Wavelength selective switch

• US 6,285,500 B1
• Filed: 11/29/1999
• Issued: 09/04/2001
• Est. Priority Date: 06/29/1999
• Status: Expired due to Fees

• Current Assignee: Corning Incorporated
• Original Assignee: Corning Incorporated
• Inventors: Ranalli, Eliseo R., Scott, Bradley A.
• Primary Examiner(s): SCHUBERG, DARREN E
• Application Number:
  US09/450,142
• Time in Patent Office: 645 Days
• Field of Search: 359/124, 359/127, 359/128, 359/130, 359/246, 359/494, 359/495, 359/497, 359/499, 385/11
• US Class Current: 359/245
• CPC Class Codes: G02B 27/28 for polarising used in stereoscopes G02B30/25
• CPC Class Codes: G02B 27/283 used for beam splitting or combining
• CPC Class Codes: G02F 1/31 Digital deflection, i.e. optical switchingG02F1/33 takes precedence
• CPC Class Codes: G02F 2203/05 wavelength dependent
• CPC Class Codes: H04J 14/0209 Multi-stage arrangements, e.g. by cascading multiplexers or demultiplexers
• CPC Class Codes: H04J 14/0212 using optical switches or wavelength selective switches [WSS]
• CPC Class Codes: H04J 14/0213 Groups of channels or wave bands arrangements
• CPC Class Codes: H04Q 11/0005 Switch and router aspects
• CPC Class Codes: H04Q 2011/0026 using free space propagation (e.g. lenses, mirrors)
• CPC Class Codes: H04Q 2011/0035 using miscellaneous components, e.g. circulator, polarisation, acousto/thermo optical

Abstract

A reconfigurable bi-directional wavelength selective switch is disclosed. It has an optical system that is symmetric about a polarization modulator. The symmetric optical system consists of an input birefringent optical system and output birefringent optical system disposed around polarization modulator. The optical system delivers the wavelength channels that are to be switched as a superimposed wavelength channel incident the polarization modulator. As a result, crosstalk is reduced below −35 dB and greater optical performance is achieved.

Claims

1. An optical device for selectively directing a first signal and a second signal to a selected output, said optical device comprising:

a birefringent optical system having a system input that receives the first signal and the second signal, and a system output to which said birefringent optical system transmits a superimposed signal formed by superimposing a first polarized signal and a second polarized signal, wherein said first polarized signal and said second polarized signal are polarized versions of the first signal and the second signal, respectively; and

a polarization modulator coupled to said system output, whereby said polarization modulator selectively rotates a polarization state of said superimposed signal, wherein the polarization modulator is selected from the group consisting of a birefringent crystal switch, a twisted nematic liquid crystal switch, a ferroelectric liquid crystal switch, a cholesteric liquid crystal switch, a magneto-optical Farady rotator, an acousto-optic rotator, or an electro-optical rotator and wherein an optical distance of the first polarized signal from the system input to the polarization modulator is substantially equal to an optical distance of the second polarized signal from the system input to the liquid crystal switch.

14. The optical device of claim 1 wherein the first polarized signal is mapped into a first linearly polarized state and the second polarized signal is mapped into a second linearly polarized state, orthogonal to said first linearly polarized state.

15. The optical device of claim 1, wherein the first polarized signal is mapped into a first circularly polarized state and the second polarized signal is mapped into a second circularly polarized state, orthogonal to said first circularly polarized state.

16. The optical device of claim 1, wherein the liquid crystal switch is selected from the group consisting of a twisted nematic liquid crystal switch, a ferroelectric liquid crystal switch, or a cholesteric liquid crystal switch.

17. The optical device of claim 1, wherein the first polarized signal and the second polarized signal are superimposed such that they are co-linear in at least one-axis of an optical path.

18. The optical device of claim 1, wherein the birefringent optical system is symmetrical about the polarization modulator.

2. An optical device for selectively directing a first signal and a second signal to a selected output, said optical device comprising:

a birefringent optical system having a system input that receives the first signal and the second signal, and a system output to which said birefringent optical system transmits a superimposed signal formed by superimposing a first polarized signal and a second polarized signal, wherein said first polarized signal and said second polarized signal are polarized versions of the first signal and the second signal, respectively; and

a polarization modulator coupled to said system output, whereby said polarization modulator selectively rotates a polarization state of said superimposed signal,

wherein the birefringent optical system further comprises an input birefringent optical system coupled to a light incident side of the polarization modulator and an output birefringent optical system coupled to a light transmitting side of the polarization modulator, and wherein the input birefringent optical system further comprises a polarization beam splitter connected to the system input, said splitter separates the first signal into first signal polarization components and the second signal into second signal polarization components, and a first half-wave retarder disposed in a path of a polarized component for each of said first signal polarization components and said second polarization components to create first signal uniformly polarized components and second signal uniformly polarized components.

3. The optical device of claim 2, wherein the first signal uniformly polarized components and the second signal uniformly polarized components are s-polarized.

4. The optical device of claim 2, wherein the first signal uniformly polarized components and the second signal uniformly polarized components are p-polarized.

5. The optical device of claim 2, wherein the input birefringent optical system further comprises:

a second half-wave retarder disposed in a path of either of the first signal uniformly polarized components or the second signal uniformly polarized components, whereby the first signal uniformly polarized components are orthogonally polarized relative to the second signal uniformly polarized components; and

a polarization beam combiner coupled to said second half-wave retarder, whereby the first signal uniformly polarized components are combined with the second signal uniformly polarized components to form two superimposed signals.

6. The optical device of claim 5, further comprising a lens for focusing the two superimposed signals onto the polarization modulator.

7. The optical device of claim 5, wherein the polarization beam splitter and the polarization beam combiner are selected from the group consisting of a parallel plate beamsplitter, a birefringent crystal, a beam splitting prism, a beamsplitting cube, or one or more thin film filters.

19. The optical device of claim 2, wherein said input birefringent optical system and said output birefringent optical system are symmetrical around the liquid crystal switch.

20. The optical device of claim 19, wherein the optical device is bidirectional.

8. An optical device for selectively directing a first signal and a second signal to a selected output, said optical device comprising:

a first polarization beam splitter for separating the first signal and second signal into first signal polarization components and second signal polarization components, respectively;

a first half-wave retarder coupled to said polarization beam splitter, said first half-wave retarder causes all of said first signal polarization components and said second signal polarization components to be uniformly polarized in a first polarization state;

a first grating coupled to said first half-wave retarder, for producing a plurality of first signal wavelength channels and a plurality of second signal wavelength channels;

a second half-wave retarder coupled to said first grating, for causing said plurality of second signal wavelength channels to be uniformly polarized in a second polarization state;

a first optical compensator coupled to said first grating, for causing an optical distance of said plurality of first signal wavelength channels to be substantially equal to an optical distance of said plurality of second signal wavelength channels;

a first polarization beam combiner coupled to said optical compensator and said second half-wave retarder, for combining said plurality of first signal wavelength channels and said plurality of second signal wavelength channels into a plurality of superimposed wavelength channels;

a focusing lens coupled to said polarization beam combiner; and

an array of polarization modulators coupled to said focusing lens, each of said modulators has a switch state, wherein each superimposed wavelength channel is focused onto a predetermined modulator.

9. The optical device of claim 8, wherein the array of polarization modulators comprises an array of liquid crystal pixels.

10. The optical device of claim 9, wherein the liquid crystal pixel selectively rotates the polarization state of the superimposed wavelength channel to thereby direct the first signal wavelength channel and the second signal wavelength channel into a selected output signal.

11. The optical device of claim 9, further comprising:

a second lens coupled to the array of liquid crystal pixels to substantially collimate each superimposed output wavelength channel directed out of the array of liquid crystal pixels;

a second polarization beam splitter coupled to said second lens, for separating superimposed output wavelength channels into first output wavelength channels and second output wavelength channels determined by the switch state of their corresponding liquid crystal pixel;

a third half-wave retarder coupled to said second polarization beam splitter, for converting said plurality of second output wavelength channels into the first polarization state;

a second optical compensator coupled to said second polarization beam splitter, for causing an optical path length of said plurality of first output wavelength channels to be substantially equal to an optical path length of said plurality of second output wavelength channels;

a second grating coupled to said third half-wave retarder and said second optical compensator, for multiplexing said plurality of first output wavelength channels into at least one first output signal component and said plurality of second output wavelength channels into at least one second output signal component, wherein said first output signal component and said second output signal component have the same polarization state;

a fourth half-wave retarder coupled to said second grating, said fourth half-wave retarder causes said at least one first output signal component to have a first parallel polarized component and a first orthogonal polarized component, and also causes said at least one second signal output component to have a second parallel polarized component and a second orthogonal polarized component; and

a second polarization beam combiner coupled to said second grating and said fourth half-wave retarder, for combining said first parallel component and said first orthogonal component into a first output signal and said second parallel component and said second orthogonal component into a second output signal.

12. A method for selectively directing a first signal and a second signal to a selected output in an optical device that includes a birefringent optical system, said method comprising:

providing an array of liquid crystal pixels, wherein each of said liquid crystal pixels includes a switch state;

demultiplexing the first signal and the second signal to thereby form a plurality of first signal wavelength channels and a plurality of second signal wavelength channels, respectively;

superimposing each first signal wavelength channel over its corresponding second signal wavelength channel to thereby form a plurality of superimposed wavelength channels; and

focusing each superimposed wavelength channel onto a predetermined liquid crystal pixel,

wherein said demultiplexing step further comprises;

converting the first signal into a first parallel component and a first perpendicular component, and the second signal into a second parallel component and a second perpendicular component;

converting said first parallel component and said first perpendicular component into two first perpendicular components, and said second parallel component and said second perpendicular component into two second perpendicular components; and

demultiplexing said two first perpendicular components and said two second perpendicular components to form two sets of first signal perpendicular wavelength channel components and two sets of second signal perpendicular wavelength channel components, respectively.

13. A method for selectively directing a first signal and a second signal to a selected output in an optical device that includes a birefringent optical system, said method comprising:

providing an array of liquid crystal pixels, wherein each of said liquid crystal pixels includes a switch state;

demultiplexing the first signal and the second signal to thereby form a plurality of first signal wavelength channels and a plurality of second signal wavelength channels, respectively;

superimposing each first signal wavelength channel over its corresponding second signal wavelength channel to thereby form a plurality of superimposed wavelength channels; and

focusing each superimposed wavelength channel onto a predetermined liquid crystal pixel,

wherein the step of superimposing further comprises converting the two sets of second signal perpendicular wavelength channel components into two sets of second signal parallel wavelength channel components and combining the two sets of first signal perpendicular wavelength channel components with said two sets of second signal parallel wavelength channel components, to form a first set of superimposed wavelength channels and a second set of superimposed wavelength channels.

21. An optical device for selectively directing a first signal and a second signal to a selected output, said optical device comprising:

a birefringent optical system having a system input that receives the first signal and the second signal, and a system output to which said birefringent optical system transmits a superimposed signal formed by superimposing a first polarized signal and a second polarized signal, wherein said first polarized signal and said second polarized signal are polarized versions of the first signal and the second signal, respectively; and

a polarization modulator coupled to said system output, whereby said polarization modulator selectively rotates a polarization state of said superimposed signal, and wherein an optical distance of the first polarized signal from the system input to the polarization modulator is substantially equal to an optical distance of the second polarized signal from the system input to the liquid crystal switch.

22. The optical device of claim 21 wherein the first polarized signal is mapped into a first linearly polarized state and the second polarized signal is mapped into a second linearly polarized state, orthogonal to said first linearly polarized state.

23. The optical device of claim 21, wherein the first polarized signal is mapped into a first circularly polarized state and the second polarized signal is mapped into a second circularly polarized state, orthogonal to said first circularly polarized state.

24. The optical device of claim 21, wherein the polarization modulator is selected from the group consisting of a birefringent crystal switch, a twisted nematic liquid crystal switch, a ferroelectric liquid crystal switch, a cholesteric liquid crystal switch, a magneto-optical Farady rotator, an acousto-optic rotator, or an electro-optical rotator.

25. The optical device of claim 24, wherein the liquid crystal switch is selected from the group consisting of a twisted nematic liquid crystal switch, a ferroelectric liquid crystal switch, or a cholesteric liquid crystal switch.

26. The optical device of claim 21, wherein the first polarized signal and the second polarized signal are superimposed such that they are co-linear in at least one-axis of an optical path.

27. The optical device of claim 21, wherein the birefringent optical system is symmetrical about the polarization modulator.

28. An optical device for selectively directing a first signal and a second signal to a selected output, said optical device comprising:

a birefringent optical system having a system input that receives the first signal and the second signal, and a system output to which said birefringent optical system transmits a superimposed signal formed by superimposing a first polarized signal and a second polarized signal, wherein said first polarized signal and said second polarized signal are polarized versions of the first signal and the second signal, respectively; and

a polarization modulator coupled to said system output, whereby said polarization modulator selectively rotates a polarization state of said superimposed signal,

wherein the input birefringent optical system further comprises a polarization beam splitter connected to the system input, so as to be able to separate the first signal into first signal polarization components and the second signal into second signal polarization components, and wherein a first half-wave retarder is disposed in a path of a polarized component for each of said first signal polarization components and said second polarization components to create first signal uniformly polarized components and second signal uniformly polarized components.

29. The optical device of claim 28, wherein the first signal uniformly polarized components and the second signal uniformly polarized components are s-polarized.

30. The optical device of claim 28, wherein the first signal uniformly polarized components and the second signal uniformly polarized components are p-polarized.

31. The optical device of claim 28, wherein the input birefringent optical system further comprises:

a second half-wave retarder disposed in a path of either of the first signal uniformly polarized components or the second signal uniformly polarized components, whereby the first signal uniformly polarized components are orthogonally polarized relative to the second signal uniformly polarized components; and

a polarization beam combiner coupled to said second half-wave retarder, whereby the first signal uniformly polarized components are combined with the second signal uniformly polarized components to form two superimposed signals.

32. The optical device of claim 31, further comprising a lens for focusing the two superimposed signals onto the polarization modulator.

33. The optical device of claim 31, wherein the polarization beam splitter and the polarization beam combiner are selected from the group consisting of a parallel plate beamsplitter, a birefringent crystal, a beam splitting prism, a beamsplitting cube, or one or more thin film filters.

34. The optical device of claim 28, wherein said input birefringent optical system and said output birefringent optical system are symmetrical around the liquid crystal switch.

35. The optical device of claim 28, wherein the optical device is bidirectional.