  We calculate the advances in near-infrared astronomy made possible through
the use of fibre Bragg gratings to selectively remove hydroxyl emission lines
from the night sky spectrum. Fibre Bragg gratings should remove OH lines at
high resolution (R=10,000), with high suppression (30dB) whilst maintaining
high throughput (~90 per cent) between the lines. Devices currently under
construction should remove 150 lines in each of the J and H bands, effectively
making the night sky surface brightness ~4 magnitudes fainter. This background
reduction is greater than the improvement adapative optics makes over natural
seeing; photonic OH suppression is at least as important as adaptive optics for
the future of cosmology.
  We present a model of the NIR sky spectrum, and show that the interline
continuum is very faint (~80 ph/s/m^s/arcsec/micron on the ecliptic plane). We
show that OH suppression by high dispersion, i.e. `resolving out' the skylines,
cannot obtain the required level of sensitivity to reach the interline
continuum due to scattering of light. The OH lines must be suppressed prior to
dispersion.
  We have simulated observations employing fibre Bragg gratings of first light
objects, high redshift galaxies and cool, low-mass stars. The simulations are
of complete end-to-end systems from object to detector. The results demonstrate
that fibre Bragg grating OH suppression will significantly advance our
knowledge in many areas of astrophysics, and in particular will enable
rest-frame ultra-violet observations of the Universe at the time of first light
and reionisation.
