Performances of a tunable birefringent filter for high density multi-wavelength applications
Résumé
We propose the use of an alternative technology to implement the optical filters dedicated for high density multi-wavelength applications: the Polarization Interference Filters (PIFs) and particularly the Lyot filters, which constitute a very interesting solution owing to their simplicity. To reach the optical network application requirements, in term of contrast, FWHM, and equalization function, we introduce a modified Lyot filter. The proposed device is a simple N-interferometer Lyot filter placed between two mirrors, to let the light beam pass through the structure back and forth. Two other interferometers, similar to the first Lyot filter interferometer, are added at the input of the filter, before the mirror. Each interferometer is composed by a retarder (calcite birefringent plate) held between two parallel polarizers. Each retarder is associated to a Liquid Crystal Cell (LCC), dedicated to the tuning function. The adequate contrast and FWHM of optical networks are attained by let the light beam passes through the filter several time and choosing judiciously the opto-geometrical characteristics of the retarders and the LCCs, respectively. The final simulation results of the filter, in the C-band (1530-1565nm), are 79,59dB and 0,84nm for the contrast and the FWHM, respectively. The equalization function is achieved continuously by changing the central-wavelength of the two additional interferometers, for continuous values of the LCCs birefringence. The dynamic is between 0 and 57,32dB (normalized values)