Ultra-compact TE and TM pass polarizers based on vanadium dioxide on silicon

"This paper was published in Optics Letters and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://dx.doi.org/10.1364/OL.40.001452. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law"[EN] Vanadium dioxide (VO2) is a metal-insulator transition (MIT) oxide recently used in plasmonics, metamaterials, and reconfigurable photonics. Because of the MIT, VO2 shows great change in its refractive index allowing for ultra-compact devices with low power consumption. We theoretically demonstrate a transverse electric (TE) and a transverse magnetic (TM) pass polarizer with an ultra-compact length of only 1 μm and tunable using the MIT of the VO2. During the insulating phase, both devices exhibit insertion losses below 2 dB at 1550 nm. Changing to the metallic phase, the unwanted polarization is attenuated above 15 dB while insertion losses are kept below 3 dB. Broadband operation over a range of 60 nm is also achieved.This work was supported by the European Commission under project FP7-ICT-2013-11-619456 SITOGA. Financial support from TEC2012-38540 LEOMIS is also acknowledged. L. Sanchez also acknowledges the Generalitat Valenciana for funding his grant in the context of the VALi+d program.Sánchez Diana, LD.; Lechago Buendía, S.; Sanchis Kilders, P. (2015). Ultra-compact TE and TM pass polarizers based on vanadium dioxide on silicon. Optics Letters. 40(7):1452-1455. https://doi.org/10.1364/OL.40.001452S14521455407Soref, R., & Larenzo, J. (1986). All-silicon active and passive guided-wave components for λ = 1.3 and 1.6 µm. IEEE Journal of Quantum Electronics, 22(6), 873-879. doi:10.1109/jqe.1986.1073057Jalali, B., & Fathpour, S. (2006). Silicon Photonics. Journal of Lightwave Technology, 24(12), 4600-4615. doi:10.1109/jlt.2006.885782Manolatou, C., Johnson, S. G., Fan, S., Villeneuve, P. R., Haus, H. A., & Joannopoulos, J. D. (1999). High-density integrated optics. Journal of Lightwave Technology, 17(9), 1682-1692. doi:10.1109/50.788575Alonso-Ramos, C., Halir, R., Ortega-Moñux, A., Cheben, P., Vivien, L., Molina-Fernández, Í., … Schmid, J. (2012). Highly tolerant tunable waveguide polarization rotator scheme. Optics Letters, 37(17), 3534. doi:10.1364/ol.37.003534Zhang, H., Das, S., Zhang, J., Huang, Y., Li, C., Chen, S., … Thong, J. T. L. (2012). Efficient and broadband polarization rotator using horizontal slot waveguide for silicon photonics. Applied Physics Letters, 101(2), 021105. doi:10.1063/1.4734640Aamer, M., Gutierrez, A. M., Brimont, A., Vermeulen, D., Roelkens, G., Fedeli, J.-M., … Sanchis, P. (2012). CMOS Compatible Silicon-on-Insulator Polarization Rotator Based on Symmetry Breaking of the Waveguide Cross Section. IEEE Photonics Technology Letters, 24(22), 2031-2034. doi:10.1109/lpt.2012.2218593Komatsu, M., Saitoh, K., & Koshiba, M. (2012). Compact Polarization Rotator Based on Surface Plasmon Polariton With Low Insertion Loss. IEEE Photonics Journal, 4(3), 707-714. doi:10.1109/jphot.2012.2195650Caspers, J. N., Alam, M. Z., & Mojahedi, M. (2012). Compact hybrid plasmonic polarization rotator. Optics Letters, 37(22), 4615. doi:10.1364/ol.37.004615Chen, G., Chen, L., Ding, W., Sun, F., & Feng, R. (2013). Ultrashort slot polarization rotator with double paralleled nonlinear geometry slot crossings. Optics Letters, 38(11), 1984. doi:10.1364/ol.38.001984Nakayama, K., Shoji, Y., & Mizumoto, T. (2012). Single Trench SiON Waveguide TE-TM Mode Converter. IEEE Photonics Technology Letters, 24(15), 1310-1312. doi:10.1109/lpt.2012.2202646Sánchez, L., & Sanchis, P. (2013). Broadband 8 μm long hybrid silicon-plasmonic transverse magnetic–transverse electric converter with losses below 2 dB. Optics Letters, 38(15), 2842. doi:10.1364/ol.38.002842Zhang, H., Huang, Y., Das, S., Li, C., Yu, M., Lo, P. G.-Q., … Thong, J. (2013). Polarization splitter using horizontal slot waveguide. Optics Express, 21(3), 3363. doi:10.1364/oe.21.003363Ding, Y., Liu, L., Peucheret, C., & Ou, H. (2012). Fabrication tolerant polarization splitter and rotator based on a tapered directional coupler. Optics Express, 20(18), 20021. doi:10.1364/oe.20.020021Ding, Y., Ou, H., & Peucheret, C. (2013). Wideband polarization splitter and rotator with large fabrication tolerance and simple fabrication process. Optics Letters, 38(8), 1227. doi:10.1364/ol.38.001227Dai, D., & Bowers, J. E. (2011). Novel concept for ultracompact polarization splitter-rotator based on silicon nanowires. Optics Express, 19(11), 10940. doi:10.1364/oe.19.010940Xiao, Z., Luo, X., Lim, P. H., Prabhathan, P., Silalahi, S. T. H., Liow, T.-Y., … Luan, F. (2013). Ultra-compact low loss polarization insensitive silicon waveguide splitter. Optics Express, 21(14), 16331. doi:10.1364/oe.21.016331Chee, J., Zhu, S., & Lo, G. Q. (2012). CMOS compatible polarization splitter using hybrid plasmonic waveguide. Optics Express, 20(23), 25345. doi:10.1364/oe.20.025345Huang, Y., Zhu, S., Zhang, H., Liow, T.-Y., & Lo, G.-Q. (2013). CMOS compatible horizontal nanoplasmonic slot waveguides TE-pass polarizer on silicon-on-insulator platform. Optics Express, 21(10), 12790. doi:10.1364/oe.21.012790Sun, X., Alam, M. Z., Wagner, S. J., Aitchison, J. S., & Mojahedi, M. (2012). Experimental demonstration of a hybrid plasmonic transverse electric pass polarizer for a silicon-on-insulator platform. Optics Letters, 37(23), 4814. doi:10.1364/ol.37.004814Alam, M., Aitchsion, J. S., & Mojahedi, M. (2011). Compact hybrid TM-pass polarizer for silicon-on-insulator platform. Applied Optics, 50(15), 2294. doi:10.1364/ao.50.002294Alam, M. Z., Aitchison, J. S., & Mojahedi, M. (2011). Compact and silicon-on-insulator-compatible hybrid plasmonic TE-pass polarizer. Optics Letters, 37(1), 55. doi:10.1364/ol.37.000055Zhoufeng Ying, Guanghui Wang, Xuping Zhang, Ying Huang, Ho-Pui Ho, & Yixin Zhang. (2015). Ultracompact TE-Pass Polarizer Based on a Hybrid Plasmonic Waveguide. IEEE Photonics Technology Letters, 27(2), 201-204. doi:10.1109/lpt.2014.2365029Avrutsky, I. (2008). Integrated Optical Polarizer for Silicon-on-Insulator Waveguides Using Evanescent Wave Coupling to Gap Plasmon–Polaritons. IEEE Journal of Selected Topics in Quantum Electronics, 14(6), 1509-1514. doi:10.1109/jstqe.2008.926284Dai, D., Wang, Z., Julian, N., & Bowers, J. E. (2010). Compact broadband polarizer based on shallowly-etched silicon-on-insulator ridge optical waveguides. Optics Express, 18(26), 27404. doi:10.1364/oe.18.027404Ryckman, J. D., Diez-Blanco, V., Nag, J., Marvel, R. E., Choi, B. K., Haglund, R. F., & Weiss, S. M. (2012). Photothermal optical modulation of ultra-compact hybrid Si-VO_2 ring resonators. Optics Express, 20(12), 13215. doi:10.1364/oe.20.013215Ruzmetov, D., Gopalakrishnan, G., Ko, C., Narayanamurti, V., & Ramanathan, S. (2010). Three-terminal field effect devices utilizing thin film vanadium oxide as the channel layer. Journal of Applied Physics, 107(11), 114516. doi:10.1063/1.3408899Briggs, R. M., Pryce, I. M., & Atwater, H. A. (2010). Compact silicon photonic waveguide modulator based on the vanadium dioxide metal-insulator phase transition. Optics Express, 18(11), 11192. doi:10.1364/oe.18.011192Kruger, B. A., Joushaghani, A., & Poon, J. K. S. (2012). Design of electrically driven hybrid vanadium dioxide (VO_2) plasmonic switches. Optics Express, 20(21), 23598. doi:10.1364/oe.20.023598Ooi, K. J. A., Bai, P., Chu, H. S., & Ang, L. K. (2013). Ultracompact vanadium dioxide dual-mode plasmonic waveguide electroabsorption modulator. 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Optics Letters, 39(13), 3997. doi:10.1364/ol.39.00399

Accurately Modeling a Photonic NoC in a Detailed CMP Simulation Framework

© 2016 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.Photonic interconnects are a promising solution for the so-called communication bottleneck in current Chip Multiprocessor (CMPs) architectures. This technology presents an inherent low-latency and power consumption almost independent of communication distance, which are really desirable features in future Networks on Chip for next CMPs generations. However, since nanophotonic technology is still growing and therefore in an immature state, current simulators of detailed systems may not provide accurate models of photonic components. In this context, non-representative results are obtained when unaccurate photonic models are assumed. This paper summarizes all of the components that conform a fully operative photonic NoC and presents their current state of the art. Moreover, we evaluate a realistic photonic network that consists of two photonic rings and a token-based arbitration mechanism and compare it against a non-realistic model. In addition, both realistic and non-realistic schemes are valuated under different configurations varying the number of wavelengths that photonic waveguides employ. The experimental results show that the non-realistic NoC presents up 6× network latency deviation with respect to the accurate model. This deviation is translated into a performance deviation higher than 10% in several applications studied, which demonstrates the importance of accurate models when simulating current technologies under development like nanophotonics. Finally, a power consumption model of the realistic photonic network is presented. The results show that the overall photonic network power consumption grows with the number of wavelengths per waveguide since the number of required modulators and receivers becomes higher. In this way, the proposed realistic photonic network, which employs only two wavelengths for arbitration and destination selection tasks, increases its power consumption up to 3%, so network designs with more complex arbitration mechanisms must take into account the impact of the number of wavelengths on the power consumption.This work was supported by the Spanish Ministerio de Economía y Competitividad (MINECO) and by Plan E funds under Grant TIN2015-66972-C5-1-R and the ExaNest project, funded by the European Union’s Horizon 2020 research andinnovation programme under grant agreement No 671553.Puche Lara, J.; Lechago Buendía, S.; Petit Martí, SV.; Gómez Requena, ME.; Sahuquillo Borrás, J. (2016). Accurately Modeling a Photonic NoC in a Detailed CMP Simulation Framework. IEEE. https://doi.org/10.1109/HPCSim.2016.756836

Low-Power Operation in a Silicon Switch Based on an Asymmetric Mach Zehnder Interferometer

[EN] Mach Zehnder interferometer (MZI) structures are widely used as optical switches in photonic integrated circuits. However, power consumption is still the key parameter to make such devices practical in the silicon platform, particularly for those based on the thermo-optic effect. A new approach to significantly decrease the power consumption of a silicon switch based on an asymmetric MZI, together with an optimum selection of the operation wavelengths, is proposed. A power consumption reduction up to 50% is experimentally demonstrated in agreement with simulation results.This work was supported by TEC2012-38540 LEOMIS and NANOMET PLUS-Conselleria d'Educacio, Cultura i EsportPROMETEOII/2014/034. The work of L. Sanchez was supported by Generalitat Valenciana in the context of the VALi+d program.Sánchez Diana, LD.; Griol Barres, A.; Lechago Buendía, S.; Brimont, ACJ.; Sanchis Kilders, P. (2015). Low-Power Operation in a Silicon Switch Based on an Asymmetric Mach Zehnder Interferometer. IEEE Photonics Journal. 7(2):1-8. https://doi.org/10.1109/JPHOT.2015.2407317S187

All-dielectric nanoantennas enabling on-chip wireless silicon photonics

Tesis por compendio[ES] La revolución posibilitada por las aplicaciones fotónicas durante las últimas décadas ha dejado su impronta en la sociedad tal y como la conocemos actualmente. Ejemplos claros de este impacto están patentes en, por ejemplo, el enorme tráfico de datos generado por el uso de Internet o el empleo extendido de algunas técnicas biomédicas con fines diagnósticos o quirúrgicos, que no podrían entenderse sin el incesante desarrollo de los sistemas ópticos. La necesidad de combinar y miniaturizar estos sistemas para generar funcionalidades más avanzadas dio lugar al nacimiento de los circuitos fotónicos integrados (PICs), que es donde esta tesis comenzó a tomar forma. En este sentido, observamos limitaciones en términos de flexibilidad o reconfigurabilidad inherentes a la naturaleza guiada de la mayoría de los PICs realizados hasta el momento. En el caso de circuitos plasmónicos, observamos también limitaciones por las pérdidas que tienen las guías metálicas a altas frecuencias. La inclusión de estructuras inalámbricas (basadas principalmente en nanoantenas plasmónicas) en la capa fotónica surgió para mitigar estas pérdidas, abriendo también nuevas vías de investigación. Sin embargo, estos dispositivos aún presentaban rendimientos muy pobres como elementos puramente radiantes en el régimen de campo lejano. Para superar estas deficiencias, en este trabajo, introdujimos un enfoque novedoso en el desarrollo de dispositivos inalámbricos en la nanoescala, que dio forma a lo que llamamos on-chip wireless silicon photonics. Este nuevo concepto se apoyó en el uso de nanoantenas de silicio compatibles con procesos CMOS, que constituyen las estructuras clave que posibilitan un vasto catálogo de aplicaciones en redes fotónicas de comunicación o en sensores ultra-integrados, así como para la interconexión de sistemas dieléctricos-plasmónicos avanzados. En el ámbito de las comunicaciones, gracias a las sencillas reglas de diseño para adaptar la directividad de estas nanoantenas a diversas aplicaciones, pudimos demostrar por primera vez transmisiones inalámbricas de datos (mediante el uso de antenas altamente directivas) en redes on-chip reconfigurables o desarrollar dispositivos para generar a voluntad focos electromagnéticos de manera dinámica en espacios bidimensionales (gracias a antenas con una directividad más baja). Por otro lado, en el campo del biosensado, diseñamos y fabricamos un dispositivo lab-on-a-chip para la identificación de micropartículas, basado en el uso de antenas dieléctricas -presentando un rendimiento equiparable a los mejores diseños desarrollados hasta el momento- que incluye el subsistema óptico más compacto demostrado hasta la fecha. Finalmente, fuimos capaces de conectar experimentalmente y de manera eficiente antenas basadas en silicio con estructuras plasmónicas para el desarrollo de nuevas aplicaciones en la nanoescala, aunando las ventajas del on-chip wireles silicon photonics para comunicaciones en chip, conformación dinámica de haces o biosensado con las ventajas de la plasmónica para la manipulación e interacción con luz.[CA] La revolució habilitada per les aplicacions fotòniques durant les últimes dècades ha deixat la seua empremta en la societat actual tal com la coneixem. Exemples clars d'aquest impacte estan patents en, per exemple, l'enorme tràfic de dades generat per l'ús d'Internet o d'algunes tècniques biomèdiques amb fins diagnòstics o quirúrgics, que no es podrien entendre sense l'incessant desenvolupament dels sistemes òptics. La necessitat de combinar i miniaturitzar aquests sistemes per produir funcionalitats més avançades va donar lloc al naixement dels circuits fotònics integrats (PICs), que és on aquesta tesi va començar a prendre forma. En aquest sentit, observem limitacions en termes de flexibilitat o reconfigurabilitat inherents a la naturalesa guiada de la majoria dels PICs realitzats fins al moment. En el circuits plasmònics, tenim a mès les limitacions de les elevades pèrdues que les guies metàl·liques tenen a altes freqüències. La inclusió d'estructures sense fil (basades principalment en l'ús de nanoantenes plasmòniques) a la capa fotònica va sorgir per mitigar aquestes pèrdues, obrint també noves vies d'investigació. No obstant això, aquests dispositius encara presentaven rendiments molt pobres com a elements purament radiants en el règim de camp llunyà. Per superar aquestes deficiències, en aquest treball, vam introduir un enfocament innovador en el desenvolupament de dispositius sense fil a la nanoescala, que va donar forma al que anomenem on-chip wireless silicon photonics. Aquest nou concepte està basat en l'ús de nanoantenes de silici compatibles amb processos CMOS, que constitueixen les estructures clau que possibiliten un vast catàleg d'aplicacions en xarxes fotòniques de comunicació o en sensors ultra-integrats, així com per a la interconnexió de sistemes dieléctrics-plasmònics avançats. En l'àmbit de les comunicacions, gràcies a les senzilles regles de disseny per adaptar la directivitat de les antenes a les diverses aplicacions, vam poder demostrar per primera vegada transmissions de dades on-chip (mitjançant l'ús d'antenes altament directives) en xarxes reconfigurables o desenvolupar un dispositiu per generar a voluntat focus electromagnètics de manera dinàmica en espais bidimensionals (gràcies a antenes amb una directivitat més baixa). D'altra banda, en el camp del biosensing, vam dissenyar i fabricar un sensor lab-on-a-chip per a la classificació de micropartícules, basat en l'emprament d'antenes dielèctriques amb un rendiment a l'avantguarda dels millors dispositius de l'estat de l'art, que inclou el subsistema òptic més compacte demostrat fins al moment. Finalment, vam ser capaços de connectar experimentalment i de manera eficient antenes basades en silici amb estructures plasmònics per al desenvolupament de noves aplicacions en la nanoescala, unint els avantatges del on-chip wireless silicon photonics per a comunicacions en xip, conformació dinàmica de feixos o biosensat amb els avantatges de la plasmònica per a la manipulació e interacció amb llum.[EN] The revolution sparked by photonic applications during the last decades has made its mark in society, as we currently know it. Clear examples of this impact are patent in, for instance, the colossal worldwide data traffic generated by the use of the Internet or the widespread utilization of some biomedical techniques for diagnostic or surgical purposes, which could not be understood without the ceaseless development of optical systems. The necessity of combining and miniaturizing these systems to enable advanced functionalities gave birth to the development of photonic integrated circuits (PICs), which is the main framework within which this thesis began to take shape. Along these lines, we noticed restricted limitations in terms of flexibility or reconfigurability inherent to the wired-based nature of most PIC implementations carried out so far. In the case of plasmonic circuitry, there are additional shortcomings arising from the prohibitive losses of metallic waveguides at very high frequencies. The inclusion of wireless structures (mostly based on plasmonic nanoantennas) at the photonic layer emerged to mitigate these limiting losses, also opening new research avenues. However, these devices still presented poor performances as purely radiating elements in the far-field regime. In order to overcome these lacks, in this work, we introduced a novel version to wireless approaches at the nanoscale in what we called on-chip wireless silicon photonics. This new concept was built upon the use of CMOS-compatible silicon-based nanoantennas, which constitute the key enabling structures of a diverse catalogue of applications in photonic communication networks or ultra-integrated sensors as well as for interfacing advanced dielectric-plasmonic systems. In the scope of communications, thanks to the easiness to tailor the antenna directivity, we were able to experimentally demonstrate on-chip data transmission flows in reconfigurable networks for the first time (by using highly directive antennas) or to develop dynamically tailor-made interference patterns to create focused spots at will on a 2D arrangement (enabled by antennas with a lower directivity). On the other hand, in the field of biosensing, we experimentally implemented a dielectric antenna-based lab-on-a-chip device for microparticle classification with state-of-the-art performance, which included the most compact optical subsystem demonstrated so far. Finally, we were able to efficiently interface silicon-based antennas to plasmonic systems to develop new advanced functionalities at the nanoscale, by putting together the advantages of on-chip wireless silicon photonics for on-chip communications, beam-shaping tailoring or lab-on-a-chip sensing with the advantages of plasmonics for light concentration and manipulation.Lechago Buendía, S. (2019). All-dielectric nanoantennas enabling on-chip wireless silicon photonics [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/133074TESISCompendi

Diseño y caracterización de nanoantenas plasmónicas y dieléctricas

By means of this Project, a simulation and implementation of several types of optical nanoantennas was shown in order to establish on-chip optical wireless data transmissions. These nanolinks were fabricated on silicon wafers, using CMOS technology at the Nanophotonics technology center in the UPVEn este proyecto se recoge la simulación y síntesis de nanoantenas ópticas para establecer comunicaciones no guiadas entre dichas nanoantenas a nivel on-chip. Mediante estos nanoenlaces se consiguió transmitir datos en chips fabricados mediante tecnología CMOS en el centro de tecnología nanofotónica de la UPVLechago Buendia, S. (2014). Diseño y caracterización de nanoantenas plasmónicas y dieléctricas. http://hdl.handle.net/10251/37255.Archivo delegad

All-fiber processing of terahertz-bandwidth signals based on cascaded tapered fibers

Tapered single-mode fibers are employed to perform dynamic pulse shaping in a bandwidth of several terahertz. The transfer function of cascaded biconical tapers is controlled by introducing a phase shift into one of them through mechanical stretching. It is a simple and low-cost technique with potential to process signals with bandwidths as large as those allocated by standard optical fiber while introducing little degradation. Femtosecond pulses are shaped to prove the concept. (C) 2013 Optical Society of AmericaThis work was supported by the Generalitat Valenciana programs PROMETEO-2010-087 R&D Excellency and GV/2012/121 Grupos Emergentes.Mas Gómez, SM.; Palací López, J.; Pérez Millán, P.; Lechago Buendía, S.; Monzón-Hernández, D.; Martí Sendra, J. (2013). All-fiber processing of terahertz-bandwidth signals based on cascaded tapered fibers. Optics Letters. 38(23):4954-4957. https://doi.org/10.1364/OL.38.004954S495449573823Lacroix, S., Gonthier, F., Black, R. J., & Bures, J. (1988). Tapered-fiber interferometric wavelength response: the achromatic fringe. Optics Letters, 13(5), 395. doi:10.1364/ol.13.000395Villatoro, J., Monzón-Hernández, D., & Mejía, E. (2003). Fabrication and modeling of uniform-waist single-mode tapered optical fiber sensors. Applied Optics, 42(13), 2278. doi:10.1364/ao.42.002278Monzón-Hernández, D., & Villatoro, J. (2006). High-resolution refractive index sensing by means of a multiple-peak surface plasmon resonance optical fiber sensor. Sensors and Actuators B: Chemical, 115(1), 227-231. doi:10.1016/j.snb.2005.09.006Villatoro, J., Monzón-Hernández, D., & Luna-Moreno, D. (2004). In-line optical fiber sensors based on cladded multimode tapered fibers. Applied Optics, 43(32), 5933. doi:10.1364/ao.43.005933Wang, Z., Sone, H., Tsuji, Y., & Imai, M. (2007). Spectral Phase and Intensity Evolutions of Supercontinuum Generation in a Biconical Tapered Fiber. Optical Review, 14(2), 81-85. doi:10.1007/s10043-007-0081-6Lu, F., & Knox, W. H. (2004). Generation of a broadband continuum with high spectral coherence in tapered single-mode optical fibers. Optics Express, 12(2), 347. doi:10.1364/opex.12.000347Jedrzejewski, K. P., & Kosinski, A. (1997). Wide-band tapered directional coupler. Technology and Applications of Light Guides. doi:10.1117/12.285622Kawasaki, B. S., Hill, K. O., & Lamont, R. G. (1981). Biconical-taper single-mode fiber coupler. Optics Letters, 6(7), 327. doi:10.1364/ol.6.000327Rusu, M., Herda, R., Kivistö, S., & Okhotnikov, O. G. (2006). Fiber taper for dispersion management in a mode-locked ytterbium fiber laser. Optics Letters, 31(15), 2257. doi:10.1364/ol.31.002257Kieu, K., & Mansuripur, M. (2007). Femtosecond laser pulse generation with a fiber taper embedded in carbon nanotube/polymer composite. Optics Letters, 32(15), 2242. doi:10.1364/ol.32.002242Weiner, A. M. (2011). Ultrafast optical pulse shaping: A tutorial review. Optics Communications, 284(15), 3669-3692. doi:10.1016/j.optcom.2011.03.084Liu, X., Premkumar, A., & Madhukumar, A. (2008). Pulse shaping functions for UWK systems. IEEE Transactions on Wireless Communications, 7(5), 1512-1516. doi:10.1109/twc.2008.061060Weling, A. S., & Heinz, T. F. (1999). Enhancement in the spectral irradiance of photoconducting terahertz emitters by chirped-pulse mixing. Journal of the Optical Society of America B, 16(9), 1455. doi:10.1364/josab.16.001455Weiner, A. M., Heritage, J. P., & Kirschner, E. M. (1988). High-resolution femtosecond pulse shaping. Journal of the Optical Society of America B, 5(8), 1563. doi:10.1364/josab.5.001563Saperstein, R. E., Alić, N., Panasenko, D., Rokitski, R., & Fainman, Y. (2005). Time-domain waveform processing by chromatic dispersion for temporal shaping of optical pulses. Journal of the Optical Society of America B, 22(11), 2427. doi:10.1364/josab.22.002427Birks, T. A., & Li, Y. W. (1992). The shape of fiber tapers. Journal of Lightwave Technology, 10(4), 432-438. doi:10.1109/50.134196Kieu, K. Q., & Mansuripur, M. (2006). Biconical Fiber Taper Sensors. IEEE Photonics Technology Letters, 18(21), 2239-2241. doi:10.1109/lpt.2006.884742Cohoon, G. (2010). Enhancing sensitivity of biconical tapered fiber sensors with multiple passes through the taper. Optical Engineering, 49(3), 034401. doi:10.1117/1.3339906Ji, W. B., Liu, H. H., Tjin, S. C., Chow, K. K., & Lim, A. (2012). Ultrahigh Sensitivity Refractive Index Sensor Based on Optical Microfiber. IEEE Photonics Technology Letters, 24(20), 1872-1874. doi:10.1109/lpt.2012.221773