Dual liquid-crystal wavelength-selective optical switch

• US 6,327,019 B1
• Filed: 02/03/1998
• Issued: 12/04/2001
• Est. Priority Date: 02/07/1997
• Status: Expired due to Fees

• Current Assignee: Tellium, Inc. (DZS, Inc.)
• Original Assignee: Tellium, Inc. (DZS, Inc.), Telcordia Technologies Incorporated (Telefonaktiebolaget LM Ericsson)
• Inventors: Jackel, Janet Lehr, Patel, Jayantilal, Tomlinson, W. John
• Primary Examiner(s): Parker, Kenneth
• Assistant Examiner(s): Qi, Mike
• Application Number:
  US09/018,097
• Time in Patent Office: 1,400 Days
• Field of Search: 349/196, 359/193, 359/180, 359/189, 385/20, 385/24, 385/17
• US Class Current: 349/196
• CPC Class Codes: G02B 6/272 comprising polarisation means for beam splitting and combining
• CPC Class Codes: G02B 6/2766 Manipulating the plane of polarisation from one input polarisation to another output polarisation, e.g. polarisation rotators, linear to circular polarisation converters
• CPC Class Codes: G02B 6/2793 Controlling polarisation dependent loss, e.g. polarisation insensitivity, reducing the change in polarisation degree of the output light even if the input polarisation state fluctuates
• CPC Class Codes: G02B 6/29302 based on birefringence or polarisation, e.g. wavelength dependent birefringence, polarisation interferometers
• CPC Class Codes: G02B 6/2931 Diffractive element operating in reflection
• CPC Class Codes: G02B 6/29395 configurable, e.g. tunable or reconfigurable switching G02B6/35
• 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: H04Q 11/0003 Details
• CPC Class Codes: H04Q 11/0005 Switch and router aspects
• CPC Class Codes: H04Q 2011/0015 using splitting combining
• CPC Class Codes: H04Q 2011/0016 using wavelength multiplexing or demultiplexing
• 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
• CPC Class Codes: H04Q 2011/0041 Optical control
• CPC Class Codes: H04Q 2011/0092 Ring

Abstract

A liquid-crystal switching element relying upon a segmented liquid-crystal polarization modulator, at least one frequency-dispersive grating and one or more polarization-dispersive elements, such as Wollaston prisms, to switch separate wavelength-divided signals among four optical paths. The switching is done complementally between the fibers of each pair, and the same switching is done for the two pairs. According to the invention, all four beams can be processed by a single set of serial optics. The invention is particularly useful as an optical interconnect between two optical fiber communications rings in which each ring includes two counter-rotating fibers. The invention advantageously uses a dielectric thin-film beam splitter for one of the polarization-dispersive elements and a Wollaston prism for the other. The reflective embodiment in which a mirror replaces all the components on the output side can be improved by using two semitransparent electrode layers on the input side separated by a quarter-wavelength of dielectric.

Claims

1. A liquid-crystal multi-wavelength switch, comprising:

a frequency-dispersive element;

a first polarization-dispersive element arranged in series with said frequency-dispersive element;

a combination of said frequency-dispersive element and said first polarization-dispersive element receiving four multi-wavelength beams and producing for each of said multi-wavelength beams a plurality of sets of single-wavelength first and a second polarization component beams, wherein the single-wavelength first polarization component beams have a first polarization and the single-wavelength second polarization component beams have a second polarization, the first and second polarizations being orthogonal;

polarization rotatory optics receiving the plurality of single-wavelength polarization component beams from said combination of said frequency-dispersive element and said first polarization-dispersive element and rotating the polarization of the plurality of single-wavelength polarization component beams such that the plurality of single-wavelength first and second polarization component beams of said first and second multi-wavelength beams have the first polarization and the plurality of single-wavelength first and second polarization component beams of said third and fourth multi-wavelength beams have the second polarization; and

a segmented liquid-crystal modulator having a plurality of electrode segments downstream of said polarization rotatory optics, each of said segments receiving a respective one of said sets of single-wavelength first and second polarization component beams from said polarization rotatory optics;

wherein said liquid-crystal modulator comprises on a side thereof facing said first polarization-dispersive element and said polarization rotatory optics;

a first semi-transparent electrode of a semi-transparent material;

a first dielectric layer formed on said first electrode and having a thickness related to a quarter wavelength of light in said single-wavelength first and second polarization component beams; and

a semi-transparent second layer formed on said dielectric layer and comprising a semitransparent material.

2. The switch of claim 1, wherein said second layer has a same thickness as and is composed of a same material as said first electrode.

3. A liquid-crystal multi-wavelength switch, comprising:

a frequency-dispersive element;

a first polarization-dispersive element arranged in series with said frequency-dispersive element;

a combination of said frequency-dispersive element and said first polarization-dispersive element receiving four multi-wavelength beams and producing for each of said multi-wavelength beams a plurality of sets of single-wavelength first and a second polarization component beams, wherein the single-wavelength first polarization component beams have a first polarization and the single-wavelength second polarization component beams have a second polarization, the first and second polarizations being orthogonal;

polarization rotatory optics receiving the plurality of single-wavelength polarization component beams from said combination of said frequency-dispersive element and said first polarization-dispersive element and rotating the polarization of the plurality of single-wavelength polarization component beams such that the plurality of single-wavelength first and second polarization component beams of said first and second multi-wavelength beams have the first polarization and the plurality of single-wavelength first and second polarization component beams of said third and fourth multi-wavelength beams have the second polarization;

a segmented liquid-crystal modulator having a plurality of electrode segments downstream of said polarization rotatory optics, each of said segments receiving a respective one of said sets of single-wavelength first and second polarization component beams from said polarization rotatory optics; and

a reflective surface disposed on a side of said liquid-crystal modulator opposite said frequency-dispersive and first polarization-dispersive elements and reflecting said single-wavelength first and second polarization component beams to said elements, wherein said reflective surface forms a second electrode of said liquid-crystal modulator.

4. A telecommunications network, comprising:

a first optical fiber ring comprising a first optical fiber and a second optical fiber for carrying a multi-wavelength signal in respective opposite directions around said first ring;

a second optical fiber ring comprising a third optical fiber and a fourth optical fiber for carrying a multi-wavelength signal in respective opposite directions around said second ring; and

a cross-connect selectively coupling said first optical fiber and said third optical fiber and coupling said second optical fiber and said fourth optical fiber and comprising

a frequency-dispersive element,

a polarization-dispersive element, and

a segmented liquid-crystal polarization modulator having a plurality of segmented electrodes, each of said segmented electrodes receiving from said frequency-dispersive and polarization-dispersive elements respective single-wavelength signals of said first, second, third, and fourth fibers.

5. The network of claim 4, wherein said polarization-dispersive element comprises a Wollaston prism.

6. The network of claim 4, further comprising a second polarization-dispersive element.

7. The network of claim 4, wherein said second polarization-dispersive element, said frequency-dispersive element, said Wollaston prism, and said liquid-crystal modulator are arranged in the stated sequence along an optical axis.

8. The network of claim 7, wherein said second polarization-dispersive element comprises a multi-layer dielectric thin-film beam splitter.