Waveguide grating devices. One includes at least one waveguide having an end, the end having an endface; and a waveguide grating fabricated on the endface, the waveguide grating having at least one waveguide layer and at least one grating layer. The waveguide layer is a separate waveguide from the waveguide on which the waveguide grating is fabricated. Systems for spectral filtering. One, which utilizes a guided-mode resonance effect in a waveguide, includes at least one waveguide having a proximal end and a distal end having an endface; and a waveguide grating fabricated on the end of the waveguide and having a plurality of variable parameters such as permittivity of the grating layer(s) and permittivity of the waveguide layer(s). Methods of forming waveguide grating devices, and methods of detecting one or more parameters of a medium using a waveguide grating device are also disclosed.