High extinction ratio and low crosstalk compact optical switches
View Patent ↗An improved optical switch utilizes one polarization modulator, with the beam components traversing it twice. Because of the twice traverse, the extinction ratio of the switch is doubled without the addition of another polarization modulator, thus avoiding the costs of additional optical components. With no additional components, the switch is more compact than conventional switches with the same extinction ratio. Fewer components also result in more thermal and long-term stability and less crosstalk.
1. An optical switch having an input port and first and second output ports, comprising:
a first birefringent polarization beam displacer;
a polarization modulator optically coupled to the first birefringent polarization beam displacer, the polarization modulator controllable between a first state and a second state;
a second birefringent polarization beam displacer optically coupled to the polarization modulator at a side opposite to the first birefringent polarization beam displacer;
a reflector optically coupled to the second birefringent polarization beam displacer at a side opposite to the polarization modulator, wherein the reflector has a first reflecting surface, a second reflecting surface and a third reflecting surface; and
a glass compensating plate optically coupled between only a portion of the first birefringent polarization beam displacer and only a portion of the polarization modulator,
wherein an optical beam traverses the first birefringent polarization beam displacer, the polarization modulator, and the second birefringent polarization beam displacer in a forward direction to the reflector,
wherein the optical beam is reflected from the first reflecting surface, then the second reflecting surface and then the third reflecting surface of the reflector into a return direction,
wherein the reflected optical beam traverses the second birefringent polarization beam displacer, the polarization modulator, and the first birefringent polarization beam displacer in a return direction and emerges from the first output port when the polarization modulator is controlled to be in the first state and from the second output port when the polarization modulator is controlled to be in the second state, and
wherein the input port and the first and second output ports are on the same side of the optical switch.
2. The switch of claim 1 , wherein when the optical beam traverses the first birefringent polarization beam displacer in the forward direction, the first birefringent polarization beam displacer spatially separates the optical beam into a first beam component with a first polarization and a second beam component with a second polarization, wherein the first polarization is orthogonal to the second polarization.
3. The switch of claim 2 , wherein the polarization modulator comprises a first pixel and a second pixel, wherein the second pixel rotates the second polarization into the first polarization when the switch is in a first state, wherein the first pixel rotates the first polarization into the second polarization when the switch is in a second state.
4. The switch of claim 3 , wherein the first beam component traverses the first pixel and the second beam component traverses the second pixel.
5. The switch of claim 2 , wherein the second birefringent polarization beam displacer displaces a traversing beam component with the first polarization and does not displace a traversing beam component with the second polarization.
6. The switch of claim 2 , wherein the first beam component traverses the glass compensating plate in both the forward and the return directions.
7. The switch of claim 1 , wherein the first reflecting surface and the second reflecting surface of the reflector includes a coating that is used to preserve the polarization of the optical beam.
8. The switch of claim 1 , wherein the reflector comprises a corner cube reflector.
9. The switch of claim 1 , wherein the polarization modulator comprises a single pixel.
10. The switch of claim 1 , wherein the first birefringent polarization beam displacer combines a first and a second beam component traversing in the return direction into an output beam.
11. The switch of claim 1 , wherein the polarization modulator comprises a twisted-nematic liquid crystal device.
12. The switch of claim 1 , wherein the first birefringent polarization beam displacer comprises a planar parallel plate made of uni-axial crystal material.
13. The switch of claim 1 , wherein the optical beam traverses the glass compensating plate in the forward direction.
14. The switch of claim 13 , wherein the reflected optical beam traverses the glass compensating plate in the return direction.
15. An optical switch having an input port and first and second output ports, comprising:
a first birefringent polarization beam displacer having a first part and a second part;
a polarization modulator optically coupled to the first birefringent polarization beam displacer, the polarization modulator having a first pixel and a second pixel, each pixel rotates the polarization of an incident beam into a first polarization when the polarization modulator is in a first state and into a second polarization when the polarization modulator is in a second state, wherein the polarization modular has a first portion and a second portion;
a glass compensating plate positioned between the first birefringent polarization beam displacer and the polarization modulator such that the first part of the first birefringent polarization beam displacer and the first portion of the polarization modulator are optically coupled via the glass compensating plate and the second part of the first birefringent polarization beam displacer and the second portion of the polarization modulator are not optically coupled via the glass compensating plate;
a second birefringent polarization beam displacer optically coupled to the polarization modulator at a side opposite to the first birefringent polarization beam displacer; and
a reflector optically coupled to the second birefringent polarization beam displacer at a side opposite to the polarization modulator,
wherein the input optical beam traverses the first birefringent polarization beam displacer, the glass compensating plate, the polarization modulator, and the second birefringent polarization beam displacer in a forward direction to the reflector,
wherein the reflector reflects the optical beam into a return direction,
wherein the reflected optical beam traverses the second birefringent polarization beam displacer, the polarization modulator, the glass compensating plate, and the first birefringent polarization beam displacer in a return direction and emerges from the first output port when the polarization modulator is in the first state and from the second output port when the polarization modulator is in the second state, and
wherein the input port and the first and second output ports are on the same side of the optical switch.
16. The switch of claim 15 , wherein when the optical beam traverses the first birefringent polarization beam displacer in the forward direction, the first birefringent polarization beam displacer spatially separates the optical beam into a first beam component with a first polarization and a second beam component with a second polarization, wherein the first polarization is orthogonal to the second polarization.
17. The switch of claim 16 , wherein the first beam component traverses the glass compensating plate in both the forward and the return directions.
18. The switch of claim 15 , wherein the first birefringent polarization beam displacer combines a first and a second beam component traversing in the return direction into an output beam.
19. The switch of claim 15 , wherein the reflector comprises a first reflecting surface and a second reflecting surface that includes a coating that is used to preserve the polarization of the optical beam.
20. The switch of claim 15 , wherein the reflector comprises a corner cube reflector.
21. The switch of claim 15 , wherein the polarization modulator comprises a twisted-nematic liquid crystal device.
22. The switch of claim 15 , wherein the first birefringent polarization beam displacer comprises a planar parallel plate made of uni-axial crystal material.
23. A method for switching an optical signal, comprising:
traversing the optical signal in a forward direction;
spatially separating the optical signal into a first beam component with a first polarization and a second beam component with a second polarization utilizing a first birefringent polarization beam displacer, wherein the first polarization is orthogonal to the second polarization;
compensating for a polarization mode dispersion resulting from a pass through the first birefringent polarization beam displacer by using a glass compensating plate, wherein the glass compensating plate is coupled between only a portion of the first birefringent polarization beam displacer and only a portion of a polarization modulator;
controlling the polarization modulator to be in a desired one of a first state and a second state and passing the first and second beam components through the polarization modulator in the forward direction, wherein the polarization modulator rotates the second polarization into the first polarization when the polarization modulator is in the first state, wherein the polarization modulator rotates the first polarization into the second polarization when the polarization modulator is in the second state;
passing the first and the second beam component through a second birefringent polarization beam displacer in the forward direction, wherein the first or the second beam component is displaced if the first or the second beam component has the first polarization;
reflecting the first and the second beam components into a return direction;
passing the reflected first or second beam component through the second birefringent polarization beam displacer in the return direction, wherein the reflected first or the second beam component is displaced if the first or the second beam component has the first polarization;
passing the reflected first and second beam components through the polarization modulator in the return direction, wherein the polarization modulator rotates the second polarization into the first polarization when the polarization modulator is in a first state, wherein the polarization modulator rotates the first polarization into the second polarization when the polarization modulator is in a second state; and
combining the reflected first and second beam components by the first birefringent polarization beam displacer into an output beam.