Direct UV-written planar Bragg grating sensors

Abstract

Integrated photonics is a proven platform for physical and chemical sensing. It offers miniaturised solutions that are suited for use in extreme environments, including strong EM-fields, EM-pulses and contact with flammable materials, often far exceeding electronic sensors in this regard. This review looks into direct UV-written planar Bragg grating technology and its application to integrated photonic sensors. The platform has been demonstrated widely for measurement of physical properties such as temperature, pressure and strain. In addition, by using an evanescent interaction, refractive index can be measured allowing for chemical and biochemical detection. Further to this, the platform has recently been utilised in quantum information processing, where quantum gate operations and single photon detection has been shown.

Monitoring Water Contamination in Jet Fuel Using Silica-Based Bragg Gratings

“…This can be used to ensure safety and potentially improve aircraft efficiency through effective fuel management. The technology has further advantages of being inherently safe in flammable environments, demonstrates an immunity to electromagnetic interference and can be spectrally multiplexed with other optical sensors [4]. Studies concerning water contamination in jet fuel have been predominately made by the American and Russian military following early developments of the jet engine and high-altitude flight.…”

“…refuel or monitoring of engine feed lines. Further, the technology can temperature self-reference [4], an important feature in practice as large temperature fluctuations are known to exist during flight.…”

“…The presented refractometer, illustrated in Figure 1, is a commercial Stratophase Ranger Probe based upon silica planar technology. It is fabricated through small-spot direct UV writing, which simultaneously defines Bragg gratings and waveguides [4]. Evanescent field exposure of the guided mode is made through chemical wet-etching and enhanced by the deposition of a thin high-index overlayer [8].…”

“…Bragg grating 1 (λ1) and Bragg grating 2 (λ2) are evanescently exposed. Sensitivity to external refractive index is enhanced for these gratings using a thin (10's of nanometers thick) titanium dioxide layer [4], [9]. Bragg grating 3 (λ3) has a doped silica overclad and is insensitive to external refractive index changes, meaning that it can be used as a thermal reference.…”

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

“…The planar gratings used are typically made from glasses that have intrinsically low nonlinearity and low losses resulting in higher Q-factor cavities. Glass waveguides can also be fabricated using direct UV-writing techniques that are capable of writing high quality apodized Bragg gratings [13,14]. Typically these planar waveguides use a silicon substrate, with the advantage that this substrate acts to thermally equilibriate the structure.…”