Diffractive fourier optics for optical communications

• US 6,795,182 B2
• Filed: 07/03/2002
• Issued: 09/21/2004
• Est. Priority Date: 07/06/2001
• Status: Expired due to Fees

• Current Assignee: Arroyo Optics, Inc. (NVIDIA Corporation)
• Original Assignee: Arroyo Optics, Inc. (NVIDIA Corporation)
• Inventors: Rakuljic, George, Kewitsch, Anthony S., Leyva, Victor
• Primary Examiner(s): Evans, F. L.
• Assistant Examiner(s): GEISEL, KARA E
• Application Number:
  US10/187,855
• Publication Number:
  US 20030011769A1
• Time in Patent Office: 811 Days
• Field of Search: 356/328, 356/334, 398/79, 398/82-84, 385/37
• US Class Current: 356/328
• 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 6/2773 Polarisation splitting or combining
• 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 6/29391 Power equalisation of different channels, e.g. power flattening
• CPC Class Codes: G02B 6/29395 configurable, e.g. tunable or reconfigurable switching G02B6/35
• CPC Class Codes: G02B 6/29397 Polarisation insensitivity
• CPC Class Codes: G02B 6/29398 Temperature insensitivity
• 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: H04J 14/02 Wavelength-division multiplex systems
• CPC Class Codes: H04J 14/0221 Power control, e.g. to keep the total optical power constant

Abstract

Systems and methods for modifying, switching, rearranging or otherwise controlling the individual wavelength components of DWDM optical signals are described, which employ compact refolding and reshaping of these dimensionally patterned beams within a confined volume. The wavelength components of the beam are diffractively dispersed with high diffraction efficiency, and then reversely converged to beam waists incident on different ones of an array of control elements such as liquid crystal cells, MEMs and other spatial light modulators, or fixed distributed patterns. With reflective control elements the wavelength components may be reversely refolded along reciprocal paths with rediffraction, to form a reconstituted and revised DWDM output signal. If the control elements transmit at least one of the wavelength components, a separate, adjacent three dimensional beam refolding path, with rediffraction, is used to feed recombined signals to a separate output. High diffraction efficiency and minimal optical aberrations are achieved by employing a diffraction grating and opposed Mangin mirror system as the principal elements for beam refolding. The approach is useful in systems servicing narrow channel separations, and in a wide variety of applications including channel equalization, interleaving, channel blocking, and channel grouping.

Claims

1. The method of separately directing individual wavelength signals from an optical DWDM beam to be modulated at different positions along an image plane, comprising the steps of:

forming a wide, low profile DWDM beam;

tightly refolding the beam at least twice in the low profile direction while diffractively dispersing components in a wavelength dependent manner; and

delivering spatially separated wavelength components of the beam at different positions along the image plane as areal images which are elongated relative to the folding direction.

2. A method as set forth in claim 1 above, further including the steps of separating the DWDM beam into polarization components closely spaced in the low profile direction, and recombining the polarization components for each wavelength component at the image plane.

3. A method as set forth in claim 2 above, wherein the beam widths at each refold are substantially parallel to a given axis, and closely separated relative to that axis, and wherein the separated polarization components for a beam converge to superimpose at the image plane.

4. A method as set forth in claim 1 above, wherein the wide, low profile beam is formed from the image at an input plane, and wherein the components at the image plane are transforms of the image at the input plane.

5. A method as set forth in claim 1 above, including the steps of modifying the wavelength components at the image plane and providing a modified DWDM beam by tight refolding of components with rediffraction.

6. A method as set forth in claim 5 above, including the steps of reflecting polarization modified wavelength components, and rejecting portions of the components in accordance with their polarization after modification and before rediffraction.

9. A method as set forth in claim 6 above, wherein the step of diffractively dispersing comprises high resolution diffraction centered along the transverse plane and along the Littrow angle and the step of converging sagitally distributed wavelength components maps the components to non-constant separations along the image plane.

10. A method as set forth in claim 9 above, wherein the step of modifying the wavelength components comprises reflecting the components with controlled ellipicity, and rejecting portions thereof in accordance with ellipicity before returning the components for refolding and rediffraction, and wherein the rediffraction reunites wavelength components into a single beam.

12. A method as set forth in claim 10 above, wherein the optical correction sequence employs four spherical corrections and a reflection, and wherein the method further includes the steps of separating polarization components in the multiwavelength signal before the spherical corrections, and comprising the polarization components at the modulator plane.

7. The method of modifying individual wavelength signals of a DWDM beam with low insertion loss, low crosstalk and flat passbands, comprising the steps of:

propagating input beam images from an input plane as sagittally spread, transversely narrow anamorphic beam patterns;

successively tightly refolding the anamorphic beam patterns along a central transverse plane with a volume of limited transverse dimension;

during the refolding, diffractively dispersing the wavelength components within the anamorphic pattern;

converging sagitally distributed wavelength components to form beam waists at an image plane, with the beam waists imaging the images at the input plane;

modifying the wavelength components at the image plane; and

returning the modified wavelength components to form an output DWDM beam by reversely refolding and redififacting the beam pattern.

8. A method as set forth in claim 7 above, wherein the wavelength components are individually modified by selective phase retardation and portions of the components are rejected in correspondence to the amount of phase retardation.

11. A method of using spectrometer dispersion of multiwavelength optical signals employing at least one diffraction grating, to provide modified signals with sharp spectral roll aft, adjacent channel crosstalk and low PDL and PDF, comprising the steps of:

directing a two dimensional pattern of the multiwavelength signals through an optical correction sequence employing at least two spherical corrections and reflections;

directing the thus corrected pattern as a two dimensional beam to reflect back from a grating at the Littrow angle to repeat the optical correction sequence with a diffractively dispersed pattern of wavelength signals;

directing the dispersed wavelength signals as linearly separated, diffraction limited optical beams incident on a modulator plane; and

modulating the separate beams at their locations at the modulator plane.

13. The method of individually modifying the channel signals in a wavelength division multiplexed input beam comprising the steps of:

repeatedly refolding the input beam along a beam path volume to provide, successively, a forwardly directed diverging anamorphic beam having a high sagittal width to height ratio within the beam path volume, a reversely directed collimated anamorphic beam, a forwardly directed anamorphic diffracted beam with diffracted beam components dispersed in the sagittal direction, and a reversely directed convergent dispersed beam in which the diffracted beam components have a height to at least equal sagittal width; and

individually modifying the dispersed components of the convergent beam.

14. A method as set forth in claim 13 above, wherein the diverging anamorphic beam is refolded at a first given plane parallel to the width of the anamorphic beam pattern and within a beam path volume of limited height in the direction perpendicular to the first plane, the collimated beam is refolded as a collimated diffracted beam at a second plane, separated in height from the first within the beam path volume, the diffracted collimated beam is refolded at a third plane spaced in height from the first plane within the beam path volume, and the diffracted convergent beam is diverted from the forward and reverse directions within the beam path volume for individual modification of the diffracted components.

15. A method as set forth in claim 13 above, wherein the diffracted convergent beam comprises a plurality of spatially separated spectral component beams wherein each constitutes a different wavelength signal, wherein the refolding steps each include angling the reflected beams toward a different levels during folding and refolding, and wherein the modification step comprises reflecting the different wavelength signals with controlled modulation of gain.

16. A method as set forth in claim 15 above, wherein the forwardly directed diverging anamorphic beam is input into the beam path volume from a given level, the repeated refoldings are at different levels, the spectral components are dispersed in the direction of the width of the anamorphic beams, and wherein the diffracted convergent beams are recombined after reflection in the region of the input region of the forwardly directed diverging beam.

17. A method as set forth in claim 13 above, including the further steps of returning the beam to a wavelength division multiplexed state by repeatedly refolding and beam shaping diffracted beam components after modification, in a reverse sequence to that employed for the input beam.

18. A method as set forth in claim 17 above, wherein the beam after modification of different components is reflected back into the beam path volume and redirected through the reverse refolding sequence in a return path with reciprocal refolding steps in the same volume to provide a combined and modified wavelength division multiplexed output signal within a selected height within the beam path volume.

19. A method as set forth in claim 18 above, wherein the modification step comprises dynamically equalizing the power levels of the spectral components of the wavelength division multiplexed beam.

20. A method as set forth in claim 18 above, wherein the modification step comprises dynamically extinguishing selected wavelength components of the wavelength division multiplexed beam.

21. A method as set forth in claim 17 above, wherein the step of modifying the wavelength components comprises transmitting selected wavelength components into a second beam path volume and the method includes the steps of effecting the return refolding sequence in the second beam path volume.

22. A method as set forth in claim 21 above, wherein the modification step further comprises reflecting wavelength components back through the refolding sequence in reverse directions in the first beam path volume and transmitting other wavelength components through the repeated refolding sequence in the second beam path volume.

23. A method as set forth in claim 17 above, further including the step of diverting at least some modified spectral components to a different level in the beani volume and refolding the said components through the beam volume in the reverse sequence but to a different region than the input beam.

24. A method of dispersing the wavelength signal components in a WDM optical beam for individual modification, the optical beam having an arbitrary state of polarization, the method employing a diffractive grating and an opposed concave reflector, wherein the grating has grating lines substantially transverse to a sagittal plane, comprising the steps of:

separating the WDM beam into orthogonally polarized beams diverging at an angle less than about 2°

;

converting the separated polarized beams to like polarizations;

directing a pair of collimated anamorphic beam patterns of the separate polarization components that are elongated in the sagittal direction and adjacent but separated in the transverse direction against the diffractive grating, with the polarization direction substantially parallel to the grating lines;

converging diffracted wavelength components dispersed by the diffractive grating off the concave reflector to form individual beam waists of each pair of polarization components at a focal plane, and

modifying the individual wavelength components by polarization rotation at the focal plane.

25. The method as set forth in claim 24 above, wherein the step of converting the beams to like polarization comprises splitting the optical beam into s and p polarization components, rotating the p polarization components into parallelism with the s components and both in parallelism to the grating lines on the grating, and the step of modifying the individual wavelength component comprises rotating the beam polarization components by selected amounts, while reflecting the components and rejecting portions of the components depending upon the directions of polarization thereof.

26. The method as set forth in claim 25 above, further including the steps of rediffraction of the modified wavelength components to form separated composite beam patterns, recombining the polarization components, and reconverging the recombined polarization components of each wavelength signal with other modified wavelength signals.

27. The method as set forth in claim 26 above, wherein the diffractive grating is polarization sensitive and wherein the pair of anamorphic beam patterns are closely adjacent and of low profile in the transverse direction and substantially span the grating in the sagittal direction.

28. The method as set forth in claim 27 above, wherein the WDM beam has channel spacings in the range of about 50 GHz or less, and wherein the step of recombining each wavelength signal with other wavelength signals precedes recombining polarization components, and wherein the anamorphic beam patterns reflected on the concave reflector are about 1 mm or less and separated by about 1 mm or less, in the transverse direction.

29. The method of effecting control of individual channels in a wavelength division multiplexed optical signal using at least one reflective grating having a two dimensional surface area and at least one spaced apart and opposing reflective concave surface, each having sagittal and transverse dimensions, comprising the steps of:

launching the optical signal input field as a diverging optical beam of anamorphic character into the spacing between the opposed surfaces with the width of the anamorphic pattern being substantially parallel to the sagittal dimension, redirecting the beam as a collimated anamorphic pattern with an optical power which is a Fourier transform of the input field onto a two dimensional area of the grating to return a high efficiency collimated diffracted beam with dispersed wavelength components onto the reflective concave surface and converging the dispersed components of the beam into a spatially linear distribution of spectral components;

selectively controlling the individual spectral components, and

transforming the field in accordance with an inverse Fourier function while diffractively recombining the controlled spectral components.

30. A method as set forth in claim 29 above, for effecting control within a small volume, wherein the beam patterns are reflected between the reflective surface and grating at different levels and the height of the anamorphic beam is at least an order of magnitude smaller than the sagittal width.

31. A method as set forth in claim 30 above, wherein the method further includes the steps of separating the spectral components in the sagittal direction and shaping the separated spectral components such that each has a substantial height to width ratio relative to the sagittal dimension, separating polarization components of orthogonally related orientation prior to the control step, and recombining the polarization components of the spectral components before recombining the spectral components.

32. A method as set forth in claim 31 above, wherein the components are selectively controlled within a predetermined field of view, and the method further includes the step of rejecting portions of the spectral components subsequent to the control step before recombination of the spectral components.

33. A method as set forth in claim 32 above, wherein the spectral components are reflected in the control step, and wherein the reflected components are inversely transformed and diffractively recombined by refolding the components between the opposed surfaces.

34. A method as set forth in claim 32 above, wherein the control step is used to extinguish selected spectral components.

35. A method as set forth in claim 32 above, wherein the control step is used for selective attenuation of spectral components.

36. A system for controlling the individual channel signals in a wavelength division multiplexed input optical beam, comprising:

an optical interface structure in an input region and having an input optical circuit, and an output optical circuit, the optical interface structure including an anamorphic optical device positioned to direct the input optical beam at an acute angle relative to a sagittal plane as a diverging anamorphic beam having its wide dimension parallel to the sagittal plane;

at least one concave reflector disposed to span the sagittal plane at a selected distance from the input region and having a reflecting face of sufficient area to encompass the anamorphic beam at different transverse positions relative to the sagittal plane, the reflector having an optical power to converging reflect a collimated anamorphic beam at an acute angle to a different transverse level relative to the plane of the optical interface structure;

at least one reflecting diffractive element disposed at the input region and having an areal face positioned to receive the collimated anamorphic beam and angled relative to the sagittal plane to reflect an impinging anamorphic beam pattern as first order diffracted beam components dispersed in the sagittal plane back toward the reflector, wherein the reflector reflects a beam of converging dispersed components toward a predetermined level relative to the sagittal plane, and

a multichannel control device at the predetermined level intercepting the converging diffracted beam components and separately controlling at least some of the diffracted beam components.

37. A system as set forth in claim 36 above, wherein the at least one concave reflector comprises at least one element having refractive optical power, and wherein the at least one reflecting diffractive element comprises a Littrow grating at the Littrow angle with in excess of about 600 lines/mm.

38. A system as set forth in claim 37 above, wherein the Littrow grating has rulings normal to the wide dimension of the collimated anamorphic beam, and wherein the wide dimension of the anamorphic beam encompasses a sufficient length of grating to provide a diffraction efficiency of greater than about 90% or more.

39. A system as set forth in claim 37 above, wherein the multichannel control device comprises an array of liquid crystal cells spanning the predetermined level relative to the sagittal plane, polarization management optics adjacent each of the cells, and an optical structure in the path of the converging diffracted beam components for directing said beam components into the cells of the array and beam components reflected therefrom back through the mirror and diffractive element combination to the optical interface structure.

40. A system as set forth in claim 36 above, wherein the at least one concave reflector comprises a pair of spaced apart optical elements having spherical lens surfaces, and including a beam terminating reflector surface on one of the spherical lens surfaces to form a Mangin mirror structure of high connective capability.

41. A system as set forth in claim 36 above, wherein the optical interface structure further includes at least two parallel optical interface structures spaced apart in the direction transverse to the sagittal plane for directing at least two optical beams of anamorphic shape concurrently therethrough, wherein the multichannel control device directs reflected beam components at two different levels back to the at least one concave reflector and at least one reflecting diffractive element.

42. A system as set forth in claim 41 above, wherein the parallel anamorphic beams are each of the order of 1 mm in transverse dimension and separated by a distance of the order of 1 mm, and wherein the control device comprises polarization beam displacers for directing reflected beam components to two different levels.

43. A system as set forth in claim 42 above, wherein the grating is a single grating at the Littrow angle having about 1100 lines/mm and transversely displaced from the level of the optical interface structure, wherein the Mangin mirror includes two spaced apart lens elements with two spherical surfaces each, the back surface of one of which is reflective.

44. A system as set forth in claim 43 above, wherein the multichannel control device comprises an array of zero twist nematic crystal cells positioned in the sagittal direction and positioned in the sagittal dimension such that the converging dispersed components are approximately centered in the cells of the array.

45. A system as set forth in claim 36 above, further including a polarization responsive beam splitter device in the path between the optical interface structure and the at least one concave reflector, configured to diverge orthogonally polarized beam components of the DWDM beam into narrowly diverging beams in the input direction, and to combine polarization components in the output direction.

46. A system as set forth in claim 44 above, wherein the array of cells are disposed in spaced apart relation to the concave reflector and reflecting diffracting element and the optical structure for the diffracted beam components at the array of cells comprises a pickoff mirror angled to direct the converging diffracted beams at an angle against the pickoff mirror, and to the array.

47. A system as set forth in claim 36 above, wherein the optical interface structure comprises separate anamorphic/collimator ports at different levels transverse to an intermediate sagittal plane therebetween, the concave reflector comprises a pair of mirrors at different sagittal sides, the at least one grating comprises different grating surfaces on opposite levels relative to the intermediate plane and individually in the optical path between the separate anamorphic ports and the mirror, and each grating surface includes at least one interior aperture encompassing the optical path associated therewith.

48. A system as set forth in claim 47 above, wherein the multichannel control device includes an array of cells sagittally positioned at the intermediate plane, and the optical structure comprises a reflector substantially at the level of the intermediate plane for directing the converging beam components transversely to impinge separately on the cells of the array, and the at least one grating comprises a pair of gratings, each angled to define a beam path between the grating surface and a different region of the reflector.

49. A system as set forth in claim 48 above, wherein the multichannel control device comprises an array of transmissive spatial light modulator cells substantially centered relative to the intermediate plane along an approximate centerline, and the system includes separate optical sections on opposite sides of the centerline, wherein the at least one grating comprises at least two gratings, one on each side of the centerline, wherein the at least one concave reflector comprises at least two mirrors, one on each side of the centerline, and wherein the optical interface structure includes an optical device on each side of the for anamorphic conversion of input and output beams.

50. A system as set forth in claim 49 above, wherein the mirrors and gratings on each side of the centerline are disposed to sequentially refold beams in anamorphic patterns in successive reflections between the mirrors and grating combinations on each side, with one side serving to separate wavelength components for the cells and the other side serving to recombine wavelength components after the light modulator cells.

51. A system as set forth in claim 49 above, wherein the gratings on each side of the cells comprise single gratings at a level displaced from the level of the cells on one side thereof and angled to direct beams reflected therefrom in a selected transverse angle relative to the sagittal plane.

52. A system as set forth in claim 51 above, wherein the multichannel control device further includes angled reflectors at the level of the cells for directing beam components to the cells and optionally into or out of the beam refolding paths between the mirror and grating on each side of the cells, whereby the optical devices can be used alternatively for input or output.

53. A system as set forth in claim 50 above, wherein the gratings on each side comprise upper and lower gratings relative to the intermediate plane, each angled to cooperate with the multiply folded anamorphic patterned beam paths, whereby either grating on a side can serve to diffract a composite beam into wavelength components or recombine wavelength components into a wavelength multiplexed beam.

54. A system as set forth in claim 50 above, wherein the optical interface structure comprises separate anamorphic/collimator ports disposed in intermediate positions relative to the surface areas of the gratings, and the gratings include interior apertures in alignment with the ports and providing access into and out of the refolding paths.

55. A compact optical system for individually modifying the wavelength components of a DWDM beam comprising:

dual and opposed reflecting structures within a circumscribing volume, said structure having both sagittal and transverse spans, a first of the structures having optical power in each of the sagittal and transverse directions, and the second of the structures being diffractive, with diffractive power in the sagittal direction;

a wavelength component modifying subassembly mounted at a selected transverse level proximate the second of the structures, the subassembly including an array of sagitally dispersed modifying elements; and

an input/output structure receiving the DWDM input beam and providing a modified DWDM beam as output, the input/output structure being proximate the second of the reflecting structures and including input optics at a predetermined transverse level and an angle to direct an asymmetric beam having its major dimension in the sagittal direction into an optical path reflecting at successively different transverse levels off the reflecting structure to impinge sagittally separated wavelength components on the separate elements of the array.

56. A compact optical system as set forth in claim 55 above, wherein the paths of the beams along directions between the reflecting structures are reflected from the second structure at wavelength dependent angles in the sagittal direction, and reflected from each structure at a non-zero wavelength independent angle in the transverse direction.

57. A compact optical system as set forth in claim 56 above further including optical elements for directing the modified wavelength components from the subassembly to the dual and opposed reflecting structures to recombine the wavelength components into the modified DWDM beam as an output beam.

58. A compact optical system as set forth in claim 57 above, wherein the modifying assembly comprises reflective elements, and wherein the optical elements direct the reflected wavelength components from the modifying elements back through the reflecting structures as the output beam.

59. A compact optical system as see forth in claim 57 above, wherein the modifying elements comprises transmissive elements, and where the dual and opposed reflecting structures comprise dual opposed reflecting structures, one on each side of the modifying elements, and further including an output beam collimator on one side of the modifying elements for receiving modified wavelength components transmitted through the elements and the associated one of the reflecting structures.

60. A compact optical system as set forth in claim 59 above, wherein the diffractive structures on each side of the modifying elements comprise a pair of gratings at different levels relative to the modifying structure, and the beam paths are directed to impinge on a grating at one level for diffraction and a grating on the other level for recombination.

61. A compact optical system as set forth in claim 60 above, wherein the input/output structures include an anamorphic/collimator lens disposed in the interior of at least one grating on each side.

62. A compact optical system as set forth in claim 61 above, wherein the modifying elements are disposed in a reference plane, and the pair of diffractive elements on each side comprise one above and one below the reference plane, and wherein each side of the system includes an anamorphic/collimator lens disposed within the interior region of each of the different gratings, whereby the system is operable reciprocally in different optical paths.

63. A system for modulating the intensity of individual wavelength components in an input DWDM optical beam of arbitrary polarization and channel spacings in the range of about 25-100 GHz, comprising:

a beam refolding system having facing and spaced apart grating and concave reflector devices, the grating comprising a high line density Littrow grating and the reflector device comprising a Mangin mirror providing a convergence factor in the sagittal direction and a collimating factor in the transverse direction, with the grating and the mirror surfaces spanning substantially the same elevations in the transverse direction;

a beam polarization splitter disposed in the path of the input before the beam refolding system;

an input optical structure disposed adjacent the Littrow grating and directing a DWDM beam through the polarization beam splitter and toward the reflector device at a given angle of inclination in the transverse direction, the input optical structure providing an anamorphic beam having its major dimension in the sagittal direction, the Littrow grating and reflector device being configured to serially refold the anamorphic beam first into a collimated beam, second into collimated diffracted beams and third into dispersed converging diffracted beam components having beam waists at a focal plane;

at least one polarization sensitive element in the path of the converging diffracted beam components adjacent the focal plane, and

an array of liquid crystal cells at the focal plane, the liquid crystal cells being reflective and individually controllable to rotate the polarization direction of the beam components to selectable vectors, the at least one polarization sensitive element being oriented to reject polarization components of other than the selected vector angle, and the reflected beam components are redirected back through the beam refolding system and the beam polarization splitter.

64. A system as set forth in claim 63 above, wherein the beam polarization splitter divides the DWDM beam into orthogonally polarized components, and wherein the system further includes a waveplate device for aligning the polarization components in the same direction while maintaining equal optical path lengths.

65. A system as set forth in claim 64 above, wherein the polarization components are parallel to the lines of the Littrow grating, and wherein the beam refolding system is configured to superimpose the polarization components of the diffracted components at the focal plane, and the liquid crystal cells have nematic surfaces oriented in the same direction as the polarization components.

66. A system as set forth in claim 65 above, wherein the orthogonally polarized components are s and p components, wherein the serial refolds are at angles of inclination of less than about 5°

relative to a transverse level plane, and wherein the diffracted beams are sagittally dispersed and asymmetric with a long dimension in the transverse direction.

67. A system as set forth in claim 65 above, wherein the Littrow grating has of the order of 1100 lines per mm, and wherein the Mangin mirror comprises a double Mangin set in the form of a reflective mirror having refractive and reflective faces and an interspersed transmissive element having spherical surfaces of selected curvature on each side, and wherein the s and p components diverge at ±

0.5°

relative to a centerline.

68. A system for separating wavelength components of an arbitrarily polarized DWDM beam having channel spacings in the range of 25 GHz to 100 GHz, and refolding the components to convergence at a local plane, and modulating the components with high efficiency and minimal polarization dependent losses comprising:

input optics receiving the DWDM beam for inputting an anamorphic beam which has a major dimension in the sagittal direction;

a beam splitting optical structure receiving the anamorphic beam from the input optics and separating polarization components in a direction transverse to the sagittal and at oppositely diverging angles relative to a median path between them, said structure including an optical rotator device for aligning both separated polarization components in the same direction and an optical element for equalizing optical path lengths for the separated components;

a beam refolding system including a polarization sensitive reflecting grating and a reflecting optical structure facing each other about a central axis, the system receiving the diverging components of the beam and sagitally dispersing the different wavelengths of the beam, wherein the grating lines of the reflecting grating are aligned with the polarization components and both substantially are transverse to the sagittal direction, and wherein the sagittal dimension of the anamorphic beam substantially fills the grating in the sagittal direction;

the beam refolding system being configured to direct the separated polarization components to a reflective focal plane, and

a reflective modulator array of liquid crystal cells at the focal plane for redirection of modulated wavelength components of the sagittally dispersed beam back through the beam refolding system to recombine the different wavelengths and polarization components to form an output DWDM beam.

69. A system as set forth in claim 68 above, wherein the beam splitting optical structure includes a Wollaston prism device in the path of the input beam for separating s and p components in opposite directions at angles of less than approximately 1°

each from the median path, a waveplate structure in the path of one of the diverging polarization components for rotating the polarization components into parallelism, and an optical element in the path for equalizing the optical path lengths of the components.

70. A system as set forth in claim 69 above, wherein the beam refolding system comprises a polarization sensitive grating at the Littrow angle and the reflecting optical structure comprises a Mangin mirror system with at least two lens elements.

71. A system as set forth in claim 70 above, wherein the Littrow grating has at least about 1000 lines/mm and has grating lines in the outer region from the center that are tilted up to 2°

from the transverse, and wherein the Mangin mirror system comprises a first element having two spherical transmissive surfaces and a second element having two spherical surfaces, one transmissive and the other reflective.

72. A system as set forth in claim 71 above, wherein the input optics and reflective surfaces direct the beam folds to different transverse levels to form anamorphic patterns on the reflective surface of the Mangin mirror that are about 1 mm high and about 1 mm separated in the transverse dimension, and wherein the beam path between reflecting surfaces is less than about 120 mm.

73. A system as set forth in claim 68 above, wherein the reflective modulator array comprises a plurality of zero twist nematic liquid crystal cells for modifying the polarization states of the beam components and polarization sensitive optics in the path of the reflected beams for rejecting portions in accordance with the modified polarization state.

74. An optical system for individually attenuating or extinguishing individual wavelength components of a DWDM signal, comprising:

a temperature stable housing of low thermal coefficient of expansion material defining a volume for multiple reflecting beam pairs;

an optical input/output device mounted in the housing and receiving the DWDM signal and having optical power for inputting an anamorphic beam having its major dimension in a sagittal plane and minor dimension in a transverse piane;

a concave Mangin mirror structure disposed about an optical centerline in the housing at a given focal length from the input/output device and having optical power in the sagittal and transverse directions to collimate the incident beam;

a reflective Littrow grating disposed in the housing about the optical centerline at a given focal length from and facing the Mangin mirror, the Littrow grating having grating lines aligned substantially with the transverse direction to reflect the incident beam as first order diffracted beam components in wavelength dependent distribution in the sagittal direction and at an angle to impinge on the Mangin mirror at a level that reflects back a converging beam of sagittally dispersed wavelength components to a different level with the wavelength components having greater transverse dimension than sagittal dimension and spacing;

a reflective modulating structure for the individual wavelength components proximate the grating and in the plane in the path of the converging wavelength components, the modulating structure comprising a linear plurality of voltage driven reflective liquid crystal cells, each in the path of a different diffracted beam component, and the modulator structure being disposed to reflect dispersed wavelength beam components back from the modulating structure to be rediffracted onto a composite beam from the grating and reflected back to the input/output device.

75. A system as set forth in claim 74 above, wherein the Mangin mirror and Littrow grating form a low numerical aperture, short focal length system, wherein the grating has approximately 1100 lines/mm, wherein the beam impinging on the grating substantially fills the grating in the sagittal direction, wherein the Mangin mirror comprises a pair of lenses with a reflecting surface at one limit thereof and wherein the modulating structure is at the focal plane of the converging dispersed wavelength components at the position of the beam waists therein.

76. An optical system as set forth in claim 75 above, wherein the anamorphic beam has a dimension in the transverse plane of the reflecting surface of the Mangin mirror of approximately 1 mm, and wherein the multiple reflecting beam path folds within a total transverse dimension of less than about 20 mm.

77. An optical system as set forth in claim 76 above, wherein the reflective wavelength component modulating structure further includes a plurality of voltage driver circuits, each coupled to a different one of the liquid crystal cells wherein the modulating structure includes polarization sensitive elements in the path of reflected wavelength components for rejecting portions of the components as determined by the modulation, and wherein the optical path for directing reflected diffracted beam components provides a series of beam folds between the Mangin mirror and the Littrow grating in substantially a reverse direction to the input elliptical beam.

78. An optical system as set forth in claim 77 above, wherein the input/output device comprises an anamorphic/collimator lens coupled into both the input path and the reverse path, and an optical circulator coupled to the anamorphic/collimator lens for separating input from the output beams.

79. An optical system as set forth in claim 77 above, where the input/output devices comprise a separated anamorphic input lens and collimator output lens, and wherein said input lens and output lens are disposed at different transverse levels, and the liquid crystal cells are tilted in the transverse direction to direct the reverse path at different transverse levels such that the recombined beam impinges on the output collimator lens.

80. An optical system as set forth in claim 74 above, wherein the temperature stable housing is hermetically sealed and wherein the internal atmosphere within the housing is adjusted in pressure and constituents to period tune the diffracted beam component wavelengths.

81. An optical system for individually attenuating or extinguishing individual wavelength components of a DWDM signal, comprising:

a temperature stable housing of low thermal coefficient of expansion material defining a volume for multiple reflecting beam paths;

an optical input/output device receiving the DWDM signal and having optical power for inputting an elliptical beam having its major dimension in a sagittal plane and minor dimension in a transverse plane;

a concave mirror system including a first concave mirror disposed in the housing at a given focal length from the input/output device and having optical power in the sagittal and transverse dimensions to collimate the incident beam in those dimensions;

a first grating at the Littrow angle disposed in the housing at a given focal length from the first concave mirror, said first Littrow grating having grating elements aligned with the transverse direction to reflect the incident beam in a wavelength dependent distribution in the sagittal plane as first order diffracted beam components which are at an angle to impinge on the concave mirror at a predetermined level such that the mirror reflects back a converging pattern to a different level, with the dispersed beam components being substantially collimated in the transverse direction;

a transmissive dispersed beam component modulating structure on the same side of the housing as the Littrow grating and in the path of the converging dispersed beam components in the different level, the modulating structure comprising a linear plurality of voltage driven transmissive liquid crystal cells, each in the path of a different dispersed beam component;

a second concave mirror disposed in the housing at the same side thereof as the first concave mirror system and having like optical properties;

a second grating at the Littrow angle disposed in the housing at the same side as the first Littrow grating and having like optical properties, and

reflective elements disposed in a plane intermediate between the predetermined level and the different level for directing converging dispersed beam components to the cells of the modulating structure and diverging diffracted beam components after attenuation through the optical path defined by the second concave mirror and the second Littrow grating, back to the input/output device.

82. An optical system as set forth in claim 81 above, wherein the input/output device includes an input lens disposed within the interior of the first Littrow grating and an output lens disposed within the interior of the second Littrow grating.

83. An optical system as set forth in claim 81 above, wherein the first Littrow grating comprises a split grating having sections at different levels relative to the intermediate plane and the second Littrow grating also comprises a split grating having grating sections at different levels relative to the intermediate plane.

84. An optical system as set forth in claim 83 above, wherein the input/output devices comprise input/output lenses disposed in the interior of each of the grating sections such that four ports are available for input and/or output usage.

85. For a system employing a diffractive assembly to separate DWDM signal communication beams, the combination of:

a beam collimator receiving the DWDM signal;

an anamorphic converter coupled to receive collimated signals from the collimator and to provide an anamorphic beam output having a high sagittal to transverse ratio, the anamorphic output having a beam waist at a distance from the exit of the converter, and

a polarization sensitive separator intercepting the beam waist of the anamorphic beam and providing output beams of orthogonally polarized components therefrom.

86. A combination as set forth in claim 85 above, wherein the polarization responsive separator comprises optical elements disposed to separate s polarization components from p polarization components with an angle of divergence of about 1°

or less.

87. A combination as set forth in claim 86 above, wherein the polarization separator device comprises a Wollaston prism device having a pair of optical wedges, and an air space therebetween, and the beam waist from the anamorphic converter exit is within the air space region.

88. A combination as set forth in claim 87 above, wherein the polarization sensitive device comprises a Wollaston beamsplitter having two pairs of oppositely tapered birefringent wedges disposed serially relative to an optical path area and including a half waveplate disposed between the two pairs of wedges.

89. A combination as set forth in claim 86 above, wherein the diffractive assembly includes grating lines substantially along a selected direction, and the combination further includes a polarization rotation element in the path of one of the wavelength component beams and a path length equalizer element in the path of the other wavelength component beams.

90. A combination as set forth in claim 85 above, wherein the anamorphic converter includes three serially disposed lenses each having power in a given direction.

91. The method of controlling individual optical beams of different wavelengths in a WDM beam to provide high resolution, low crosstalk and high extinction comprising the steps of:

diverging in input WDM beam into a beam of two dimensional cross-section that is substantially greater in a first dimension than in a second orthogonal dimension,

diffractively dispersing the wavelength components through the first dimension while maintaining the wavelength components substantially collimated in the second dimension, to provide physically spaced, spectrally separate beam components longer in the second dimension than the first;

individually adjusting the intensities of the wavelength components by modifying the polarization thereat while reflecting the beam components, rejecting components in the reflected beam components from the intensity adjusted components;

diffractively recombining the intensity adjusted wavelength components into a collimated beam that is substantially greater in a first dimension than in a second, orthogonal dimension, and

converging the recombined beam to an output WDM beam.

92. The method of claim 91 above, further including the steps of diverging the input beam into an anamorphic pattern having like oriented spaced apart polarization components concurrently collimating the anamorphic pattern by reflective and refractive optical correction, distributing the collimated anamorphic pattern by reflective and refractive optical correction, distributing the collimated anamorphic pattern in a direction to provide maximum resolution during diffraction, individually adjusting the beams by variably retarding each pair of components, varying the intensities by rejecting beam components in accordance with the retardation, diffractively recombining the adjusted wavelength components while counterpropagating the beams, and reforming the state of polarization of the output WDM beam.

93. A system for deriving separate combinations of modulated wavelength outputs from a DWDM input optical beam comprising:

an input/output structure receiving the input beam, and including at least two parallel collimators separated by a predetermined distance to define at least two parallel beam paths, anamorphic converter lenses adjacent the at least two parallel collimators and intercepting the beam paths, and a high numerical aperture beam splitter adjacent the anamorphic converter lenses and intercepting the beam paths;

a diffractive Fourier beam refolding system receiving the input beam and providing a plurality of spatially dispersed wavelength components converging toward a focal plane; and

a wavelength component modulating array of reflective cells receiving the individual wavelength components, the cells modulating the wavelength components by varying the polarization thereof, and including at least one polarization beam displacer for diverting wavelength polarization components of a selected direction by the predetermined distance for return via one of the beam paths to a selected collimator in the input/output structure via the beam refolding system.

94. A system as set forth in claim 93 above, wherein the input beam is provided to one beam path and the diverted reflected signals are returned via the other beampath.

95. A system as set forth in claim 93 above, wherein the input beam is provided to one beam path and modulated signals are returned on the same beam path while diverted signals are returned on the other beam path.

96. A system as set forth in claim 93 above, wherein the at least two collimators are each 1 mm O.D. collimators, separated by about 1 mm, and wherein the at least one polarization beam displacer comprises two polarization beam displacers in series of equal optical path length and birefringence to separate modulated components from diverted components by about 1 mm.

97. An optically stable fiber-coupled spectrometer comprising:

an optical spectrometer receiving an input beam containing multiple wavelengths and providing a wavelength dispersed output beam and including at least one stationary modulator element at an object plane, the spectrometer transferring at least one wavelength of the input beam to the at least one modulator element and back as an output beam;

a circuit for modifying the instantaneous state of the modulator element, and

an input/output system coupled to the spectrometer and including an input fiber both providing the input beam and receiving the output beam and optical elements coupling the input fiber to the spectrometer and including elements coupled to the input fiber and arranged such that minor errors in angular or positional locations of the input and output beams nominally have no effect on fiber coupling efficiency.

98. A spectrometer as set forth in claim 97 above, wherein the optical elements include a shared collimator coupled to both launch the input beam and receive the output beam, and wherein the spectrometer further includes an optical circulator coupled to the input fiber for separating the input beam from the output beam.