Tunable add drop optical filtering method and apparatus

An optical filter for use with wavelength division multiplexed signals comprising a plurality of frequency components, the optical filter operable to remove at least one frequency component from a wavelength division multiplexed signal, the optical filter comprising:

• a) a first wavelength grating router, the router including a plurality of inputs and a plurality of outputs, the plurality of outputs further comprising a set of one or more drop outputs and a set of one or more retain outputs, the router operable such that when an input signal including a plurality of frequency components is received at one of the router inputs, each frequency component of the input signal is provided to a distinct router output, and the distinct output at which each frequency component is provided is dependant upon the router input at which the input signal is received;
• b) an optical switch comprising an input and a plurality of outputs connected to the first wavelength grating router, each switch output connected to one of the plurality of router inputs, the switch operable to receive an optical signal at the switch input and provide the received optical signal at a select one of the plurality of switch outputs;
• c) a second waveguide grating router comprising a first set of inputs and a plurality of outputs, each of the first set of inputs coupled to one of the set of retain outputs of the first wavelength grating router;
• and
• d) a second optical switch comprising a plurality of inputs and an output, each of the plurality of optical switch inputs connected to one of the plurality of second wavelength grating router outputs, the switch operable to provide at its output an optical signal received at a select one of the plurality of switch inputs.

An optical filter for use with wavelength division multiplexed signals comprising a plurality of frequency components, the optical filter operable to remove at least one frequency component from a wavelength division multiplexed signal, the optical filter comprising:

• a) a wavelength grating router, the router including a plurality of inputs and a plurality of outputs, the plurality of outputs further comprising a set of one or more drop outputs and a set of one or more retain outputs, the router operable such that when an input signal including a plurality of frequency components is received at one of the router inputs, each frequency component of the input signal is provided to a distinct router output, and the distinct output at which each frequency component is provided is dependant upon the router input at which the input signal is received;
• b) an optical switch comprising an input and a plurality of outputs connected to the wavelength grating router, each switch output connected to one of the plurality of router inputs, the switch operable to receive an optical signal at the switch input and provide the received optical signal at a select one of the plurality of switch outputs;
• and
• c) a star coupler comprising a first set of inputs and an output, each of the first set of inputs coupled to one of the set of retain outputs of the wavelength grating router.

An optical filter for use with wavelength division multiplexed signals comprising a plurality of frequency components, the optical filter operable to remove at least one frequency component from a wavelength division multiplexed signal, the optical filter comprising:

• a) a wavelength router comprising
• a plurality of inputs for receiving a wavelength division multiplexed signal;
• a first free space region optically coupled to the plurality of inputs;
• a second free space region;
• an optical grating providing optical communication between the first free space region and the second free space region;
• a plurality of outputs to which the plurality of frequency components comprising the wavelength division multiplexed signal are provided, which outputs are further optically coupled to the second free space region, including at least one drop output and a set of retain outputs,
• wherein the output at which each frequency component of the plurality is provided is dependent upon the router input at which the multiplexed optical signal is received;
• b) an optical switch comprising;
• at least one input operable to receive multiplexed optical signals;
• a plurality of outputs operable to provide multiplexed optical signals, the plurality of outputs connected to the plurality of wavelength router inputs;
• c) a means for multiplexing a plurality of frequency components, the multiplexing means coupled to the set of retain outputs of the waveguide router;
• and
• d) a drop line connected to at least one drop output of the wavelength router.

A method of dropping a select frequency from a wavelength division multiplexed optical (WDM) signal, the WDM signal comprising a plurality of frequency components, the method comprising:

• a) controllably providing the WDM signal to a select input of a wavelength grating router (WGR) having a plurality of inputs and a plurality of outputs, the plurality of outputs including a drop output, the WGR operable to demultiplex the WDM signal provided at the select input and to route each of the frequency components of the demultiplexed WDM signal to one of the outputs, the output to which each of the frequency components are routed being dependent upon the select input of the WGR so that the select frequency component can be controllably routed to the drop output;
• b) propagating the select frequency component from the drop output to a drop line;
• and
• c) multiplexing a second plurality of frequency components, the second plurality of frequency components comprising the plurality of frequency components substantially without the select frequency component.

A system for transmitting optical signals in the form of wavelength division multiplexed (WDM) signals, each WDM signal comprising a plurality of frequency components, the system comprising:

• a) a central switching office, the central switching office including a multiplexer and a demultiplexer;
• b) a tunable optical filter operable to remove at least one frequency component from a WDM signal, the optical filter comprising
• a wavelength grating router, the router including a plurality of inputs and a plurality of outputs including at least one drop output, the router operable such that when an input signal comprising a plurality of frequency components is received at one of the router inputs, each frequency component of the input signal is provided at a distinct output, and the distinct output at which each frequency component is provided is dependant upon the router input at which the input signal is received;
• an optical switch comprising an input and a plurality of outputs connected to the wavelength grating router, each switch output connected to one of the plurality of router inputs, the switch operable to receive an optical signal at the switch input and provide the received optical signal at a select one of the plurality of switch outputs;
• and
• a multiplexer for wavelength division multiplexing a plurality of frequency components, the multiplexer coupled to less than all of the plurality of waveguide grating router outputs;
• c) a length of optical fiber optically coupled to the central switching office multiplexer and the input of the optical switch of the tunable filter;
• d) a length of optical fiber optically coupled to the central switching office demultiplexer and the multiplexer of the tunable optical filter;
• and
• e) a network node optically connected to at least one drop output of the wavelength grating router.