  We experimentally demonstrate an all-fiber spectrometer consisting of a
photonic bandgap fiber bundle and a black and white CCD camera. Photonic
crystal fibers used in this work are the large solid core all-plastic Bragg
fibers designed for operation in the visible spectral range and featuring
bandgaps of 60nm - 180nm-wide. 100 Bragg fibers were chosen to have
complimentary and partially overlapping bandgaps covering a 400nm-840nm
spectral range. The fiber bundle used in our work is equivalent in its function
to a set of 100 optical filters densely packed in the area of ~1cm2. Black and
white CCD camera is then used to capture spectrally "binned" image of the
incoming light at the output facet of a fiber bundle. To reconstruct the test
spectrum from a single CCD image we developed an algorithm based on
pseudo-inversion of the spectrometer transmission matrix. We then study
resolution limit of this spectroscopic system by testing its performance using
spectrally narrow test peaks (FWHM 5nm-25nm) centered at various positions
within the 450nm-700nm spectral interval. We find that the peak center
wavelength can always be reconstructed within several percent of its true value
regardless of the peak width or position. We believe that photonic bandgap
fiber bundle-based spectrometers have a potential to become an important
technology in multispectral imaging because of their simplicity (lack of moving
parts), instantaneous response, and high degree of integration.

Optics