Short pulse operation of fiber lasers operating at wavelengths up 3 micron have been reported in recent years. At longer wavelengths, fiber lasers have only been demonstrated with a continuous operation mode. Short pulse operation in the mid-IR is necessary for utilizing such lasers in laser radars and for medical applications. Our previous numerical work suggested that Q-switching is possible on the 3.5 μm transition in erbium-doped ZBLAN in a similar manner to work demonstrated on the 2.8 μm transition in erbium. In this work we report on initial experimental results of a Q-switched, dualwavelength pumped fiber laser operating on the 3.5 μm transition in erbium-doped ZBLAN glass fibers. Using a hybrid fiber and open resonator configuration utilizing an acousto-optic modulator we demonstrated stable single pulse Q-switching while operating at repetition rates of 20 kHz and up to 120 kHz. The laser achieved a peak power of 8 W with pulse energy of 7 μJ while operating at 25 kHz. Long pulse widths on the order of 1 μs were obtained. The low peak power and long pulses are likely the result of both low gain of the transition and additional losses in the resonator which are currently being investigated. Our latest results will be presented.
For decades Surface Plasmon Resonance (SPR) has been one of the corner stones of label free biosensing with a wide range of architectures including optical fiber based SPR. Traditionally, the resonance is monitored through reflectivity measurements at a single wavelength as a function of the incident angle in a standard Kretschmann configuration, or transmission of broadband light through an optical fiber. In both cases, SPR is inferred through optical losses. An alternative approach is to use SPR scattering induced by rough metallic coatings, enabling to turn an intrinsically nonradiative process into a radiative one. As a result, the SPR signal corresponding to the resonance can be seen as light at specific wavelengths being re-emitted by the rough metallic coating.<p> </p>Here, we present results we have achieved using SPR scattering as an alternative approach for optical fiber based plasmonic sensors. Although the use of a rough metallic coating induces some inherent limitations, such as a lower resolution, the architectural advantages and simplicity of the approach offer additional opportunities, such as multiplexing and self-referencing, which are not possible otherwise with a single fiber SPR sensor. A way to overcome the lower resolution that involves the use of microstructured optical fibers, as well as a new perspective on a complementary application, such as Metal Enhanced Fluorescence, which greatly benefits from SPR scattering, will be presented.
Surface Plasmon Resonance has been one of the corner stone of label free biosensing for decades with a wide range of architectures, including fiber based SPR. Here we present the work we have achieved, using SPR scattering as an alternative approach for fiber based sensors, using rough metallic coating enabling to turn an intrinsically non radiative process into a radiative one. Although the use of rough metallic coating induces some inherent limitations, the architectural advantages and higher efficiency in some application such as Metal Enhanced Fluorescence as well as ways forward to overcome these limitation will be presented.
Metal Enhanced Fluorescence (MEF) takes advantage of the coupling between surface plasmons, in either a metallic thin film or metallic nanoparticles, and fluorophores located in proximity of the metal, yielding an increase of the fluorophore emission. While MEF has been widely studied on metallic nanoparticles with the emphasis on creating brighter fluorescent labels, planar surfaces have not benefitted from the same attention. Here we investigate the influence of the surface roughness of a thin metallic film on the fluorescence enhancement. 50nm thick silver films were deposited on glass slides using either thermal evaporation with different evaporation currents or an electroless plating method based on the Tollens reaction to vary the surface roughness. Multiple layers of positively and negatively charged polyelectrolytes were deposited on top of the metallic coating to map out the enhancement factor as function of the gap between the metallic coating and fluorophore molecules covalently bound to the last polyelectrolyte layer. We show that fluorescence is enhanced by the presence of the metallic film, and in particular that the enhancement increases by a factor 3 to 40 for roughness ranging from 3 nm to 8 nm. Although these enhancement factors are modest compared to the enhancement produced by complex metallic nanoparticles or nano-patterned metallic thin films, the thin films used here are capable of supporting a plasmonic wave and offer the possibility of combining different techniques, such as surface plasmon resonance (with its higher refractive index sensitivity compared to localized plasmons) and MEF within a single device.
Surface Plasmon Resonance (SPR) scattering offers significant advantages compared to traditional reflectivity measure- ments, essentially turning a non-radiative process into a radiative one. Recently, we have shown that SPR scattering can be used in an optical fiber, enabling higher signal to noise ratio, reduced dependence on the metallic thickness as well as the unique capability of multiplexed detection with a single fiber. Here we report a novel SPR scattering based sensor fabricated based on an exposed-core silica Microstructured Optical Fiber (MOF). This MOF presents a structure with a relatively small core (Ø = 10µm), exposed along the whole fiber length. This exposed core MOF allows for fabrication of SPR supporting metallic thin films directly onto the fiber core offering the new prospect of exploiting SPR in a waveguide structure that supports only a relatively small number of guided optical modes, with a structure that offers ease of fabri- cation and handling. A thin silver film of 50 nm thickness was deposited onto the fiber core by thermal evaporation. The significant surface roughness of the prepared metallic coatings facilitates strong scattering of the light wave coupled into the surface plasmon. Performance characteristics of the new exposed core fiber sensor were compared to those of a large bare core silica fiber (Ø = 140µm). Although sensitivity of both sensors was comparable (around 2500nm/RIU ), full width at half maximum (FWHM) of the SPR peaks for the new exposed core fiber sensor decreased by a factor of 3 offering an significant enhancement in the detection limit of the new sensing platform in addition to the prospect of a sensor with a lower detection volume.