Optical-dispersion-relations

Added

* Transcendential equations for trilayer plasmonic dispersion relations:
* `transcendential_trilayer_even_magnetic_field`
* `transcendential_trilayer_odd_magnetic_field`

Changed

* BREAKING: Change DrudeLorentz default plasma frequency to 1.
* BREAKING: Change function names and parameter orders:
* `metal_insulator_metal_collin_approximation` -> `metal_dielectric_metal_collin_approximation`
* `metal_insulator_metal_sondergaard_narrow_approximation` -> `metal_dielectric_metal_sondergaard_narrow_approximation`

Fixed

* DrudeLorentz doc permittivity return type.

Added

* `wavelength_to_wavenumber` utility function.
* `dielectric_waveguide` module function parameter and return types.
* `DrudeLorentz` class for building Drude-Lorentz dispersion relations.

Changed

* BREAKING: Change polarisation to lowercase in transendential slab waveguide functions:
* `transcendential_slab_waveguide_te`
* `transcendential_slab_waveguide_tm`

Fixed

* `lorentz_oscillator` return type.

Fixed

* Enable dielectric waveguides to handle negative numbers internally.

Added

* Transcendential equation for TE and TM slab waveguides.
* Example figures and scripts under `./examples`

Fixed

* Documentation format to match numpy.
* Documentation for:
* `metal_insulator_metal_collin_approximation`
* `metal_insulator_metal_sondergaard_narrow_approximation`

Added

* Single pole Drude-Lorentz permittivity.
* Double pole Drude-Lorentz permittivity.
* Surface plasmon polariton dispersion relation.
* Metal-insulator-metal dispersion approximations from
* [Waveguiding in nanoscale metallic apertures](https://doi.org/10.1364/OE.15.004310)
* [General properties of slow-plasmon resonant nanostructures: nano-antennas and resonators](https://doi.org/10.1364/OE.15.010869)
* Utilities:
* permittivity to extinction coefficient.
* permittivity to refractive index.
* refractive index to permittivity.

Changed

* [src-layout](https://setuptools.pypa.io/en/latest/userguide/package_discovery.html#src-layout) package directory structure.