The explosive growth of information worldwide emerges as a great challenge for the currently-available big data center platform and compels the development of novel methods and storage devices. Far-field super-resolution techniques have shown the potential to achieve nanoscale three-dimensional optical data storage resulting in a single-disc capacity towards petabytes. In particular, super-resolution photoinduction-inhibited nanolithography (SPIN) has been used to write features with size of 9 nm, while stimulated emission depletion (STED) microscopy is suitable for super-resolution optical data reading. However, the combination of SPIN and STED microscopy for super-resolution optical data storage is presently limited by the high intensity required for the inhibition beam, which results in high energy consumption and damage of the data bits, and the lack of an optically-activatable material for data read-out after SPIN. Recently, rare-earth doped nanocrystals, featuring long luminescence lifetime and emission bands ranging from ultraviolet to near-infrared, have been proven adapt for low-power super-resolution optical data reading through STED microscopy and may be implemented for super-resolution data writing fully based on optical methods. Here, we report about the development of rare-earth doped nanocrystals for ultra-low power, ultra-high capacity super-resolution optical data storage. Core-shell nanoparticles were prepared via co-precipitation and measurements of emission intensity and fluorescence lifetime have been performed. Subsequently, rare-earth doped nanocrystals have been used for optical data storage under 980-nm laser excitation and the data bits were successfully retrieved back by STED microscopy. Finally, simulation results indicate the feasibility of nano-sized recordings and thus a boost of storage capacity is expected.

We propose a new recording scheme by which arbitrary polarization states are stored in volumetric and polarization insensitive photorefractive materials. In the scheme, Stokes parameters of an arbitrary polarization state are recorded as grating strength by using the relation between the interference intensity in recording process and the diffraction efficiency in reading process. We show the experimental setup to retrieve linear, circular, and elliptic polarization states using a typical non-polarization dependent photorefractive media, an iron-doped lithium niobate crystal. The polarization state introduces an additional degree of freedom for storing information, and is useful for expanding the capacity in holographic data storage.

In this paper, a novel and efficient approach to digital optical data storage using rare-earth ion doped inorganic insulators is demonstrated. More specifically, the nanocrystalline alkaline earth halide BaFCl:Sm is shown to hold great potential for multilevel optical data storage. Proof-of-concept demonstrations show that these phosphors could be used for rewritable, multilevel optical data storage down to the physical dimensions of a single nanocrystal. Multilevel information storage is based on the highly-efficient and reversible conversion of Sm³⁺ to Sm²⁺ ions upon exposure to UV-C light. The stored information is efficiently read-out by employing the photoluminescence of the Sm ²⁺ ions in the nanocrystals, with the signal strength being dependent on the UV-C intensity used during the write step. This serves as the mechanism for multilevel data storage in the individual nanocrystals. This data storage platform has the potential to be extended to 2D and 3D memory for storage densities that could approach tera- or even petabyte/cm³ levels.

Optical disc systems usually have several detection channels in order to obtain information and objective lens control signals. As well as used in the area of wireless communication known as Multiple-Input Multiple-Output (MIMO) or the diversity technique, these multiple-channel signals should bring a higher quality of the information for the optical disc systems. Partial Response (PR) signal processing is an effective method to increase the recording density for the current optical disc systems. In this report, dual-input channels, sum and tangential push-pull detections are considered. Different PR classes can be adapted to the dual-input channels. Three kinds of signal modulation methods, the 1-7 RLL, the Eight-Fourteen Modulation (EFM) and un-modulated signals are examined. The qualities of the dual-channel signals are expressed by drawing the constellation maps. Compare to the conventional single-channel detection case, dual- channel one tend to indicate smaller signal level deviations normalized by the detection window. The normalized signal level deviation in multiple-channel detection is defined as the deviation in the channel dimension space normalized by the minimum distance between the average levels of the states. In many cases, levels of states are separated in dual- channel detection case though those are degenerated in single-channel detection case. The signal levels of the additional channel increase the number of states. It should enhance the performance of the later signal processing part such as maximum likelihood (ML) method.

This paper reports the theoretical analysis and experimental results of a far-field focus sensor. This system utilizes moving interference fringes at the far-field caused by the one-dimension uniform-pitch grating embedded inside a disc. The intensity of the moving fringes was sampled and processed by a digital signal processor and synchronization circuits including a phase lock loop. A well-shaped and low-offset focus error signal was observed all over the disc rotation, as well as, the focus serve operation being confirmed. Finally, how this sensor can be adopted to the collinear hologram data storage system is discussed.

The wavelength tolerance in microholographic recording is reported to be narrow, but the actual value is uncertain. Therefore, the effect of various factors on the wavelength tolerance in microholographic recording was investigated through a numerical simulation. The recording and readout beams were expressed as the superposition of plane waves. The diffraction efficiency of a microhologram was calculated using the coupled wave theory. The wavelength tolerance was defined as the wavelength range where the diffraction efficiency was higher than the half of its maximum value. The center wavelength of the laser was 405 nm, the numerical aperture of the objective lenses was 0.85, and the refractive index, maximum refractive index change, and thickness of the recording medium were 1.5, 1.0 x 10^-3, and 300 μm, respectively. In this case, the wavelength tolerance was as narrow as ±0.18 nm. First, random aberrations were added to the recording and readout beams. Even when the root-mean-square wavefront aberration was increased to 0.14 λ, the maximum diffraction efficiency decreased but the wavelength tolerance did not change. Next, multiple microholograms were recorded in the in-plane and vertical directions and the center microhologram was reproduced. Even when the number of recorded microholograms was increased to 5 x 5 x 5, the maximum diffraction efficiency decreased but the wavelength tolerance only slightly increased to ±0.21 nm. If the actual wavelength tolerance would be much wider, there might be another factor that makes the equivalent thickness of the recording medium much thinner (e.g. nonlinearity of the recording medium).

To get higher resolution and higher SNR optical image data or digital picture, characterizing noise of image sensor helps to make better image sensor and better image signal processor. There are lots of manners with regards to characterizing image and noise quality of CMOS image sensors. And one of the most important performances is FPN(fixed pattern noise), because this kind of noise cannot be removed by temporal signal processing. This FPN can be divided into DSNU(dark signal non-uniformity) and PRNU (photo-response non-uniformity). PRNU depends on the uniform performance of sensitivity among pixels in general. Additionally, this uniformity of sensitivity is different from each color filter channels Red, Green and Blue in linear response region. And those performances were almost same in nonlinear response region for dim light condition. In this paper, in order to diagnose this tendency of PRNU regarding each color channel, special techniques are introduced to minimize other noise sources excluding PRNU from target images. And it also introduces that the different PRNU result between color and mono sensor by changing different color temperature light source. And it suggests ways to understand these results with simple manner as well.

Holography can offer unique solutions to the specific problems faced by automotive optical systems. Frequently, when possibilities have been exhausted using refractive and refractive designs, diffraction can come to the rescue by opening a new dimension to explore. Holographic optical elements (HOEs), for example, are thin film optics that can advantageously replace lenses, prisms, or mirrors. Head up display (HUD) and LIDAR for autonomous vehicles are two of the systems where our group have used HOEs to provide original answers to the limitations of classical optic. With HUD, HOEs address the problems of the limited field of view, and small eye box usually found in projection systems. Our approach is to recycle the light multiple times inside a waveguide so the combiner can be as large as the entire windshield. In this system, a hologram is used to inject a small image at one end of a waveguide, and another hologram is used to extract the image several times, providing an expanded eye box. In the case of LIDAR systems, non-mechanical beam scanning based on diffractive spatial light modulator (SLM), are only able to achieve an angular range of few degrees. We used multiplexed volume holograms (VH) to amplify the initial diffraction angle from the SLM to achieve up to 4π steradian coverage in a compact form factor.

Metalenses have great ability in light focusing and can be tailored to exhibit varied functionalities for ultrathin optical applications. Here, we demonstrate a GaN metalens array which can be regarded as a light shaping generator for the structured light generation. The metalens array consists of 60 x 60 metalenses which can project a 42 cm x 42 cm light spots area at the distance of 1.5 M. The distance can be estimated by identifying the deformation of light spot distribution. The advantages of this metadevice is light weight, small, ultrathin, durable and easy to compact with other devices. Our design provides a new avenue for the structured light applications such as distance sensing and 3D environmental construction.

We designed the image guide with discretely depth-chirped holographic grating for head mounted display to equalize luminance over the Field of View (FOV) and increase throughput. To reduce the time required to optimize depth-chirped pattern, the mathematical optical efficiency prediction method was devised. The design approach enables, rapid turnaround in design process and precise prediction of optical performance of image guide incorporated depth-chirped grating. Display performance of the depth-chirped image guide identified by the mathematical optimization was verified by the geometrical and physical hybrid optical simulation that the RCWA code is integrated to geometrical ray trace code via DLL to incorporate effects of the diffraction. As a results, the design exhibited 315 cd/m²/lm for the FOV (35° (H) x 20° (V)) and eye box size (±8.5 mm (H), ±6.5 mm (V)). The value of luminance was increased by 37% than unchirped image guide. Uniformity of luminance was further improved, from 33% to 47%. In conclusion, we made clear the effect of depth-chirped image guide to increasing the performance of the image guide.

In recent years, high-performance environment perception sensors are increasingly expected to realize autonomous driving systems. Light detection and ranging (LiDAR) is one of the most promising sensors due to its high angular resolution and range accuracy. Recently we've developed two types of cost-effective MEMS-LiDAR systems which consist of a single-pair of an emitter, a photodetector and a two-axis MEMS scanner in coaxial optics. The front-facing type takes advantage of telescopic optics to enlarge effective aperture for long range detection. The wide-view type utilizes omni-directional optics to achieve 360-degree panoramic scanning. In this study, we've investigated catadioptric devices and unique scanning MEMS mirrors for compact omni-directional LiDARs. The concept has been experimentally confirmed on a test bench. Here we report on the recent progress and describe the challenges and the prospects for MEMS-LiDAR systems.

A novel method of beam steering, utilizing a mass-produced Digital Micromirror Device (DMD), enables a reliable single chip Light Detection and Ranging (LIDAR) with a large field of view while having minimum moving components. In the single-chip LIDAR, a short-pulsed laser is fired in a synchronous manner to the micromirrors rotation during the transitional state. Since the pulse duration of the laser pulse is substantially short compared to the transitional time of the mirror rotation, virtually the mirror array is frozen in transition at several discrete points, which forms a programmable and blazed grating. The programmable blazed grating efficiently redirects the pulsed light to a single diffraction order among several while employing time of flight measurement. Previously, with a single 905nm nanosecond laser diode and Si avalanche photo diode, a measurement accuracy and rate of <1 cm and 3.34k points/sec, respectively, was demonstrated over a 1m distance range with 48° full field of view and 10 angular resolution. We have also increased the angular resolution by employing multiple laser diodes and a single DMD chip while maintaining a high measurement rate of 3.34k points/s. In addition, we present a pathway to achieve 0.65° resolution with 60° field of view and 23k points/s measurement rate.

Spatial light modulators (SLMs) that operate in a phase modulation mode enable beam steering with higher diffraction efficiency compared to amplitude modulation mode, thus potentially be used for an efficient beam steering with no moving part. Currently, Twisted Nematic phase SLMs are widely adopted for phase modulation. However, their refresh rate is typically in the range below kilohertz. Recently, a new method for binary and spatial phase modulation using Digital Micromirror Device (DMD) was proposed by a research group in Germany. In the method, complemental self-images of DMD, corresponding to on- and off-pixels, are formed by two auxiliary optics while adding a pi phase shift between two images. The optics function as recycling of light in a coherent manner. The method enables over kilohertz refresh rate and higher diffraction efficiency in binary phase modulation mode to conventional amplitude binary modulation.

As alternatives to the binary phase modulation, we propose and experimentally evaluated high-speed beam steering by DMD based on light recycling. In our experiment, with binary phase modulation mode, system output efficiency reaches 8%. It can be doubled to 16% with light recycling method. Efficiency is still low compared to the reported value of 27% without light recycling. To further increase beam efficiency, system loss was analysed.

An imaging lidar system is presented which combines the high speed of a Digital Micromirror Device (DMD) and the higher range of a 1D collimated scanning output. The system employing 1D line object illumination along with DMD placed at focal plane enables flexible optimization of system metrics, such as field of view, angular resolution, maximum range distance and frame rate.

Imaging LIDARs capture location of objects in three-dimensional (3D) space, 2D field-of-view (FOV) or 2D in angular space, and 1D in distance, thus are used for variety of applications such as autonomous driving cars, robotics, and gesture recognitions. Imaging LIDAR, in its implementation of optics, has several options. One of the most commonly used optical architectures is a mechanical scanning of angular space while employing distance mapping on point by point basis. The architecture is suitable for long distance range finding and wide field of view imaging, though scan speed is limited by mechanics. Also, completely non-mechanical scanning approach, a lens with 2-dimensional sensor array, is adopted however the measurement range is ingeneral limited. Alternatively, we propose a new architecture, an optical phased array that can be used in both transmit and receive modes. The photonic based phased array produces a single main beam that can be electrically steered similar to modern day advanced radars. By using a photonic based array architecture very small, tightly spaced elements can be formed. Since the array produces a grating lobe free radiation pattern gain is maximized. This enables longer range, faster scans, and unambiguous angular data when compared to other optical phased arrays.