Mattias L. Åslund

Temperature independent highly birefringent photonic crystal fibre

A highly birefringent photonic crystal fibre has been characterised as a function of temperature. The modal birefringence has been found to be independent of temperature from -25 to 800 degrees C.

Narrow linewidth, 100 W cw Yb3+-doped silica fiber laser with a point-by-point Bragg grating inscribed directly into the active core.

We report on the power scaling to 103 W of a 1.1 microm continuous-wave Yb(3+)-doped silica fiber laser incorporating a point-by-point (PbP) fiber-Bragg grating inscribed directly into the active core using 800 nm femtosecond laser pulses. The spectrum of the laser exhibited a narrow linewidth that broadened to 260 pm at 103 W. The output was frequency doubled using an 11 mm long periodically poled MgO:LiNbO3 crystal to generate 2.1 W of green with an internal conversion efficiency of 10% at high power and 0.81%/W at low power.

Annealing properties of gratings written into UV-presensitized hydrogen-outdiffused optical fiber.

Accelerated aging of gratings written in UV presensitized hydrogen outdiffused optical fibers show that these gratings are more stable than standard gratings written in hydrogen-loaded fibers. They are observed to grow initially by as much as 2%. The predicted decay after 25 years at 80 degrees C is ~0.1% . The results suggest that the index modulation decay is so slow that postfabrication annealing can be avoided.

Locking in photosensitivity within optical fiber and planar waveguides by ultraviolet preexposure

Strong photosensitivity is locked in permanently after hydrogen outdiffusion of hydrogen-loaded waveguides presensitized with UV light by either pulsed 193-nm or cw 244-nm laser output.

Optical loss mechanisms in femtosecond laser-written point-by-point fibre Bragg gratings

Fibre Bragg gratings inscribed with the point-by-point method using a Ti-sapphire femtosecond laser operating at 800 nm are shown to display strong increasing attenuation towards shorter wavelengths with a large and spectrally sharp recovery observed below 400 nm. The origin of this loss is shown to be Mie scattering, and the sharp recovery in the transmission results from wavelength dependent scattering within the numerical aperture of the core. The permanent losses from these Type II gratings have implications for high temperature sensors and fibre lasers.

Spun elliptically birefringent photonic crystal fibre

Elliptically birefringent fibre has been fabricated by spinning the preform of a highly linearly birefringent photonic crystal fibre (PCF) during the drawing process. The resulting Spun Highly Birefringent (SHi-Bi) PCF offers intrinsic sensitivity to magnetic fields through the Faraday effect without the high inherent temperature sensitivities suffered by conventional spun stress birefringence fibres. The ellipticity of the birefringence has been measured and temperature independence has been demonstrated.

Antisymmetric grating coupler: experimental results

The principle of an antisymmetric grating coupler was recently proposed theoretically as a planar waveguide add-drop multiplexer. It has the potential to enhance significantly the functionality of an add-drop multiplexer based on grating-assisted coupling. Here we realize the concept experimentally in an all-fiber geometry. We show that conventional devices exhibit two high-reflection bands. In contrast, the antisymmetric grating coupler has only a single reflection band, thereby dramatically improving its filtering characteristics.

Birefringence control in plasma-enhanced chemical vapor deposition planar waveguides by ultraviolet irradiation

Complete birefringence compensation is demonstrated in plasma-enhanced chemical vapor deposition waveguides by 193-nm postexposure. A single relaxation process dominates the decay in stress anisotropy, indicating that compressive stress from the substrate leads to an elastic stress anisotropy at the core.

Thermal stabilization of Type I fiber Bragg gratings for operation up to 600°C

The thermal stability of Type I gratings is increased by postthermal tuning of the grating. Optimization of the procedure leads to gratings that can withstand temperatures as high as 600 degrees C. Aging tests lead to lifetime predictions as high as 25 years with <3 dB reduction at 400 degrees C. Single exponential relaxation is observed. Above 800 degrees C regeneration is obtained.

Regenerated Fibre Bragg Gratings

Silica remains the key optoelectronic and photonic medium, the essence of nearly all modern optical transport systems. Engineering of silica in its various forms ranges from 1 to 3-dimensional waveguide and periodic structures, including recent interest in 3-D photonic crystals. Most of the processing methods involve complex vapour deposition and various co-dopants, which have an advantage of overcoming the lack of finesse involved with general formation of glass structure through high temperature processing and quenching. Nevertheless, to obtain micron or sub-micron precision over the processing of glass for device purposes, invariably post processing methods are commonly used, ranging from etching of systems with dopants, often through patterned masks, to laser processing using UV to mid IR lasers. Concrete examples of micron scale laser processing of glass include direct written waveguides, Bragg gratings in waveguides and optical fibres and photonic crystals. The drawback with these post-processing techniques is that they often produce glass that is structurally less stable than the starting phase. For many applications the thermal stability of laser induced glass changes determines the limits in which they can operate – an excellent example which will form the basis for this chapter, is the optical fibre Bragg grating. Fibre Bragg gratings are used in many industrial and technological applications. Within standard telecommunications applications, for example, type I fibre Bragg gratings that can operate to 80°C for 25 years are required – such gratings can in principle operate for lengthy periods up to 300°C. Gratings that can operate at temperatures well above standard telecommunication requirements are critical to the success of many real time sensing applications. In the oil and gas industries, an alternative application, although standard oil bores are typically quoted as having an environment no more than ~(180-250)°C [Schroeder et al. 1999; Kersey 2000], variations can occur and the increasing depth of the next generation bores suggest sensors that can operate to 400°C or more are desirable for long term or permanent operation. In industries involving high temperature furnaces, such as aluminium smelting or coal based power stations, it would be of interest to be able to monitor temperatures in excess of 1000°C. Similar temperature requirements span many