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Photonic Crystals

The following files were developed to generate relatively simple periodic patterns for metallo-dielectric infrared photonic crystal filter fabrication. Photonic crystals are formed by periodic variation in optical properties. As part of my Ph.D. research, I investigated the infrared properties of periodic structures of metal in a dielectric (non-conducting) matrix.

Initially, I attempted to use the MAGIC CAD application. However, it was not easy to generate, for example, large numbers of circles arranged in honeycombs, or giant meshes. Also, the conversion to Calma GDS-II stream format was extremely slow, and did not take advantage of the periodicity to create compact files.

GDS-II is a binary format, and has a non-IEEE format for floating point numbers. It was particularly fun to use Lisp's excellent support for bit-twiddling to support this.

The major thrust of the development created a CLOS model for geometries representable in the MAGIC CAD program, or in terms of the MAGIC primitive rectangles. I started to develop a CLOS model of the Calma geometric model, but decided to simply emit Calma equivalents for my MAGIC-compatible models, with a CLOS representation of the Calma file format. Most probably because the only tool I had to look at the results was MAGIC, and the Calma documentation I had was limited, so I could only verify those parts that MAGIC would understand.

Component files

• magic-cad.lisp The basic objects and geometric primitives
• mesh.lisp A cross shape, which can be replicated to generate square mesh screens
• align.lisp An alignment mark that fits around a cross. The idea is that successive layers of metal would be fabricated at fixed offsets; these alignment marks would allow the mask to be aligned at an offset with respect to a cross fabricated in the layer below.
• fcc.lisp generate fcc layers (honeycomb lattices) repeating a primitive subcell.
• ident.lisp Code to create shapes of digits. This code got a little macro-happy; essentially I developed a domain-specific language representing scalable series of strokes as lists of numbers. MARK-IDENT-NUMBER prints a decimal integer out of these shapes.
• calma.lisp Basic CLOS objects to represent the Calma GDS-II binary stream format.
• calma-file.lisp Utility routines to write the Calma GDS-II binary format. Includes a dilemma regarding a Y2K bug, for nostalgia, with multiple options for survival in the aftermath.
• calma-float.lisp Routines to translate Lisp floats to and from the Calma format. This is probably my favorite bit of this project.
• calma-cad.lisp The methods for dumping MAGIC CLOS objects into Calma stream format.

Example Files

• circ.lisp Sample code to make small arrays of circles in a MAGIC file.
• mask.lisp Code actually used to generate photomasks in MAGIC format.
• calma-mask.lisp Code actually used to generate photomasks in GDS-II stream format.

Comments

As far as code goes, this is probably somewhat immature. It lacks package discipline. Also, as some of the comments indicate, I was just learning how CLOS worked. I clearly did not understand when to use PRINT-UNREADABLE-OBJECT.

I'm very sure some version of this code was used in real photomask development. I can't piece together without digging up my lab notebook, whether I allowed MAGIC to translate the magic-cad version over a couple days runtime, or whether I went direct to GDS-II format with the Calma versions, although it appears I did testing to make sure I could replicate the result of the MAGIC translation. Note also my tendency to put useful tests inside #| |# comment brackets, instead of making a test suite.