The Edit menu helps in the editing of designs by cutting layers, copying them, copying parts of designs and so on. It also permits the entry of a design from a formula and the changing of the way in which layers are displayed. Some parameters that are used in refinement can also be set or canceled from this menu. Note particularly that the commands in this menu cannot be undone. Save the design before major editing!
Cut Layers
Layers that are selected in an active design window are cut out and placed on the clipboard. From there they can be pasted into another design, into a different part of the same design, or pasted into a text document for editing by a word processor. In fact the clipboard is the normal vehicle for importing or exporting data to or from the program.
A word about selecting layers is necessary. To select a range of layers, first select one of the layers at the extreme end of the range. Then move the cursor to the selection box for the layer at the other end of the range and press <Shift> this time while clicking in the box for the second time. The entire range of layers between the two limits will now be selected. To deselect a layer or range of layers, first select one of the boxes belonging to one of the selected layers. Then click once in the box and all layers will be deselected. It is sometimes useful to be able to select layers that are not contiguous. To select an additional layer that is separated from the others press <Ctrl> while clicking in the selection box.
Copy Design
This command will copy an entire design and place it on the clipboard.
Copy Layers
This command is similar to the Cut Layers command except that the layers are not removed but only copied.
Copy Thicknesses
This command copies the entire set of layer thicknesses from the design and places them on the clipboard. The thickness convention (optical, geometric, physical) is specified by selecting the convention from the sub-menu. The reason for this is to make systematic alteration of the thicknesses possible. It may be required, for example, to change the thicknesses gradually from one end of the design to the other to simulate, say, a gradual change in the pattern of distribution. This command extracts just the
thicknesses and a companion command, Paste Thicknesses will return them. Note that noncontiguous layers can be selected for copying and pasting. Press <Ctrl> when clicking in the selection box to select a noncontiguous layer.
Paste Design
This command pastes a design from the clipboard into a selected design window or selected design icon. The design may have been copied from another design file. The format of the design on the clipboard will then be a private format that exactly corresponds to the new design window and the pasting operation will proceed automatically and accurately. The pasted design will replace completely the existing design.
The Paste Design command may be used, however, to paste a design imported from elsewhere. A typical example is a design in text form in a text processor. The design should be in the form of tabulated data. Each row in the table corresponds to a layer in the design and each column in the table corresponds to a property of a layer such as thickness. The character used for delimiting columns is not important, it can be specified when the design data is imported. When the Paste Design command is activated the data import tool is displayed. Using this tool you specify the layout of the table by choosing the column delimiter and identifying the data contained in each column. At the end of this process, the data will be imported into the design editor. The section Importing Data on page 44 describes the use of the data import tool. After the table data has been imported, the materials used in the table need to be identified. A second dialog box will appear. In the example below, the copied design used materials numbered 1 and 2. They must now be translated into materials in the current database. The converted names may be typed in or the arrow at the end of the cell used to activate a drop down list for selection. Should the materials in the database not correspond to what is required the materials should be converted into different arbitrary, but existing, materials. This way the design can be imported. It is easy to change the materials later to those in a new database or to ones that have been added to the current database. See the Edit Materials... command below.
Paste Layers
This command pastes layers from the clipboard into an active design window. The layers are pasted into the design immediately before whichever layer has been selected, that is, has an active cell.
Paste Thicknesses
This command permits manipulations of layer thicknesses outside the package and adds flexibility to the design editor. It pastes a set of thicknesses from the clipboard into a design. The convention of the pasted thicknesses (optical, geometric, physical) is
specified by selecting the convention from the sub-menu.
Should the number of layer thicknesses to be pasted not correspond exactly with the number of layers in the design, then a dialog box will ask whether the updating process should continue. If continued then the thicknesses will be applied, in order, to the layers starting with layer 1 and stop when either the number of entries on the clipboard or the final layer of the design is reached.
The flexibility of the command can be increased if it is used along with other Edit Menu commands such as Copy Layers and Paste Layers. For example, create a temporary design as a holding area and paste thicknesses into it. Then use Copy Layers and Paste Layers to place the layers anywhere in the actual design.
Note that no information on the thickness convention is carried with the thickness values on the clipboard. Such information is, of course, included when Copy Layers and Paste Layers are used.
The format of the thicknesses on the clipboard must be correct and especially important is that there should be no final formatting character such as an end of line or paragraph marker. When copying them to the clipboard it is best to avoid including the line terminator for the final thickness. Place the cursor immediately after the last digit of the final thickness and drag to the start of the column to select it. If, when attempting to paste the thicknesses, a message: "The data on the clipboard are not suitable for updating the thicknesses of the layers" is displayed, it will usually mean that the copying to the clipboard has included some extra control characters and another attempt at selecting and copying will usually succeed. Note that some word processors do not place the data on the clipboard in a compatible format. If difficulty with such processors or other systems
is experienced then an intermediate step of pasting the contents into either Notepad or Wordpad and then recopying them to the clipboard will usually strip off the offending characters. Sometimes too, the command Paste Design will function when Paste Thicknesses fails. Since Paste Design with only one column of results will lose any material information that is present in the existing file, it is better to paste the layers first into a new, temporary design and then to use the copy commands to move them to the correct place.
Insert Layers...
A dialog box asks for the number of layers required. They are then inserted in the design immediately before the currently selected layer. The thickness of the inserted layers is zero and the material is nominal, usually Na3AlF6. Once the layers have been inserted they should be edited as required. Note that insertion of a small number of layers is most easily carried out by first making sure that the editor is in insert mode shown by Insert on the bar at the foot of the application window. If Overstrike is shown then press
<Ins> once to change it. Click anywhere in the layer before the place where the new layer is to be inserted. Press <Enter> repeatedly until the active cell becomes the last one in the row. The next press of <Enter> will create a new layer in the correct place.
Delete Layers...
This deletes a specified number of layers starting with the currently selected layer and working towards the substrate.
Reverse Layers
This could be the most important menu item in the package. The convention throughout the package for the order of layers in a design is is set by the user. In the default mode layer 1 is the layer next to the incident medium. In the Formula the layers run from incident medium at the left to substrate at the right (this is the same convention usually used in simple optical systems) unless this too has been specified. There is, no universal agreement on either direction or numbering arrangement. The difficulties are compounded because the convention is not always clearly stated and it is only when a design is calculated that it becomes obvious that the order is incorrect. It is quite possible, therefore, that a laboriously entered design might have been placed in the tables in reversed order. This menu item affords a simple remedy. Reverse Layers immediately reverses the order of the layers without altering the position of substrate and incident medium. If a contiguous set of layers is selected, then Reverse Layers will modify only those layers.
Reverse layers makes it straightforward to calculate back reflectance. The substrate and incident medium must be changed manually.
Reverse Design
Reverse Design reverses the order of the layers, swaps the substrate and incident medium and changes the incident angle
Formula
Formula permits designs to be set up or edited using shorthand notation and handles the definition of the symbols used. The shorthand notation is a particularly convenient way to enter layer data. The design is represented in terms of basic layers, of differing
materials, which are represented by symbols such as H, L, A, B, c, d etc. The Formula command does not differentiate between upper and lower case characters. The basic layer definition is given by the material, the layer thickness (either physical or optical), the packing density, lock and link specifications for refinement, the void material and the void material density, inhomogeneity factor, minimum and maximum physical thickness limits for refinement. Layer thicknesses other than the basic thickness are represented by multiples of the basic thickness, as in, for example, 2.5H or 0.4L (representing 2.5*0.25 = 0.625 full waves and 0.4*0.25 = 0.1 full waves respectively, if the basic thickness were 0.25). The symbols can be combined into a formula using a simple sequence as in A2LB2LA or repeated sequences can be included in brackets with an exponent or replication factor, e.g.
(HL)^6 3.4H2.1L or
((H1.2L2B)^2 HL)^3 (LBH)^2
Note the space between the exponent and what follows. If it is omitted the program will reject the formula. Multiplying factors outside brackets can be used. They will be applied to all layers inside the brackets. For example 2.3(HL)^3 would be interpreted as (2.3H 2.3L)^3 and 1.1(A 2.3(HL)) would be interpreted as 1.1A 2.53H 2.53L. The incident medium may either be at the left end or the right end of the formula and depends upon the setting specified in the Design tab of the General command in the Options menu. There are some keyboards where the caret symbol ^ is not readily available (German keyboards for example), and the asterisk, *, can be used as an alternative.
Brackets can be nested within brackets with almost no limit on depth.
Selection of the option brings up a dialog box for the entry of the basic layer
definitions. Any existing symbols are retained and presented first in the list. To delete an entry, select the symbol and press <Del>. Once the symbols have been defined, the formula can be entered in the Formula box. For clarity, the formula may be entered on more than one line to show, for example, structure in the design. Arrow keys or the scroll bars can be used to scroll to either end of the formula if it is too large to be displayed completely in the box. Select the OK button to replace the current design with the design given by the formula. Should there be an error in the syntax of the formula it will be flagged at this stage with an indication of the specific error. A corrected formula can then be entered.
The text box in which the formula is entered accepts the usual copy, cut and paste commands. These can also be used to transfer part or all of a formula to a different design.
Note that the interpretation of the entered formula does take account of the match angle. Match angle is described below. If Formula… ever appears to be operating in a curious way, check the match angle option to make sure it has not been set inadvertently to an incorrect angle.
Generate Rugate…
This command allows you to easily generate models of rugate coatings. The continuously varying refractive index of a rugate coating is modeled by a sufficiently large number of layers with a discretely varying refractive index. The variation in refractive index is achieved by varying the packing density of each layer. The Generate Rugate command allows you to easily specify the index variation and control the number of layers that are used to model the rugate structure. See the section “Modeling Rugate a Coating” below (page 102) for more information on modeling rugate coatings.
Generate Design…
This command allows you to generate more complex designs than can be produced by the Formula command. For example, chirped reflector models may be produced using this command. See the section “Generating Complex Designs” below for more information.
Scale Thicknesses...
Occasionally layers of a particular material or that have the same link number should have their thicknesses changed in the same way. This would happen most commonly in reverse engineering when investigating the effects of lack of uniformity but there are also times when slight adjustments must be made to the width of a pass or stop band. It is also sometimes necessary to retain the value of a particular reference wavelength but to change all layer thicknesses in the same ratio so that the characteristic is shifted but otherwise essentially unchanged. The Scale Thicknesses... command makes all this particularly easy.
The dialog box that appears will show either the materials that are used in the design, or the links that are used. Click on the Materials tab to show the materials or click on the Links tab to show the links used. The scale factor that is entered applies to all selected
materials when the OK button is clicked and the Materials list is visible. If the Links list is visible, then the scale factor is applied to the layers with the selected link numbers.
Note that the changes cannot be undone except by entering an inverse canceling scale factor.
Match Angle...
All the parameters listed in the design table and the output of the Formula... command assume normal incidence. But whenever a multilayer is tilted, the phase thicknesses of the layers vary with the cosine of the angle of incidence in the layer and this effect is responsible for the shift in the characteristic towards shorter wavelengths. A coating that is actually to be used at oblique incidence should have the thicknesses of the layers adjusted accordingly. The lower the refractive index of the material the greater is the necessary adjustment. Layers that have been corrected for a particular angle of incidence are said to be matched for that angle. The Match Angle... menu item makes the
calculations and adjustments automatically.
Metals and dielectrics behave differently, although the same fundamental principles are involved. High performance metals, because they have very low refractive index and high extinction coefficient, do not exhibit the appreciable shift of dielectrics and should not be corrected. In order to classify materials either as metals or dielectrics an arbitrary dividing line uses a preset level of extinction coefficient. This level is normally unity but can be changed by the user. If the actual extinction coefficient is higher than the limit, then the material is classed as a metal and no correction is made. If the extinction coefficient is lower, then the dielectric correction is implemented.
Note that the correction changes the normal incidence thickness to correct the behavior at oblique. The design table values still apply to normal incidence. Any pasting operation ignores the match angle. Formula..., however, does recognize the match angle and does correct layers accordingly. If Formula… ever appears to be operating in a curious way, check the match angle option to make sure it has not been set to an incorrect angle.
Changing the match angle is straightforward. The new value is entered in the dialog box. The operation first returns the layers to normal incidence and then applies the new angle. The current match angle can always be found by selecting the match angle menu item and looking at the displayed value.
Global Edit…
This command changes either all layers in the design or selected layers only, if at least one layer has been selected to values entered on the Global Edit form.
If a value is entered into one of the fields, then the layers will be updated with the new value. If the field is left blank, then the value held in the layer will be not altered. For the layer parameter limits fields, there is the additional option of specifying that the entered value is a scale factor. When Scale Factor is checked, the value entered into the appropriate limit cell in the Design will be the product of the scale factor and the corresponding layer parameter. For example, if a Minimum Physical Layer Thickness of 0.95 is entered and Scale Factor is checked, the minimum physical thickness of each layer will be set to 0.95 * the layer’s physical thickness. This makes it easy, for example, to set thickness limits as a percentage of the current layer thickness. Click on OK to cause any changes to be made. Clicking on Cancel causes the edit operation to be aborted. In the example the material of the layers will be changed to MgF2, the packing density will be set to unity and the void density will be set to zero.
If a value is entered into one of the fields, then the layers will be updated with the new value. If the field is left blank, then the value held in the layer will be not altered. For the layer parameter limits fields, there is the additional option of specifying that the entered value is a scale factor. When Scale Factor is checked, the value entered into the appropriate limit cell in the Design will be the product of the scale factor and the corresponding layer parameter. For example, if a Minimum Physical Layer Thickness of 0.95 is entered and Scale Factor is checked, the minimum physical thickness of each layer will be set to 0.95 * the layer’s physical thickness. This makes it easy, for example, to set thickness limits as a percentage of the current layer thickness. Click on OK to cause any changes to be made. Clicking on Cancel causes the edit operation to be aborted. In the example the material of the layers will be changed to MgF2, the packing density will be set to unity and the void density will be set to zero.