Patent ID: 7831114

Claim:
A method for providing tunable dispersion compensation in an optical system, comprising: using a coupling device to couple into the system first and second pathways into which are connected respective first and second tunable chirped fiber Bragg gratings, each grating providing a respective tunable amount of compensatory chromatic dispersion D 1 and D 2 , dispersion D 1 being tunable in an operating range extending from a minimum value D 1 ( min ) to a maximum value D 1 ( max ) that is ΔD 1 greater than D 1 ( min ), and dispersion D 2 being tunable in an operating range extending from a minimum value D 2 ( min ) to a maximum value D 2 ( max ) that is ΔD 2 greater than D 2 ( min ), dispersion D 1 and dispersion D 2 defining a tuning space, the first grating introducing a first differential group delay DGD 1 into the system that varies as a function of D 1 , and the second grating introducing a second differential group delay DGD 2 into the system that varies as a function of D 2 , the first grating introducing into the system a first midpoint differential group delay DGD 1 ( midpoint ) corresponding to a midpoint dispersion D 1 ( midpoint ) halfway between D 1 ( min ) and D 1 ( max ); and the second grating introducing into the system a second midpoint differential group delay DGD 2 ( midpoint ) corresponding to a midpoint dispersion D 2 ( midpoint ) halfway between D 2 ( min ) and D 2 ( max ); connecting into the first pathway a first set of PMD-compensating DGD elements, comprising at least one fixed PMD-compensating DGD element, the first set of PMD-compensating DGD elements introducing into the system a first bias differential group delay DGD 1 ( bias ), DGD 1 ( bias ) having an absolute value that is substantially equal to that of D 1 ( midpoint ), and connecting into the second pathway a second set of PMD-compensating DGD elements, comprising at least one fixed PMD-compensating DGD element, the second set of all such elements introducing into the system a second bias differential group delay DGD 2 ( bias ), DGD 2 ( bias ) having an absolute value that is substantially equal to that of D 2 ( midpoint ), whereby at D 1 ( midpoint ) the total combined differential group delay DGD( total FBG1 ) introduced by the first grating and the first set of PMD-compensating DGD elements is substantially equal to zero, and at D 2 ( midpoint ) the total combined differential group delay DGD( total FBG2 ) introduced by the second grating and the second set of PMD-compensating DGD elements is substantially equal to zero, and whereby the combined total DGD for the first and second gratings is minimized over the tuning space defined by compensatory chromatic dispersions D 1 and D 2 .