微透镜阵列光学相控阵扫描技术研究进展

光学相控阵光束扫描技术在激光雷达、空间光通信和光开关等领域拥有巨大的应用潜力。微透镜阵列光学相控阵可以通过微透镜阵列间μm量级的相对位移同时对多个出射光束的二维倾斜相位进行调制,从而实现大角度二维光束扫描,具有出射口径大、结构简单、体积小、微惯性、多功能等优点。首先介绍了微透镜阵列光学相控阵的扫描原理,之后对微透镜阵列光学相控阵国内外的发展现状、应用和现阶段存在的问题进行了阐述,最后对微透镜阵列光学相控阵的发展趋势进行了展望。

     

伸缩式全金属反射阵列扫描天线

提出了一种伸缩式全金属反射单元,在此基础上设计了一个可用于高功率微波领域的全金属反射阵列波束扫描天线。通过反射单元的上下独立滑动,阵列中每个阵元所接收电磁波的传输路径可改变,从而实现了相控波束扫描。由电磁仿真可知,设计的反射单元能够在10～13 GHz的频带范围内实现0～360°的线性相位调节,且可在15°～40°偏馈条件下相位调节时保持高功率容量。由该型单元组成的中心工作频率为10 GHz的伸缩式全金属反射阵列扫描天线具备90°锥角范围内的二维波束扫描能力,功率容量可达5 GW/m2。同时,在波束扫描过程中,天线增益变化小于3 dB,副瓣电平低于?13 dB,最大口径效率为54.59%。     

微透镜阵列误差对半导体激光匀化性能的影响

为了减小微透镜阵列误差对匀化光斑的影响,深入研究微透镜阵列光束匀化系统中微透镜阵列相对位置误差对光束匀化性能的影响,设计了一种微透镜阵列光束匀化系统。依据相对位置误差类型的不同,将双列微透镜阵列间六个自由度变化导致的误差分为距离误差、偏移误差以及转动误差进行分析,并对每种误差对光束匀化性能的影响进行了研究。采用6板条半导体激光器堆栈对上述匀化系统进行实验验证,实现了均匀性为90.75%的光斑,并对系统影响光斑性能的原因进行了分析。     

微透镜阵列误差对半导体激光匀化性能的影响

为了减小微透镜阵列误差对匀化光斑的影响,深入研究微透镜阵列光束匀化系统中微透镜阵列相对位置误差对光束匀化性能的影响,设计了一种微透镜阵列光束匀化系统。依据相对位置误差类型的不同,将双列微透镜阵列间六个自由度变化导致的误差分为距离误差、偏移误差以及转动误差进行分析,并对每种误差对光束匀化性能的影响进行了研究。采用6板条条半导体激光器堆栈对上述匀化系统进行实验验证,实现了均匀性为90.75%的光斑,并对系统影响光斑性能的原因进行了分析。     

Second-harmonic-generation microscope with a microlens array scanner

We propose a multifocus scanning technique in second-harmonic-generation (SHG) microscopy in which the SHG detection efficiency and the image acquisition rate are improved by several tens of times compared with typical single-focus scanning techniques. Because of a microlens array scanner, the laser beam of a mode-locked Ti:sapphire laser is split into ~100 beamlets, and the same number of foci are formed in the specimen. Parallel scanning of the foci enables us to observe real-time images of the specimen. The imaging properties and the usefulness of the microscope are demonstrated by SHG images of living HeLa cells and rat cardiac myocytes.     

Addressable microlens array for parallel laser microfabrication

Parallel processing in femtosecond-laser-based microfabrication is demonstrated using a microlens array in conjunction with a liquid-crystal spatial light modulator (SLM). A portion of the SLM is mapped onto each individual lenslet in the array and can be used to effectively switch foci on and off for fabrication. In addition, the technique allows for homogenizing the intensity of the array of foci and translating spots relative to their natural focus. The technique demonstrates the potential for high efficiency processing of aperiodic structures.     

飞秒平顶光束经微透镜阵列在熔融石英中的成丝及其超连续辐射

实验研究了平顶激光光束经微透镜阵列在熔融石英中成丝的演化以及超连续辐射的产生,并进一步与高斯光束的成丝和超连续辐射进行了对比研究.分别对这两种光束的多丝传输进行了横向和纵向成像.结果表明,使用平顶光束可以获得更为均匀的多丝分布,成丝的起点也更为一致;尤其重要的是,相对于高斯光束,平顶光束可以使用更高的入射激光脉冲能量而不会造成介质的损伤,从而可以获得更高脉冲能量和更高转换效率的超连续辐射.     

Direct space-to-time pulse shaper with reflective arrayed waveguide gratings and phase masks

We demonstrate for what we believe to be the first time the generation of sequences of ultrafast optical pulses by phase modulation in a direct space-to-time pulse shaper. The pulse shaper is based on the combination of a reflective arrayed waveguide grating multiplexer and an external reflector. The spatial modulation of the phase was obtained by fabricating corrugated patterns on the external reflector. We demonstrate that pulse sequences with different repetition rates can be obtained by changing the period in the patterned mask.     

光学微透镜阵列模压成形研究进展与展望

光学微透镜阵列在光学系统中的应用广泛,需求量大,而玻璃模压成形技术是最高效的微透镜阵列量产加工方法,具有精度高,一致性好,生产成本低等特点,有重要的应用研究价值。本文介绍了光学微透镜阵列的设计原理,模具制造技术,模压成形技术及相应检测技术;重点介绍了微透镜阵列模压成形试验与有限元仿真研究的最新进展;最后对微透镜模压成形发展前景进行了展望,包括微透镜阵列模压材料,模具表面镀层技术及超声复合加工技术在微透镜阵列模压成形中的应用等。     

Silver-halide fiber tip as a beam homogenizer for infrared hollow waveguides

A beam-homogenizing device consisting of a short tip of silver-halide infrared fiber eliminates the low-order multimode effect generated by bending of hollow guides. A series of experiments with a CO(2) laser shows that the solid fiber functions as a homogenizer with a small insertion loss of 0.2dB.     

Microlens array diffuser for a light-emitting diode backlight system

Microlens array (MLA) diffusers for light-emitting diode (LED) backlight systems have been developed. A high fill-factor photoresist mold for the MLA was fabricated using three-dimensional diffuser lithography, and the patterns were transferred to a nickel master mold for UV-curable polymer replication. The fabricated microlens had various paraboloidal profiles, and its aspect ratio was controlled from 1.0 to 2.1. The MLA diffuser showed a batwing radiation pattern with a radiation angle of 150 degrees. The fabricated MLA diffuser may greatly enhance the color-mixing characteristics of LED backlight systems and help reduce the number of LEDs required.     

Polarization Sagnac interferometer with a reflective grating beam splitter

All-reflective interferometric gravitational-wave detector configurations with a diffraction grating as a power beam splitter have been proposed to reduce thermal lensing. We demonstrate the use of a diffraction grating as a polarization beam splitter in a zero-area polarization Sagnac interferometer.     

Simple reflow technique for fabrication of a microlens array in solgel glass

A simple reflow method for fabrication of refractive microlens arrays in inorganic-organic SiO2-ZrO2 solgel glass is presented. To our knowledge, this is the first report that presents a simple reflow technique for transforming a negatively induced hybrid solgel material into desirable spherical microlenses. It is shown that the microlenses have excellent smooth surfaces and uniform dimensions. The reflow technique is considerably cheaper than use of a high-energy beam-sensitive gray-scale mask and is suitable for mass production.     

Multiple-spot optical tweezers created with microlens arrays fabricated by proton beam writing

We report two different applications for using arrays of microlenses on glass substrate to facilitate multiple-spot optical trapping of colloidal microbeads. The array of microlenses was made of SU8 or PMMA resist and created by a combination of Proton-Beam writing followed by thermal reflow processes. Firstly, similar to previous reports [8, 9, 10 ], the lenses were utilized as an optical element in generating multiple laser spot arrays that were subsequently focused down to impose a microbead array. In addition, we demonstrated the feasibility of a novel approach of integrating the microlens array into a sample chamber to provide localized optical trapping. PACS 07.60.Pb; 41.75.Ak; 42.15.Eq; 42.65.Jx; 42.79.Bh     

Nonlinear beam shaper for femtosecond laser pulses, from Gaussian to flat-top profile

We present a straightforward method to transform a spatially Gaussian femtosecond laser beam into a flat-top shaped beam. The proposed technique takes advantage of a nonlinear phase induced in positive Kerr medium followed by a simple optical system. The variation of the refractive index with the laser intensity creates a phase plate which induces changes in the beam profile after propagation; flat-top and doughnut profiles are observed. The shaping conditions are computed numerically and confirmed experimentally. The method does not introduce energy losses. The device is very simple, self-regulated, flexible and does not need a manufactured phase plate or precise alignment. This method can be useful for light-matter interaction and laser machining.     

Theoretical analysis for integral imaging performance based on microscanning of a microlens array

An integral imaging method based on microscanning of a microlens array is proposed. The effects of microscanning on the depth resolution and the product of depth of focus and lateral resolution squared (PDLRS) of an integral imaging system are quantitatively analyzed. Calculation results show that microscanning can improve not only the depth resolution, but the PDLRS can be increased. The amount of improvement of different microscanning modes to the performance of integral imaging is closely related to the fill factor of the detector and the diffraction factor of the microlens.     

Refractive microlens array for wave-front analysis in the medium to hard x-ray range

We report an alternative approach to x-ray wave-front analysis that uses a refractive microlens array as a Shack-Hartmann sensor. The sensor was manufactured by self-assembly and electroplating techniques and is suitable for high-resolution wave-front analysis of medium to hard x rays. We demonstrate its effectiveness at an x-ray energy of 3 keV for analysis of x-ray wave-front perturbations caused by microscopic objects. The sensor has potential advantages over other methods for x-ray phase imaging and will also be useful for the characterization of x-ray beams and optics.     

Rapid laser fabrication of microlens array using colorless liquid photopolymer for AMOLED devices

Microlens array (MLA) is microfabricated using Ultra Violet (UV) laser for display device applications. A colorless liquid photopolymer, Norland Optical Adhesive (NOA) 60, is spin-coated and pre-cured via UV light for completing the laser process. The laser energy controlled by a galvano scanner is radiated on the surface of the NOA 60. A rapid thermal volume expansion inside the material creates microlens array when the Gaussian laser energy is absorbed. The fabrication process conditions for various shapes and densities of MLA using a non-contact surface profiler are investigated. Furthermore, we analyze the optical and display characteristics for the Organic Light Emitting Diode (OLED) devices. Optimized condition furnishes the OLED with the enhancement of light emission by 15%. We show that UV laser technique, which is installed with NOA 60 MLA layer, is eligible for improving the performance of the next generation display devices.     

Diffractive beam splitting microlens for fiber coupling fabricated by UV imprinting process

A polymeric diffractive microlens (DML) for coupling the incident light to two individually plastic optical fibers was designed and fabricated by imprinting process. The DML pattern of this dual-focal-point DML was designed with an optimal rotation-angle and realized by template fabrication and UV imprinting. Tetraethoxysilane oxide etching was developed and employed in the template fabrication process to minimize the related processing errors such as misalignment and dimension accuracy. A modified imprinting process is proposed in the experiment; DML with flexible polyethylene terphthalate substrate was imprinted by roller. After curing and demolding, the DML structure was successfully duplicated on polyethylene terphthalate substrate. The prototype was inspected and to confirm the optical properties and the results showed that the diffraction efficiency is 51% (designed value is 57%) and the uniformity error is only 1.5%.