See also: What's new in Optilayer.

A New Automated Feature
for the Design of WDM Filtres

The new feature combines the most useful classical results related to the design of WDM filters with the specific integer programming optimization approach. Available theoretical knowledge is utilized in the form of an interactive dialog which enables the user to specify a filter prototype. Behind this dialog are such things as equivalent layers, Chebyshev and maximally flat filters, some other results of the microwave theory, etc. The user however, isn't required to know anything about all these powerful theoretical results. A filter prototype is specified in a few seconds, after that an optimization is started. In another few seconds, or may be minutes, the final design is obtained. Optical thicknesses of all its layers but last one of two are integers of a quarter-wave at the central wavelength of the filter. The final design transmittance meets the initially specified requirements on the filter bandwidth and shape factor and has an excellent flatness at a high transmission region.             

Design Examples

Plots bellow present transmittances of several filter designs with the central wavelength of 1550 nm, 0.8 nm bandwidth at a 50% transmittance level, and blocking better than 30 dB  outside the 1.6 nm bandwidth wavelength region. Designs differ in the total number of layers, spacer orders, and number of filter cavities. The high and low refractive index values are taken equal to 2.2 and 1.45, while the substrate and ambient refractive indices are 1.52 and 1.00, respectively.

Automatic approach to the WDM filter monitoring.   

A new entirely automatic approach to the WDM filter monitoring has been developed. It is based on a single wavelength optical monitoring at the central filter wavelength. From a physical point of view this approach is based on a well known effect of selfcompensation of filter thickness errors. This effect enables maintaining filter transmittance properties even with individual layer thickness errors up to several percents. Mathematical ideas of the new approach are based on the results of the regularization theory (the theory of ill-posed inverse problems).  

Simulated deposition runs have been used to test both potentialities of the automatic monitoring approach and the manufacturability of WDM filter designs obtained with the new OptiLayer WDM design option. During the simulated deposition runs, errors in layer thicknesses are not introduced intentionally but originate from simulated actual error sources. Currently the instability of deposition rates, random and systematic noises in measured transmittance data are simulated. Other sources of errors, like the divergency of the test light beam or its non-monochromacity can be easily simulated as well. Figures below present typical plots of the layer deposition rate and measured transmittance data with systematic and random noises.

Next figure shows typical values of layer optical thicknesses obtained during the simulated deposition runs (QWOT Dep (1) and QWOT Dep (2) columns ) as compared to theoretical thickness values (QWOT Theor. column).

Inspite of relatively high individual thickness errors the automatic monitoring approach maintains an excellent correspondence between the final transmittance of deposited folder and theoretical transmittance. This is demonstrated by the following figure.