Saeed Rehman

Generation of infrared surface plasmon resonances with high refractive index sensitivity utilizing tilted fiber Bragg gratings

We demonstrate the use of tilted fiber gratings to assist the generation of localized infrared surface plasmons with short propagation lengths and a sensitivity of dlambda/dn = 3,365 nm in the aqueous index regime. It was also found that the resonances could be spectrally tuned over 1,000 nm at the same spatial region with high coupling efficiency (in excess of 25 dB) by altering the polarization of the light illuminating the device.

Characterization of infrared surface plasmon resonances generated from a fiber-optical sensor utilizing tilted Bragg gratings

We demonstrate the use of tilted fiber gratings to assist with the generation of infrared surface plasmons on a metal film coating the flat of a D-shaped fiber. The wavelength of the strong (>25 dB) resonance is tunable over similar to 1000 nm by adjusting the polarization state of the light and is highly sensitive to the refractive index of any aqueous medium surrounding the fiber (sensitivity= 3365 nm).

Exploitation of multilayer coatings for infrared surface plasmon resonance fiber sensors

We demonstrate surface plasmon resonance (SPR) fiber devices based upon ultraviolet inscription of a grating-type structure into both single-layered and multilayered thin films deposited on the flat side of a lapped D-shaped fiber. The single-layered devices were fabricated from germanium, while the multilayered ones comprised layers of germanium, silica, and silver. Some of the devices operated in air with high coupling efficiency in excess of 40 dB and an estimated index sensitivity of Delta lambda/Delta n=90 nm from 1 to 1.15 index range, while others provided an index sensitivity of Delta lambda/Delta n=6790 nm for refractive indices from 1.33 to 1.37.

Formation and Characterization of Ultra-Sensitive Surface Plasmon Resonance Sensor Based Upon a Nano-Scale Corrugated Multi-Layered Coated D-Shaped Optical Fiber

We present experimental results on the performance of a series of coated, D-shaped optical fiber sensors that display high spectral sensitivities to external refractive index. Sensitivity to the chosen index regime and coupling of the fiber core mode to the surface plasmon resonance (SPR) is enhanced by using specific materials as part of a multi-layered coating. We present strong evidence that this effect is enhanced by post ultraviolet radiation of the lamellar coating that results in the formation of a nano-scale surface relief corrugation structure, which generates an index perturbation within the fiber core that in turn enhances the coupling. We have found reasonable agreement when we modeling the fiber device. It was found that the SPR devices operate in air with high coupling efficiency in excess of 40 dB with spectral sensitivities that outperform a typical long period grating, with one device yielding a wavelength spectral sensitivity of 12000 nm/RIU in the important aqueous index regime. The devices generate SPRs over a very large wavelength range, (visible to 2 μm) by alternating the polarization state of the illuminating light.

Low refractive index gas sensing using a surface plasmon resonance fibre device

A series of surface plasmonic fibre devices were fabricated using multiple coatings deposited on a lapped section of a single mode fibre. Coupling from the guided mode to surface plasmons was promoted following UV laser irradiation of the coated region through a phase mask, which generated a surface relief grating structure. The devices showed high spectral sensitivities and strong coupling for low refractive indices as compared to other grating-type fibre devices. The plasmonic devices were used to detect the variation in the refractive indices of alkane gases with measured wavelength and coupling sensitivity to index of 3400 nm RIU-1 and 8300 dB RIU-1, respectively. As a demonstration of the performance of these gas sensors, a minimum concentration of 2% by volume of butane in ethane was achieved.

Aptamer-based surface plasmon fibre sensor for thrombin detection

A series of surface plasmonic fibre devices were fabricated using multiple coatings deposited on a lapped section of a single mode fibre and post-fabrication UV laser irradiation processing with a phase mask, producing a surface relief grating structure. These devices showed high spectral sensitivity in the aqueous index regime ranging up to 4000 nm/RIU for wavelength and 800 dB/RIU for intensity. The devices were then coated with human thrombin binding aptamer. Several concentrations of thrombin in buffer solution were made, ranging from 1nM to 1μM. All the concentrations were detectable by the devices demonstrating that sub-nM concentrations may be monitored.

Surface Plasmon Resonance Generation Utilising Gratings for Biochemical Sensing

We demonstrate the use of gratings to assist in the generation of surface plasmon resonances resulting in a device having a high index resolution of 3×10-5 in the aqueous index regime.

A surface plasmon resonance fibre device for environmental sensing

We demonstrate a surface plasmon resonance sensor that operates in air and has index resolution ~10-4 in the 1 to 1.3 index range. The sensor comprises a multi-layered thin film on a D-shaped fibre.

Bend insensitive multimode fibers with extreme bend loss tolerance and high bandwidth

Security, defense and sensing applications often require routing of optical fibers through constrained spaces. Fibers or fiber cables must frequently be tightly matched or mounted onto structures having arbitrary shapes or forms, which inevitably leads to requirement for tight fiber bends. In such case macro bend loss presents one of the major concerns and limitations in practical applicability of optical fibers. Fibers with high bend tolerance are therefore required in such environments. To date, significant works relating to the understanding and improvement of bend-loss sensitivity have been carried on for single-mode fibers and fiber systems. However, in security and defense applications, robust connectivity and installation reliability issues often favor multimode fiber systems.

Multilayered coated infra-red surface plasmon resonance fibre sensors for chemical sensing

Promising potential fields of applications for fibre optic sensors are chemistry, biochemistry and biology [1]; this is based upon the ability of some of these sensors to detect changes in the refractive index in the surrounding medium. Several types of sensors are being investigated such as long period gratings (LPGs), fibre Bragg gratings (FBGs), tilted fibre Bragg gratings (TFBGs) [2]. The majority of these sensors have their highest intrinsic sensitivities for indices over 1.4, which is well beyond the aqueous index. One type of sensor based on surface plasmon resonance (SPR) has shown high spectral sensitivity in the aqueous index regime [4]. There is very little published with regards to multi-layered thin film infra-red SPR fibre devices, and the majority of the papers, such as [5], address the optical properties and not the index sensing potential. In this paper we report on the sensing potential of these infra-red SPR fibre devices using various metal overlay coatings and compare the performance of these sensors to a long period grating sensor. This comparison shows that the SPR fibre sensors out-perform the LPG sensor in the low and aqueous index regime.