Loaded Surface Plasmon Polariton Waveguides Research Articles

Monolithically integrated mid-infrared sensor with a millimeter-scale sensing range.

On-chip sensors based on quantum cascade laser technology are attracting broad attention because of their extreme compactness and abundant absorption fingerprints in the mid-infrared wavelength range. Recent continuous wave operation microcavity quantum cascade lasers are well suited for high-density optoelectronic integration because their volumes are small and thresholds are low. In this experimental work, we demonstrate a monolithically integrated sensor comprising a notched elliptical resonator as transmitter, a quantum cascade detector as receiver, and a surface plasmon structure as light-sensing waveguide. The sensor structure is designed to exploit the highly unidirectional lasing properties of the notched elliptical resonator to increase the optical absorption path length. Combined with the evanescent nature of the dielectric loaded surface plasmon polariton waveguides, the structure also ensures a strong light-matter interactions. The sensing transmission distance obtained is approximately 1.16 mm, which is about one order of magnitude improvement over the traditional Fabry-Perot waveguide. This sensor opens new opportunities for long-range and high-sensitivity on-chip gas sensing and spectroscopy.

Observation of the Wannier-Stark ladder in plasmonic waveguide arrays.

Evanescently coupled waveguides are a powerful platform to study and visualize the wave dynamics in tight-binding systems. Here, we investigate the propagation of surface plasmon polaritons in arrays of dielectric loaded surface plasmon polariton waveguides with a propagation constant gradient acting as an effective external potential. Using leakage radiation microscopy, we observe in real-space for single site excitation a periodic breathing of the wave packet and an oscillatory motion in the case of Gaussian excitation of multiple waveguides. The corresponding momentum-resolved spectra are composed of sets of equally spaced modes. We interpret these observations as the plasmonic analogs of Bloch oscillations and the Wannier-Stark ladder, respectively.

Radiation Leakage Images For Two Different Dielectric-Loaded Surface Plasmon Polariton Waveguides

We have studied about leakage radiation images obtained for two different dielectric-loaded surface plasmon polariton waveguides based on routing structures; linear couplers and bent waveguides. By simultaneously imaging the conjugated aperture and field planes of the microscope, we unambiguously quantify the degeneracy lift occurring for strongly interacting dielectric loaded surface plasmon polariton waveguides and visualize the symmetry of the coupled modes. We have obtained the wave vector distribution and showed its evolution with the bend radius. We have developed a numerical and an analytical analysis for momentum distribution. We have found that for large radii i.e. for vanishing bending loss, we can link the plasmon in Fourier space with the geometrical and modal properties of the bend structure. It was also found that the radial dependence of the wave vector distribution is governed by the phase difference. The obtained results were found in good agreement with previously obtained results.

Electrically pumped dielectric loaded surface plasmon waveguides

Several schemes for the electrical pumping of dielectric loaded surface plasmon polariton waveguides are analysed. Two schemes that are designed to move the electrical contact away from the plasmon mode are compared to a Schottky contact scheme which has the electrical contact at the same metal/semiconductor interface which supports the surface plasmon mode. One scheme involves transporting carriers from lateral contacts via a thin semiconductor pathway. The other scheme involves burying the electrical contact inside the metal surface and having the surface plasmon mode skip over the break in the metal/semiconductor interface. The Schottky contact scheme is shown to have the best confinement of the surface plasmon mode on the gain medium. However, the other two alternative schemes can be engineered to require significantly less gain to overcome metal losses. Current densities required in the non Schottky contact schemes are found to be compatible with current semiconductor laser electrical contacts.

Transverse Anderson localization of surface plasmon polaritons.

We investigate the effect of disorder on the propagation of surface plasmon polaritons in arrays of evanescently coupled dielectric loaded surface plasmon polariton waveguides. Diagonal disorder is implemented by randomly varying the heights of the waveguides. Real-space as well as momentum-space images of the surface plasmon polariton intensity distribution in the waveguide arrays are recorded by leakage radiation microscopy. In real space, increasing disorder results in a transverse localization of surface plasmon polaritons. In the momentum distribution, we observe for the first time a disorder-induced transition from a continuous band to a set of discrete modes.

Highly Sensitive Biochemical Sensor Based on Two-Layer Dielectric Loaded Plasmonic Microring Resonator

In this paper, we propose and design a highly sensitive optical biochemical sensor based on two-layer dielectric loaded surface plasmon polariton waveguide (TDLSPPW)-based microring resonator (MRR). By optimizing the structure parameters, the propagation length of the proposed waveguide is ~126 μm, which is about 3 times of that of the polymer dielectric loaded surface plasmon polariton waveguide (DLSPPW) reported. It is demonstrated that the TDLSPPW-based MRR is operated at the under-coupling state, along with the quality factor (Q) of 541.2 and extinction ratio (ER) of 12.2 dB. Moreover, the Q and ER are much more sensitive to the structure parameters of the waveguide, including the waveguide width w, total thickness t, and coupling gap Wgap, compared to the low refractive index (RI) layer thickness t2. The simulation results on the biochemical RI sensing show that the sensitivities of 408.7 and 276.4 nm/RIU for glucose concentration in urine and chemical gases can be achieved, respectively. It is believed that the proposed sensor has potential applications in photonic-integrated biochemical sensing.

Ultra-large nonlinear parameter in graphene-silicon waveguide structures.

Mono-layer graphene integrated with optical waveguides is studied for the purpose of maximizing E-field interaction with the graphene layer, for the generation of ultra-large nonlinear parameters. It is shown that the common approach used to minimize the waveguide effective modal area does not accurately predict the configuration with the maximum nonlinear parameter. Both photonic and plasmonic waveguide configurations and graphene integration techniques realizable with today's fabrication tools are studied. Importantly, nonlinear parameters exceeding 10(4) W(-1)/m, two orders of magnitude larger than that in silicon on insulator waveguides without graphene, are obtained for the quasi-TE mode in silicon waveguides incorporating mono-layer graphene in the evanescent part of the optical field. Dielectric loaded surface plasmon polariton waveguides incorporating mono-layer graphene are observed to generate nonlinear parameters as large as 10(5) W(-1)/m, three orders of magnitude larger than that in silicon on insulator waveguides without graphene. The ultra-large nonlinear parameters make such waveguides promising platforms for nonlinear integrated optics at ultra-low powers, and for previously unobserved nonlinear optical effects to be studied in a waveguide platform.

Grating Couplers for Fiber-to-Fiber Characterizations of Stand-Alone Dielectric Loaded Surface Plasmon Waveguide Components

Dielectric loaded gratings (DLGs) comprised of polymer gratings lying on a thin gold film are used to couple light at telecommunication frequencies in and out of plasmonic waveguides featuring sub-micron cross-sections. The grating couplers are found to be efficient and easy to implement to perform direct fiber-to-fiber telecommunication characterizations of dielectric loaded surface plasmon polariton waveguide (DLSPPW) components. By analyzing the dispersion of the plasmonic Bloch modes supported by DLGs as a function of the period and the filling factor of the gratings, efficient couplers comprised of gratings with a filling factor around 0.5 are designed and fabricated by a simple one-step electron beam lithography process. Typical losses in the range of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${-}10$</tex></formula> dB per coupler are obtained for gratings designed to operate at normal and 30 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{\circ}$</tex></formula> -tilted incidence. The performance of the couplers for normal incidence can be further improved by adding a back-reflecting Bragg mirror. We demonstrate the transmission of a 10 Gbits/s signal along a 75 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\mu$</tex> </formula> m-long DLSPPW by using DLG couplers for light injection and extraction. A power penalty below below 0.4 dB on the bit-error-rate has been measured over the entire C-band demonstrating the suitability of DLSPPWs for Wavelength-Division-Multiplexed high bit rate traffic and the efficiency of DLG couplers for fiber-to-fiber characterizations of stand alone DLSPPW components.

Thermo-optic plasmo-photonic mode interference switches based on dielectric loaded waveguides

We demonstrate an efficient thermo-optic dielectric loaded surface plasmon polariton waveguide (DLSPPW) 2 × 2 switch using a high thermo-optic coefficient polymer and a dual mode interference configuration. Unlike previous configurations relying on single-mode waveguide circuitry, the switch we consider is based on the interference between a plasmonic and a low-damping photonic mode of the DLSPPW, thus leading to the minimization of insertion losses of the device. Switching extinction ratios of 7 dB are measured for a compact 119 μm-long device. The overall device performances are in good agreement with numerical simulations performed using the beam propagation method.

Liquid crystal-based dielectric loaded surface plasmon polariton optical switches

An optical switch based on liquid crystal dielectric loaded surface plasmon polariton waveguides is proposed and theoretically analyzed. The infiltration of the plasmonic structure with a nematic liquid crystalline material serving as the dielectric loading is shown to allow for extensive electrical tuning of its waveguiding characteristics. Both the electrical switching and optical properties of the proposed waveguide are investigated in the context of designing a directional coupler optical switch, which is found to combine efficient voltage control, low power consumption, high extinction ratio, and relatively low insertion losses.

Resonant coupling in dielectric loaded plasmonic waveguides

Light propagation in dielectric loaded surface plasmon polariton waveguide (DLSPPW) resonant coupling devices operating at visible frequencies was experimentally investigated. The transmission characteristics of these devices were studied by leakage radiation microscopy. We show that a strong coupling between DLSPPWs can be achieved with nanoscale gaps. We demonstrate the operation of compact DLSPPW linear couplers and 3 dB power splitters. The performances of micro-DLSPPW racetrack resonators and signal drop filter are also discussed.

Plasmonic waveguide as an efficient transducer for high-density data storage

A design of high optical throughput nanoscale light sources has been proposed based on plasmonic wedge waveguides. It provides localization of the 1500 nm wavelength light at the output of less than 30×30 nm2 area at about 80% coupling efficiency from a dielectric loaded surface plasmon polariton waveguide and nearly 90% efficient power deposition in the absorbing media placed at the output for an experimentally viable 10 nm apex radius of the wedge. Such nanoscale light sources can be useful for high-density data storage, scanning near-field optical microscopy, and sensing.

Bound modes analysis of symmetric dielectric loaded surface plasmon-polariton waveguides

A symmetric dielectric loaded surface plasmon polariton waveguide is proposed and numerically analyzed. The characteristics of the symmetric and asymmetric bound modes, including the effective mode indices, propagation lengths, mode sizes and mode shapes at telecom wavelength 1.55 microm are investigated in detail. The simulation results show that the sub-wavelength confinement (about1.45 microm ) and a long propagation (about 820 microm ) can be realized. Although the mode sizes are a bit larger than that of the dielectric loaded surface plasmon polariton waveguide, an order longer propagation length can be achieved. The proposed symmetric dielectric loaded surface plasmon polariton waveguide provides a potential for low loss and high density photonic integration.

Differential method for modeling dielectric-loaded surface plasmon polariton waveguides

This paper demonstrates the efficiency of the differential method, a conventional grating theory, to investigate dielectric loaded surface plasmon polariton waveguides (DLSPPWs), known to be a potential solution for optical interconnects. The method is used to obtain the mode effective indices (both real and imaginary parts) and the mode profiles. The results obtained with the differential method are found to be in good agreement with those provided by the effective index method or finite elements. The versatility of the differential method is demonstrated by considering complex configurations such as trapezoidal waveguides or DLSPPWs lying on a finite width metal stripe.