Optical devices with integral isolators
An isolator assembly, for use internally within a multi-port optical switch, and which operates on a preselected number of input port channels. The assembly incorporates a sequence of a birefringent crystal with a half wave plate on part of its output face acting as a linear polarizer, a 45° Faraday rotator element and a half wave plate aligned at 22.5° to the polarization direction of the light rotated by the Faraday rotator. This arrangement ensures that any light spuriously returned from a reflective beam switching element of the switch is blocked from transmission out of the paths of light which the isolator assembly covers because of the orientation of the light polarization returned to the birefringent crystal. The isolator assembly is arranged such that it does not cover the beam path leading to the output port or ports, such that legitimate output beams are transmitted unhindered.
1. An optical switch comprising:
a plurality of input ports;
at least one output port;
at least one polarization diversity device receiving input light from one of said input ports and oriented to transmit linearly polarized light within said optical switch;
a polarization rotator receiving said linearly polarized light and adapted to rotate its polarization direction through essentially 45°; and
a switchable reflective element receiving said input light after passage through said polarization rotator, and adapted to reflect said light such that it impinges only on a preselected one of said at least one output port,
wherein said polarization rotator is disposed such that it covers the free space propagation paths within said switch of light passing through said input ports, but not the free space propagation paths within said switch of light passing through said at least one output port.
2. An optical switch according to claim 1 and wherein said polarization rotator is a Faraday rotator.
3. An optical switch according to claim 1 and wherein light returned from said switchable reflective element of said switch is blocked from transmission along said paths within said switch of light passing through said input ports.
4. An optical switch according to claim 1 , further comprising a linear polarizer disposed at the output of said polarization rotator, said linear polarizer being aligned such that its polarization axis is parallel to the polarization direction of said light received from said polarization rotator.
5. An optical switch according to claim 1 , further comprising a linear polarizing element disposed between said at least one polarization diversity device and said polarization rotator, and oriented with its polarization axis aligned parallel to the polarization direction of said light output from said at least one polarization diversity device.
6. An optical switch according to claim 1 , further comprising:
a linear polarizing element disposed between said at least one polarization diversity device and said polarization rotator, said linear polarizing element being oriented with its polarization axis aligned parallel to the polarization direction of said light output from said at least one polarization diversity device; and
a linear polarizer disposed at the output of said polarization rotator, said linear polarizer being oriented such that its polarization axis is rotated by essentially 45° in the same direction as the rotation direction of said polarization rotator, to the polarization axis of said linear polarizing element.
7. An optical switch according to claim 1 and wherein said at least one polarization diversity device comprises a birefringent crystal with a half wave plate over part of its optical output.
8. An optical switch according to claim 1 further comprising a second half wave plate receiving light from said polarization rotator, said second half wave plate being aligned such that its optical axis makes an angle of essentially 22.5° with the polarization direction of said light received from said polarization rotator.
9. An optical switch according to claim 8 further comprising a linear polarizer disposed between said polarization rotator and said second half wave plate, with its polarization axis aligned parallel with the polarization direction of said light output from said polarization rotator.
10. An optical switch comprising:
a plurality of input ports;
a birefringent crystal having a half wave plate over part of its optical output, receiving an input beam of light from one of said input ports, and outputting said input beam of light as linearly polarized beams of light;
a polarization rotator receiving said linearly polarized beams of light and rotating the polarization directions thereof by essentially 45°; and
a switchable reflective element receiving said linearly polarized beams of light after passage through said polarization rotator,
wherein said linearly polarized beams of light received at said switchable reflective element, have a polarization after passage through said polarization rotator, rotated from that of said linearly polarized light received by said polarization rotator, and light returned from said switchable reflective element and re-entering said birefringent crystal is birefracted in a direction different from that from which said input beam of light was received.
11. An optical switch according to claim 10 , further comprising a linear polarizer disposed at the output of said polarization rotator, said linear polarizer being aligned such that its polarization axis is parallel to the polarization direction of said 45° rotated polarized beams output from said polarization rotator.
12. An optical switch according to claim 10 , further comprising a linear polarizing element disposed between said birefringent crystal and said polarization rotator, and oriented with its polarization axis aligned parallel to the polarization direction of said light output from said birefringent crystal.
13. An optical switch according to claim 10 , further comprising:
a linear polarizing element disposed between said birefringent crystal and said polarization rotator, said linear polarizing element being oriented with its polarization axis aligned parallel to the polarization direction of said light output from said birefringent crystal; and
a linear polarizer disposed at the output of said polarization rotator, said linear polarizer being aligned such that its polarization axis is parallel to the polarization direction of said 45° rotated polarized beams output from said polarization rotator.
14. An optical switch according to claim 10 further comprising a second half wave plate receiving light from said polarization rotator, said second half wave plate being aligned such that its optical axis makes an angle of essentially 22.5° with the polarization direction of said 45° rotated polarized beams output from said polarization rotator.
15. An optical switch according to claim 14 further comprising a linear polarizer disposed between said polarization rotator and said second half wave plate, with its polarization axis aligned parallel with the polarization direction of said 45° rotated polarized beams output from said polarization rotator.
16. An optical switch according to claim 14 , wherein said second half wave plate rotates the polarization direction of said 45° rotated polarized beams output from said polarization rotator, by a further 45°.
17. An optical switch according to claim 10 and wherein said polarization rotator is a Faraday rotator.
18. An optical switch according to claim 1 and wherein said input light received at said switchable reflective element, after passage through said polarization rotator, has a polarization rotated from that of said linearly polarized light received by said polarization rotator.
19. An optical switch according to claim 1 and wherein light received from an input port other than that from which said input light is received is blocked from being directed by said switch to any of said plurality of input ports and said at least one output port.
20. An optical switch according to claim 1 and wherein said polarization rotator is a non-variable polarization rotator.
21. An optical switch according to claim 10 and wherein said polarization rotator is a non-variable polarization rotator.