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WO2002005009A1 - Modulateur de reseau de diffraction deformable capable de moduler a la fois la phase et l'amplitude - Google Patents

Modulateur de reseau de diffraction deformable capable de moduler a la fois la phase et l'amplitude Download PDF

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Publication number
WO2002005009A1
WO2002005009A1 PCT/US2001/021715 US0121715W WO0205009A1 WO 2002005009 A1 WO2002005009 A1 WO 2002005009A1 US 0121715 W US0121715 W US 0121715W WO 0205009 A1 WO0205009 A1 WO 0205009A1
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WO
WIPO (PCT)
Prior art keywords
bars
grating
phase
amplitude
spatial light
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/US2001/021715
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English (en)
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WO2002005009A9 (fr
Inventor
Charles F. Hester
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
OPTS Inc
Original Assignee
OPTS Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by OPTS Inc filed Critical OPTS Inc
Priority to AU2001280504A priority Critical patent/AU2001280504A1/en
Publication of WO2002005009A1 publication Critical patent/WO2002005009A1/fr
Publication of WO2002005009A9 publication Critical patent/WO2002005009A9/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
    • G02B26/08—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light
    • G02B26/0808—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light by means of one or more diffracting elements
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/18—Diffraction gratings
    • G02B5/1828—Diffraction gratings having means for producing variable diffraction
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H2225/00—Active addressable light modulator
    • G03H2225/30—Modulation
    • G03H2225/33—Complex modulation
    • G03H2225/34—Amplitude and phase coupled modulation

Definitions

  • the present invention relates to a deformable grating light modulator that is capable of modulating both the phase and the amplitude of incident light.
  • the spatial light modulator is a frequently used component in optical processing and computing. It is a structure that allows a light beam to be controllably spatially (as opposed to frequency) modulated.
  • programmable spatial light modulators including, for example, modulators employing liquid crystal devices, magneto optical materials, and acousto optical materials.
  • Various types of spatial light modulators are described in "Two- Dimensional Spatial Light Modulators: A tutorial” by John A. Neff et al., Proceedings of the IEEE, Vol. 78, No. 5 (May 1990), pages 826-855, which is incorporated entirely herein by reference.
  • Light modulators are used for a variety of purposes, including inputting information into an optical system, modulating carrier light during an optical computation, such as in a Fourier filter, and as a neural network interconnect. Spatial light modulators are particularly useful as digital optical switches. Digital optical switches are employed in, for example, fiber-optic routing networks, printer heads, and displays.
  • One particular type of spatial light modulator is the deformable grating modulator, which uses mirrors formed on the surfaces of micromechanical switches. These devices electrostatically actuate these miniaturized mirrors to switch light from being reflected at one angle to being reflected at another angle.
  • Microelectromechanical switches are easily manufactured using conventional semiconductor techniques, can be very small (several tens of microns), and have very simple moving parts. They can operate in either digital or analog fashion, and typically have a hinge or actuator that is electrostatically or piezoelectrically driven. Typically, a group of switches are arranged together as a set of parallel reflecting bars that form a grating.
  • this type of modulator 101 has a number of reflective parallel bars 103 suspended above a reflective surface 105. Each bar 103 is supported on either end by a support post 107. The modulator 101 also has one or more electrodes 201 corresponding to the bars 103.
  • the distance d between the bars 103 and the reflective surface 105 is ⁇ /2 (or an integral multiple of ⁇ /2), where ⁇ is the wavelength of the light to be modulated.
  • ⁇ is the wavelength of the light to be modulated.
  • the light 203 reflected from the upper reflective surface of the bars 103 is in phase with the light 205 reflected from the reflective surface 105, so the modulator 101 acts as a mirror. This is the "off state of the modulator 101.
  • a charge is applied to the bars 103, and an opposite charge is applied to the electrodes 201.
  • each bar 103 is supported at either end by a support post 107.
  • the end portions of the bars 103 serve as hinges and flex in order to allow the height of the center portion of the bar 103 to change. While these end portions must flex, however, they must also be stiff enough to support the reflective bar 103. Accordingly, both the bars 103 and the electrodes 201 must carry a large amount of electric charge in order to sufficiently flex the bars 103.
  • modulators One problem with all types of presently available modulators, however, is that they either suffer from poor overall space bandwidth or cannot represent full four quadrant complex numbers, i.e., they cannot perform full phase and amplitude modulation. Indeed, conventional liquid crystal modulators experience a coupled phase and amplitude modulation. That is, conventional liquid crystal modulators cannot control the amplitude of a light signal without simultaneously modifying the phase of that signal.
  • phase and amplitude constraint filter designers who program pattern recognition systems must use suboptimum designs based on the remapping of the filter to the limited constraint curve provided by the spatial light modulator.
  • using a spatial light modulator as an input device requires the input to have a coupled phase and amplitude, or by design be limited to only amplitude or only phase, thus limiting the operation to input constraint curves.
  • phase-only modulation in particular binary phase-only modulation.
  • layering of the optical processor i.e., taking the output of one stage of processing and feeding it into the next stage, is best performed if full complex number representation is performed in the second stage.
  • the performances of filters that open up the convex hull in pattern space have an inherent need for complex number representation. Accordingly, it would be desirable to have a spatial light modulator that is capable of simultaneously being able to independently modulate both the phase and amplitude of a light signal.
  • the invention is directed to a type of spatial light modulator that may advantageously provide simultaneous independent control of both the phase and amplitude modulation of an incident light signal.
  • One embodiment of the invention is a grating type spatial light modulator having two sets of grating bars. The two sets of grating bars are interleaved and each set is independently controllable. The amplitude of incident light can then be modulated by controlling the relative distance between adjacent bars of either set.
  • the phase of incident light can be modulated by controlling the relative position of the two sets of bars (i.e., the relative position of the halfway line between the two sets of bars relative to an arbitrary plane parallel to the bars).
  • Fig. 2 is a cross-sectional view of the spatial light modulator shown in Fig. 1 taken along section line 2-2'.
  • Fig. 3 is a cross-sectional view of the spatial light modulator shown in Fig. 1 taken along section line 3-3'.
  • Fig. 4 is a cross sectional view showing the relationship between a phase front produced by a deformable grating spatial light modulator and the spacing ⁇ between the bars of the grating.
  • Fig. 5 is a cross sectional view showing the relationship between the phase and amplitude of reflected light to the displacement of bars x and y with respect to a reference surface.
  • Fig. 6 is a cross sectional view of a deformable grating spatial light modulator according to one embodiment of the invention.
  • Fig. 7 is a cross sectional view of a deformable grating spatial light modulator according to another embodiment of the invention Detailed Description Of Preferred Embodiments
  • the field distribution from a reflective surface, such as a deformable grating spatial light modulator, at the coordinate (x,y,z) is
  • the input is the sampled version of the original signal s(x,y).
  • a coherent wave impinging on the surface will undergo diffraction producing orders at angles according to spacing ⁇ and the wavelength ⁇ of the light.
  • This is graphically illustrated in Fig. 4, where the bars 401 and 403 reflect a coherent wave of light 405 to produce a phase front 407.
  • a two-dimensional array of gratings forming a spatial light modulator (SLM) array can be used to input an image into, for example, the optical train of an optical processor for compression.
  • SLM spatial light modulator
  • the information input is seen as the sampled version of a complex function i(x,y), where (x,y) is a coordinate pair.
  • Each grating has a characteristic function c(x,y) that is laid out in a grid for an overall SLM array, giving
  • the grating function has a fundamental frequency as determined by the internal sampling produced by the grating period, P.
  • the grating function is
  • W is the grating width
  • b(x, y) is the bar function.
  • the bar function represents the field over a single grating period .
  • P g For the grating two offset bars of width P g are indicated. With no loss of generality, the width may be just X A P g .
  • the bar function is constant in the y dimension.
  • b( ⁇ ,y) e i ⁇ V - [ ⁇ . - *] * * " * ** [ ⁇ T ⁇ ] the bar fills the pixel vertically.
  • the index of refraction equal to 1 (i.e., the vacuum case)
  • optical phase is , s where d, and cf-_are the displacement of alternate bias.
  • G ⁇ ⁇ dxg ⁇ x)e- 2 ' 0& .
  • complex numbers can be represented and used for display and processing by assigning the amplitude A of a function value as the amplitude of the electric field and assigning the phase as the field phase, U(x,y)-Ae' ⁇ . From the foregoing, it will also be appreciated that this information can now be defined by, for example, deformable gratings in a spatial light modulator array, i.e., that a spatial light modulator array can be used to represent complex numbers.
  • each grating corresponding to a pixel the information is sampled g(n,m) ⁇ f ⁇ x,y)-comb ⁇ x
  • the sampled r s J information is placed in an array of pixels, i(x,y)
  • the pixel information array is then mixed with a grating
  • the grating 601 has a first set of grating bars 603 and a second set of grating bars 605. These bars are interleaved, such that each bar 603 is adjacent to only a bar 605 and each bar 605 is adjacent only to a bar 603. With this arrangement, the grating pitch for the grating is the length of a bar 603 and its adjacent bar 605.
  • Both the bars 603 and the bars 605 can be independently moved relative to, a fixed reference plane 607.
  • bars 603 can be moved toward the reference plane 607 while the bars 605 remain stationary, and vice versa.
  • Another embodiment of the invention is illustrated in Fig. 7.
  • the deformable grating spatial light modulator of Fig. 7 has two sets of independently controllable bars 703 and
  • each bar 703 and 705 are arranged in pairs. That is, each bar 703 (except for an end bar) will be adjacent to both another bar 703 and a bar 705. Simliarly, each bar 705 (except for an end bar) will be adjacent to both another bar 705 and a bar
  • the grating pitch for the grating is the length of two bars 703 and two bars 705.
  • spatial light modulators according to the invention can mix information on a grating carrier to effect, by diffraction, large separation of modulation information in the Fourier plane.
  • the modulation is well-separated in diffraction orders +1, 0, -1 of the grating pitch, the on to off states are of high dynamic range.
  • the carrier modulation requires only two drive voltages per sample point, one for phase and one for amplitude, with each drive voltage controlling the position of one of two sets of bars.
  • a separate grating carrier, un-modulated can be used in conjunction with the primary carrier at 2:1 ration that will result in a side band that suppresses in band off state modulation and even higher dynamic ranges.

Landscapes

  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Mechanical Light Control Or Optical Switches (AREA)
  • Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)

Abstract

L'invention porte sur un modulateur de lumière spatial de type réseau de diffraction possédant deux ensembles de barres (703, 705, ce modulateur assurant la commande indépendante et simultanée de la modulation de phase et d'amplitude d'un signal optique incident. Le deux ensembles de barres du réseau de diffraction sont entrelacés et chaque ensemble peut être commandé indépendamment. On module l'amplitude de la lumière incidente en réglant la distance relative entre des barres adjacentes de l'un ou l'autre des ensembles. On module la phase de la lumière incidente en réglant la position relative des deux ensembles de barres par rapport à un plan de référence fixe (707).
PCT/US2001/021715 2000-07-10 2001-07-10 Modulateur de reseau de diffraction deformable capable de moduler a la fois la phase et l'amplitude Ceased WO2002005009A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU2001280504A AU2001280504A1 (en) 2000-07-10 2001-07-10 Deformable grating modulator capable of both phase and amplitude modulation

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US61302000A 2000-07-10 2000-07-10
US09/613,020 2000-07-10

Publications (2)

Publication Number Publication Date
WO2002005009A1 true WO2002005009A1 (fr) 2002-01-17
WO2002005009A9 WO2002005009A9 (fr) 2002-07-18

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AU (1) AU2001280504A1 (fr)
WO (1) WO2002005009A1 (fr)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2428830A4 (fr) * 2009-06-24 2012-05-02 Huawei Tech Co Ltd Filtre optique et son procédé de spectroscopie
DE202013004066U1 (de) 2013-04-30 2014-08-01 Dieter Folland Luft- und rieseldichte Dosier- Faltschachtel
CN112731577A (zh) * 2020-12-26 2021-04-30 华中光电技术研究所（中国船舶重工集团公司第七一七研究所） 用于振幅/相位双重调制的四区域光栅及其制作方法

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5677783A (en) * 1992-04-28 1997-10-14 The Board Of Trustees Of The Leland Stanford, Junior University Method of making a deformable grating apparatus for modulating a light beam and including means for obviating stiction between grating elements and underlying substrate
US5949570A (en) * 1995-06-20 1999-09-07 Matsushita Electric Industrial Co., Ltd. Diffractive optical modulator and method for producing the same, infrared sensor including such a diffractive optical modulator and method for producing the same, and display device including such a diffractive optical modulator
US5999319A (en) * 1997-05-02 1999-12-07 Interscience, Inc. Reconfigurable compound diffraction grating
US6252697B1 (en) * 1998-12-18 2001-06-26 Eastman Kodak Company Mechanical grating device

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5677783A (en) * 1992-04-28 1997-10-14 The Board Of Trustees Of The Leland Stanford, Junior University Method of making a deformable grating apparatus for modulating a light beam and including means for obviating stiction between grating elements and underlying substrate
US5949570A (en) * 1995-06-20 1999-09-07 Matsushita Electric Industrial Co., Ltd. Diffractive optical modulator and method for producing the same, infrared sensor including such a diffractive optical modulator and method for producing the same, and display device including such a diffractive optical modulator
US5999319A (en) * 1997-05-02 1999-12-07 Interscience, Inc. Reconfigurable compound diffraction grating
US6252697B1 (en) * 1998-12-18 2001-06-26 Eastman Kodak Company Mechanical grating device

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2428830A4 (fr) * 2009-06-24 2012-05-02 Huawei Tech Co Ltd Filtre optique et son procédé de spectroscopie
DE202013004066U1 (de) 2013-04-30 2014-08-01 Dieter Folland Luft- und rieseldichte Dosier- Faltschachtel
CN112731577A (zh) * 2020-12-26 2021-04-30 华中光电技术研究所（中国船舶重工集团公司第七一七研究所） 用于振幅/相位双重调制的四区域光栅及其制作方法

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Publication number Publication date
WO2002005009A9 (fr) 2002-07-18
AU2001280504A1 (en) 2002-01-21

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