An optical filter for filtering a spectral profile of an optical signal for
providing an output signal having a desire gain profile, such as a flatten
gain profile. The filter comprises an optical waveguide that includes a
core disposed within a cladding having an outer dimension greater than 0.3
mm. A Bragg grating is imparted or written in the core of the waveguide
that attenuates the received optical input signal in accordance with a
defined reflection or transmission filter profile. The Bragg grating may
be a slanted grating. The filter profile is complementary to the spectral
gain profile of the input signal to provide an output signal having a
substantially flat spectral profile of a desired wavelength band. The
cladding of the waveguide may have a mechanically advantageous outer
geometry (e.g., a "dogbone" shape) for allowing an axial compressive force
to tune the Bragg grating. The waveguide may be package within an athermal
device, which tunes the grating to compensate for temperature dependent
changes. Further, the waveguide may be packaged in a tuning device to
selective tune the gratings to shift the center wavelength of the spectral
profile of the filter, or to change the shape of the filter profile.
