[go: up one dir, main page]

WO2012069810A1 - Modulateurs de lumière spatiaux - Google Patents

Modulateurs de lumière spatiaux Download PDF

Info

Publication number
WO2012069810A1
WO2012069810A1 PCT/GB2011/052257 GB2011052257W WO2012069810A1 WO 2012069810 A1 WO2012069810 A1 WO 2012069810A1 GB 2011052257 W GB2011052257 W GB 2011052257W WO 2012069810 A1 WO2012069810 A1 WO 2012069810A1
Authority
WO
WIPO (PCT)
Prior art keywords
slm
pixels
pixel
image
lateral plane
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/GB2011/052257
Other languages
English (en)
Inventor
Adrian James Cable
Gareth John Mccaughan
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.)
Light Blue Optics Ltd
Original Assignee
Light Blue Optics Ltd
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 Light Blue Optics Ltd filed Critical Light Blue Optics Ltd
Publication of WO2012069810A1 publication Critical patent/WO2012069810A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/22—Processes or apparatus for obtaining an optical image from holograms
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/02—Details of features involved during the holographic process; Replication of holograms without interference recording
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/22—Processes or apparatus for obtaining an optical image from holograms
    • G03H1/2202—Reconstruction geometries or arrangements
    • G03H1/2205—Reconstruction geometries or arrangements using downstream optical component
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N5/00—Details of television systems
    • H04N5/74—Projection arrangements for image reproduction, e.g. using eidophor
    • H04N5/7416—Projection arrangements for image reproduction, e.g. using eidophor involving the use of a spatial light modulator, e.g. a light valve, controlled by a video signal
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H2210/00—Object characteristics
    • G03H2210/20—2D object
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H2210/00—Object characteristics
    • G03H2210/40—Synthetic representation, i.e. digital or optical object decomposition
    • G03H2210/44—Digital representation
    • G03H2210/441—Numerical processing applied to the object data other than numerical propagation
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H2223/00—Optical components
    • G03H2223/50—Particular location or purpose of optical element
    • G03H2223/55—Arranged at a Fourier plane
    • 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
    • G03H2225/20—Nature, e.g. e-beam addressed
    • G03H2225/24—Having movable pixels, e.g. microelectromechanical systems [MEMS]
    • 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
    • G03H2225/32—Phase only
    • 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
    • G03H2225/52—Reflective modulator
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H2240/00—Hologram nature or properties
    • G03H2240/50—Parameters or numerical values associated with holography, e.g. peel strength
    • G03H2240/61—SLM related parameters, e.g. pixel size

Definitions

  • This invention relates to spatial light modulator (SLM) devices, in particular for modulating optical phase for the purpose of diffracting light to form images or provide illumination.
  • SLM spatial light modulator
  • holographic projection The formation of images or illumination using a laser-illuminated spatial light modulator to diffract light using phase modulation is an established technique (often termed holographic projection) and has many advantages over conventional image projection techniques, including significantly improved efficiency due to the formation of images using interference (effectively loss-less), compared with conventional techniques (such as LCOS (Liquid Crystal on Silicon) imaging or DLP (Digital Light ProcessorTM) imaging which form images by blocking light.
  • LCOS Liquid Crystal on Silicon
  • DLP Digital Light ProcessorTM imaging which form images by blocking light.
  • LCOS Liquid Crystal on Silicon
  • DLP Digital Light ProcessorTM imaging which form images by blocking light.
  • Such a holographic projection approach can be used to form full-colour images in their entirety (e.g. Choi, Jim et al., Practical Holography XVI and Holographic Materials VIII, Proc. SPIE Vol. 4659 [2002]), in which case the SLM resolution may be comparable to, or larger than the image resolution (e.g.
  • Adaptive optics for astronomical imaging have employed MEMS (micro- electromechanical systems) SLM (spatial light modulator) technology, and a MEMS device with hexagonal pixels in a hexagonal array is described in US2004/0160 18.
  • MEMS micro- electromechanical systems
  • SLM spatial light modulator
  • a MEMS device with hexagonal pixels in a hexagonal array is described in US2004/0160 18.
  • SLM spatial light modulator
  • US2004/0165243 these devices are adapted for use in adaptive optics and the requirements of a diffractive imaging system are significantly different and special, as explained further later.
  • the aim of maximising the diffraction efficiency makes certain pixel shapes and array structures especially advantageous.
  • light loss is proportional to the square of the dead space between pixels whereas in a diffractive imaging system this loss is approximately proportional to the fourth power of the dimension of the dead space between pixels.
  • JP8122760 A JP8122760 A.
  • a method of providing a diffractive image display comprising: displaying a diffraction pattern on pixels of a spatial light modulator (SLM), the SLM comprising a plurality of optical phase modulating pixels; and illuminating said SLM with a beam of light to reconstruct a far field image formed by said diffraction pattern; and wherein the method further comprises: providing a hexagonal or diamond shape for said pixels.
  • SLM spatial light modulator
  • the pixel shape is selected to substantially optimise a diffraction efficiency of the SLM, in particular by minimising the dead space between pixels (subject to any other design constraints which may be present).
  • This in turn can be achieved by selecting a pixel shape which aims to maximise the ratio of the area of a pixel to the perimeter of the pixel, and this leads to a hexagonal or diamond shape for a pixel (noting that one can broadly speaking squash a hexagon to form a diamond).
  • the pixel shape in the diffracted image is dependent on the Fourier transform of the outline of the pixel array, and in some preferred embodiments this is substantially rectangular. It is preferable that the pixels are rectangularly spaced in the sense that the pixels have a regular spacing in the X- and Y- perpendicular directions in a lateral plane of the device.
  • the pixels have a shape given by a shape parameter S the calculation of which is described later.
  • S is greater than 0.333, 0.4, 0.5, 0.6, 0.7, 0.8 or 0.9.
  • a first diffraction order of light diffracted by the SLM as a substantially square shape.
  • this square shape is achieved when the SLM is illuminated by a beam of light at an angle to a normal to the substrate of the SLM which is greater than 0, for example substantially 45°. This facilitates optical design of the holographic projection system.
  • a pixel of the SLM includes a phase ramp and/or at least one phase step, for example a binary phase step of approximate ⁇ 30 mn.
  • a phase ramp or step in Fourier space corresponds to a position shift in image space
  • incorporating a phase ramp/step into the SLM pixel has the effect of shifting the diffraction pattern attenuation envelope (for example a sine envelope) away from a zero order spot and towards a centre of the displayed image. This decreases the attenuation caused by the diffraction attenuation envelope in the Y- direction and thus improves diffraction efficiency.
  • the pixel pitch of the SLM is less than 30 pm by 20 pm in the horizontal and vertical directions respectively, and, preferably, a (perpendicular or minimum) distance between the pixels is less than 1 pm.
  • the pixel pitch in the X- and Y- directions is approximately 15 pm x 10 pm and a space between the pixels is approximately 0.5 pm. Selecting these values of pixel pitch and pixel spacing helps to maximise diffraction efficiency.
  • a pixel comprises a piston-type MEMS optical phase modulation pixel, that is pixel in which a light reflecting surface may be translated in a direction substantially perpendicular to the substrate, for example by application of an electrostatic force.
  • the diffraction pattern displayed on the pixels of the SLM comprises a hologram. More particularly and in preferred implementations the hologram is of a first, low spatial frequency component of an input image, and the reconstructed far field image is used to illuminate a second spatial light modulator which amplitude modulates the reconstructed far field image using a second, substantially higher spatial frequency component of the input image.
  • Embodiments of the method/system may thus further comprise (means for) inputting display image data defining an image for display, processing the image data to determine first in which data representing a first spatial frequency portion of the image data and second image data representing a second spatial frequency portion of the image data, where the second spatial frequency is higher than the first spatial frequency.
  • the method may then comprise displaying a hologram of the first image data on an SLM as described above to form a holographically generated intermediate real image, the method then modulating this intermediate real image using the second image data to display the image.
  • the computation of the hologram becomes relatively quick and straightforward, the resolution of the projection system may readily be changed by changing the resolution of the second SLM without changing that of the hologram SLM, and other benefits such as miniaturisation of the optical system can also be achieved.
  • the active pixel area of the (hologram) SLM may have a lateral dimension of less than 5mm, 4mm, 3mm, 2mm or 1 mm.
  • the invention provides a diffractive image display system
  • a spatial light modulator comprising a plurality of optical phase modulating pixels for displaying a diffraction pattern; at least one light source to illuminate said SLM to reconstruct a far field image formed by said diffraction pattern; wherein said SLM pixels have a hexagonal or diamond shape.
  • the invention provides a phase-modulating spatial light modulator (SLM) comprising a plurality of optical phase modulating pixels for displaying a diffraction pattern, wherein said pixels have a shape parameter S of greater than 0.333 where S is given by:
  • Figure 1 shows a first example of a holographic image projection system for use with an SLM according to an embodiment of the invention
  • Figure 2 shows an improved holographic image projection system for use with an SLM according to an embodiment of the invention
  • Figures 3a to 3d show an example of a holographic image display system without aberration correction illustrating, respectively, a block diagram of a hologram data calculation system, operations performed within the hardware block of the hologram data calculation system, energy spectra of a sample image before and after multiplication by a random phase matrix, and an example of a hologram data calculation system with parallel quantisers for the simultaneous generation of two sub- frames from real and imaginary components of complex holographic sub-frame data;
  • Figures 4a and 4b show, respectively, an outline block diagram of an adaptive OSPR- type system, and details of an example implementation of the system;
  • Figure 5 shows a schematic representation of a pixel layout of an SLM according to an embodiment of the invention, comprising a regular array of irregular hexagonal pixels;
  • Figure 6 shows example techniques for the separation of light incident onto and diffracted from the SLM of Figure 5, by polarization (left) and by angle (right);
  • Figure 7 shows a schematic view from above of a portion of an SLM according to an embodiment of the invention showing four parameters defining pixel shape
  • Figure 8 shows an example of image placement within the first diffraction order of light diffracted by an SLM according to an embodiment of the invention.
  • a spatial light modulator SLM device comprising an array of non-rectangular, in particular hexagonal, pixels for modulating optical phase, for the purpose of diffracting light to form images or illumination.
  • SLM spatial light modulator
  • Such a spatial light modulator is particularly useful for diffractive image formation in a diffractive holographic projector.
  • Figure 1 shows an example optical layout for a first example of a holographic image projection system 100 to project a 2D image onto a screen 110.
  • a holographic image projection system 100 to project a 2D image onto a screen 110.
  • red R, green G, and blue B lasers are red R, green G, and blue B lasers.
  • the system also includes the following additional elements:
  • SLM is the hologram SLM (spatial light modulator).
  • L1, L2 and L3 are collimation lenses for the R, G and B lasers respectively (optional, depending upon the laser output).
  • M1, M2 and M3 are corresponding dichroic mirrors; they may be implemented as a prism assembly.
  • ⁇ PBS (Polarising Beam Splitter) transmits the incident illumination to the SLM.
  • Diffracted light produced by the SLM - naturally rotated in polarisation by 90 degrees (with a liquid crystal SLM) - is then reflected by the PBS towards L4.
  • Lenses L4 and L5 form an output telescope (demagnifying optics).
  • the output projection angle is proportional to the ratio of the focal length of L4 to that of L5.
  • L4 may be encoded into the hologram(s) on the SLM, for example using the techniques we have described in WO2007/110668, and/or output lens L5 may be replaced by a group of projection lenses.
  • L5 may comprise a wide-angle or fisheye lens, mounted for translation perpendicular to the output optical axis (e.g left-right in Figure 1), to enable configuration of the output optical system as an off-axis system for table- down projection.
  • D1 is a diffuser located at intermediate image plane to reduce speckle. It may comprise a plastic plate, and optionally, may be piezoelectrically-actuated so that it can be moved rapidly in two orthogonal directions to reduce streaking
  • the diffuser increases the etendue of the source, increasing safety and reducing speckle.
  • a processor 102 acts as a system controller and performs signal processing in either dedicated hardware, or in software, or in a combination of the two, as described further below.
  • processor 102 inputs image data and provides hologram data 104 to the SLM.
  • the different colours are time-multiplexed and the sizes of the replayed images are scaled to match one another, for example by padding a target image for display with zeros (the field size of the displayed image depends upon the pixel size of the SLM not on the number of pixels in the hologram).
  • the SLM may be a liquid crystal device.
  • SLM technologies to effect phase modulation may be employed, such as a pixellated MEMS-based piston actuator device.
  • Figure 2 shows an optical architecture for a second example of a holographic image projection system 200, in which like elements to Figure 1 are indicated by like reference numerals. This is described in more detail later.
  • the SLM is modulated with holographic data approximating a hologram of the image to be displayed.
  • this holographic data is chosen in a special way, the displayed image being made up of a plurality of temporal sub-frames, each generated by modulating the SLM with a respective sub- frame hologram, each of which spatially overlaps in the replay field (in embodiments each has the spatial extent of the displayed image).
  • Each sub-frame when viewed individually would appear relatively noisy because noise is added, for example by phase quantisation by the holographic transform of the image data.
  • the replay field images average together in the eye of a viewer to give the impression of a low noise image.
  • the noise in successive temporal subframes may either be pseudo-random (substantially independent) or the noise in a subframe may be dependent on the noise in one or more earlier subframes, with the aim of at least partially cancelling this out, or a combination may be employed.
  • Such a system can provide a visually high quality display even though each sub-frame, were it to be viewed separately, would appear relatively noisy.
  • sets of holograms may form replay fields that exhibit mutually independent additive noise. An example is shown below:
  • Step 1 forms N targets G x ( " ] equal to the amplitude of the supplied intensity target l xy , but with independent identically-distributed (i.i.d.), uniformly-random phase.
  • Step 2 computes the N corresponding full complex Fourier transform holograms .
  • Steps 3 and 4 compute the real part and imaginary part of the holograms, respectively. Binarisation of each of the real and imaginary parts of the holograms is then performed in step 5: thresholding around the median of ensures equal numbers of -1 and 1 points are present in the holograms, achieving DC balance (by definition) and also minimal reconstruction error. The median value of may be assumed to be zero with minimal effect on perceived image quality.
  • Figure 3a shows a block diagram of a hologram data calculation system configured to implement this procedure.
  • the input to the system is preferably image data from a source such as a computer, although other sources are equally applicable.
  • the input data is temporarily stored in one or more input buffer, with control signals for this process being supplied from one or more controller units within the system.
  • the input (and output) buffers preferably comprise dual-port memory such that data may be written into the buffer and read out from the buffer simultaneously.
  • the control signals comprise timing, initialisation and flow-control information and preferably ensure that one or more holographic sub-frames are produced and sent to the SLM per video frame period.
  • the output from the input comprises an image frame, labelled /, and this becomes the input to a hardware block (although in other embodiments some or all of the processing may be performed in software).
  • the hardware block performs a series of operations on each of the aforementioned image frames, /, and for each one produces one or more holographic sub-frames, h, which are sent to one or more output buffer.
  • the sub- frames are supplied from the output buffer to a display device, such as a SLM, optionally via a driver chip.
  • a ferroelectric liquid crystal SLM can be advantageous because of its fast switching time.
  • the SLM may be binary phase or multi-phase - binary phase devices can be convenient but binary quantization results in a conjugate image whereas the use of a multi-phase SLM suppresses this.
  • Figure 3b shows details of the hardware block of Figure 3a; this comprises a set of elements designed to generate one or more holographic sub-frames for each image frame that is supplied to the block.
  • one image frame, Ixy is supplied one or more times per video frame period as an input.
  • Each image frame, Ixy is then used to produce one or more holographic sub-frames by means of a set of operations comprising one or more of: a phase modulation stage, a space-frequency transformation stage and a quantisation stage.
  • a set of N sub-frames is generated per frame period by means of using either one sequential set of the aforementioned operations, or a several sets of such operations acting in parallel on different sub-frames, or a mixture of these two approaches.
  • phase-modulation block The purpose of the phase-modulation block is to redistribute the energy of the input frame in the spatial-frequency domain, such that improvements in final image quality are obtained after performing later operations.
  • Figure 3c shows an example of how the energy of a sample image is distributed before and after a phase-modulation stage in which a pseudo-random phase distribution is used. It can be seen that modulating an image by such a phase distribution has the effect of redistributing the energy more evenly throughout the spatial-frequency domain.
  • pseudo-random binary-phase modulation data may be generated (for example, a shift register with feedback).
  • the quantisation block takes complex hologram data, which is produced as the output of the preceding space-frequency transform block, and maps it to a restricted set of values, which correspond to actual modulation levels that can be achieved on a target SLM (the different quantised phase retardation levels may need not have a regular distribution).
  • the number of quantisation levels may be set at two, for example for an SLM producing phase retardations of 0 or ⁇ at each pixel, or more for a multi-phase SLM.
  • the quantiser is configured to separately quantise real and imaginary components of the holographic sub-frame data to generate a pair of holographic sub- frames, each with two (or more) phase-retardation levels, for the output buffer.
  • Figure 3d shows an example of such a system. It can be shown that (depending on the implementation of the procedure) for discretely pixellated fields, the real and imaginary components of the complex holographic sub-frame data are uncorrelated, which is why it is valid to treat the real and imaginary components independently and produce two uncorrelated holographic sub-frames. In other approaches only the real or only the imaginary part may be used.
  • subframe holograms are generated independently and thus exhibit independent noise.
  • this is an open-loop system.
  • the generation process for each subframe takes into account the noise generated by the previous subframes - in order to cancel it out, effectively "feeding back" the perceived image formed after, say, n OSPR frames to stage n+1 of the algorithm.
  • this is a closed-loop system.
  • One example of this approach comprises an adaptive OSPR algorithm which uses feedback as follows: each stage n of the algorithm calculates the noise resulting from the previously-generated holograms H 7 to H ⁇ , and factors this noise into the generation of the hologram H n to cancel it out.
  • noise variance falls as MN 2 in comparison to the 1/ ⁇ / falloff for (non-adaptive) OSPR.
  • An example procedure takes as input a target image T, and a parameter N specifying the desired number of hologram subframes to produce, and outputs a set of N holograms H, to H N which, when displayed sequentially at an appropriate rate, form as a far-field image a visual representation of T which is perceived as high quality.
  • An optional pre-processing step performs gamma correction to match a CRT display by calculating T(x, y) 1 3 .
  • Other pre-processing may include colour space conversion and geometry correction (if projecting at an angle).
  • an array F zero at the procedure start
  • keeps track of a "running total” (desired image, plus noise) of the image energy formed by the previous holograms H 1 to /-/roy., so that the noise may be evaluated and taken into account in the subsequent stage:
  • a random phase factor ⁇ is added at each stage to each pixel of the target image, and the target image is adjusted to take the noise from the previous stages into account, calculating a scaling factor a to match the intensity of the noisy "running total” energy F with the target image energy ( ⁇ ) 2 .
  • H represents an intermediate fully-complex hologram formed from the target T" and is calculated using an inverse Fourier transform operation. It is quantized to binary phase to form the output hologram H n , i.e.
  • an ADOSPR-type method of generating data for displaying an image comprises generating from the displayed image data holographic data for each subframe such that replay of these gives the appearance of the image, and, when generating holographic data for a subframe, compensating for noise in the displayed image arising from one or more previous subframes of the sequence of holographically generated subframes.
  • the compensating comprises determining a noise compensation frame for a subframe; and determining an adjusted version of the displayed image data using the noise compensation frame, prior to generation of holographic data for a subframe.
  • the adjusting comprises transforming the previous subframe data from a frequency domain to a spatial domain, and subtracting the transformed data from data derived from the displayed image data. More details, including a hardware implementation, can be found in WO2007/141567 hereby incorporated by reference.
  • holographic image projection system architecture 200 of Figure 2. This employs dual SLM modulation - low resolution phase modulation and higher resolution amplitude (intensity) modulation. This can provide substantial improvements in image quality, power consumption and physical size.
  • the primary gain of holographic projection over imaging is one of energy efficiency.
  • the low spatial frequencies of an image can be rendered holographically to maintain efficiency and the high-frequency components can be rendered with an intensity-modulating imaging panel, placed in a plane conjugate to the hologram SLM.
  • diffracted light from the hologram SLM device (SLM1) is used to illuminate the imaging SLM device (SLM2).
  • the hologram SLM is preferably be a fast multi-phase device, for example a pixellated MEMS-based piston actuator device.
  • SLM1 is the hologram SLM (spatial light modulator), for example a 160 ⁇ 160 MEMS or ferroelectric liquid crystal device with pixels of sizeA ; it may have physically small lateral dimensions, e.g ⁇ 1mm.
  • ⁇ L1, L2 and L3 are the collimation lenses.
  • M1 , M2 and M3 are dichroic mirrors a implemented as prism assembly.
  • M4 is a turning beam mirror
  • SLM2 is the imaging SLM and has a resolution at least equal to the target image resolution (e.g. 854 * 480); it may comprise a LCOS (liquid crystal on silicon) panel.
  • target image resolution e.g. 854 * 480
  • LCOS liquid crystal on silicon
  • Diffraction optics 210 comprises lenses LD1 and LD2, forms an intermediate image plane on the surface of SLM2, and has effective focal length f such that / ⁇ / ⁇ covers the active area of imaging SLM2.
  • optics 210 perform a spatial Fourier transform to form a far field illumination pattern in the Fourier plane, which illuminates SLM2.
  • PBS2 (Polarising Beam Splitter 2) transmits incident light to SLM2, and reflects emergent light into the relay optics 212.
  • PBS2 preferably has a clear aperture at least as large as the active area of SLM2.
  • Relay optics 212 relay light to the diffuser D1.
  • ⁇ M5 is a beam turning mirror.
  • D1 is a diffuser to reduce speckle, as previously described.
  • Projection optics 214 project the object formed on D1 by the relay optics 212, and preferably provide a large throw angle, for example >90°, for angled projection down onto a table top (the design is simplified by the relatively low optice from the diffuser).
  • a system controller and hologram data processor 202 performs signal processing in either dedicated hardware, or in software, or in a combination of the two, as described further below.
  • controller 202 inputs image data and provides low spatial frequency hologram data 204 to SLM1 and higher spatial frequency intensity modulation data 206 to SLM2.
  • the controller also provides laser light intensity control data 208 to each of the three lasers.
  • the hologram SLM size is M * M pixels.
  • the input image target amplitude, T is of size P * P pixels. Amplitude range for the input is between 0 (black) and 1 (white).
  • D is a diffraction efficiency boost parameter controlling the trade-off between reconstruction error and diffraction efficiency
  • a value of 1.0 gives theoretically perfect reconstruction; larger values of D increase the optical efficiency at the expense of increasing the noise. (Simulations suggest using a value for D of approximately 1.5).
  • the relative laser power K used to display this frame is given by mID.
  • the image is projected by displaying F on the imaging SL , while sequentially displaying the N hologram subframes on the hologram SLM.
  • WO2010/007404 hereby incorporated by reference.
  • FIG. 5 shows a schematic representation of an SLM 500 according to an embodiment of the invention comprising a rectangular array of irregular optical phase modulating pixels 502.
  • the usable diffraction efficiency of the device (that is, the light in the first-order diffraction image formed as a proportion of the total light illuminating the SLM) is related to the pixel shape and arrangement in a non-trivial way.
  • the optimal pixel shape and arrangement depend on a number of factors, including the angle at which the SLM is mounted in the system, and factors such as pixel dead- space that relate to the resolution of the semiconductor fabrication process employed when the SLM is made, but that in general optimal performance is obtained not from rectangular arrays of rectangular pixels, but from substantially rectangular arrays of pixels which are generally irregular hexagons, as illustrated.
  • the image projected by diffraction from such a device is still a rectangular array of rectangularly-spaced pixels - because the diffracted image is given by the Fourier transform of the array, the pixel shape of the diffracted image is not equal or related to the pixel shape of the SLM, but rather given by the Fourier transform of the outline of the entire array, which in this arrangement is still substantially rectangular.
  • a pixel can include (for example) a step such that one-half of the pixel is raised above the other by a few tens of nanometres, which can improve diffraction efficiency by up to 25%.
  • a step such that one-half of the pixel is raised above the other by a few tens of nanometres, which can improve diffraction efficiency by up to 25%.
  • Pixellated SLMs lose light into higher diffraction orders, essentially due to diffraction that results from the shape of the pixel. Different pixel shapes lead to different relative proportions of light diffracted into the desired first order (where the image is formed) against higher diffraction orders (where any light is not usable and therefore wasted).
  • the regular hexagon has the lowest perimeter to area ratio of any tesseliating shape, and therefore potentially satisfies this criterion.
  • the relative distribution of diffraction efficiencies into each order is determined by the Fourier transform of the pixel shape and it also turns out that, for tesseliating shapes, a hexagonal pixel (albeit not necessarily regular) maximises the proportion of light diffracted into the first diffraction order.
  • the optimal hexagon is indeed irregular, with its shape determined by a number of variables, as described further later.
  • One determining factor is the angle of light illuminating the SLM.
  • LCOS liquid crystal
  • the device rotates polarisation as well as modulating phase, so incident light can be separated from diffracted light using a polarising beam splitter (PBS) 604, and therefore a normal angle of incidence can be employed.
  • PBS polarising beam splitter
  • MEMS-based SLM 606 polarisation is not rotated, and therefore a PBS cannot straightforwardly be used to separate incident from diffracted light; instead the SLM may be mounted at an angle, for example 45 degrees, as shown. Similar considerations apply to other SLM technology used to modulate phase.
  • this shows four pixels from an SLM pixel array, illustrating the dimensions used to determine a pixel shape parameter: mathematical modelling can be used to determine the optimal pixel shape for a given illumination condition and SLM pixel array structure. Assuming a hexagonal structure, variables defining a general display pixel layout are the pixel pitch (horizontal ⁇ and vertical A y ), pixel deadspace ADS, and the hexagon height H. A normalised shape parameter S can then be defined in ter
  • the shape parameter S determines the diffraction efficiency of the SLM, and thus for a particular application one can optimise this shape parameter and hence determine an optimum shape for pixels of the SLM, some examples of which are given in Table 1. There is no analytic expression to determine the value of S to optimise diffraction efficiency for a given set of input variables but if desired a value for S can be determined to high accuracy using numerical analysis techniques.
  • an approximate value of the shape parameter may be employed, as indicated in Table 1.
  • the shape parameter effectively defines the pixel shape; for a small pixel dead space the hexagonal shape approaches a diamond shape - that is the vertically orientated sides of the hexagon have a length which approaches zero.
  • the dead space between pixels (which should be small) is limited by the fabrication process and the need to provide clearance between adjacent pixels. Then for a given desired shape parameter knowing the pixel dead space enables values of the horizontal and vertical pixel pitch, and pixel height to be determined.
  • the SLM can then be fabricated with pixels of this shape.
  • the SLM In general, it is desirable for the SLM to produce a diffracted image as large as possible, which makes small pixels desirable. This is subject to a potential constraint that the drive electronics fit underneath a pixel - although it is also practical to put the electronics to one side of the SLM. Additionally, it may be desirable for the first diffraction order, 800 in Figure 8 to be square in aspect ratio, because for various reasons (including the desire to avoid the zero-order undiffracted light region 802 in the middle of the first order) it is practical often to use only one half 804 of the first diffraction order. As this half has an aspect ratio of 2:1 this is suitable for containing a wide variety of image formats.
  • a square first diffraction order is formed when the pixel pitch (distance between centres of adjacent pixels) is a factor of sqrt(2) longer in the x-direction than in the y-direction.
  • a typical suitable pixel pitch may be around 14 x 9.9 um, and MEMS-type processing considerations may give rise to a deadspace of around 0.5 um between adjacent pixels.
  • the pixel contains a step (as described in GB Patent 2454246), mathematical analysis can show that the optimal shape parameter to maximise diffraction efficiency is around 0.775, as shown in Table 2 below:
  • the apparatus comprising a pixellated spatial light modulator with substantially non-rectangular pixels.
  • the light illuminating the SL is preferably coherent although in principle a light emitting diode with a sufficiently small source size may alternatively be employed.
  • the width and height of the pixels may be unequal; more particularly the pixels may be substantially hexagonal in shape.
  • the shape of the pixels is chosen to maximise diffraction efficiency of the image/illumination formation, and the pixels act to modulate phase of light incident on the SLM.
  • the SLM may be fabricated using a range of technologies including, but not limited to: liquid crystal, magneto-optic, acousto-optic, optically-addressed, Kerr or Pockels effect- based, MEMS (micro-electro-mechanical-system), or other technologies.
  • a MEMS SLM may have pixels which translate along an axis substantially perpendicular to the device surface and/or which tilt around one or more axes substantially parallel to the device surface. Movement of the MEMS pixels may be controlled, for example, by electrostatic, magnetic or thermo-mechanical means. No doubt many other effective alternatives will occur to the skilled person. It will be understood that the invention is not limited to the described embodiments and encompasses modifications apparent to those skilled in the art lying within the spirit and scope of the claims appended hereto.

Landscapes

  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Holo Graphy (AREA)
  • Liquid Crystal (AREA)

Abstract

La présente invention concerne un procédé de réalisation d'affichage d'image à diffraction. Ce procédé consiste à afficher un motif de diffraction sur les pixels d'un modulateur de lumière spatial ou "SLM" (Spatial Light Modulator), ce SLM comprenant une pluralité pixels modulant les phases optiques. Le procédé consiste ensuite à éclairer avec un faisceau de lumière ledit SLM de façon à reconstruire une image à l'infini formée par ledit motif de diffraction. Le procédé consiste en outre à donner auxdits pixels une forme hexagonale ou en losange. Dans certains modes de réalisation, ces pixels se caractérisent par un paramètre de forme S supérieur à 0,333, S étant fonction d'un pas d'intervalle entre pixels selon un axe horizontal inscrit dans un plan latéral dudit SLM (DELTAx), d'un pas d'intervalle entre pixels selon un axe vertical inscrit dans un plan latéral dudit SLM (DELTAy), d'une longueur d'espace mort entre pixels (DELTAos), et d'une dimension maximale d'un pixel dans un plan latéral dudit SLM, mesurée selon ledit axe vertical (H).
PCT/GB2011/052257 2010-11-22 2011-11-18 Modulateurs de lumière spatiaux Ceased WO2012069810A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB1019745.7 2010-11-22
GB1019745.7A GB2485607B (en) 2010-11-22 2010-11-22 Spatial light modulators

Publications (1)

Publication Number Publication Date
WO2012069810A1 true WO2012069810A1 (fr) 2012-05-31

Family

ID=43467085

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/GB2011/052257 Ceased WO2012069810A1 (fr) 2010-11-22 2011-11-18 Modulateurs de lumière spatiaux

Country Status (2)

Country Link
GB (1) GB2485607B (fr)
WO (1) WO2012069810A1 (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2019144092A1 (fr) * 2018-01-22 2019-07-25 University Of Tennessee Research Foundation Imagerie à grande vitesse utilisant une détection optiquement modulée périodique
CN115291490A (zh) * 2022-01-24 2022-11-04 四川大学 基于光学计算的拓展距离全息显示方法

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2628535A (en) * 2023-03-24 2024-10-02 Envisics Ltd Driver for a display device

Citations (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20040160118A1 (en) 2002-11-08 2004-08-19 Knollenberg Clifford F. Actuator apparatus and method for improved deflection characteristics
US20040165243A1 (en) 2002-11-08 2004-08-26 Helmbrecht Michael Albert Deformable mirror method and apparatus including bimorph flexures and integrated drive
WO2006134398A2 (fr) 2005-06-14 2006-12-21 Light Blue Optics Ltd Systemes de traitement de signal
WO2007085874A1 (fr) 2006-01-25 2007-08-02 Light Blue Optics Ltd Procédés et appareil pour afficher des images au moyen d'hologrammes
WO2007110668A2 (fr) 2006-03-28 2007-10-04 Light Blue Optics Ltd Dispositifs d'affichage holographique
WO2007141567A1 (fr) 2006-06-02 2007-12-13 Light Blue Optics Ltd Procédés et appareil pour afficher des images couleur en utilisant des hologrammes
EP1892557A1 (fr) * 2006-08-25 2008-02-27 Spatial Photonics, Inc. Modulateur de lumière spatiale basé sur un miroir à fort rapport de remplissage
US20080049291A1 (en) * 2004-11-08 2008-02-28 Stereo Display, Inc. Micromirror arry lens with optical surface profiles
GB2454246A (en) 2007-11-02 2009-05-06 Light Blue Optics Ltd Holographic image display using phase modulation to shift displayed image from zero order
GB2456170A (en) 2008-01-07 2009-07-08 Light Blue Optics Ltd Holographic image display systems
GB2461894A (en) 2008-07-16 2010-01-20 Light Blue Optics Ltd Holographic Display Combining High and Low Resolution Representations of an Image

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH08122760A (ja) * 1994-10-19 1996-05-17 Matsushita Electric Ind Co Ltd 空間光変調素子及びその製造方法

Patent Citations (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20040160118A1 (en) 2002-11-08 2004-08-19 Knollenberg Clifford F. Actuator apparatus and method for improved deflection characteristics
US20040165243A1 (en) 2002-11-08 2004-08-26 Helmbrecht Michael Albert Deformable mirror method and apparatus including bimorph flexures and integrated drive
US20080049291A1 (en) * 2004-11-08 2008-02-28 Stereo Display, Inc. Micromirror arry lens with optical surface profiles
WO2006134398A2 (fr) 2005-06-14 2006-12-21 Light Blue Optics Ltd Systemes de traitement de signal
WO2007085874A1 (fr) 2006-01-25 2007-08-02 Light Blue Optics Ltd Procédés et appareil pour afficher des images au moyen d'hologrammes
WO2007110668A2 (fr) 2006-03-28 2007-10-04 Light Blue Optics Ltd Dispositifs d'affichage holographique
WO2007141567A1 (fr) 2006-06-02 2007-12-13 Light Blue Optics Ltd Procédés et appareil pour afficher des images couleur en utilisant des hologrammes
EP1892557A1 (fr) * 2006-08-25 2008-02-27 Spatial Photonics, Inc. Modulateur de lumière spatiale basé sur un miroir à fort rapport de remplissage
GB2454246A (en) 2007-11-02 2009-05-06 Light Blue Optics Ltd Holographic image display using phase modulation to shift displayed image from zero order
GB2456170A (en) 2008-01-07 2009-07-08 Light Blue Optics Ltd Holographic image display systems
GB2461894A (en) 2008-07-16 2010-01-20 Light Blue Optics Ltd Holographic Display Combining High and Low Resolution Representations of an Image
WO2010007404A2 (fr) 2008-07-16 2010-01-21 Light Blue Optics Limited Systèmes d’affichage d’images holographiques

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
CHOI, JIM ET AL.: "Practical Holography XVI and Holographic Materials VIII", PROC. SPIE, vol. 4659, 2002
R. W. GERCHBERG; W. O. SAXTON: "A practical algorithm for the determination of phase from image and diffraction plane pictures", OPTIK, vol. 35, 1972, pages 237 - 246, XP000615059

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2019144092A1 (fr) * 2018-01-22 2019-07-25 University Of Tennessee Research Foundation Imagerie à grande vitesse utilisant une détection optiquement modulée périodique
US11960100B2 (en) 2018-01-22 2024-04-16 University Of Tennessee Research Foundation High-speed imaging using periodic optically modulated detection
CN115291490A (zh) * 2022-01-24 2022-11-04 四川大学 基于光学计算的拓展距离全息显示方法
CN115291490B (zh) * 2022-01-24 2023-11-03 四川大学 基于光学计算的拓展距离全息显示方法

Also Published As

Publication number Publication date
GB201019745D0 (en) 2011-01-05
GB2485607B (en) 2017-12-27
GB2485607A (en) 2012-05-23

Similar Documents

Publication Publication Date Title
US8432590B2 (en) Holographic image display system
US12345884B2 (en) Holographic image projection with holographic correction
US11803156B2 (en) Near-eye device
US9939781B2 (en) Image phase retrieval
US8154780B2 (en) Holographic image projection systems
US20090002787A1 (en) Holographic Display Devices
WO2012069811A2 (fr) Systèmes holographiques
JP2017198994A (ja) ホログラムを計算する方法
GB2461294A (en) Holographic image display systems
WO2008075096A1 (fr) Systèmes d'affichage holographique d'images
EP2232339A2 (fr) Systèmes d'affichage holographique d'images
GB2445958A (en) Holographic image display systems
WO2012069810A1 (fr) Modulateurs de lumière spatiaux

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 11788917

Country of ref document: EP

Kind code of ref document: A1

NENP Non-entry into the national phase

Ref country code: DE

122 Ep: pct application non-entry in european phase

Ref document number: 11788917

Country of ref document: EP

Kind code of ref document: A1