阅读说明：本技术 激光调制 (Laser modulation ) 是由 J.克里斯特马斯 于 2019-12-02 设计创作，主要内容包括：提供了一种全息图像生成系统,其包括：空间光调制器；光源；时间调制器；光传感器和解调器。空间光调制器具有像素。光源被配置成照射空间光调制器。时间光调制器被布置成随着时间调制光源的输出强度,以编码表示全息图的全息数据。光传感器与空间光调制器相关联。光传感器被配置成接收来自光源的光,并生成代表光源输出强度的信号。解调器连接到光传感器以接收信号。解调器被布置成解码信号以获得全息数据。解调器还连接到空间光调制器,以根据全息数据设置空间光调制器的像素,从而显示准备好被光源照射的全息图,以形成全息重建。(There is provided a holographic image generation system comprising: a spatial light modulator; a light source; a time modulator; a light sensor and a demodulator. The spatial light modulator has pixels. The light source is configured to illuminate the spatial light modulator. The temporal light modulator is arranged to modulate the output intensity of the light source over time to encode holographic data representing the hologram. The light sensor is associated with a spatial light modulator. The light sensor is configured to receive light from the light source and generate a signal representative of the intensity of the light source output. The demodulator is connected to the light sensor to receive the signal. The demodulator is arranged to decode the signal to obtain holographic data. The demodulator is also connected to the spatial light modulator to set the pixels of the spatial light modulator in accordance with the holographic data to display a hologram ready to be illuminated by the light source to form a holographic reconstruction.)

1. A holographic image generation system, comprising:

a spatial light modulator having pixels;

a light source configured to illuminate the spatial light modulator;

a time modulator arranged to modulate the output intensity of the light source over time to encode holographic data representing a hologram;

a light sensor associated with the spatial light modulator and configured to receive light from the light source and generate a signal representative of an output intensity of the light source;

a demodulator connected to the light sensor to receive the signal and decode the signal to obtain the holographic data and to the spatial light modulator to set the pixels of the spatial light modulator in accordance with the holographic data to display a hologram ready to be illuminated by the light source to form a holographic reconstruction.

2. The system of claim 1, wherein the holographic data represents a subsequent frame of video, and the temporal modulator is configured to modulate the output intensity to encode the holographic data representing the subsequent frame while the light source illuminates the spatial light modulator set with holographic data of a current frame of the video to reconstruct the current frame of the video, wherein the subsequent frame follows the current frame.

3. The system of claim 2, further comprising a memory configured to store decoded holographic data of the subsequent frame.

4. The system of any preceding claim, wherein the light sensor is disposed on the spatial light modulator.

5. The system of any preceding claim, wherein the spatial light modulator has a regular arrangement of pixel locations at which pixels are located, and wherein the light sensor is disposed at one of the pixel locations.

6. The system of any preceding claim, wherein the light source comprises a laser.

7. The system of claim 6, wherein the laser comprises a laser diode, and wherein the time modulator comprises control circuitry for the laser diode.

8. The system of any preceding claim, wherein the temporal modulator comprises a light modulator arranged between the light source and the spatial light modulator for modulating the intensity of light output from the light source.

9. The system of any preceding claim, wherein, when the signal representative of the output intensity of the light source indicates that the light source is off, the demodulator is arranged to set the pixels of the spatial light modulator in accordance with the holographic data.

10. A method of arranging pixels of an SLM to represent a hologram, the method comprising:

illuminating a spatial light modulator having pixels with light;

modulating the intensity of the light while illuminating the spatial light modulator to encode holographic data representing a hologram;

sensing a modulated intensity of the light and decoding the modulated intensity to obtain the holographic data;

setting pixels of the spatial light modulator according to the obtained holographic data; and

after setting the pixels of the spatial light modulator, the spatial light modulator is further illuminated with light to form a holographic reconstruction of the hologram.

11. The method of claim 10, wherein sensing comprises sensing at the spatial light modulator.

12. The method of claim 10 or 11, wherein the step of illuminating and the step of further illuminating are performed with the same light source.

13. The method of claim 10 or claim 11 or claim 12, further comprising repeating the illuminating and further illuminating the spatial light modulator to form a holographic reconstruction sequence.

14. The method of claim 13, wherein the holographic reconstruction sequence is equal to a sequence of frames defining a holographic reconstructed video.

15. The method of claim 14, wherein the holographic data represents a subsequent frame of the video, and the method comprises illuminating the spatial light modulator and modulating the intensity of the light to encode holographic data representing a subsequent frame, while setting the spatial light modulator according to holographic data representing a current frame of the video, wherein the subsequent frame follows the current frame.

16. The method of claim 15, further comprising further modulating the intensity of the light while further illuminating the spatial light modulator to encode holographic data representative of another subsequent frame subsequent to the subsequent frame.

17. The method of claim 16, wherein the current frame, a subsequent frame, and another subsequent frame directly follow each other.

18. The method of any of claims 10 to 17, wherein the spatial light modulator has a regular arrangement of pixel locations at which pixels are located, and wherein sensing comprises sensing with a light sensor arranged at one of the pixel locations.

19. The method of any one of claims 10 to 18, wherein the light is emitted by a laser.

20. The method of claim 19, wherein modulating comprises modulating an output intensity of the laser.

21. The method of any one of claims 10 to 20, further comprising turning off the light source between the steps of illuminating and further illuminating, the method comprising setting pixels of the spatial light modulator according to the obtained holographic data while the light source is turned off.

22. The method of any one of claims 10 to 21, further comprising:

setting pixels of the spatial light modulator according to the obtained holographic data when the modulation intensity of the sensed light indicates that the spatial light modulator is not illuminated.

Technical Field

The present disclosure relates to a system for laser modulation. More particularly, the present disclosure relates to an image generation system for communicating holographic data by laser modulation. Some aspects relate to a holographic projector or holographic projection system comprising an image generation system. Some aspects relate to head-up displays and head-mounted displays. Some aspects relate to a method of communicating holographic data by laser modulation.

Background

The light scattered from the object contains amplitude and phase information. This amplitude and phase information can be captured, for example, on a light-sensing plate by well-known interference techniques to form a holographic recording or "hologram" that includes interference fringes. The hologram may be reconstructed by illuminating it with suitable light to form a two-or three-dimensional holographic reconstruction or replay image representative of the original object.

Computer generated holography can numerically simulate the interference process. The computer generated hologram "CGH" may be calculated by a technique based on a mathematical transform, such as a fresnel transform or a fourier transform. These types of holograms may be referred to as fresnel holograms or fourier holograms. A fourier hologram may be considered to be a fourier domain representation of an object or a frequency domain representation of an object. The CGH may also be calculated by coherent ray tracing or point cloud techniques, for example.

The hologram may be displayed, represented or encoded on a spatial light modulator "SLM" arranged to modulate the amplitude and/or phase of incident light. For example, light modulation may be achieved using electrically addressable liquid crystals, optically addressable liquid crystals, or micro-mirrors.

The SLM may comprise a plurality of individually addressable pixels, which may also be referred to as cells or elements. The light modulation scheme may be binary, multilevel or continuous. Alternatively, the device may be continuous (i.e. not comprising pixels) and thus the light modulation may be continuous over the whole device. The SLM may be reflective, meaning that modulated light is reflected off the SLM. The SLM may also be transmissive, meaning that the modulated light output from the SLM is transmissive.

The techniques may be used to provide a holographic projector for imaging. Such projectors have found application in head-up displays "HUDs" and head-mounted displays "HMDs", including, for example, near-eye devices.

Speckle is the result of forming an image using a highly coherent light source. In particular, speckle is the result of interference of many waves having the same frequency but different phases (and in some cases different amplitudes). The different phases cause waves to interfere, so the amplitude and intensity of the resulting waves vary randomly. It is desirable to reduce this speckle because speckle reduces image quality.

Disclosure of Invention

Aspects of the disclosure are defined in the appended independent claims.

There is provided a holographic image generation system comprising: a spatial light modulator; a light source; a time modulator; a light sensor and a demodulator. The spatial light modulator has pixels (or light modulation elements). The light source is configured to illuminate the spatial light modulator (more specifically, illuminate pixels of the spatial light modulator). The temporal light modulator is arranged to modulate the output intensity of the light source over time to encode holographic data representing the hologram. The light sensor is associated with a spatial light modulator. The light sensor is configured to receive light from the light source and generate a signal representative of an output intensity of the light source. The demodulator is connected to the light sensor to receive the signal. The demodulator is arranged to decode the signal to obtain holographic data. The demodulator is also connected to the spatial light modulator to set the pixels of the spatial light modulator in accordance with the holographic data to display a hologram ready to be illuminated by the light source to form a holographic reconstruction.

The holographic data representing the hologram may comprise first data representing the hologram and second data representing the lens function and/or the grating function. The first data and the second data may be combined by addition. The first and second data may each include a plurality of phase delay values. The hologram may be a fourier hologram or a fresnel hologram. The first data may be frequency domain data-that is, the hologram may be said to be a frequency domain hologram. The frequency domain hologram comprises a spatial distribution of spatial frequencies. The hologram may be a phase hologram. The lens function may include a plurality of phase retardation values corresponding to the lens. The grating function may comprise a phase ramp function, such as a wrapped (e.g., modulo 2 π) phase ramp function. In other embodiments, only the first data (i.e. the data representing the hologram) is modulated onto the light output by the light source, and the second data (i.e. the data representing the lens and/or grating) is added to the first data at the SLM side (i.e. after demodulation).

The holographic image generation system may be integrated in another device, for example, the system may be integrated with a holographic projector or a head-up display for a vehicle.

The holographic image generation system may facilitate providing holographic data to a spatial light modulator or SLM without requiring direct electrical connections. Instead, the holographic data may be optically transmitted to the SLM by the same light source used to form the holographic reconstruction of the hologram represented by the holographic data. In particular, the light source may be modulated with holographic data while the SLM is illuminated by the light source. In this way, holographic data can be provided to the SLM without the need for physical/wired/cabled electrical or optical connections (e.g., optical fibers). This helps to provide a simpler, more efficient system, as losses can be reduced.

In some embodiments, the holographic data represents a subsequent frame of the video, the temporal modulator is configured to modulate the output intensity to encode the holographic data representing the subsequent frame, while the light source illuminates the spatial light modulator set with the holographic data of the current frame of the video to reconstruct the current frame of the video, wherein the subsequent frame follows the current frame. In other words, the system operates to encode data for one frame in a sequence of frames while reconstructing a previous frame in the sequence. For example, the holographic data may represent the (n +1) th frame of the video (or sequence of frames), and the temporal modulator may be arranged to encode the holographic data of the (n +1) th frame while the light source illuminates the SLM, which is arranged with the holographic data representing the nth frame of the video, to form a holographic reconstruction of the nth frame of the video. In this way, the current or nth frame of the sequence of frames may be holographically reconstructed while the holographic data of the subsequent (n +1) th frame in the sequence of frames is encoded and provided to the SLM. In some embodiments, the holographic data representing the current and subsequent frames is the same and represents the same image.

In some embodiments, the system further comprises a memory configured to store the decoded holographic data. For example, the memory may be configured to store decoded holographic data of a subsequent frame, while the pixels of the SLM are set according to the holographic data of the current frame. The memory may be configured to store decoded holographic data representing one frame or more than one frame.

In any of the above embodiments, the temporal modulator is arranged to modulate the output intensity of the light source for the entire duration that the light source is arranged to illuminate the spatial light modulator. Alternatively, the temporal modulator is arranged to modulate the output intensity of the light source for a portion of the duration that the light source is arranged to illuminate the spatial light modulator. In other words, the SLM is illuminated for a set time (e.g. a time corresponding to the frame length of the frame being holographically reconstructed), but the light source may be modulated by the time modulator only for a small or part of this time.

In some embodiments, a light sensor associated with the SLM is disposed on the SLM. Alternatively, in some embodiments, the SLM has a regular arrangement of pixel locations at which pixels are located, and the light sensor is arranged at one of these pixel locations. This arrangement can improve the optical efficiency and compactness of the system, since illuminating any area of the SLM other than the pixel area with the light source results in a loss of efficiency.

Optionally, the temporal modulator forms part of the light source. In some embodiments, the light source is a laser source comprising a laser diode, and the time modulator comprises a control circuit for the laser diode. In this way, the laser light is directly modulated, which may improve the optical efficiency of the system. In other embodiments, the temporal modulator comprises an external light modulator arranged in the path of a light source arranged to illuminate the SLM, e.g. a light modulator arranged between the light source and the SLM. The temporal modulator may include control circuitry for the laser diode and/or the external optical modulator, as well as any other suitable components for modulating the intensity of the light source output.

Optionally, a demodulator connected to the light sensor forms part of the light sensor. For example, the demodulator and the light sensor form a single integrated component. Alternatively, the demodulator may be integrated into the driver of the spatial light modulator.

Optionally, the light sensor is arranged to detect when the light source is off (and thus not illuminating the SLM), the light sensor further being arranged to generate a signal indicative of the light source being off, the signal acting as a trigger for the demodulator to set the pixels of the spatial light modulator in accordance with the holographic data.

Optionally, the holographic image generation system further comprises a hologram calculation engine. The hologram calculation engine is arranged to calculate or generate a hologram and holographic data.

Optionally, the controller is coupled to the light source and provides a control signal to the light source. Alternatively or additionally, the controller is coupled to the time modulator and provides a control signal to the time modulator. For example, when the light source is a laser, the controller may provide a control signal to a laser diode control circuit of the laser. The control signal indicates a time period during which the light source should be driven to properly reconstruct the hologram represented by the holographic data. For example, the control signal may indicate a different time period for each frame of video. The control signal may control the light source and/or the time modulator on a frame-by-frame basis.

Optionally, the controller may be coupled to the light source, the spatial light modulator, and the hologram calculation engine. The controller may include a clock that generates the timing signal. The controller may be configured to provide timing signals to the light source, the spatial light modulator, and the hologram calculation engine in order to synchronize these components.

Optionally, the controller may also be coupled to a memory configured to select, store or receive information representing an image to be holographically reconstructed. In this way, the information provided to the hologram calculation engine is synchronized with the calculation or generation of the hologram by the hologram calculation engine to ensure that the correct holographic data is provided to the spatial light modulator for holographic reconstruction.

In a different configuration, the time modulator is arranged to modulate light from the light source with the source image data. In this different configuration, the hologram is determined (e.g., computed or retrieved from memory) at the SLM side.

Alternatively, the hologram calculation engine may provide control signals to the time modulator and/or the light source to synchronize these components, rather than the controller. The control signal may control the light source and/or the time modulator on a frame-by-frame basis.

Optionally, the spatial light modulator is a liquid crystal on silicon spatial light modulator. Optionally, the spatial light modulator is an optically addressed SLM. Preferably, the SLM is arranged to spatially modulate the phase and/or amplitude of the light of the input light beam. Alternatively, the holographic reconstruction is formed by interference of spatially modulated light.

In some embodiments, the hologram provided to the SLM for display or representation on the SLM is a computer generated hologram. In other words, the hologram is computed by the hologram computation engine, not just stored in memory or displayed or represented on the SLM. Alternatively, when the hologram is a computer generated hologram, the computer generated hologram is a mathematical transformation of the holographic reconstruction. Alternatively, when the hologram is a computer generated hologram, a memory may be provided to store holographic data representing the hologram. Optionally, the computer generated hologram is a fourier transform or fresnel transform of a holographic reconstruction. Optionally, the computer generated hologram is a fourier hologram or a fresnel hologram. Alternatively, the computer generated hologram is generated by a point cloud method.

There is also provided a method of arranging pixels of a spatial light modulator, SLM, to represent a hologram, the method comprising: illuminating a spatial light modulator having pixels with light; modulating the intensity of the light while illuminating the spatial light modulator to encode holographic data representing the hologram; sensing a modulation intensity of the light and decoding the modulation intensity to obtain holographic data; setting pixels of a spatial light modulator according to the obtained holographic data; and after the spatial light modulator is set, the spatial light modulator is further illuminated with light to form a holographic reconstruction of the hologram.

Optionally, the sensing step comprises sensing at a spatial light modulator or SLM. In some embodiments, the SLM has a regular arrangement of pixel locations at which pixels are located, and the sensing step comprises sensing with a photosensor arranged at one of the pixel locations.

Optionally, the light is emitted by a laser, and modulating comprises modulating an output intensity of the laser. This modulation may be direct or indirect. In direct modulation, the output intensity of the laser may be directly modulated, for example by a control circuit controlling the laser diode of the laser. Alternatively, the modulation may be indirect, for example with an external modulator, such as an optical modulator.

Optionally, the illuminating step and the further illuminating step are performed with the same light source. In some embodiments, the SLM may be repeatedly illuminated to obtain holographic data representing a hologram encoded within the light source, and then further illuminated to form a holographic reconstruction of the hologram. This enables a holographic reconstruction sequence to be formed. Optionally, the holographic reconstruction sequence is equal to the sequence of frames defining the holographic reconstructed video.

In some embodiments, the step of illuminating forms the nth frame of the sequence of frames, and the step of further illuminating forms the (n +1) th frame of the sequence of frames. In particular, the holographic data represents a subsequent frame of the video, and the step of illuminating and modulating comprises illuminating the spatial light modulator and modulating the intensity of the light to encode holographic data representing a subsequent (n +1) th frame, while setting the spatial light modulator according to the holographic data representing a current nth frame of the video, wherein the subsequent frame follows the current frame.

The method may further comprise further modulating the intensity of the light while further illuminating the spatial light modulator to encode holographic data representative of another subsequent frame subsequent to the subsequent frame. Optionally, the current, subsequent and further subsequent frames directly follow each other. By providing holographic data for a subsequent frame while holographically reconstructing the current frame, and similarly by providing holographic data for a further subsequent frame while holographically reconstructing the subsequent frame, holographic data can be efficiently and effectively provided to the SLM without affecting the reconstruction of the video. In other words, during the illumination step, the current frame is reconstructed, the holographic data of the next frame is transmitted, and during the further illumination step the next frame is reconstructed.

Optionally, the method further comprises turning off the light source between the illuminating and the further illuminating, the method comprising setting pixels of the spatial light modulator according to the obtained holographic data while turning off the light source. In this way, the spatial light modulator is illuminated for a first time period (in which the holographic data is transmitted) and then for a second time period (in which the holographic reconstruction represented by the transmitted data is reconstructed), wherein the first time period follows the second time period. During a third time period between the first and second time periods, the light source is turned off and the pixels are set with holographic data transmitted during the first time period to enable holographic reconstruction during the third time period.

The method may also include a method of implementing any of the above-described features of the holographic image generation system, as well as alternative embodiments described herein.

Any of the above alternative embodiments may be combined in any suitable combination. Moreover, although different embodiments and groups of embodiments may be disclosed separately in the detailed description that follows, any feature of any embodiment or group of embodiments may be combined with any other feature or combination of features of any embodiment or group of embodiments. That is, all possible combinations and permutations of the features disclosed in this disclosure are contemplated.

The terms "set", "encode", "write" or "address" are used to describe the process of providing a plurality of control values to a plurality of pixels of the SLM, which determine the modulation level of each pixel, respectively. It can be said that in response to receiving a plurality of control values, the pixels of the SLM are configured to "display" or "represent" the light modulation profile.

It has been found that a holographic reconstruction of acceptable quality can be formed from a "hologram" that contains only phase information relating to the original object. Such holographic recording may be referred to as phase-only hologram. The embodiments relate to pure phase holograms, but the disclosure is equally applicable to pure amplitude holograms. The present disclosure is equally applicable to forming a holographic reconstruction using amplitude and phase information associated with the original object. In some embodiments, this is achieved by complex modulation using a so-called full complex hologram that contains both amplitude and phase information related to the original object. Such holograms may be referred to as full composite holograms because the value (grey level) assigned to each pixel of the hologram has both amplitude and phase components. The value (gray level) assigned to each pixel can be represented as a complex number with amplitude and phase components. In some embodiments, a fully composite computer generated hologram is calculated.

Reference may be made to phase values, phase components, phase information, or simply, computer generated holograms or pixel phases of spatial light modulators, as shorthand for "phase retardation". That is, any phase value described is actually a number (e.g., in the range of 0 to 2 π) representing the amount of phase retardation provided by the pixel. For example, a pixel of a spatial light modulator described as having a phase value of π/2 will change the phase of the received light by π/2 radians. In some embodiments, each pixel of the spatial light modulator may operate in one of a plurality of possible modulation values (e.g., phase delay values). The term "gray scale level" may be used to refer to a plurality of available modulation levels. For example, for convenience, the term "gray scale level" may be used to refer to a plurality of available phase levels in a phase-only modulator, even if different phase levels do not provide different gray scales. For convenience, the term "gray scale" may also be used to refer to a plurality of available complex modulation levels in a complex modulator.

Drawings

Specific embodiments are described, by way of example only, with reference to the following drawings:

FIG. 1 is a schematic diagram showing a reflective SLM producing a holographic reconstruction on a screen;

FIG. 2A shows a first iteration of a Gerchberg-Saxton type algorithm;

FIG. 2B shows a second and subsequent iteration of a Gerchberg-Saxton type algorithm;

FIG. 2C illustrates an alternative second and subsequent iterations of an example Gerchberg-Saxton-type algorithm;

FIG. 3 is a schematic diagram of a reflective LCOSSLM;

FIG. 4 shows a schematic diagram of a conventional holographic projector;

FIG. 5 shows a timing example of the conventional holographic projector of FIG. 4;

fig. 6 shows a holographic projector comprising a holographic image generation system according to an embodiment;

FIG. 7 shows a schematic diagram of a holographic projector comprising a holographic image generation system according to an embodiment; and

fig. 8 shows a method of setting pixels of an SLM according to an embodiment.

Detailed Description

The present invention is not limited to the embodiments described below, but extends to the full scope of the appended claims. That is, the present invention may be embodied in different forms and should not be construed as limited to the described embodiments, which have been set forth for the purpose of illustration.

Unless otherwise indicated, singular terms may include plural forms.

The structure described as being formed on the upper/lower portion of the other structure or on/under the other structure should be construed to include a case where the structures contact each other, and further, to include a case where the third structure is disposed therebetween.

In describing temporal relationships, for example, when a temporal sequence of events is described as "after," "subsequent," "next," "before," and the like, the disclosure should be considered to include continuous and discontinuous events unless otherwise noted. For example, unless the language "immediately," "immediately," or "directly" is used, the description is to be understood to include instances where it is not continuous.

Although the terms "first," "second," etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the appended claims.

Features of different embodiments may be partially or fully coupled or combined with each other and may interoperate differently from each other. Some embodiments may be performed independently of each other or may be performed together in an interdependent relationship.

Optical arrangement

FIG. 1 shows an embodiment in which a computer generated hologram is encoded on a single spatial light modulator. Computer generated holograms are fourier transforms of objects used for reconstruction. Thus, the hologram can be said to be a fourier domain or frequency domain or spectral domain representation of the object. In this embodiment, the spatial light modulator is a silicon-based reflective liquid crystal "LCOS" device. The hologram is encoded on a spatial light modulator and the holographic reconstruction is formed on a replay field, for example on a light receiving surface such as a screen or diffuser.

A light source 110, such as a laser or laser diode, is arranged to illuminate the SLM 140 through a collimating lens 111. The collimating lens causes a substantially planar wavefront of light to be incident on the SLM. In fig. 1, the direction of the wavefront is off normal (e.g. two to three degrees off true orthogonal to the plane of the transparent layer). However, in other embodiments, the generally planar wavefront is provided at normal incidence and a beam splitter arrangement is used to separate the input and output optical paths. In the embodiment shown in FIG. 1, the arrangement is such that light from the light source is reflected from the mirrored back surface of the SLM and interacts with the light modulation layer to form an emergent wavefront 112. The emergent wavefront 112 is applied to optics comprising a fourier transform lens 120, which is focused on a screen 125. More specifically, Fourier transform lens 120 receives the modulated beam from SLM 140 and performs a frequency-space transform to produce a holographic reconstruction on screen 125.

It is worth noting that in such holography, each pixel of the hologram contributes to the entire reconstruction. There is no one-to-one correlation between a particular point (or image pixel) and a particular light modulation element (or holographic pixel) in the replay field. In other words, the modulated light leaving the light modulating layer is distributed over the entire playback field.

In these embodiments, the location of the holographic reconstruction in space is determined by the dioptric (focusing) power of the fourier transform lens. In the embodiment shown in fig. 1, the fourier transform lens is a physical lens. That is, the fourier transform lens is an optical fourier transform lens, and fourier transform is optically performed. Any lens can act as a fourier transform lens, but the performance of the lens can limit the accuracy with which it can perform a fourier transform. Those skilled in the art understand how to perform an optical fourier transform using a lens.

Hologram calculation

In some embodiments, the computer-generated hologram is a fourier transform hologram, or simply a fourier hologram or fourier-based hologram, wherein the image is reconstructed in the far field by exploiting the fourier transform properties of the positive lens. The fourier hologram is calculated by fourier transforming the desired light field in the replay plane back into the lens plane. The computer-generated fourier hologram may be calculated using a fourier transform.

The Fourier transform hologram may be computed using an algorithm such as the Gerchberg-Saxton algorithm. Furthermore, the Gerchberg-Saxton algorithm can be used to compute holograms in the Fourier domain (i.e., Fourier transform holograms) from pure amplitude information in the spatial domain (e.g., photographs). Phase information associated with the object is effectively "retrieved" from pure amplitude information in the spatial domain. In some embodiments, holograms are computer generated from pure amplitude information using the Gerchberg-Saxton algorithm or a variant thereof.

The Gerchberg Saxton algorithm considers the intensity profile I of the beam in plane A and plane B, respectively_A(x, y) and I_B(x, y) are known and I_A(x, y) and I_B(x, y) case of correlation by a single fourier transform. For a given intensity profile, the phase distribution Ψ in plane A and plane B, respectively, is found_A(x, y) and Ψ_B(x, y) approximate values. The Gerchberg-Saxton algorithm finds a solution to this problem through an iterative process. More specifically, the Gerchberg-Saxton algorithm iteratively applies spatial and spectral constraints while repeatedly transmitting the representative I between the spatial and Fourier (spectral or frequency) domains_A(x, y) and I_BData set (amplitude and phase) of (x, y). A corresponding computer-generated hologram in the spectral domain is obtained by at least one iteration of the algorithm. The algorithm is convergent and arranged to produce a hologram representing the input image. The hologram may be a pure amplitude hologram, a pure phase hologram or a fully multiplexed hologram.

In some embodiments, the phase-only hologram is calculated using an algorithm based on the Gerchberg-Saxton algorithm, such as the algorithms described in british patent 2,498,170 or 2,501,112, which are incorporated herein by reference in their entirety. However, the embodiments disclosed herein describe calculating a phase-only hologram by way of example only. In these embodiments, the Gerchberg-Saxton algorithm retrieves the Fourier transformed phase information Ψ [ u, v ] of the data set, which yields the known amplitude information T [ x, y ], where the amplitude information T [ x, y ] represents the target image (e.g., photograph). Since the amplitude and phase are inherently combined in the fourier transform, the transformed amplitude and phase contain useful information about the accuracy of the computed data set. Thus, the algorithm can be used iteratively, with feedback of both amplitude and phase information. However, in these embodiments, only the phase information Ψ [ u, v ] is used as a hologram to form a hologram representing the target image on the image plane. A hologram is a data set (e.g. a 2D array) of phase values.

In other embodiments, an algorithm based on the Gerchberg-Saxton algorithm is used to compute the full composite hologram. A full composite hologram is a hologram having an amplitude component and a phase component. A hologram is a data set (e.g. a 2D array) comprising an array of complex data values, wherein each complex data value comprises an amplitude component and a phase component.

In some embodiments, the algorithm processes complex data and the fourier transform is a complex fourier transform. The complex data may be considered to include (i) real and imaginary components, or (ii) amplitude and phase components. In some embodiments, the two components of the composite data are processed differently at different stages of the algorithm.

FIG. 2A illustrates a first iteration of an algorithm for computing phase-only holograms according to some embodiments. The input to the algorithm is an input image 210 comprising a 2D array of pixel or data values, where each pixel or data value is an amplitude or amplitude value. That is, each pixel or data value of the input image 210 has no phase component. Thus, the input image 210 may be considered to be a pure amplitude or a pure intensity distribution. An example of such an input image 210 is a photograph or a frame of a video comprising a time sequence of frames. The first iteration of the algorithm begins with a data formation step 202A, which includes assigning a random phase value to each pixel of the input image using a random phase distribution (or random phase seed) 230 to form a starting composite data set, where each data element of the set includes an amplitude and a phase. The starting composite data set may be said to represent the input image in the spatial domain.

The first processing block 250 receives the starting composite data set and performs a composite fourier transform to form a fourier transformed composite data set. The second processing block 253 receives the fourier transformed composite data set and extracts a set of phase values. Second processing block 253 quantizes each phase value to form hologram 280A. Each phase value is quantized according to a phase level that can be represented on the pixels of the spatial light modulator that will be used to "display" the hologram. For example, if each pixel of the spatial light modulator provides 256 different phase levels, each phase value of the hologram is quantized to one of the 256 possible phase levels. Hologram 280A is a phase-only fourier hologram representing the input image. Hologram 280A may be said to represent an input image in the spectral or fourier or frequency domain. In some embodiments, the algorithm stops at this point.

However, in other embodiments, the algorithm continues as indicated by the dashed arrow in FIG. 2A. In other words, the steps following the dashed arrows in FIG. 2A are optional (i.e., not necessary for all embodiments). If the algorithm continues, the second processing block 253 additionally replaces the amplitude values of the complex data set of the Fourier transform with new amplitude values. The new amplitude value is a distribution of values representing an amplitude distribution of a light pattern to be used for illuminating the spatial light modulator. In some embodiments, each new amplitude value is 1. In other embodiments, the second processing block 253 processes the amplitude values of the second composite data set, e.g., performs a mathematical operation or a series of mathematical operations on each amplitude value to form new amplitude values. The second processing block 253 outputs a composite data set comprising quantized phase values and new amplitude values.

The third processing block 256 receives the composite data set output by the second processing block 253 and performs an inverse fourier transform to form an inverse fourier transformed composite data set. The inverse fourier transformed composite data set can be said to represent the input image in the spatial domain.

A fourth processing block 259 receives the inverse fourier transformed composite data set and evaluates the distribution of amplitude values 211A. In particular, the fourth processing block 259 compares the distribution of amplitude values 211A of the inverse fourier transformed composite data set with the input image 510, the input image 510 itself of course being a distribution of amplitude values. If the difference between the distribution of amplitude values 211A and the input image 210 is sufficiently small, the fourth processing block 259 determines that the hologram 280A is acceptable. That is, if the difference between amplitude value 211A and input image 210 is small enough, fourth processing block 259 determines that hologram 280A represents input image 210 accurately enough. In some embodiments, phase value distribution 213A of the inverse fourier transformed composite data set is ignored for purposes of comparison.

It should be understood that any number of different methods may be employed to compare amplitude value distribution 211A and input image 210, and the present disclosure is not limited to any particular method. In some embodiments, the mean square error is calculated, and if the mean square error is less than a threshold, the hologram 280A is considered acceptable. If fourth processing block 259 determines that hologram 280A is not acceptable, further iterations of the algorithm are performed.

Fig. 2B represents a second iteration of the algorithm and any further iterations of the algorithm. The phase value distribution 213A of the previous iteration is fed back through the processing block of the algorithm. The amplitude value distribution 211A is rejected, giving priority to the amplitude value distribution of the input image 210. In a first iteration, the data forming step 202A forms a first composite data set by combining the distribution of amplitude values of the input image 210 with the random phase distribution 230. However, in the second and subsequent iterations, the data forming step 202B includes forming a composite data set by combining (i) the distribution of phase values 213A from the previous iteration of the algorithm with (ii) the distribution of amplitude values of the input image 210.

The composite data set formed by the data formation step 202B of FIG. 2B is then processed in the same manner as described with reference to FIG. 2A to form a second iterative hologram 280B. Therefore, an explanation of the process will not be repeated here. The algorithm may stop when the second iterative hologram 280B has been calculated. However, any number of further iterations of the algorithm may be performed. It will be appreciated that the third processing block 256 is only required when the fourth processing block 259 is required or further iterations are required. Output hologram 280B generally becomes better with each iteration. However, in practice, a point is usually reached at which no measurable improvement is observed, or the positive benefits of performing further iterations are offset by the negative effects of additional processing time. Thus, the algorithm is described as iterative and convergent.

Fig. 2C shows an alternative embodiment for the second and subsequent iterations. The phase value distribution 213A of the previous iteration is fed back through the processing block of the algorithm. Amplitude value distribution 211A is rejected, giving priority to the alternate distribution of amplitude values. In this alternative embodiment, an alternative distribution of amplitude values is derived from the distribution of amplitude values 211 from the previous iteration. In particular, the processing block 258 subtracts the distribution of amplitude values of the input image 210 from the distribution of amplitude values 211 of the previous iteration, scales the difference by the gain factor α, and subtracts the scaled difference from the input image 210. This is mathematically represented by the following equation, where subscripted text and numbers represent the number of iterations:

R_n+1[x,y]＝F'{exp(iψ_n[u,v])}

ψ_n[u,v]＝∠F{η·exp(i∠R_n[x,y])}

η＝T[x,y]-α(|R_n[x,y]|-T[x,y])

wherein:

f' is the inverse Fourier transform;

f is a forward Fourier transform;

r [ x, y ] is the composite data set output by the third processing block 256;

t [ x, y ] is the input or target image;

the angle is a phase component;

Ψ is a phase-only hologram 280B;

η is new amplitude value distribution 211B; and

alpha is the gain factor.

The gain factor a may be fixed or variable. In some embodiments, the gain factor α is determined based on the size and rate of incoming target image data. In some embodiments, the gain factor α depends on the number of iterations. In some embodiments, the gain factor α is only a function of the number of iterations. The embodiment of fig. 2C is identical to the embodiment of fig. 2A and 2B in all other respects. It can be said that the phase-only hologram Ψ (u, v) comprises a phase distribution in the frequency or fourier domain.

In some embodiments, the fourier transform is computationally performed by including lens data in the holographic data. That is, the hologram includes data representing the lens and data representing the object. In these embodiments, the physical fourier transform lens 120 of fig. 1 is omitted. In the field of computer generated holograms it is well known how to calculate holographic data representing a lens. The holographic data representing the lens may be referred to as a software lens. For example, a phase-only holographic lens may be formed by calculating the phase retardation caused by each point of the lens due to its refractive index and spatially varying optical path length. For example, the optical path length at the center of a convex lens is longer than the optical path length at the edge of the lens. The pure amplitude holographic lens may be formed of a fresnel zone plate. In the field of computer generated holograms, it is also known how to combine holographic data representing a lens with holographic data representing an object so that a fourier transform can be performed without a physical fourier lens. In some embodiments, the lens data is combined with the holographic data by simple vector addition. In some embodiments, a physical lens is used in conjunction with a software lens to perform a fourier transform. Alternatively, in other embodiments, the fourier transform lens is omitted entirely so that the holographic reconstruction occurs in the far field. In a further embodiment, the hologram may comprise grating data, i.e. data arranged to perform a grating function (such as beam steering). Also in the field of computer generated holograms, it is known how to calculate and combine such holographic data with holographic data representing an object. For example, a phase-only holographic grating may be formed by simulating the phase delay caused by each point on a blazed grating surface. A pure amplitude holographic grating may simply be superimposed on a pure amplitude hologram representing the object to provide angular control of the pure amplitude hologram.

In some embodiments, a real-time engine is provided, arranged to receive the image data and to calculate the hologram in real-time using the algorithm. In some embodiments, the image data is a video comprising a sequence of image frames. In other embodiments, the hologram is pre-computed, stored in computer memory, and recalled as needed for display on the SLM. That is, in some embodiments, a repository of predetermined holograms is provided.