Reduction Of Propagation Loss Research Articles

Loss Reduction Mechanism for Coupled Cavity Waveguides in One-Dimensional Photonic Crystals

This paper presents a loss reduction mechanism for coupled cavity waveguides (CCWs) relying on 1-D photonic crystals microcavities. The mechanism is based on structural modification in the vicinity of the cavity defects. With appropriate modifications, the tangential wavenumber components of the leaky guided modes, which can couple to cladding modes, can be decreased, resulting in the reduction of propagation losses due to diffraction. We numerically demonstrate the usefulness of this mechanism through the design of low loss CCWs. The diffraction losses in the CCWs, where air holes adjacent to the defects are changed in size, decrease dramatically compared with CCWs with air holes of constant size. This loss reduction mechanism can be applied even to the CCWs with an increased number of intercavity air holes, while the group velocity can be further decreased.

Enhanced stitching for the fabrication of photonic structures by electron beam lithography

Large-area electron beam lithography tools pattern substrates as a series of writing fields that are stitched together. Pattern defects, termed stitching errors, can arise at field boundaries and these can have detrimental effects on device performance. These problems are exaggerated by substrate tilt. In this article, the authors demonstrate the application of a substrate tilt correction procedure to minimize stitching errors in the fabrication of photonic structures by electron beam lithography. The authors show that the magnitude of stitching errors is dependent on the position within the field boundary and is influenced by substrate tilt. Application of tilt correction procedures is shown to reduce stitching errors and give rise to a corresponding reduction in propagation losses in photonic wire waveguides. The authors show that the results of measured propagation losses arising from stitching errors are in good agreement with numerical results.

Fabrication and Measurement of AlN Cladding AlN/GaN Multiple-Quantum-Well Waveguide for All-Optical Switching Devices Using Intersubband Transition

We measured intersubband (ISB) absorption in high-mesa waveguides consisting of AlN cladding layers and AlN/GaN multiple quantum wells (MQW). Inductively coupled plasma (ICP) dry etching for waveguide fabrication was optimized to reduce propagation loss by achieving vertical and smooth sidewalls. We changed the ICP/RF power and introduced intervals during the etching process in order to overcome the induction time of the etching rate and the instability of plasma observed from long etching experiments. The ISB absorption greater than 20 dB was clearly observed at around 1.5 µm. The insertion loss of an 800-µm-long waveguide was 5–10 dB including the coupling loss between a fiber and the end of the waveguide. With this low-loss waveguide, we observed a saturation of 10 dB in the ISB absorption with 100 pJ probe light introduced to the waveguide. We thus demonstrated the possibility of achieving all-optical switching devices with low loss using the ISB transition of AlN-based materials.

Integrated electro‐optic Mach–Zehnder modulator fabricated by vapour Zn‐diffusion in LiNbO3

AbstractA novel integrated Mach–Zehnder modulator fabricated on Z‐cut lithium niobate wafers is presented. The optical waveguides were fabricated by the Zn‐diffusion method, which allows monomode TM propagation at the wavelength of interests by choosing the channel waveguide width. The TM‐mode is shown to be buried beneath the surface, which avoids the need of using a dielectric buffer to reduce propagation losses induced by the metallic electrodes to perform electro‐optic modulation. A figure of merit of 9.2 V cm has been obtained for the switching voltage‐interaction length product, which is slightly higher than the calculated theoretical value using the overlap between the externally applied electrical field and the propagating optical field. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49:1194–1196, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22376

Low-loss high-index-contrast planar waveguides with graded-index cladding layers

We experimentally demonstrate, for the first time, propagation loss reduction via graded-index (GRIN) cladding layers in high-index-contrast (HIC) glass waveguides. We show that scattering loss arising from sidewall roughness can be significantly reduced without compromising the high-index-contrast condition, by inserting thin GRIN cladding layers with refractive indices intermediate between the core and topmost cover of a strip waveguide. Loss as low as 1.5 dB/cm is achieved in small core (1.6 mum x 0.35 mum), high-index-contrast (Deltan = 1.37) arsenic-based sulfide strip waveguides. This GRIN cladding design is generally applicable to HIC waveguide systems such as Si/SiO2.

Single-mode optical waveguides fabricated in LiNbO 3 by multienergy C 2+ implantations

Single-mode waveguides in LiNbO 3 are demonstrated by use of prism coupling method. The waveguides are fabricated by three different energies and single energy C 2+ implantations at the equal total doses, respectively. Dark modes and propagation loss are measured by use of prism coupling and moving fiber methods, respectively. Damages produced by implantation are measured by RBS/channeling technique. The waveguide structures are investigated in two different implantation cases. The results of analysis indicate that the heavy ion-implanted waveguides are still defined by synergetic characteristics from both the raised-index region and the low-index barrier. The broadened barrier from multienergy implantation is demonstrated to play a significant role in reducing propagation loss.

Surface acoustic wave device and electronic component comprising it

In a surface acoustic wave device, a common portion and a strip portion of a reflector electrode are partially cut off to increase a space between the electrodes. The increase of the space between the electrodes reduces the influence of the amount of charges and the influence of an unbalance between the amounts of charges in etching of a metallic film, thereby preventing the electrodes from having a curved shape in section. Consequently, the surface acoustic wave device has a reduced propagation loss.

Self-guiding of infrared and visible light in photonic crystal slabs

We experimentally demonstrate diffractionless guidance and efficient routing of light in two-dimensional photonic crystal slabs at infrared and visible wavelengths. Our particular design allows for simultaneous guidance of TE and TM polarized light beams at the same wavelength. Routing performance and possibilities of propagation loss reduction are investigated experimentally. Experimental results are in excellent agreement with three-dimensional simulations.

Fabrication and optical properties of lead silicate glass holey fibers

We report on recent progress in lead silicate holey fibers for non-linear device applications. Improvements in the fabrication have resulted in core diameters as small as 1.7μm, increased air-suspension of the core and reduced propagation loss of 2.6dB/m. This small core fiber exhibits a record non-linearity of 640W−1km−1.

Reduction of Propagation Loss to 0.1 dB/mm: Flat-Core Channel Waveguides Consisting of Periodic Structures

We successfully fabricated channel waveguides utilizing photonic crystal (PhC) dispersion having a very low loss of /spl sim/0.1 dB/mm by the autocloning method. We achieved the loss reduction by improving the fabrication condition and adjusting the core width. The result of propagation loss can be regarded as a milestone, and it enables us to realize practical PhC circuits that contain functional components such as chromatic dispersion equalizers and high Q wavelength filters.

Waveguide Shaping and Writing in Fused Silica Using a Femtosecond Laser

Fused silica waveguides were written and reshaped with an 800-mn amplified femtosecond laser in a lateral writing configuration. The asymmetry of the waveguide shape and the index profile was partially corrected through multiple scans shifted by 1 or 2 /spl mu/m. Following the careful adjustment of both laser pulse energy and writing speed, the resulting waveguides exhibited substantial reduction in propagation and coupling losses by more than 50% in the C-band.

Propagation loss reduction of photonic crystal slab waveguides by microspheres

Dielectric microspheres are theoretically studied to reduce the propagation loss of Si-based photonic crystal slab waveguides. Two-dimensional photonic crystal formed by etched air hole can act as a template for microsphere sedimentation. The analytical results show that the transmission of the photonic crystal slab waveguides with microspheres can be enhanced to be around twice that without microspheres.

Reduction of propagation and bending losses of heterostructured photonic crystal waveguides by use of a high-delta structure.

We describe the fabrication and evaluation of a low-loss, high-delta optical waveguide consisting of heterostructured photonic crystals. The waveguide is composed of a multilayer stack of Ta2O5/SiO2 and is prepared by use of the autocloning technique. Light is guided in the waveguide by the difference in the effective refractive indices of the constituent photonic crystals. By improving the design of the core region so that is has a flat multilayer structure, we achieve delta = 3.09% for the in-plane direction and net propagation loss of 0.56 dB/mm at lambda = 1.6 microm. Experiments also suggest that the bending loss of the waveguide can be reduced to less than 0.1 dB if the curvature radius is larger than 700 microm.

Characteristics of intermixed InGaAs/InGaAsP Multi-Quantum-Well Structure

The intermixing of a InGaAs/InGaAsP multi-quantum-well (MQW) structure induced by SiO2 dielectric cap layer deposition and heat treatment was investigated. Photoluminescence experiments reveal a large blue shift of the effective bandgap for the intermixed quantum well. By secondary ion mass spectroscopy, the group III and V elements of a MQW are found to interdiffuse at a similar rate after the intermixing process. An optical waveguide was fabricated using intermixed material where a propagation loss reduction of 450 dB was recorded at a wavelength close to the original bandgap wavelength.

Effect of SiOx buffer layer on propagation loss in LiNbO3 channel waveguides

SiO x buffer layer is widely employed in metal-clad Z-cut LiNbO3 optical waveguides to prevent excessive propagation loss and disturbances induced by the direct loading of the metal on the guiding layer. The dependence of propagation loss in proton-exchange LiNbO3 channel waveguides induced by a SiOx buffer layer on the annealing time is studied using a nondestructive measurement method. These studies reveal that the propagation loss is degraded for annealing times of less than 3 h, while it can be improved by about 0.08 dB/cm for annealing times longer than 6 h. By extending the annealing time to 8 h, we demonstrate a propagation loss reduction of 0.09 dB/cm. The physical mechanisms, including surface roughness, refractive index changes, oxidation of the SiOx buffer layer, optical confinement, and surface scattering of the LiNbO3 channel waveguide are also investigated.

A significant reduction of propagation losses in InGaAsP-InP buried-stripe waveguides by hydrogenation

We show here that the high propagation losses often measured at /spl sim/1.56 μm in InGaAsP-InP buried-ridge stripe waveguides can be significantly brought down by implementing hydrogenation (exposure to deuterium plasma) as the last step to device termination. For example, losses as high as /spl sim/30 dB/cm measured in conventional as-processed structures have dropped down after hydrogenation to typically 4-5 dB/cm. This improved loss value is totally compatible for the realization of passive sections in photonic circuits. We further present preliminary data describing the good thermal stability of these propagation losses in post-hydrogenated structures.

Silicon-on-silicon rib waveguides with a high-confining ion-implanted lower cladding

The realization of single-mode rib waveguides in standard epitaxial silicon layer on lightly doped silicon substrate, using ion implantation to form the lower cladding, is reported. The implanted buffer layer enhances' the vertical confinement and improves the propagation characteristics. Respect to similar standard all-silicon waveguides a propagation loss reduction of about 7 dB/cm, in the single-mode regime, has been measured. A numerical analysis has been performed to evaluate the theoretical attenuation and the transverse optical field profiles. As a result of the presence of the ion implanted buffer layer, an increase of the fundamental mode confinement factor from 0.3 to 0.85 has been calculated. This results in a great enhancement of the coupling efficiency with standard single-mode optical fibers. Moreover, the proposed technique is low cost, fully compatible with standard VLSI processes, and allows a great flexibility in the integration of guided-wave devices and electronic circuits. Finally, the very high thermal conductivity characterizing these waveguides makes them attractive host-structures for electrically and thermally controlled active optical devices.

Evaluation of the properties of hydrogenated InP/InGaAsP double heterostructure waveguides

The potentiality of H passivation in InP-based photonic device technology was investigated by evaluating the properties of hydrogenated InP (Zn)/InGaAsP double heterostructure (DHS) waveguide (WG) samples. Subsequent to plasma exposure, conventional photoluminescence (PL) measurements were employed to monitor the optical quality, and Fabry-Perot damping oscillation measurements at ~ 1.55μm to evaluate the propagation losses. We report here that hydrogenation significantly improves the optical quality of DHS samples and further brings about an efficient (90%) neutralization of Zn acceptors in the upper p-InP confinement layer, and to a lesser extent, also of those that are involuntarily introduced into the nominally undoped InGaAsP quaternary (Q) guiding layer. These two features are shown to be profitable in photon device technology as they can be engineered to reduce propagation losses (due to free-carrier absorption) in the DHS buried WG structures.

Magnetostatic wave soliton in nonuniformly magnetized YIG film

In this paper, experiments on the Magnetostatic Forward Volume Wave (MSFVW) solitons in a nonuniformly magnetized YIG film are reported. It is observed that compared to solitons in uniformly magnetized YIG films, solitons of narrower durations that show stronger nonlinearity with input power can be excited in nonuniformly magnetized film. Two explanations of the above mentioned behavior are given that are based on the numerical simulation of solitons satisfying nonlinear Schrodinger equation (NLSE). One reason is the reduction in propagation loss in the YIG film due to nonuniform magnetization. The other reason may be the adiabatic excitation of soliton due to the varying dispersion along the length of the film.

ＣＯ２レーザーアニールによるＺｎＯ薄膜光導波路の伝搬損失低減

ＣＯ２レーザーアニールによるＺｎＯ薄膜光導波路の伝搬損失低減