Photonic band structure devices may be incorporated in a range of different optical systems to provide optical signal processing. In particular, photonic band structures incorporated in planar waveguide structures provide a range of functions in integrated optical circuitry or in telecommunications systems. This type of photonic band structure can also be used in other applications such as biosensors and optical data storage systems.
WO 98/53351 filed by BTG International Limited provides a detailed description for photonic band structures in planar waveguides. The photonic band structure is provided by a lattice of sub-regions embedded in a background region. Initially the sub-regions were simply holes etched into a dielectric waveguide. Developments in the field have led to the formation of sub-regions of one dielectric material being used in a background region of a different dielectric material. This is described in co-pending U.S. patent application Ser. No. 10/196,727, filed by Mesophotonics Limited.
The properties of the photonic band structure, i.e. the optical response, determines its usefulness for a particular function. The photonic band structure is dependent on a number of independent factors, such as the geometry of the array of sub-regions, the geometry of each sub-region and the materials used. Photonic band structures can be designed so that bandgaps or band edges occur at particular wavelengths, but often these structures suffer from undesirable properties away from a particular wavelength for which it was designed. In particular, for a finite length of photonic band structure, Fabry-Perot resonances can form close to the band edges.
For devices for use in systems carrying multiple wavelengths or switching devices using a change in the photonic band structure this can lead to a severe loss of performance.
The present invention aims to provide a more flexible photonic band structure which can be tailored to meet the demands of a particular optical application.