Apparatus (10) for interrogating an optical signal (not shown) propagating
in an optical waveguide, such as an optical fiber, having an input section (12)
and a second section (14) through which light entering from the input section
(12) will subsequently propagate. The second section (14) includes
a grating portion, such as a tilted chirped fiber Bragg grating (16). The
grating (16) causes at least part of the optical signal to be coupled out
of the optical fiber, through the fiber cladding. A photodetector (18) is
provided generally alongside the grating (16). The photodetector (18)
is arranged to collect and detect substantially all of the outcoupled optical signal.
The relationship between the optical power outcoupled by the grating (16)
and the wavelength of the optical signal is known, allowing a measurement of the
outcoupled optical power to be used to determine the wavelength of the optical
signal propagating through the grating (16).
