Compact spectrometers fabricated by placing a wedged etalon or a linear variable filter in front of a linear photodiode array typically do not exhibit the spectral resolution of a parallel filter of the same finesse. A theoretical analysis of the beam emerging from a wedged etalon is shown to predict a comalike aberration, explaining the loss in resolution. This analysis also predicts a focused beam waist whose axial position depends on the incidence angle, indicating that resolution can be improved by placing this waist on the detector. These results are experimentally confirmed in a multicavity linear variable filter to achieve 0.09 nm spectral resolution at 1550 nm.
© 2005 Optical Society of America
(060.4510) Fiber optics and optical communications : Optical communications
(070.2580) Fourier optics and signal processing : Paraxial wave optics
(300.6190) Spectroscopy : Spectrometers
(310.6860) Thin films : Thin films, optical properties
Robert R. McLeod and Tokuyuki Honda, "Improving the spectral resolution of wedged etalons and linear variable filters with incidence angle," Opt. Lett. 30, 2647-2649 (2005)