The subject of this project is the design; analysis, fabrication and characterisation of first order Bragg
Grating optical filters in Silicon-on-Insulator (SOI) planar waveguides. It is envisaged that this work will
result in the possibility of Bragg Grating filters for use in Silicon Photonics. It is the purpose of the work to
create as far as is possible flat surface waveguides so as to facilitate Thermo-Optic tuning and also the
incorporation into rib-waveguide Silicon Photonics.
The spectral response of the shallow Bragg Gratings was modelled using Coupled Mode Theory (CMT) by way of RSoft Gratingmod TM. Also the effect of having a Bragg Grating with alternate layers of refractive index of 1.5 and 3.5 was simulated in order to verify that Silica and Silicon layered Bragg Gratings could be viable. A series of Bragg Gratings were patterned on 1.5 micron SOI at Philips in Eindhoven, Holland to investigate the variation of grating parameters with a) the period of the gratings b) the mark to space ratio of the gratings and c) the length of the region converted to Bragg Gratings (i.e. the number of grating period repetitions).
One set of gratings were thermally oxidised at Philips in Eindhoven and another set were ion implanted with Oxygen ions at the Ion Beam Facility, University of Surrey, England. The gratings were tested and found to give transmission minima at approximately 1540 nanometres and both methods of creating flat surfaces were found to give similar minima. Atomic Force Microscopy was applied to the grating area of the as-implanted samples in the Advanced Technology Institute, University of Surrey, which were found to have surface undulations in the order of 60 nanometres.
The field of Silicon Photonics has gained a significant amount of momentum in recent years. Announcements of high
speed modulators and cost-efficient light sources in the Silicon-on-insulator material system have helped to make Silicon
Photonics a viable contender as a low-cost active photonic platform. As a pioneer in the field, the University of Surrey
continues to investigate the prospects of silicon photonics. Herein we present a summary of our work on several key
areas such as ion implanted grating devices, high-speed modulators, switches and ring resonators. We conclude with a
discussion on an advanced fabrication technique, proton beam writing.
In this paper we report two novel fabrication techniques for silicon photonic circuits and devices. The techniques are
sufficiently flexible to enable waveguides and devices to be developed for telecommunications wavelengths or indeed
other wavelength ranges due to the inherent high resolution of the fabrication tools. Therefore the techniques are
suitable for a wide range of applications. In the paper we discuss the outline fabrication processes, and discuss how they
compare to conventional processing. We compare ease of fabrication, as well as the quality of the devices produced in
preliminary experimental fabrication results. We also discuss preliminary optical results from fabricated waveguide
devices, as measured by conventional means. In these preliminary results we discuss fundamental properties of the
waveguides such as loss and spectral characteristics, as it is these fundamental characteristics that will determine the
viability of the techniques. Issues such as the origins of the loss are discussed in general terms, as resulting fabrication
characteristics such as waveguide surface roughness (and hence loss), or waveguide profile and dimensions may be
traded off against cost of production for some applications. We also propose further work that will help to establish the
potential of the technique for future applications.