ADVANCES in NATURAL and APPLIED SCIENCES

ADVANCES in NATURAL and APPLIED SCIENCES ISSN: 1995-0772 Published BYAENSI Publication EISSN: 1998-1090 http://www.aensiweb.com/anas 2017 June 11(8): pages 639-644 Open Access Journal Design And Implementation Of Heterodyne Detection Based On Photonic Crystal Fiber Sensor 1 Marwa Mustafa Sami, 2 Mohammed Abdelwahab Munshid, 3 Salah Aldeen Adnan 1 Marwa Mustafa Sami student, Laser Engineering Department, University of Technology, Baghdad, Iraq, 2 Mohhamed Abdelwahab Munshid, Professor, Laser & Optoelectronics Engineering, University of Technology, Baghdad, Iraq. 3 Salah Aldeen Adnan, Assistant Professor, Optoelectronics Engineering Department, University of Technology, Baghdad, Iraq. Received 28 March 2017; Accepted 7 June 2017; Available online 12 June 2017 Address For Correspondence: Marwa Mustafa, University of Technology, Laser Engineering Department, engineering collage, Baghdad, Iraq. E-mail: lasermm88@gmail.com Copyright 2017 by authors and American-Eurasian Network for ScientificInformation (AENSI Publication). This work is licensed under the Creative Commons Attribution International License (CC BY). http://creativecommons.org/licenses/by/4.0/ ABSTRACT Optical fibers have been widely used in the field of sensors. In this paper heterodyne detection is designed and constructed for detecting the wavelength shift between the reference and sensing signals that is caused by the temperature change based on photonic crystal fiber. Optical Source of 1550nm is used. The reference arm include PCF 50mm in length, while the sensing arm include of Fiber Brag Grating to generate a different wavelength than reference wavelength, PCF 50mm length. The beat signal is shown by Optical Spectrum Analyzer. The sensitivity of heterodyne system is (- 65.83 pm/ ) at temperature range of (30-70). The obtained results from the optical spectrum analyzer show that the wavelength is slightly shifted linearly to shorter wavelength with decreasing temperature. Also observed from the results, relation between the wavelength shifting and temperature change was linear. The sensitivity of the detection were analyzed and presented. KEYWORDS: fiber-optic sensors, Photonic Crystal Fiber, heterodyne detection, Fiber Brag Grating(FBG). INTRODUCTION Recently, Optical fiber sensors OFS have been widely used to measure a variety of physical quantities such as temperature,strain, pressure, humidity and etc [1], due to their advantages like electromagnetic immunity, stability, compactness, good electric insulation, high sensitivity and the aptitude for remote.[2] Fundamentally, Some of these sensors depend on properties of the applied light (intensity, polarization, wavelength changes, and phase).[3] Nowadays a wide range of fiber sensors have been introduced based on Photonic Crystal Fiber(PCF). in this paper heterodyne detection has been used and implemented depending on the principle of different wavelength which has an important advantage in terms of weak signal detection with high resolution. optical heterodyne detection can mix the reference light with signal light (FBG term) to extract a selective wavelength, and based on PCF sensor as a temperature sensor, as well as adding a FBG gives enhancement to system, thus the spectral characteristics such as interference spectra and sensitivity will analyzed. Theory: Photonic Crystal Fiber: PCF is made of silica with a hexagonal array of air holes that run along the fiber length and have a set of different shapes, sizes, and distributions, The schematic of a common solid -core PCF is shown in figure (2.4). [4] ToCite ThisArticle: Marwa Mustafa Sami, Salah Al deen Adnan, Mohhamed Abd-Elwahab, Design And Implementation Of Heterodyne Detection Based On Photonic Crystal Fiber Sensor. Advances in Natural and Applied Sciences. 11(8); Pages: 639-644

640 Fig. 1: schematic of solid-core PCF [5]. The biggest features in PCFs is that by varying the location and size of the cladding holes and the core the fiber, mode shape, dispersion, nonlinearity and birefringence, that can be tuned to reach the values that can not be achieved with conventional optical fibers. Additionally, the presence of air holes allows the possibility of light propagation in the air.[4] This enable interaction between light and samples well-controlled leading to new applications in sensing such as temperature sensor[6] Photonic Crystal Fiber has thermo-optic coefficient ζ =1 [10]^(-5)/ and low thermal expansion coefficient υ = 5 10 ^(-7)/. [7] The wavelength shift of mth order of interference peaks with respect to temperature variation can be described as [10]: 1 λ m T = [1 L + 1 n eff L T n eff ] (1) λ T Where neff=neff(co) neff(cl) is the symbol of difference between the effective refractive indices of the core and cladding, L is the symbol of physical length in PCF. In sensors the Temperature sensitivity depend on guiding mechanism of fiber, such as wavelength and material that used in manufacture the sensor; temperature sensitivity of the sensor (KT) is described as: [10] KT = λ T Optical Heterodyne Detection: The basic principle of optical heterodyne detection is to extract difference frequency signal of two beams of light. The two beams of light are used as local oscillator as and signal light with the measured information. The ultimate goal is to measure the frequency difference of the two beams of light. The frequency difference is achieved by photomixing, The optical information contained in this intermediate frequency signal includes: frequency, amplitude, phase, etc. [8] the electromagnetic field due to the two beams of coherent light waves can be represent by E 1= A r cos (ω rt +θ 1) (3) E 2= A s cos (ω st +θ 2) (4) (2) Where, E is the light field, A r is the amplitude of reference signal, A s is the amplitude of sensing signal, ω s ω r is the angular frequencies of sensing signal and reference signal, respectively. The output signal generated by the photodiode is described as following: [9] I= [ E 1 +E 2 ] 2 (5) By Substituting (3) and (4) into equation (5) is obtained; I = [(A r cos(ω r t + θ 1 )) + (A s cos(ω s t + θ 2 ))] 2 (6) the high frequency components and constant components out are filtered, leaving (beat) frequency in optical heterodyne detection. The photodiode will act as a low-pass filter for the optical frequencies. Therefore, the output current is given by; [1]

641 I = A cos( ωt + θ) (7) Where; ω = ω s ω r (8) And; θ = θ 2 θ 1 (9) Where, the amplitude A depends on A1, A2, ω depending on the difference between sensing and reference signal after heat effect and θ is the difference phase. Compared with the direct detection, the heterodyne detection technique has a high sensitivity and more accuracy, which is extremely beneficial for weak signal detection this is the most basic advantage. [8] Experimental Method: A novel design of heterodyne detection was implemented in this work depending on the (FBG-SMF-PCF- SMF) as sensor. Laser diode at 1550nm wavelength have been used, passes through the single mode fiber SMF-28 and split by optical coupler (1x2) into the two arms with the same wavelength the reference arm and sensing arm, the light waves passing through the reference arm consist of (SMF-PCF-SMF), endlessly single mode PCF(ESM- 12) has been used with short length 50mm, and the sensing arm consist of (SMF-FBG) to generate a different wavelength than source, depending on the transmitted wavelength of FBG (1550nm at wavelength), which investigate basic theory of heterodyne detection, and the sensing arm connected with PCF at length 50 mm, which spliced at the end with conventional single mode fibers (SMF-28). Then recombined the reference arm and the sensing arm by optical coupler 2x1 at the output to optical spectrum analyzer (OSA) thorlab type (203) to detecting the transmission spectrum of the system. In this experiment the PCF sensor was exposed to heat, the evaluation of the temperature measurements was carried out for 30 to 70 by using hot plate connected with heater. The schematic diagram of experiment is shown in the Figure (2). Fig. 2: schematic diagram of heterodyne detection. RESULTS AND DISCUSSION The two input different wavelengths that have been achieved in heterodyne detection represented, as shown in Figure (3) measure the optical spectrum of reference and optical spectrum of fiber brag grating. (a)

642 (b) Fig. 3: (a) Measured optical for whole spectrum of source and FBG spectrum, (b) Selective region of the spectrum of source and FBF in heterodyne detection, measured optical spectrum of two input different wavelengths in heterodyne detection Figure (3.a) shows optical spectrum of a wide range owing to input mode of source, Figure (3.b) shows the spectrum of a narrower range, which was chosen for calculating the amount of sensitivity. The two input arms of heterodyne detection system, represented in reference arm and the sensing arm which connected with FBG to get a tunable wavelength as shown in table (1(. Table 1: measured wavelength in both reference and sensing arms. Interferometer arms Measured Peak (nm) Fitted Peak (nm) Reference 1550.027 1550.1 sensing 1549.67 1549.8 The beat frequency of heterodyne detection was investigated at room temperature, Fig. (4) shows the reference arm, sensing arm and the beat frequency. Fig. 4: beat frequency of heterodyne detection at room temperature.

643 As expected, the reference wavelength was same the wavelength of input source, and the measured heterodyne wavelength shifts (beat frequency) in different temperature towards the left as the temperature decreases. The experimental data were obtained with the sensor in different temperature shows that the beat frequency shifted towards blue region in case of decreases temperature, because the temperature in the heating process was rise rapidly and therefore could not record the spectra of each case, so the cooling mechanism have been used where the temperature is decreasing slowly and can be recording the spectra easily and sequentially. In this experiment the data was obtained with decreasing temperature and recorded as shown in Figure (5). Fig. 5: interference spectra of heterodyne detection. The sensitivity in heterodyne detection, defined as the slope of the line, was evaluated to be about (-65.83) pm/, sensitivity signal indicates that the experiment was conducted with decreasing temperature. The curve shows excellent linear dependence of beat frequency on the decreasing in temperature. This number is much higher than the sensors in homodyne detection and in conventional optical fiber. In addition, the sensitivity was enhanced with adding FBG. Finally that higher sensitivity can be achieved in heterodyne detection as shown in Figure (6). Fig. 6: the relationship between beat frequency and temperature for heterodyne detection.

644 Conclusion: A novel technique of heterodyne detection has been used for measuring temperature using PCF as sensor. The system has been enhanced with adding FBG in sensing arm, optical heterodyne system has been designed and implemented to sense the temperature from 70CO to 30CO. The sensitivity of this sensor is -65.83 pm/co when the source is 1550nm wavelength. the wavelength is slightly shifted linearly to blue region with decreasing temperature. The slop of sensitivity is negative due to starting at high temperatures and down to the lowest value. This system can be used for measuring the shift wavelength of temperature sensor with high resolution. REFRENCES 1. Bellil, H., M.A.G. Abushagur, 2000, "Heterodyne detection for Fiber Bragg Grating sensors", Elsevier - Optics & laser technology, 32: 5. 2. Wang, R., J. Yao, Y. Miao, Y. Lu, D. Xu, N. Luan and C. Hao, 2013. " A reflective photonic crystal fiber temperature sensor probe based on infiltration with liquid mixtures', Sensors, 13(6): 7916-7925,. 3. Kirkendall, C.K. and A. Dandridge, 2004. "Overview of high performance fibre-optic sensing", Journal of Physics D: Applied Physics, 37(18): R197. 4. Benabid, F., J.C. Knight, G. Antonopoulos and P.S.J. Russell, 2002." Stimulated Raman scattering in hydrogen-filled hollow-core photonic crystal fiber", Science, 298(5592): 399-402. 5. Xiao, L., 2008." Novel splice techniques and micro-hole collapse effect in photonic crystal fibers", Doctoral dissertation, The Hong Kong Polytechnic University,. 6. Villatoro, J., V. Finazzi, G. Badenes and V. Pruneri, 2009. "Highly sensitive sensors based on photonic crystal fiber modal interferometers", Journal of Sensors. 7. Laouar, R., E.R. Colby, R.J. England and R.J. Noble, 2011. " Measurement of thermal dependencies of pbg fiber properties"., In 2011 Particle Accelerator Conference Proceedings, pp: 1343. 8. Miao, C., C. Wenjie and Y. Qinghua, 2016. " The Design of All Fiber Laser Heterodyne Detection System", International Journal of Signal Processing, Image Processing and Pattern Recognition, 9: 5. 9. Zheng, B., S. Tong, 2015. " Performance simulation of heterodyne synchronous receiving system in coherent optical communication", Selected Proceedings of the Photoelectronic Technology Committee Conferences held August-October 2014 (pp. 952106-952106). International Society for Optics and Photonics. 10. Myoung, K., H. Seob, Young, Se-Jong, Kiegon, Lee, 2008. High temperature sensor based on a photonic crystal fiber interferometer, In Proc. SPIE, 7004, p: 700407.