Second-order distributed-feedback surface plasmon resonator for single-mode fiber end-facet biosensing

Surface plasmon resonance (SPR) devices on single-mode optical fiber (SMF) end facets are desired for label-free biosensing, due to flexible light delivery, in vivo inspection capability, and seamless integration with fiber-optic communication techniques. We report a plasmonic crystal cavity structure that has a steep resonance near the plasmonic bandedge, a fabrication process to efficiently transfer and align the structure onto a bare SMF end facet, and characterization of its sensing performance. With a sensitivity of 571 nm RIU−1, a figure of merit of 68 RIU−1 and a real-time refractive index detection limit of 3.5 × 10−6 RIU, our sensors can be readily applied in common SPR biosensing experiments. They are over an order of magnitude more sensitive than reported modified-end multimode fiber SPR devices, while there are no reports on previous SMF end facet devices' detection limits which have very low figures of merit.

Numerical investigation of finite thickness metal-insulator-metal structure for waveguide-based surface plasmon resonance biosensing

A new fabrication method for a surface plasmon resonance (SPR) device with a gradual SPR shift—namely, using a nanostructure self-assembled by using a mixed block copolymer as a template—was developed. By this method, it was demonstrated that the diameter of a self-assembled nanohole can be controlled by changing the film thickness of a mixed block copolymer. It was also demonstrated that SPR wavelength shift can be controlled according to the nanohole structure (with diameter controlled according to film thickness). An actual SPR device with a gradually shifted SPR wavelength was fabricated, and it was confirmed that this SPR device can detect refractive-index change in its surroundings. This device has the potential to expand the application of SPR devices.

All-optical control of Surface Plasmon Polaritons (SPPs) can switch light with high speed and a large signal to noise ratio. We demonstrate 25 ps-time scale switching of continuous wave light by pump pulses copropagating in the same single mode fiber at different wavelengths near 1550 nm. The switching is due to hot carriers from the SPPs in a 45 nm-thin gold coating on the fiber cladding. The SPPs are generated by pump pulses coupled from the core to cladding modes by a tilted fiber Bragg grating (TFBG). Hot carriers modify the complex permittivity of the metal coating on a time scale of the order of picoseconds and hence the cladding mode resonance wavelengths of the TFBG. A probe light signal copropagating in the same fiber can therefore be modulated by the transmission resonance shifts. With 25 ps pulses at 1540.4 nm and 1 MHz and 50 mW average power, the modulation depth of a CW probe at 1543.4 nm copropagating in the core reached 4.5% ± 1% with a pulse width broadened to 56 ps. Under these conditions, the pump power density was 0.147 GW/cm2 in the metal layer, for a conversion efficiency as high as 30% ± 7% per GW/cm2. Since many other plasmonic and nonlinear active materials can be deposited on fiber claddings, we believe that this very simple all-fiber configuration to perform all-optical switching of core-guided light in single mode fibers by plasmon-modulated resonances has strong potential applications in studies of light-matter interactions over fast and ultrafast time scales.

Imprinted solution-processible gold nanoparticle (AuNP) grating films were fabricated for use as a grating-coupled surface plasmon resonance (SPR) excitation substrate. The imprinted AuNP grating pattern, which consists of a 1.72 μm grating pitch, was fabricated on flat glass substrates by imprinting AuNP on silicon grating templates. In this study, the SPR measurements were carried out on an SPR device in the grating-coupling configuration with a He–Ne laser ( λ = 632.8 nm) as the excitation source, and multimode surface plasmon excitations were observed upon irradiation with white light. SPR excitation of our substrate was observed at the incident angle of 47.1°. For SPR measurements using white light irradiation, multimode surface plasmon excitation resulting from several diffraction orders was observed in the wavelength region of 500–850 nm. The surface plasmon dispersion branches were calculated to obtain the diffraction order in this region. SPR excitation of the imprinted AuNP grating substrate was further studied by fabrication of a layer-by-layer ultrathin film of iron containing bis(terpyridine) polymer (Fe(II)-BTP) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). A shift of the SPR excitation spectrum was observed when the ultrathin film was deposited on the imprinted AuNP grating surface. Thus, this substrate should be a useful SPR substrate in a variety of applications such as photoelectric conversions and sensors.

We present a high-power ridge waveguide distributed feedback (DFB) laser with a high-reflective coating and a phase shift section at the rear facet. The phase shift section is realized by means of a micro heater that is placed parallel to the ridge waveguide and the uniform grating. This type of heater section is easy to integrate into existing laser designs and allows adjusting and controlling the spectral behavior of the distributed feedback laser by shifting the rear facet phase condition, which makes it possible to overcome the challenges of mode-hop-free tuning of regular DFB lasers with highly reflective cleaved rear facet. Accordingly, we use the device to quantify rear facet phase conditions where mode hops occur, which are compared to theory with good agreement.

The ability to distinguish between specific and nonspecific binding is important for assessing the interactions between protein receptors and ligands. Surface plasmon resonance (SPR) spectroscopy is an advanced tool to measure binding events, yet the ability to distinguish between specific and nonspecific binding remains a limitation. To address this problem, we use SPR spectroscopy correlated with surface enhanced Raman scattering (SERS). The chemical information present in SERS spectra provides insight into the molecular interactions between functionalized nanoparticles and proteins, which are not detectable by SPR alone. Using a custom instrument with the Kretschmann configuration, we successfully demonstrate simultaneous affinity and the chemical characterization of streptavidin-functionalized gold nanoparticles (STV-NPs) binding to biotin immobilized on a gold film in both air and flowing phosphate buffered saline (PBS). The SPR performance is consistent with that of previous reports. The association constant (KA) for streptavidin/biotin and STV-NPs/biotin interactions observed (2 ± 1 × 107 M-1 and 2.4 ± 0.3 × 1010 M-1, respectively) agree with literature values and show a strong avidity effect associated with the STV-NPs. The SERS scattering from STV-NPs is excited by the surface plasmon polariton and collected from an objective lens mounted over the fluidic channel. The SERS spectra are recorded simultaneously with the SPR sensorgram, and the detected Raman bands provide chemical insight into the binding event. Multivariate curve resolution analysis of the spectra can differentiate specific from nonspecific binding. This label-free, real time, and surface sensitive detection method provides chemical information to protein/ligand binding affinity measurements.

Micro-Lab on Tip: High-Performance Dual-Channel Surface Plasmon Resonance Sensor Integrated on Fiber-Optic End Facet

A novel optical fiber hydrogen sensor based on Surface Plasmon Resonance (SPR) is proposed and experimentally validated. It is composed of a multimode fiber–single-mode fiber–multimode fiber (MMF-SMF-MMF) hetero-core structure coated with Ag/PDMS/Pt-WO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub>. Due to the PDMS's significant thermal refractive index (RI) response and the SPR device's extremely high RI sensitivity, when the proposed hydrogen sensor is exposed to hydrogen, the exothermic reaction between Pt-WO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> and hydrogen causes a considerable resonance wavelength shift in the sensor's transmission spectrum. As a result, detecting the shift in the SPR resonance wavelength yields a simple and low-cost hydrogen sensor. Experimental results reveal that the sensor has an excellent linear response to the hydrogen concentration within the range of 0 to 1.8% (vol%) and an ultra-high sensitivity of up to -52.12 nm/% (vol%) which is far greater than most previously reported hydrogen sensor. Moreover, the proposed sensor exhibits a short response time of ∼21 s and recovery time of ∼15 s.

Plasmonics have been identified as an ideal platform for ultra-sensitive, label-free biosensors mainly due to the high field confinement on a metal-dielectric interface and the resulting strong light-matter interaction offered by surface plasmon resonances (SPRs) that can be entirely exposed to test analytes. Well-established SPR-based biosensors exploiting propagating SPRs yield superior specifications regarding bulk sensitivity compared to localized counterparts leading to already commercial available sensor devices. However, most of these systems require bulky prism-based configurations to couple light into the Surface Plasmon Polariton (SPP) mode impeding system miniaturization. In addition, SPR-based sensors suffer from intrinsic high propagation losses restricting the potential for multiple on-chip functionalities. In this context, co-integration of plasmonics with a low-loss photonic platform emerges as a viable solution towards highly sensitive, low-loss and small footprint optical sensors. In this work, we present an ultra-compact, interferometric plasmonic sensor co-integrated on a TiO2 photonic waveguide platform. The device consists of two access TiO2 photonic waveguides separated by a gold-based metal stripe which is located on top of an appropriately shorter TiO2 waveguide layer. Two metal/insulator interfaces are formed at the top (sensing arm) and bottom surfaces (reference arm) of the metal able to support SPP modes which upon excitation through the input photonic waveguide propagate along the two metal surfaces and interfere at the output waveguide realizing a single-arm Mach-Zehnder Interferometer. After optimization of the device in aqueous environment, we achieved sensitivity values as high as 2430 nm/RIU at near-infrared spectrum region for a 65 um long plasmonic stripe.

Surface plasmon resonance (SPR) reflectance imaging: Far-field recognition of near-field phenomena

A surface plasmon resonance cavity on an optical fiber end-facet is designed and demonstrated for ultrasound detection. A noise equivalent pressure of 25 KPa over 20 MHz, almost omni-directional response and stable performance are reported.

High Resolution Surface Plasmon Microscopy: From Nano-colloids To Single Nucleosome Imaging

The fiber surface plasmon resonance (SPR) sensor is widely used in high-sensitivity refractive index detection, and there are few reports on SPR sensors used for strain measurement. In this paper, we propose and demonstrate an S-type fiber strain sensor based on SPR. The simulation and testing results indicate that the smaller the vertical axis offset of S-type fiber is, the larger the incidence angle of SPR is, and the closer the working band of SPR is to the shorter wavelength direction. By electrofusion, we fabricated an S-type structure on the single-mode fiber, and by the S-type structure, the high-order cladding mode was excited. A 50 nm gold film was coated on the surface of the fiber cladding behind the S-type structure. The evanescent field of the cladding mode contacted the gold film to produce SPR, and the strain can change the vertical axis offset of the S-type fiber and further change the incidence angle of SPR; hence an S-type fiber strain sensor based on SPR was realized. When the refractive index of the ambient medium is 1.345 RIU, the vertical axis offset and length of the S-shaped structure are 87 and 501 µm, respectively, the resonance wavelength of the fiber SPR strain sensor changes from 648.06 to 631.77 nm with a strain detection range of 0-1200µε, and its sensitivity is -14.38pm/µε. The proposed sensor provides a new solution for the strain measurement of the fiber SPR sensor, which is expected to be used in the fields of engineering, health monitoring, and early warning.

We report high slope efficiency and low noise characteristics in a distributed feedback (DFB) laser lasing at 1.3 /spl mu/m with narrow beam divergence by employment of a laterally tapered active stripe over the whole cavity. This tapered structure is designed to realize narrow beam divergence, low threshold current, and high longitudinal mode selectivity. The fabricated tapered-active-stripe DFB lasers demonstrated of 9.20/spl times/13.40 and a record slope efficiency, for a narrow beam DFB laser, of 0.59 mW/mA. The temperature characteristics from -10/spl deg/C to 85/spl deg/C shows high output power at high temperature, stable single longitudinal mode oscillation and stable far-field patterns. Furthermore, for the first time ever, a low relative intensity noise characteristic of under -155 dB/Hz has been realized when butt-coupling into a single-mode fiber.