Optical switching with ferroelectric liquid crystal SLMs

• US 6,975,786 B1
• Filed: 10/04/2000
• Issued: 12/13/2005
• Est. Priority Date: 10/04/1999
• Status: Expired due to Fees

• Current Assignee: Thomas Swan & Company Limited (Aixtron AG)
• Original Assignee: Thomas Swan & Company Limited (Aixtron AG)
• Inventors: Tan, Kim Leong, Holmes, Melanie, Manolis, Ilias, Warr, Steven, Robertson, Brian, Crossland, William, Wilkinson, Timothy, Redmond, Maura
• Primary Examiner(s): Lee, John D.
• Application Number:
  US10/110,031
• Time in Patent Office: 1,896 Days
• Field of Search: 385 15- 18, 385/37, 385/39, 359/15, 359/19, 359/20, 359559-561
• US Class Current: 385/17
• CPC Class Codes: G02B 5/32 Holograms used as optical elements
• CPC Class Codes: G02B 6/264 with optical elements between opposed fibre ends which perform a function other than beam splitting having lens focusing means G02B6/32; utilising prism or grating G02B6/34
• CPC Class Codes: G02B 6/32 having lens focusing means positioned between opposed fibre ends with lens being an integral part of the single fibre end G02B6/262
• CPC Class Codes: G02F 1/133638 Waveplates, i.e. plates with a retardation value of lambda/n
• CPC Class Codes: G02F 1/136277 formed on a semiconductor substrate, e.g. of silicon
• CPC Class Codes: G02F 1/1393 the birefringence of the liquid crystal being electrically controlled, e.g. ECB-, DAP-, HAN-, PI-LC cells G02F1/1396, G02F1/141 take precedence
• CPC Class Codes: G02F 1/1395 Optically compensated birefringence [OCB]- cells or PI- cells
• CPC Class Codes: G02F 1/141 using ferroelectric liquid crystals
• CPC Class Codes: G02F 1/31 Digital deflection, i.e. optical switchingG02F1/33 takes precedence
• CPC Class Codes: G02F 2203/02 reflective
• CPC Class Codes: G02F 2203/12 spatial light modulator
• CPC Class Codes: G02F 2203/50 Phase-only modulation
• CPC Class Codes: G03H 1/0005 Adaptation of holography to specific applications holographic optical element G02B5/32; holographic scanner G02B26/106; recognition using holographic mask G06V10/88; holographic memories G11B7/0065, G11C13/042
• CPC Class Codes: G03H 1/02 Details of features involved during the holographic process; Replication of holograms without interference recording
• CPC Class Codes: G03H 1/08 Synthesising holograms, i.e. holograms synthesized from objects or objects from hologramsusing electric digital computers G06F; G06T
• CPC Class Codes: G03H 1/2294 Addressing the hologram to an active spatial light modulator
• CPC Class Codes: G03H 2001/0224 Active addressable light modulator, i.e. Spatial Light Modulator [SLM] corresponding details, see subgroups of G03H2225/00
• CPC Class Codes: G03H 2001/0825 Numerical processing in hologram space, e.g. combination of the CGH [computer generated hologram] with a numerical optical element
• CPC Class Codes: G03H 2001/085 Kinoform, i.e. phase only encoding wherein the computed field is processed into a distribution of phase differences
• CPC Class Codes: G03H 2001/221 Element having optical power, e.g. field lens
• CPC Class Codes: G03H 2001/261 : in optical contact
• CPC Class Codes: G03H 2001/306 : Tiled identical sub-holograms
• CPC Class Codes: G03H 2210/20 : 2D object
• CPC Class Codes: G03H 2222/31 : Polarised light
• CPC Class Codes: G03H 2222/32 : Unpolarised light
• CPC Class Codes: G03H 2222/34 : Multiple light sources
• CPC Class Codes: G03H 2223/19 : Microoptic array, e.g. lens array
• CPC Class Codes: G03H 2223/20 : Birefringent optical element, e.g. wave plate
• CPC Class Codes: G03H 2225/22 : Electrically addressed SLM [EA-SLM]
• CPC Class Codes: G03H 2225/32 : Phase only
• CPC Class Codes: G03H 2225/52 : Reflective modulator
• CPC Class Codes: G03H 2227/03 : Means for moving one component G03H1/0476, G03H2001/2695 take precedence
• CPC Class Codes: G03H 2240/41 : Binary
• CPC Class Codes: H04Q 2213/1301 : Optical transmission, optical switches
• CPC Class Codes: H04Q 2213/1319 : Amplifier, attenuation circuit, echo suppressor

Abstract

An optical switch uses two ferroelectric liquid crystal spatial light modulators (10, 11) with an interconnect region in between. The switch uses bulk lenses (2, 8) to focus light from an input fibre array (1) to a first spatial light modulator (10), and from the second spatial light modulator (11) to an output array (9). Each spatial light modulator displays a respective hologram selected from a previously calculated set, to cause a desired switching of light from the input fibre array to the output array.

Claims

1. An optical switch comprising an input optical fiber array, the input optical fiber array having plural input optical fibers, an output optical fiber array, and an optical system connecting the input optical fiber array to an output optical fiber receiver array wherein the optical system comprises a first bulk collimating lens, a first ferroelectric liquid crystal spatial light modulator, a first bulk focusing lens, a second bulk collimating lens, a second ferroelectric liquid crystal spatial light modulator, an interconnect region between said first and second ferroelectric liquid crystal spatial light modulators, and a second bulk focusing lens;

wherein the plural input optical fibers of said input optical fiber array in use provide light, said first collimating bulk lens is disposed to receive said light from all of the plural input optical fibers of the input optical fiber array, said first bulk collimating lens is disposed to provide a plurality of collimated light beams from said input optical fiber array, each spatial light modulator is adapted for providing a respective selectable set of holograms, the first bulk focusing lens is disposed to receive light beams from the first ferroelectric liquid crystal spatial light modulator, the second bulk collimating lens is disposed to receive light beams from the first bulk focusing lens and provide a light beam to the second ferroelectric liquid crystal spatial light modulator and the second bulk focusing lens is disposed to provide output light to the output optical fiber array.

2. The optical switch of claim 1, wherein said spatial light modulators are transmissive.

3. The optical switch of claim 1, wherein the optical system has an optical axis, and the input and output optical fiber arrays are mutually offset to opposite sides of the optical axis, other components remaining on-axis.

4. The optical switch of claim 1, wherein the spatial light modulators are reflective.

5. The optical switch of claim 4, wherein the optical system has a zigzag axis, and each of said first bulk focusing lens and second bulk collimating lens is disposed with respect to an associated spatial light modulator such that light travelling along said axis passes twice through each of said lenses.

6. The optical switch of claim 4, wherein each of said first bulk focusing lens and second bulk collimating lens has an associated further lens disposed to form an optical magnification stage.

7. The optical switch of claim 4, wherein a relay lens is disposed in the interconnect region.

8. The optical switch of claim 7, wherein said relay lens is disposed off-axis.

9. The optical system of claim 4, wherein a field lens is disposed in the interconnect region.

10. The optical switch of claim 9, wherein said field lens is disposed off-axis.

11. The optical switch of claim 1, wherein said input optical fiber array and said output optical fiber array have respective input and output ports each comprising a respective 32×

32 array of ports, and said ports are disposed at normalized co-ordinate locations defined by;

Input PortOutput PortLocationsLocations(+72 _i , +86 _i)(+72 _o , +86 _o)(+31 1/60+0 , +31 1/12)(+30 1/60+0 , +31 1/12)(+31 1/30+0 , +31 1/12)(+30 1/30+0 , +31 1/12)(+31 1/20+0 , +31 1/12)(+30 1/20+0 , +31 1/12)(+31 1/60+0 , +31 1/15)(+30 1/60+0 , +31 1/15)(+31 1/30+0 , +31 1/15)(+30 1/30+0 , +31 1/15)(+31 1/20+0 , +31 1/15)(+30 1/20+0 , +31 1/15)(+31 1/60+0 , +31 1/20)(+30 1/60+0 , +31 1/20)(+31 1/30+0 , +31 1/20)(+30 1/30+0 , +31 1/20)(+31 1/20+0 , +31 1/20)(+30 1/20+0 , +31 1/20)(+31 1/60+0 , +31 1/30)(+30 1/60+0 , +31 1/30)(+31 1/30+0 , +31 1/30)(+30 1/30+0 , +31 1/30)(+31 1/20+0 , +31 1/30)(+30 1/20+0 , +31 1/30)(+31 1/60+0 , +31 1/60)(+30 1/60+0 , +31 1/60)(+31 1/30+0 , +31 1/60)(+30 1/30+0 , +31 1/60)(+31 1/20+0 , +31 1/60)(+30 1/20+0 , +31 1/60)(+31 1/60+0 ,

     0)(+30 1/60+0 ,

     0)(+31 1/30+0 ,

     0)(+30 1/30+0 ,

     0)(+31 1/20+0 ,

     0)(+30 1/20+0 ,

     0)(+31 1/60+0 , +30 1/60)(+30 1/60+0 , +30 1/60)(+31 1/30+0 , +30 1/60)(+30 1/30+0 , +30 1/60)(+31 1/20+0 , +30 1/60)(+30 1/20+0 , +30 1/60)(+31 1/60+0 , +30 1/30)(+30 1/60+0 , +30 1/30)(+31 1/30+0 , +30 1/30)(+30 1/30+0 , +30 1/30)(+31 1/20+0 , +30 1/30)(+30 1/20+0 , +30 1/30)(+31 1/60+0 , +30 1/20)(+30 1/60+0 , +30 1/20)(+31 1/30+0 , +30 1/20)(+30 1/30+0 , +30 1/20)(+31 1/20+0 , +30 1/20)(+30 1/20+0 , +30 1/20)(+31 1/60+0 , +30 1/15)(+30 1/60+0 , +30 1/15)(+31 1/30+0 , +30 1/15)(+30 1/30+0 , +30 1/15)(+31 1/20+0 , +30 1/15)(+30 1/20+0 , +30 1/15)(+31 1/60+0 , +30 1/12)(+30 1/60+0 , +30 1/12)(+31 1/30+0 , +30 1/12)(+30 1/30+0 , +30 1/12)

where (η

_i, ξ

_i) are the input port coordinates and (η

_o, ξ

_o) are the output port coordinates.

12. An optical switch comprising an input optical fiber array, the input optical fiber array having plural input optical fibers, and an output optical fiber array, and an optical system connecting the input optical fiber array to the output optical fiber array wherein the optical system comprises first to fifth lenses, the first lens being a first bulk lens for receiving light from all of the plural input optical fibers of the input optical fiber array, a first ferroelectric liquid crystal spatial light modulator, and a second ferroelectric liquid crystal spatial light modulator, each spatial light modulator being adapted for providing a respective selectable set of holograms, wherein the first bulk lens is disposed to receive light from all of the plural input optical fibers and to provide a plurality of collimated light beams from said input optical fiber array to be incident upon the first ferroelectric liquid crystal spatial light modulator, said first ferroelectric liquid crystal spatial light modulator providing a corresponding plurality of light beams, a second lens, a third lens and a fourth lens, the said second lens being disposed to receive said corresponding plurality of light beams and to provide a corresponding plurality of mutually convergent beams, the third lens having a negative power, said third lens disposed to receive said convergent beams and to provide plural mutually divergent output beams, and the fourth lens being disposed to receive said plural mutually divergent beams and collimate said plural mutually divergent beams to be incident upon said second liquid crystal spatial light modulator, said second ferroelectric liquid crystal spatial light modulator providing a corresponding plurality of light beams, the fifth lens being disposed for focussing said corresponding plurality of light beams from said second ferroelectric liquid crystal spatial light modulator onto said output optical fiber array.

13. The optical switch of claim 12, wherein the optical system has an optical axis, the input and output optical fiber arrays, the first, second, fourth and fifth lenses are disposed on the optical axis and the third lens is laterally offset therefrom.

14. An optical switch comprising an input optical fiber array, the input optical fiber array having plural input optical fibers, an output optical fiber array, and an optical system connecting the input optical fiber array to the output optical fiber array wherein the optical system comprises a first bulk lens for receiving light from all of said plural input optical fibers of the input optical fiber array, a first ferroelectric liquid crystal spatial light modulator, a second ferroelectric liquid crystal spatial light modulator, each spatial light modulator being adapted for providing a respective selectable set of holograms, an interconnect region between said first and second ferroelectric liquid crystal spatial light modulators, and a second bulk lens providing output light to the output optical fiber array wherein the first bulk lens is disposed to provide a plurality of collimated light beams from said input optical fiber array, said optical switch further comprising a second lens and a fourth lens, the said second lens for receiving said collimated light beams and providing a corresponding plurality of mutually convergent beams, the optical system further comprising a third lens having a positive power, receiving said convergent beams and providing mutually divergent output beams as a unity conjugate lens, and the fourth lens being disposed for receiving said mutually divergent beams and collimating said beams wherein said second bulk lens is a fifth lens being disposed for focussing said beams onto said output optical fiber array.

15. The optical switch of claim 14, wherein the optical system has an optical axis, the input and output optical fiber arrays, the first, second, fourth and fifth lenses are disposed on the system optical axis and the third lens is laterally offset therefrom.

16. An optical switch comprising an input optical fiber array and a receiver array, and an optical system connecting the input optical fiber array to the receiver array wherein the optical system comprises a first binary reconfigurable spatial light modulator, a second binary reconfigurable spatial light modulator, each spatial light modulator being adapted for providing a respective selectable set of holograms each for a desired switching operation, and a pair of lenses between said first and second binary reconfigurable spatial light modulators for defining therebetween an interconnect region, wherein each spatial light modulator comprises a display screen, memory circuitry for storing a plurality of sets of hologram data, and selection circuitry for selecting one of said sets according to a desired switching function, each stored set of hologram data being calculated by:

determining principal replay co-ordinates of a said hologram according to a desired switching function;

using said co-ordinates, calculating the size in pixels of a base cell;

evaluating a base cell pattern by a phase-quantization procedure; and

replicating said base cell pattern data until the entire aperture of the spatial light modulator is filled.

17. The optical switch of claim 16 wherein said step of determining principal replay co-ordinates of a desired hologram comprises determining the normalized angular deviation upon a collimated paraxial beam required of a desired hologram;

deriving from said deviation the principal replay mode co-ordinates for said desired hologram.

18. The switch of claim 16, having circuitry for scrolling the hologram pattern across the display device by one or more pixels at a time.

19. An optical switch comprising an input optical fiber array and a receiver array, and an optical system connecting the input optical fiber array to the receiver array wherein the optical system comprises a first ferroelectric liquid crystal spatial light modulator, a second ferroelectric liquid crystal spatial light modulator, each spatial light modulator being adapted for providing a respective selectable set of holograms each for a desired switching operation, and a pair of lenses between said first and second ferroelectric liquid crystal spatial light modulators for defining therebetween an interconnect region, wherein each spatial light modulator comprises a display screen, memory circuitry for storing a plurality of sets of hologram data, and selection circuitry for selecting one of said sets according to a desired switching function, each stored set of hologram data being calculated by:

determining principal replay co-ordinates of a said hologram according to a desired switching function;

using said co-ordinates, calculating the size in pixels of a base cell and evaluating a base cell pattern by a phase-quantization procedure; and

replicating said base cell pattern data until the entire aperture of the spatial light modulator is filled.

20. The optical switch of claim 19 wherein said step of determining principal replay co-ordinates of a desired hologram comprises determining the normalized angular deviation upon a collimated paraxial beam required of a desired hologram;

deriving from said deviation the principal replay mode co-ordinates for said desired hologram.

21. The switch of claim 19, having circuitry for scrolling the hologram pattern across the display device by one or more pixels at a time.

22. A method of producing a phase-only computer generated hologram for a pixellated hologram device, having a respective (x,y) plane and a predetermined number of uniformly distributed phase levels, the method comprising:

determining principal replay co-ordinates of a desired hologram;

using said co-ordinates;

calculating the size in pixels of a base cell; and

evaluating a base cell pattern by a phase-quantization procedure; and

replicating said base cell in the plane of the said hologram device until the entire aperture of the device is filled.

23. The method of claim 22 wherein said step of determining principal replay co-ordinates of a desired hologram comprises:

determining the normalized angular deviation upon a collimated paraxial beam required of a desired hologram;

deriving from said deviation the principal replay mode co-ordinates for said desired hologram.

24. The method of claim 22 wherein said step of evaluating comprises:

converting said co-ordinates to rational numbers each comprising a numerator and a denominator, wherein said rational numbers are simplified so that said denominators have their lowest integer values, and using said denominators as the number of pixels for said base cell pattern.

25. The method of claim 24, and further comprising constraining said numerator and denominator by a predetermined mathematical relationship.

26. The method of claim 25 wherein said mathematical relationship is specified by

−

½

D_x≦

N_x≦

½

D_x −

½

D_y 1≦

D_x≦

R_x 1≦

D_y≦

R_y

where N_x, N_y are said numerators D_x, D_y are said denominators, and (R_x, R_y) represent the resolution in number of pixels of the hologram device.

27. The method of claim 25, wherein said evaluating step comprises defining a spatially sampled phase screen Φ

using said rational numbers such that $\mathrm{\varphi <br><br>}<br><br>\left(k,l\right)=k<br><br>\frac{N_x}{D_x}+l<br><br>\frac{N_y}{D_y}$

wherein f is the phase screen, k=0,1,2 . . . (D_x−

1) 1=0,1,2 . . . (D_y−

1), and N_x, N_y are said numerators and D_x, D_y are said denominators.

28. The method of claim 27 wherein said evaluating step further comprises:

phase-quantizing said phase screen to said predetermined number of uniformly distributed phase levels using

φ

_s(k,l)=exp(2π

j×

int{Φ

(k,l)×

Ψ

}/Ψ

)

where φ

_s(k,l) is the final sampled and quantized representation of the base-cell pattern for the target hologram device, ψ

is the number of phase levels supported,

j is the complex operator (−

1)½

,

exp ( . . . ) is the exponential operator, and

int { . . . } is a quantization function that rounds its argument to the nearest integer towards minus infinity.

29. A method of operating an optical switch comprising an input optical fiber array and a receiver array, and an optical system connecting the input optical fiber array to the receiver array wherein the optical system comprises a first binary reconfigurable spatial light modulator, a second binary reconfigurable spatial light modulator, each spatial light modulator being adapted for providing a respective selectable set of holograms each for a desired switching operation, and a pair of lenses between said first and second binary reconfigurable spatial light modulators for defining therebetween an interconnect region, wherein each spatial light modulator comprises a display screen, memory circuitry for a plurality of sets of hologram data and selection circuitry for selecting one of said sets according to a desired switching function, each stored set of hologram data being calculated by:

determining principal replay co-ordinates of a said hologram according to a desired switching function;

using said co-ordinates, calculating the size in pixels of a base cell; and

evaluating a base cell pattern by a phase-quantization procedure; and

replicating said base cell pattern data until the entire aperture of the spatial light modulator is filled, the method comprising;

scrolling the hologram pattern (in either 1- or 2-dimensions as appropriate) across the display device by one or more pixels at a time and at regular intervals.

30. A method of operating an optical switch comprising an input optical fiber array and a receiver array, and an optical system connecting the input optical fiber array to the receiver array wherein the optical system comprises a first ferroelectric liquid crystal spatial light modulator, a second ferroelectric liquid crystal spatial light modulator, each spatial light modulator being adapted for providing a respective selectable set of holograms each for a desired switching operation, and a pair of lenses between said first and second ferroelectric liquid crystal spatial light modulators for defining therebetween an interconnect region, wherein each spatial light modulator comprises a display screen, memory circuitry for a plurality of sets of hologram data and selection circuitry for selecting one of said sets according to a desired switching function, each stored set of hologram data being calculated by:

determining principal replay co-ordinates of a said hologram according to a desired switching function;

using said co-ordinates, calculating the size in pixels of a base cell; and

evaluating a base cell pattern by a phase-quantization procedure; and

replicating said base cell pattern data until the entire aperture of the spatial light modulator is filled, the method comprising;

scrolling the hologram pattern (in either 1- or 2-dimensions as appropriate) across the display device by one or more pixels at a time and at regular intervals.