Miniature fiber optic spectrometer: response functions and bandpasses

Abstract

Response functions and bandpasses of a miniature fiber optic spectrometer with three read fibers of different core diameters are measured both interferometrically and directly. In interferometrically measured response functions and bandpasses, timedomain and spectral-domain interference oftwo light beams from a laser diode TOLD 9140 operated below the threshold is utilized. It is revealed, in accordance with the theory, that the visibility function for the spatial interference fringes measured in the Michelson interferometer configuration with a broadband detector consists of a Gaussian central peak whose width gives the source spectral width. Similarly, it is revealed, in accordance with the theory, that the visibility functions for the spectral interference fringes measured in the Michelson interferometer configuration by the fiber optic spectrometer are the functions related to the spectrometer response functions whose widths give overall bandpasses. Subtracting the effect of the source spectral width, the spectral bandpasses of the fiber optic spectrometer are determined. In directly measured response functions and bandpasses, the delta-function spectrum of the same laser diode operated far above the threshold is utilized. It is revealed, in accordance with the theoretical assumptions, that the response functions are Gaussian functions. These are compared with the interferometrically measured bandpasses confirming good agreement.