Dynamic spatial equalizer based on a spatial light modulator

• US 6,667,824 B2
• Filed: 11/19/2001
• Issued: 12/23/2003
• Est. Priority Date: 11/20/2000
• Status: Expired due to Fees

• Current Assignee: Alcatel SA (Nokia Corporation)
• Original Assignee: Alcatel SA (Nokia Corporation)
• Inventors: De Bougrenet De La Tocnaye, Jean-Louis, Dupont, Laurent, Bayart, Dominique, Chevallier, Raymond
• Primary Examiner(s): MACK, RICKY LEVERN
• Application Number:
  US09/988,377
• Publication Number:
  US 20020080466A1
• Time in Patent Office: 764 Days
• Field of Search: 359/291, 359/292, 359/295, 359/321, 359/254, 359/296, 349/24, 349/25
• US Class Current: 359/254
• CPC Class Codes: G02F 1/1334 based on polymer dispersed liquid crystals, e.g. microencapsulated liquid crystals
• CPC Class Codes: G02F 2201/305 diffraction grating
• CPC Class Codes: G02F 2203/02 reflective
• CPC Class Codes: G02F 2203/055 wavelength filtering
• CPC Class Codes: G02F 2203/48 Variable attenuator

Abstract

A spatial light modulator (SLM) is made up of a cell filled with a liquid crystal (LC) based substance. Latter has a variable scattering property with respect to an electric field present in the cell. By using a plurality of electrodes in the direct vicinity of said cell, it is then possible to build an electric field inside it which will permit advantageously to modulate a continuous spectrum from optical signals transmitted through said cell. The different pass bands present in said continuous spectrum while at least few of them comprise at least a respective different wavelength will have to be transmitted through said cell at different regions. Latter will correspond to different values of the amplitude of scattering such to be adapted to modulate the respective different pass bands. Such SLM is used to build a dynamic spectral equalizer. Latter contains a spectral dispersive element placed on an optical path of an incident light beam. This spectral dispersive element will spread continuously said incident light beam onto said SLM such that at least each different wavelength present in said incident light beam are focused or imaged towards a different spatial region of said SLM.

Claims

1. A spatial light modulator comprising:

a planar cell, said planar cell including;

a liquid crystal based substance having a variable scattering property with respect to an electric field,

at least two electrodes enclosing said planar cell from each side of its plane, at least on one side of said plane said electrode is divided into a plurality of adjacent electrodes configured to be controlled separately,

said two electrodes configured to apply a voltage, on said liquid crystal, said applied voltage being non-uniform in space implying an electric field inside said cell with a variable spatial distribution along said plane,

said cell having a variable spatial distribution configured to modulate at least a pass band comprising at least a wavelength at which an optical signal is transmitted through said cell, while said modulation taking the form of a variable attenuation.

2. The spatial light modulator according to claim 1, wherein said variable spatial distribution is adapted for the modulation of at least two different pass bands comprising each at least a respective wavelength at which optical signals are transmitted through said cell respectively at two different regions along said plane.

3. The spatial light modulator according to claim 1, wherein at least on one side of said plane said electrode is divided into a plurality of adjacent electrodes giving rise to said variable spatial distribution adapted to modulate a continuous spectrum containing a number of different pass bands, while at least few of them comprise at least a respective wavelength at which optical signals are transmitted through said cell at a different region along said plane for each of these respective different wavelengths.

4. The spatial light modulator according to claim 1, wherein said plurality of adjacent electrodes are controlled independently with a variable voltage allowing to adapt said spatial light modulator to a change of optical properties of said incident light beam.

5. The spatial light modulator according to claim 2, wherein said modulation acts as a variable attenuator by flattening or equalizing said pass band comprising at least said respective wavelength.

6. The spatial light modulator according to claim 1, wherein said electrode being at the rear of said cell with respect to incident optical signals comprises a reflective plane for said incident optical signals.

7. The spatial light modulator according to claim 1, wherein said liquid crystal based substance filling said cell is made of a suspension of liquid crystal droplets of nematic or possibly chiral form, in a host medium of a polymer.

8. The spatial light modulator according to claim 2, wherein said droplets are of an average size comparable or smaller than said wavelength at which an optical signal is transmitted through said cell such that said droplets act as light scatters when their liquid crystal director axes are not aligned with the propagation axis of said light.

9. A dynamic spectral equalizer comprising:

an optical input for an incident light beam consisting of optical signals transmitted via at least a wavelength,

an optical output for collecting a resulting light beam, said dynamic spectral equalizer comprising further a spatial light modulator on which said incident light beam is focused or imaged and out of which said resulting light beam is collected, said spatial equalizer including;

a planar cell filled with a liquid crystal based substance having a variable scattering property with respect to an electric field, and

at least two electrodes enclosing said planar cell from each side of its plane, wherein at least on one side of said plane said electrode is divided into a plurality of adjacent electrodes configured to be controlled separately,

said two electrodes configured to apply a voltage on said liquid crystal, said applied voltage being non-uniform in space implying an electric field inside said cell with a variable spatial distribution along said plane,

said cell with variable spatial distribution configure to modulate at least a pass band comprising at least a wavelength at which an optical signal is transmitted through said cell, while said modulation taking the form of a variable attenuation.

10. The dynamic spectral equalizer according to claim 9, wherein it comprises further a spectral dispersive element on an optical path of said incident light beam such that said spectral dispersive element spread continuously said incident light beam onto said spatial light modulator such that at least each different wavelength present in said incident light beam are focused or imaged towards a different spatial region of said spatial light modulator.

11. The dynamic spectral equalizer according to claim 10, wherein the direction of propagation of each different wavelength when reaching said spatial light modulator are almost perpendicular to it such that said modulator is almost polarization independent.

12. The dynamic spectral equalizer according to claim 10, wherein the focus or image of each different wavelength when reaching said spatial light modulator is adapted to give rise of a spot size of at least several times bigger than the average size of the liquid crystal droplets according to claim 8 such that said spatial light modulator is almost polarization independent.

13. The dynamic spectral equalizer according to claim 9, wherein said spatial light modulator is used in reflection mode such that said incident light beam will be transmitted through said cell twice before being collected as said resulting light beam.

14. The dynamic spectral equalizer according to claim 9, wherein said optical input and output are given by at least an optical fiber.

15. A telecommunications device comprising:

a dynamic spectral equalizer, said dynamic spectral equalizer including;

an optical input for an incident light beam consisting of optical signals transmitted via at least a wavelength,

an optical output for collecting a resulting light beam, said dynamic spectral equalizer comprising further a spatial light modulator on which said incident light beam is focused or imaged and out of which said resulting light beam is collected, said spatial light modulator having;

a planar cell, said planar cell including;

a liquid crystal based substance having a variable scattering Property with respect to an electric field,

at least two electrodes enclosing said planar cell from each side of its plane, at least on one side of said plane said electrode is divided into a plurality of adjacent electrodes configured to be controlled separately,

said two electrodes configured to apply a voltage, on said liquid crystal, said applied voltage being non-uniform in space implying an electric field inside said cell with a variable spatial distribution along said plane,

said cell having a variable spatial distribution configured to modulate at least a pass band comprising at least a wavelength at which an optical signal is transmitted through said cell, while said modulation taking the form of a variable attenuation.