Optical Fiber Acoustic Sensor Based on Nonstandard ... - IEEE Xplore

IEEE SENSORS JOURNAL, VOL. 14, NO. 7, JULY 2014

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Optical Fiber Acoustic Sensor Based on Nonstandard Fused Coupler and Aluminum Foil Shun Wang, Ping Lu, Liang Zhang, Deming Liu, and Jiangshan Zhang

Abstract— An optical fiber acoustic sensor based on nonstandard fused coupler and aluminum foil is proposed and experimentally demonstrated. Acoustic vibration is measured by detecting the insertion loss of the nonstandard fused coupler. As the number of the coupling cycle increases, sensitivity of the multicycle fused coupler-based sensors to acoustic vibration could be improved. Under the same experimental conditions of input light power ∼10 dBm and acoustic pressure level ∼59 dB, this assumption was experimentally conformed with results of 0.18 mW/Pa (1 cycle), 0.65 mW/Pa (3 cycles), and 1.71 mW/Pa (5 cycles), respectively. In addition, multimode fused couplerbased sensor shows sensitivity of 2.63 mW/Pa, in the frequency range from 20 Hz to 20 kHz and with average signal-to-noise ratio about 20 dB. This sensor may have potential applications in future fiber optic microphone. Index Terms— Fiber fused coupler, aluminum foil, acoustic sensor.

I. I NTRODUCTION

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HERE has been a great deal of research in the last three decades contributing to the development of fiber-optic acoustic sensors since the first fiber-optic sensor for acoustic vibration detection was proposed in 1977 [1]. Comparing to the conventional electronic acoustic sensor, fiber-optic acoustic sensors possess some distinctive advantages such as smallsize, light-weight, high sensitivity, electrical passive operation, immunity to electromagnetic interference for harsh environment [2], [3], and good multiplexing capability [4]. These research efforts reported to date can be summarized as the following different schemes, such as FP interferometers [4]–[8], fiber Bragg grating (FBG) [9]–[12], DFB/DBR lasers [13], [14], MEMS [15], etc. However, in contrast to a conventional microphone, these schemes are often not easy to achieve

Manuscript received January 15, 2014; revised March 3, 2014; accepted March 3, 2014. Date of publication March 14, 2014; date of current version May 29, 2014. This work was supported by the Natural Science Foundation of China under Grant 61275083 and Grant 61290315. The associate editor coordinating the review of this paper and approving it for publication was Dr. Anna G. Mignani. (Corresponding author: P. Lu.) S. Wang, P. Lu, L. Zhang, and D. Liu are with the School of Optical and Electronic Information, National Engineering Laboratory for Next Generation Internet Access System, Huazhong University of Science and Technology, Wuhan 430074, China (e-mail: [email protected]; [email protected]; qichunzhangliang@ 163.com; [email protected]). J. Zhang is with the Department of Electronics and Information Engineering, Huazhong University of Science and Technology, Wuhan 430074, China (e-mail: [email protected]). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/JSEN.2014.2309963

for high cost and complexity of demodulation system. Besides these conventional structures, some unique designs have come into view and attracted widespread attention over recent years. For example, an important class of FOMs (fiber optic microphone), the fiber-end diaphragm based fiber acoustic sensors. These microphones employed silicon photonic crystal or graphene diagrams as their transducers [16], [17], and have demonstrated very high acoustic sensitivity with extremely small size, while cost a lot and be difficult to fabricate. Besides, FOMs based on fused-tapered coupler are competitive for small size and low cost. However, most of these fusedtapered FOMs are based on the principle of acoustic-optic modulation [18], [19], in which the refractive index of the optical fiber is directly modulated by external acoustic wave, resulting in the coupling ratio of optical fiber coupler changed. But a limitation at the range of frequency detection in an ultrasonic frequency band can be their common feature [20]. In this paper, an optical fiber acoustic sensor based on a non-standard fused coupler and aluminum foil is proposed and investigated. This special scheme offers an alternative way to detect acoustic vibration. We numerically investigate and experimentally demonstrate that the multi-cycle fused coupler based acoustic sensor will achieve higher sensitivity with more cycles. Moreover, we systematically study the characteristics of multimode fused coupler based acoustic sensor, including its sensitivity, frequency range, and hammer impact test response. The experimental results show the proposed sensors exhibit good sensitivity, high SNR, and large frequency response. In addition, it also has the advantages of low cost, simple fabrication process and demodulation system compare with other above mentioned schemes. Additionally, approaches for improving the sensitivity, frequency response, as well as the stability of the sensor system are also fully discussed. This current sensor may play an important role in some acoustic applications such as fiber optic microphone (FOM), structural health monitoring (SHM), noise measurement, fiber optic hydrophone, and so on. II. S ENSING P RINCIPLE A. Multi-Cycle Fused Coupler-Based Sensor As we know, the formation process of a 2 × 2 single-mode fiber coupler can be regarded as two fiber tapers close to each other. For a symmetrical coupler, the propagation constant β1 = β2 , coupling coefficient C12 = C21 = C, so their coupled

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Fig. 1. Schematic diagram of the multi-cycle fused coupler based sensor. The simulation of the relationship between CR and d during the fused process.

equations are [22] ⎧ ⎨ P1 = P0 cos2 4nV λla 2 exp[−c0 + c1 d/a + c2 (d/a)2 ] 0 ⎩ P = P sin2 V λl exp[−c + c d/a + c (d/a)2 ] 2 0 0 1 2 4n a 2

Fig. 2. Sensing mechanism of multimode fused coupler based sensor. Aluminum foil has thickness and diameter 3 um and 3.5 cm, respectively. SMF: single mode fiber; MMFC: multimode fused coupler.

(1)

0

where V is the normalized frequency of the optical fiber, λ denotes the wavelength of incident light, n0 and a are the refractive index and radius of fiber core respectively. The coupling length l depends on coupling coefficient, and coupling coefficient is dependent on the distance d between centers of the two optical fibers. So the coupling ratio (CR) of two output ports P1, P2 will depend on the variation of d, and this relationship can be simulated by MATLAB. As shown in Fig. 1, the dependence of the CR on the center distance of the two optical fibers d is described, and the “coupling cycle” shortens with decreasing d (from right to left of the horizontal axis). That means the optical power will be more sensitive to d with more coupling cycles, moreover, as an assumption, the power variation would enable us to detect the weak acoustic wave which changes d, and its sensitivity may be improved by increasing the coupling cycle number of the multi-coupling cycle fused coupler. Here the coupling cycle means the oscillation cycle of optical power change. In general, coupling detection for ultrasonic wave employs the theory of “resonant coupling” in which coupling length is several times of the acoustic wavelength. This theory does not work in sonic and infrasound wave detection, in which the coupling length is far shorter than the acoustic wavelengths. However, the coupler is still sensitive to the acoustic disturbance for its signal amplification from aluminum foil. B. Multimode Fused Coupler-Based Sensor For multimode fibers, the coupling process can be described as core-to-cladding-to-core power fluctuation simply. Its highest coupling ratio is around 50% [23] in spite of its coupling length, which is longer than conventional SMF coupler or special multi-cycle fused coupler. When acquiring the same coupling length and center distance between two fibers, multimode fused coupler is more sensitive to bending, not only for this special characteristic but also for its larger fiber core, multiple modes which induce the light power more likely to leak out. So the multimode fused coupler based sensor may obtain a higher sensitivity than the multi-cycle fused coupler based sensors in the case of the comparable coupling length. The sensing mechanism of multimode fused coupler based sensor is shown in Fig. 2. Three conventional SMFs are

Fig. 3. Schematic diagram of the proposed sensors. The common speaker is connected to a signal generator. MCFC: multi-cycle fused coupler; MMFC: multimode fused coupler; PD: photo detector; ESA: electron spectrum analyzer.

used as input and output fibers, respectively. A pair of multimode fibers SI105-125-26-250 (YOFC, inc.) are chosen with core/cladding diameter of 105/125 um, and numerical aperture 0.26. As described in reference [17], wondering to get larger acoustic sensitivity, we should select the materials with small Young’s modulus and Poisson’s relatively as the thin film transducer. Secondly, the size, the diameter of the film should be as large as possible, while the thickness as small as possible. As a result, taking the cost and feasibility into account, a circular aluminum foil (Goodfellow, AL000320, with Young’s modulus 68 GPa, Poisson’s ratio 0.32) with 3 um thickness and 3.5 cm diameter is selected as our transducer. It works as an elastic vibration foil which is fixed on a mount and transfers acoustic vibration to multimode fused coupler with a splitting ratio of about 50:50. The external acoustic pressure causes the vibration of the foil, which yields bending of multimode fused coupler structure. Both the propagated modes in MMF and CR are very sensitive to the bending of multimode fiber, hence the output power is relatively sensitive to the acoustic pressure at the end of MMF. Consequently, the acoustic vibration can be detected by the power fluctuation of transmission light at the end of output SMFs. III. E XPERIMENT AND D ISCUSSION The experimental setup in this paper is shown in Fig. 3. The acoustic vibration signal is generated by a speaker which is driven by a signal generator. The light source is an amplified spontaneous emission (ASE) source with a wavelength range 1525–1565 nm and an output power of ∼10 dBm. The demodulation system consists of a photo detector (ET5000FEOT, inc.) with a responsivity of 1 A/W around 1.55 um, an optical

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Fig. 5. The time domain waveform of the optical oscilloscope with 1 kHz acoustic wave on the sensor. (1T, 3T, 5T mean 1 cycle, 3 cycles, 5 cycles, respectively).

Fig. 4. The experimental mechanism diagram of multi-cycle fused coupler based sensors with 1 cycle (a), 3 cycles (b), 5 cycles (c). The later cycles are shorter than the front cycles in time.

oscilloscope CSA7404B (Tektronix, inc.) with function of digital storage and optical input, and an Electron Spectrum Analyzer (ESA) (E4447A Agilent,inc.) which operates over a frequency range of 10 Hz–40 GHz and a resolution of 0.01 Hz. We can acquire higher accuracy by comparing the time domain waveform of the optical oscilloscope and the frequency spectrum of the ESA. A. Multi-cycle Fused CouplerBased Sensor The multi-cycle fused coupler employed in the current article is fabricated by a pair of SMFs in a fiber fused biconical-taper (FBT) system. As we know, the diameter of fiber decreases in the fused process, and the optical powers in outputs P1 and P2 change symmetrically. So the fiber coupler with different CRs can be fabricated by controlling the fused time. Usually, the stopping point is set in the first cycle, in which the power loss is the least. But here we employ the multi-cycle fused coupler with multiple cycles and longer coupling length by prolonging the fusing time. It can be seen that Fig. 4 shows the power change of outputs of multi-cycle fused coupler, and it is apparent that the

power becomes more sensitive to the coupling length which is increased during the fusing process, and center distance of the two optical fibers d is decreasing simultaneously, so this result is consistent with our aforementioned assumption. From 1 cycle (a), 3 cycles (b), to 5 cycles (c) we can observe that the later cycles are shorter than the front cycles in time, which means the light power is easier to change and may be more sensitive to external acoustic disturbance. When the speaker is driven by a signal generator continuously, which generates a sinusoidal waveform, at a frequency of 1 kHz, three sensors with different cycles (1T, 3T, 5T) are employed to detect the signal. Fig. 5 illustrates the outputs from these sensors in response to an incident excitation at 1 kHz. The peak-to-peak value is increasing from 1T, 3T to 5T with peak-to-peak change 32.64 μW, 116 μW, and 304 μW, respectively, corresponding to light power to sound pressure sensitivity 0.18 mW/Pa, 0.65 mW/Pa, and 1.71 mW/Pa, respectively with the acoustic pressure produced in the current paper 0.178 Pa detected by a commercial sound level meter. Therefore, the assumption is proved to be correct that multi-cycled fused coupler based sensor with more cycles could obtain higher sensitivity to the same acoustic disturbance signal. The frequency responses to 1 kHz sinusoidal acoustic signal from multi-cycle fused coupler based sensors in the FFTs of the signals are presented in Fig. 6. It is clear that all the responses of the signals are about 1 kHz, which is the speaker’s driven frequency. It has an average signal-noiseratio (SNR) around 38.47 dB, corresponding to an equivalent noise floor of 6.864 uPa/Hz1/2 at 1 kHz for a 13.6 Hz resolution bandwidth. That means all the three multi-cycle fused coupler based sensors detected the incident acoustic signal successfully. Besides the vibration frequency of 1 kHz, we also notice 2 kHz and 3 kHz harmonic components, which are mainly caused by the slightly non-axial alignment between the vibration film and the multi-cycled fused couplers [24]. However, the major strongest frequency response at 1 kHz is higher than the first harmonic component 2 kHz for an

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Fig. 7. The experimental mechanism diagram of multimode fused coupler based sensor. It can achieve a maximum CR around 50% despite its longer fuse time.

Fig. 8. The time domain waveform of the optical oscilloscope at 1 kHz and its frequency spectrum. (a) The time domain waveform detected at 1 kHz. (b) The frequency domain waveform at 1 kHz. Fig. 6.

The FFT frequency spectrum from Fig. 5.

average amount 16.3 dB, and much higher than the other higher harmonic components. So we can clearly identify the induced vibration frequency and the harmonic components here do little matter to our sensing work. B. Multimode Fused CouplerBased Sensor In the same fiber FBT system, the experimental multimode fiber-optic coupler is fabricated by fusing a pair of step-index multimode fibers which are spliced between conventional SMFs. When light propagates through the multimode fiber pair from SMF (YOFC G.652), with motors moving at a certain speed and flame burning in a specific hydrogen flow rate, CR will come to achieve the desired one set before. From Fig. 7, we can see that the CR could not be much higher than about 50% even though the coupling length becomes longer till almost broken. That agrees with the reference [21]. Fig. 8 shows the multimode fused coupler based sensor’s response to 1 kHz incident acoustic signal. Fig. 8(a) shows the time domain waveform of the optical oscilloscope on the left and its frequency spectrum on the right (b). In Fig. 8(a), the peak-to-peak is about 468 μW corresponding to a light power to sound pressure sensitivity 2.63 mW/Pa at 1 kHz with sound pressure of 0.178 Pa. The sound pressure sensitivity is relatively high for the foil amplifying design and the multimode coupling mechanism. Besides, it is higher than the multi-cycle fused coupler based sensors for the larger fiber core and multiple modes propagating in it that would both

Fig. 9. Frequency response of the multimode fused coupler based acoustic sensor under different driver frequency. It obtains an average SNR about 20 dB, and the maximum one is above 35.5 dB around 500Hz.

induce the light power more likely to leak out. It can be seen clearly from Fig. 8(b) that the frequency spectrum has a SNR about 15 dB. And besides the expected frequency at 1 kHz has been detected, there still exist some other frequency components such as 910 Hz and 1080 Hz whose amplitudes are much lower than that of 1 kHz, which may caused by the noise from the sensor head or interrogate system. As shown in Fig. 9, the frequency responses of the multimode fused coupler based acoustic sensor at different frequency are also measured. Besides the detected frequency

WANG et al.: OPTICAL FIBER ACOUSTIC SENSOR

Fig. 10. The SNR fitting of the detected signal in the detected frequency range. Signal and noise maximum fitting curve are also depicted.

Fig. 11. The transient frequency response of the multimode fused coupler based sensor to a hammer impact test. (a) The time domain power signal shows damping oscillation. (b) The corresponding frequency spectrum tells the fundamental frequency of 21.25 Hz.

expectant, the phase noise [25] can be obtained apparently. The average SNR is about 20 dB with a maximum SNR above 35.5 dB at 500 Hz with a resolution bandwidth of 10 Hz, corresponding to an equivalent noise floor 15.866 uPa/Hz1/2. And here 500 Hz may be the sensor’s resonance frequency. Fig. 10 illustrates the SNR fitting curve of the frequency detection for the proposed multimode fused coupler based acoustic sensor in the audible range. It shows a relatively high and flat SNR curve despite the highest value around 500 Hz which is around the sensor’s resonance frequency. The signal maximum fitting curve and noise maximum fitting curve are also depicted in Fig. 10. It tells that a flat response of our sensor from 1 kHz to 20 kHz. In order to test the transient frequency response of the multimode fused coupler based acoustic sensor, a hammer impact test is made by applying a hammer to beat the metal mount close to the sensor head. Fig. 11(a) shows the time domain power signal detected by the oscilloscope, which illustrates a damping oscillation and the detail is displayed in the inset. It is shown in Fig. 11(b) the main frequency of 21.25 Hz by fast Fourier transform of the time-domain spectra in Fig. 11(a). This main frequency is relevant to parameters of the sensor setup including both the sensor head and the table supporting the sensor. It is possible to achieve a higher sensitivity by optimizing the structural parameters of the multimode fused coupler

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Fig. 12. Repeatedly, frequency response results of the multimode fused coupler based sensor to an acoustic signal excitation at the frequency of 1 kHz. The results are recorded in a step of five minutes.

acoustic sensor. However, the relatively poor stability of our sensor head with touching between the coupler and the aluminum foil may be one defect of the acoustic sensor. To improve the stability and repeatability of our sensor, a series of measures have been taken to fix the sensor head including use the brackets, glue, screws. Besides, the SNR is seriously affected by environmental noise arising from the demodulation system, light source or other environmental perturbation. So an anechoic chamber for sensor head is necessary if better experimental results are expected. Here we integrate the sensor head into a small metal box with some anechoic foam placed on the inner wall. After doing these, a stability test has been done in 90 minutes as shown in Fig. 12. Results with a better stability of ± 1.1 dBm in power and an increased SNR ∼28 dB are obtained. It will also be helpful to improve the sensor system by optimizing the sensor head design and employing high resolution interrogation system. IV. C ONCLUSION In summary, a novel and sensitive optical fiber acoustic sensor based on non-standard fused coupler is presented. Results show that this scheme possesses some advantages over the above-mentioned fused-tapered FOMs: 1) high sensitivity, as a multi-cycle fused coupler, the optical power becomes more sensitive as the taper length increases; In regard to multimode fused coupler, the multimode fiber is more sensitive to bending than SMF. 2) wide frequency response band, the non-standard fused couplers are not packaged and in touch with an aluminum foil, this structure lower the sensor’s nature frequency so as to be capable of detecting not only ultrasound [21] but also audible range. 3) easy to interrogate, due to its direct intensity demodulation which is more accurate than phase demodulation employed in most optical fiber acoustic sensors. The sensitivity and frequency response are expected to be improved by optimizing the sensor head design and employing high resolution interrogation system. Besides, the affection of the power fluctuation of the light source and other environment factors can be effectively reduced by using the substraction method between the two outputs of non-standard fused coupler based sensors. What’s more, the

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sensitivity of the acoustic sensor can also be doubled. That is a work in progress. R EFERENCES [1] J. A. Bucaro, H. D. Dardy, and E. F. Carome, “Fiber optic hydrophone,” Acoust. Soc. Amer., vol. 62, no. 5, pp. 1302–1304, 1977. [2] A. Kots and A. Paritsky, “Fiber optic microphone for harsh environment,” Proc. SPIE, vol. 3852, pp. 106–112, Dec. 1999. [3] J. P. F. Wooler and R. I. Crickmore, “Fiber-optic microphones for battlefield acoustics,” Appl. Opt., vol. 46, no. 13, pp. 2486–2491, 2007. [4] N. Furstenau, H. Horack, and W. Schmidt, “Extrinsic fabry-perot interferometer Fabry–Pérot microphone,” IEEE Instrum. Meas., vol. 47, no. 1, pp. 138–142, Feb. 1998. [5] J. Bush, F. McNair, and F. DeMetz, “Low-cost fiber optic interferometric microphones and hydrophones,” Proc. SPIE Int. Symp. Opt., Imaging, Instrum., Int. Soc. Opt. Photon., vol. 2292, no. 323, pp. 83–86, Aug. 1994. [6] J. H. Song, H. M. Gu, H. J. Park, and S. S. Lee, “Optical microphone based on a reflective micromirror diaphragm,” Microw. Opt. Technol. Lett., vol. 48, no. 4, pp. 707–709, 2006. [7] F. Xu et al., “High-sensitivity Fabry–Pérot interferometric pressure sensor based on a nanothick silver diaphragm,” Opt. Lett., vol. 37, no. 2, pp. 133–135, 2012. [8] F. Guo, T. Fink, M. Han, L. Koester, J. Turner, and J. Huang, “Highsensitivity, high-frequency extrinsic Fabry–Pérot interferometric fibertip sensor based on a thin silver diaphragm,” Opt. Lett., vol. 37, no. 9, pp. 1505–1507, 2012. [9] A. Cusano et al., “Plastic coated fiber Bragg gratings as high sensitivity hydrophones, ”in Proc. 5th IEEE Conf. Sensors, Oct. 2006, pp. 166–169. [10] M. Moccia, M. Pisco, A. Cutolo, V. Galdi, P. Bevilacqua, and A. Cusano, “Opto-acoustic behavior of coated fiber Bragg gratings,” Opt. Exp. vol. 19, no. 20, pp. 18842–18860, 2011. [11] D. Tosi, M. Olivero, and G. Perrone, “Low-cost fiber Bragg grating vibroacoustic sensor for voice and heartbeat detection,” Appl. Opt., vol. 47, no. 28, pp. 5123–5129, 2008. [12] L. Mohanty, L. M. Koh, and S. C. Tjin, “Fiber Bragg grating microphone system,” Appl. Phys. Lett., vol. 89, no. 16, p. 161109, 2006. [13] S. W. Løvseth, J. T. Kringlebotn, E. Rønnekleiv, and K. Bløtekjær, “Fiber distributed-feedback lasers used as acoustic sensors in air,” Appl. Opt., vol. 38, no. 22, pp. 4821–4830, 1999. [14] B. O. Guan, Y. N. Tan, and H. Y. Tam, “Dual polarization fiber grating laser hydrophone,” Opt. Exp. vol. 17, no. 22, pp. 19544–19550, 2009. [15] J. Bingli, Y. Kuntao, and W. Jiangan, “Design of the optical fiber MEMS infrasound sensor,” in Proc. IEEE ICMTMA, Mar. 2010, pp. 1049–1051. [16] O. C. Akkaya, O. Kilic, M. J. F. Digonnet, G. S. Kino, and O. Solgaard, “High-sensitivity thermally stable acoustic fiber sensor,” in Proc. IEEE Sensors Conf., Nov. 2010, pp. 1148–1151. [17] J. Ma, H. Xuan, H. L. Ho, W. Jin, Y. Yang, and S. Fan, “Fiber-optic fabry–pérot acoustic sensor with multilayer graphene diaphragm,” IEEE Photon. Technol. Lett., vol. 25, no. 10, pp. 932–935, May 15, 2013. [18] D. O. Culverhouse, S. G. Farwell, T. A. Birks, and P. St. J. Russell, “Four port fused taper acousto-optic devices using standard singlemode telecommunications fibre,” Electron. Lett. vol. 31, no. 15, p. 1279, 1995. [19] T. A. Birks, P. S. J. Russell, and D. O. Culverhouse, “The acousto-optic effect in single-mode fibre tapers and couplers,” J. Lightw. Technol., vol. 14, no. 11, pp. 2519–2529, 1996. [20] R. Chen, G. F. Durando, T. Butler, and R. A. Badcock, “A novel ultrasound fibre optic sensor based on a fused-tapered optical fibre coupler,” Meas. Sci. Technol., vol. 15, no. 8, p. 1490, 2004. [21] J. Y. Wang, L. Min, H. Qi, and C. Wang, “An over-coupled fused coupler based acoustic emission sensor for detecting partial discharges,” in Proc. IEEE Symp. Photon. Optoelectron. (SOPO), May 2012, pp. 1–4. [22] C. Shuai, J. Duan, and J. Zhong, “Relationship between rheological manufacturing process and optical performance of optical fiber coupler,” J. Central South Univ. Technol. vol. 13, no. 2, pp. 175–179, 2006. [23] D. R. Moore and D. L. Wuensch, “Multimode fiber optic coupler and method for making,” U.S. Patent 4 772 085, Sep. 20, 1988. [24] B. Xu et al., “Acoustic vibration sensor based on nonadiabatic tapered fibers,” Opt. lett. vol. 37, no. 22, pp. 4768–4770, 2012. [25] P. E. Bagnoli et al., “Development of an erbium-doped fiber laser as a deep-sea hydrophone,” J. Opt. A, Pure Appl. Opt., vol. 8, no. 7, pp. S535–S539, 2006.

Shun Wang received the B.S. degree in automation from the Xi’an University of Posts and Telecommunications, Xi’an, China, in 2011. He is currently pursuing the doctor’s degree at the National Engineering Laboratory for Next Generation Internet Access System, Huazhong University of Science and Technology, Wuhan, China.

Ping Lu received the master’s and doctor’s degrees from the Huazhong University of Science and Technology, Wuhan, China, in 1999 and 2005, respectively. She has been an Associate Professor with the College of Optical and Electronic Information, Huazhong University of Science and Technology, since 2006. In 2009, she was with the Arizona Optical Center in America as a Visiting Scholar for one year. She has been a Professor with the College of Optical and Electronic Information, Huazhong University of Science and Technology, since 2011. She has authored and co-authored more than 40 international communications or papers, and holds patents in fiber-optic sensing. Her current research interests include optical fiber communication, optical fiber sensing, fiber lasers, and optical waveguide technology.

Liang Zhang received the bachelor’s degree in optoelectronic science and engineering from the Huazhong University of Science and Technology, Wuhan, China, in 2009. He is currently pursuing the doctor’s degree with the National Engineering Laboratory for Next Generation Internet Access System, Huazhong University of Science and Technology, Wuhan.

Deming Liu received the master’s degree from the University of Electronic Science and Technology of China, Chengdu, China, and the doctor’s degree from the Huazhong University of Science and Technology, Wuhan, China, in 1984 and 1999, respectively. He has been a Professor with the College of Optical and Electronic Information, Huazhong University of Science and Technology, since 1994. He was a Visiting Professor with the University of Duisburg-Essen, North Rhine-Westphalia, Germany, from 1994 to 1996, and the Nanyang Technological University, Singapore, from 1999 to 2000. He was the Director of the Department of Optoelectronics from 2000 to 2005, and the Vice Director of the College of Optical and Electronic Information, Huazhong University of Science and Technology, from 2005 to 2008. Since 2008, he has been the Director of the National Engineering Laboratory for Next Generation Internet Access System. He has authored and co-authored more than 200 international communications or papers, and he holds more than 50 patents in his areas of expertise. His current research interests include optical access networks, optical communication devices, and fiber-optic sensors.

Jiangshan Zhang received the master’s and doctor’s degrees from the Huazhong University of Science and Technology, Wuhan, China, in 1997 and 2005, respectively. He has been an Associate Professor with the Department of Electronics and Information Engineering, Huazhong University of Science and Technology, since 2006. He has authored and co-authored more than 10 international communications or papers. His current research interests include signal processing.