Wide free-spectral-range, widely tunable and hitless-switchable optical channel add-drop filters

A combination comprising:

• first, second, and third optical devices, each comprising:
• a splitter device configured to split an input spectrum among a plurality of output ports, and a combiner device configured to combine at least a portion of the split input spectrum into a single output port, each of the splitter and combiner devices having respective first and second input ports, respective first and second output ports, and a respective transfer matrix;
• a first optical path optically coupling the first output port of the splitter device and the first input port of the combiner device;
• a second optical path optically coupling the second output port of the splitter device and the second input port of the combiner device;
• and
• an optical filter optically coupled to at least one of the first and the second optical paths,
• wherein the first and second optical paths are configured to introduce, at least at a wavelength of the input spectrum, a phase shift of π radians to the optical radiation propagating through the first optical path with respect to the optical radiation propagating through the second optical path, said transfer matrix of the combiner device is a diagonal transpose of the transfer matrix of the splitter device, the splitter device is configured to split the input spectrum into the first and second optical paths such that (i) at a first wavelength of the input spectrum, a ratio of a portion of an input signal transferred to the first optical path to a portion of the input signal transferred to the second optical path is greater than 10 and (ii) at a second wavelength of the input spectrum, the ratio of the portion of the input signal transferred to the first optical path to the portion of the input signal transferred to the second optical path is less than 0.1, a wavelength spacing between the first wavelength and the second wavelength is less than 100 nanometers, the first optical device is disposed in a symmetric nested arrangement with the second and the third optical devices, the first optical path of the first optical device comprises the second optical device, the second optical path of the first optical device comprises the third optical device, the filter of the first optical device comprises one of the second and third optical devices, and the filter of at least one of the second and third optical devices comprises a straight waveguide.

A combination comprising:

• a first optical device comprising
• a splitter device configured to split an input spectrum among a plurality of output ports, and a combiner device configured to combine at least a portion of the split input spectrum into a single output port, each of the splitter and combiner devices having respective first and second input ports, respective first and second output ports, and a respective transfer matrix;
• a first optical path optically coupling the first output port of the splitter device and the first input port of the combiner device;
• a second optical path optically coupling the second output port of the splitter device and the second input port of the combiner device;
• and
• an optical filter optically coupled to at least one of the first and the second optical paths,
• wherein the first and second optical paths are configured to introduce, at least at a wavelength of the input spectrum, a phase shift of π radians to the optical radiation propagating through the first optical path with respect to the optical radiation propagating through the second optical path, said transfer matrix of the combiner device is a diagonal transpose of the transfer matrix of the splitter device, the splitter device is configured to split the input spectrum into the first and second optical paths such that (i) at a first wavelength of the input spectrum, a ratio of a portion of an input signal transferred to the first optical path to a portion of the input signal transferred to the second optical path is greater than 10 and (ii) at a second wavelength of the input spectrum, the ratio of the portion of the input signal transferred to the first optical path to the portion of the input signal transferred to the second optical path is less than 0.1, and a wavelength spacing between the first wavelength and the second wavelength is less than 100 nanometers, and a second optical device comprising:
• a second splitter device configured to split an input spectrum among a plurality of output ports, and a second combiner device configured to combine at least a portion of the split input spectrum into a single output port, each of the second splitter and combiner devices having respective first and second input ports, respective first and second output ports, and a respective transfer matrix,
• a third optical path optically coupling the first output port of the second splitter device and the first input port of the second combiner device;
• and
• a fourth optical path optically coupling the second output port of the second splitter device and the second input port of the second combiner device,
• wherein the third and fourth optical paths are configured to introduce, at least at a wavelength of the input spectrum, a phase shift of π radians to the optical radiation propagating through the third optical path with respect to the optical radiation propagating through the fourth optical path, said transfer matrix of the second combiner device is the diagonal transpose of the transfer matrix of the second splitter device, the first optical device is disposed in a non-symmetric nested arrangement with the second optical device such that the third optical path of the second optical device comprises the first optical device.

A tunable optical device comprising:

• a first and a second optical path;
• an optical filter disposed in at least the first optical path;
• a tunable wavelength-dependent optical splitter device for splitting input optical radiation into the first and second optical path, such that at one filter resonance, the splitter device has substantially unity transmission to the first optical path, at one or more adjacent filter resonances has substantially null transmission to the first optical path, and the splitter device is configured to split at least one wavelength channel substantially between both optical paths, the at least one wavelength channel selected from a range between the substantially-unity-transmission wavelength and the substantially-null-transmission wavelengths;
• and
• a combiner device for combining into a single output optical path the outputs from the two optical paths,
• wherein the first and second optical paths introduce a phase shift of π radians between optical radiation propagating through the first and the second optical paths.