Dynamic optical filter having a spatial light modulator

• US 7,019,883 B2
• Filed: 04/03/2002
• Issued: 03/28/2006
• Est. Priority Date: 04/03/2001
• Status: Expired due to Term

• Current Assignee: II-VI Delaware, Inc. (Coherent Corp.)
• Original Assignee: Cidra Sarl (Nordic Cultural & Educational Foundation)
• Inventors: Kersey, Alan D., Davis, Michael, Moon, John, Dunphy, James, Pinto, Joseph, Sirkis, James, Szczepanek, Paul
• Primary Examiner(s): Dang, Hung Xuan
• Assistant Examiner(s): Martinez, Joseph
• Application Number:
  US10/115,647
• Publication Number:
  US 20020176151A1
• Time in Patent Office: 1,455 Days
• Field of Search: 359297-298, 359/308, 359/900, 359571-573, 359290-292, 359/295
• US Class Current: 359/290
• CPC Class Codes: G02B 26/0833 the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD G02B26/0825 takes precedence; micromechanical devices in general B81B
• CPC Class Codes: G02B 26/0841 the reflecting element being moved or deformed by electrostatic means
• CPC Class Codes: G02B 27/1006 for splitting or combining different wavelengths G02B27/1086, G02B27/141 take precedence
• CPC Class Codes: G02B 27/1073 characterized by manufacturing or alignment methods
• CPC Class Codes: G02B 27/108 for sampling a portion of a beam or combining a small beam in a larger one, e.g. wherein the area ratio or power ratio of the divided beams significantly differs from unity, without spectral selectivity
• CPC Class Codes: G02B 27/1086 operating by diffraction only
• CPC Class Codes: G02B 27/126 The splitting element being a prism or prismatic array, including systems based on total internal reflection
• CPC Class Codes: G02B 27/144 using partially transparent surfaces without spectral selectivity G02B27/147 takes precedence
• CPC Class Codes: G02B 27/147 using averaging effects by spatially variable reflectivity on a microscopic level, e.g. polka dots, chequered or discontinuous patterns, or rapidly moving surfaces G02B27/1086 takes precedence
• CPC Class Codes: G02B 6/262 Optical details of coupling light into, or out of, or between fibre ends, e.g. special fibre end shapes or associated optical elements
• CPC Class Codes: G02B 6/266 the optical element being an attenuator
• CPC Class Codes: G02B 6/2713 cascade of polarisation selective or adjusting operations
• CPC Class Codes: G02B 6/272 comprising polarisation means for beam splitting and combining
• CPC Class Codes: G02B 6/278 Controlling polarisation mode dispersion [PMD], e.g. PMD compensation or emulation PMD minimised transmission systems H04B10/2569
• 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 6/2931 Diffractive element operating in reflection
• CPC Class Codes: G02B 6/29311 Diffractive element operating in transmission
• CPC Class Codes: G02B 6/29313 characterised by means for controlling the position or direction of light incident to or leaving the diffractive element, e.g. for varying the wavelength response switching G02B6/35
• CPC Class Codes: G02B 6/29314 by moving or modifying the diffractive element, e.g. deforming
• CPC Class Codes: G02B 6/29395 configurable, e.g. tunable or reconfigurable switching G02B6/35
• CPC Class Codes: G02B 6/29398 : Temperature insensitivity
• CPC Class Codes: G02B 6/3516 : the reflective optical element moving along the beam path, e.g. controllable diffractive effects using multiple micromirrors within the beam
• CPC Class Codes: G02B 6/356 : in an optical cross-connect device, e.g. routing and switching aspects of interconnecting different paths propagating different wavelengths to (re)configure the various input and output links switching polarized beams G02B6/3594; power equalizers G02B6/356 and G02B6/3594; path selecting means H04Q11/0001
• CPC Class Codes: G02B 6/3588 : of the processed beams, i.e. controlling during switching of orientation, alignment, or beam propagation properties such as intensity, size or shape
• CPC Class Codes: G02B 6/359 : of the position of the moving element itself during switching, i.e. without monitoring the switched beams
• CPC Class Codes: G02B 6/4226 : Positioning means for moving the elements into alignment, e.g. alignment screws, deformation of the mount
• CPC Class Codes: G02B 6/4246 : Bidirectionally operating package structures
• CPC Class Codes: H04J 14/021 : Reconfigurable arrangements, e.g. reconfigurable optical add/drop multiplexers [ROADM] or tunable optical add/drop multiplexers [TOADM]
• CPC Class Codes: H04J 14/0213 : Groups of channels or wave bands arrangements
• CPC Class Codes: H04J 14/0221 : Power control, e.g. to keep the total optical power constant
• CPC Class Codes: H04Q 2011/0009 : using wavelength filters
• CPC Class Codes: H04Q 2011/0026 : using free space propagation (e.g. lenses, mirrors)

Abstract

An dynamic optical filter 10 is provided to selectively attenuate or filter a wavelength band(s) of light (i.e., optical channel(s)) or a group(s) of wavelength bands of an optical WDM input signal 12. The optical filter is controllable or programmable to selectively provide a desired filter function. The optical filter 10 includes a spatial light modulator 36, which comprises an array of micromirrors 52 that effectively forms a two-dimensional diffraction grating mounted in a retro-reflecting configuration. Each optical channel 14 is dispersed separately or overlappingly onto the array of micro-mirrors 52 along a spectral axis or direction 55 such that each optical channel or group of optical channels are spread over a plurality of micromirrors to effectively pixelate each of the optical channels or input signal. Each channel 14 or group of channels may be selectively attenuated by flipping or tilting a selected number of micromirrors to thereby deflect a portion of the incident radiation away from the return optical path. The micro-mirrors operate in a digital manner by flipping between a first and second position in response to a control signal 56 provided by a controller 58 in accordance with an attenuation algorithm and an input command 60. The switching algorithm may provide a bit (or pixel) map or look-up table indicative of the state of each of the micro-mirrors 52 of the array to selectively attenuate the input signal and provide a modified output signal 38 at optical fiber 40.

Claims

1. A dynamically selectable optical filter, comprising:

a light dispersive element which receives input light and provides a separated light having various wavelengths of light spatially distributed;

a pixellating filter device, which receives said separated light, having a two-dimensional array of pixels, each of said wavelengths of light being incident on a plurality of pixels, each of said pixels having a first reflection state and a second reflection state in response to a pixel control signal, and said pixellating filter device providing a selected reflected separated light indicative of light provided from said pixels in said first reflection state based on a filter function;

a light combining element, which receives said selected reflected separated light and recombines said selected reflected separated light to provide an output light; and

a controller which generates said pixel control signal indicative of said filter function and wherein said filter function is selectable.

2. The apparatus of claim 1 wherein said pixelating filter device comprises a micro-mirror device and said pixels comprise micromirrors.

3. The apparatus of claim 1 wherein said filter function is:

a band pass filter, a low pass filter, a band reject filter, or a high pass filter.

4. The apparatus of claim 1 wherein said filter function is a predetermined optical loss function.

5. The apparatus of claim 1 wherein said filter function changes dynamically over a predetermined time period.

6. The apparatus of claim 1 wherein said filter function changes continuously based on a predetermined filter change profile.

7. The apparatus of claim 1, wherein the light dispersive element comprises a diffraction grating.

8. The apparatus of claim 1, wherein the light dispersive element disperses optical channels of the input light onto the pixellating filter device to substantially separate the optical channels on the pixellating filter device.

9. The apparatus of claim 1, wherein the cross-sectional area of at least one channel of separated input light is generally circular in shape.

10. The apparatus of claim 1, wherein the cross-sectional area of at least one channel of separated input light is generally elliptical in shape.

11. The apparatus of claim 1, wherein at least one optical channel of said input light is projected onto at least 50 micro-mirrors of said pixellating filter device.

12. The apparatus of claim 1, wherein micro-mirrors discretely switch from a first position to a second position.

13. The apparatus of claim 1, wherein the optical filter further comprises:

a prism element, which receives said separated light having an incidence angle, and which provides a first stabilized light signal, said prism element providing a second stabilized light signal in response to said reflected separated light signal, said second stabilized light being substantially independent of changes in said incidence angle of said separated light.

14. The apparatus of claim 1, wherein the optical filter further comprises:

an optical lens, located a predetermined lens distance from said light dispersive element and having a lens focal length, which receives said separated light, and which provides a focussed light signal, said optical lens distance being different from said focal length so as to provide a substantially constant optical loss over a predetermined wavelength range.

15. The apparatus of claim 1, wherein said light dispersive element dispersing the optical channels of the input light onto said pixelating device to substantially overlap the optical channels on said pixellating filter device.

16. The apparatus of claim 1, wherein said pixellating filter device is oriented such that the optical path length for a given wavelength channel is substantially constant across the projected image on the pixellating filter device.

17. The apparatus of claim 1, wherein the filter function is selectable in response to an input selection provided by a user.

18. The apparatus of claim 1, wherein the two-dimensional array of pixels includes an array of mnicromirrors, each micromirror being about 14–

20 microns wide.

19. The apparatus of claim 1, wherein the two-dimensional array of pixels includes an array of micromirrors having adjacent micromirrors that are closely spaced at approximately 1 micron.

20. The apparatus of claim 1, wherein said filter function is selectable based on a desired spectral filter profile.