'Hexagon-type' photonic crystal slabs based on SOI

In this paper we discuss the design of a novel category of photonic crystal slabs (PCS) and as an example, we consider structures based on SOI wafers. Fabrication issues related to lithographic accuracy are addressed, too. The geometry consists in a triangular lattice of hexagons having their symmetry axes rotated with respect to the lattice.We show that the mirror-symmetric 'hexagon-type' PCS with air claddings can have an absolute (i.e. polarization independent) gap in guided modes with normalized width of approximately 10%. This gap, although reduced to about 4%, is still present in an asymmetric geometry, when the under-cladding is a silicon oxide layer with deeply etched holes

Focused Ion Beam Nano-structuring for Applications in Photonics

To date, nano- and micro-structuring has commonly been implemented by a combination of specifically optimized processes of electron-beam lithography and reactive ion etching, thus limiting the range of materials that can be structured to only a few. In this talk we will introduce focused ion beam (FIB) milling as an emerging technology that enables fast, reliable and well-controlled nanometer-size feature definition. Since the method involves physical removal of material by a beam of ions, the technique can be adapted and optimized almost for any material system. We will introduce the technique and discuss the basic application areas. In particular, we have investigated the impact of parameters such as ion beam current, dwell time, scanning strategy, and dielectric charging. We will discuss strategies to optimize the nano-structuring processes that are strongly dependent on the geometry of the desired structure. Finally, we will report our recent results on utilization and optimization of the focused ion beam technique for fabrication of nano-structures in integrated photonic devices on several material platforms such as Si, Al2O3, Y2O3, Sc2O3, and KY(WO4)2

Permalloy thin-film magnetic sensors

An introduction to the theory of the anisotropic magnetoresistance effect in ferromagnetic thin films is given, ending in a treatment of the minimalization of the free energy which is the result of the intrinsic and extrinsic anisotropies of the thin-film structure. The anisotropic magnetoresistance effect in long strips is reviewed. Attention is given to problems like the formation of domains and measures like biasing and linearization. The paper concludes with a description of some applications which are being developed by the authors: (1) an analyser for the stray field of recording heads; (2) a sensitive magnetometer; (3) an accurate absolute angle detector; and (4) an absolute (linear) position detector

Narrow-Linewidth Distributed Feedback Channel Waveguide Laser in Al2_2O3_3:Er3+^{3+}

We report on the fabrication and characterization of a distributed feedback channel waveguide laser in erbium-doped aluminium oxide on a standard thermally oxidized silicon substrate. Holographically-written surface-relief Bragg gratings have been integrated with the aluminium oxide waveguides via reactive ion etching of a silicon dioxide overlay film. The laser operates at a wavelength of 1545.2 nm and exhibits a threshold of 2.2 mW absorbed pump power, while it produces a maximum output power of 3 mW. The emission is TE polarized and has a Lorentzian linewidth of 1.70±0.58 kHz, which corresponds to a Q-factor of 1.14×E11

Passband flattening and rejection band broadening of a periodic Mach-Zehnder wavelength filter by adding a tuned ring resonator

A thermo-optically tuneable periodic wavelength filter having a rectangular wavelength response with a 50 GHz free spectral range, based on a Mach-Zehnder interferometer with ring resonator has been fabricated in SiON waveguide technology

Far-field scattering microscopy applied to analysis of slow light, power enhancement, and delay times in uniform Bragg waveguide gratings

A novel method is presented for determining the group index, intensity enhancement and delay times for waveguide gratings, based on (Rayleigh) scattering observations. This far-field scattering microscopy (FScM) method is compared with the phase shift method and a method that uses the transmission spectrum to quantify the slow wave properties. We find a minimum group velocity of 0.04c and a maximum intensity enhancement of ~14.5 for a 1000-period grating and a maximum group delay of ~80 ps for a 2000-period grating. Furthermore, we show that the FScM method can be used for both displaying the intensity distribution of the Bloch resonances and for investigating out of plane losses. Finally, an application is discussed for the slow-wave grating as index sensor able to detect a minimum cladding index change of $10^{-8}$, assuming a transmission detection limit of $10^{-4}$

Grated waveguide-based optical cavities as compact sensors for sub-nanometre cantilever deflections, and small refractive-index changes

The paper reports on theoretical and experimental results of integrated optical (IO) cavities defined by grated waveguides in $Si_3N_4$ and Si, for the accurate detection of cantilever deflection and bulk index changes

Line-Defect Waveguides in Hexagon-Hole type Photonic Crystal Slabs: Design and Fabrication using Focused Ion Beam Technology

Photonic-crystal slabs (PCS) patterned with a 2D triangular-lattice having hexagonal holes rotated with respect to their symmetry axis can provide a larger bandgap than similar slabs with circular holes. A step forward towards integrated optical devices is introducing line ‘defects’ in PCS, the goal being the achievement of single-mode waveguiding over a frequency range as large as possible, inside the gap. We present the design for defect waveguides with reduced width and a novel fabrication technique, which is an integration of optical lithography with focused ion beam (FIB) high-resolution etching. This technique allows a good alignment between a line ‘defect’ and conventional ridge waveguides

High-Q distributed-Bragg-grating laser cavities

Applying Bragg gratings in Al2O3 channel waveguides, we demonstrate distributed Bragg reflectors with Q-factors of 1.02x10e6. An integrated Al2O3:Yb3+ waveguide laser with 67% slope efficiency and 47 mW output power is achieved with such cavities

Modal fields calculation using the finite difference beam propagation method

A method is described to construct modal fields for an arbitrary one- or two-dimensional refractive index structure. An arbitrary starting field is propagated along a complex axis using the slowly varying envelope approximation (SVEA). By choosing suitable values for the step-size, one mode is maximally increased in amplitude on propagating, until convergence has been obtained. For the calculation of the next mode, the mode just found is filtered out, and the procedure starts again. The method is tested for one-dimensional refractive index structures, both for nonabsorbing and for absorbing structures, and is shown to give fast convergenc