Retinal projection displays (RPDs) are an important development direction for head-mounted displays (HMDs). This paper reviews the literature on optical engineering aspects based on the data on advanced technology in RPD design and development. The review includes the principles and applications of four theories, e.g., the Maxwellian view and its modified modality and the monocular and binocular depth cues of stereoscopic objects in the physiology of the human visual system. To support the Maxwellian view and achieve retinal projection systems with depth cues, results of previous design works were summarized using different methods and their advantages and disadvantages are analyzed. With an extremely long focal depth, a prototype of a full-color stereoscopic see-through RPD system was discussed. Finally, a brief outlook of the future development trends and applications of the RPDs was presented
The propagation property of Laguerre-Gaussian (LG) beams passing through a diffractive ring-lens (RL) was studied, where the RL was generated by a liquid crystal spatial light modulator (LC-SLM). It was found that the LG beam was transformed into a sharp ring at the focal plane first, and then a Bessel-similar beam was formed behind the focal plane but the beam size was enlarged with the increase of propagation distance. With the help of a group of lenses, the beam was further collimated into a Bessel beam. Finally, the “non-diffractive” and self-reconstruction properties of the generated Bessel beams were experimentally verified.
A multi-operation laser oscillator is developed and built with multiple operation modes (OMs): injection-seeding mode, cavity-dumping mode and Q-switching mode. With the same electrical energy pumping, the multi-operation laser oscillator provides different output energies and pulse durations for different OMs. In the Q-switching mode, the output coupling is optimized for different electrical energy pumping. The laser oscillator operation can be switched between different modes conveniently. The multi-operation laser sources could be operated in multiple OMs for various research and application requirements.
Antimony selenide (Sb2Se3) is a promising absorber material for thin film photovoltaics because of its attractive material, optical and electrical properties. In recent years, the power conversion efficiency (PCE) of Sb2Se3 thin film solar cells has gradually enhanced to 5.6%. In this article, we systematically studied the basic physical properties of Sb2Se3 such as dielectric constant, anisotropic mobility, carrier lifetime, diffusion length, defect depth, defect density and optical band tail states. We believe such a comprehensive characterization of the basic physical properties of Sb2Se3 lays a solid foundation for further optimization of solar device performance.
Textured surface boron-doped zinc oxide (BZO) thin films were fabricated by metal organic chemical vapor deposition as transparent conductive oxide (TCO) for solar cells. The surface microstructure was characterized by X-ray diffraction spectrum and scanning electron microscope. The optical transmittance was shown by optical transmittance microscope and the electrical properties were tested by Hall measurements. The thickness of the BZO film has crucial impact on the surface morphology, optical transmittance, and resistivity. The electrical and optical properties as well as surface microstructure varied inconsistently with the increase of the film thickness. The grain size and the surface roughness increased with the increase of the film thickness. The conductivity increased from 0.96×103 to 6.94×103 S/cm while the optical transmittance decreased from above 85% to nearly 80% with the increase of film thickness from 195 to 1021 nm. The BZO films deposited as both front and back transparent electrodes were applied to the bifacial p-type a-Si:H/i-type a-Si:H/n-type c-Si/i-type a-Si:H/n+-type a-Si:H heterojunction solar cells to obtain the optimized parameter of thickness. The highest efficiency of all the samples was 17.8% obtained with the BZO film thickness of 829 nm. Meanwhile, the fill factor was 0.676, the open-circuit voltage was 0.63 V and the short-circuit density was 41.79 mA/cm2. The properties of the solar cells changing with the thickness were also investigated.
Paper-based generators are essential elements for building all paper-based systems. To obtain robust paper-based generators with outstanding high power outputs, this paper introduced a new type of double-folding paper-based generator by folding two paper components together. The output performance levels of the double-folding generator were twice higher than that of the single-folding and parallel-plate generators. A peak power of ~3.24 mW was achieved under a stimulating frequency of 3 Hz. Furthermore, 47 light-emitting diodes (LEDs) were lit directly by a double-folding paper-based generator assembled to the crack of a door that opens and closes. This finding indicated the potential applications of the double-folding generator in the production of door ornaments or for security in places where doors frequently open and close.
This paper presents a new compensation pixel circuit suitable for active-matrix organic light-emitting diode (AMOLED) stereoscopic three dimensional (3D) displays with shutter glasses. The simultaneous emission method was used to solve the crosstalk problem, in which the periods of initialization and threshold voltage detection occur for each pixel of whole panel simultaneously. Furthermore, there was no need of the periods of initialization and threshold voltage detection from the second frame beginning by employing threshold voltage one-time detection method. The non-uniformity of the proposed pixel circuit was considerably low with an average value of 8.6% measured from 20 discrete proposed pixel circuits integrated by In-Zn-O thin film transistors (IZO TFTs). It was shown that the OLED current almost remains constant for the number of frames up to 70 even the threshold voltage detection period only exists in the first frame.
This study experimentally investigated a Yb:YAG pulse laser amplifier with a high amplification gain and a high signal-to-noise ratio (SNR). The highest amplification gain of 172 and highest pulse energy of 131 mJ were obtained with the highest SNR of 24.9 dB from a volume gain of 10 mm × 10 mm × 1 mm. The output beam quality values of Mx 2=1.91 in the slow axis and My 2=1.58 in the fast axis were also achieved.
This paper proposed a novel variable optical splitter, of which the splitting ratio can be dynamically adjusted according to different wavelengths. A novel intelligent passive optical network (PON) system based on this splitter was also presented. Experimental results demonstrated that the insertion loss can be reduced corresponding to the decrease of the splitting ratio.
In this study, a hybrid algorithm combining genetic algorithm (GA) with back propagation (BP) neural network (GA-BP) was proposed for extracting the characteristics of multi-peak Brillouin scattering spectrum. Simulations and experimental results show that the GA-BP hybrid algorithm can accurately identify the position and amount of peaks in multi-peak Brillouin scattering spectrum. Moreover, the proposed algorithm obtains a fitting degree of 0.9923 and a mean square error of 0.0094. Therefore, the GA-BP hybrid algorithm possesses a good fitting precision and is suitable for extracting the characteristics of multi-peak Brillouin scattering spectrum.
This study proposes a novel scheme of a cross-correlation frequency-resolved optical gating (X-FROG) measurement for an optical arbitrary waveform (OAW) based on the sum frequency generation (SFG) effect of a periodically poled lithium niobate (PPLN) waveguide. Based on the SFG effect and combined with the principal component generalized projects algorithm on a matrix, the theory model of the scheme is established. Using Matlab, the proposed OAW measurement X-FROG scheme using the PPLN waveguide is simulated and studied. Simulation results show that a rectangular pulse is a suitable gate pulse because of its low errors. Moreover, the increased complexity of OAW and phase mismatch decrease measurement accuracy.
Although the performance of space cameras has largely improved, the micro vibration from flywheel disturbances still significantly affects the image quality of these cameras. This study adopted a passive isolation method to reduce the negative effect of flywheel disturbance on image quality. A metal-rubber shock absorber was designed and installed in a real satellite. A finite element model of an entire satellite was constructed, and a transient analysis was conducted afterward. The change in the modulate transfer function was detected using ray tracing and optical transfer function formulas. Experiments based on real products were performed to validate the influence of the metal-rubber shock absorber. The experimental results confirmed the simulation results by showing that the negative effects of flywheel disturbance on the image quality of space cameras can be diminished significantly using the vibration isolation method.
In this paper, a foveated imaging system using a reflective liquid crystal spatial light modulator (SLM) was designed. To demonstrate the concept of foveated imaging, we simulated with software Code V and established a laboratory prototype. The result of the experiment shows that an SLM can be used to correct the aberration of region of interest (ROI) while the resolution of other area was still very low. The vary-resolution system was relative simple compared to the traditional high resolution system and obviously can reduce the amount of data transmission. Such systems will have wide application prospect in various fields.