Tunable optical dispersion by using two fiber Bragg gratings with nonlinear group delays

A device, comprising:

• a first fiber Bragg grating operable to receive an input optical signal to produce a first output optical signal by reflection within a first Bragg reflection band and configured to have a first grating pattern which produces a group delay in said first output optical signal as a nonlinear function of a frequency detuning of a wavelength of said input optical signal from a center wavelength of said first Bragg reflection band;
• a second fiber Bragg grating coupled to receive said first output optical signal to produce a second output optical signal by reflection within a second Bragg reflection band and configured to have a second grating pattern which produces a group delay in said second output optical signal as a nonlinear function of a frequency detuning of a wavelength of said first output optical signal from a center wavelength of said second Bragg reflection band,
• wherein each fiber Bragg grating is configured to produce a grating dispersion having a constant dispersion independent of a wavelength of reflected light, a linear dispersion as a linear function of a wavelength of reflected light, and a quadratic dispersion as a quadratic function of a wavelength of reflected light;
• a first fiber control unit coupled to said first fiber Bragg grating and operable to control said first fiber Bragg grating to tune a first grating dispersion in said first output signal;
• and
• a second fiber control unit coupled to said second fiber Bragg grating and operable to control said second fiber Bragg grating to tune a second grating dispersion in said second output signal,
• wherein said first and said second grating patterns are configured so that said first and said second fiber control units are operable to tune a total induced dispersion at an operating wavelength in said second output signal by changing lengths of said first and said second fiber Bragg gratings in a first manner, and to tune a rate of change in said total induced dispersion with respect to wavelength by changing lengths of said first and said second fiber Bragg gratings in a second, different manner.

A device, comprising:

• a first fiber Bragg grating operable to receive an input optical signal and to produce a first output optical signal by reflection;
• and
• a second fiber Bragg grating coupled to receive said first output optical signal and to produce a second output optical signal by reflection,
• wherein each of said first and said second fiber Bragg gratings has a spatial grating pattern to produce a grating dispersion having a constant dispersion that is independent of a wavelength of reflected light, a linear dispersion that is a linear function of a wavelength of reflected light, and a quadratic dispersion that is a quadratic function of a wavelength of reflected light;
• a first fiber control unit coupled to said first fiber Bragg grating and operable to control said first fiber Bragg grating to tune a first grating dispersion in said first output signal;
• and
• a second fiber control unit coupled to said second fiber Bragg grating and operable to control said second fiber Bragg grating to tune a second grating dispersion in said second output signal,
• wherein said first and said second grating patterns are configured so that both a total induced dispersion in said second output signal and a rate of change in said total induced dispersion with respect to wavelength are tunable by changing lengths of said first and said second fiber Bragg gratings in a first manner while said rate of change in said total induced dispersion with respect to wavelength is not tunable by changing lengths of said first and said second fiber Bragg gratings in a second, different manner which tunes said total induced dispersion.

A method, comprising:

• providing first and second fiber Bragg gratings, each grating having a grating pattern which produces a group delay in reflecting an optical signal as a nonlinear function of a frequency detuning of a wavelength of said optical signal from a center wavelength of a Bragg reflection band of said grating, wherein said group delay corresponds to a grating dispersion having a constant dispersion independent of a wavelength of reflected light, a linear dispersion as a linear function of a wavelength of reflected light, and a quadratic dispersion as a quadratic function of a wavelength of reflected light;
• directing an input optical signal into said first fiber Bragg grating to produce a first output signal by reflection;
• directing said first output signal into said second fiber Bragg grating to produce a second output signal by reflection;
• controlling lengths of said first and said second fiber Bragg gratings in a first way to tune a total induced dispersion in said second output signal;
• and
• controlling lengths of said first and said second fiber Bragg gratings in a second, different way to tune a rate of change in said total induced dispersion with respect to wavelength.

A method, comprising:

• providing first and second fiber Bragg gratings, each grating having a grating pattern which produces a group delay in reflecting an optical signal as a nonlinear function of a frequency detuning of a wavelength of said optical signal from a center wavelength of a Bragg reflection band of said grating, wherein said group delay corresponds to a grating dispersion having a constant dispersion independent of a wavelength of reflected light, a linear dispersion as a linear function of a wavelength of reflected light which has opposite signs in said first and said second gratings, and a quadratic dispersion as a quadratic function of a wavelength of reflected light which has opposite signs in said first and said second gratings;
• directing an input optical signal into said first fiber Bragg grating to produce a first output signal by reflection;
• directing said first output signal into said second fiber Bragg grating to produce a second output signal by reflection;
• and
• changing a length of at least one of said first and said second fiber Bragg gratings to tune a property of a total induced dispersion in said second output signal.

A method, comprising:

• providing first and second fiber Bragg gratings, each grating having a grating pattern which produces a group delay in reflecting an optical signal as a nonlinear function of a frequency detuning of a wavelength of said optical signal from a center wavelength of a Bragg reflection band of said grating, wherein said group delay corresponds to a grating dispersion having a constant dispersion independent of a wavelength of reflected light, a linear dispersion as a linear function of a wavelength of reflected light which has the same sign in both said first and said second gratings together, and a quadratic dispersion as a quadratic function of a wavelength of reflected light which has the same sign in both said first and said second gratings together;
• directing an input optical signal into said first fiber Bragg grating to produce a first output signal by reflection;
• directing said first output signal into said second fiber Bragg grating to produce a second output signal by reflection;
• and
• changing a length of at least one of said first and said second fiber Bragg gratings to tune a property of a total induced dispersion in said second output signal.

A method, comprising:

• directing an input optical signal into a first fiber Bragg grating to produce a first output optical signal by reflection, said first fiber Bragg grating having a first grating pattern which produces a group delay in said first output optical signal as a nonlinear function of a wavelength of reflected light;
• directing said first output optical signal into a second fiber Bragg grating to produce a second output optical signal by reflection, said second fiber Bragg grating having a second grating pattern which produces a group delay in said second output optical signal as a nonlinear function of a wavelength of reflected light, wherein said first and said second grating patterns are designed to produce a net dispersion in said second output signal that is independent of a wavelength of reflected light;
• and
• controlling a length of at least one of said first and said second fiber Bragg gratings to tune said net grating dispersion in said second output signal.