Vendors {disclaimer: non-incentivized list}
Optics: Thorlabs, Newport, Edmund Optics, Eksmaoptics, OptoSigma
Gratings: Wasatch, Ibsen, Richardson, Lightsmyth
Fiber: Ozoptics
Nonlinear crystals: Covesion
Mechanical: McMasterCarr
Electrical: Digikey
Free online calculators
Outside reading / literature
E&M lectures & discussions by Prof Mansuripur; by Prof Kaplunovsky; UIUC Physics Van
Free online tutorial on optics basics by Ansys; Webinars on polarization.
FDTD online book by Dr. Schneider
Beyond science readings