We report evidence of intermittent behavior between chaotic and self-organized patterns while writing lines with a femtosecond lasers on the surface of a fused silica substrate. The patterns are accompanied by resolidified sub-microspheres and non-aligned grating lamellae. We observe that such dynamic behavior exhibits a striking similarity with the fluctuating content of a queuing system which alternate between random busy and idle periods.

Femtosecond laser written nanogratings show a random transition from self-organized to disordered structure and vice versa. A reason for the transition is proposed. Overlapping laser scans create nanogratings with apparent self-aligned fringes.

We have realized phase encoding and sensing of signals for quantum cryptography in compact circuits made with standard silica-on-silicon technology. The circuits include Bragg grating filters allowing multichannel cryptography with dense channel spacing, and they are thermally balanced to avoid crosstalk.

Narrow polarization-mixing resonances in planar photonic crystals are studied as candidate components for label-free refractive index sensors for detecting bacteria causing sepsis through the identification of DNA strands.

Based on a series of 1x2 beam splitters, novel direct excitation of slow-light from input- to output-region in photonic crystal waveguides is investigated theoretically and experimentally. The study shows that the slow-light excitation provides over 50 nm bandwidth for TE-polarized light splitting between two output ports, and co-exists together with self-imaging leading to ~20 nm extra bandwidth. The intensity of the direct excitation is qualitatively explained by the overlap integral of the magnetic fields between the ground input- and excited output-modes. The direct excitation of slow light is practically lossless compared with transmission in a W1 photonic crystal waveguides, which broadens the application-field for slow-light and further minimizes the size of a 1x2 splitter.

Grating writing in structured optical fibers is reviewed. Various laser sources have been used including UV and near IR nanosecond and femtosecond lasers, each enabling different material processing regimes. The issue of scattering is modeled through simulation and compared with experiment. Good agreement has been established.

Using a time-resolved interferometric technique, we study the laser-induced carrier-trapping dynamics in SiO2 and Ge-doped SiO2. The fast trapping of electrons in the band gap is associated with the formation of self-trapped excitons (STE). The STE trapping is doping dependent in SiO2. The mean trapping time of electrons excited in the conduction band was found to be significantly lower in Ge-doped silica (75 +/- 5 fs) when compared to pure silica (155 +/- 5 fs). At our concentration level, this indicates that the plasma properties are determined by the presence of easily ionizable states such as the presence of Ge atoms in the glass network. Therefore, we suggest that in Ge-doped silica there exist an additional trapping pathway that leads to a significantly faster excitons trapping and a higher plasma density when compared to undoped silica.

The power imbalance between different waveguide outputs is compensated by manipulating the dispersion of the guided propagation in the multimode interference (MMI) region. This is attainable using a tapered region at the beginning of the MMI region that has been verified through simulation and experiment. From this, the fabrication tolerance for the diameters of holes in a tapered 1×3 photonic crystal waveguide (PhCW) splitter is relaxed up to a range of at least 27 nm. The output power is well-balanced to within 1 dB. The effective bandwidth of the splitters shifts only around 13 nm, for a reduction of 10 nm in the diameter of the PhCW holes. The optimized component is an outstanding ultracompact 1×3 splitter for the photonic integrated circuit (PIC).

We present TE transmission measurements of photonic crystal waveguides with high hole radius to period ratio r/Λ = 0.388. This geometry introduces a unique low loss transmission band in addition to the traditional PhC guiding band and very sharp transmission edges for devices with a length of 50 μm or longer. Finite difference time domain and plane wave expansion simulations confirm the results and show that the sharpness of the cutoffs can be explained by the spectral shape of the guiding mode in the band diagram.

The development of new techniques for writing and tailoring the properties of Bragg gratings has generated a suite of distinct grating types that are optimised for performance within different temperature windows. These cover gratings produced by recipes such as hypersensitisation, thermal processing and single and multiphoton writing. In this paper, we review four types of high temperature gratings that offer comprehensive coverage of temperature space for most applications of interest. Up to 1200°C novel processing methods allow standard silica-based optical fibres to be used. However, beyond these temperatures, optical fibres made from other materials, such as sapphire, need consideration.

The infrared femtosecond laser damage threshold is found to be independent of OH content in pure silica glass. Additionally, the density and the mean trapping time of electrons excited in the conduction band are also found to be independent on OH concentration.

We report some of our recent progress in the area of Bragg grating writing in photonic crystal fibres (PCFs). The various challenges that PCFs present are discussed and the methods used to overcome these challenges are presented. The fabrication of highly-durable type-IIa gratings in highly nonlinear photonic crystal fibre is demonstrated, the rotational variance of grating inscription is also investigated through both experiments and numerical modeling. In other experiments we fabricate a narrow-linewidth distributed feedback (DFB) laser in erbium-doped PCF, achieving stable, single-mode and CW operation. The potential of such a DFB PCF in sensing applications is assessed by accurately measuring an absorption line of acetylene gas.

The growth rate of Bragg gratings written using 193-nm light from an ArF excimer laser is shown to be non-linear with the pulse energy density for Er 3+ co-doped Al silica. This yields a refractive-index increase up to a few 10 −3 . We then use phase-shift interferometry to measure the sample surface topography following exposure. Subsequently, we formulate an inhomogeneous stress model to analyse the observed change of volume within the core material. Below pulse energies of 550 mJ/cm 2 , the results show that refractive-index changes are primarily due to a densification process. At higher pulse energies material re-expansion occurs.

Fibre Bragg gratings were written into the core of air-clad optical fibre using the point-by-point grating writing method with an 800 nm femtosecond laser. Visible wavelength scattering from the grating fringes is shown.

A well-known side-effect from fibre Bragg grating UV-fabrication is short wavelength attenuation, where irradiation with laser light, usually in the UV, generates both defect-induced absorption and scattering. These losses are especially problematic for high power optical fibre lasers operating at shorter wavelengths where resonant assisted coupling into the glass matrix through the rare earth ions can take place (e.g. Yb3+). In this, work we present a study of the relative magnitude of short wavelength attenuation in gratings written by the point-by-point method using a Ti-sapphire femtosecond laser operating at 800 nm. Such gratings are very stable and have been used as the feedback elements in fibre lasers with powers exceeding 100 W. We show that the scattering properties responsible for the attenuation are analogous to those associated with type II gratings written with UV lasers.

A distributed feedback laser was fabricated in Er3+-doped photonic crystal fibre. Single mode lasing is obtained with <10kHz linewidth. The output was amplified to 12mW using a commercial erbium doped fibre amplifier (EDFA).

The measurement of the tuning speed in fiber Bragg gratings is an increasingly important parameter for characterizing the dynamics of tunable devices. Optical spectrum analyzers and wavelength meters are not suitable due to their slow response for measuring the wavelength shift in time. In this paper we report on a technique for estimating the tuning speed of a fiber Bragg grating which is based on accessing the wavelength shift through a calibration curve and measuring the time in which the shift occurs with the help of a fast photo-detector.