Phase modulation device, receiver, transmitter and a phase modulating method

Abstract

A phase modulation device is provided that comprises a retardation device and a control device. The retardation device is characterized by first and second polarization eigenstates SOPand SOP. Light polarized according to the second polarization eigenstate SOPacquires, upon passing through said retardation device, a delay with regard to light polarized according to the first polarization eigenstate SOP, which delay corresponds to λ/2±30%, preferably λ/2±20% and most preferably λ/2±10%. The retardation device is arranged to receive input light having a polarization state SOP; that defines an angle with respect to one of the first and second polarization eigenstates SOP, SOPwithin a predetermined angle range and to emit output light. The control device is configured to control at least one of a change of the angle between the polarization state SOP; of the input light and the respective polarization eigenstate SOP, SOPby less than 0.1*π, preferably less than 0.05*π and most preferably less than 0.02*π; and a change of the amount of said delay upon passing through said retardation device by less than 0.3*λ, preferably less than 0.2*λ and most preferably less than 0.1*λ, such that a phase shift of π±30%, preferably π±20% and most preferably π±10% on the output light is obtained.