We report on a refractive index sensor based on a planar Bragg grating (PBG) capable to online monitor the water
content in Biodiesel and the amount of ethanol admixture to conventional fuels, respectively. Our results demonstrate the
capability of the sensor to distinguish the transition between about 190 and 500 ppm water in Biodiesel, enabling to
monitor the production process of Biodiesel in the relevant range according to industrial standards. The ethanol content
in petrol has been investigated in the range of 0-100%, covering the entire standardized range of E-5 to E-85 fuel mixing
ratios. These experiments reveal a sensitivity of 112 nm/riu allowing the measurement of the ethanol content with a
resolution of 8.9·10-6.
An evanescent field refractive index sensor consisting of a Bragg grating that is written into a silica-on-silicon planar
optical waveguide structure by UV laser radiation is utilized to monitor the composition of liquid binary chemical
systems. We have investigated various selected liquid compounds that are commonly used in the pharmaceutical and
chemical industry, finding sensitivities on the order of 100nm/RIU and minimum detectable index resolution on the
order of 5•10-6 fulfilling industrial demands on detection limits and partly being superior to other electrical transducer
systems. The planar structure of the sensor chip allows on chip integration of fluidic structures that we have generated by
laser ablation using a pulsed fiber laser, enabling connection to the adjacencies.
A novel optical sensor system for rapid, sensitive and robust biological detection is presented. Sensor elements based on integrated optical circuits confine all optical signals into a planar format, resulting in a small, low-cost and mechanically stable refractive index sensor, without any external bulk optics. Consequently, the sensor elements are able to operate in real-world environments, resilient to vibration and temperature changes, whilst maintaining refractive index resolution of 10-6. Oxide surfaces on the sensor are ideal for protein attachment and have a long lifetime in buffer solutions (>100hrs). Real-time, label-free detection of biological agents has been demonstrated using antibodies attached to the sensor surface. The sensor design results in a large penetration depth of the sensing light, up to 1μm into the sample liquid, conferring the ability to detect various classes of biological targets, spanning toxins, viruses and bacteria. Each sensing element utilizes parallel multiple wavelength data to provide additional information at the point of measurement, resulting in on-chip temperature and strain referencing, focused towards increased accuracy and reduction of false alarms. The large size range of biological detection, coupled with the long lifetime of the sensors makes the system ideally suited to applications ranging from medical diagnostics to confirmatory detectors for homeland security
We report on the experimental demonstration of electrically tunable Bragg grating using liquid crystals. Such concept and device have been modelled in the past, but not realised experimentally. Using Direct UV writing technique, a waveguide and Bragg grating are simultaneously patterned in a planar silica on silicon substrate. Overcladding in the vicinity of the grating can be replaced by liquid crystals to exploit their electro-optic properties. The interactions of the evanescent field with the variable refractive index of the liquid crystal allow the tuning of the centre wavelength of the filter. In this way a 35 GHz tunable planar Bragg grating using liquid crystal and electric field was demonstrated.
A planar Bragg grating in silica is used to form an integrated optical refractive index sensor. The device, inherently suited to remote sensing using single mode transmission fibre, is shown to clearly detect phase transitions in a nematic liquid crystal and in water. Transitions from ordered to isotropic, gas to liquid and liquid to solid as well as the reverse transitions can all be clearly identified. The sensor also allows supercooled liquid to be easily identified, a task previously found challenging by other sensor technologies.
Direct UV-writing is an ideal technique for rapid prototyping and small batch fabrication of integrated optical circuits. Based on the refractive index increase of a glass from exposure to a tightly focused UV beam. The translation of this beam relative to a suitable substrate allows the definition of 2-d waveguide structures such as s-bends and power couplers without the need for subsequent processing.
Our alternative technique, Direct Grating Writing retains the advantages of Direct UV writing for channel definition but allowing both the grating and channel structure to be formed in the same process. Using this new technique, we present the fabrication of conventional channel waveguides and Bragg channel waveguides. We demonstrate the independence of the Bragg grating strength from the strength of the channel waveguide, the sensitivity of this process as a characterization technique, and the ability to use this technique to fabricate more complex 2-D structures for integrated optical circuits. We finally present the fabrication of a range of gratings spanning the entire wavelength span commonly used for optical communication with no change in the equipment.