Directional excitation of surface plasmon using multi-mode interference in an aperture.

Plasmonics is a promising technology that can find many applications in nanophotonics and biosensing. Local excitation of surface plasmons with high directionality is required for many of these applications. We demonstrate that by controlling the interference of light in a metal slot with the adjustment of the angle of incidence, it is possible to achieve highly directional surface plasmon excitation. Our numerical analysis of the structure showing a strong directionality of excited surface plasmon is confirmed by near field scanning measurements. The proposed structure can be useful for many applications including excitation of plasmonic waveguides, nanolithography, and optical sensing. To illustrate its usefulness, we experimentally demonstrate that it can be used for highly directional excitation of a dielectric loaded plasmonic waveguide. We also propose a simple structure for surface plasmon interference lithography capable of providing high image contrast using this scheme.

Hybrid plasmonic waveguide-based ultra-low insertion loss transverse electric-pass polarizer.

We have designed and experimentally demonstrated an integrated transverse electric (TE)-pass polarizer on silicon-on-insulator platform. The polarizer consists of an asymmetric coupling section where only the transverse magnetic (TM) mode is coupled to the cross-hybrid plasmonic waveguide and attenuated. The TE mode does not couple and passes through the polarizer. The polarizer was fabricated on the silicon-on-insulator platform. The device is 30 µm long, has a high extinction ratio of more than 28 dB over 150 nm bandwidth, and has a good fabrication tolerance. Most important, the proposed polarizer has an ultra-low insertion loss of less than 0.04 dB for the TE mode.

Polarization rotator based on augmented low-index-guiding waveguide on silicon nitride/silicon-on-insulator platform.

Using a newly proposed augmented low-index-guiding scheme with silicon nitride/silicon dual-core waveguide, we have designed, fabricated, and characterized a transverse electric (TE) to transverse magnetic (TM) and TM-to-TE compact polarization rotator. The polarization rotation is realized in an asymmetric directional coupler. The measured peak conversion efficiencies for the TE-to-TM and TM-to-TE rotations are approximately 97%. The measured polarization extinction ratio for the TE-to-TM rotation is greater than 20 dB over 50-nm bandwidth, while for the TM-to-TE rotation it is greater than 15 dB over the C-band.

Compact and broadband polarization beam splitter based on a silicon nitride augmented low-index guiding structure.

We propose a compact polarization beam splitter (PBS) based on a silicon nitride enhanced silicon-on-insulator platform using an augmented low-index guiding (ALIG) waveguide structure. In the ALIG structure, the TM mode is mostly confined in the low-index silicon nitride, while the TE mode is confined in the high-index silicon. Since the two modes are confined in two separate layers, their properties can be controlled independently. The PBS is formed using an asymmetric multimode interference (MMI) section. The TM mode is directed to an output port by the ALIG waveguide, while the TE mode is coupled to the other output port via the multimode interferometer. Such a PBS has a very small footprint, low insertion loss, high polarization extinction ratio, and broadband response.

Compact low loss and broadband hybrid plasmonic directional coupler.

We propose a novel broadband coupler for silicon photonics using a hybrid plasmonic waveguide section. The hybrid plasmonic waveguide is used to create an asymmetric section in the middle of a silicon nanowire waveguide coupler to introduce a phase delay to allow for a 3-dB power coupling ratio over a 150 nm bandwidth around 1.55 µm. The device is very compact (<8.5 µm) and has a low insertion loss (<0.15 dB).

Experimental demonstration of a hybrid plasmonic transverse electric pass polarizer for a silicon-on-insulator platform.

We experimentally demonstrate a transverse electric (TE)-pass polarizer using the recently proposed hybrid plasmonic waveguide. The device consists of a silicon film separated from a chromium layer by a silica spacer. The device was characterized using a tunable laser in the 1.52-1.58 µm wavelength range. For a 30 µm long polarizer, the extinction ratio in this wavelength range varies from 23 to 28 dB and the insertion loss for the TE mode is 2-3 dB. The device is compact; its fabrication is completely compatible with silicon-on-insulator technology, and its performance compares favorably against previously reported silicon-based integrated optic TE-pass polarizers.

Polarization-independent hybrid plasmonic coupler for a silicon on insulator platform.

Hybrid plasmonic waveguides consisting of a high-index slab separated from a metal plane by a low-index spacer provide an optimal compromise between the loss and confinement for surface plasmon waves in passive medium. In such hybrid structures, because power for the TE and TM modes are concentrated in two different regions of the guide, the characteristics of the two modes can be controlled independently by changing the waveguide dimensions. We propose to use this property to implement a hybrid plasmonic polarization-independent directional coupler for a silicon on insulator platform. We also investigate the effects of variations of wavelength and device dimensions on the performance of the proposed device.

Propagation characteristics of hybrid modes supported by metal-low-high index waveguides and bends.

Hybrid-mode waveguides consisting of a metal surface separated from a high index medium by a low index spacer have attracted much interest recently. Power is concentrated in the low index spacer region for this waveguide. Here we investigate the properties of the hybrid mode in detail and numerically demonstrate the possibility of realizing compact waveguide bends using this wave guiding scheme.

Surface plasmon polariton discrete diffraction compensation.

We report on the observation of discrete diffraction in surface plasmon polariton waveguide arrays at a wavelength of 1550 nm. We also adopt the effective index method to reduce our simulation geometry to two-dimensions, predict the spread of single-waveguide excitation in parallel waveguide arrays, and explore changing the excitation angle to detune the waveguides. Our experimental results show discrete diffraction compensation at an angle of 2.2 degrees as predicted by simulations.

Linear and quadratic dispersion characterization of millimeter-length fibers and waveguides using common-path interferometry.

We measured linear and quadratic dispersion on millimeter-length fibers, waveguides, and nanowires based on common-path spectral interferometry. We obtained the linear dispersion parameter, beta', with a relative precision of 1.45 x 10(-4), and extracted the quadratic dispersion parameter, beta'', from the Taylor expansion of beta' x beta'' values show a discrepancy of < 1% when compared with simulation as well as with measurement results obtained by a conventional Michelson interferometer. Using this method, we experimentally confirmed the sign inversion of the group velocity dispersion of AlGaAs nanowires for what is believed to be the first time.

Hamiltonian formulation of coupled-mode theory in waveguiding structures.

We present a Hamiltonian formulation of coupled mode theory for scenarios in which the coupled modes are associated with different "parent structures," such as two nearby waveguides. The relativistic nature of the photon leads to the complication that not any set of orthonormal modes can be used as a basis if the associated amplitudes are to satisfy canonical commutation relations. This difficulty is circumvented by the introduction of "dressed parent modes," which are in fact seen to be the "coupled modes" of the system. While an exact solution of the linear problem within the restricted basis of interest formally must be found before these modes can be constructed, in practice they can be constructed directly from the modes of the parent structures. The approach can be applied to periodic parent structures, such as photonic crystal waveguiding structures, as well as to simpler waveguides. We illustrate the accuracy of the various approximations employed by studying two sample systems in detail. We derive the linear coupled mode equations, and show how the approach can be immediately generalized from the linear regime to treat problems in nonlinear quantum optics.

Deep and shallow trap contributions to the ionic current in the thermal-electric field poling in soda-lime glasses.

In this paper, we investigate the contribution of deep and shallow trapped ions on the second-order nonlinearity during typical poling procedures in soda-lime glass. The zero-electric field potential barriers of each contribution were estimated. The shallow traps, measured through the electrical ionic current, was determined as ~0.34 eV; while deep trap activation energy, measured by means of the thermal/electric field activated luminescence, was estimated ~3.8 eV. The traps show different dependence on its thermal energy onset for different applied electric field. The ionic current is linearly dependent on the electric field. The luminescence has a minimum electric field ~3.6 kV/cm and thermal energy ~31 meV (~87 degrees C) to occur. The average ionic jump lengths for both processes are also estimated, and the deep trap length is about ten times shorter than the shallow trap one. Samples poled at the border of the luminescence onset parameters revealed that the higher its contributions the more stable the induced second order nonlinearity.

Gain assisted surface plasmon polariton in quantum wells structures.

In this paper we propose a structure to compensate the propagation loss of surface plasmons by using multiple quantum wells as a gain medium. We analyze the required gain for lossless surface plasmon propagation for different thicknesses and widths of the metallic guiding layer. We study the effects of the gain layers and a finite height superstrate on the surface plasmon mode and its propagation loss. It is shown that the gain required for lossless plasmon propagation is achievable with present technology.

Group velocity inversion in AlGaAs nanowires.

We investigated the dispersion characteristics of submicron sized AlGaAs waveguides. Numerical simulations shows that the tight confinement of the optical waves in such nanowires leads to strong variations of the dispersion characteristics compared to classic, weakly guided waveguides of the same material system. We found numerically that the investigated structure has negative GVD for the TE mode provided the waveguide width is between 670 nm and 280 nm. Experimental data obtained from 300 mum - 1 mm long wires confirms the numerical results.

Ultrafast deflection of spatial solitons in AlxGa(1-x)As slab waveguides.

We demonstrate ultrafast all-optical deflection of spatial solitons in an AlxGa(1-x)As slab waveguide, using 190 fs, 1550 nm pulses to generate and deflect the spatial soliton. The steering beam is focused onto the top of the waveguide near the soliton pathway, and the soliton is steered by refractive-index changes induced by optical Kerr, or free-carrier (Drude), effects. Angular deflections up to 8 mrad are observed.

Incoherent blocker soliton interactions in Kerr waveguide arrays.

We have observed the incoherent interaction between a highly confined (blocker) soliton and wide, moving signal beams of a different wavelength in a one-dimensional discrete Kerr medium. Digital switching of the blocker solitons to successive adjacent channels was measured with increasing signal power via both one and two cascaded interactions in an AlGaAs waveguide array, operations equivalent to a reconfigurable three-output router.

Beam interactions with a blocker soliton in one-dimensional arrays.

We investigate experimentally and numerically the interaction of a highly localized, single-channel discrete soliton (blocker) with a wide, tilted beam in a one-dimensional AlGaAs array. In agreement with theory the blocker is observed to discretely shift its position by multiple channels, depending on the intensity and relative phase of the tilted beam.

Near-field imaging of nonlinear pulse propagation in planar silica waveguides.

A simplified near-field scanning optical microscope is employed to image the propagation of short laser pulses in planar silica waveguides, in the anomalous dispersion regime, under varying conditions of input beam power and width. Our results show a complex evolution of the transverse intensity profiles of the beam when there is a pronounced difference between the input diffraction and dispersion lengths. Numerical simulations confirm that these complex spatial dynamics are intimately related to the temporal and spectral evolution of the pulse.

Nonlinear optical beam interactions in waveguide arrays.

We report our investigation of Kerr nonlinear beam interactions in discrete systems. The influence of power and the relative phase between two Gaussian shaped beams was investigated in detail by performing numerical simulations of the discrete nonlinear Schrödinger equation and comparing the results with experiments done in AlGaAs waveguide arrays. Good agreement between theory and experiment was obtained.

Experimental observation of discrete modulational instability.

We report the first experimental observation of modulation instability in a discrete optical nonlinear array.