Signal characteristics by optimization the output coupling ratio of multi-wavelength Brillouin fiber laser incorporating fiber Bragg grating in a ring cavity technique A. Zakiah Malek, N. A. M. Ahmad Hambali, M. H. A. Wahid, and M. M. Shahimin
Citation: AIP Conference Proceedings 1835, 020002 (2017); doi: 10.1063/1.4981824 View online: https://doi.org/10.1063/1.4981824 View Table of Contents: http://aip.scitation.org/toc/apc/1835/1 Published by the American Institute of Physics
Articles you may be interested in Multiple lasing and gain medium characteristics of Brillouin fiber laser exploiting reflectivity from fiber Bragg grating AIP Conference Proceedings 1835, 020003 (2017); 10.1063/1.4981825 The optimal input voltage and emission rate characteristics for different LED chips material AIP Conference Proceedings 1835, 020001 (2017); 10.1063/1.4981823 A study of tensile and thermal properties of 3D printed conductive ABS – ZnO composite AIP Conference Proceedings 1835, 020008 (2017); 10.1063/1.4981830 Crystallinity and ferroelectric analysis on sol-gel derived Ba0.7Er0.3TiO3 thin films AIP Conference Proceedings 1835, 020005 (2017); 10.1063/1.4981827 Effect of halloysite content on carboxymethyl cellulose/halloysite nanotube bio-nanocomposite films AIP Conference Proceedings 1835, 020006 (2017); 10.1063/1.4981828 Deformation behavior of open-cell dry natural rubber foam: Effect of different concentration of blowing agent and compression strain rate AIP Conference Proceedings 1835, 020007 (2017); 10.1063/1.4981829
Signal Characteristics by Optimization the Output Coupling Ratio of Multi-wavelength Brillouin Fiber Laser Incorporating Fiber Bragg Grating in a Ring Cavity Technique A Zakiah Malek1,2,a), N A M Ahmad Hambali1,2,b), M H A. Wahid1,2 and M M Shahimin3 1
School of Microelectronics Engineering, Universiti Malaysia Perlis (UniMAP), 02600 Arau, Perlis, Malaysia. 2 Semiconductor Photonics & Integrated Lightwave Systems (SPILS), Tun Abdul Razak Laser Laboratory (TAReL), School of Microelectronic Engineering, Universiti Malaysia Perlis, Pauh Putra Main Campus, 02600 Arau, Perlis, Malaysia. 3 Department of Electrical and Electronic Engineering, Faculty of Engineering, National Defence University of Malaysia (UPNM), Kem Sungai Besi, 57000 Kuala Lumpur. a)
[email protected] [email protected]
b)
Abstract. An efficient multi-wavelength Brillouin fiber laser incorporating fiber Bragg grating is presented by using the ring cavity technique. With the utilization of fiber Bragg grating’s reflectivity, up to maximum 28 Brillouin Stokes signals with 15.65 dB of average optical signal to noise ratio are generated with constant downshifted frequency of 0.08 nm. The laser system consumes 18 dBm of amplified Brillouin pump power and 90 % of the output coupling ratios at 11 km of single mode fiber. The Brillouin pump wavelength was fixed at 1550 nm corresponds to the center wavelength of fiber Bragg Grating. The optical signal to noise ratio was also observed to be not less than 13.05 dB at 18 dBm of amplified Brillouin pump power in all cases of the output coupling ratios.
INTRODUCTION Over many decades, fiber optic has tremendously transformed the telecommunication industry in many aspects and offers the reliable data innovation for internet users either in terms of global coverage or data rates [1]. This growth is due to the development of a wide tuning range of the fiber laser system which offers almost unlimited bandwidth at high speed [2]. As the interest for data transfer expands, this situation increased the great opportunity to more research and investigation on new applications and technologies. Since the first investigation of stimulated Brillouin scattering (SBS) effect has been studied in 1964 by Chiao et al [3], the deployment of light for fiber optic communication received vigorous attentions as the future direction communication system. It is well known that SBS is principally caused by the propagation of back-reflected optical signal. The back-reflected signal is downshifted and normally called as Brillouin Stokes (BS) signal, resulted when the injected Brillouin pump (BP) power exceeds a certain level namely as threshold condition. Once the laser system attained the above threshold condition, the BP power has slightly transferred to the first BS signal. Thus, the BS signal power is depends by the material of gain medium in which allow the propagation of light.
Advanced Materials Engineering and Technology V AIP Conf. Proc. 1835, 020002-1–020002-6; doi: 10.1063/1.4981824 Published by AIP Publishing. 978-0-7354-1505-8/$30.00
020002-1
In the past few years, the integration of the narrow linewidth Brillouin laser was implemented in the multiwavelength Brillouin fiber laser (MWBFL) system [4, 5] and its applications. However, the Brillouin gain is typically very low to achieve high performance of multi-wavelength generation in the Brillouin fiber laser (BFL) operation. Thus, additional of optical amplifier such as an Erbium doped fiber amplifier (EDFA) is necessary to counter the transmission attenuation especially in a long haul optical telecommunication. Alternatively, with its narrow linewidth signal, the MWBFL system offers a lot of advantages for applications such as optical metrology [6], fiber-optic sensor, high-resolution spectroscopy, gyroscopes, interferometric sensing [7], narrow bandwidth amplification, dense wavelength division multiplexing (DWDM) system [8] and other optical fiber communications. After development of MWBFL system, it also has led to the subsequent studies of multi-wavelength Brillouinerbium fiber laser (MWBEFL) system [9] and multi-wavelength Brillouin Raman fiber laser (MWBRFL) system [10]. These techniques have been widely studied as a prominent method in order to generate a high number BS signal and lower threshold power. However, the major drawback of wavelength tunability and the competition of oscillating modes (self-lasing cavity) at the peak of Erbium doped fiber (EDF) caused the output instability in MWBEFL structure. Meanwhile, the spectral broadening mechanism of laser modes in the MWBRFL system limits the number of lasing signals. Another special type of fiber, such as dispersion compensating fiber (DCF) is needed to enhance the Raman gain since the stability of multi-wavelength generation is difficult to obtain. In the MWBRFL system, the multi-wavelength generation is constrained and only available at the certain Brillouin and Raman pump source [11]. In order to rectify these limitations, the implementation of MWBFL system utilizing Fiber Bragg Grating (FBG) is highly needed to produce a high number of multi-wavelength generations. The combination processes of SBS effect and FBG’s reflectivity at a center BP wavelength of 1550 nm are blended in this proposed ring cavity laser system. The optimization of different amplified BP powers and output coupling ratios are utilized throughout the investigation to minimize the cavity loss in the structure. Even though the utilization of MWBFL system has not been considered seriously before due to low generation of multi-wavelength, this limitation gives the aim and motivation to find another alternative by incorporated with FBG and hence increases the scattering effect in the main gain medium.
EXPERIMENTAL SETUP The experimental setup for the multi-wavelength generation of BFL is depicted in Figure 1. The BP signal was provided by the external tunable laser source (TLS) with a linewidth of 100 kHz, which then was amplified by an EDFA in order to multiply the output power. The amplified BP power was tunable from 8 dBm to 18 dBm with a step increment of 1 dBm while the BP wavelength was fixed at 1550 nm. After the amplification process, this amplified BP signal was injected into the ring cavity through port-1 of the circulator. The circulator has an insertion loss of below 0.1 dB, minimum isolation of more than 40 dB and return loss of more than 50 dB. From port-1 of the circulator, the amplified BP signal propagated into FBG via port-2 of the circulator. The FBG has a 3 dB bandwidth of 5 nm at the center wavelength of 1550 nm. The reflectivity of 70% was used to enhance the signal quality inside the FBG’s grating length. About 30% of the amplified BP signal transmitted into the single mode fiber (SMF) while another 70% amplified BP signal propagated in the opposite direction. About 11 km of SMF was tested as a Brillouin gain medium for multi-wavelength generation. Once the Brillouin threshold power in the SMF was attained, the first Brillouin Stokes (BS) signal propagated in the opposite direction through SBS effect. During its propagation, the 70% of FBG’s reflectivity improve the BS signal quality and continues travel into port-3 via port-2 of the circulator. This process repeated as long as the next-order BS signal has enough power to round-trip the Brillouin gain. The output coupling ratios of 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80% and 90% are optimized in order to minimize the cavity loss. A part of the BS signal was guided into the ring cavity meanwhile another part (output coupling ratio) is measured as an output signal by using an optical spectrum analyzer (OSA) with 0.02 nm resolution bandwidth.
020002-2
FIGURE 1. Multi-wavelength BFL incorporating FBG in a ring cavity technique.
RESULTS AND DISCUSSION In this experiment, the BP wavelength was fixed at 1550 nm which is according to the properties of FBG. The output coupling ratio was set at 90% while the amplified BP power was launched at 18 dBm. Figure 2 illustrates the selected optical spectrum with the formation of anti-Stokes signals and BS signals. The generation of multiwavelength was generated as the Brillouin threshold was achieved in the ring cavity. The SBS effect produced the first BS signals and at the same time interacts with the pump beam to generate a new beam called as anti-Stokes signals. The anti-Stokes signals generated through four wave mixing (FWM) process [12]. These interactions again interact with each other to produce the next generation of BS signals and anti-Stokes signals until the power of subsequent BS signal becomes lower and failed to overcome the Brillouin threshold condition. As could be seen in Figure 3, the magnified view of optical spectrum demonstrated the formation of BP signal, first BS signals, subsequent BS signals and anti-Stokes signals. A constant downshifted signal around 0.08 nm was also generated from the incident light through the Doppler Effect. The Doppler Effect was manifest from the changed in frequency of a wave with grating moving at acoustic velocity [13].
FIGURE 2. The generated optical spectrum at 90% output coupling ratio with 18 dBm of amplified BP power.
FIGURE 3. The magnified view of optical spectrum at 90% output coupling ratio with 18 dBm of amplified BP power.
In the next step, the relationship between the number BS signals and amplified BP powers with variation output coupling ratios at 11 km of SMF are intensively studied as illustrated in Figure 4. Overall, it was observed that the increment of amplified BP power influenced the increment of number BS signal for all proposed output coupling ratios. This abrupt change was associated with higher Brillouin gain induced a higher SBS effect which yielded the back-reflected signal called as BS signal. Therefore, by increasing the amplified BP power, more additional energy translates from the BP signal to subsequent BS signals. The highest number BS signal of 28 was recorded when 18
020002-3
dBm of the amplified BP power was injected into the ring cavity. This laser system was performed by allowing 10% of the signal oscillates in the ring cavity while another 90% of the signal was extracted as the output signal. The lowest number BS signals of 6 were obtained when 18 dBm of amplified BP power with 10% output coupling ratio was utilized. Besides that, by launching 8 dBm to 11 dBm of amplified BP powers only 1 BS signal was recorded in all cases of the output coupling ratios. Meanwhile, from 12 dBm to 18 dBm of amplified BP powers, the BS signals increases linearly with the increases of amplified BP power. Furthermore, the increment of number BS signals was also dependent specifically on the output coupling ratios. This condition can be explained by the amount of cavity loss inside the cavity. By increasing the output coupling ratio from 10% to 90%, the cavity loss was increased. Hence the light intensity that propagated inside the ring cavity was reduced. As a result, higher outputs in terms of BS signals were achieved at 90% output coupling ratio.
FIGURE 4. The number BS signals versus amplified BP powers by utilizing 11 km of SMF.
Figure 5 illustrates the average optical signal to noise ratio (OSNR) value by varying the amplified BP power and output coupling ratios at 11 km of SMF. From this figure, the average OSNR values show a clear flatness trend from 8 dBm to 12 dBm of amplified BP powers in all cases of the output coupling ratios. This flat trend was the evidence of energy transfer from BP signal to BS signal in which propagates in both directions clockwise and anticlockwise. In this case, the laser system acquired more Brillouin gain to increase the additional energy inside the ring cavity and thus produced a higher average OSNR value. As a result, a lower average OSNR value was recorded in this region. At 8 dBm of amplified BP power, the lowest average OSNR value of 10.09 dB was recorded by utilizing 10% output coupling ratio. Afterward, at 13 dBm to 18 dBm of amplified BP powers, it was found that the average OSNR values were steadily increased for all proposed output coupling ratios. The highest average OSNR value of 15.65 dB was attained when the 18 dBm of amplified BP power and 90% optimum output coupling ratio were utilized. Furthermore, it was also noticed that when the output coupling ratio was increased, the average OSNR value was further improved. This increment of average OSNR value inline with the increment of number BS signals as discussed earlier in Figure 4. As a result, at amplified BP power of 18 dBm, the average OSNR values were recorded at 13.05 dB, 14.06 dB, 14.11 dB, 14.27 dB, 14.33 dB, 14.46 dB, 14.92 dB, 14.99 dB and 15.65 dB for the output coupling ratios of 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80% and 90%, respectively.
020002-4
FIGURE 5. The average OSNR value versus amplified BP powers by utilizing 11 km of SMF.
In order to compare the output coupling ratios characteristic between the number BS signals and average OSNR value, the graph in Figure 6 is plotted. The amplified BP power was fixed at 18 dBm. From the graph, it was clearly shows that the increment of the output coupling ratios influenced the number BS signal. This trend corresponds to the abrupt growth of cavity loss through higher output coupling ratios. It is compatible with the experimental justification in Figure 4 which the increment output coupling ratios create larger cavity loss and leads to produce better number BS signals. The highest number BS signal was achieved at 90% output coupling ratio. In the meantime, the average OSNR value depicts almost a clear flatness trend as a function of output coupling ratios from 20% to 80% of the output coupling ratios. The sufficient amounts of amplified BP power shared among the BS signals are found to be the reason for these constant changed. Although the output coupling ratios were increased, the energy experienced by each of the BS signals remains fairly static with a small changed of value due to the stability operation of MWBFL system. At 90% of the output coupling ratio, the behaviour of light intensity was reflected with the available energy oscillated inside the optical fiber. This was done when the SBS effect initiated at a higher rate and thus produced higher average OSNR value with the increment of output coupling ratio. Overall, from the graph it was also found that the average OSNR value was found not less than 13.05 dB for all cases of the output coupling ratios.
FIGURE 6. The correlation between output coupling ratios with the number BS signals and average OSNR value at 18 dBm amplified BP power.
020002-5
SUMMARY The multi-wavelength BFL incorporating FBG in a ring cavity technique was successfully demonstrated. The optimization of different output coupling ratios and amplified BP powers at 1550 nm of BP wavelength was studied. Up to 28 BS signals with 15.65 dB of average OSNR value were generated with constant downshifted frequency of 0.08 nm. This was done by utilizing 90% of the output coupling ratio and 18 dBm of amplified BP power. As the amplified BP power was increased, the number BS signals and average OSNR value were increased for all proposed output coupling ratios. This was happened due to the higher amplified BP power yielded a stronger Brillouin gain to initiate the SBS effect efficiently. Thus, higher energy was translated from the BP signal to the next order of BS signal. The highest number BS signals and average OSNR value were achieved at 90% of the output coupling ratio while the lowest were recorded at 10% of the output coupling ratio for all cases amplified BP power. ACKNOWLEDGMENTS This work was fully supported by the Ministry of Higher Education, Malaysia under research grant # FRGS/9003-00532#. The authors would like to thank the School of Microelectronics Engineering, Universiti Malaysia Perlis (UniMAP) especially SPILS for their support in this work. REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13.
C. Kinlin, “The Future of Asian Optical Communication”, (Conference on Optical Fiber Communication & Optoelectronic Exposition & Conference, 2006), pp. 1-3. B. A. Ahmad, A. W. Al-Alimi, A. F. Abbas, M. Mokhtar, S. W. Harun and M. A. Mahdi, IEEE Photonics J. 4, 1087-1094 (2012). R. Y. Chiao, C. H. Townes and B. P. Stoicheff, Phys. Rev. Lett. 12, 592-595 (1964). M. R. Nurdik, N. S. Abdul Rahim, and M. K. Abd Rahman, “Brillouin fiber laser with 200-nm tuning range, (IEEE 2nd Internatinal Conference on Photonics 2011), pp. 1-4. R. Parvizi, S. W. Harun, N. M. Ali, N. S. Shahabuddin and H. Ahmad, Chin. Opt. Lett. 9, 021403 (2011). J. Subías, C. Heras, J. Pelayo and F. Villuendas, Opt. Express 17, 6753-6758 (2009). J. Geng, S. Staines, Z. Wang, J. Zong, M. Blake and S. Jiang, IEEE Photonics Technol. Lett. 18, 1813-1815 (2006). A. Mansor, Y. N. Phua, M. Othman, Nurul Shahrizan Shahaduddin and Z. Yusoff, “Double-Frequency Spaced Multiwavelength Brillouin-Erbium Fiber Laser in a Hybrid Linear-Ring Configuration”, (IEEE International Conference on Photonic 2011), pp. 1-3. M. K. Abd. Rahman, M. R. Nurdik and N.S.A Rahim, IEEE J. Sel. Top. Quantum Electron. 20, (2014). M. A. Toor, N. A. M. Ahmad Hambali, H. A. Abdul-Rashid and Z. Yusoff, “Multiwavelength BrillouinRaman fiber laser utilizing a partially fiber Bragg grating in L-band”, (IEEE on International Conference Photonics 2014), pp. 90-92. A. K. Zamzuri, M. A. Mahdi, A. Ahmad, M. I. Md Ali and M. H. Al-Mansoori, Opt. Express 15, 3000-3005 (2007). Jianguan Tang, Junqiang Sun, Liang Zhoa, Toa Chen, Tianye Huang and Yujie Zhou, Opt. Express 19, 1468214689 (2011). R. W. Boyd, Nonlinear Optics (Academic Press, San Diego, 1992), pp. 8.
020002-6
