Ag Waveguide Research Articles

Keeping Good Sensing Performance of Metal–Dielectric–Metal Waveguides After Coating Treatment

Good sensing performance is observed in metal–dielectric–metal (MDM) waveguides in recent research. However, Ag will be oxidized in air. The oxidization layer makes the sensing performance not as high as before. Plating an SiO2 film on the surface of the Ag waveguide not only can avoid oxidization but can keep good sensing performance through our numerical discussion as well. The decaying rate of electric field E at the interface and inside is also defined to illustrate the phenomenon mentioned above. We hope our findings will provide guidance for the integrated plasmonic devices.

Mode properties in metallic and non-metallic plasmonic waveguides.

Non-metallic plasmonic materials have recently attracted research interest due to their adjustable plasmonic material properties and the potential low loss, which is important to plasmonic waveguides with ultrahigh mode confinement. In this paper, we analyzed the mode properties of four types of plasmonic waveguides based on noble metals, aluminum-zinc-oxide (AZO), and TiN, where the propagation length and mode size are chosen to compare the figures of merit. It is found that AZO has the smallest imaginary part of permittivity in the near-infrared region, while AZO waveguides have propagation lengths comparable to those of Cu waveguides but shorter than those of Au and Ag waveguides. Furthermore, due to the larger real part of permittivities, the mode sizes of the AZO and TiN waveguides are smaller than those of the metal waveguides, in particular, for the insulator-metal-insulator waveguide and dielectric-loaded plasmonic waveguide. AZO/ZnO films with tunable carrier density between 1.8×1017/cm3 and 8.6×1020/cm3 were grown by pulsed-laser deposition. Metal-like properties, i.e., negative real part of permittivity around 1550nm, were observed, predicting an interesting candidate in the plasmonic optical interconnect.

High-extinction-ratio and low-insertion-loss Plasmonic Filter with Coherent Coupled Nano-cavity Array in a MIM Waveguide

In this paper, a novel plasmonic filter with very high extinction ratio and low insertion loss is proposed based on the coherent coupled nano-cavity array in a metal–insulator–metal (MIM) waveguide. The coherent coupling interactions among nano-cavities are investigated with an analytical model which is derived based on the temporal coupled-mode theory and transfer-matrix method. The destructive interference of the surface plasmon polaritons coupled from the nano-cavities at the resonant wavelength is achieved by suitably designing the period of the cavity array, which may be used for increasing the extinction ratio of the filter based on the nano-cavity array in the MIM waveguide. A plasmonic filter with an extinction ratio higher than 60 dB and an insertion loss less than 1.0 dB is obtained by applying the destructive interference in the design of a six-rectangular-cavity array in an Ag–air–Ag waveguide. And the correctness of the design for the filter is verified by the results obtained with the finite-difference time-domain simulation technique. This work may provide useful schemes and approaches for realization of various wavelength-sensitive devices in plasmonic integrated circuits.

Interference of the surface plasmon polaritons with an Ag waveguide probed by dual-probe scanning near-field optical microscopy

The propagation of surface plasmon polaritons (SPPs) on Ag waveguides with two different widths is directly observed using dual-probe scanning near-field optical microscopy (DSNOM). We find that the waveguide structure strongly affects the propagation of locally excited SPPs. SPPs in a flat plane structure spread radially, whereas SPPs in a 3.4-μm wide waveguide structure form two-dimensional interference fringes due to the multiple reflections at the side edges. The experimental results agree well with finite-difference time-domain calculations. The results suggest that the DSNOM technique can visualize the nanoscale characteristics of the SPP waves in various plasmonic waveguides.

Optimizing the design of planar heterostructures for plasmonic waveguiding

We theoretically investigate planar heterostructures for subwavelength guiding of surface plasmon modes and optimize their design to enhance the waveguiding efficiency. We show that by appropriately selecting the thicknesses of metallic and dielectric layers of a two-layer waveguide, one can compensate the intrinsic damping of the mode by having minimal optical gain in the dielectric region. We also reveal that mode confinement can be significantly improved by the use of an additional metal layer adjacent to the dielectric, to form a metal–dielectric–metal (MDM) structure. By varying the layer thicknesses in the MDM waveguide, we demonstrate that the propagation length of the plasmonic mode can be maximized. We further show that the losses may be suppressed by minimal gain in the dielectric region by the careful choice of geometrical parameters. We note that the associated gain levels are relatively small; for example, the losses in a 300 nm thick Ag–ZnO–Ag waveguide can be compensated by a gain of ∼225 cm−1. Our results may prove useful for the realization of efficient optical interconnects in high-density nanophotonic circuity.

Enhanced Nonlinear Optical Effects with a Tapered Plasmonic Waveguide

Infrared surface plasmon polaritons (SPPs) are concentrated in a laterally tapered planar Ag waveguide. The near field of SPPs excited with 1490 nm light at a Ag-sapphire interface is probed using the photoluminescence of upconverted Er ions at 550 and 660 nm. SPP interference patterns are observed that exhibit clear evidence of SPP concentration toward the taper end. The concentration leads to an enhancement of the upconversion luminescence intensity from Er energy levels that are populated by multiphoton processes.

Characterization of long-range surface-plasmon-polariton waveguides

Measurements of the attenuation and excitation efficiency of the long-range surface-plasmon-polariton mode supported by waveguides comprised of one or many thin metal films of finite width embedded in dielectric were made in the near infrared (λ0=1550nm). Au films 31, 25, and 20 nm thick, and Ag films 20 nm thick were used to implement the structures. The lowest attenuations measured among the Au and Ag waveguides are 0.42 and 0.32dB∕mm, respectively, corresponding to propagation lengths of 10 340, and 13572μm, respectively. These propagation lengths are longer than those of the single-interface surface-plasmon polariton in the corresponding semi-infinite structures by factors of 93 and 138, respectively. These factors are the largest reported to date for long-range surface-plasmon-polariton waves. The largest excitation efficiency measured among the set of Au structures is 98%. Theoretical results were obtained for all of the structures characterized experimentally using an accurate electromagnetic-field model. Theory and experiment agree to within about 5% over the 31- and 25-nm-thick Au structures, but a thickness-dependant permittivity must be assumed in order to achieve agreement to within 12% for the 20-nm Au structures.

Low-loss metallic hollow waveguides coated with durable and nontoxic ZnS

ZnS-coated Ag hollow waveguides are newly proposed and fabricated to realize a durable and nontoxic waveguide for CO2 laser light transmission. The fabrication method is based on rf-sputtering and electroplating techniques and a polyimide tube is used as a hollow mandrel. As a result of measurements, low-loss property of the ZnS-coated waveguide is shown and the beam profile with a sharp energy peak is obtained. The result of the aging test proves good durability of the ZnS-coated Ag waveguide.

Fabrication of low-loss zinc-selenide coated silver hollow waveguides for CO2 laser light

ZnSe coated Ag hollow waveguides transmitting CO2 laser light were developed. An inner ZnSe coating of good quality was obtained with high rf power and high translating speed in deposition by rf sputtering. The inner ZnSe layer was found to be amorphous by x-ray diffraction analysis; A layer structure (ZnSe-Ag) was observed by Auger electron spectroscopy analysis. Transmission properties of the short waveguides with 25 cm length were evaluated by measurements of loss spectra in the mid-IR region. As a result, ZnSe coated Ag waveguides showed lower loss than the Ge coated one fabricated previously, and the loss for CO2 laser light was predicted to be 0.021 dB/m. Furthermore, it was found that a ZnSe coated Ag waveguide is durable in practical use.

Investigation of a Bragg modulator with an apodized electrode structure based on LiTaO3:Ag waveguides

An investigation was made of an electrooptic Bragg modulator based on an LiTaO3:Ag waveguide with a variable period with an apodized longitudinal structure of the electrodes. A calculation of an integral representing the overlap of the mode and electrode fields was used to determine how the length of the zone of interaction between light and a grating varied with the waveguide and electrode parameters. A prototype modulator was constructed: its control voltage was 7.2 V, the maximum depth of modulation was 97%, and the focal length was 13 mm.

Optical damage resistance of monovalent ion diffused LiNbO3 and LiTaO3 waveguides

We report measurements of the zero field photorefractive sensitivity (optical damage) of waveguides fabricated by silver ion exchange in both LiNbO3 and LiTaO3 and of LiNbO3 :Ti guides diffused in the presence of H20. Marked differences in the photorefractive sensitivity are found for the different fabrication proceseses. In particular, LiNbO3 :Ti guides diffused in the presence of H20 were significantly less susceptible to optical damage than those diffused in a dry atmosphere, and no index changes were observed in LiTaO3 :Ag waveguides for exposures up to 105 J/cm2 at 4579 Å.