Hybrid multinary modulation using a phase modulating spatial light modulator and a low-pass spatial filter

We propose a method for performing binary intensity and continuous phase modulation of beams with a spatial light modulator (SLM) and a low-pass spatial filtering 4-f system. With our method it is possible to avoid the use of phase masks in holographic data storage systems or to enhance the phase encoding of the SLM by making it capable of binary amplitude modulation. The data storage capabilities and the limitations of the method are studied.     

Characterization of a high efficiency, ultrashort pulse shaper incorporating a reflective 4096-element spatial light modulator

We demonstrate pulse shaping via arbitrary phase modulation with a reflective, 1 × 4096 element, liquid crystal spatial light modulator (SLM). The unique construction of this device provides a very high efficiency when the device is used for phase modulation only in a prism based pulse shaper, namely 85%. We also present a single shot characterization of the SLM in the spatial domain and a single shot characterization of the pulse shaper in the spectral domain. These characterization methods provide a detailed picture of how the SLM modifies the spectral phase of an ultrashort pulse.     

Correction to: Generation of amplitude- and phase-modulated signal beam with a phase-only spatial light modulator and its detection by the transport of intensity equation method for holographic data storage

This study evaluates a novel holographic data storage (HDS) that uses a phase-only spatial light modulator (SLM) for the multilevel complex amplitude modulation of a signal beam and the transport of intensity equation (TIE) method to detect the signal beam without interferometry, to increase the capacity of the HDS, simplifying its optical system, and improving the stability of the signal beam modulation and detection. Both the amplitude and phase of the signal beam were modulated by a computer-generated hologram displayed in a phase-only SLM, a 4-f optical system, and a pinhole placed in the Fourier plane. The complex amplitude-modulated signal beam generated by this scheme does not always perfectly match the target complex amplitude, and deviations from the amplitude and phase of the target complex amplitude may exist. It is unclear whether the TIE method, which is sensitive to the state of the beam intensity and the phase distributions to be detected (such as zero-intensity points and phase discontinuities), can accurately detect a signal beam whose complex amplitude is modulated by the modulation scheme with a phase-only SLM. Here, we demonstrate via numerical simulations and experiments that several methods of complex amplitude generation using a phase-only SLM can achieve multilevel modulation of the amplitude and phase of a signal beam and are suitable for detection by the TIE method in HDS.

     

Dynamic complex wave-front modulation with an analog spatial light modulator

A method of producing an arbitrary complex field modulation by use of two pixels of an analog ferroelectric spatial light modulator (SLM) is demonstrated. The method uses the gray-scale modulation capabilities of a SLM to spatially encode the complex data on two pixels. A spatial filter is used to remove the carrier signal. This technique gives fast gray-level amplitude and phase modulation.     

用双折射晶体相位延迟法选纵横的理论分析和实验研究

提出了一种新的固体激光器纵模选择技术，分析了该方法的损耗调制原理，用半经典理论建立二模光场竞争的运动方程，并对这种方法的纵模选择能力进行了计算。实验中用KTP和方解石两种双折射晶体都实现了固体激光器的单纵模振荡，用KTP晶体获得了CW 44 mW的单纵模激光输出，稳定性优于±3％。实验表明在半导体激光泵浦的中小功率固体激光器中用该方法选纵模具有稳定、可靠的优点。     

Diffractive characteristics of the liquid crystal spatial light modulator

The liquid crystal spatial light modulator (LC SLM) is very suitable for wavefront correction and optical testing and can produce a wavefront with large phase change and high accuracy. The LC SLM is composed of thousands of pixels and the pixel size and shape have effects on the diffractive characteristics of the LC SLM. This paper investigates the pixel effect on the phase of the wavefront with the scalar diffractive theory. The results show that the maximum optical path difference modulation is 41\,$\mu$m to produce the paraboloid wavefront with the peak to valley accuracy better than $\la$/10. Effects of the mismatch between the pixel and the period, and black matrix on the diffraction efficiency of the LC SLM are also analysed with the Fresnel phase lens model. The ability of the LC SLM is discussed for optical testing and wavefront correction based on the calculated results. It shows that the LC SLM can be used as a wavefront corrector and a compensator.     

Full-range, complex spatial light modulator for real-time holography

We demonstrate a full-range complex and transmissive spatial light modulator (SLM) for simultaneous and independent amplitude and phase modulation of an input wave field. Arbitrary scalar complex optical fields are generated by stacking a pixelated liquid crystal display operating in phase-only (2π) modulation with passive polarization-sensitive components. The principle is based on optical combining the light fields of two neighboring phase-only modulating pixels, which were made orthogonally polarized by a structured half-wave plate, then passing through a birefringent plate to laterally shift one of the beams collinear to the other, and finally bringing to interference by a linear polarizer. Complex modulation by the proposed SLM is experimentally verified in monochrome green operation.     

Multilevel phase and amplitude modulation method for holographic memories with programmable phase modulator

The utilization of spatial quadrature amplitude modulation (SQAM) signals with amplitude and phase modulation is a simple method used to improve storage capacity in a holographic data storage system. We propose a multilevel phase and amplitude modulation method for holographic memories with a programmable phase modulator (PPM). In this method, holographic page data is recorded by a two-step exposure process for different phase-modulated data. There is no need to adjust the positions of spatial light modulators (SLM) with high accuracy because we use only one spatial modulator. We estimate the quality of 16 SQAM signals produced by our technique.     

Common-path phase-shifting lensless holographic microscopy

We present an approach capable of high-NA imaging in a lensless digital in-line holographic microscopy layout even outside the Gabor's regime. The method is based on spatial multiplexing at the sample plane, allowing a common-path interferometric architecture, where two interferometric beams are generated by a spatial light modulator (SLM) prior to illuminating the sample. The SLM allows phase-shifting interferometry by phase modulation of the SLM diffracted beam. After proper digital processing, the complex amplitude distribution of the diffracted object wavefront is recovered and numerically propagated to image the sample. Experimental results are reported that validate the proposed method.     

高精度纯相位液晶空间光调制器的研究

研制了平行排列液晶空间光调制器（LC SLM）。论述了平行排列液晶相位调制的理论,进行了计算模拟。对液晶空间光调制器相位调制特性和振幅调制特性进行了测量,实验结果表明,在整个灰度级范围内是纯相位调制的空间光调制器,并且调制的范围可达到0．6λ。在ZYGO菲佐干涉仪上进行了精度特性的研究,得到了非常好的结果,在1cm^2的面积上,进行了畸变波前的调制,其精度峰谷值可达0．098λ,均方根值可达0．017λ。在此精度的基础上产生了π相位差的栅结构,证明了这种液晶空间光调制器可以很好的进行相位调制。     

Microscope system with on axis programmable Fourier transform filtering

We propose an on-axis microscope optical system to implement programmable optical Fourier transform image processing operations, taking advantage of phase and polarization modulation of a liquid crystal on silicon (LCOS) display. We use a Hamamatsu spatial light modulator (SLM), free of flickering, which therefore can be tuned to fully eliminate the zero order component of the encoded diffractive filter. This allows the realization of filtering operation on axis (as opposed to other systems in the literature that require operating off axis), therefore making use of the full space bandwidth provided by the SLM. The system is first demonstrated by implementing different optical processing operations based on phase-only blazed gratings such as phase contrast, band-pass filtering, or additive and substractive imaging. Then, a simple Differential interference contrast (DIC) imaging is obtained changing to a polarization modulation scheme, achieved simply by selecting a different incident state of polarization on the incident beam.     

Oblique-Incidence Characteristics of a Parallel-Aligned Nematic-Liquid-Crystal Spatial Light Modulator

We have developed optically-addressed and electrically-addressed liquid crystal spatial phase-only light modulators having no pixelized structures. We obtained a large depth of phase-only modulation and high diffraction efficiency based on the electro-optical characteristics of a parallel-aligned nematic liquid crystal. These spatial light modulators (SLM) are of the reflection type, so there would be a loss of power in the readout light from the half mirror, which was set up so as to separate the incident and reflected lights. To optimize the characteristics of a reflection type spatial phase-only light modulator, we have proposed an oblique incident optical readout setup. We have examined the effect of conditions such as the polarization direction and the incidence angle of the readout light, and the orientation of liquid crystal molecules in the SLM. High diffraction efficiency close to the theoretical maximum value was obtained by adjusting the above conditions. The simulation analysis can well explain the experimental results of phase modulation.     

Binary Phase SLMs Based on the LC Matrix of Video Projector

Binary phase modulation is demonstrated with the aid of commercially available LC matrix. Elements of plane diffraction optics (cylindrical and spherical lenses) are fabricated and experimentally studied. Limitations related to a finite size of a pixel of a binary diffraction SLM are considered.     

Smart pixels in a focal-plane image compression system

Image compressors improve the handling of image data in image-processing systems. In our proposed image-compression system, we employ a smart complementary metal oxide semiconductor (CMOS) sensor and an integrated spatial light modulator (SLM) and then the optoelectronic architecture performs a large part of image-compression processes. Each pixel of the integrated SLM consists of multiple modulation pads; the integrated SLM then performs decoding and optical D/A conversion. A paired configuration of the smart CMOS sensor and the integrated SLM transforms optical analog signals into electronic digital signals. A theoretical analysis showed that the error ratio of the proposed systems was 3%.     

Universal generation of higher-order multiringed Laguerre-Gaussian beams by using a spatial light modulator

Laguerre-Gaussian (LG) beams of various higher-order radial modes are generated by using a reflective phase-only liquid crystal on silicon (LCOS) spatial light modulator (SLM). Because of the LCOS SLM's phase-modulation characteristic of a wide spatial bandwidth, a phase modulation scheme effectively generates higher-order LG beams of up to the fifth-order radial mode. We also perform correlation analyses between the observed and the theoretical two-dimensional mode profiles to universally obtain correlation coefficients of more than 0.946, which suggest mode generations of high quality.     

体全息存储系统图像质量因素MTF数值模拟分析

影响体全息存储系统中读出图像误码率的因素很多,其中输入与输出器件SLM、CCD的性能以及它们信号匹配关系起着关键的作用。针对这一实际问题,利用CCD成像系统的调制传递函数理论和数值模拟方法,通过对4f系统中周期性SLM像素分布的CCD输出响应分析,研究了SLM和CCD的填充因子、对比度、位相匹配关系对读出图像误码率的影响,并给出计算机仿真结果。     

基于光学全息的任意矢量光的生成方法

基于光学全息的角度复用特性, 根据空间光调制器对光场的相位和振幅调制原理, 通过加载产生任意矢量光所需要的相位分布, 设计了一种生成任意矢量光的方法. 该方法首先利用光学全息技术记录空间光调制器加载的相位, 从而制作一个全息光栅; 再现过程中, 两束具有相同入射角度的参考光照射全息光栅, 使得两束再现光相干叠加, 进而获得可调控的任意矢量光. 该方法能够避免复杂偏振态的出现, 并且具有生成光路简单、方便操作、生成矢量光的偏振纯度高等优势. 通过计算机模拟生成了任意矢量光, 获得了很好的效果.     

Phase modulated gray-scale data pages for digital holographic data storage

We propose a method for gray level holographic digital data storage by using three-gray levels in the phase mode. Gray level data pages are displayed on a SLM operating in the phase mode to obtain a homogenized Fourier spectrum by suppressing the extremely high intensity DC component in the Fourier spectrum of conventional amplitude based binary/gray level data pages. Holographic interferometry has been used to recover the gray level amplitude data page from phase data page. Numerical simulation results are presented for three-gray level data pages. Fourier plane homogeneity, bit-error-rate, storage density, phase modulation error of the SLM, and misalignment tolerances are investigated through computer modeling. A comparison of the present method with the amplitude-modulated gray level case with and without using a phase mask in conjunction with the data page is carried out. An experimental demonstration of the proposed three-gray level phase data page method is also presented.     

Holographic Femtosecond Laser Processing with Multiplexed Phase Fresnel Lenses Displayed on a Liquid Crystal Spatial Light Modulator

Parallel femtosecond laser processing with a computer-generated hologram displayed on a spatial light modulator (SLM) is demonstrated. Use of the SLM enables performance of an arbitrary and variable patterning in laser processing. The hologram uses multiplexed phase Fresnel lenses (MPFLs) with features of independent tunability, three-dimensional (3D) parallelism of the diffraction peaks, optimization of the hologram with low computational costs, and low contribution of zero-order light to the processing. To make uniform the reconstructed diffraction peaks, an MPFL is optimized by changing the center phase and size of each phase Fresnel lens while taking account of the intensity distribution of the irradiated laser pulse and the spatial frequency response of an SLM. Using the holographic technique, two-dimensional parallel processing with a single-pulse irradiation of glass is demonstrated and the processing performance is analyzed.     

Nonlinear response studies and corrections for a liquid crystal spatial light modulator

The nonlinear response of light transmission characteristics of a liquid crystal (LC) spatial light modulator (SLM) is studied. The results show that the device exhibits a wide range of variations with different control parameters and input settings. Experiments were performed to obtain intensity modulation that is best described by either power-law or sigmoidal functions. Based on the inverse transformation, an appropriate pre-processing scheme for electrically addressed input gray-scale images, particularly important in several optical processing and imaging applications, is suggested. Further, the necessity to compensate the SLM image nonlinearities in a volume holographic data storage and retrieval system is demonstrated.