Optical transmission systems have evolved rapidly in recent years with the emergence of new technologies for gain
management, wavelength multiplexing, tunability, and switching. WDM networks are increasingly expected to be agile,
flexible, and reconfigurable which in turn has led to a need for monitoring to be more widely distributed within the
network. Automation of many actions performed on these networks, such as channel provisioning and power balancing,
can only be realized by the addition of optical channel monitors (OCMs). These devices provide information about the
optical transmission system including the number of optical channels, channel identification, wavelength, power, and in
some cases optical signal-to-noise ratio (OSNR). Until recently OCMs were costly and bulky and thus the number of
OCMs used in optical networks was often kept to a minimum. We describe a family of tunable thin film filters which
have greatly reduced the cost and physical footprint of channel monitors, making possible 'monitoring everywhere' for
intelligent optical networks which can serve long haul, metro and access requirements from a single technology platform.
As examples of specific applications we discuss network issues such as auto provisioning, wavelength collision
avoidance, power balancing, OSNR balancing, gain equalization, alien wavelength recognition, interoperability, and
other requirements assigned to the emerging concept of an Optical Control Plane.