  We demonstrate for the first time, a new type of aperiodic phase mask (APM)
for fabricating multi-channel aperiodic fiber Bragg gratings. The mask is made
of individual diffraction phase gratings with discrete unequal phase-steps
incorporated at periodic locations. The diffraction at the discrete phase-steps
in the phase mask produces corresponding half phase-steps at periodic locations
along the fiber. The accumulated phase, along with index modulation, generates
the desired multinotch reflection spectrum. Complex fiber Bragg grating filters
fabricated using APM, in a standard phase mask based fabrication setup, can be
used to simultaneously suppress multiple aperiodic OH emission wavelengths in
near infrared (NIR) existing in upper atmosphere, and increase the sensitivity
of ground based telescopes.
