Diffractive detector & Multi frequency phasor

[txdai]

This pull request introduces significant updates to the fdtdx package, specifically enhancing the functionality of the diffractive and phasor detectors. The changes include the addition of a new DiffractiveDetector class and modifications to the PhasorDetector class to support multiple frequencies. Also, the "wavelength" parameter is changed to "frequency" due to wavelength being variable in mediums.

New Features:

• Diffractive Detector:
  • Introduced a new DiffractiveDetector class for computing Fourier transforms of fields at specific frequencies and diffraction orders. This detector can measure diffraction in either positive or negative direction along the propagation axis.

Enhancements to Existing Features:

• Phasor Detector:
  • Added support for analyzing multiple frequencies by introducing a frequencies attribute. This allows the PhasorDetector to compute phasor representations at specified frequencies, enabling more detailed frequency-domain analysis.
  • Removed the wavelength attribute and the frequency property, replacing them with precomputed angular frequencies for vectorized calculations. This simplifies the phasor computation process.
  • Updated the _shape_dtype_single_time_step method to account for the new frequencies attribute, ensuring the shape includes the number of frequencies.
  • Modified the update method to handle multiple frequencies, performing vectorized calculations for phasors at each frequency. This includes changes to the computation of phase angles and the application of complex exponentials. [1] [2] [3]