Patent ID: 8311411

Claim:
A polarization stabilizing device for stabilizing the state of polarization of an optical radiation, comprising: a first and a second birefringent element having fixed polarization eigenstates and operable to provide in sequence to the optical radiation respectively first and second controllable phase retardation (Φ 1 , Φ 2 ); a detecting system apt to generate at least a first monitor signal representative of an optical power of a first polarized portion of the optical radiation output from the second birefringent element; a third and a fourth birefringent element having fixed polarization eigenstates and operable to provide respectively third and fourth controllable phase retardations (Φ 3 , Φ 4 ) in sequence to the optical radiation outputting from the second birefringent element; and a further detecting system apt to generate a second monitor signal representative of an optical power of a further polarized portion of the optical radiation output from the fourth birefringent element; and a controller connected for receiving said first monitor signal from the detecting system and for supplying first and second control signals (φ 1 , φ 2 ), responsive to said first monitor signal, respectively to the first and second birefringent elements so as to control said first and second controllable phase retardations, and connected for receiving said second monitor signal from the further detecting system and for supplying third and fourth control signals (φ 3 , φ 4 ), responsive to said second monitor signal, respectively to the third and fourth birefringent elements so as to control said third and fourth controllable phase retardations; the controller being configured: to set the second control signal (φ 2 ) so as to maintain the polarization state of the optical radiation output from the second birefringent element at a defined great circle Γ on a Poincare sphere, and, in case the second controllable phase retardation reaches a first limit value, to set the first control signal (φ 1 ) so as to commute the first controllable phase retardation between first and second values; and to set the fourth control signal (φ 4 ) so as to maintain the state of polarization of the optical radiation output from the fourth birefringent element at a defined state of polarization, and to set, in case the fourth controllable phase retardation reaches a second limit value, the third control signal (φ 3 ) so as to commute the third controllable phase retardation between third and fourth values; wherein the controller is further configured to set the first control signal (φ 1 ) so as to keep constant the first controllable phase retardation while the third controllable phase retardation is commuting between said third and fourth values.