Laser Pico-projectors Research Articles

A Low Speckle Laser Pico-Projector with Dynamic Light Scattering Liquid Crystal Devices

A Low Speckle Laser Pico-Projector with Dynamic Light Scattering Liquid Crystal Devices

A low speckle laser pico-projector using dynamic light scattering liquid crystal devices

A dynamic light scattering liquid crystal (DLS-LC) device is applied to reduce speckle from a laser pico-projector. The DLS-LC device produces time-varying scattering patterns, which can decrease the degree of spatial and temporal coherence of the laser and achieve a very effective reduction in the speckle. The influence of the amplitude and frequency of the applied electric field for the DLS-LC device on the light scattering characteristics and speckle contrast are studied. The speckle contrast is reduced by as much as 62% with a low electric field amplitude (4.2 V/μm).

High speckle reduction rate in a laser projection system.

In this paper, we demonstrate a design for a laser picoprojector with a high rate of reduction in the speckle contrast value. The method utilizes a holographic diffuser, deformable mirror, and fast electrically tunable (FET) lens. Then we compare the reduction rate of the speckle contrast value for holographic diffusers with different divergence angles and an FET lens with different optical power ranges combined with a deformable mirror. The increase in reduction rate of speckle contrast value means that the minimum value of the speckle can be reached faster. There reduction rate increases from 4.76 to 5.74 for the 5×5 holographic diffuser, 3.45 to 5.66 for the 10×10 holographic diffuser, and 1.52 to 4.58 for the 30×30 holographic diffuser.

An integrated augmented reality surgical navigation platform using multi-modality imaging for guidance.

An integrated augmented reality (AR) surgical navigation system that potentially improves intra-operative visualization of concealed anatomical structures. Integration of real-time tracking technology with a laser pico-projector allows the surgical surface to be augmented by projecting virtual images of lesions and critical structures created by multimodality imaging. We aim to quantitatively and qualitatively evaluate the performance of a prototype interactive AR surgical navigation system through a series of pre-clinical studies. Four pre-clinical animal studies using xenograft mouse models were conducted to investigate system performance. A combination of CT, PET, SPECT, and MRI images were used to augment the mouse body during image-guided procedures to assess feasibility. A phantom with machined features was employed to quantitatively estimate the system accuracy. All the image-guided procedures were successfully performed. The tracked pico-projector correctly and reliably depicted virtual images on the animal body, highlighting the location of tumour and anatomical structures. The phantom study demonstrates the system was accurate to 0.55 ± 0.33mm. This paper presents a prototype real-time tracking AR surgical navigation system that improves visualization of underlying critical structures by overlaying virtual images onto the surgical site. This proof-of-concept pre-clinical study demonstrated both the clinical applicability and high precision of the system which was noted to be accurate to <1mm.

Impact of structure and system parameters for speckle suppression in laser pico-projectors based on the tracked moving flexible DOE loop

The impact of parameters based on the tracked moving flexible DOE loop for speckle suppression in laser pico-projectors was analyzed numerically. The optical scheme of the experimental setup we used is introduced, and the calculation formula of speckle contrast is briefly described. The simulation results show the acceptable tolerance range of DOE structure parameters (including the inclination angle, the width of elementary unit, and the height) and the effect of laser wavelength fluctuation on speckle contrast. The obtained results provide a range of optimal parameters for designing a flexible DOE loop and for avoiding the effect of structural deformation of a DOE loop on speckle suppression in the process of using. In addition, the simulations also provide assistance for subsequent system optimization and integration to produce more compact, low-cost, reliable and stable speckle-free laser pico-projectors.

Speckle reduction by employing two green lasers and two-dimensional vibration of lenses

A method of speckle reduction suitable for use in a laser projector was proposed in the paper. Speckle contrast ratio (SCR) reduction was achieved by combining wavelength diversity and angular diversity methods. First, wavelength diversity was demonstrated by the use of two green laser sources (a 520 nm laser diode (LD) and a 532 nm diode-pumped solid-state (DPSS) laser) at a power ratio of 4:1. Second, angular diversity was achieved via the vibration of two lenses in two orthogonal directions placed directly after the laser source. The vibrating lenses are small and do not require changes to the beam path of the laser source, allowing for more compact projector designs. The frequency of vibration of these lenses was optimized to minimize the SCR in the output image. A SCR of less than 4% was achieved without the use of optical diffusers, which significantly reduces optical losses. Optical transmission could be further increased with the optimization of optical coatings on the lenses. This result shows great promise for applications such as laser pico-projectors within the realm of heads-up displays (HUDs) and mobile devices.

The very compact and efficient speckle suppression device for laser picoprojector

The very compact and efficient speckle suppression device for laser picoprojector

Autostereoscopic transparent display using a wedge light guide and a holographic optical element: implementation and results.

We present a transparent autostereoscopic display consisting of laser picoprojectors, a wedge light guide, and a holographic optical element. The holographic optical element is optically recorded, and we present the recording setup, our prototype, as well as the results. Such a display can superimpose 3D data on the real world without any wearable.

Speckle reduction with fast electrically tunable lens and holographic diffusers in a laser projector

We proposed a speckle reduction system in the laser pico-projector. The holographic diffusers and the fast electrically tunable lens (FET lens) were adopted in the method of the speckle reduction. This research focuses on speckle reduction by the different divergence angle of the holographic diffusers. Moreover, the speckle contrast value can be further reduced by the fast electrically tunable lens. Different divergence angle of the holographic diffuser provides the different angular diversity to compare the speckle reduction ability. We propose three experimental methods to explore speckle reduction. In experiment 1, we use a holographic diffuser and the FET lens. The speckle contrast value can be reduced to 0.08353. In experiment 2, the speckle contrast value can be reduced to 0.06403 under the balance between power consumption and speckle reduction. In experiment 3, we adjust different waveforms to get lower speckle contrast value. Finally, the speckle contrast value is 0.048 at 400Hz. That is lower than 0.05 successfully. That caused the speckle phenomenon is undetectable by human eye.

Fast method of speckle suppression for reflection phase microscopy

Light propagating in turbid medium is randomly altered by optical inhomogeneities, which not only change the momentum and polarization of light but also generate a speckle pattern. All these effects strongly limit capabilities of laser based, quantitative phase–sensitive optical biomedical imaging modalities by hindering a reconstruction of phase distribution. Here we introduce the method of rapid incident light modulation, which allows to suppress speckle noise and preserve the spatial phase distribution. We implement this approach in the full-field Michelson interferometer, where the incident light is modulated using the digitalmicromirror device (DMD). Full Text: PDF ReferencesF. Zernike, "Phase contrast, a new method for the microscopic observation of transparent objects part II," Physica 9, 974-986 (1942). CrossRef M. C. Pitter, C. W. See, and M. G. Somekh, "Full-field heterodyne interference microscope with spatially incoherent illumination," Opt. Lett. 29, 1200-1202 (2004). CrossRef N. B. E. Sawyer, S. P. Morgan, M. G. Somekh, C. W. See, X. F. Cao, B. Y. Shekunov, and E. Astrakharchik, "Wide field amplitude and phase confocal microscope with parallel phase stepping," Review of Scientific Instruments 72, 3793-3801 (2001). CrossRef G. W. John and I. H. Keith, "A diffuser-based optical sectioning fluorescence microscope," Measurement Science and Technology 24, 125404 (2013). CrossRef S. Lowenthal and D. Joyeux, "Speckle Removal by a Slowly Moving Diffuser Associated with a Motionless Diffuser," J. Opt. Soc. Am. 61, 847-851 (1971). CrossRef S. Kubota and J. W. Goodman, "Very efficient speckle contrast reduction realized by moving diffuser device," Applied Optics 49, 4385-4391 (2010). CrossRef Y. Li, H. Lee, and E. Wolf, "The effect of a moving diffuser on a random electromagnetic beam," Journal of Modern Optics 52, 791-796 (2005). CrossRef C.-Y. Chen, W.-C. Su, C.-H. Lin, M.-D. Ke, Q.-L. Deng, and K.-Y. Chiu, "Reduction of speckles and distortion in projection system by using a rotating diffuser," Optical Review 19, 440-443 (2012). CrossRef J. Lehtolahti, M. Kuittinen, J. Turunen, and J. Tervo, "Coherence modulation by deterministic rotating diffusers," Opt. Express 23, 10453-10466 (2015). CrossRef J.-W. Pan and C.-H. Shih, "Speckle reduction and maintaining contrast in a LASER pico-projector using a vibrating symmetric diffuser," Opt. Express 22, 6464-6477 (2014). CrossRef J. I. Trisnadi, "Hadamard speckle contrast reduction," Optics Letters 29, 11-13 (2004). CrossRef M. Szkulmowski, I. Gorczynska, D. Szlag, M. Sylwestrzak, A. Kowalczyk, and M. Wojtkowski, "Efficient reduction of speckle noise in Optical Coherence Tomography," Opt. Express 20, 1337-1359 (2012). CrossRef J. W. Goodman, Speckle phenomena in optics: theory and applications (Roberts and Company Publishers, 2006). DirectLink Y. Choi, P. Hosseini, W. Choi, R. R. Dasari, P. T. C. So, and Z. Yaqoob, "Dynamic speckle illumination wide-field reflection phase microscopy," Opt. Lett. 39, 6062-6065 (2014). CrossRef Y. Choi, T. D. Yang, K. J. Lee, and W. Choi, "Full-field and single-shot quantitative phase microscopy using dynamic speckle illumination," Opt. Lett. 36, 2465-2467 (2011). CrossRef R. Zhou, D. Jin, P. Hosseini, V. R. Singh, Y.-h. Kim, C. Kuang, R. R. Dasari, Z. Yaqoob, and P. T. C. So, "Modeling the depth-sectioning effect in reflection-mode dynamic speckle-field interferometric microscopy," Optics Express 25, 130-143 (2017). CrossRef M. Schmitz, T. Rothe, and A. Kienle, "Evaluation of a spectrally resolved scattering microscope," Biomedical optics express 2, 2665-2678 (2011). CrossRef P. Judy, The line spread function and modulation transfer function of a computer tomography scanner, Med. Phys (1976), Vol. 3, pp. 233-236. CrossRef

Experimental demonstration of a flexible DOE loop with wideband speckle suppression for laser pico-projectors.

The compact and straightforward construction of a pico-projector using an original method for speckle suppression via a simple 1D diffractive optical element (DOE) structure on a loop of flexible film with tracked motion is demonstrated. The 1D-DOE structure is based on binary pseudorandom sequences. The method requires very little energy and space and can decrease speckle noise to levels below the detection sensitivity of the human eye. Large speckle suppression coefficients and low speckle contrasts are obtained for blue, green, and red lasers. Speckle suppression efficiency will be further significantly improved by optimization of the DOE structure and film material.

Speckle reduction using deformable mirrors with diffusers in a laser pico-projector.

We propose a design for speckle reduction in a laser pico-projector adopting diffusers and deformable mirrors. This research focuses on speckle noise suppression by changing the angle of divergence of the diffuser. Moreover, the speckle contrast value can be further reduced by the addition of a deformable mirror. The speckle reduction ability obtained using diffusers with different divergence angles is compared. Three types of diffuser designs are compared in the experiments. For Type 1 which uses a circular symmetric diffuser the speckle contrast value can be decreased to 0.0264. For Type 2, the speckle contrast value can be reduced to 0.0267 because of the inclusion of an elliptical distribution diffuser. With Type 3 which includes a combination of the circular distribution diffuser and elliptical distribution diffuser, the speckle contrast value can be reduced to 0.0236. For all three types, the speckle contrast value is lower than 0.05. Under this speckle value, the speckle phenomenon is invisible to the human eye.

Sidestep and Sneak Peek: Spatial Actions in Augmented Reality Games

We propose a novel concept of game, which allows players to experience tangible interaction with the virtual world of digital games by mixing motorized scenery (object support) with dynamically generated spatial augmented reality. A specific hardware, which includes a turntable platform, on where players can setup customized polygonal shaped scenery to play the game projected onto its surfaces, and a single, or a pair, of focus free laser pico-projectors pointed toward the platform is proposed as a game console able to run this experiment. The turntable platform orientation is synchronized with the game play in a way the physical object rotates aligned with the projected virtual reality in relation to the player’s fixed perspective. By designing 3-dimensional animations, which are rendered and projected in accordance with the surface orientations, we were able to enhance the illusion of depth toward these planar structures during the game play. The use of spatial augmented reality is justified by exploiting the characteristics of projected 2-dimensional light onto 3- dimensional objects in order to extend the game possibilities. As an example, the number and orientation of polygons found on the support can be directly associated with the complexity of the game universe, affecting the game difficulty, scale and game play. In this paper we discuss about spatial actions, which are actions players can perform at object support creases. When synchronized with motor movements, these actions extend the sense of volume in relation to the game avatars providing a tangible connection between players and digital content.

Speckle reduction in laser picoprojector by combining optical phase matrix with twin green lasers and oscillating MEMS mirror for coherence suppression

The combined speckle reduction method is proposed and designed for laser picoprojectors taking small size, high optical power, and good image preservation into account. An optical phase matrix, twin green lasers, and an oscillating MEMS scanning mirror are used to suppress the speckle by reducing spatial and temporal coherences. The optical phase matrix is designed using a 5 µm pixel pitch based on Matlab simulation results and fabricated by imprinting. The twin green lasers with a modulation configuration and an oscillating MEMS scanning mirror are also applied taking the resolution of the display image and the scanning frequency of the MEMS scanning mirror into account. From the experimental results, it is confirmed that the speckle contrast is reduced by 47.47% by the optical phase matrix, 27.93% by the twin green lasers, and 18.89% by the oscillating MEMS scanning mirror. Finally, the combined speckle contrast results in a speckle reduction efficiency of 53.80% with a relatively small optical power loss of 18.21%.

Non-moving Hadamard matrix diffusers for speckle reduction in laser pico-projectors

Personal electronic devices such as cell phones and tablets continue to decrease in size while the number of features and add-ons keep increasing. One particular feature of great interest is an integrated projector system. Laser pico-projectors have been considered, but the technology has not been developed enough to warrant integration. With new advancements in diode technology and MEMS devices, laser-based projection is currently being advanced for pico-projectors. A primary problem encountered when using a pico-projector is coherent interference known as speckle. Laser speckle can lead to eye irritation and headaches after prolonged viewing. Diffractive optical elements known as diffusers have been examined as a means to lower speckle contrast. This paper presents a binary diffuser known as a Hadamard matrix diffuser. Using two static in-line Hadamard diffusers eliminates the need for rotation or vibration of the diffuser for temporal averaging. Two Hadamard diffusers were fabricated and contrast values measured showing good agreement with theory and simulated values.

Speckle reduction and maintaining contrast in a LASER pico-projector using a vibrating symmetric diffuser

We proposed a design for a LASER pico-projector with a low speckle contrast value and high contrast ratio that maintains system efficiency. The method for speckle contrast reduction utilizes two diffusers and a Voice Coil Motor (VCM) oscillator. The two different diffusers for a high contrast ratio and high system efficiency can be divided into two categories. In Category 1, the speckle contrast value can be decreased to 2.80% by using a circular symmetric diffuser. At the same time, the full-on/full-off (FO:FO) contrast ratio can be maintained within 1200:1-1300:1, but the system efficiency decreases 1.50%. In Category 2, the speckle contrast value can be reduced to 6.50% by using an elliptically scattering diffuser. At the same time, the FO:FO contrast ratio can be maintained within 1300:1-1400:1, and the system efficiency decreases by only 1.00%.

Polychromatic speckle reduction in laser pico-projectors using stationary dual Hadamard diffusers

Speckle from coherent light sources continues to be a limiting factor in the design and manufacturing of laser projectors. Utilizing diffractive diffusers has been an effective method for reducing monochromatic speckle contrast. Color laser projection devices require the use of red, green, and blue laser sources therefore; using a monochromatic diffractive diffuser may not be optimal for color speckle contrast reduction. A new static dual-diffuser system utilizing Hadamard matrices has been designed to reduce full color speckle. This paper analyzes the effectiveness of the new Hadamard diffusers in reducing speckle using three separate RGB laser diodes. A simulation of the Hadamard diffusers is conducted to determine the optimum spacing between the two diffusers for polychromatic speckle reduction. Experimental measured results are presented using the optimal spacing of Hadamard diffusers for RGB color speckle reduction showing 60% reduction in contrast.

Evaluation of anisotropic chitosan hydrogels using analytical Mueller matrix method and scanned laser pico-projector

Chitosan has excellent biodegradable, biocompatible and bio-absorbable properties and has been found increasing use in the biomedical field in recent decades. The linear birefringence (LB), linear diattenuation (LD), circular birefringence (CB), circular diattenuation (CD), and depolarization properties of chitosan hydrogel films crosslinked in citrate acid buffer solution (CBS) are extracted using an analytical Mueller matrix method. It is shown that the optical phase retardance property of the hydrogel films provides a reliable indication of both the chitosan concentration of the film and the pH value of the CBS crosslinking environment. In addition, chitosan hydrogel suspension with low-concentration crosslinked in CBS environments with various pH values are studied by the speckle contrast of the projected images obtained when illuminating the suspension with a scanned laser pico-projector (SLPP). It is found that for the samples crosslinked in an acidic environment, the speckle contrast decreases with an increasing pH value. By contrast, for the samples crosslinked in an alkaline CBS environment, the speckle contrast increases as the pH value increases. It is concluded that both the phase retardance and the speckle contrast enable the pH value of the CBS crosslinking solution to be reliably determined. However, of the two methods, the SLPP method yields improved measurement sensitivity. Overall, the results presented in this study show that the analytical Mueller matrix method and SLPP method provide an effective means of characterizing the optical properties, concentration and crosslinking environment of chitosan hydrogel films and suspensions.

Spatial coherence measurement of a scanning laser system and applicability of the Zernike’s approximation to the exit pupil on the scan mirror

Spatial coherence of the scanning laser beam was observed on the Young’s experimental set up using 50-μm-wide, 200-μm-separation double slits, which measured the less than unity fringe visibility in the Fraunhofer diffraction pattern of the double slits illuminated by the scanning laser beam at horizontal scan frequency 21 kHz, while approximately unity in case of the illumination by the laser beam at rest. This fact allow us to use the Zernike’s approximation when applying the van Cittert Zernike theorem to the scanning laser system such as the laser pico-projectors in order to estimate its speckle contrast in the projected image on the screen diffuser. The predicted and measured speckle contrasts showed excellent agreement on the screen illuminated by the laser projector.

Relative two-dimensional nanoparticle concentration measurement based on scanned laser pico-projection

Abstract The images projected by scanned laser pico-projectors (SLPPs) contain speckle noise caused by the reflection of the high coherent laser light source from the projection screen. The speckle contrast varies in accordance with the volume roughness of the screen and can be applied for relative two-dimensional (2-D) nanoparticle concentration measurement in both solid and liquid solutions. The great advantage in this study is that it can measure several samples simultaneously. The experimental results show that the green laser within the SLPP provides a better measurement sensitivity and resolution than the red or blue lasers. In solid solution measurement, different concentrations of nanoparticles embedded in a poly (methyl methacrylate) (PMMA) matrix are tested and the maximum sensitivity and resolution are found to be −8.59 ((speckle contrast %)/(wt%)) and 0.013 (wt%), respectively. In liquid solution measurement, different concentrations of nanoparticles dissolved in deionized water are also tested and the maximum sensitivity and resolution of green laser in SLPP are found to be −2050 ((speckle contrast %)/(molar concentration (M)) and 7.51 × 10−5 M, respectively. Finally, the system shows ability to measure the collagen concentrations from 0.125 to 0.025%. Accordingly, the proposed system provides a viable, low-cost solution for high-sensitivity in biomedical, chemical and environmental applications.