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.
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.
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.
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.
Thermo-optical silicon-on-insulator (SOI) waveguide switch has been fabricated and characterized. The switch is based on a 2x2 Mach-Zehnder interferometer and 9 microns thick ridge waveguides. The extinction ratio of the switch is 17 dB with ultra-slow modulation and it is limited by the unoptimized directional coupler lengths. Thermo-optical switching with conventional on/off modulation was demonstrated up to 10 kHz. The average power consumption was 150 mW and the extinction ratio was 15 dB in 10 kHz square wave modulation. By using a novel modulation principle the maximum frequency was rised up to 167 kHz, while still maintaining the 15 dB extinction ratio in square wave modulation. With random binary modulation at 167 kHz frequency (3 μs per bit) the extinction ratio remained above 13 dB and the average power consumption was 590 mW. The obtained frequency limits for square wave modulation correspond to a maximum of 1% deviation from the attainable extinction ratio limits. With less strict extinction ratio requirements the maximum frequencies can be much higher. The new modulation method can be used to radically speed up interferometric switches with a tolerable increase in the power consumption.
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.
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.
In our work we have fabricated Bragg grating structures in silicon-on-insulator (SOI) waveguides. SOI waveguides enable integration of both passive and active functions, e.g. thermal, electrical or micromechanical tuning and optical receiving with the gratings. As silicon is a high refractive index material the first order grating period at 1550 nm wavelength is short, only 225 nm, and this period must be precisely controlled. Moreover, the grating must be spatially coherent over its entire length. All this introduces a great challenge for the fabrication techniques used to pattern the grating. Our approach to process gratings in SOI waveguides is based on direct e-beam writing and silicon etching with inductively coupled plasma (ICP). We show results on high aspect ratio Bragg gratings integrated with SOI waveguides with large core size.