Patent ID: 8625999

Claim:
A frequency-shift keying modulator for optical communications comprising: a first filter stage having an input optical path to receive a multi-tone optical signal having a plurality of tones, an output optical path and a first microring resonator having a first optical path length and being disposed between the input and output optical paths, the first microring resonator having an electro-optic modulator disposed therein to modulate the first optical path length in response to a first control signal having a time-dependent signal value determined according to a communications signal to be transmitted, wherein a subset of the tones in the multi-tone optical signal are provided in a first filtered optical signal in the output optical path of the first filter stage; and a second filter stage having an input optical path in optical communication with the output optical path of the first filter stage, an output optical path and a second microring resonator having a second optical path length and disposed between the input and output optical paths, the second microring resonator having an electro-optic modulator disposed therein to modulate the second optical path length in response to a second control signal having a time-dependent signal value determined according to the communications signal to be transmitted, the second control signal having a number of time-dependent signal values that is twice a number of time-dependent signal values of the first control signal, wherein a subset of the tones in the first filtered optical signal are provided in a second filtered optical signal in the output optical path of the second filter stage.