We describe the synthesis of optical quality thin film materials with high refractive index, employing zirconium based
hybrid sol-gel precursors. As the zirconium propoxide precursor is unstable in the presence of a strong nucleophilic agent
such as water, two synthesis routes have been performed employing a chelating agent and an organosilane precursor to
avoid the formation of any undesired ZrO2 agglomerates, leading to organo-zirconate complexes and silicato-zirconate
copolymers, respectively. The prepared hybrid sol-gel materials were deposited by spin-coating to form a transparent
thin film on silicon substrates, and heat treated at 100 °C for the final stabilisation of the layer.
The effect of the two synthesis routes on the optical properties of zirconium based hybrid sol-gel material is discussed. It
was found that the nature and concentration of the organosilane precursor can significantly affect the structural properties
of the deposited films. A correlation was also demonstrated between the concentration of the organosilane precursor and
the refractive index of the material. By reducing the concentration of organosilane precursor, high refractive index
materials were obtained. Similar behaviour was observed for the materials synthesised via chelating agent. The synthesis
employing an organosilane precursor produces films with higher refractive index. A maximum refractive index of 1.746
was measured at 635nm for the deposited thin films.
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 -2.10-4/°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.