Speckle removal method and apparatus

Abstract

1. A system comprising: an actuator; a signal generator configured to apply an electrical signal to the actuator to extend or shorten the actuator; an optical fiber associated with the actuator, the optical fiber configured to lengthen when the actuator extends and to shorten when the actuator contracts; and a coherent light source configured to send coherent light through the optical fiber to provide illumination during lengthening and shortening of the optical fiber.

Description

[Technical field]

[0001] Technical Field This disclosure relates to mechanisms for reducing interference observed in a coherent wavefront. In a particular example, a method is described for reducing speckle observed in light generated by a coherent light source (e.g., a laser). [Background technology]

[0002] background Light can be used to read optical storage media. This can be accomplished by illuminating an area on the optical storage media and detecting the light emitted from the optical storage media. Optical storage media are under development (e.g., Project Silica) that have advantages over other example data storage technologies such as hard disk drives, magnetic tape, flash memory, and optical disks. One such advantage is that data is required to be copied to other replacement media less frequently. This reduces energy use and hardware requirements.

[0003] In some systems involving coherent wavefronts (eg, radar, medical ultrasound, lasers), speckle patterns can arise due to mutual interference of the coherent wavefronts.

[0004] Speckle in the laser output can be reduced using a "despeckler." A despeckler includes an oscillating diffuser. Such a diffuser changes the field distribution as it moves. The motion of the oscillating diffuser can be rotational or translational. Such a system is described in Joshua M. Cobb, Paul Michalowski, "A laser speckle reduction system", Corning Advanced Optics. The quality of such a despeckler is limited by the achievable diffuser speed. If the diffuser is off-axis, intensity fluctuations can occur. The rotation speed of a rotating diffuser cannot easily be made fast enough to generate the required interference pattern and provide speckle reduction for high bandwidth applications. Summary of the Invention

[0005] overview According to a first aspect disclosed herein, a system is provided that includes an actuator. The system also includes a signal generator configured to apply an electrical signal to the actuator to expand or contract the actuator. The system also includes an optical fiber associated with the actuator. The optical fiber is configured to lengthen when the actuator expands and shorten when the actuator contracts. The system also includes a coherent light source coupled to the optical fiber and guided through a core of the optical fiber during lengthening and shortening of the optical fiber to provide illumination. In some examples, partially coherent output light may be used to provide homogeneous illumination with reduced or no speckle.

[0006] This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Additionally, the claimed subject matter is not limited to implementations that eliminate any or all of the disadvantages described herein.

[0007] BRIEF DESCRIPTION OF THE DRAWINGS To aid in understanding the present disclosure and to show how embodiments may be carried into effect, reference will now be made by way of example to the accompanying drawings in which: [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic block diagram of an imaging system disclosed herein. [Diagram 2] FIG. 1 is a schematic block diagram of an imaging system disclosed herein. [Diagram 3] FIG. 2 is a diagram of a despeckler according to an embodiment disclosed herein. [Figure 4] FIG. 2 is a diagram of a despeckler according to an embodiment disclosed herein. [Diagram 5] 4 is a histogram illustrating noise associated with different examples for reading an optical storage medium according to embodiments disclosed herein. [Figure 6] 1 is a flow diagram of a method. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Detailed Description The present disclosure relates to systems, methods, and computer readable storage devices for reducing speckle in light transmitted from a coherent light source. The computer readable storage device may include computer program instructions for performing a method for reducing speckle in light transmitted from a coherent light source.

[0010] An example application is reading optical storage media. Optical data storage media may comprise a transparent substrate, for example a quartz glass substrate. Data may be encoded in three-dimensional structures formed in the substrate. These structures are called voxels. An example application may be a high throughput optical reader for imaging high density data in silica glass. This may be used for optical storage. In one such example, a high radiance source may be required. To meet this high radiance illumination requirement, a coherent light source may be used. However, in some examples, the coherent source produces "noisy" illumination in the form of a speckle pattern. Examples provide a speckle reduction system, method, computer program, and computer readable medium for reducing speckle from a coherent light source to provide a more homogenous high radiance illumination.

[0011] Voxels have different optical properties than the surrounding bulk substrate. Voxels can be birefringent such that they can exhibit different refractive indices depending on the direction and polarization of incident light. During the writing process of an optical storage medium, the optical properties can be controlled (altered) to encode data.

[0012] To read data from an optical storage medium, an imaging system using a light source is used. FIG. 1 shows an example system 100 in which data can be read from an optical storage medium 102. A light source 104 sends light 120 towards the optical storage medium 102. The optical storage medium 102 can include voxels in which data is encoded. The light source 104 can include a coherent light source, for example a laser source. Thus, the light 120 can include coherent light 120, for example light emitted by a laser. It should be noted that the system 100 can include fewer optics, filters and lenses, and in some cases, more optics, filters and lenses. The light 120 can be sent towards an optical system 106 to provide, for example, a light beam at the right angle. In some cases, the optical system can include one or more optical fibers. A filter 108 can then be used to filter the light 120. The filter 108 can include one or more wavelength filters. The filter 108 may also comprise one or more polarizing filters in addition to or instead of one or more wavelength filters. In some examples, polarizing filters may be used in the system 100 where one or more of the filters 108 and 114 are used in combination with the camera 118 to detect birefringence. In some examples, the filter 108 may be considered to include a polarization control unit. The polarization control unit may set the illumination polarization using one or more polarizing components and / or wavelength filters. The polarization control unit may include one or more polarizing components. As an example, the one or more polarizing components may include one or more of a polarizer, a retarder, a liquid crystal variable retarder. The filtered light passes through one or more focusing lenses 110, which focus the light onto a portion of the optical storage medium 102.

[0013] A portion of the optical storage medium 102 is illuminated to read one or more features of the optical storage medium 102. The light may then be further focused by one or more focusing lenses 112. The light may then pass through a filter 114 and further optics 116 before being read by a camera 118. The filter 114 may include one or more wavelength filters. The filter 114 may also comprise one or more polarizing filters in addition to or instead of the one or more wavelength filters. In some examples, polarizing filters may be used in the system 100 to detect birefringence, with one or more of the filters 108 and 114 being used in combination with the camera 114. In some examples, the filter 114 may be considered to include a polarization control unit. The polarization control unit may use one or more polarizing components and / or wavelength filters to set the polarization of the light imaged by the camera 118. The one or more polarizing components may include one or more polarizing components. As an example, the one or more polarizing components may include one or more of a polarizer, a retarder, and a liquid crystal variable retarder. The camera 118 then captures the transmitted light to provide one or more images 122. The images 122 may include a wide field image. The camera may simultaneously image two or more features in the optical storage medium 102. The images 122 may be used to read data stored in the optical storage medium 102. The camera 118 may include a shutter. The shutter may open and close at a shutter speed. In an example, the shutter may be a mechanical shutter that physically opens and closes. In another example, the shutter may be an electronic shutter that does not physically open and close, but instead electronically sets the image exposure duration.

[0014] It should be noted that while Figure 1 illustrates a system in which illumination is transmitted through the optical storage medium 102, in other examples, the light may be reflected from the optical storage medium 102 and then captured by the camera 118. Such examples may include similar optics, which in some examples may include fewer components, and in some examples may include one or more additional lenses, filtering lenses, beam splitters, and polarizing components. The polarizing components may include, for example, one or more of a deflector, a retarder, and a liquid crystal variable retarder.

[0015] In some examples, the camera 118 may be replaced by any other light detection method, including any known 1D, 2D, or 3D imaging system.

[0016] If speckle is present when imaging the optical storage medium 102, it may obscure characteristic features of the optical storage medium 102 used to store data, thereby preventing accurate reading of data from the optical storage medium 102. Speckle may result from the interaction of coherent light as it passes through 102 and may be imaged through the optical system 100 by the camera 118. In such situations, a despeckler, as described below, may be used to reduce the speckle. Various other situations are also contemplated in which such a despeckler may be used, for example, in video projectors, other imaging systems, holography, etc.

[0017] FIG. 2 shows an expanded view of a section between the focusing lens 110 and the optical storage medium 102. Light 120 passes through the focusing lens 110 in a first direction. The light 120 is focused at an acute angle θ to the first direction to provide a cone of illumination of the optical storage medium 102. The cone of illumination illuminates an area of ​​interest 124 on the surface of the optical storage medium 102. This can be used to illuminate voxels of the optical storage medium 102. To provide high throughput reading (MB / s) of the optical storage medium 102, it is necessary to increase the rate of the number of features illuminated per unit time. This links to data throughput, since each feature will encode data. To read the optical storage medium 102, it can be useful to provide a certain number of photons per feature of the optical storage medium 102. This is because, for a given feature quality and technique, there is an illumination level that is required for correct decoding. In this situation of a constant number of photons per feature, it is necessary to increase the number of photons passing through the optical storage medium 102 per unit time. This must be taken into account while delivering photons to the voxels in the area A 124 and the illumination cone angle θ. These requirements can be taken into account using the emission brightness. In other words, by increasing the radiance of the illumination 120 incident on the optical storage medium 102, more photons can be delivered per unit time to the voxels in the region of interest A 124 within the illumination cone angle θ. With a constant number of photons per feature, increasing the radiance of the illumination 120 increases the rate of features illuminated per unit time, providing a higher throughput reading of the optical storage medium 102.

[0018] Radiance can be thought of as the power of the illumination source divided by the etendue of the illumination source. Etendue is equal to the emitter area multiplied by the solid angle of illumination of the illumination source. Fluorescent lamps have low radiance compared to lasers, which have high radiance.

[0019] Therefore, when reading optical storage media, it can be useful to use a laser due to the high radiance provided by the laser. However, when using a coherent light source such as a laser, there is a problem with speckle that prevents reliable reading of the optical storage medium 102. Speckle is the result of interference between many waves of the same frequency with different phases and amplitudes that add up constructively or destructively to produce waves whose amplitudes, and therefore intensities, vary randomly over space.

[0020] Consider an experiment where the desired read throughput is 100MB / s. For this estimation, we are shot-noise limited in the camera, and an exposure time of around 0.5ms is used, with moderate optical losses. In one such experiment, we used 3W / mm 2 This value is calculated as radiance in 0.1 W / mm 2 When compared to available LEDs, which have a radiance of around 100 W / mm2, it is clear that LEDs cannot provide the required radiance. Lasers (e.g. multimode lasers) can provide up to 100 W / mm2. 2 / sr. It is therefore clear that a laser, rather than an LED, must be used to provide the required radiance in this example. Note that in some cases a pulsed mode of light source may be operated, requiring even higher radiance to achieve the same average radiance. Thus, a laser would need to be used to provide the required radiance of 3 W / mm 2 / sr with a higher radiance (100W / mm 2 / sr) would be useful.

[0021] Speckle produced by a coherent light source can be reduced using a despeckler. The despeckler averages many patterns of the light source to reduce the random interference observed between the coherent waves. The despeckler produces many independent random speckles that, when summed together over the integration time of the detector (e.g., camera 118), non-coherently sum together and average each other, producing a deterministic image from the optical storage media feature itself (e.g., of the optical storage media 102). The produced image can be similar to that which can be produced if a non-coherent source (e.g., an LED) is used. There are many factors that affect the contrast a given optical setup has, e.g., how broadband (in wavelength) a particular light source is. However, given a particular setup, there will be a certain static contrast. If a despeckler is used that can be repeated through N independent speckle patterns (each with the same contrast) during time T, the observed contrast will be 1 / √N of the static contrast. Therefore, to achieve a 1 / 100 contrast reduction (1% contrast), a 100 2 =10 4 independent patterns are needed. The rate of independent patterns is also inversely proportional to T: if T is halved, one still needs the same N to achieve the same image, but now the rate of independent patterns doubles.

[0022] In an example, the despeckler can be considered to provide the rate of independent patterns (N / T), or the repetition rate in the case of repeating patterns. For example, the repetition rate of a rotational diffuser is determined by how often the same point on the rotational diffuser is reached. When the same point on the rotational diffuser is reached, the same speckle pattern is provided. In the examples of FIGS. 3 and 4 below, the same speckle pattern is provided each time the optical fiber has the same dimensions. Thus, the repetition rate is determined by how often the fiber is lengthened and shortened. When the repetition time < T, all N independent patterns are captured and contribute to speckle removal. When the repetition time > T, not all possible independent patterns are utilized during the period T. This can occur, for example, in a situation where the repetition frequency is about 100 Hz and the exposure time is < 1 ms. When T > the repetition time of the despeckler, the rate of independent patterns is not as important as the total number of independent patterns that can be generated with the repeating pattern. When T < the repetition time of the despeckler, N is determined by the rate of independent patterns and the time T. When the repetition period < the exposure time, a certain performance property independent of the shutter time is provided (since the performance is limited by the maximum number of independent patterns that can be achieved). Taking this into account in one example, when the exposure time T is 1 ms, it is useful to have a despeckler repetition rate from 10 kHz to 100 kHz such that the repetition period (1 / repetition rate) is < T.

[0023] In an example, the interference pattern resulting from the overlap of different fiber modes of an optical fiber generates a clearly defined speckle pattern at a given time t1. At time t2, the lengthening / shortening of the fiber can change the mode characteristics, and more importantly, the relative phase between them, and thus their interference generates a new, independent speckle pattern. The same occurs from time t3 to t n which occurs, and if the integration time of the detector is from t n to t1, independent speckle patterns are provided where the intensities are summed together to produce non-coherent, homogeneous illumination.

[0024] In examples, speckle reduction is achieved through time averaging of mode changes caused by lengthening and stressing the optical fiber. The optical fiber can be a multimode optical fiber. In the examples that follow, one or more actuators can be used to lengthen and shorten the optical fiber. The one or more actuators can include piezoelectric elements such as piezoelectric cylinders, linear piezoelectric actuators, stripe piezoelectric cylinders, etc. In some examples, the one or more actuators can include voice coil actuators.

[0025] 3 illustrates an example system 300 that can be used to despeckle a coherent light source 304. The coherent light source 304 can include a laser. In some examples, the coherent light source 304 can include a multimode (MM) laser.

[0026] Coherent light 331 passes through optical fiber 335. Signal generator 326 generates an electrical signal, and in some cases, the electrical signal is amplified by amplifier 328. In some cases, an amplifier may not be present. The electrical signal may oscillate at a frequency between 10-20 kHz. In some cases, the electrical signal may oscillate at a frequency of 17 kHz. In other cases, the electrical signal may oscillate at a frequency between 2 kHz and 100 kHz. In some cases, the electrical signal may oscillate at a resonant frequency of actuator 330.

[0027] An electrical signal is applied to the actuator 330. In the example of FIG. 3, the actuator 330 includes a piezoelectric element, although other actuators that expand and contract upon receiving an electrical signal may be used. In the example of FIG. 3, the piezoelectric element includes a piezoelectric cylinder. The signal causes the piezoelectric cylinder 330 to bend radially when the signal is applied. The signal causes the piezoelectric cylinder 330 to expand and contract in directions 336 and 338, followed by expansion. The electrical signal causes the actuator 330 to expand and contract over time. In some examples, the electrical signal may have a periodic waveform. In some examples, the electrical signal may oscillate at a frequency. In some examples, the electrical signal may be sinusoidal. In some examples, the actuation (expansion and contraction) of the actuator 330 may be synchronized with pulsed illumination or pulsed detection by using a shutter. This may be, for example, the shutter of the camera 118 in the example of FIG. 1. In some examples, this may be a relatively low duty cycle of the light used for the measurement, reducing power consumption. In one such example, a periodic signal may be applied to the actuator 330 during strobe.

[0028] The optical fiber 335 may be mechanically coupled to the actuator 330. The optical fiber 335 may be wrapped around the actuator 330 in loops 332 and 334. As the piezoelectric cylinder 330 bends at the oscillation frequency of the signal generator, the length of the optical fiber lengthens and shortens at the oscillation frequency. At the same time, coherent light is sent through the optical fiber. By averaging the pattern of lengthening and shortening of the optical fiber 335, the speckle from the illumination 340 at the end of the optical fiber 335, i.e., the observed speckle, may be reduced. This is accomplished by using a despeckler to reduce the coherence of the illumination.

[0029] In some examples, instead of providing a complete loop 332 of optical fiber 335 around the piezoelectric cylinder 330, the optical fiber 335 may be curved around only a portion (e.g., a half circle) of the piezoelectric cylinder 330. In some examples, the optical fiber 335 may be attached to a portion of the piezoelectric cylinder 330 to lengthen and shorten the optical fiber 335.

[0030] To increase the amount that the optical fiber 335 is lengthened and shortened, the number of loops of the optical fiber 335 around the piezoelectric cylinder 330 can be increased. This can be used to improve the despeckle performance.

[0031] To increase the amount that the optical fiber 335 is lengthened and shortened, a further actuator may be provided, also driven at an oscillating frequency. In the given example of FIG. 3, a second actuator 330a is provided in which the signal generator 326 provides an electrical signal (optionally via amplifier 238a) to bend the piezoelectric cylinder 330a along directions 336a and 338a. In some examples, a signal generator separate from the signal 326 may drive the actuator 330a. The electrical signal causes the actuator 330a to expand and contract over time. In some examples, the electrical signal may have a periodic waveform. In some examples, the electrical signal may have an oscillating frequency. In some examples, the electrical signal may be sinusoidal. In some examples, the actuation (expansion) of the actuator 330a may be synchronized with pulsed illumination or pulsed detection by using a shutter. This may be, for example, the shutter of the camera 118 in the example of FIG. 1. In some examples, this may be a relatively low duty cycle of the light used for the measurement, reducing power consumption. In one such example, a periodic signal may be applied to the actuator 330a during strobe. 3, the actuator 330a includes a piezoelectric cylinder, although other actuators may be used that expand and contract upon receiving an electrical signal. This may be used to lengthen and shorten the optical fiber 335 due to loops 332a and 334a around the cylinder 330a. Note that in some examples, a second signal generator may be provided to provide an electrical signal to the actuator 330a separate from the actuator 330. The optical fiber 335 may be mechanically coupled to the actuator 330a.

[0032] In some examples, only one piezoelectric element is provided, such as piezoelectric element 330. In some examples, one or more piezoelectric elements are provided, such as piezoelectric element 330a. The one or more piezoelectric elements may include a linear piezoelectric actuator, as described below with respect to FIG.

[0033] The despeckled coherent light 340 can be used to read an optical storage medium. The despeckled coherent light 340 can be directed to one or more voxels.

[0034] In some examples, the system 300 is designed to ensure that the minimum radius of curvature of the optical fiber 335 is not exceeded. This avoids damage to the optical fiber 335. The minimum radius of curvature may be provided by the manufacturer of the optical fiber 335. For example, the piezoelectric element may be selected to ensure compliance with the minimum radius of curvature of the optical fiber 335. For example, the piezoelectric cylinder 330 and, if provided, the piezoelectric cylinder 330a may have a radius that is larger than the minimum radius of curvature of the optical fiber 335. This ensures that the optical fiber 335 is achieved by a "macrobend" of the optical fiber 335 rather than a "microbend" of the optical fiber 335, which may cause damage to the optical fiber 335.

[0035] In some examples, at least one of the piezoelectric elements 330 and 330a may include a striped piezoelectric cylinder.

[0036] FIG. 4 illustrates a different system 400 for despeckling a coherent light source 404. It should be noted that one or more elements of FIG. 4 (e.g., linear piezoelectric actuator 430 and / or linear piezoelectric actuator 430a) can be combined with elements of FIG. 3 (e.g., piezoelectric cylinder 330 and / or piezoelectric cylinder 330a) to provide oscillation lengthening and shortening of the optical fiber to despeckle the coherent light sent through the optical fiber. In the example of FIG. 4, actuators 430 and 430a each include a linear piezoelectric actuator, but other actuators that expand and contract when an electrical signal is received may be used. For example, a voice coil actuator may be used. An optical fiber 435 may be mechanically coupled to linear piezoelectric actuators 430 and 430a.

[0037] A signal generator 426 provides an electrical signal that is provided to the actuator 430. When the electrical signal is applied, the piezoelectric element 430 bends along its longitudinal axis, lengthening and shortening along a direction 436. The electrical signal may be provided via an amplifier 428. The electrical signal causes the actuator 430 to expand and contract over time. In some examples, the electrical signal may have a periodic waveform. In some examples, the electrical signal may have an oscillating frequency. In some examples, the electrical signal may be sinusoidal. In some examples, the actuation (expansion and contraction) of the actuator 430 may be synchronized with pulsed illumination or pulsed detection by using a shutter. This may be, for example, the shutter of the camera 118 in the example of FIG. 1. In some examples, this may be a relatively low duty cycle of the light used for the measurement, reducing power consumption. In one such example, a periodic signal may be applied to the actuator 430 during a strobe.

[0038] The optical fiber 435 may be connected to the piezoelectric element 430 at 442. The connection 442 may be a mechanical connection (e.g., clip, adhesive) or any other suitable connection.

[0039] The signal generator 426 provides an electrical signal that is provided to the linear piezoelectric actuator 430a. Note that in some examples, a separate signal generator from the signal generator 426 may be provided for the piezoelectric element 430a. When an electrical signal is applied, the piezoelectric element 430a bends along its longitudinal axis, lengthening and shortening along the direction 436a. The electrical signal may be provided via an amplifier 428a. The electrical signal causes the actuator 430a to expand and contract over time. In some examples, the electrical signal may have a periodic waveform. In some examples, the electrical signal may have an oscillating frequency. In some examples, the electrical signal may be sinusoidal. In some examples, the actuation (expansion) of the actuator 430a may be synchronized with pulsed illumination or pulsed detection by using a shutter. This may be, for example, the shutter of the camera 118 in the example of FIG. 1. In some examples, this may be a relatively low duty cycle of the light used for the measurement, reducing power consumption. In one such example, a periodic signal may be applied to the actuator 430a during strobe.

[0040] The optical fiber 435 may be connected to the piezoelectric element 430a at 444. The connection 444 may be a mechanical connection (e.g., clip, adhesive) or any other suitable connection.

[0041] The length X 446 of a section of optical fiber 435 lengthens and shortens at the frequency of the oscillating electrical signal of signal generator 426 .

[0042] Coherent light 431 passes through optical fiber 435. The electrical signal may oscillate at a frequency between 10 and 20 kHz. In some examples, the electrical signal may oscillate at a frequency of 17 kHz. In other examples, the electrical signal may oscillate at a frequency between 2 kHz and 100 kHz. In some examples, the electrical signal may oscillate at the resonant frequency of piezoelectric elements 430 and / or 430a.

[0043] In some examples, the optical fiber 435 may be wrapped around the piezoelectric element 430 or piezoelectric element 430a to increase the amount that the length X is lengthened and shortened, which can be used to increase the despeckle performance.

[0044] In some examples, the system 400 is designed to ensure that the minimum bend radius of the optical fiber 435 is not exceeded. This avoids damage to the optical fiber 435. The minimum bend radius may be provided by the manufacturer of the optical fiber 435. For example, the piezoelectric element may be selected to ensure compliance with the minimum bend radius of the optical fiber 435. For example, the piezoelectric element 430 and the piezoelectric element 430a may be positioned such that the amount that the optical fiber 435 needs to be bent to be attached to both piezoelectric elements has a curve radius that is greater than the minimum bend radius of the optical fiber 435. This ensures that the optical fiber 435 is achieved by a "macrobend" of the optical fiber 435 rather than a "microbend" of the optical fiber 435, which may cause damage to the optical fiber 435.

[0045] Further systems using actuators powered by electrical signals are contemplated. For example, a single actuator 430 can be used in system 400, such that actuator 430a is not present. Optical fiber 435 can be connected to actuator 430 at point 442 and can also be connected to actuator 436 at another point displaced along direction 436. Thus, the optical fiber is mechanically coupled to the actuator. When an electrical signal is applied, illumination can pass through optical fiber 435 as actuator 430 lengthens and shortens along direction 436. Due to the lengthening and shortening of optical fiber 435 during illumination, speckle is reduced. The actuator can include, for example, a piezoelectric element. In some examples, the actuator can include a linear piezoelectric actuator.

[0046] Further example systems may include an optical fiber such as 335 or 435 wound around a cylinder similar to the example of FIG. 3. Inside the cylinder, an actuator may be located along the diameter of the cylinder. The actuator may have a length similar to the diameter of the cylinder. When an electrical signal is applied to the actuator, the actuator may lengthen and shorten, correspondingly increasing or decreasing the diameter of the cylinder. In other words, rather than the bending of the cylinder due to application of an electrical signal to the cylinder as in FIG. 3, an electrical signal may be applied to an actuator inside the cylinder, which may cause the cylinder to bend. Thus, the optical fiber is mechanically coupled to the actuator. In some examples, the actuator may be linear or approximately linear. The actuator may include, for example, a piezoelectric element. In some examples, the actuator may include a linear piezoelectric actuator.

[0047] Figure 5 shows a comparison of data from a laser passing through an empty glass in a single shot method. The number of pixels is provided on the y-axis and the number of cameras is counted on the x-axis. The ideal distribution is shown in 554. The distribution of the LED is shown in 552. In the distribution 552, the variance σ Tot 2 = σ Shot 2 +σ Camera 2 and σ Shot 2 is the noise introduced by shot noise, and σ Camera 2 is the noise introduced by the camera. Shot noise can include noise that follows a Poisson process and is present in the electron / photon stream resulting from its discrete particle nature. Shot noise can be considered a property of the signal being sampled rather than a property of the camera. The distribution of the laser is shown in 550. In the distribution 550, the variance σ Tot 2 = σ Shot 2 +σ Camera 2 +σ Speckle 2 and σ Speckle 2is the noise caused by coherent source speckle. The system described above has a Speckle 2 can be significantly reduced.

[0048] 6 illustrates an example method flow that may be applied in a system such as system 300, system 400, or a similar system. At 601, an electrical signal is applied to an actuator to cause the actuator to extend and retract.

[0049] At 603, the optical fiber lengthens and shortens as the actuator expands and contracts. The optical fiber may be associated with the piezoelectric element by being wound around the actuator or by being attached or connected to the actuator.

[0050] At 605, coherent light is sent through the optical fiber to provide illumination while the optical fiber is being lengthened and shortened.

[0051] Exemplary systems can provide high speed despeckling, with application speed limited only by the drive frequency. Use of fast drive elements, e.g., resonant piezoelectric elements at 10 kHz or higher, can provide despeckling in the sub-millisecond time frame.

[0052] The example system may provide a low-loss despeckler by ensuring that optical fiber bend radius constraints are observed. This ensures minimal optical loss and allows for designs with higher radiance. The example system may provide scalable performance without image degradation compared to incoherent light sources (e.g., LEDs), providing negligible residual speckle contrast. The number of sections of optical fiber that can be stretched can be increased to improve performance. The number of turns around the stretching cylinder (when in use) can be used to increase performance. Thus, performance can be increased without increasing sampling time. The system also includes a solid-state design that requires little maintenance. In an example, the system may have one or more interchangeable piezoelectric elements to account for different applications. Different applications may require different optical fiber diameters with different safe bend radii (minimum bend radii), and stressing the fiber may cause some modes to attenuate preferentially over others. By interchanging the piezoelectric elements, a wide range of optical specifications can be achieved.

[0053] In an example, the combination of a laser source with flexible optical specifications (longer and shorter optical fiber oscillations) and low losses allows etendue engineering to optimize the efficiency of the illumination.

[0054] One or more elements of the above-described system may be controlled by a processor and associated memory that includes computer-readable instructions for controlling the system. The processor may control one or more signal generators. The processor may control one or more light sources. A circuit or processing system may also be provided to control one or more systems. It will be understood that the processor, processing system, or circuit referred to herein may actually be provided by a single chip or integrated circuit or multiple chips or integrated circuits, and may optionally be provided as a chipset, application specific integrated circuit (ASIC), field programmable gate array (FPGA), digital signal processor (DSP), graphics processing unit (GPU), etc. The one or more chips may include circuitry (and possibly firmware) for implementing at least one or more of one or more data processors, one or more digital signal processors, baseband circuitry, radio frequency circuitry, which may be configured to operate according to exemplary embodiments. In this regard, the exemplary embodiments may be stored in (non-transitory) memory and implemented at least in part by a processor, by hardware, or by a combination of tangibly stored software and hardware (and tangibly stored firmware).

[0055] Reference is made herein to data storage for storing data. This may be provided by a single device or multiple devices. Suitable devices include, for example, hard disks and non-volatile semiconductor memories (e.g., solid state drives or SSDs).

[0056] At least some aspects of the embodiments described herein with reference to the drawings include computer processes executed on a processing system or processor, but the invention also extends to computer programs adapted to carry out the invention, in particular computer programs on or in a carrier. The programs may be in the form of code-intermediate source and object code, such as non-transitory source code, object code, partially compiled form, or any other non-transitory form suitable for use in carrying out the process according to the invention. The carrier may be any entity or device capable of carrying out a program. For example, the carrier may include a storage medium such as a solid state drive (SSD) or other semiconductor-based RAM; a ROM, such as a CD ROM or semiconductor ROM; a magnetic recording medium, such as a floppy disk or hard disk; an optical memory device in general.

[0057] According to a first aspect, there is provided a system comprising an actuator, a signal generator configured to apply an electrical signal to the actuator to cause the actuator to extend and contract, an optical fiber associated with the actuator, the optical fiber configured to lengthen when the actuator extends and shorten when the actuator contracts, and a coherent light source configured to send coherent light through the optical fiber to provide illumination during lengthening and shortening of the optical fiber.

[0058] According to some examples, the actuator includes a piezoelectric element.

[0059] In some examples, the electrical signal oscillates at a frequency between 2 kHz and 100 kHz.

[0060] According to some examples, at least a portion of the optical fiber is wound around at least a portion of the actuator.

[0061] According to some examples, the optical fiber is configured to lengthen when the actuator expands and shorten when the actuator contracts by bending the optical fiber through a bend radius larger than a minimum bend radius, the minimum bend radius being to avoid breakage of the optical fiber.

[0062] According to some examples, the actuator includes a piezoelectric cylinder and a portion of the optical fiber is wound around at least a portion of the piezoelectric cylinder.

[0063] According to some examples, the system is configured to increase the amount that the optical fiber is wound around the piezoelectric cylinder, thereby increasing the amount that the optical fiber lengthens when the actuator extends and increasing the amount that the optical fiber shortens when the actuator contracts.

[0064] According to some examples, the system is configured to increase the amount that the optical fiber is wrapped around the piezoelectric cylinder by increasing the number of times that the optical fiber is wrapped around the piezoelectric cylinder.

[0065] According to some examples, the actuator includes a linear piezoelectric actuator, and the optical fiber is mechanically coupled to the linear piezoelectric actuator.

[0066] In some examples, the system includes one or more further actuators configured to expand and contract when an electrical signal is applied, and the optical fiber is configured to further lengthen and shorten as the one or more further actuators expand and contract.

[0067] According to some examples, illumination is delivered to one or more voxels.

[0068] According to some examples, the coherent light is despeckled by sending the coherent light through lengthening and shortening of the optical fiber.

[0069] According to some examples, the electrical signal oscillates at a resonant frequency of the actuator.

[0070] According to some examples, the electrical signal has a periodic waveform.

[0071] According to a second aspect, there is provided a method that includes applying an electrical signal to an actuator, thereby expanding or contracting the actuator, lengthening and shortening an optical fiber associated with the actuator as the actuator expands or contracts, and sending coherent light through the optical fiber during the lengthening and shortening of the optical fiber, thereby providing illumination. In some examples, the second aspect may be computer-implemented.

[0072] According to some examples, the actuator includes a piezoelectric element.

[0073] In some examples, the electrical signal oscillates at a frequency between 2 kHz and 100 kHz.

[0074] According to some examples, at least a portion of the optical fiber is wound around at least a portion of the actuator.

[0075] According to some examples, the method includes lengthening the optical fiber when the actuator extends and shortening the optical fiber when the actuator contracts by bending the optical fiber through a bend radius larger than a minimum bend radius, the minimum bend radius to avoid breakage of the optical fiber.

[0076] According to some examples, the actuator includes a piezoelectric cylinder and a portion of the optical fiber is wound around at least a portion of the piezoelectric cylinder.

[0077] According to some examples, the method includes increasing the amount that the optical fiber is wound around the piezoelectric cylinder, thereby increasing the amount that the optical fiber lengthens when the actuator extends, and increasing the amount that the optical fiber shortens when the actuator contracts.

[0078] According to some examples, the method includes increasing the amount that the optical fiber is wrapped around the piezoelectric cylinder by increasing the number of times that the optical fiber is wrapped around the piezoelectric cylinder.

[0079] According to some examples, the actuator includes a linear piezoelectric actuator, and the optical fiber is mechanically coupled to the linear piezoelectric actuator.

[0080] According to some examples, the method includes expanding and contracting one or more further actuators upon application of an electrical signal, the optical fiber being configured to further lengthen and shorten as the one or more further actuators expand and contract.

[0081] According to some examples, illumination is delivered to one or more voxels.

[0082] According to some examples, the coherent light is despeckled by sending the coherent light through lengthening and shortening of the optical fiber.

[0083] According to some examples, the electrical signal oscillates at a resonant frequency of the actuator.

[0084] According to some examples, the electrical signal has a periodic waveform.

[0085] According to a third aspect, there is provided a system comprising two or more actuators; signal generation configured to apply an electrical signal to each of the two or more actuators to expand or contract each of the two or more actuators; an optical fiber configured to lengthen when at least one of the two or more actuators expands, the optical fiber configured to shorten when at least one of the two or more actuators contracts; and a coherent light source configured to send coherent light through the optical fiber to provide illumination during lengthening and shortening of the optical fiber, wherein the coherent light is despeckled by sending the coherent light during lengthening and shortening of the optical fiber, and the illumination is delivered to an optical storage medium.

[0086] According to some examples, the two or more actuators include piezoelectric elements.

[0087] In some examples, the electrical signal oscillates at a frequency between 2 kHz and 100 kHz.

[0088] According to some examples, at least a portion of the optical fiber is wound around at least a portion of at least one of the two or more actuators.

[0089] According to some examples, the optical fiber is configured to lengthen when at least one of the two or more actuators expands and to shorten when at least one of the two or more actuators contracts by bending the optical fiber through a curvature radius greater than a minimum curvature radius, the minimum curvature radius being to avoid breakage of the optical fiber.

[0090] According to some examples, at least one of the two or more actuators includes a piezoelectric cylinder, and a portion of the optical fiber is wound around at least a portion of the piezoelectric cylinder.

[0091] According to some examples, the system is configured to increase the amount that the optical fiber is wound around the piezoelectric cylinder, thereby increasing the amount that the optical fiber lengthens when the piezoelectric cylinder expands and increasing the amount that the optical fiber shortens when the piezoelectric cylinder contracts.

[0092] According to some examples, the system is configured to increase the amount that the optical fiber is wrapped around the piezoelectric cylinder by increasing the number of times that the optical fiber is wrapped around the piezoelectric cylinder.

[0093] According to some examples, at least one of the two or more actuators includes a linear piezoelectric actuator, and the optical fiber is mechanically coupled to the linear piezoelectric actuator.

[0094] According to some examples, illumination is delivered to at least one voxel.

[0095] According to some examples, an optical storage medium comprises a substrate and at least one three-dimensional structure formed on the substrate.

[0096] According to some examples, the electrical signal oscillates at a resonant frequency of at least one of the two or more actuators.

[0097] According to some examples, the electrical signal has a periodic waveform.

[0098] According to a fourth aspect, there is provided a method including applying an electrical signal to two or more actuators, thereby causing the two or more actuators to expand or contract; lengthening and shortening an optical fiber associated with at least one of the two or more actuators as at least one of the two or more actuators expands or contracts; and during the lengthening and shortening of the optical fiber, sending coherent light through the optical fiber, thereby providing illumination, which illumination is delivered to an optical storage medium.

[0099] According to some examples, the two or more actuators include piezoelectric elements.

[0100] In some examples, the electrical signal oscillates at a frequency between 2 kHz and 100 kHz.

[0101] According to some examples, at least a portion of the optical fiber is wound around at least a portion of at least one of the two or more actuators.

[0102] According to some examples, lengthening of the optical fiber is performed when at least one of the two or more actuators extends, and shortening of the optical fiber is performed when at least one of the two or more actuators contracts by bending the optical fiber at a bend radius greater than a minimum bend radius, the minimum bend radius being to avoid breakage of the optical fiber.

[0103] According to some examples, at least one of the two or more actuators includes a piezoelectric cylinder, and a portion of the optical fiber is wound around at least a portion of the piezoelectric cylinder.

[0104] According to some examples, the method includes increasing the amount that the optical fiber is wound around the piezoelectric cylinder, thereby increasing the amount that the optical fiber lengthens when the piezoelectric cylinder expands, and increasing the amount that the optical fiber shortens when the piezoelectric cylinder contracts.

[0105] According to some examples, the method includes increasing the amount that the optical fiber is wrapped around the piezoelectric cylinder by increasing the number of times that the optical fiber is wrapped around the piezoelectric cylinder.

[0106] According to some examples, at least one of the two or more actuators includes a linear piezoelectric actuator, and the optical fiber is mechanically coupled to the linear piezoelectric actuator.

[0107] According to some examples, the method includes delivering to at least one voxel.

[0108] According to some examples, an optical storage medium comprises a substrate and at least one three-dimensional structure formed on the substrate.

[0109] According to some examples, the electrical signal oscillates at a resonant frequency of at least one of the two or more actuators.

[0110] According to some examples, the electrical signal has a periodic waveform.

[0111] According to a fifth aspect, there is provided a computer readable storage device comprising instructions executable by a processor to perform the method of the second aspect, the fourth aspect, or an example of any of the second or fourth aspects.

[0112] According to a sixth aspect, there is provided a computing device comprising a memory including one or more memory units and a processing device including one or more processing units, the memory storing code configured to be executed on the processing device, the code being configured, when on the processing device, to perform a method of the second aspect, the fourth aspect, or an example of any of the second or fourth aspects.

[0113] The examples described herein should be understood as illustrative examples for embodiments of the invention. Further embodiments and examples are contemplated. Any feature described in connection with any example or embodiment may be used alone or in combination with other features. In addition, any feature described in connection with any example or embodiment may be used in combination with one or more features of any other example or embodiment or any combination of any other example or embodiment. Moreover, equivalents and modifications not described herein may be utilized within the scope of the invention as defined by the claims.

Claims

1. 1. A system comprising: two or more actuators; a signal generator configured to apply an electrical signal to each of the two or more actuators to expand or contract each of the two or more actuators; an optical fiber configured to lengthen when at least one of the two or more actuators expands, the optical fiber configured to shorten when at least one of the two or more actuators contracts; a coherent light source configured to send coherent light through the optical fiber to provide illumination during lengthening and shortening of the optical fiber, the coherent light being despeckled by sending the coherent light during lengthening and shortening of the optical fiber, and the illumination being delivered to an optical storage medium; A system with.

2. The system of claim 1 , wherein the two or more actuators include piezoelectric elements.

3. 3. The system of claim 1, wherein the electrical signal oscillates at a frequency between 2 kHz and 100 kHz.

4. The system of claim 1 , wherein at least a portion of the optical fiber is wound around at least a portion of at least one of the two or more actuators.

5. 5. The system of claim 4, wherein the optical fiber is configured to lengthen when at least one of the two or more actuators expands and shorten when at least one of the two or more actuators contracts by bending the optical fiber at a bend radius greater than a minimum bend radius to avoid breakage of the optical fiber.

6. The system of claim 1 , wherein at least one of the two or more actuators includes a piezoelectric cylinder, and a portion of the optical fiber is wound around at least a portion of the piezoelectric cylinder.

7. The system comprises: increasing the amount by which the optical fiber lengthens when the piezoelectric cylinder expands; and to increase the amount by which the optical fiber shortens when the piezoelectric cylinder contracts; The system of claim 6 , configured to increase the amount the optical fiber is wrapped around the piezoelectric cylinder.

8. 8. The system of claim 7, wherein the system is configured to increase the amount of the optical fiber wrapped around the piezoelectric cylinder by increasing the number of times the optical fiber is wrapped around the piezoelectric cylinder.

9. The system of claim 1 , wherein at least one of the two or more actuators includes a linear piezoelectric actuator, and the optical fiber is mechanically coupled to the linear piezoelectric actuator.

10. The system of claim 1 , wherein the illumination is delivered to at least one voxel.

11. The system of claim 1 , wherein the optical storage medium comprises a substrate and at least one three-dimensional structure formed on the substrate.

12. The system of claim 1 , wherein the electrical signal oscillates at a resonant frequency of at least one of the two or more actuators.

13. The system of claim 1 , wherein the electrical signal has a periodic waveform.

14. 1. A method comprising: applying electrical signals to two or more actuators to expand or contract the two or more actuators; lengthening and shortening an optical fiber associated with said at least one of said two or more actuators as said at least one of said two or more actuators expands and contracts; sending coherent light through the optical fiber to provide illumination during the lengthening and shortening of the optical fiber, the coherent light being despeckled by sending the coherent light during the lengthening and shortening of the optical fiber, and the illumination being delivered to an optical storage medium; A method comprising:

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