An optical channel monitor is provided that sequentially or selectively
filters an optical channel(s) 11 of light from a (WDM) optical input
signal 12 and senses predetermined parameters of the each filtered
optical signal (e.g., channel power, channel presence,
signal-noise-ratio). The OCM 10 is a free-space optical device that
includes a collimator assembly 15, a diffraction grating 20 and a mirror
22. A launch pigtail emits into free space the input signal through the
collimator assembly 15 and onto the diffraction grating 20, which
separates spatially each of the optical channels 11 of the collimated
light, and reflects the separated channels of light onto the mirror 22. A
.lamda./4 plate 26 is disposed between the mirror 22 and the diffraction
grating 20. The mirror reflects the separated light back through the
.lamda./4 plate 26 to the diffraction grating 20, which reflects the
channels of light back through the collimating lens 18. The lens 18
focuses each separated channel of light (.lamda..sub.1-.lamda..sub.N) at
a different focal point in space. One of the optical channels 11 is
focused onto a receive pigtail 28, which then propagates to a
photodetector 30. A pivoting mechanism 34 pivots the diffraction grating
20 or mirror 22 about a pivot point 36 to sequentially or selectively
focus each optical channel 11 to the receive pigtail 28. A position
sensor 42 detects the displacement of the diffraction grating 24 or
mirror.