Alexander Jantzen

External cavity diode laser based upon an FBG in an integrated optical fiber platform

An external cavity diode laser is demonstrated using a Bragg grating written into a novel integrated optical fiber platform as the external cavity. The cavity is fabricated using flame-hydrolysis deposition to bond a photosensitive fiber to a silica-on-silicon wafer, and a grating written using direct UV-writing. The laser operates on a single mode at the acetylene P13 line (1532.83 nm) with 9 mW output power. The noise properties of the laser are characterized demonstrating low linewidth operation (< 14 kHz) and superior relative intensity noise characteristics when compared to a commercial tunable external cavity diode laser.

Leaky mode integrated optical fibre refractometer

A route to monitor external refractive indices greater than the core index of the waveguide is presented. Initial application utilizes an integrated optical fibre (IOF) platform due to its potential for use in harsh environment sensing. IOF is fabricated using a bespoke flame hydrolysis deposition process to fuse an optical fibre to a planar substrate achieving an optical quality, ruggedized glass layer between the fibre and substrate was fabricated. The presented refractometer is created by direct UV writing of multiple fibre Bragg gratings into an etched (22 μm diameter) optical fibre post fabrication. Linear regression analysis is applied to quantify propagation loss by monitoring each FBGs back reflected power. The device operates with a sensitivity of approximately 350 dB/cm/RIU at a refractive index of 1.451 at 1550 nm. Numerical simulations using a transfer matrix method are presented and potential routes for development are discussed.

Pressure characterisation Data 180118NB318-2-chip2-27-500um

Dataset supports: Jantzen, A. et al (2018). Pressure Sensing Based on Ratiometric Bragg Grating Loss in a Planar Silica Diaphragm Platform. Advanced Photonics Congress JTu2A.62bg represents the background measurement with reflection from before entering the circuit. loss represents the device response to decreasing pressure.Pressure readings were respectively: 2 24 23.5 23 22.5 22 21.5 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2.5 with an error of 0.25 in Hg. The reading to begin with is the offset value of the gauge.

Dataset for Consolidation of Flame Hydrolysis Deposited silica with a 9.3 µm wavelength CO2 laser

Alphastep stylus profiler measurements and Zescope white light interferometer measurements of the surface profile of silica soot on the surface of a silicon wafer that had undergone consolidation through exposure to a 9.3 micron wavelength CO2 laser. The data show measurements for the laser operating at different duty cycles and spot translation speeds.

An integrated optical fiber device for harsh environment refractometry at indices above silica for monitoring hydrocarbon fuels (Conference Presentation)

Integrated Optical Fibre (IOF) allows for robust planar integration and seamless monolithic coupling. Fabrication is achieved through an adapted Flame Hydrolysis Deposition (FHD) technique, which forms a ruggedized glass alloy between the fibre and planar substrate. It has been previously demonstrated as a low linewidth external cavity lasers diode and a hot-wire anemometer, inherently suitable for harsh environments. This work looks at implementing the platform for harsh environment refractometry, in particular monitoring hydrocarbon fuels in the C14 to C20 range (e.g. Jet A1 and diesel). The platform uses SMF-28 fibre and direct UV written Bragg gratings to infer refractive index and thus the quality of the fuel. A challenge arises as the refractive index of these fuels are typically greater than the refractive index of the waveguide. Therefore, the guided mode operation of FBG refractometers is unsuitable. This work uniquely reports leaky mode operation and a regression analysis, inferring propagation loss through changes in amplitude of successive gratings. In effect, the proposed methodology utilises the imaginary part of the effective index as opposed to the real part, typically used by such sensors. Initial results have shown a 350 (dB/cm)/riu sensitivity is achievable above a refractive index of 1.45. This was measured for a SMF-28 fibre wet etched to 30 µm and planarized. Considering a 0.01 dB/cm propagation loss resolution, refractive index changes of the order 10-5 can be approached. Work will be presented on the fabrication of an IOF platform for refractometers as well as metrics for survivability in harsh environments.

Pressure sensing based on ratiometric Bragg grating loss in a planar silica diaphragm platform

In this paper the first demonstration of a planar silica-on-silicon chip pressure sensor based on monitoring ratiometric Bragg grating amplitude loss across a diaphragm is made. The device resolution was found to be 0.46 kPa.

Enhanced temperature sensitivity of thermally regenerated direct ultraviolet written gratings in germanium doped core fiber

The use of thermally regenerated gratings for monitoring harsh environments is becoming increasingly attractive due to their thermal resilience and high precision. They are a unique type of Bragg grating created through annealing UV-laser written Fiber Bragg Gratings (FBGs) at high temperatures (above 600°C) and they have been demonstrated to operate at temperatures over 1000 °C in oxygen free environments [1]. In this work we report two new observations. Firstly, a second phase thermal regeneration process at temperatures above 650 °C and secondly an enhanced thermal response for these second phase regenerated gratings of over 140%. Uniquely, fabrication of the gratings was made through a small spot Direct Ultraviolet Writing (DUW) process. This utilizes a high precision four-axis stage system and a frequency double argon-ion continuous wave 244 nm laser that is split and recombined at a focus to form a ∼7 μm diameter interferometric spot [2]. A series of 46 different FBGs, from 1400 to 1620 nm, were written into a single non-hydrogen loaded double clad germanium doped 4 μm core fiber (Nufern GF4A). Gratings in the series were written with fluences ranging from 0.05 kJ/cm2 up to 90 kJ/cm2.

Integrated optical fibre coupler

Integrated Optical Fibre (lOF) is a low-loss photonic platform that directly integrates optical fibre to a planar substrate. The platform possess advantages associated with optical fibre including low propagation loss, whilst at the same time enabling planar functionality associated with integrated optics. IOF fabrication is achieved through a modified Flame Hydrolysis Deposition (FHD) technique that forms a robust glass alloy between the fibre and substrate. The binding medium is of optical quality and mechanically robust, illustrated in fig 1 (a). Although non-trivial seamless on/off-chip coupling has also been demonstrated, which could further act to minimise coupling losses typically associated with integrated optics.

Extreme environment refractometers designed in integrated optical fibre

Integrated Optical Fibre (IOF) is a passive optical platform that directly integrates optical fibre to a planar substrate, illustrated in Fig 1(a). It possess advantages associated with optical fibre such a low propagation loss, whilst enabling planar functionality commonplace with integrated optics. Planarization is uniquely achieved through a modified Flame Hydrolysis Deposition (FHD) technique that forms a robust glass alloy between the fibre and substrate. The binding medium is of optical quality and resistant against common solvents, chemicals and elevated temperatures of up to 1000oC. Furthermore as fibre can be brought seamlessly on-off chip there is no need for glues or cumbersome coupling arrangements, which are typically a point of mechanical weakness when monitoring harsh environments.

Direct 9.3 μm CO 2 laser consolidation of FHD silica for planar devices

Flame Hydrolysis Deposition (FHD) is a traditional route to deposit layers of doped silica onto the surface of a substrate for planar lightwave circuits. To form a uniform layer of fused glass the deposited soot must be consolidated, typically within a furnace at temperatures between 1200 °C and 1400 °C. This thermal processing is not localised as the temperature of the entire wafer is raised. This could be an issue for thermally sensitive, metallic or active photonic structures. This also limits the materials used for the substrate and requires the silica glass to have sufficient dopants to permit consolidation. CO2 lasers have previously been used for smoothing and polishing of silica [1, 2] and were performed with CO2 lasers operating with a wavelength of 10.6 μm. Silica however has a large absorption peak between 9 to 9.5 μm [4]. This paper demonstrates that using a CO2 laser operating at 9.3 μm allows for highly localised heating and consolidation of FHD silica soot on a silicon wafer, this greatly reduces processing time and relaxes the constraints on dopants and substrate used in FHD, and to knowledge of the authors is the first example of FHD consolidation with a 9.3 μm laser.