Sanna Yliniemi

UV-exposed Bragg gratings for laser applications in silver-sodium ion-exchanged phosphate glass waveguides

High reflectivity Bragg gratings have been written by ArF excimer laser through a phase mask into IOG-1 hybrid phosphate glass. After grating exposure, a waveguide was fabricated by silver-sodium ion-exchange. Reflectivities around 80% at a wavelength of ~ 1535 nm were measured from the waveguide for both quasi-TE and -TM polarizations. Waveguide laser operation with the photowritten waveguide grating as another mirror was demonstrated. Output power of 3.8 mW with a pump power of 199 mW could be extracted from the laser configuration.

Photosensitivity and volume gratings in phosphate glasses for rare-earth-doped ion-exchanged optical waveguide lasers

Phosphate glasses containing enough sodium to allow the fabrication of optical channel waveguides by ion exchange are photosensitive to intense ultraviolet irradiation from excimer lasers at 193 and 248nm. Permanent submicrometer-period volume index gratings with modulation amplitudes larger than 10−4 were obtained even after annealing the irradiated samples for 2h at 230°C. Ultraviolet-visible absorption changes were measured in the irradiated areas, as well as structural modifications observed by surface profiling. Comparative studies were carried out for glasses that were also codoped with erbium and ytterbium to provide high gain at wavelengths near 1.5μm. Finally, we demonstrate narrowband gratings with reflectivities larger than 80% in silver ion-exchanged channel waveguides made in these phosphate glass substrates.

Ion-exchanged glass waveguides with low birefringence for a broad range of waveguide widths

Optical communications networks require integrated photonic components with negligible polarization dependence, which typically means that the waveguides must feature very low birefringence. Recent studies have shown that waveguides with low birefringence can be obtained, e.g., by use of silica-on-silicon waveguides or buried ion-exchanged glass waveguides. However, many integrated photonic circuits consist of waveguides with varying widths. Therefore low birefringence is consequently required for waveguides having different widths. This is a difficult task for most waveguide fabrication technologies. We present experimental results on waveguide birefringence for buried silver-sodium ion-exchanged glass waveguides. We show that the waveguide birefringence of the order of 10(-6) for waveguide mask opening widths ranging from 2 to 10 microm can be obtained by postprocessing the sample through annealing at an elevated temperature. The measured values are in agreement with the values calculated with our modeling software for ion-exchanged glass waveguides. This unique feature of ion-exchanged waveguides may be of significant importance in a wide variety of integrated photonic circuits requiring polarization-independent operation.

Fabrication and characterization of waveguide structures on SOI

A survey of the most common silicon-on-insulator (SOI) substrates and waveguide structures, as well as an evaluation of their applicability in optical telecommunication at the 1550 nm wavelength is presented. The design, fabrication and characterization of straight and bent SOI waveguides, as well as a thermo-optical SOI switch are described. The propagation loss of the realized SOI waveguides is below 0.25 dB/cm and thermo-optical switching is demonstrated at 10 kHz. The effect of cladding material on top SOI ridge waveguides on the polarization properties of straight and bent waveguides, as well as on directional couplers, is discussed. Both polarization independent and polarization maintaining waveguides are demonstrated. Finally, a basic principle of multi-step SOI waveguides is proposed. As examples of the potential in multi-step processing, efficient coupling between different rectangular, ridge and photonic crystal waveguides, ultra-small bends, waveguide mirrors, and extremely short multi-mode interference couplers are described.

Silver film ion-exchanged Er-doped waveguide lasers and photowritten waveguide gratings in phosphate glass

We report on an experimental study of waveguide lasers in Er/Yb-codoped phosphate glass. The waveguides serving as laser cavities were fabricated by electric field assisted silver-film ion exchange technology. Threshold power, slope efficiency, and output power were measured from these lasers and compared to previously reported data. We also report on waveguide DBR-lasers using photowritten gratings in a hybrid glass.

Buried ion-exchanged glass waveguides featuring low birefringence with a broad range of waveguide widths

Optical communications networks require integrated photonic components with negligible polarization dependence, which typically means that the waveguides must feature very low birefringence. Recent studies have shown that waveguides with low birefringence can be obtained, e.g., by using silica on Si waveguides and by buried ion-exchanged glass waveguides. However, many integrated photonic circuits consist of waveguides with varying widths. Therefore, low birefringence is consequently required for waveguides having different widths. This is a difficult task for most waveguide fabrication technologies. In this paper we present theoretical and experimental results on waveguide birefringence for buried silver ion-exchanged glass waveguides. We show that the waveguide birefringence is on the order of 10-6 for waveguide mask opening widths ranging from 2 to 9 μm. The measured values are in good agreement with the values calculated with our modeling software for ion-exchanged glass waveguides. This unique feature of ion-exchanged waveguides may be of significant importance in a wide variety of integrated photonic circuits requiring polarization independent operation.

Fabrication of photonic crystal waveguide elements on SOI

Photonic crystal angle elements fabricated in silicon-on-insulator (SOI) are reported. These elements are modelled using three-dimensional finite difference time domain (FDTD) method. Photonic crystals have a two-dimensional trigonal lattice structure with cylindrical air columns. The period of the crystal is approximately 420 nm and the cylinder diameter is about 330 nm. Defect creation is performed by removing air columns from certain lattice sites. The SOI-layer is one micron thick and it also defines the column height. The FDTD modelling results imply that photonic crystal angle elements with lower height do not exhibit proper light transmission at the telecommunications wavelength window, 1550 nm. FDTD modelling results give higher transmission for TE-polarised light than for TM-polarisation. For better light coupling a taper element with widened waveguide end is designed.

Comparison of Photodarkening in Ytterbium-doped fibers

Development of photodarkening in two similar large-mode-area ytterbium doped fibers from different sources is compared. The excess loss induced by photodarkening is derived from transmission loss measurements of pristine and pumped or photodarkened samples. To accelerate the photodarkening process, cladding pumping is used so as to achieve high and uniform inversion through the sample. Further, intensity profiles are measured and compared in effort to detect possible radial variations in the induced losses.

Negligible birefringence in dual-mode ion-exchanged glass waveguide gratings

Polarization dependence of UV-written Bragg gratings in buried ion-exchanged glass waveguides is investigated. A polarization-dependent shift in Bragg wavelength of less than 0.02 nm is measured, both for the even and the odd modes of a laterally dual-mode waveguide. The measured wavelength shift corresponds to a waveguide birefringence of the order of 10(-5), which is negligible for most applications in optical communications. It is observed that the UV-induced birefringence is small, within the limits of the measurement accuracy. The thermal stability of the fabricated gratings is also very good. The results are of particular importance for devices considered here since they require a polarization-independent mode-converting waveguide Bragg grating. Polarization-independent performance of these gratings enables the fabrication of a new class of integrated optical devices for telecommunication applications.

A study of silver-film ion-exchanged glass waveguides in phosphate glass

In this work, properties of Ag thin-film ion exchange in Schott IOG-1 phosphate glass has been studied. Emphasis has been put on finding the proper diffusion parameters (self-diffusion coefficient for Ag+ ions and the mobility ratio between the participating ions) at process temperatures of 90°C and 230°C. In order to extract the diffusion parameters a following procedure was utilized: An ion-exchanged slab waveguide was fabricated using the same process conditions as in the case of a two-dimensional waveguide fabrication. After slab waveguide fabrication, the effective refractive indices of the propagating modes were measured by prism coupling. Thereafter, a smooth refractive index profile was constructed by improved inverse Wentzel-Kramers-Brillouin method. This refractive index profile was compared with the Ag+ ion concentration profile calculated from the diffusion equation by Crank-Nicolson method. The self-diffusion coefficient for Ag+ ions and the ratio of the self-diffusion coefficients of Ag+ and Na+ ions were varied until convergence between the refractive index profile and the concentration profile was found. Using the diffusion parameters obtained from these experiments, two-dimensional waveguide mode profiles were calculated by finite difference method. These theoretically obtained mode profiles were compared with the measured mode profiles with different mask opening widths.