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Advanced plasmonic-on-fibre devices for optical communication and sensing applications

Final Report Summary - PLASM-ON-FIBRE (Advanced plasmonic-on-fibre devices for optical communication and sensing applications)

The research objectives of the plasm-on-fibre project cover two aspects: First, integrating AIPT start-of-the-art fibre grating technology with Marie Curie fellow Dr J Zhang’s special knowledge and expertise in nano-photonics to develop novel and high function plasmonic-on-fibre devices for biosensors for environmental, medical and food industrial applications and high speed communications. The novel and high function plasmonic-on-fibre devices can be conducted by exploring UV laser inscription, nanomaterials and nanostructures, coating and immobilisation of molecules and laser photonics. Second, transferring Dr J Zhang’s solid knowledge and abundant research experience, expertise and skills in plasmonics and nano photonics to the EU main host (AIPT of Aston University) and establish long term collaboration and research network among the IIF and EU partners as well as provide training to the young Post-docs, Ph.D and Master students. The activity and output of this project will not just significantly enhance the EU R&D leading position in this area but also generate a new range of plasmonic-on-fibre technologies to benefit the EU research and industry community and new knowledge in modern plasmonics and high performance plasmonic-on-fibre devices to meet the increasing application demands in environmental sensing, medical and health care and food quality and security control.
Since the start of the project, Dr J Zhang has designed and investigated plasmonic cavity resonators, and further developed plasmonic-on-fibre technologies and their sensing applications, resulting in many novel results. He has transferred his knowledge and skills about plasmonics and nanomaterials to the Ph.D and master students at Aston University through supervising the students to do some experiments and giving talks and lectures. During the two years, Dr. J Zhang has attended some international conferences and meetings and given talks. He also visited and made the long term collaborations with some universities and companies in Europe and establish some collaborations networks with in Europe and China.
Through this project, we have achieved a significant number of good results in plasmonic resonant cavity devices and plasmonic-on-fibre sensors, as listed below:

(1) We have investigated the coupling from the fibre core mode to cladding modes and then to the surface plasmon (SP) modes in plasmonic-on-fibre gratings. We have calculated the grating periods with the tilt angles of the tilted fibre gratings (TFGs) for the excitation of the SP modes in the Au/Al2O3 plasmonic structure. Additionally, we have simulated the effective refractive index of the gold nanorod arrays as metamaterials on fiber gratings based on the dispersion equation, and explored the phase match conditions between the cladding modes of TFGs and the SP modes.
(2) To excite the SP modes on the interfaces between plasmonic structures and fibre gratings, many sorts of fibre gratings such as small and large angle TFGs and long period gratings (LPGs) with different parameters have been fabricated by the UV inscription systems.
(3) We have successfully designed and fabricated plasmonic resonators based on a metamaterial consisting of periodic arrays of gold nanotubes embedded into anodic aluminum oxide and demonstrated strong confinement of local fields with low losses. We have observed higher-order resonance modes of surface plasmons localized in gold nanotubes, and their electric fields are mainly localized at the interfaces between aluminum oxide and gold in the form of the standing-wave longitudinal plasmonic modes, partially localized in the pores and at two ends of the nanotubes owing to the strong Fabry-Pérot resonances with extraordinary optical transmission through the inner nanochannels of the nanotubes, so that the nanotubes play a role of efficient cavity resonators. We have revealed the existence of hybrid resonant cavity modes resulting from the near-field coupling of transverse and longitudinal modes in the gold nanotube metamaterials.
(4) We have presented experimental and theoretical investigation on plasmonic coupling and cavity modes in silver nanorod metamaterials. The open nanocavities illustrate multiple resonance modes of surface plasmons, and longitudinal resonances exhibit standing wave modes with multiple harmonics due to the near-field coupling between adjacent nanorods, the harmonics present half wave modes. In addition, we have observed a new plasmonic coupling mode between nanorods and gold substrate, the coupling mode can be tuned by the gap between nanorods and substrate, and the energy of local electric fields perform transformation from nanorods to substrate. The open cavity metamaterials will perform significant applications in label-free plasmonic biosensors.
(5) We have developed fabrication methods to the gold and silver nanorod arrays on the surfaces of D-fibres, TFGs and LPGs by using a very thin PMMA layer as a resin to adhere the as-prepared gold nanorod arrays on fibre surfaces and subsequently etching treatment.
(6) We have used silver nanorods for sensing applications based on the size and the ambient dielectric medium dependence of transversal resonance modes of localized surface plasmons (LSPs). It has been observed that the transversal resonances are strongly sensitive to the surrounding dielectric medium, which can be used for sensitive quantification of chemical and biological species.
(7) We have successfully prepared gold nanoparticle arrays on surfaces of small angle TFGs by using monolayer polystyrene (PS) colloidal crystal template based approach and subsequently coating gold films. Furthermore, we have found the plasmonic-on-fibre gratings demonstrate obvious polarization dependence of sensing properties, the peaks with the SPR characteristics perform red shifts from 1495 to 1540 nm with increasing the refractive index of surrounding media from 1.340 to 1.424 for p-polarization light, we have achieved high sensitivity (over 500 nm/RIU). We have used the plasmonic-on-fibre gratings to detect glucose molecules with different concentrations of 3 to 30 mM dissolved in 5 M sodium acetate buffer solution. We have observed the SPR peaks present red shifts centered around 1512 nm with increasing the glucose concentration.
(8) We have successfully prepared gold nanoparticle arrays on surfaces of large angle TFGs by using monolayer PS template based approach and subsequently coating gold films. The PS array on large angle TFGs (e.g. 81º) coated gold films display both the intensity and the position of the peaks distinct change with the refractive index of ambient medium. In particular, we have observed an enhanced birefringence phenomenon in the PS/Au particle arrays on large angle TFGs.
(9) We have fabricated ZnO/PS particles on large angle TFGs for enhanced refractive index sensing. The nanoparticle-on-fiber gratings show improved sensitivities with respect to the bare TFGs.
(10) We have developed a highly sensitive ambient refractive index sensor based on TFGs (81°) structure UV-inscribed in standard telecom fiber (62.5μm cladding radius) with carbon nanotube (CNT) overlay deposition. The sensing mechanism is based on the ability of CNT to induce change in transmitted optical power and the high sensitivity of TFGs to ambient refractive index.
(11) We have reported an enzyme-functionalized biosensor based on LPGs in transition mode at dispersion turning point. The dual-peak LPGs have high sensitivity for sugar and glucose. The sensor has potential applications in food safety, medical diagnosis and environmental monitoring.

With Dr J Zhang’s help, the research platform for plasmonics devices and plasmonic-on-fibre gratings for sensing has been further improved at AIPT. Knowledge transfer from Dr J Zhang to the host AIPT have been conducted by giving talks and seminars to the group and post-docs and Ph.D students. The IIF fellow Dr J Zhang has participated in various meetings with AIPT members and students at Aston University with topics related to the project. In addition, he has given two talks on the results of his research work during the project:

(i) “Plasmonic nanostructures for fibre devices”, 3th floor, North Wing, Main building Aston University,10 December, 2014.
(ii) “Gold nanotube metamaterial for plasmonic cavity resonator”, MB559, Main building, Aston University, 21 July, 2016.