Simulations and experimental results for novel refractometric-sensing platforms are presented here. The first platform is based on a
multi-mode interference coupler (MMIC) in which the top and sidewalls of the coupler are exposed to a humidity-sensing enrichment layer. Sensor operation is based on the creation of self-images of the input field into the coupler, at regular intervals along the coupler. This phenomenon is due to interference between the optical modes in MMICs. Changes in the refractive index of the sensing layer cause predictable shifts in the position of the output image, which in turn affects the amount of light coupled into the output waveguide. Sensitivity enhancement has been demonstrated by fabricating longer MMICs capturing higher-ranking self-images, which are shifted more than the first self-image. Consequently, more significant changes in the amount of light coupled to the output are observed for a given refractive index change.
The second platform demonstrated is a Multi-Channel Directional Coupler sensor (MCDC). It differs from the MMIC in that the sensing
region now consists of multiple single-mode waveguides, which are in close enough proximity to allow light to transfer between the waveguides. Sensitivity dependance on platform length has been investigated and compared with that of the MMIC.
The devices have been fabricated by the direct laser writing process on UV curable hybrid sol-gel materials. Such materials allow
implementation of planar technology enabling integration on a silicon substrate. Future applications of these platforms include chemical and bio-chemical sensing is the areas of process, environmental and bio-diagnostic monitoring.
There is a clear need for low cost, high performance and large-scale production of photonic chips. Network development requires more interconnecting components. A flexible and low-cost process using good quality material is necessary.
The sol-gel process is a chemical method to fabricate glasses at ambient pressure and moderate temperature. The resulting material properties can be tuned depending on the precursors used. Hybrid materials, mixing organic and inorganic parts, offer the advantages of polymer-like materials and glasses.
We have developed sol-gel-processed integrated optical circuits using hybrid materials. We report on the development of active devices based on the thermo-optic effect. Thermo-optic coefficients as high as -2.10<sup>-4</sup>/°K have been measured in our materials. This enables the design of compact devices with low power consumption. Our goal is to utilise the thermo-optic effect in the development of integrated optical switches. The kHz response time of such switches makes them unsuitable for modulation applications, but they can be used for network protection, reconfiguration purposes in routing and multiplexing applications such as Code Division Multiplexing. New designs, based on multimode interference couplers (MMIC), have also been created.
In this work we first describe the synthesis of the hybrid materials as well as the fabrication processes. Using the measured properties of the materials developed, we can simulate the optical and thermal properties of the target devices. The simulation results have been exploited to model and optimise a range of switch designs, including MMI-based 1xN switches. Finally, we report on the full characterisation of the different structures and devices created in terms of fabrication quality and optical and thermal response.
The detection and measurement of vapour-phase or liquid-phase water is important in many industrial and chemical processes. Water exhibits strong absorption bands compared to other substances in the near infrared (NIR), and for this reason NIR spectroscopy is especially well suited to moisture determination. A lack of suitable sources in the NIR, however, has impeded the application of optical sensors to water detection. We have developed a modulatable IR source for use in a moisture sensor. In the system, the luminescent emission from optically pumped rare earth doped glasses is used. Thulium doped zirconium fluoride glass, which luminesces at 1.83 mm was the material chosen. The spectral overlap with the water absorption band is significant, and the output stability matches that of the pump source, which is typically an internally modulated diode laser emitting at 685nm. The detection system uses a reference beam and a probe beam to monitor changes in absorption due to moisture or water vapour. Results illustrating the effectiveness of the novel IR source in a sensor platform to measure trace amounts of liquid water and water vapor will be presented.
Planar lightwave circuits (PLCs) made from photo-patternable sol-gel materials are attracting considerable R&D interest. This is due to the advantages they offer for applications in optical telecommunications and their compatibility with existing silicon technology process equipment. In particular, the ability to produce devices compatible with silica optical fibres using a straightforward, environmentally friendly, photolithographic process is very attractive. The approach is now well-established in the literature and typically involves the incorporation of an acrylate moiety in the sol-gel precursor mixture, thereby providing a photo-polymerisability function. In this work, we report on the fabrication of passive optical components and devices designed for datacomms applications using visible diode lasers or the 1st telecom window. Silica-based sol-gel waveguides have been integrated in an opto-electronic multichip module (OE-MCM) demonstrator for optical interconnect applications. We have fabricated an 8-channel transmitter module for parallel optical interconnects (POI) based on 2 sub-modules: (a) an optical interface sub-assembly based on photo-patterned sol-gel optical waveguides, and (b) an optoelectronic component sub-module comprising an array of VCSELs. We describe here the fabrication, characterization and performance of the optical components and a POI Transmitter chip.
An optical sensor system, which provides real-time process information during the curing of DVD adhesive within the DVD manufacturing process, is reported. Incomplete or non-uniform curing of the adhesive in the centre of the disk can cause variation in layer thickness or create stresses, which may cause warping of the disk. The monitoring of adhesive cure is then of vital importance to manufacturers, particularly if this can be achieved in situ and within the production cycle time for disk manufacture. The operating principle of the sensor is the detection of changes in the infrared absorption spectrum of the adhesive as it cures. The use of infrared absorption in itself is not straightforward as the adhesive is sandwiched between two polycarbonate disks. One of these disks is completely opaque throughout the infrared due to the aluminium layer deposited on it and the other disk has a semi-reflective layer of a material such as silicon, gold or silver. The sensor employs a reflectance based interrogation technique, which uses the highly reflective aluminium coated surface of the DVD. The work described here deals principally with (i) definition of the specifications of the sensor system and the measurement methodology, (ii) development and optimization of a laboratory prototype sensor and (iii) design of an industrial prototype system. Results are presented from both prototype systems.
The development of a novel Teflon-coated optical fiber sensor for chlorinated organic determination and a PVC- coated sensor for pesticide determination is described. Current analytical techniques for these compounds in water are not suited to in-situ or on-site measurements. As a result, straight-forward techniques that feature a short analysis time, sufficient selectivity and adequate sensitivity are in high demand. An infrared fiber optic sensor which operates in the 4 to 16 micrometer wavelength region has been developed for the in-situ monitoring of chlorinated hydrocarbons and pesticides in water. The sensing element consists of a silver halide (AgCl<SUB>x</SUB>Br<SUB>1- x</SUB>) optical fiber, coated with Teflon or poly (vinyl chloride) (PVC) which enriches the analyte in the evanescent wave region of the fiber. Enrichment of the analytes occurs in the minute range and is reversible. Using trichloroethylene (TCE) and alachlor as representative pollutants, evanescent wave spectrometry in the mid-infrared (MIR) region is shown to provide good performance down to single ppm levels. Absorbance data were recorded at 938 cm<SUP>-1</SUP> and 1104 cm<SUP>-1</SUP> for TCE and alachlor respectively. Furthermore, it is shown that the technique can be applied to multi-analyte samples.