Performance...
The performance parameters consist mainly of the choice of the quantities and scales of the axes in the performance plots that are to be produced. One or two Y axes may be defined. Tables will use the same parameters and range of independent variable and just the independent variable interval for the tables needs to be separately specified. The content of the table will be defined by the performance requested in the Vertical Axis tab.
A typical dialog box for entry of the performance parameters is shown below and is reasonably self-explanatory. Items not available for the particular choice of dependent quantity are gray and cannot be accessed. The parameters described here only apply to designs that consist solely of thin layers. When a design includes one or more thick layers , a modified performance parameters dialog is shown. This dialog excludes the phase related options, but adds cone and bandwidth calculation options.
The package computes the response, the dependent variable, in terms of a variable parameter, the independent variable. Except for a very few special cases, throughout the package the vertical axis in the plots corresponds to the dependent variable while the horizontal axis corresponds to the independent variable.
The dependent variable, the performance, may be chosen from the scrolling list under Vertical Axis. This list comprises
Transmittance Magnitude (%) Reflectance Magnitude (%) Transmittance Phase (deg) Reflectance Phase (deg) Density
Absorptance (%) Reflectance GD (fs) Reflectance GDD (fs^2) Reflectance TOD (fs^3) Transmittance GD (fs) Transmittance GDD (fs^2) Transmittance TOD (fs^3) Transmittance Delta (deg) Transmittance Psi (deg) Reflectance Delta (deg) Reflectance Psi (deg) Transmittance CDC (fs/nm) Reflectance CDC (fs/nm) Transmittance PM Reflectance PM
The phase parameters may be calculated in two ways depending on whether Unwrap Phase is checked or not. If Unwrap Phase is checked, the phase values will not be constrained to a principal angle range but allowed to continuously increase (or decrease) beyond the principal angle limits. If Unwrap Phase is not checked, the phase values will be constrained to the principal angle range. For example if the Phase limits have been set to –180 to +180 degrees and Unwrap Phase is checked, the resultant value of a phase calculated as –179 degrees where the previous value is +179 degrees will be 181 degrees.
This form of phase plot will show the phase characteristic as a continuous line, whereas the wrapped form will have discontinuities where the phase crosses the principal angle boundaries.
GD indicates Group Delay, GDD, Group Delay Dispersion and TOD is Third Order Dispersion. These quantities are important in components for ultrafast applications and are directly related to the derivatives of phase shift with respect to the angular frequency of the light.
CDC indicates Chromatic Dispersion Coefficient. This quantity is similar to Group Delay Dispersion in that it indicates pulse spreading. It is more commonly used in the communications field.
PM indicates Polarization Maintenance. This parameter calculates how much the coating changes the polarization state of the incident beam. Polarization maintenance is typically measured by placing a polarizer in the incident beam aligned at 45° to the p and s-directions, and an analyzer in the emergent beam. The analyzer is first aligned parallel to the input polarization to give the signal irradiance and then orthogonal to it to give the leakage irradiance. The irradiance in the signal orientation divided by the sum of the irradiances, expressed as a percentage, is the measure of polarization maintenance.
Derivatives with respect to wavelength of those quantities that are not already derivatives can be specified by entering the appropriate derivative order in the derivative field. For example, the first derivative can be specified by entering unity in the box.
Please note the comments under Derivatives in the Essential Macleod earlier in this manual.
The independent variable is specified in a similar scrolling list under Horizontal Axis.
There are essentially four different types of independent variable, wavelength, frequency, incident angle and layer thickness. The actual terms displayed in the scrolling list follow the names that have been entered in the General Units dialog box.
The thickness of a chosen layer may be used as the independent variable. This is immediately applicable to the case of an etalon with variable spacer layer but there are often cases where the sensitivity of performance to variations in the thickness of a particular layer are in question.
Plots and tables using the current values of the parameters can always be initiated from the Performance menu. However, the Performance Parameters dialog box gives immediate access to either plots or tables without the necessity of returning to the menu.
If the OK button is chosen then the only immediate action taken will be to change the current values of the parameters to those entered so that they will then be used by the plot and table commands in the Performance menu. They will not be stored permanently in the design file until it is actually saved.
To aid in identifying traces on a plot, plot parameters may be automatically added to the plot legend by checking the Add to Label box next to each parameter. If the Plot Targets box is checked, then the targets will be added to the plot if the performance type of the targets matches the performance specification of the plot.
Refinement
Choosing Refinement in the Parameters menu brings up a submenu that gives access to the various parameters that must be set before effective refinement and synthesis is
possible. There are two aspects of the parameters that need definition. First there are the specifications of the desired performance levels. These are called Targets and they are common to all the various techniques. Then there are various attributes that must be set correctly for the particular technique that is to be used. The principal technique in the Essential Macleod is Optimac, a powerful synthesis method that can also carry out refinement. Five further refinement techniques are Nonlinear Simplex, called nonlinear to distinguish it from a similarly named but different technique used in the solution of linear equations, a statistical method known as Simulated Annealing, two derivative methods:
Conjugate Gradient and Quasi-Newton and an evolutionary method: Differential Evolution. Additionally, the Needle synthesis method is available for generating designs.
Refinement and synthesis are discussed in a later dedicated section.
3D Performance...
The 3D performance parameters consist mainly of the choice of the quantities and scales of the axes in the 3D performance plots that are to be produced. A typical dialog box for entry of the 3D performance parameters is shown below and is reasonably self-explanatory. Items not available for the particular choice of dependent quantity are gray and cannot be accessed.
The package computes the response, the dependent variable, in terms of two variable parameters, x and y.
The dependent variable, the performance, may be chosen from the scrolling list under Z Axis. This list is the same as in the Vertical Axis in the Performance Parameters dialog.
The independent variables are specified in similar scrolling lists under X & Y Axes.
There are essentially four different types of independent variable, wavelength, frequency, incident angle and layer thickness. The actual terms displayed in the scrolling lists follow the names that have been entered in the General Units dialog box.
The thickness of a chosen layer may be used as the independent variable. This is immediately applicable to the case of an etalon with variable spacer layer but there are often cases where the sensitivity of performance to variations in the thickness of a particular layer are in question.
The surface computed in a 3D plot is calculated at a fixed number of equally spaced points in the x and y directions. The Number of Intervals parameter specifies then number of points calculated.
3D Plots using the current values of the parameters can always be initiated from the Performance menu. However, the 3D Performance Parameters dialog box gives immediate access to a plot without the necessity of returning to the menu. If the OK button is chosen then the only immediate action taken will be to change the current values of the parameters to those entered so that they will then be used by the 3D plot command in the Performance menu. They will not be stored permanently in the design file until it is actually saved.