Tunable add-drop filter with an active resonator

An add-drop filter for transmitting at least one signal, the add-drop filter comprising:

• a first tapered optical fiber and a second tapered optical fiber, the first tapered optical fiber defining a through channel configured to carry the at least one optical signal;
• and
• an active resonator side-coupled between the first tapered optical fiber and the second tapered optical fiber, the active resonator doped with at least one rare earth ion, the at least one rare earth ion configured to provide an optical gain to the active resonator in proportional response to an amount of laser energy produced by a tunable pump laser coupled to the active resonator;
• wherein the first tapered optical fiber, the second tapered optical fiber, and the active resonator define:
• an add channel configured to insert an add optical signal into the at least one optical signal the add channel coupled to the through channel;
• and
• a drop channel configured to remove a drop optical signal from the at least one optical signal, the drop channel coupled to the through channel;
• and
• wherein the optical gain is tuned to modulate at least one tunable parameter selected from the group consisting of an add-drop bandwidth, an add efficiency of the add channel, a drop efficiency of the drop channel, and a crosstalk between the add channel, the drop channel, and the through channel.