Holographic display with LED illumination based on phase-only spatial light modulator

Phase-only liquid crystal spatial light modulator (SLM) has been widely used for accurate phase-manipulation in holographic display, optical tweezers, lithography, etc. Due to the nonlinear optical response of liquid crystal and manufacturing defects, the grayscale-phase response could be different for every single SLM device. The calibration for phase modulation is needed for improving the performance of the SLM involved system. The principles of phase-only SLM are reviewed. The main phase calibration methods for SLM are discussed and compared.

Digital Micro-mirror Device (DMD) is an important tool in holographic display owning high-speed refresh rate and good diffraction efficiency. However, the reconstruction light source has great impact to image quality. A new holographic display system based on DMD for using light-emitting diodes (LEDs), is proposed in this paper. LEDs are chosen as light source to replace the laser, since it can reduce the speckle noise effectively, which is caused by both temporal and spatial coherence of laser. In order to solve the problem using LED as DMD holographic display light source, the characteristics of DMD as the display device for holographic displays are studied. An aspheric collimator for LED is used to improve the optical efficiency. A spatial filter is used to improve the coherence. The experimental results show that this lighting system has a good display quality.

Holographic display and imaging are usually implemented with coherent lasers, which usually suffer from speckles. Incoherent light sources have long been highly desired for holographic applications, but the corresponding spatial modulation scheme is still lacking. Here we demonstrate a hyperspectral complex field modulation based on a single spatial light modulator (SLM) for an incoherent white light-emitting diode (LED) with a 200 nm bandwidth. The technique encodes the complex fields of multiple wavelengths into a phase hologram. The hologram has an analytical expression and is the superposition of multiple fringe patterns with different frequencies. By tuning the local fringe frequency on the hologram, one can modulate the local output spectrum. The method is applied for sweeping wavelength and projecting color images, where tens of spectral channels are modulated independently. Moreover, the method can achieve complex modulation and is applied in multi-plane holographic projections.

A speckle noise suppression method in digital holography is proposed by the angular diversity with a phase-only spatial light modulator (SLM). The minimal angular difference of illumination beams is quantitatively analyzed to ensure the noncorrelation of any two speckle patterns, and then the phase-only SLM is employed to generate a series of tilted illumination beams. Comparing with the typical methods, the tilted illumination beams are controlled dynamically and accurately, which makes it possible to record a large number of holograms. Finally, using an image-plane digital holographic system, 117 holograms are recorded respectively, and the synthesized reconstructed images are obtained with the greatly suppressed speckle noise which is in good agreement with the theoretical results. The experimental results demonstrate the effectiveness, repeatability, and practicability of the proposed approach.

Due to the various advantages on illumination, high-power light emitting diode (LED) system has been focused recently. Because the light source that consists of red, green and blue LEDs can provide full high definition color gamut with advantage of longer lifetime, LED light source starts to be applied in digital display system. However, much heat is dissipated from LED and operating temperature severely influences the characteristics of LEDs including dominant luminosity wavelength, luminosity and lifetime. Therefore careful thermal management is crucial to ensure accurate image quality of display device as well as guaranteed lifetime. The present study is conducted to investigate the performance of thermal management system for LED light source in rear projection TV. The result shows that the reducing thermal resistance between LEDs and substrate is the most effective way to dissipate heat and the applicable limit of thermal resistance is existed for various heat-dissipating conditions of LEDs. And it is also suggested that the efficacy of heat transport system from LED to ambient applied in red, green and blue LED light system to ensure the product quality

High-throughput fabrication of graphically encoded hydrogel microparticles is achieved by combining flow contact lithography in a multichannel microfluidic device and a high capacity 25 mm LED UV source. Production rates of chemically homogeneous particles are improved by two orders of magnitude. Additionally, the custom-built contact lithography instrument provides an affordable solution for patterning complex microstructures on surfaces.

Recent developments in ultra-high-definition (UHD) displays have a major impact on holographic displays as well as conventional display systems. A spatial light modulator (SLM) can reproduce hologram data through wavefront modulation of the incident light, and a holographic printer can record a high-quality hologram by sequentially recording a number of holograms reproduced by the SLM on a holographic material. As UHD (4K) resolution SLMs have been popularized, higher quality holograms can be reproduced compared to previous 2K resolution SLMs. When applied to the holographic printer, it is possible to manufacture holographic optical elements (HOEs) having a multifunctioning property and a wide field of view. In this paper, we introduce the holographic printer system using an amplitude UHD SLM and its applications. The holographic printer consists of optical systems to generate high-quality hologram from UHD SLM and mechanical systems to record the hologram on holographic material. The details of the total system are introduced. Furthermore, we introduce a holographic near-eye display system using UHD SLM and an image combiner HOE which is manufactured by the holographic printer.

White light emitting diode (LED) with high brightness has attracted a lot of attention from both industry and academia for its high efficiency, ease to drive, environmental friendliness, and long lifespan. They become possible applications to replace the incandescent bulbs and fluorescent lamps in residential, industrial and commercial lighting. The realization of this new lighting source requires both tight LED voltage regulation and high power factor as well. This paper proposed a single-stage flyback converter for the LED lighting applications and input power factor correction. A type-II compensator has been inserted in the voltage loop providing sufficient bandwidth and stable phase margin. The flyback converter is controlled with voltage mode pulse width modulation (PWM) and run in discontinuous conduction mode (DCM) so that the inductor current follows the rectified input voltage, resulting in high power factor. A prototype topology of closed-loop, single-stage flyback converter for LED driver circuit designed for an 18W LED lighting source is constructed and tested to verify the theoretical predictions. The measured performance of the LED lighting fixture can achieve a high power factor greater than 0.998 and a low total harmonic distortion less than 5.0%. Experimental results show the functionality of the overall system and prove it to be an effective solution for the new lighting applications.

Light emitting diodes (LED) are a new source for replacing traditional light sources including under water illumination. As traditional underwater light sources operate under a radiative transfer model, the luminous intensity is dispersed evenly at each emission angle, with the scattering factors included in the attenuation coefficient. By contrast, LED light sources are characterized by being highly directional, causing underwater luminous energy to vary with different emission angles. Thus, the traditional theory of underwater optical transfer becomes inapplicable when an underwater LED lighting module is designed. Therefore, to construct an underwater transfer model for LED light sources, this study employed the average cosine of the underwater light field, the method for light scattering probability, the LED luminous intensity distribution curve (LIDC) and axial luminous intensity. Afterwards, an underwater LED fish-attracting lamp was designed. Experimental results showed that, compared with the simulation values, the luminous intensity of the underwater LED lighting module at all emission angles had a percentage error of less than 10%.

Electrical lighting has seen many advancements since Edison first patented his version of the incandescent lamp. From those early days, lighting technology eventually changed with the introduction of mercury vapor, fluorescent, metal halide, and high-pressure sodium lamps. While each of these new light sources offered tremendous benefits over the incandescent lamp, their acceptance and any further advancement happened over a number of decades. Light-emitting diodes (LEDs) as a method of general lighting entered the market in the early 2000s. They were expensive and not very energy efficient. Within a few years, these lighting LEDs had dramatically improved. By 2006, they became trendy for residential and commercial applications, crossing over into the roadway lighting market a couple of years later. By 2010, they had become very “popular” as an industrial light source. In 2011, LEDs became mainstream and more affordable. Moving forward, LEDs are poised to dominate. Over the next decade, it is expected that LEDs will render most other light sources obsolete. The dilemma is that just about every evaluation method used for the past 140 years for every other light source cannot be applied directly to LED light sources. This paper will examine the LED revolution and what you need to know to survive.

The effects of different light-emitting diodes on the growth, morphogenesis, and tuberization of ‘Favorita’ potato (Solanum tuberosum L.) plantlets were determined. Shoot cuttings were cultured in vitro for 21 days under six different light types: fluorescent lamp, 100% red LED, 100% blue LED, and three blue and red LED combinations (80R/20B, 70R/30B, 50R/50B). Plant height was the greatest under 100R LED, whereas root length and fresh weight were the greatest under 80R/20B LED. Chlorophyll content and total soluble carbohydrate content were greatest when R LED was combined with at least 30% B LED. Carotenoid content and average weight of tubers were the greatest when both R and B LED were present. The diameter of the biggest tuber was the greatest under 70R/30B LED. Under 100% R, single tubers had the least average weight, while other treatments showed no significant difference. In conclusion, 70R/30B LED is best for growing Favorita potato plantlets in vitro.

Mach-Zehnder-based measurement of light emitting diodes temporal coherence

Objective: To compare the possible toxic effects of three light sources used in vitreoretinal endoillumination systems; halogen, xenon, and light-emitting diode (LED) on retinal pigment epithelium (RPE) cell cultures, after two different exposure times.Material and methods: ARPE-19 human RPE cell cultures were exposed to halogen, xenon, and LED light sources at a distance of 1.5 cm for 30 and 60 min with equal lumen output levels. Cells in the control group were not exposed. RPE cell cultures were compared in terms of cell viability, DNA damage, apoptosis rate, and IL-1ß, IL-6, and TNF- α levels.Results: The halogen light group showed significantly more DNA damage, higher TNF-α, IL-1β, and IL-6 levels, and lower viable cell count at 30 min compared to the control group. The rates of early and late apoptosis were also significantly higher at 60 min. There were no statistically significant differences in any of the parameters between the xenon and LED light sources and the control group at 30 or 60 min.Conclusion: New generation lights, xenon, and LED, seem to be safe in terms of RPE cells. Halogen light may cause toxic effects on RPE cells when used for a long time with maximal power output.

Cherenkov radiation is used to study the production of particles during collisions, cosmic rays detections and distinguishing between different types of neutrinos and electrons. The optical properties of water are very important to the research of Cherenkov Effect. Lambert-beer law is a method to study the attenuation of light through medium. In this paper, optical properties of water are investigated by use of a water attenuation performance test system. The system is composed of the light-emitting diode (LED) light source and the photon receiver models. The LED light source model provides a pulse light signal which frequency is 1 kHz and width is 100ns. In photon receiver model, a high sensitivity photomultiplier tube (PMT) is used to detect the photons across the water. Because the output voltage amplitude of PMT is weak which is from 80mv to 120mV, a low noise pre-amplifier is used to improve the detector precise. An effective detector maximum time window of PMT is 100ns for a long lifetime, so a peak holder circuit is used to hold the maximum peak amplitude of PMT for the induced photons signal before the digitalization. In order to reduce the noise of peak holder, a multi-pulse integration is used before the sampling of analog to digital converter. At last, the detector of photons from the light source to the PMT across the water is synchronized to the pulse width of the LED. In order to calculate the attenuation coefficient and attenuation length of water precisely, the attenuation properties of air-to-water boundary is considered in the calculation.

Amid the growing global demand for sustainable crop production, plant factories with artificial lighting (PFALs) have gained attention as the systems provide stable, optimal growth environments for crops, and are largely unaffected by climate change. However, a limitation of widely used light-emitting diodes (LEDs) in PFALs is their decreased energy conversion efficiency at high output levels, prompting the search for more efficient light sources. This study focused on laser diodes (LDs), which has shown superior energy conversion efficiency, as an alternative. We developed an LD lighting system capable of mixing red and blue light at arbitrary ratios and mounted it onto a commercial gas-exchange measurement system. Using this system, photosynthetic parameters in rice were obtained under conditions of red light alone and as well as combined red and blue light illumination. Under red LD illumination alone, steady-state CO2 assimilation rate, stomatal conductance, and transpiration rate in rice were significantly higher than those under red LED illumination, whereas intrinsic water-use efficiency decreased due to a relatively greater increase in stomatal conductance. Notably, stomatal conductance and transpiration rate exhibited pronounced temporal oscillations with a period of approximately 900 s, which closely corresponded to oscillations in stomatal aperture confirmed by microscopic observations. Under combined red and blue LD illumination, steady-state photosynthetic parameters did not differ significantly from those under LED illumination; however, the dominant oscillatory frequency observed under red LD alone was not detected, and some photosynthetic capacity parameters tended to decline. Furthermore, CO2 response analyses revealed that, despite lower CO2 assimilation, stomatal conductance responded more strongly to changes in intercellular CO2 concentration under combined red and blue LD illumination. Taken together, these results demonstrate that LD lighting, particularly red LD, enhances stomatal dynamics and induces characteristic oscillatory behavior compared with LED lighting. While red LD appears to be a promising cultivation light source for PFALs capable of maintaining high photosynthetic activity, the physiological impacts associated with blue LD, including potential reductions in photosynthetic capacity, require further study to optimize blue-light proportions for rice cultivation.