R. Dekker

Ultrafast nonlinear all-optical processes in silicon-on-insulator waveguides

In this review we present an overview of the progress made in recent years in the field of integrated silicon-on-insulator (SOI) waveguide photonics with a strong emphasis on third-order nonlinear optical processes. Although the focus is on simple waveguide structures the utilization of complex structures such as microring resonators and photonic crystal structures is briefly discussed as well. Several fabrication methods are explained and methods which improve optical loss, coupling efficiency and polarization dependence are presented. As the demand for bandwidth increases communication systems are forced to use higher bit rates to accommodate the load. A consequence of high-bit-rate systems is that they require short pulses where the importance of waveguide dispersion tailoring becomes increasingly important. The impact of short pulses on the efficiency of all-optical processes is discussed and recent accomplishments in this field are presented. Numerical results of femtosecond, picosecond and nanosecond pulse propagation in SOI waveguides are compared to provide an insight into the physical processes that dominate at these different time scales. In this work we focus on two-photon absorption (TPA), free-carrier absorption (FCA), plasma dispersion and the optical Kerr effect. After describing these nonlinear effects, some other important all-optical processes based on plasma dispersion and the Kerr effect are described, namely cross-absorption modulation (XAM), self-phase modulation (SPM), cross-phase modulation (XPM), four-wave mixing (FWM) and stimulated Raman scattering (SRS). The latter provides the best hope for practical and/or commercial applications and finds its use in amplification and lasing. Furthermore, we present some guidelines for efficient numerical modelling of propagation in SOI waveguides. This review is a good starting point for those who are new in this hot and rapidly emerging field and gives an overview of important considerations that need to be taken into account when designing, fabricating and characterizing SOI waveguides for ultrafast third-order nonlinear all-optical processing.

Ultrafast Kerr-induced all-optical wavelength conversion in silicon waveguides using 1.55 μm femtosecond pulses

The propagation of 300 femtosecond optical pulses in Silicon-on Insulator waveguides has been studied by means of a pump-probe set-up. The ultrafast pulses allowed the observation of large Kerr-induced red and blue shifts (9nm and 15nm, respectively) of the probe signal depending on the delay between pump (1554nm) and probe (1683nm) pulses. A numerical model taking into account the Kerr effect, Two Photon Absorption and Free Carrier Absorption is presented and provides good agreement with our experimental data and data in literature. A microring resonator based device is proposed that exploits the observed wavelength shift for sub-picosecond all-optical switching.

Stimulated emission and optical gain in LaF3:Nd nanoparticle-doped polymer-based waveguides

We report experiments which show evidence that stimulated emission at 863 nm takes place in hybrid monomode Si3N4 waveguides where LaF3 :Nd nanoparticle-doped polymethylmethacrylate (PMMA) was used as a top cladding material. Furthermore, optical gain at 1319 nm in LaF3:Nd nanoparticle dispersed PMMA s0.1 dB/cmd and photodefinable epoxy (Microchem SU-8) multimode waveguides has been observed at pump powers below 10 mW. This class of composite materials based on polymers with dispersed nanoparticles shows promising properties for planar optical amplifiers. Simulation showed that optical gain in the order of 10 dB can be achieved at 100 mW pump power in a 20 cm long monomode waveguide.

Fluorescence monitoring of microchip capillary electrophoresis separation with monolithically integrated waveguides

Using femtosecond laser writing, optical waveguides were monolithically integrated into a commercial microfluidic lab-on-a-chip device, with the waveguides intersecting a microfluidic channel. Continuous-wave laser excitation through these optical waveguides confines the excitation window to a width of 12 microm, enabling high-resolution monitoring of the passage of different types of fluorescent analytes when migrating and being separated in the microfluidic channel by microchip capillary electrophoresis. Furthermore, we demonstrate on-chip-integrated waveguide excitation and detection of a biologically relevant species, fluorescently labeled DNA molecules, during microchip capillary electrophoresis. Well-controlled plug formation as required for on-chip integrated capillary electrophoresis separation of DNA molecules, and the combination of waveguide excitation and a low limit of detection, will enable monitoring of extremely small quantities with high spatial resolution.

Large-scale integrated optics using TriPleX waveguide technology: from UV to IR

We present a new class of low-loss integrated optical waveguide structures as CMOS-compatible industrial standard for photonic integration on silicon or glass. A TriPleXTM waveguide is basically formed by a -preferably rectangular- silicon nitride (Si3N4) shell filled with and encapsulated by silicon dioxide (SiO2). The constituent materials are low-cost stoichiometric LPVCD end products which are very stable in time. Modal characteristics, birefringence, footprint size and insertion loss are controlled by design of the geometry. Several examples of new applications will be presented to demonstrate its high potential for large-scale integrated optical circuits for telecommunications, sensing and visible light applications.

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).

Stress-optic modulator in TriPleX platform using a piezoelectric lead zirconate titanate (PZT) thin film

We will demonstrate a stress-optic phase modulator in the passive SiN-based TriPleX platform using a layer of piezoelectric material. Regarding the stress-optic effect, the piezoelectric layer deposited on top of an optical waveguide is employed to control the phase of propagating light in the structure by applying an electrical field across the layer. In this work, it is demonstrated that the stress-optic effect lowers the power consumption by a factor of one million for quasi-DC operation and increases the modulation speed by three orders of magnitude, compared to currently used thermo-optic modulation in the TriPleX platform.

TriPleX waveguide platform: low-loss technology over a wide wavelength range

In this article a selection of highlights of the TriPleX™ technology of LioniX is given. The basic waveguide technology is explained with recent benchmark measurements done by University California Santa Barbara (UCSB) and University Twente (UT-TE). In order to show the low loss transparency over a wide wavelength range three examples of applications in different wavelength regimes are described in more detail. These are the Integrated Laser Beam Combiner (ILBC) of XiO Photonics in the visible light, a ringresonator sensing platform of LioniX around 850 nm and a phased array antenna with an Optical Beam Forming Network in the 1550 nm band. Furthermore it is shown that the technology is easily accessible via Multi Project Wafer Runs for which the infrastructure and design libraries are also set up.

Low-cost and low-loss multimode waveguides of photodefinable epoxy

To satisfy the urgent need for low-cost multimode planar waveguides, we developed photodefined, multimode-fiber compatible waveguides with low-cost commercially available epoxies showing low losses from 550 to 1100 nm and around 1300nm

Fabrication and characterization of high-quality uniform and apodized Si/sub 3/N/sub 4/ waveguide gratings using laser interference lithography

A method is presented for fabricating high-quality ridge waveguide gratings by combining conventional mask lithography with laser interference lithography. The method, which allows for apodization functions modulating both amplitude and phase of the grating is demonstrated by fabricating a grating that is chirped by width-variation of the grated ridge waveguide. The structure was optically characterized using both an end-fire and an infrared camera setup to measure the transmission and to map and quantify the power scattered out of the grating, respectively. For a uniform grating, we found a Q value of ~8000 for the resonance peak near the lower wavelength band edge, which was almost completely suppressed after apodization