WO2020202011A1

WO2020202011A1 - Speckle reduced laser image projection method and apparatus

Info

Publication number: WO2020202011A1
Application number: PCT/IB2020/053065
Authority: WO
Inventors: Chang-Qing Xu; Mahmoud Mohamed Talaat Mohamed Ibrahim Eldesouky Khalil MOHAMED; Liam FLANNIGAN; Qianli Ma
Original assignee: Mcmaster University
Priority date: 2019-04-01
Filing date: 2020-03-31
Publication date: 2020-10-08

Abstract

An optical pickup actuator for a laser image projector, including an objective lens having an optical axis; a movement coil coupled to the objective lens to move the objective lens along a movement axis, the movement axis perpendicular or parallel to the optical axis; and a control unit coupled to the movement coil and operable to supply a time varying current to the movement coil to generate an electromagnetic force to induce in the objective lens a vibrating movement along the movement axis during a projection of a laser beam through the objective lens.

Description

TITLE: Speckle Reduced Laser Image Projection Method and Apparatus RELATED APPLICATIONS

[0001 ] This application claims the benefit of United States Provisional Application Serial No. 62/827,451 , filed April 1 , 2019, the entirety of which is hereby incorporated by reference.

FIELD

[0002] The specification relates generally to apparatus and methods associated with laser projection, and more specifically to speckle reduced laser image projection.

BACKGROUND

[0003] U.S. Pat. No. 7,271 ,962 purports to disclose a two-dimensional image formation apparatus provided with laser sources, diffusers for diffusing light, illumination optical systems for irradiating the diffusers with lights emitted from the laser sources, diffuser vibration units for vibrating the diffusers, and spatial light modulators disposed near the diffusers, for modulating the lights emitted from the laser sources and diffused by the diffusers, wherein the diffusers are vibrated by the diffuser vibration units at a velocity that satisfies a relationship, V>dx30 (millimeters/sec), which is established between the grain size d of the diffusers and the vibration speed V of the diffusers, whereby speckle noise existing in an image projected on a screen can be effectively reduced.

[0004] U.S. Pat. No. 6,895,149 purports to disclose an invention which greatly improves the quality of images obtained using optical systems illuminated by coherent light. It does so by removing the undesirable pseudo-random variations in the final image due to interference speckle and inhomogeneities in the spatial intensity distribution of the light source. A bundle of light-guiding fibers is interposed between the illumination source and the imaging system. Non-uniform propagation within the fiber bundle creates a pseudo-random phase variation across the illumination beam, which gives rise to a dynamic interference speckle pattern superimposed upon the desired image acquired by the optical system. Rotating the fiber bundle around the axis of propagation, whilst simultaneously integrating the output of the photosensitive detector over a period of time, substantially removes variations due to source inhomogeneities and coherent interference.

[0005] U.S. Pat. App. No. 2014/0071406 purports to disclose an apparatus comprising a laser and/or LED light source(s), multimode optical fiber(s), light coupler(s), an optional spatial light modulator(s), and an optional projection lens(es). The light source has a 1/e half-width emission bandwidth. The light coupler couples the light source to the multimode optical fiber(s) such that objective speckle contrast is reduced. The multimode optical fiber(s) may pass light from the coupler to an optional spatial light modulator. The spatial light modulator may modulate the light to form an image. The projection lens may transfer light onto an image plane or to illuminate objects. The objective speckle contrast at the end of the multimode fiber in combination with the projection lens diameter (if employed) and wavelength diversity may result in viewed images at the viewer's eye, or other detector, exhibiting speckle contrast that may be 1 % or less.

[0006] U.S. Pat. App. No. 2013/0010356 purports to disclose systems and related methods for reducing speckle on display screen. More specifically, screen vibration is used to reduce speckle, and in accordance with the disclosed principles, the vibration may be achieved by using wave-based actuation (e.g., acoustic or electromagnetic waves) to vibrate the screen. In an exemplary embodiment, a speckle reducing system may comprise at least one actuating element located proximate to, but not in physical contact with, a display screen. In addition, the at least one actuating element may be configured to generate waves directed towards the display screen. When the waves impact the display screen, the waves impart vibration to the display screen.

[0007] U.S. Pat. No. 9,778,478 purports to disclose a projector with image plane modal vibration for speckle reduction is provided. The projector includes: a laser light source; a light modulator; and optics that convey light from the laser to the modulator and project modulated light from the modulator, the optics comprising an image plane. The projector further includes: a surface comprising at least a first region located at the image plane, the first region being at least as large as an image formed at the image plane, the first region configured to one or more of transmit and reflect the image; and at least three actuators, positions of interaction of the actuators with the surface are asymmetric relative to the surface, the actuators configured to generate respective moving surface waves in the first region at respective frequencies, the respective frequencies comprising non-integer multiples of each other.

[0008] U.S. Pat. App. No. 2008/0192327 purports to disclose a system and method for reducing speckle of a laser beam. The system includes at least an active device capable of temporally and/or spatially averaging the speckle pattern of a laser. The device can be used with an external diffuser or have an integrated diffusive layer within its structure to enhance the speckle reduction. The speckle reduction system alters the phase and/or path of light rays within an input laser beam as they pass through a transmissive device or reflect off of the surface of a reflective device.

SUMMARY

[0009] The following summary is intended to introduce the reader to various aspects of the applicant’s teaching, but not to define any invention.

[0010] According to some aspects, there is provided a laser image projector, comprising a laser source to project a laser beam along a projection path; an optical pickup actuator fixed adjacent the laser source, the optical pickup actuator including an objective lens held in the projection path, the objective lens having an optical axis parallel to a first portion of the projection path extending through the objective lens, the objective lens having a focusing axis parallel to the optical axis and a tracking axis perpendicular to the focusing axis, a focusing coil coupled to the objective lens to move the objective lens along the focusing axis, a tracking coil coupled to the objective lens to move the objective lens along the tracking axis, and a control unit coupled to at least one of the focusing coil and the tracking coil and operable to supply a time varying current to the at least one of the focusing coil and the tracking coil to generate an electromagnetic force to induce a vibrating movement in the objective lens during a projection of the laser beam; and a set of projection optics received in the projection path, and wherein the objective lens is a laser coupling lens received in the projection path between the laser source and the set of projection optics. [001 1 ] In some examples, the laser image projector further comprises a housing containing the laser source, the optical pickup actuator and the set of projection optics.

[0012] In some examples, the projection optics includes a diffuser and a projection lens each received in the projection path, and the diffuser received in the projection path between the optical pickup actuator and the projection lens.

[0013] In some examples, the projection optics includes a condensing lens and at least one homogenization component each received in the projection path after the optical pickup actuator.

[0014] In some examples, the time varying current is an alternating current.

[0015] In some examples, the time varying current has a frequency of between 30 Hz and 120 Hz.

[0016] In some examples, the time varying current has a voltage of between 1 volt and 4 volts.

[0017] In some examples, increasing a voltage amplitude of the time varying current increases a vibration amplitude of the vibrating movement, and wherein decreasing the voltage amplitude of the time varying current decreases the vibration amplitude of the vibrating movement.

[0018] According to some aspects, there is provided an optical pickup actuator for a laser image projector, comprising an objective lens having an optical axis, the objective lens having a focusing axis parallel to the optical axis and a tracking axis perpendicular to the focusing axis; a focusing coil coupled to the objective lens to move the objective lens along the focusing axis; a tracking coil coupled to the objective lens to move the objective lens along the tracking axis; and a control unit coupled to at least one of the focusing coil and the tracking coil, and operable to supply a time varying current to the at least one of the focusing coil and the tracking coil to generate an electromagnetic force to induce a vibrating movement in the objective lens during a projection of a laser beam through the objective lens.

[0019] In some examples, the time varying current is an alternating current.

[0020] In some examples, the time varying current is a square wave current. [0021 ] In some examples, the time varying current has a frequency of between 30 Hz and 120 Hz.

[0022] In some examples, the time varying current has a frequency of between 60 Hz and 80 Hz.

[0023] In some examples, the time varying current has a voltage of between 1 volt and 4 volts.

[0024] In some examples, the varying current has a voltage of between 1 volt and 2 volts.

[0025] In some examples, increasing a voltage amplitude of the time varying current increases a vibration amplitude of the vibrating movement, and wherein decreasing the voltage amplitude of the time varying current decreases the vibration amplitude of the vibrating movement.

[0026] In some examples, each of the focusing coil and the tracking coil includes a copper wire wrapped around a magnetic core.

[0027] In some examples, the objective lens is secured in a lens casing, and wherein an extent of the vibrating movement is limited to a dimension of the lens casing.

[0028] In some examples, the at least one of the focusing coil and the tracking coil is the tracking coil.

[0029] According to some aspects, there is provided an optical pickup actuator for a laser image projector, comprising an objective lens having an optical axis; a movement coil coupled to the objective lens to move the objective lens along a movement axis, the movement axis perpendicular or parallel to the optical axis; and a control unit coupled to the movement coil and operable to supply a time varying current to the movement coil to generate an electromagnetic force to induce in the objective lens a vibrating movement along the movement axis during a projection of a laser beam through the objective lens.

BRIEF DESCRIPTION OF THE DRAWINGS [0030] The drawings included herewith are for illustrating various examples of articles, methods, and apparatuses of the present specification and are not intended to limit the scope of what is taught in any way. In the drawings:

[0031 ] Figure 1 is a schematic diagram of a laser image projector;

[0032] Figure 2 is a schematic diagram of a first optical pickup actuator;

[0033] Figure 3 is a schematic diagram of a vibrating second optical pickup actuator;

[0034] Figure 4 is a graph of a vibration amplitude as a function of a driving frequency for a four peak voltages;

[0035] Figure 5 are graphs of speckle contrast ratio as a function of vibration frequency and peak voltage for two example laser sources;

[0036] Figure 6 are pictures of projected speckle images;

[0037] Figure 7 is a schematic diagram of vibrating third and fourth optical pickup actuators;

[0038] Figure 8 is a schematic diagram of a second laser image projector; and

[0039] Figure 9 is a schematic diagram of a third laser image projector.

DETAILED DESCRIPTION

[0040] Various apparatuses or processes will be described below to provide an example of an embodiment of each claimed invention. No embodiment described below limits any claimed invention and any claimed invention may cover processes or apparatuses that differ from those described below. The claimed inventions are not limited to apparatuses or processes having all of the features of any one apparatus or process described below or to features common to multiple or all of the apparatuses described below. It is possible that an apparatus or process described below is not an embodiment of any claimed invention. Any invention disclosed in an apparatus or process described below that is not claimed in this document may be the subject matter of another protective instrument, for example, a continuing patent application, and the applicants, inventors or owners do not intend to abandon, disclaim, or dedicate to the public any such invention by its disclosure in this document.

[0041 ] Referring to Figure 1 , an example of an optical pickup actuator 106 is depicted. In some examples, the optical pickup actuator 106 is a speckle-reducing member. In some examples, the optical pickup actuator 106 is a speckle-reducing member for use in a laser image projector. In some examples, the optical pickup actuator 106 includes an objective lens operable to be vibrated during a projection of a laser beam through the objective lens. In some examples, vibrating an objective lens perpendicular and/or parallel to the propagation direction of a laser beam passing through the objective lens reduces the time-coherence of the laser light and results in improved image quality.

[0042] In some examples, use of a laser in an image projector allows for one or more of high brightness, high contrast, long lifetime, high efficiency, and desirable color representation. In some examples, laser speckle is the set of random interference patterns generated by the coherent light source impinging on a rough surface. These interference patterns cause the intensity of the light to vary randomly, resulting in a grainy image of reduced quality. In some examples, laser speckle can take the form of image noise.

[0043] In some examples, the speckle is described using the Speckle Contrast Ratio (SCR). In some examples, the SCR is defined as the standard deviation of the intensity changes s divided by the average intensity <l>, such that the SCR = s / <l>. In some examples, a SCR greater than 5% results in a degraded image. In some examples, a SCR greater than 5% is noticeable to the human eye. In some examples, a laser image projector includes one or more speck-reducing member.

[0044] In some examples, laser speckle can take the form of image noise that can distract the viewer. In some examples, laser speckle can affect laser scanning applications, where a laser is used to detect a line or spot. In some examples, laser speckle can introduce errors to a scan. In some examples, errors introduced to a scan due to laser speckle prevent a laser scanning apparatus from locating a center point. In some examples, laser speckle causes issues in LIDAR systems, resulting in erroneous distance measurements that decrease measurement reliability.

[0045] Referring again to Figure 1 , in some examples the optical pickup actuator 106 is part of a laser image projector 100. In the illustrated example, the laser image projector includes a laser source 102 to project a laser beam along a projection path 103, the optical pickup actuator 106 fixed adjacent the laser source in the projection path 103, and a set of projection optics 1 10 received in the projection path 103 following the optical pickup actuator 106.

[0046] In some examples, the laser source 102, the optical pickup actuator 106, and the set of projection optics 1 10 are contained in a housing 1 1 1 . In some examples, the housing 1 1 1 is a portable housing. In some examples, the housing 1 1 1 is a mountable housing to be mounted to a wall or ceiling or rested on a desk or table. In some examples, the set of projection optics 1 10 includes a projection lens through which the projection path 103 passes out of the housing 1 1 1 .

[0047] In some examples, the optical pickup actuator 106 includes an objective lens. In some examples, the objective lens is a laser coupling lens received in the projection path 103 between the laser source 102 and the set of projection optics 1 10.

[0048] Referring now to Figure 2, illustrated is an example of an optical pickup actuator 206. The illustrated example optical pickup actuator 206 is similar in many respects to the optical pickup actuator 106, and like features are indicated with like reference numbers incremented by 100.

[0049] In some examples, the optical pickup actuator 206 includes an objective lens 214 to be held in a projection path of a laser source. The objective lens 214 includes an optical axis 215. The illustrated example objective lens 214 also includes a focusing axis 216 parallel to the optical axis 215 and at least one tracking axis 217 perpendicular to the focusing axis 216.

[0050] In some examples, the objective lens 214 includes at least one movement axis along which the objective lens 214 can be linearly moved and at least one movement coil coupled to the objective lens 214 to move the objective lens 214 along the movement axis. In some examples, the movement axis is perpendicular or parallel to the optical axis.

[0051 ] In the illustrated example, the at least one movement axis includes at least one of the tracking axis 217 and the focusing axis 216. In the illustrated example, the movement coil includes at least one of a focusing coil 218 coupled to the objective lens 214 to move the objective lens 214 along the focusing axis 216 and a tracking coil 222 coupled to the objective lens 214 to move the objective lens 214 along the tracking axis 217. In some examples, an optical pickup actuator 206 includes only a single tracking coil 222 and a single focusing coil 218. In some examples, an optical pickup actuator 206 including only a single tracking coil 222 and a single focusing coil 218 is a simpler optical pickup actuator and/or more economical optical pickup actuator.

[0052] In some examples, having only a single movement coil results in a simpler apparatus. In some examples, the movement coil is only one of a single focusing coil 218 or a single tracking coil 222. In some examples, the movement coil is the tracking coil 222. In some examples, the movement coil as the tracking coil 222 produces more effective vibrational movement than the movement coil as the focusing coil 218.

[0053] In some examples, the movement coil includes a copper wire wrapped around a magnetic core. In some examples, each of the focusing coil 218 and the tracking coil 222 includes a copper wire wrapped around a magnetic core. In some examples, one or both of the focusing coil 218 and the tracking coil 222 is actuated by passing a current through the copper wire to generate electromagnetic force.

[0054] In some examples, the focusing coil 218 is operable to move the objective lens 214 parallel to the light propagation direction, which serves to help focus a laser beam onto a target. In some examples, the tracking coil 222 is operable to move the objective lens 214 perpendicular to the light propagation direction. In some examples, having both the focusing coil 218 and the tracking coil 222 allows 2-dimensional objective lens motion of the objective lens 214.

[0055] In some examples, the optical pickup actuator 206 includes a control unit 226 coupled to the at least one movement coil to supply a time varying current to the at least one movement coil. In some examples, supplying the time varying current to the at least one movement coil generates an electromagnetic force and induces a vibrating movement in the objective lens 214. In some examples, the control unit 226 is coupled to the at least one movement coil to supply a time varying current to the at least one movement coil and is operable to supply a time varying current to the at least one movement coil to generate an electromagnetic force to induce a vibrating movement in the objective lens 214 during a projection of a laser beam through the objective lens 214.

[0056] In some examples, the time varying current changes the laser direction rapidly. In some examples, the time varying current changes the laser direction rapidly to generate homogenized light fields with reduced SPR. In some examples, an objective lens vibrates at a small amplitude with high frequency. In some examples, an objective lens vibrates to introduce speckle reduction without reducing image quality. In some examples, an objective lens vibrates at a small amplitude with high frequency to introduce speckle reduction without reducing image quality.

[0057] In some examples, as the laser beam passes through the vibrating objective lens 214 multiple independent speckle patterns are generated. In some examples, multiple independent speckle patterns reduce overall speckle over the integration time of a detector. In some examples, a detector is a human eye. In some examples, vibration frequency and vibration amplitude determine effectiveness in reducing laser speckle.

[0058] In some examples, one or more speckle reduction components require space for the speckle reduction component itself, as well as one or more motors and/or coil required to move, rotate, or vibrate the speckle reduction component. In some examples, speckle reduction components increase one or more of system size, system weight, and system power consumption of a laser projection system. In some examples, a vibrating optical pickup actuator is a speckle reduction component with comparatively small size and/or power consumption. In some examples, vibrating an objective lens by passing current through one or more coils attached to the objective lens and/or an objective lens holder or housing results in a low power consumption and/or small device size speckle reduction component.

[0059] In the illustrated example, the control unit 226 is coupled to at least one of the focusing coil 218 and the tracking coil 222. The illustrated control unit 226 is operable to supply a time varying current to the at least one of the focusing coil 218 and the tracking coil 222 to generate an electromagnetic force to induce a vibrating movement in the objective lens 214 during a projection of a laser beam through the objective lens 214.

[0060] In some examples, optical pickup actuator 206 includes or is coupled to a power source from which the control unit 226 is operable to supply a time varying current. In some examples, the power source is external to the optical pickup actuator 206 and/or a laser image projector that includes the optical pickup actuator. In some examples, the power source is a dedicated power source for supplying power to vibrate the optical lens. In some examples, the power source is a common power source used for other power requirements of the optical pickup actuator 206 and/or a laser image projector that includes the optical pickup actuator. In some examples, the power sources includes at least one of a battery and a wall outlet of a power grid.

[0061 ] In some examples, the time varying current supplied by the control unit 226 is a variable current. In some examples, the time varying current supplied by the control unit 226 is a periodic or pulsating current. In some examples, the time varying current supplied by the control unit 226 is an alternating current. In some examples, the time varying current supplied by the control unit 226 is a square wave current. In some examples, a regular pulsating current results in a more predictable vibration movement of the objective lens 214 than a variable current.

[0062] In some examples, the time varying current has a voltage of between 1 volt and 4 volts. In some examples, the varying current has a voltage of between 1 volt and 2 volts. In some examples, increasing a voltage amplitude of the time varying current increases a vibration amplitude of the vibrating movement. In some examples, decreasing the voltage amplitude of the time varying current decreases the vibration amplitude of the vibrating movement. In some examples, the time varying current has a frequency of between 30 Hz and 120 Hz. In some examples, the time varying current has a frequency of between 60 Hz and 80 Hz.

[0063] In some examples, the objective lens 214 is secured in a lens casing 230. In some examples, the vibrating movement of the objective lens 214 is limited to a dimension of the lens casing 230. In some examples, the lens casing 230 may include a lens holder, and the vibrational movement of the objective lens 214 may be constrained by a dimension of the lens holder.

[0064] Referring now to Figure 3, illustrated is an example of an optical pickup actuator 306 being vibrated. The illustrated example optical pickup actuator 306 is similar in many respects to the optical pickup actuator 106, and like features are indicated with like reference numbers incremented by 200.

[0065] The illustrated optical pickup actuator 306 is being vibrated in a movement direction 334. In the illustrated example, the movement direction 334 is along the tracking axis 317 and perpendicular to the focusing axis 316. In the illustrated example, the control unit is supplying a time varying current to the tracking coil coupled to the objective lens to move the objective lens along the tracking axis 317.

[0066] In the illustrated example of Figure 3, a laser scan line 338 is shown schematically on screen 342. The laser scan line 338 is produced by the direction of vibration.

[0067] Referring now to Figures 4 to 6, illustrated are experimental results for an example laser image projection system. In the example system, an optical pickup actuator 306 was used. The tracking coil 322 was driven with alternating current with a square wave from a multifunction generator at four separate peak voltages; 1 V peak voltage, 1 .5 V peak voltage, 2 V peak voltage, and 4 V peak voltage. Two green laser sources where used in separate tests. The two green laser sources were a frequency doubled diode pumped solid state (DPSS) green laser emitting at 532 nm and a semiconductor green laser diode (Diode) emitting at 515 nm and having an attached Peltier element to stabilize the operating temperature. [0068] For the results indicated in Figures 4 to 6, the example experimental setup included a laser placed at a built-in focal length of the optical pickup actuator 306 and then coupled into the optical pickup actuator 306. The optical pickup actuator 306 output was launched into a 50x microscopic lens (acting as a projecting lens) before reaching a white paper projector“screen”. A charged-coupled device (CCD) camera was placed behind the laser projection screen to capture the shape of the imaged amplitude. Different driving signals were used for the lens vibrating module to test the effect of vibration frequency and amplitude on SCR reduction.

[0069] For some of the results indicated in Figures 4 to 6, the output of the optical pickup actuator 306 was passed into a diffuser. In some examples, as the laser beam was passing into the diffuser with different angles, the diversity annihilated the temporal and spatial coherence of the laser beam, creating multiple speckle patterns that were averaged over the integration time of the detector. In some examples, by increasing the length of the generated laser line due to oscillation of the optical pickup actuator 306, the speckle reduction will increase as it increases the number of uncorrelated speckle patterns (N) according to: C=1/VN.

[0070] For the results indicated in Figures 4 to 6, in order to ensure that the speckle contrast reduction is recorded as a function of the optical pickup actuator 306 alone, the measurements were repeated both with and without the diffusing element (as the diffuser added some level of SCR reduction). Additionally, the camera parameters were kept fixed across all experiments in order to minimize the effect of the camera on the recorded SCR values. The F-number selected with the focal length of the camera lens was selected such that the speckle size was not smaller than the pixel size to guarantee the recorded speckle reduction values were accurate.

[0071 ] Illustrated in Figure 4 is a graph 437 of a vibration amplitude as a function of a driving frequency for the example tracking coil 322. Graphed in the graph 437 are four peak voltages; 1 V peak voltage 439, 1 .5 V peak voltage 440, 2 V peak voltage 441 , and 4 V peak voltage 443.

[0072] For the example of Figure 4, the tracking coil 322 was driven with a square wave, and the different lines represent different peak voltages. The real amplitude values (h) were predicted using the lens magnification relation (h = IM/M) where M is the lens magnification (M = 50x) and IM is the measured line on the screen in mm. The line is a result of the vibration of the objective lens, which produces a bright laser line as opposed to the typical Gaussian beam dot that is observable when the optical pickup actuator 306 is turned off.

[0073] For the example of Figure 4, after the laser was focused by the objective lens of the optical pickup actuator 306, an applied signal of a given peak voltage and frequency caused an objective lens of the optical pickup actuator 306 to oscillate in one dimension. This resulted in a scanning effect due to the curvature of the objective lens. In some examples, at frequencies above 25 frames per second, the human eye will see a laser line at the position of the focal length of the lens.

[0074] In the illustrated example, it can be seen that a peak voltage of 1 .5 V allowed a vibration amplitude very close to the maximum allowed by the physical dimensions of the housing. Applied voltages larger than this caused the vibration amplitude to saturate, which can be seen in the 2 V line where the amplitude flattens out around 1 .1 mm amplitude from 60 to 100 Hz.

[0075] In the illustrated example, the vibration amplitude hit a maximum in the 60- 80 Hz range. In the illustrated example, higher peak voltages increased vibration amplitude. In the illustrated example, the time varying current supplied was an alternating current from a multifunction generator applied on the tracking coil 322.

[0076] Referring now to Figure 5, illustrated are example graphs 545, 547 of speckle contrast ratio as a function of vibration frequency and peak voltage for two example laser sources.

[0077] The graph 545 is of a frequency doubled diode pumped solid state (DPSS) green laser emitting at 532 nm. Graphed in the graph 545 are four peak voltages; 1 V peak voltage 548, 1 .5 V peak voltage 549, 2 V peak voltage 551 , and 4 V peak voltage 552.

[0078] The graph 547 is of a semiconductor green laser diode (Diode) emitting at 515 nm, which had an attached Peltier element to stabilize the operating temperature. Graphed in the graph 547 are four peak voltages; 1 V peak voltage 553, 1 .5 V peak voltage 554, 2 V peak voltage 555, and 4 V peak voltage 556.

[0079] As illustrated in example graphs 545, 547, the reduction in SCR was maximized around the 70 Hz peak, which aligns with the maximum amplitude of vibration before saturating in Figure 4. The example graphs 545, 547 also illustrate that the SCR will, in some examples, return to previous values quickly once the optimal driving frequency is surpassed. In some examples, care must be taken to select the correct driving frequency and/or amplitude to maximize speckle reduction.

[0080] Referring now to Figure 6, the illustrated examples are the speckle contrast ratio and speckle image for both the DPSS and Diode in multiple situations.

[0081 ] Shown in Figures 6A and 6B are the SCR and speckle image without any speckle reduction components for the DPSS and Diode, respectively.

[0082] Shown in Figures 6C and 6D are the SCR and speckle image for the DPSS without the diffuser when the optical pickup actuator 306 is off and when the optical pickup actuator 306 is on, respectively. Shown in Figures 6E and 6F are the SCR and speckle image for the Diode without the diffuser when the optical pickup actuator 306 is off and when the optical pickup actuator 306 is on, respectively.

[0083] Shown in Figures 6G and 6H are the SCR and speckle images for the DPSS with the diffuser when the optical pickup actuator 306 is off and when the optical pickup actuator 306 is on, respectively. Shown in Figures 6I and 6J are the SCR and speckle images for the Diode with the diffuser when the optical pickup actuator 306 is off and when the optical pickup actuator 306 is on, respectively.

[0084] For the illustrated examples, the efficiency of the optical pickup actuator 306 without the diffuser from the original SCR shows a reduction of 31 .75% for the DPSS and 32.22% for the Diode. For the illustrated example, the total efficiency comparing the original speckle values to the final speckle values with the optical pickup actuator 306 and the diffuser are 66.35% for the DPSS and 76.19% for the Diode.

[0085] Referring now to Figure 7, in some examples a laser image projector includes more than one optical pickup actuator, each having a single movement coil operable to induce in an objective lens a vibrating movement. In some examples, a laser image projector includes two optical pickup actuators, each having a single movement coil operable to induce in an objective lens a vibrating movement, and each optical pickup actuator operable to move an objective lens perpendicular to a propagation direction of a laser beam therethrough and perpendicular to one another.

[0086] Illustrated in the example of Figure 7 are optical pickup actuators 406 and 506, each being vibrated. The illustrated example optical pickup actuators 406 and 506 are similar in many respects to the optical pickup actuator 106, and like features are indicated with like reference numbers incremented by 300 and 400, respectively.

[0087] The optical pickup actuators 406 and 506 are each vibrating in a direction perpendicular to both the propagation direction of the laser beam and the vibration direction of the other optical pickup actuator 406, 506, producing a 2D scan line 646 as a combination of the two directions of vibration.

[0088] The optical pickup actuator 406 is being vibrated in a movement direction 435. In the illustrated example, the movement direction 435 is along a tracking axis 458 perpendicular to the focusing axis 416. In the illustrated example, the control unit is supplying a time varying current to the tracking coil coupled to the objective lens to move the objective lens along the tracking axis 458.

[0089] The optical pickup actuator 506 is being vibrated in a movement direction 534. In the illustrated example, the movement direction 534 is along a tracking axis 517 perpendicular to the focusing axis 516 and the tracking axis 458. In the illustrated example, the control unit is supplying a time varying current to the tracking coil coupled to the objective lens to move the objective lens along the tracking axis 517.

[0090] Referring now to Figure 8, illustrated is an example of a laser image projector 700. The illustrated example laser image projector 700 is similar in many respects to the laser image projector 100, and like features are indicated with like reference numbers incremented by 600.

[0091 ] In the illustrated example, a laser source 702 is coupled into one or two optical pickup actuators 706 to project a laser beam along a projection path 703. The one or two optical pickup actuators 706 are fixed adjacent the laser source 702 in the projection path 703, and are between the laser source 702 and a set of projection optics 710. In the illustrated example, an objective lens of the one or two optical pickup actuators 706 has an optical axis parallel to a first portion 705 of the projection path 703 extending through the objective lens.

[0092] In some examples, a third optical pickup actuator is added. In some examples, a third optical pickup actuator is added to a position close to the projection lens 766 and in the projection path to further improve speckle reduction.

[0093] In some examples, a set of projection optics 710 includes only a projection lens 766. In some examples, the projection optics 710 includes, received in the projection path 703 ahead of the projection lens 766, one or more of a diffuser 754, a condensing lens 750, a homogenization component 758, and intermediate optics 762. In some examples the homogenization component 758 is a homogenizing light pipe, as illustrated in Figure 8. In the illustrated example, the projecting lens 766 directs the projection path 703 to a screen 770.

[0094] In some examples, the de-speckle effects of the one or two optical pickup actuators 706 can be enhanced by employing a condensing lens, since the condensing lens can facilitate directing the light waves towards the homogenization component of the system. In some examples, the intermediate optical elements 762 are used for collecting the refined adjusted light from the homogenization component 758.

[0095] Referring now to Figure 9, illustrated is an example of a laser image projector 800. The illustrated example laser image projector 800 is similar in many respects to the laser image projector 100, and like features are indicated with like reference numbers incremented by 700.

[0096] In the illustrated example, a laser source 802 is coupled into one or two optical pickup actuators 806 to project a laser beam along a projection path 803. The one or two optical pickup actuators 806 are fixed adjacent the laser source 802 in the projection path 803, and are between the laser source 802 and a set of projection optics 810. [0097] In some examples, a set of projection optics 810 includes only a projection lens 866. In some examples, the projection optics 810 includes, received in the projection path 803, one or more of a diffuser 854, a condensing lens 850, a homogenization component 858, and intermediate optics 862. In some examples the homogenization component 858 is a homogenizing lens array, as illustrated in Figure 9. In the illustrated example, the projecting lens 866 directs the projection path 803 to a screen 870.

[0098] In some examples, a third optical pickup actuator is added. In some examples, a third optical pickup actuator is added to a position close to the projection lens 866 and in the projection path to further improve speckle reduction.

Claims

CLAIMS:

1 . A laser image projector, comprising:

a laser source to project a laser beam along a projection path; an optical pickup actuator fixed adjacent the laser source, the optical pickup actuator including:

an objective lens held in the projection path, the objective lens having an optical axis parallel to a first portion of the projection path extending through the objective lens, the objective lens having a focusing axis parallel to the optical axis and a tracking axis perpendicular to the focusing axis, a focusing coil coupled to the objective lens to move the objective lens along the focusing axis, a tracking coil coupled to the objective lens to move the objective lens along the tracking axis, and

a control unit coupled to at least one of the focusing coil and the tracking coil and operable to supply a time varying current to the at least one of the focusing coil and the tracking coil to generate an electromagnetic force to induce a vibrating movement in the objective lens during a projection of the laser beam; and

a set of projection optics received in the projection path, and wherein the objective lens is a laser coupling lens received in the projection path between the laser source and the set of projection optics.

2. The laser image projector of claim 1 , further comprising a housing containing the laser source, the optical pickup actuator and the set of projection optics.

3. The laser image projector of any proceeding claim, wherein the projection optics includes a diffuser and a projection lens each received in the projection path, and the diffuser received in the projection path between the optical pickup actuator and the projection lens.

4. The laser image projector of any proceeding claim, wherein the projection optics includes a condensing lens and at least one homogenization component each received in the projection path after the optical pickup actuator.

5. The laser image projector of any proceeding claim, wherein the time varying current is an alternating current.

6. The laser image projector of any proceeding claim, wherein the time varying current has a frequency of between 30 Hz and 120 Hz.

7. The laser image projector of any proceeding claim, wherein the time varying current has a voltage of between 1 volt and 4 volts.

8. The laser image projector of any proceeding claim, wherein increasing a voltage amplitude of the time varying current increases a vibration amplitude of the vibrating movement, and wherein decreasing the voltage amplitude of the time varying current decreases the vibration amplitude of the vibrating movement.

9. An optical pickup actuator for a laser image projector, comprising: an objective lens having an optical axis, the objective lens having a focusing axis parallel to the optical axis and a tracking axis perpendicular to the focusing axis;

a focusing coil coupled to the objective lens to move the objective lens along the focusing axis;

a tracking coil coupled to the objective lens to move the objective lens along the tracking axis; and

a control unit coupled to at least one of the focusing coil and the tracking coil, and operable to supply a time varying current to the at least one of the focusing coil and the tracking coil to generate an electromagnetic force to induce a vibrating movement in the objective lens during a projection of a laser beam through the objective lens.

10. The optical pickup actuator of claim 9, wherein the time varying current is an alternating current.

1 1 . The optical pickup actuator of any of claims 9 to 10, wherein the time varying current is a square wave current.

12. The optical pickup actuator of any of claims 9 to 1 1 , wherein the time varying current has a frequency of between 30 Hz and 120 Hz.

13. The optical pickup actuator of any of claims 9 to 12, wherein the time varying current has a frequency of between 60 Hz and 80 Hz.

14. The optical pickup actuator of any of claims 9 to 13, wherein the time varying current has a voltage of between 1 volt and 4 volts.

15. The optical pickup actuator of any of claims 9 to 14, wherein the varying current has a voltage of between 1 volt and 2 volts.

16. The optical pickup actuator of any of claims 9 to 15, wherein increasing a voltage amplitude of the time varying current increases a vibration amplitude of the vibrating movement, and wherein decreasing the voltage amplitude of the time varying current decreases the vibration amplitude of the vibrating movement.

17. The optical pickup actuator of any of claims 9 to 16, wherein each of the focusing coil and the tracking coil includes a copper wire wrapped around a magnetic core.

18. The optical pickup actuator of any of claims 9 to 17, wherein the objective lens is secured in a lens casing, and wherein an extent of the vibrating movement is limited to a dimension of the lens casing.

19. The optical pickup actuator of any of claims 9 to 18, wherein the at least one of the focusing coil and the tracking coil is the tracking coil.

20. An optical pickup actuator for a laser image projector, comprising:

an objective lens having an optical axis;

a movement coil coupled to the objective lens to move the objective lens along a movement axis, the movement axis perpendicular or parallel to the optical axis; and a control unit coupled to the movement coil and operable to supply a time varying current to the movement coil to generate an electromagnetic force to induce in the objective lens a vibrating movement along the movement axis during a projection of a laser beam through the objective lens.