Phase modulation device, receiver, transmitter and a phase modulating method
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 SOP f and SOP s . Light polarized according to the second polarization eigenstate SOP s acquires, upon passing through said retardation device, a delay with regard to light polarized according to the first polarization eigenstate SOP f , 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 f ; that defines an angle with respect to one of the first and second polarization eigenstates SOP f , SOP s within 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 i ; of the input light and the respective polarization eigenstate SOP f , SOP s by 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.
1. A phase modulation device configured to receive a light signal comprising input light, comprising:
a retardation device characterized by a first polarization eigenstate SOP f and a second polarization eigenstate SOP s ,
wherein light having a wavelength γ and polarized according to the second polarization eigenstate SOP s acquires, upon passing through the retardation device, a delay relative to light having the wavelength γ and polarized according to the first polarization eigenstate SOP f , which delay corresponds to λ/2±30% wherein γ is the wavelength γ, and
wherein the retardation device is arranged to:
receive the input light, wherein the input light has a wavelength equal to γ and a polarization state SOP i that defines a first angle with respect to one of the first polarization eigenstate SOP f and the second polarization eigenstate SOP s within a predetermined angle range; and
to emit output light; and
a control device for controlling at least one of:
a change of the first angle by less than 0.1*π,
a change the delay by an amount corresponding to less than 0.3*λ,
such that a phase shift of π±30% on the output light is obtained.
2. The phase modulation device of claim 1 , wherein the control device is configured to receive a signal according to which at least one of the change of the first angle and the change of the amount of delay is controlled by the control device.
3. The phase modulation device of claim 1 , wherein
the retardation device includes a birefringent optical device.
4. The phase modulation device of claim 1 , wherein
the retardation device comprises a half wave plate.
5. The phase modulation device of claim 1 , wherein
the control device is configured to manipulate the polarization state SOP i of the input light.
6. The phase modulation device of claim 1 , wherein
the control device is configured to manipulate the first polarization eigenstate SOP f and the second polarization eigenstate SOP s of the retardation device.
7. The phase modulation device of claim 6 , wherein
the control device is configured to manipulate the first polarization eigenstate DOP f and the second polarization eigenstate SOP s by rotating the retardation device.
8. The phase modulation device of claim 1 , wherein the control device is configured for changing the first angle according to one of the following:
from an angle below π/4 to an angle above π/4 ;
from an angle above π/4 to an angle below π/4.
9. The phase modulation device of claim 1 , wherein
the control device is configured to manipulate an optical path length covered by light while passing through the retardation device.
10. The phase modulation device of claim 1 , wherein
the obtained phase shift is caused by a geometrical phase shift effect.
11. The phase modulation device of claim 1 , wherein the predetermined angle range is π/4±10%,
wherein a second angle between SOP f and SOP i is defined as
∠(SOP f ,SOP i )= a cos((SOP f ·SOP i )/((SOP i ·SOP i )*(SOP f ·SOP f ))),
wherein SOP f , SOP i are expressed by two dimensional complex Jones vectors, and
wherein “·” represents the complex dot product.
12. A receiver for receiving a light signal comprising input light, which is modulated with respect to polarization, the receiver comprising:
an optical input operable to receive the light signal; and
a retardation device optically connected to the optical input, the retardation device characterized by a first polarization eigenstate SOP f and a second polarization eigenstate SOP s ,
wherein light having a wavelength γ and polarized according to the second polarization eigenstate SOP s acquires, upon passing through the retardation device, a delay relative to light having the wavelength γ and polarized according to the first polarization eigenstate SOP f , which delay corresponds to λ/2±30% wherein γ is the wavelength γ, and
wherein the retardation device is arranged to:
receive the input light, wherein the input light has a wavelength equal to γ and a polarization state SOP i that defines a first angle with respect to one of the first polarization eigenstate SOP f and the second polarization eigenstate SOP s in a predetermined angle range, and
emit output light.
13. The receiver of claim 12 , further comprising a control unit for adjusting the first polarization eigenstate SOP f and the second polarization eigenstate SOP s of the retardation device such that a change in the polarization state SOP i of the input light due to the polarization modulation leads to a phase shift of π±30% of the output light of the retardation device.
14. The receiver of claim 13 , wherein the control unit is configured for adjusting the first polarization eigenstate SOP f and the second polarization eigenstate SOP s by rotating the retardation device.
15. A transmitter comprising a phase modulation device according to claim 1 .
16. A phase modulating method, comprising the steps of:
guiding polarized light through a phase modulation device according to claim 1 ;
controlling one of:
a change of the first angle by less than 0.3*λ,
a change of the delay by an amount corresponding to less than 0.3*γ,
such that a phase shift of π±30% on the output light is obtained.
17. The method of claim 16 , wherein the step of controlling the change of the first angle includes rotating the polarization state SOP i of the input light relative to the first polarization eigenstate SOP f and the second polarization eigenstate SOP s of the retardation device.
18. The method of claim 16 , wherein the step of controlling the change of the first angle includes rotating the retardation device relative to the polarization state SOP i of the input light.
19. The method of claim 16 , wherein the step of controlling the change of the amount of the delay includes manipulating a length covered by light while passing through the retardation device.
20. A method for phase modulation, comprising:
receiving input light having a wavelength γ and a polarization state SOP i that defines a first angle, within a predetermined angle range, with respect to at least one of a first polarization eigenstate SOP f and a second polarization eigenstate SOP s ;
creating, with respect to light having the wavelength γ and polarized according to the second polarization eigenstate SOP s , a delay relative to light having the wavelength γ and polarized according to the first polarization eigenstate SOP f , which delay corresponds to λ/2±30% wherein γ is the wavelength γ;
obtaining output light having a phase shift of π±30% by controlling at least one of:
a change of the first angle by less than 0.1*π,
a change of the delay by an amount corresponding to less than 0.3*λ; and
emitting the output light.