High reflectivity Bragg gratings fabricated by 248nm excimer laser holographic ablation in thin Ta₂O₅ films overlaid on glass waveguides

Relief Bragg grating reflectors inscribed on channel waveguides may be used in optical communications as add-drop wavelength multiplexers, gain-flattening filters, distributed feedback laser mirrors, or in sensing technology as high sensitivity devices for precise monitoring of chemical or biomedical processes. We present strong Bragg grating reflectors in Ta2O5 thin oxide films overlaid on potassium ion exchanged channel waveguides in BK-7 glass, inscribed using 248nm excimer laser holographic ablation. The grating pattern was created employing two-beam interference using a modified Mach-Zehnder interferometric cavity and the output of a narrow-lined injection cavity 248nm excimer laser. The experimental data presented are divided into two sections: the first section refers to the study of the grating ablation process of thin Ta2O5 films with respect to the exposure conditions; and the second focuses in the implementation of those relief grating in functional waveguide devices

Characterization of fiber optic distributed temperature sensors for tissue laser ablation

Fiber optics is the most promising technology for distributed temperature sensing. The paper investigates the characterization of probes based on single or multiplexed fiber Bragg gratings, specifically conceived to evaluate the temperature distribution in applications that imply large temperature gradients, such as in laser induced thermal treatments of solid tumors. A setup for the characterization of fiber Bragg grating sensors in non uniform temperature conditions is described and examples of applications in case that mimic actual working conditions are reported

Optical fibre long period grating spectral actuators utilizing ferrofluids as outclading overlayers

Results are presented on the spectral tuning of optical fibre long period gratings utilizing water and oil based ferrofluids as outclading overlayers, under static magnetic field stimulus. Two approaches are adopted for modifying the ambient refractive index at the position of the long period grating. In the first approach, a water based ferrofluid is controllably translated along the length of the grating via a magnetic field. Changes as high as 7.5nm and 6.5dB are monitored in the wavelength and strength, respectively, of the attenuation bands of the grating. The repeatable performance of this device for repetitive forward and backward translation verifies that no ferrofluidic residue is left on the fibre, due to silanization cladding functionalisation. In the second approach, the refractive index of an oil based ferrofluidic overlayer is modified through the magneto-optical effect. For an applied static magnetic field in the order of 400 Gauss the strength of the attenuation band of the grating is modified by more than 10% while its spectral position remains unaffected. Accordingly for the implementation of the last approach, the magnetically induced refractive index changes of ferrofluids of different solution concentrations are studied by employing diffraction efficiency measurements

Investigations on the Bragg grating recording in all-silica, standard and microstructured optical fibers using 248 nm 5 ps, laser radiation

oai:ojs.pkp.sfu.ca:article/309The fabrication of Bragg reflectors in hydrogenated, all-silica, fluorine cladding depressed and microstructured optical fibers using 248 nm, 5 ps laser radiation, is investigated here. Comparative Bragg grating recordings are performed in both optical fibers, for investigating effects related to the scattering induced by the capillary micro-structure, to the photosensitivity and index engineering yield. Further, finite difference time domain method is employed for simulating the scattering from the above capillary structure and the nominal intensity reaching the fiber core for side-illumination. The maximum modulated refractive index changes inscribed in the standard, step-index fiber were of the order of 8.3x10-5, while the maximum refractive index changes inscribed in one of the microstructured optical fibers was 32% lower and 5.7x10-5, for nominal pulse intensities of 20 GW/cm2 and modest accumulated energy densities

Chemical and physical changes induced in optical materials under high-intensity laser irradiation

Editorial for the 2008 volume of Laser Chemistry

Bioresorbable optical fiber Bragg gratings

We demonstrate, for the first time, an inscription and wet dissolution study of Bragg gratings in a bioresorbable calcium-phosphate glass optical fiber. Bragg gratings, with average refractive index changes of 5.8 × 10^−4, were inscribed using 193 nm excimer laser radiation. Results on the dissolution of the irradiated fiber in simulated physiological conditions are presented after immersing a tilted Bragg grating in a phosphate buffered saline solution for 56 h; selective chemical etching effects are also reported. The investigations performed pave the way toward the use of such phosphate glass fiber Bragg gratings for the development of soluble photonic sensing probes for the efficient in vivo monitoring of vital mechanical or chemical parameters

Bragg gratings in optical waveguides, glasses and thin oxide films induced by excimer laser radiation

The purpose of this thesis is the fabrication and characterisation of sub-micron period (~500nm) Bragg relief grating reflectors in optical waveguide structures using interferometric excimer laser ablation. Furthermore, the work presented in this thesis describes investigation of the feasibility of the application of excimer laser grating micromachining for the fabrication of waveguide gratings which may be used as wavelength filters in the 1.5µm band for optical communications applications. For this purpose the following studies were carried out: (i) the ablation of sub-micron relief gratings on Tl+ ion-exchanged channel waveguides in Er/Yb-codoped B1664 glass, using 193nm excimer laser radiation and (ii) the ablation of sub-micron relief gratings in InOx and Ta2O5 thin oxide films overlaid on K+ ion-exchanged channel waveguides in BK-7 glass, using 248nm excimer laser radiation. For the waveguide gratings in Tl+ ion-exchanged Er/Yb-codoped B1664 glass reflectivities greater than 28dB were obtained from a 6mm long grating. Similarly, reflectivities greater than 4.7dB and 18dB were produced by 16mm long gratings in K+ ion-exchanged channel waveguides in BK-7 glass overlaid with InOx and Ta2O5 thin oxide films, respectively. In parallel, the ablation behavior of borosilicate glass using 193nm radiation and that of InOx and Ta2O5 thin oxide films using 248nm radiation were studied experimentally. Waveguide grating theory based on the study of the dispersion properties of multi-layer step-index planar and graded-index channel waveguides and on the scattering behaviour of grating structures in waveguides, has been developed and analysed. This theoretical background is employed to design the waveguide gratings used and to explain the experimental results obtained. Finally, the photorefractive properties of InOx and Ta2O5 thin oxide films under UV radiation are experimentally investigated

High-reflectivity Bragg gratings fabricated by 248-nm excimer laser holographic ablation in thin Ta₂O₅ films overlaid on glass waveguides

We demonstrate strong Bragg grating reflection in Ta2O5 (tantalum pentoxide) thin films overlaid on potassium ion-exchanged channel waveguides in BK-7 glass, inscribed using 248-nm excimer laser holographic ablation. The experimental data presented are divided into two sections: the first section refers to the study of the grating ablation process of thin Ta2O5 films with respect to the exposure conditions, while the second focuses on the implementation of these relief gratings in functional waveguide devices. Firstly, experimental data on grating morphology versus exposure conditions, accomplished with scanning electron microscopy microscans, are presented. In the second section diffraction spectra for waveguide gratings are presented and analysed. Spectral notches in transmission of depth -18 dB for the TM polarisation were obtained from 16-mm-long gratings patterned in waveguides overlaid with a 105-nm-thick Ta2O5 film, using 50 pulses of 60 mJ/cm2 energy density