| In optical communications, tunable filters play a crucial role of optical channel/wavelength selection, and reassignment, optical routing, optical switching, and network reconfiguration while in spectroscopy they can be used as wavelength scanners. In the investigation reported here an optical tunable filter based on grating assisted asymmetric waveguide coupling is developed at the communication wavelength of 1550nm and the filter's figures of merit measured to determine its viability in either optical communications systems or spectroscopic systems. Tuning of the optical filter is achieved by thermally varying the refractive index of the waveguide core material. The thermally sensitive polymer NOA61 is used as the waveguide core material. Based on this core material, the device structure is simulated and optimized using Beamprop software. Optical filters are then fabricated using standard photo-lithography techniques on GaAs wafers. Geometrical optics is used to couple light into the waveguide and the output at the other end of waveguide is observed using an IR camera. Once light is propagating through waveguide, a voltage is applied to waveguide device which heats the structure and causes a thermally varying refractive index in the material. This results in a change in the output power of device. The variation of optical power with changes in applied voltage is measured and the experimental results are compared with simulation results. Simulations suggest than a tuning bandwidth of over 50 nm can be achieved by tuning the input voltage from 0--3V. |
