Pair Of Waveguides Research Articles

Surface Loading Sensitivity Characterization of a Resonant Planar Optical Waveguide Stack

Detuning of a coupled planar waveguide pair through surface loading of the top waveguide that is in contact with the analyte serves as a transducer for a Stacked Planar Affinity-Regulated Resonant Optical Waveguide (SPARROW) sensor. Here we investigate the surface loading detection sensitivity of a SPARROW transducer composed of a stack of two planar alumina waveguides grown using ion beam assisted e-beam deposition. Using a sucrose analyte solution introduced to the stack surface in a poly-di-methyl-siloxane (PDMS) microfluidic channel, the change in optical output power through the coupled waveguide pair as a function of sucrose analyte solution concentration was experimentally determined. Based on the analyte in the evanescent field penetration depth volume, the effective minimum detectable surface loading of the stack was determined to be 20 with a bulk index sensitivity of 5.6 refractive index units (RIU) for this stack configuration and experimental setup.

Design and fabrication of center frequency and bandwidth tunable HTS filter

We have developed a bandwidth and a center frequency tuning method for use in high-temperature superconducting microstrip filters. A pair of waveguide is placed between the resonators, and the bandwidth is adjusted by changing the switch states of the waveguides. Additional electrical pads are placed open ends of the resonators for tuning the center frequency. Pads are also placed around the input/output coupled-line elements to enable the external quality factors to be adjusted, thereby reducing the insertion loss caused by tuning. A prototype three-pole tunable bandpass filter was fabricated by depositing YBa2Cu3O7 thin film on an MgO substrate and has a measured center frequency of 4.83GHz and bandwidth of 121MHz. Use of the waveguides to adjust the coupling coefficients, the electrical pads to adjust the effective lengths of the resonators and the pads to adjust the external quality factors resulted in 120-MHz bandwidth tuning and 400-MHz center frequency tuning without increased insertion loss.

Wave scattering on a domain wall in a chain ofPT-symmetric couplers

We study wave propagation in linear arrays composed of pairs of conjugate waveguides with balanced gain and loss, i.e. arrays of the PT-symmetric couplers, where the linear spectrum is known to feature high-frequency and low-frequency branches. We introduce a domain wall by switching the gain and loss in a half of the array, and analyze the scattering of linear waves on this defect. The analysis reveals two major effects: amplification of both reflected and transmitted waves, and excitation of the reflected and transmitted low-frequency and high-frequency waves by the incident high-frequency and low-frequency waves, respectively.

Power transfer between neighboring planar waveguides

The ability to control light over very small distances is a problem of fundamental importance for a vast range of applications in communications, nanophotonics, and quantum information technologies. For this purpose, several methods have been proposed and demonstrated to confine and guide light, for example in dielectric and surface plasmon polariton (SPP) waveguides. Here, we study the interaction between different kinds of planar waveguides, which produces dramatic changes in the dispersion relation of the waveguide pair and even leads to mode suppression at small separations. This interaction also produces a transfer of power between the waveguides, which depends on the gap and propagation distances, thus providing a mechanism for optical signal transfer. We analytically study the properties of this interaction and the power transfer in different structures of interest including plasmonic and particle-array waveguides, for which we propose an experimental realization of these ideas.

2x2 Optical Switch Based on Silicon-on-Insulator Microring Resonator

In near future, silicon-on-insulator (SOI) microring resonator are expected to be basic components for wavelength filtering and switching due to their compact size and wide free spectral range (FSR). In this paper, a 2X2 optical switch by using active microring resonator is proposed. The switch is consists of second order serially cascaded microring coupled to a pair of waveguide. The ON/OFF state of the design is control by electric signal which will vary the refractive index. The device is design to operate at 1.55µm wavelength. With a 500nm x 200nm rib dimensions, the design is proven to have single mode behaviour. Finite-Difference Time-Domain (FDTD) method simulation by RSOFT software is use to characterize the device performance. The results show that the 2X2 optical switch proposed can be an efficient device to be functioning in WDM application.

Detection and location of partial discharge in cast-resin dry-type transformers using a waveguide and a new acoustic emission sensor pair design

The acoustic emission (AE) method could be used to detect and locate partial discharges (PD) in cast-resin dry-type transformers. However, due to the high sound attenuation in the filled epoxy, the signal is prone to interference from external noises and thus, in practice, there is little possibility of detecting PD. In this study, two techniques were developed to alleviate the shortcomings of the AE method. First, a waveguide is installed on the high-voltage (HV) windings, so that the acoustic signals of PD will propagate to the AE sensors that are installed on both terminals of the waveguide. The location of the winding that has PD can then be detected from the difference in arrival time of the acoustic signals. Test results indicate that the waveguide technique is able to enhance the safety of a measurement system and offers the advantages of easy installation and higher flexibility. Second, a specially designed AE sensor pair is used to distinguish whether acoustic signals are generated by PD inside the HV winding or by the corona outside the transformers. Using these two techniques of waveguide and AE sensor pair not only greatly improves sensitivity but also increases the reliability of the measurement system. Practical test results show that the new techniques can be used to locate precisely the PD in HV windings.

Localization of electromagnetic energy by a pair of parallel waveguides with contradirectional coupling

The contradirectional coupling between a pair of planar dielectric waveguides, whose guiding layers are respectively a negative index medium and a positive index medium (PIM, i.e., the conventional medium), is theoretically investigated using the coupled mode theory. It is shown that, by tapering the middle segment of the PIM guiding layer to introduce a certain phase shift, the energy flow circulation can be established based on the contradirectional coupling effect, and, thus, the electromagnetic energy is localized in the waveguide system. This phenomenon is further verified numerically with the finite-difference time domain method. The quality factor of this open waveguide cavity is also discussed.

Manipulation of subwavelength optical fields and resonant field enhancements of a silver-shell nanocylinder pair and chain waveguides with different core–shell patterns

Near field optical properties and surface plasmon resonances on a pair of silver-shell nanocylinder and nanochain waveguides with different core–shell patterns which interact with incident plane wave along chain axis are numerically investigated by using the finite element method. Simulation results show that the peak wavelengths and resonant field enhancements are highly tunable by using the nanoshell particles instead of solid ones, revealing a critical relationship among the wavelengths and illuminated direction of incident light, interparticle spacing, radii, and medium of dielectric holes and the patterns of chain waveguides. Besides, nanochain waveguides with different patterns of core–shell that are operated on resonant multipolar modes can provide higher propagation intensities and the transmission ability can be increased by decreasing the size of nanocylinders along the chain axis.

Three-Dimensional Negative Index of Refraction at Optical Frequencies by Coupling Plasmonic Waveguides

We identify a route towards achieving a negative index of refraction at optical frequencies based on coupling between plasmonic waveguides that support backwards waves. We show how modal symmetry can be exploited in metal-dielectric waveguide pairs to achieve negative refraction of both phase and energy. Control of waveguide coupling yields a metamaterial consisting of a one-dimensional multilayer stack that exhibits an isotropic index of -1 at a free-space wavelength of 400nm. The concepts developed here may inspire new low-loss metamaterial designs operating close to the metal plasma frequency.

Resonant mode coupling of optical resonances in stacked nanostructures

We propose a method to obtain the resonance frequencies of coupled optical modes for a stack of two periodically corrugated slabs. The method is based on the modes in each slab, which are derived by the Fourier modal method in combination with the optical scattering matrix theory. We then use the resonant mode approximation of the scattering matrices to develop a linear eigenvalue problem with dimensions equal to the number of resonant modes. Its solutions are the resonance frequencies of the coupled system and exhibit a good agreement with exact solutions. We demonstrate the capabilities of this method for pairs of planar waveguides and gratings of one-dimensional wires.

Open waveguide cavity using a negative index medium

An open waveguide cavity formed by a pair of planar waveguides, in which one guiding layer is a negative index medium and the other is a positive index medium, is theoretically demonstrated. For such a waveguide cavity the resonant frequency is independent of the total length of the waveguide system. With the coupled mode theory it is shown that energy flow circulation can be established through the special coupling between the waveguides at the resonant frequency, and thus the wave fields are localized. This phenomenon is further verified numerically with the finite-difference time-domain method. The quality factor of the open waveguide cavity is also discussed.

Longitudinal character of atom-chip-based rf-dressed potentials

We experimentally investigate the properties of radio-frequency-dressed potentials for Bose-Einstein condensates on atom chips. The three-dimensional potential forms a connected pair of parallel waveguides. We show that rf-dressed potentials are robust against the effect of small magnetic-field variations on the trap potential. Long-lived dipole oscillations of condensates induced in the rf-dressed potentials can be tuned to a remarkably low damping rate. We study a beam-splitter for Bose-Einstein condensates and show that a propagating condensate can be dynamically split in two vertically separated parts and guided along two paths. The effect of gravity on the potential can be tuned and compensated for using a rf-field gradient.

Generation of ultrawideband pulses using a distributed fiber-link system

This work develops a simple distributed fiber-link system with a newly designed antenna to generate ultrawideband (UWB) pulses for indoor wireless communications. The proposed system comprises a gain-switched distributed feedback laser diode (DFB-LD), electro-absorption modulator (EAM), a photodetector and a pair of coplanar waveguide (CPW) antennas. This optical approach can tolerate pulse dispersion and prevent the generation of intersymbol interference (ISI), since the optical pulse width is easily adjustable, providing better radio communication, as determined by the generation of UWB signal. Furthermore, the simulated and experimental results demonstrate that the proposed system can generate high-quality UWB pulse signals for application to future indoor high-bit-rate wireless communications.

A novel 2 × 2 wavelength selective cross-connect based on Mach-Zehnder interferometer

A novel 2×2 wavelength selective cross-connect (WSXC) module, which is composed of a Bragg-grating-based Mach-Zehnder interferometer (MZI), a pair of optical waveguides, a pair of 1×2 optical switches (OSWs) and a pair of Y-model combiners is proposed. The mathematical description of the proposed 2×2 WSXC module is given and explained. Multi-channel multi-wavelength selective cross-connect can be fabricated with the proposed 2×2 WSXC module, together with multistage interconnection networks (MINs). A four-wavelength 4×4 WSXC is demonstrated by simulation to validate the flexibility of the proposed WSXC.

Spontaneous parametric down-conversion in periodically poled KTP waveguides and bulk crystals

We present a theoretical and experimental comparison of spontaneous parametric down-conversion in periodically poled waveguides and bulk KTP crystals. We measured a waveguide pair generation rate of 2.9.10(6) pairs/s per mWof pump in a 1-nm band: more than 50 times higher than the bulk crystal generation rate.

Waveguide-Based Off-Axis Holography with Hard X Rays

We present an off-axis holography experiment based on the coherent cone beams emitted from a pair of x-ray waveguides. A magnified off-axis hologram is recorded, from which the phase of the optical transmission function of a sample is obtained by digital holographic reconstruction. A spatial resolution of about 100 nm has been achieved at 10.4 keV photon energy. Spatial resolution is determined by the cross-sectional dimensions of the waveguide and could approach a fundamental limit of about 10 nm in future experiments. In addition, we propose a new experimental setup that might overcome this limitation.

Distant perturbation asymptotics in window-coupled waveguides. I. The nonthreshold case

We consider a pair of straight adjacent quantum waveguides of constant, and in general different widths. These waveguides are coupled laterally by a pair of windows in the common boundary, not necessarily of the same length, at a distance 2l. The Hamiltonian is the respective Dirichlet Laplacian. We analyze the asymptotic behavior of the discrete spectrum as the window distance tends to infinity for the generic case, i.e., for eigenvalues of the corresponding one-window problems separated from the threshold.

Discrete spectrum of an asymmetric pair of waveguides coupled through a window

In this paper one analyses the discrete spectrum of an asymmetric pair of two-dimensional quantum waveguides with common boundary in which a window of finite size is made. The phenomenon of new eigenvalues arising at the boundary of the essential spectrum as the length of the window passes over critical values is considered. For the newly arising eigenvalues one constructs asymptotic expansions with respect to the small parameter equal to the difference between the window length and the closest critical value. The behaviour of the spectrum under an unrestricted growth of the length of the window is also under investigation; asymptotic expansions for eigenvalues with respect to the large parameter, the length of the window, are constructed.

Building blocks for a polarimeter-on-a-chip

For the “Primordial Anisotropy Polarization Pathfinder Array (PAPPA)” balloon flight project, we have designed and made thin-film niobium microstrip circuits as building blocks for a “polarimeter-on-a-chip” in which superconducting transmission lines are used to couple millimeter wave signals from planar antennas to superconducting transition edge sensor (TES) detectors. Our goal is to demonstrate technology for precision measurements of the polarization of the cosmic microwave background. To enable characterization and verification of our microstrip components, we have incorporated waveguide probes on each chip that can bring millimeter wave signals from a room temperature vector network analyzer to the superconducting circuits on the chip and back again for S-parameter measurements. We have designed a planar antenna and RF choke on the probes to efficiently couple radiation between waveguide and thin-film microstrip. To support the probe antennas in waveguides, we sculpted thin silicon cantilevers that extend from an edge of each silicon chip into a pair of waveguides within a specially designed split-block mount. This technique will allow us to make calibrated measurements at low temperatures of the velocity, impedance, and loss properties of our niobium transmission lines, the frequency response of microstrip filters, hybrid couplers, or terminations, and the performance of integrated detectors.

Micro-encoder based on higher-order diffracted light interference

A micro-encoder based on higher-order diffracted light interference has been developed for use in high-precision positioning. It uses ±3-order diffracted beams to obtain interference fringes for displacement detection and provides six signal periods for moving the scale grating by one grating period (3.2 µm) without an interpolation electric circuit. This micro-encoder head includes a distributed feedback laser diode, edge-illuminated refracting-facet photodiodes, a pair of polyimide waveguides, each with a total internal reflection mirror, and a micro-grating that causes ±3-order beams, diffracted by the scale grating, to interfere coaxially. All of these components are on a micromachined Si optical bench (3 × 2 mm2).