We show how scalar diffraction theory can be used to quantitatively ev
aluate insertion losses in integrated optic spectrometers based on pla
nar waveguide and etched grating technologies. This approach is applie
d to optimize the loss-limited spectral operating range of these devic
es. We also show how limitations in the photolithographic process used
for grating definition can result in appreciable spectrometer inserti
on losses.