Slot waveguide ring resonators coated by an atomic layer deposited organic/inorganic nanolaminate.

In this study, slot waveguide ring resonators patterned on a silicon-on-insulator (SOI) wafer and coated with an atomic layer deposited nanolaminate consisting of alternating layers of tantalum pentoxide and polyimide were fabricated and characterized. To the best of our knowledge, this is the first demonstration of atomic layer deposition (ALD) of organic materials in waveguiding applications. In our nanolaminate ring resonators, the optical power is not only confined in the narrow central air slot but also in several parallel sub-10 nm wide vertical polyimide slots. This indicates that the mode profiles in the silicon slot waveguide can be accurately tuned by the ALD method. Our results show that ALD of organic and inorganic materials can be combined with conventional silicon waveguide fabrication techniques to create slot waveguide ring resonators with varying mode profiles. This can potentially open new possibilities for various photonic applications, such as optical sensing and all-optical signal processing.

Towards broad-bandwidth polarization-independent nanostrip waveguide ring resonators.

We demonstrate a new method for accessing the broad-bandwidth polarization-independent operation of a microring resonator based on the standard photonic nanostrip waveguides. The method employs the selective application of atomic layer deposition to form highly uniform TiO(2) overlayers with the specific dispersion properties. The wide operation window is achieved by matching the wavelength dependencies of the free spectral ranges of the two orthogonal polarizations.

Towards athermal organic-inorganic guided mode resonance filters.

We demonstrate guided-mode resonance filters featuring an amorphous TiO(2) layer fabricated by atomic layer deposition on a polymeric substrate. The thermal properties of such filters are studied in detail by taking into account both thermal expansion of the structure and thermo-optic coefficients of the materials. We show both theoretically and experimentally that these two effects partially compensate for each other, leading to nearly athermal devices. The wavelength shift of the resonance reflectance peak (< 1 nm) is a small fraction of the peak width (~11 nm) up to temperatures exceeding the room temperature by tens of degrees centigrade.

Low-loss silicon slot waveguides and couplers fabricated with optical lithography and atomic layer deposition.

We demonstrate low-loss silicon slot waveguides patterned with 248 nm deep-UV lithography and filled with atomic layer deposited aluminum oxide. Propagation losses less than 5 dB/cm are achieved with the waveguides. The devices are fabricated using low-temperature CMOS compatible processes. We also demonstrate simple, compact and efficient strip-to-slot waveguide couplers. With a coupler as short as 10 µm, coupling loss is less than 0.15 dB. The low-index and low-nonlinearity filling material allows nonlinearities nearly two orders of magnitude smaller than in silicon waveguides. Therefore, these waveguides are a good candidate for linear photonic devices on the silicon platform, and for distortion-free signal transmission channels between different parts of a silicon all-optical chip. The low-nonlinearity slot waveguides and robust couplers also facilitate a 50-fold local change of the waveguide nonlinearity within the chip by a simple mask design.

Reduced propagation loss in silicon strip and slot waveguides coated by atomic layer deposition.

When silicon strip and slot waveguides are coated with a 50 nm amorphous titanium dioxide (TiO2) film, measured losses at a wavelength of 1.55 µm can be as low as (2 ± 1)dB/cm and (7 ± 2)dB/cm, respectively. We use atomic layer deposition (ALD), estimate the effect of ALD growth on the surface roughness, and discuss the effect on the scattering losses. Because the gap between the rails of a slot waveguide narrows by the TiO2 deposition, the effective slot width can be back-end controlled. This is useful for precise adjustment if the slot is to be filled with, e. g., a nonlinear organic material or with a sensitizer for sensors applications.

Atomic layer deposited titanium dioxide and its application in resonant waveguide grating.

We demonstrate good optical quality TiO(2) thin films grown by atomic layer deposition at 120 degrees C. The optical properties were studied using spectroscopic ellipsometry and prism coupling methods. The refractive index was 2.27, and the slab waveguide propagation loss was less than 1dB/cm at 1.53microm. A high quality resonant waveguide grating was fabricated using a thin TiO(2) layer on top of a SiO(2) grating.

Angled sidewalls in silicon slot waveguides: conformal filling and mode properties.

Effect of angled sidewalls on the filling and properties of silicon slot waveguides is discussed. We demonstrate complete filling of slot waveguide structures with oxide material systems using the atomic layer deposition technique and discuss use of various slot filling materials. Properties of the optical modes in angled-sidewall slot waveguides are studied. Enhanced vertical confinement is obtained with certain waveguide parameters. The reduced effective mode area enhances e.g. nonlinear effects in the waveguide. We discuss the use of atomic layer deposition in realization of filled slot waveguides optimized for all-optical functionalities.

Model for waveguide fabrication in glass by two-step ion exchange with ionic masking.

A theory for optical waveguide fabrication processes, in which potassium ions exchanged into glass are used as a mask to regulate a subsequent silver-ion exchange, is presented. The model is used to examine the use of this technique in restricting the width of narrow-channel waveguides. The diffusion of silver through the potassium-ion mask is calculated, and a novel method of fabricating buried waveguides is described.

Feasibility of potassium-exchanged waveguides in BK7 glass for telecommunication devices.

Based on recent results for potassium-exchanged optical waveguides in BK7 glass [Appl. Opt. 34, 455-458 (1995)], the feasibility of fiber-compatible waveguide fabrication for telecommunication wavelengths is studied. Modeling of waveguides gives the result that such waveguides with good properties cannot be achieved with this fabrication technique because of the observed saturation of diffusion depth.

Inverse ion-exchange method for glass waveguide fabrication.

A new method, inverse ion exchange, is proposed and demonstrated for the fabrication of single-mode channel waveguides. In this method the channel waveguide is formed by backdiffusion of the refractive-index-increasing ions from an ion-exchanged planar waveguide. Finite-difference methods are used to model the fabrication technique and to calculate the field of the fundamental mode of the waveguide. It is also proved experimentally that single-mode waveguides can be fabricated with the the reinverse ion-exchange method using a 10-microm mask stripe width.

Double-ion-exchange process in glass for the fabrication of computer-generated waveguide holograms.

We experimentally optimize double-ion-exchange process parameters to achieve a designed phase modulation for a wave front passing through a computer-generated waveguide hologram and numerically analyze the effects of fabrication errors. We also demonstrate a gradient-thickness waveguide hologram for ? beam splitting.

Birefringence control for ion-exchanged channel glass waveguides.

We show that at 1.55-mum wavelength the waveguide birefringence of ion-exchanged channel waveguides in glass can be broadly tuned by a potassium and silver double-ion exchange. Two different potassium and silver double-ion-exchange processes are used to make surface waveguides with negligible waveguide birefringence. This process is crucially important in the manufacture of devices for dense wavelength-division multiplexing systems. The dependence of the waveguide birefringence on the channel width is also reported.

Waveguide coupler for potassium- and silver-ion-exchanged waveguides in glass.

A waveguide coupler for integrating potassium- and silver-ion-exchanged glass waveguides in a single device is proposed and demonstrated. The measured insertion loss is 1.2 dB.

Glass integrated optics circuit for 1.48/1.55- and 1.30/1.55-µm-wavelength division multiplexing and 1/8 splitting.

We demonstrate the integration, in a single glass substrate, of a 1.48/1.55-µm-wavelength multiplexer and a 1.30/1.55-µm-wavelength multiplexer followed by a 1/8 splitter by using potassium- and silver-double-ion-exchange processes. The wavelength multiplexers are based on nonsymmetric three-port Mach-Zehnder interferometers, and symmetrical Y junctions are used for achromatic splitting. The facet-to-facet excess loss in both the 1.48/1.55-µm multiplexer and in the integrated 1.30/1.55-µ m multiplexer and 1/8 splitter is less than 2.7 dB. The device can be used, in connection with an erbium-doped fiber, in future wavelength division multiplexing subscriber networks in which amplification is needed in the 1.55-µm-wavelength region.

Examination of two-step fabrication methods for single-mode fiber compatible ion-exchanged glass waveguides.

A computer model was used to study important two-step ion-exchange processes for fabrication of singlemode optical waveguides with fiberlike mode field distributions. As a first process step, a field-assisted method was calculated to have a better controllability than a diffusion method. As a second process step, field-assisted burial was found to optimize the coupling loss to fiber to 0.05 dB, but losses lower than 0.2 dB were calculated also for less complex diffusion process steps. On the basis of modeling, a solid state fabrication process was proposed, and the near field distributions of fabricated waveguides were measured to confirm the model.

Binary-phase zone-plate arrays based on hybrid solgel glass.

An organically modified silane zirconate-based solgel material is used for the fabrication of binary-phase zone-plate arrays. The synthesized hybrid solgel material has a negative tone under UV exposure and can be patterned by a UV-lithography process. The transmittance of the material is nearly 100%, and the refractive index is 1.52. Two different diffractive lens arrays with focal lengths of 5 and 42 cm have been fabricated. The average roughness of the zone surface is less than 20 nm. The diffraction efficiencies of the lens arrays are measured as a function of modulation depth and exposure dose. A diffraction efficiency of 30% is achieved.

Ion-exchanged Mach-Zehnder interferometers in glass.

Ion-exchanged Mach-Zehnder interferometers are produced in glass. The effect of fabrication parameters on their optical response in relation to their constituent components is investigated.

Buried ion-exchanged glass waveguides: burial-depth dependence on waveguide width.

A detailed theoretical and experimental study of the depth dependence of buried ion-exchanged waveguides on waveguide width is reported. Modeling, which includes the effect of nonhomogeneous time-dependent electric field distribution, agrees well with our experiments showing that burial depth increases linearly with waveguide width. These results may be used in the proper design of integrated optical circuits that need waveguides of different widths at different sections, such as arrayed waveguide gratings.