Volume 2, Issue 11, November 2014 ISSN

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1 Experimental Investigation of Bending Loss in Multimode optical fiber used for the Delivery of Optical Power From Sources at 650nm and 532nm Wavelength Samar Y. Al Dabagh 1 and Duaa H. Al Saud 1 1 Department of Physics, College of Science for woman, University of Baghdad, Baghdad, Iraq ABSTRACT Loss of optical power of laser diodes in multimode fiber due to bending has been investigated. In this experiment, the effects of bending diameter (12.5,.5, 8, 6, 4, 3, 2, and 1) cm and wrapping turns (1- turns) of optical fiber on the power loss of laser diodes at (650, 532) nm wavelength have been studied. We found that as the bending radius of the fiber decreases and the number of wrapping turns increases, the power loss through the fiber increases. Also as the length of the fiber increases the power loss through the fiber increases. Key Words:- Bending, optical fiber, loss, bend diameter, turns in optical fibers 1. INTRODUCTION Optical fiber communication plays a vital role in the development of high quality and high-speed telecommunication systems [1]. Radiative losses occur whenever an optical fiber undergoes a bend of finite radius of curvature. In the past a few years, there have been increasing efforts in reducing bending losses for single-mode fibers to meet the challenges for FTTH (Fiber-To-The-Home). Several fiber designs have been proposed to meet different bend loss requirements [2,3]. Expanding medical application of laser power have resulted in an in demand for silica optical fiber, but these applications require the fiber to the endure the damaging combination of high laser power levels and increasing tighter bends [4, 5]. The most important source of lose is the bending that occurs in the fiber-optic cable during installation or in the manufacturing process. When the fiber cable is installed and pressed onto an irregular surface, tiny bends can be created in the fiber cable. Light is lost due to these irregularities [6]. The benefits from using a bend insensitive fiber is minimizes bend-induced attenuation, bend-insensitive fiber allows for installation in more places than regular fibers, because of the ability to withstand tight bends and challenging cabling routes without substantially less signal loss [7]. 2. EXPERMENTAL WORK The components and the experimental setup is shown in Figure 1 1Red laser diode (650 nm wavelength and its output power (250mW). Or Green laser diode (532nm wavelength and its output power (0mW). 2Multimode optical fiber with different lengths (, 0 and 1) m was made by corning glass. Core Diameter: 62.5/125 micron 3.0 pvc, Insertion loss: 0.30 db 3Power meter: Device made by (corning cable system) OTS-300 Express series. Used to measure the output optical power from +3 to -70 dbm. 4 Optical bench for alignment Figure 1: The setup of the experiment. The calculated power in milliwatt is given by [ 8 ]: P (mw) = 1mW (P(dBm) / ) (1) Volume 2, Issue 11, November 2014 Page 18

2 3.RESULTS &DISSCUSTION 3.1 Results of Red Laser diode (λ=650 nm): Table 1, 2 and 3 show bending loss of laser diode at (λ=650nm) in multimode fiber at bending diameter (12.5,.5, 8, 6, 4, 3, 2, 1) cm with different length (, 0 and 1m) respectively. Figures 2,3 and 4 show the relationship between the power of laser source (λ=650nm) as a function of No. turns for multimode fiber with length (, 0, 1m) at different bend diameters (12.5,.5, 8, 6, 4, 3, 2, 1) cm. The results show that as the bending diameter is increased from 1cm to 12.5cm; the output power is also increased. Also from figures the power begin to decreases exponentially as the number of turns increases, and then as wrapping number gets higher, the power starts to show a sort of saturation behavior, and remains roughly constant. When (2r) is small(1,2) cm, the power decreases very sharply The losses produced are mainly because of the increase in leaky rays at the outer side of the core in the cladding. This work is similar to [9]. Table 1: The of no. of wrapping turns on the output power of laser source (λ=650nm) form multimode fiber at different bend diameter. Table 2: The effect of no. of wrapping turns on the output power of laser source (λ=650nm) for multimode fiber with length (0m) at different bend diameter. Table 3: The output power of laser source (λ=650nm) as a function of no. of wrapping f for multimode fiber with length (1m) at different bend diameter. Volume 2, Issue 11, November 2014 Page 19

3 .6 Fiber length (L) = m Power(mW) * Figure 2 laser power as a function of no. of turns of (m) multimode fiber at different bend diameter. Fiber length (L) = 0m Power (mw) * Figure 3: laser power as a function of of (0m) multimode fiber at different bend diameter. Fiber length (L) = 1m Power (mw) * Figure 4: laser power as a function of of (1m) multimode fiber at different bend diameter Table 4:The effect of no. of wrapping turns on the output power of laser source (λ=650nm) for multimode fiber of different length at bend diameter (12.5cm). Volume 2, Issue 11, November 2014 Page 20

4 Table 5 :The effect of no. of wrapping turns on the output power of laser source (λ=650nm) for multimode fiber of different length at bend diameter (4cm). 11 Diameter of turns (2r) = 12.5cm Power (mw) * L=m L=1m 5 Figure 5 The power of laser source at (λ=650nm) as a function of wrapping turns for multimode fiber (, 0, 1) m at bend diameter (12.5cm). 11 Diameter of turns (2r) = 4cm Power (mw) * L=m L=1m 5 Figure 6 The power of laser source at (λ=650nm) as a function of wrapping turns for multimode fiber (, 0, 1) m at bend diameter (4cm). Figure 5 and 6 show the relationship of the power of laser source (λ=650nm) as a function of No. wrapping turns for multimode fiber with length (, 0, 1m) at diameter (12.5, 4) cm respectively. The results show that as the bend diameter is increased from 1cm to 12.5cm; the output power is also increases. If the bend diameter is fixed, the number of turns increased the power loss also increased. Figure 5 and 6, shows that as the length of the fiber increases, the Volume 2, Issue 11, November 2014 Page 21

5 output power is decreases at the fixed bend diameter. The power fiber of laser diode (λ=650nm) in (m) optical fiber is much higher than the power of laser diode in (1m) optical fiber at same bending diameter. Figure 7 shows an exponential increase of the power of laser diode as the bending diameter increases. Also figure 7 shows as the length of the of fiber increase, the power of laser diode decreases. Bending loss can be due to coupling between fundamental propagation field either by core and clad structure, or by the coating (protecting) layers, (which is the so-called whispering-gallery mode). These results show that smaller bending radius induces a greater bending loss. Table 6: The effect of bending diameter on the output power of laser source at (λ=650nm) for multimode fiber (, 0, 1 m ) length at sixth wrapping turn (N=6) 11 N=6 Power (mw) * L=m L=1m Diameter (cm) Figure 7: The power of laser source at (λ=650nm) as a function of bending diameter for multimode fiber (, 0, 1m) length at sixth wrapping turn (N=6) 3.2 Results of green Laser (λ=532 nm): Table7: The effect of no. of wrapping turns on the output power of laser source (λ=532nm) for multimode fiber with (m) length at different bending diameter. Volume 2, Issue 11, November 2014 Page 22

6 Table 8: The effect of no. of wrapping turns on the output power of laser source (λ=532nm) for multimode fiber with (0m) length at different bending diameter. Table 9: The effect of no. of wrapping turns on the output power of laser source (λ=532nm) for multimode fiber with (1m) length at different bend diameter. Fiber length (L) = 0m Power (mw) * - 4 Figure 8: laser power as a function of No. of wrapping turns of (m) multimode fiber at different diameter. Fiber length (L) = 0m Power (mw) * - 4 Figure 8: laser power as a function of No. of wrapping turns of (m) multimode fiber at different diameter. Volume 2, Issue 11, November 2014 Page 23

7 Fiber length (L) = 0m Powe r (mw) * Figure 9 laser power as a function of No. of wrapping turns of (0m) multimode fiber at different diameter Fiber length (L) = 1m Power (mw) * Figure laser power as a function of No. of wrapping turns of (1m) multimode fiber at different diameter When the fiber is bent from (12.5 to 1 cm) as shown in the figure (8), the power will decrease from (48.083* -4 ) mw to (41.114* -4 ) mw at first turn of m fiber length. Obviously, the smaller bending radius will induce the bigger bending loss. Especially, the bending loss is obviously become higher with radius R < 1cm. The reason which stops us to use R less than 1cm was that in very low R, bending loss was very high, and secondly the presence of micro cracks in optical fibers, especially in very low radius of bending, can cause problems and affect its performance. For radius more than 12.5 cm, the amount of attenuation due to bending was very small, and loss was very low. So the measurements would give wrong results (so the loss is neglected). Table The effect of no. of wrapping turns on the output power of laser source (λ=532nm) for multimode fiber with different length at bending diameter (12.5cm). Volume 2, Issue 11, November 2014 Page 24

8 Table 11 The effect of no. of wrapping turns on the output power of laser source (λ=532nm) for multimode fiber with different length at bending diameter (4cm). Diameter of turns (2r) = 12.5cm Power (mw) * L=m L=1m Figure 11 The power of laser source at (λ=532nm) as a function of for multimode fiber at (, 0, 1m) at bending diameter (12.5cm). Diameter of turns (2r) = 4cm Power (mw) * -4 L=m L=120m 34 Figure 12 The power of laser source at (λ=532nm) as a function of for multimode fiber at (, 0, 1m) at bending diameter (4cm). Figure 12 Shows the relation between number of wrapping turns and the output power of laser source (λ=532nm) for multimode fiber (, 0, 120 m) at bending diameter 4 cm. At first turn of m multimode fiber, the power was ( * -4 ) mw and decreased with increasing number of turns to reach (.565 * -4 ) mw at ten turns. Increasing bending diameter to 12.5 cm as in figure11, led to increase the power ( * -4 ) mw at first turn of m multimode fiber. Increasing number of turns led to decrease the power to be ( * -4 ) mw at ten turn. Volume 2, Issue 11, November 2014 Page 25

9 Table (12) The effect of bend diameter on the output power of laser source at (λ=650nm) for multimode fiber (, 0, 1 m) at six turn (N=6) Power (mw) * N=6 L=m L=1m Figure 13 The power of laser source at (λ=650nm) as a function of bend diameter for multimode fiber (, 0, 1m) at sixth wrapping turn (N=6) Fiber length (L) = m Attenuation (db/km) Figure 14 The attenuation of laser diode at (λ=532nm) as a function of no. of wrapping turn for (m) multimode fiber at different bending diameter. Attenuation(dB/km) Fiber length (L) = m Figure15 The attenuation of laser diode at (λ=650nm) as a function of no. of wrapping turn for (m) multimode fiber at different bending diameter. Volume 2, Issue 11, November 2014 Page 26

10 From Figure (14) and (15) when the bending radius increase, the attenuation is decreases exponentially until it reaches o-at a certain critical radius. For any radius a bit smaller than this point, the losses suddenly become extremely large and from the graph there is a point where attenuation becomes steady. 4. CONUCLUSTIONS In this paper the power loss of the fiber cable at different bending radius at different wavelength of multimode fiber have been investigated. It is observed that as the bending diameter decrease and number of bends increase the output power also decreases i.e. the loss of power increases. It is also observed that the power loss is more in the case (1cm) than in the case of (12.5cm). And as the fiber length is increases from ( to 1m) the power decreases. It has been shown that laser diode at(λ=650nm, λ=532nm) had same behaviors as bending diameter decreases and no. of wrapping turns increases the power of laser diode decreases exponentially. References [1] A. P. Alvaro, Su D., D. R. Hall and J. D. C Jones, " Bend Loss in Large core multimode optical fiber beam delivery systems " Applied optics, 30, No. 3, pp , [2] Q. Wang, G. Farrell and T. Freir, " Theoretical and Experimental Investigations of Macro-Bend Losses for Standard Single Mode Fibers ", Optics Express 76, 13, No. 12, PP , Optical Society of America, [3] Q. Wang, G. Farrell,T. Freir, G. Rajan and P. Wang, " Low-Cost Wavelength measurement based on a Macrobending Single-Mode Fiber ", Optics Letters, 31, No. 12, pp , [4] S. Xiaoguang, J Li. and A. Hokansson, " Study of Optical Fiber Damage Under Tight Bend With High Optical Power at 21 nm ", Proc. SPIE 6433, Optical Fibers and Sensors for Medical Diagnostics and Treatment Applications, [5] A. M. Rocha, A. Martins, M Facao. and P.S. Andre, " Effect of Bending in SMF Fibers Under High Power ", ICTON '09. 11th International Conference on,pp.1-4, [6] H. Elzein, " Application on Optical Backscattering Reflectometer (OBR) ", California State University, Northridge, [7] Thai L. Th., " New Development in Fiber Technologies ", Department of Electronics and Telecommunications, Norwegian University of Science and Technology, [8] " Understanding Range for RF Devices ", Laird Technologies, Inc., [9] A. Azendehnam, M. Mirzaei, A. Farashiani and L. H. Farahani, " Investigation of Bending Loss in a Single- Mode Optical Fiber ", Pramana Journal of Physics, 74, No. 4, PP , Indian Academy of Science, 20. Volume 2, Issue 11, November 2014 Page 27