig. 5 correspond to the high-order cladding modes. Those interferences between the core mode and the high-order cladding modes also modify the envelope of the interference in Fig. 4. It is also observed that when the sensor is put in the index matching oil to remove the cladding modes, the interference phenomenon almost disappears, which can be seen from Fig. 3 with the MMF length of 22cm. It is again believed that the cladding modes are excited different from the core mode LP11 in Ref. [16

16. J. Canning and A. L. G. Carter, “Modal interferometer for in situ measurements of induced core index change in optical fibers,” Opt. Lett. 22(8), 561–563 (1997). [CrossRef] [PubMed]

].

3. Sensing applications and discussion

In the Section 2, the design and principle of the SMTS fiber structure sensor has been presented. In the following part, we will describe and discuss the applications of this sensor in the measurement of liquid level, refractive index, temperature and axial strain with the TF length L of 9.00mm. The transmission spectrum of the sensor in the air is shown in Fig. 4(b). In these experiments, a broadband optical source (C and L band) is used to inject light into the structure, and an optical spectrum analyzer (YOKOGAWA AQ6370C) is used to measure the transmission spectral response of the sensor.

3.1 Liquid level sensor

We experimentally examine the liquid level and refractive index with the length L of 9.00mm. Figure 6(a)
Fig. 6 (a) The schematic diagram of the experimental system. (b) Measured wavelength shift for water level, and (c) sensor response at a wavelength of 1538.7228nm with different refractive indices.
shows the schematic diagram of the experimental system. The sensor is set on a fixing skeleton, which is placed vertically inside the beaker. The lead-in and lead-out fibers are connected with a broad band optical source and an optical spectrum analyzer, respectively. The liquid level is increased by using a buret step by step, which is metered by the vernier caliper. The transmission spectrum is measured as the liquid level rises slowly. When the spectrum starts to shift, it is chosen as the initial state, and the level is marked as the reference liquid level.

The relationship between the sensitivitySnand the refractive indexnis also investigated in detail by putting the sensor into different liquids, at range from 1.3345 to 1.3775. The temperature is still kept at 20 °C. Figure 7
Fig. 7 The liquid level sensitivity as a function of refractive indices.
shows the linear fitting lines of the level sensitivity with respect to the refractive index, and the regression equation can be expressed as
Sn=1868.4233n+2314.9878,1.3345n1.3775
(5)
where Snis the level sensitivity, and nis the liquid refractive index. The slope of equation gives an average refractive index sensitivity of the measured liquid [26

26. B. Shuai, L. Xia, Y. Zhang, and D. Liu, “A multi-core holey fiber based plasmonic sensor with large detection range and high linearity,” Opt. Express 20(6), 5974–5986 (2012). [CrossRef] [PubMed]

]. An average sensitivity of −1868.4233 (pm / mm) / RIU is obtained in our experiment with the sensing range from 1.3345 to 1.3775. The linearity of the Sn-ncurve is about 0.99278, indicating a high linearity of the SMTS sensor. This provides another advantage to our sensor, because we can measure the surrounding liquid refractive index by monitoring the sensitivity of the sensor. This method is quite different from the traditional way to measure the RI based on monitoring the wavelength shift [27

27. J. E. Antonio-Lopez, J. J. Sanchez-Mondragon, P. LiKamWa, and D. A. May-Arrioja, “Fiber-optic sensor for liquid level measurement,” Opt. Lett. 36(17), 3425–3427 (2011). [CrossRef] [PubMed]

] or the changing of the fringe visibility [28

28. Q. Jiang, D. Hu, and M. Yang, “Simultaneous measurement of liquid level and surrounding refractive index using tilted fiber Bragg grating,” Sens. Actuators A Phys. 170(1-2), 62–65 (2011). [CrossRef]

], for the first time to our knowledge.

Therefore, the procedure of measurements of liquid level and refractive index can be the following: Firstly, the RI information can be obtained by dipping the sensor entirely into the liquid for the measurement of the liquid level sensitivity, since the cavity length L of MZI and the wavelength shifts of both in the air and in the liquid are all known. And then, the sensor is placed vertically and fixed for the monitoring the changes of liquid level. The largest sensing range is limited by the cavity length L. We believe that this range can be as large as up to tens of centimeters, for we observe that the interference fringes still exist there. When the outside refractive index approaches to that of the thinned fiber cladding (around 1.45), the interference fringes will disappear, thus it limits the maximum sensing range.

3.2 Refractive index sensor

From the Section 3 part 1, it is known that the attenuation peak wavelength will shift to a short wavelength when the refractive index surrounding the thinned fiber rises. The response of the sensor to the external refractive index is investigated by putting the sensor entirely into the NaCl solution, while the temperature is kept at 20 °C. The schematic diagram of the experimental setup for the refractive index is shown in Fig. 6(a) with TF length L of 9.00mm. The RI of the solutions is calibrated by an Abbe refractometer with the resolution of 0.0001.

Figure 8(a)
Fig. 8 (a) Measured wavelength shift for various RI at a wavelength of 1566.47858nm, and (b) RI response at different wavelengths.
shows the wavelength shift of transmission spectra as the external refractive index increases from 1.3345 to 1.3775. As shown in the inset, the selected order (114) experiences 1.0739 nm blueshift as the surrounding refractive index increases. It is due to the fact that the accumulated difference of the effective refractive indices between the core and the cladding modes will decrease more for a higher outside refractive index. Therefore, the attenuation peak will shift to a shorter wavelength. The measured RI responses to different orders of attenuation peaks are analyzed in Fig. 8(b). The sensitivities of the selected order attenuation peaks are analyzed by using linear regression fits, and they exhibit good linear responses. For the wavelengths selected at 1538.7228nm (order 116), 1551.5819nm (order 115) and 1566.4785nm (order 114), the average corresponding sensitivities are −17.5224nm/RIU, −22.5952nm/RIU and −25.2935nm/RIU, respectively. The experimental results show that the lower order attenuation peak exhibits a larger wavelength shift than the higher order peak.

3.3 Temperature sensor

When the external temperature around the TF rises, both the effective refractive index of the core and cladding modes increase. While that of the core mode changes more since the thermo-optic coefficient of the Ge-doped silica core is higher than that of the cladding consisting of fused silica. As result, the effective refractive index indices between the core and cladding modes increase [25

25. P. Lu, L. Men, K. Sooley, and Q. Chen, “Tapered fiber Mach-Zehnder interferometer for simultaneous measurement of refractive index and temperature,” Appl. Phys. Lett. 94(13), 131110 (2009). [CrossRef]

], and from Eq. (2), it is known that the attenuation peak wavelength will change to a longer wavelength.

For the temperature measurement, Fig. 9(a)
Fig. 9 (a) Schematic diagram of the experimental setup. (b) Measured wavelength shift at a wavelength of 1566.4785nm as temperature varies, and (c) temperature response of the sensor.
illustrates the schematic diagram of the experimental setup with TF sensor length of 9.00mm. The sensor is put into the water bath with temperature increasing from 20°C to 80°C. The attenuation peak at a wavelength of 1566.4785nm (order 114) is chosen to record, and the peak experiences 3.8923nm redshift as the temperature increases which is shown in the Fig. 9(b). The Fig. 9(c) shows the measured temperature response of the selected order peak. The coefficient of the peak is analyzed using the linear regression fits, as 0.0667nm/°C.

It is known that the refractive index (RI) of the water decreases when the temperature increases [29

29. D. R. Lide, Handbook of Chemistry and Physics, 70th ed. (CRC Press, 2004), Chap. 6.

]. So the coefficient of the temperature is the sum of the direct contribution of the temperature change and the indirect contribution of the induced change of the RI of the water.

Assuming the temperature sensitivity of the sensor can be linearly approximated as [30

30. J. Yan, A. P. Zhang, L. Y. Shao, J. F. Ding, and S. He, “Simultaneous measurement of refractive index and temperature by using dual long-period gratings with an etching process,” IEEE Sens. J. 7(9), 1360–1361 (2007). [CrossRef]

]:
k=kT+kRI×RRI,T
(6)
where kTand kRI is the pure sensitivity of the temperature and refractive index, and RRI,Tis the dependency of thke liquid refractive index on temperature. Since the RRI,Tof the water is 2.04×104 from the data given in [29

29. D. R. Lide, Handbook of Chemistry and Physics, 70th ed. (CRC Press, 2004), Chap. 6.

] when the temperature increases from 20°C to 80°C, thus the pure sensitivity of the temperature kTcan be calculated from Eq. (6) as 0.0615nm/°C.

3.4 Axial strain sensor

Besides the above sensing applications, the sensor also can be used in the axial strain measurement. The schematic diagram of the experimental setup is the same as Fig. 9(a), while the container is filled with air, and the experiment is conducted at the room temperature (20°C). When the axial strain applied on the SMTS fiber structure sensor is increased from 0 με to 1000με, the selected attenuation peak shifts to a shorter wavelength. It is known that when the axial strain increases, the length of sensor will increase. From Eq. (2), the attenuation peak wavelength will shift to a longer wavelength. At the same time, the decreases in the ratio of the fiber core and cladding result in the difference in the effective refractive indices between the core and the cladding modes reduce. The influence of increase in the sensor length has a weaker impact than the decrease in theΔneff, so the peak wavelength will have a blueshift with axial strain increasing. Figure 10
Fig. 10 The axial strain response of the sensor
shows the axial strain response of the sensor using the linear regression fits. It is noted that the average axial strain sensitivity of the selected peak is about −2.99pm / με,.

Finally, it is worth noting that the specific peak order for the measurement can be achieved from accurately controlling the length of the TF from Eq. (2). The resolution of the liquid level, refractive index, temperature and axial strain response also depends on the interference order and the length of the MZI. The low order and long length of the TF can increase the sensitivity, which can be obtained from Eq. (2). However, it should be noted that longer TF sections increase the interferometer sensitivity, but the sensing range decreases accordingly because the fringes become much more closely spaced in wavelength. From the Ref [23

23. S. M. Nalawade and H. V. Thakur, “Photonic crystal fiber strain-independent temperature sensing based on modal interferometer,” IEEE Photon. Technol. Lett. 23(21), 1600–1602 (2011). [CrossRef]

] and our experimental process, it is also known that the layout of MMF does not influence the measurement results in practical application. If the length of MMF is long, after the part of MMF (~8cm) is placed straightly, the extra MMF still can be coiled. In fact, all the sensors [14

14. L. V. Nguyen, D. Hwang, S. Moon, D. S. Moon, and Y. Chung, “High temperature fiber sensor with high sensitivity based on core diameter mismatch,” Opt. Express 16(15), 11369–11375 (2008). [CrossRef] [PubMed]

,16

16. J. Canning and A. L. G. Carter, “Modal interferometer for in situ measurements of induced core index change in optical fibers,” Opt. Lett. 22(8), 561–563 (1997). [CrossRef] [PubMed]

,25

25. P. Lu, L. Men, K. Sooley, and Q. Chen, “Tapered fiber Mach-Zehnder interferometer for simultaneous measurement of refractive index and temperature,” Appl. Phys. Lett. 94(13), 131110 (2009). [CrossRef]

] that exploited by the same effect from the difference in effective index of Eq. (2) will also exhibit the similar sensitivity. It is simply based on the fact the sensitivity of the interferometer is a function of the group index difference induced by the interaction of the propagated mode(s) with the environment. The sensitivity depends therefore trivially on the length of the interferometer arm and on the fraction of the mode volume that propagates in the evanescent wave. Long interferometers propagating high-index cladding modes (or core modes through a nanowire) are therefore more sensitive.

4. Conclusion

In conclusion, we have proposed and demonstrated a novel and simple in-line all-fiber sensor for multi-purpose sensing applications. The sensor is based on the thinned fiber Mach-Zehnder interferometers by using singlemode-multimode-thinned-singlemode (SMTS) fiber structure. Due to the MMF in the structure, the cladding modes of the TF could be excited, and the fringe visibility of the spectrum could be improved by several times. The principle of the operation relies on the interference of the core mode and cladding modes of the thinned fiber. Experiments show that by measuring the shifts of the arbitrarily selected interference order with the changing of the external environment, the sensitivities of the liquid level, refractive index, temperature and axial strain can be experimentally measured. It should be noted that the fiber sensor can also detect the refractive index by monitoring the sensitivity of the sensor to the liquid level, for the first time to our knowledge. Moreover, the proposed sensor also can operate in the reflection mode by coating the end of the TF or lead-out SMF with a mirror. Finally, since the fabrication is so easy, safe and cost effective, includes only the fusion splicing that it makes the device properly attractive for physical, biological and chemical sensing in practical applications.

Acknowledgments

This work is supported by the National Natural Science Foundation of China (60937002), International Cooperation Projects between China and Singapore (2009DFA12640) and Professional Talents Fund (0124182015, Huazhong University of Science and Technology).

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5.

P. Lu and Q. Chen, “Fiber Bragg grating sensor for simultaneous measurement of flow rate and direction,” Meas. Sci. Technol. 19(12), 125302–125309 (2008). [CrossRef]

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9.

Y. J. Rao, T. Zhu, X. C. Yang, and D. W. Duan, “In-line fiber-optic etalon formed by hollow-core photonic crystal fiber,” Opt. Lett. 32(18), 2662–2664 (2007). [CrossRef] [PubMed]

10.

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14.

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S. M. Nalawade and H. V. Thakur, “Photonic crystal fiber strain-independent temperature sensing based on modal interferometer,” IEEE Photon. Technol. Lett. 23(21), 1600–1602 (2011). [CrossRef]

24.

H. Y. Choi, G. Mudhana, K. S. Park, U. C. Paek, and B. H. Lee, “Cross-talk free and ultra-compact fiber optic sensor for simultaneous measurement of temperature and refractive index,” Opt. Express 18(1), 141–149 (2010). [CrossRef] [PubMed]

25.

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26.

B. Shuai, L. Xia, Y. Zhang, and D. Liu, “A multi-core holey fiber based plasmonic sensor with large detection range and high linearity,” Opt. Express 20(6), 5974–5986 (2012). [CrossRef] [PubMed]

27.

J. E. Antonio-Lopez, J. J. Sanchez-Mondragon, P. LiKamWa, and D. A. May-Arrioja, “Fiber-optic sensor for liquid level measurement,” Opt. Lett. 36(17), 3425–3427 (2011). [CrossRef] [PubMed]

28.

Q. Jiang, D. Hu, and M. Yang, “Simultaneous measurement of liquid level and surrounding refractive index using tilted fiber Bragg grating,” Sens. Actuators A Phys. 170(1-2), 62–65 (2011). [CrossRef]

29.

D. R. Lide, Handbook of Chemistry and Physics, 70th ed. (CRC Press, 2004), Chap. 6.

30.

J. Yan, A. P. Zhang, L. Y. Shao, J. F. Ding, and S. He, “Simultaneous measurement of refractive index and temperature by using dual long-period gratings with an etching process,” IEEE Sens. J. 7(9), 1360–1361 (2007). [CrossRef]

OCIS Codes
(060.2310) Fiber optics and optical communications : Fiber optics
(060.2340) Fiber optics and optical communications : Fiber optics components
(060.2370) Fiber optics and optical communications : Fiber optics sensors
(280.4788) Remote sensing and sensors : Optical sensing and sensors

ToC Category:
Sensors

History
Original Manuscript: March 16, 2012
Revised Manuscript: April 26, 2012
Manuscript Accepted: April 26, 2012
Published: April 30, 2012

Citation
Lecheng Li, Li Xia, Zhenhai Xie, and Deming Liu, "All-fiber Mach-Zehnder interferometers for sensing applications," Opt. Express 20, 11109-11120 (2012)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-20-10-11109


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References

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  27. J. E. Antonio-Lopez, J. J. Sanchez-Mondragon, P. LiKamWa, and D. A. May-Arrioja, “Fiber-optic sensor for liquid level measurement,” Opt. Lett.36(17), 3425–3427 (2011). [CrossRef] [PubMed]
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  29. D. R. Lide, Handbook of Chemistry and Physics, 70th ed. (CRC Press, 2004), Chap. 6.
  30. J. Yan, A. P. Zhang, L. Y. Shao, J. F. Ding, and S. He, “Simultaneous measurement of refractive index and temperature by using dual long-period gratings with an etching process,” IEEE Sens. J.7(9), 1360–1361 (2007). [CrossRef]

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