Experimental Research on Focusing Property of Radially Polarized Beam Based on Solid Immersion Lens

Realization of a near-field optical virtual probe based on an evanescent Bessel beam is strongly dependent on a radially polarized beam; this makes it essential to study the focusing property of the beam. In this paper, two experimental setups based on a fiber device and a liquid crystal device, respectively, are built to generate a radially polarized beam. This beam and an annular radially polarized beam are focused by means of a high numerical aperture objective and a solid immersion lens (SIL). Near-field distribution of the focus spot, the evanescent Bessel field, is experimentally measured with a scanning near-field optical microscope (SNOM). The full width at half maximum (FWHM) of the central peak of the evanescent Bessel field is about 200 nm in the close vicinity of the bottom surface of SIL. This has potential for use as a near-field optical virtual probe.     

Laser micro-machining using near-field optics

Solid immersion lenses (SIL) facilitate high numerical aperture (NA) and consequent sub-wavelength diffraction limited focusing in near-field optics based systems. Such systems are in commercial and research use for various applications including near-field scanning optical microscopy, ultra-high-density magneto-optic data storage and near-field nanolithography. Here, we present a novel manufacturing method using SIL-based near-field optics for laser-induced patterning on silicon wafers. The near-field effect of SILs was investigated by using hemispherical lenses made of three different materials (BK7, Sapphire, LaSFN9) to superfocus an incident Q-switched, 532 nm Nd:YAG laser beam transmitted through a focusing objective. This optical arrangement achieved a laser-processed feature resolution near the diffraction limit in air. Results of experiments that were conducted at various processing conditions to investigate the effects of varying incident laser power (with peak pulse power less than 1 W), pulse width, number of pulses and size of SIL on processed feature size and resolution are presented. Experimental results are compared with numerical simulations using the simplified model.     

High-intensity bowtie-shaped nano-aperture vertical-cavity surface-emitting laser for near-field optics

We report a high-intensity nano-aperture vertical-cavity surface-emitting laser (VCSEL) utilizing a bowtie-shaped aperture. A maximum power of 188 microW is achieved from a 180 nm bowtie aperture at a wavelength of 970 nm. The near-field full width at half-maximum intensity spot size 20 nm away from the bowtie aperture is 64 nm x 66 nm from simulation, and the peak near-field intensity is estimated to be as high as 47 mW/microm(2). This intensity is high enough to realize near-field optical recording, and the small spot size corresponds to storage densities up to 150 Gbits/in(2). The bowtie-aperture VCSEL also enables other applications, such as compact high-intensity probes for ultrahigh-resolution near-field imaging and single molecule fluorescence and spectroscopy.     

Dispersion effect in optical microscopy systems with a supersphere solid immersion lens

This paper studies the dispersion effect of the supersphere solid immersion lens (SIL) on a near field optical microscopy system by using the vector diffraction theory. Results show that when a real non-monochromatic beam illuminates a supersphere SIL microscopy, the dispersion effect of the SIL has an important influence on the image quality. As the wavelength bandwidth of the non-monochromatic beam increases, the size of the focused spot increases and its intensity decreases in near-field microscopy systems with a supersphere SIL.     

Near-field double-spot photolithography with subwavelength spacing

We theoretically report a method of the near-field double-spot subwavelength-photolithography by attaching an optical anisotropic metamaterial (OAM) and polymer composite film to a solid immersion lens (SIL). The OAM made up of metallic nanowires embedded in a dielectric matrix can realize all-angle negative refraction for TM waves in the visible regime. When the SIL near-field photolithography system with a nanoscale OAM-polymer composite film is illuminated by a linearly-polarized beam, the longitudinal component of electric field in the focal region of the objective is largely enhanced by surface plasmons and the transverse component is suppressed. Consequently, a spot in the conventional near-field photolithography system with a bare SIL is split into two spots with subwavelength spacing. If the present focusing system with an OAM-polymer film is used to near-field photolithography, a subwavelength-spacing (wavelength/5) and deep photoetching pattern can be achieved and, compared with the conventional single-spot photolithography, the photoetching speed can be doubled.     

Experimental research on high density data storage using solid immersion lens

We have set up a solid immersion lens (SIL) near-field static recording system for demonstrating preliminarily the feasibility of SIL technology in the higher density storage. The experimental result with recording mark size of 240 nm is obtained corresponding to a potential of density of tens of gigabits per square inch. Some factors in the SIL near-field recording are discussed.     

Laser-tweezer-controlled solid immersion microscopy in microfluidic systems

We describe the creation and implementation of a near-field scanning solid immersion microscope that is specifically tailored for use in microfluidic systems. The microscope comprises a newly fabricated Weierstrass solid immersion lens (SIL), which is detached from its substrate and is free floating in the fluid, and a laser optical tweezer, which serves both as a trapping beam for alignment and positioning of the SIL and as a near-field scanning beam that images the sample through the SIL. A discussion of the SIL's fabrication method is presented along with experimental results that demonstrate the effectiveness of our microscope design.     

Single-frequency, single-polarization ytterbium-doped fiber laser by self-injection locking

We demonstrated a stable single-frequency, single-polarization operation of ytterbium-doped fiber laser. As a novel practical method to realize single-polarization operation of fiber distributed Bragg reflector (DBR)laser, we proposed self-injection locking (SIL) with an active fiber ring feedback cavity. The laser has high output power exceeding 15 mW, wavelength of 1053.20 nm, and side-mode suppression ratio greater than 60 dB. The SIL fiber laser shows the improvements in output power and side-mode suppression compared with the fiber DBR laser. No mode-hopping is observed within 2 hours.     

Enhancement of the far-field output power and the properties of the very-small-aperture lasers

We report on a VSAL structure fabricated by a 650 nm edge emitting laser diode with an Au-coated facet and an aperture size of 250 × 500 nm. The far field output power can maintain at 1 mW and the power density is 7.5 mW/μm². Some properties of the VSAL including the threshold current change, the red-shift of the spectral position, and the strong relative-intensity-noise are presented. The physical mechanisms responsible for these phenomena are also discussed, which may contribute to the understanding and application of the potential device for near-field optics.     

A global design of an erbium-doped fiber and an erbium-doped fiber amplifier

A global design of an erbium-doped fiber and an open-loop erbium-doped fiber amplifier (EDFA) in a steady-state operation is discussed by applying genetic algorithms. Taking a signal gain and a bandwidth as objective functions, 7 parameters of the EDFA (erbium concentration, core radius, erbium-doped radius, refractive index difference, fiber length, pumping wavelength and signal power) are optimized by solving optical propagation equations, assuming a homogenous two-level active medium and a single-mode propagation. There is evidence to show that the 1480 nm pump utilized in usual EDFAs is not an optimal choice, which should be chosen around 1460 nm. The optimal core radius ranges 0.465–0.548 μm on pumping power 50–200 mW. Under different design objects and with different pumping powers, however, there are different optimal Er-doped concentrations, reflective index differences and fiber lengths. As a single fiber EDFA, 35 dB signal gain or 35 nm bandwidth is obtained with the 7 optimal parameters, 100 mW pumping power and 0.001 mW input signal power.     

(Tm,Ho):YLF微片激光器的实验研究

报道了一台连续792 nm Ti:Al2O3激光器纵向抽运的(Tm,Ho):YLF微片激光器.在室温条件下,当抽运功率为680 mW时,激光器在2.06 μm波长的输出功率达到90 mW.激光器阈值为380 mW,光光转换效率为13%,斜率效率为26%.     

固体浸没透镜飞行高度的气浮控制

采用固体浸没透镜的光存储方法是提高光存储密度的比较实用的近场光存储方法,而严格控制SIL下底面与光存储介质之间的亚波长级距离是此光存储系统正常工作的前提.本文采用电容法测量SIL的飞行高度,采用弹性悬臂将SIL加载在转盘表面上,转盘以不同速度转动时SIL将悬浮在不同的高度.计算机首先采集到SIL的飞行高度信息,再与设定的飞行高度作比较,根据比较结果调整转盘转速,从而达到调整SIL飞行高度的目的.采用此方法,可以动态地将SIL的下底面控制在距高速转动的转盘表面上150～600 nm范围内的一定高度上.     

Multilevel phase Fresnel zone plate lens as a near-field optical element

We propose and develop a new solid immersion lens (SIL), which is called the multilevel phase Fresnel zone plate lens (FZPL) for the near-field (evanescent wave) microscopy. The simple analysis is presented by using the scalar diffraction theory. The outstanding advantages of this FZPL are that it both focuses incident waves and produces evanescent waves. A FZPL can effectively concentrate the high angle rays important for the high resolution in comparison with the conventional SILs. The optical system equipped with the FZPL is not only simple in the assembly but also effective in making an optical head unit.     

用于Rb原子冷却系统的半导体激光放大(TPA)装置

报道了我们最近研制的780 13m半导体激光放大装置.激光放大管采用Eagleyard公司生产的(EYP-TPA-0780-01000)半导体锥形放大器,当输入的种子源激光功率为25 mW时,放大器输出的激光功率达600mW左右,该光束经过透镜整形,声光调制器频移,然后耦合到单模保偏光纤后,输出功率达110 mW.该激光放大装置可很好的用于高密度冷原子的俘获.     

All-optical controllable trapping and transport of subwavelength particles on a tapered photonic crystal waveguide

We propose that a tapered photonic crystal waveguide design can unify optical trapping and transport functionalities to advance the controllability of optical manipulation. Subwavelength particles can be trapped by a resonance-enhanced field and transported to a specified position along the waveguide on demand by varying the input wavelength. A simulated transport ability as high as 148 (transport distance/wavelength variation) is obtained by the waveguide with 0.1° tilted angle. Stable trapping of a 50 nm polystyrene particle can be achieved with input power of 7 mW. We anticipate that this design would be beneficial for future life science research and optomechanical applications.     

高功率,红光至中红外可调谐腔内和频光学参量振荡器

本文利用高重复频率,高平均功率大模场面积飞秒光纤激光器作为同步抽运源,抽运以多周期极化掺氧化镁铌酸锂为非线性晶体的单共振光学参量振荡器,获得了高功率可调谐红光至中红外光,信号光调谐范围为1450—2200 nm,闲频光调谐范围为2250—4000 nm,在2 W的抽运功率下,信号光输出波长为1502 nm时获得最大输出功率374 mW,转换效率为18.7%,脉冲宽度为144 fs,此时中红外输出中心波长为3.4μm,平均功率为166 mW.再利用BBO晶体对信号光进行腔内和频,获得和频光输出波长调谐范围为610—668 nm,在4.1 W抽运的情况下,最高平均功率为615 nm处的694 mW,转换效率达16.9%.     

低功耗聚合物Mach-Zehnder热光开关

采用传统的半导体工艺制作了聚合物Mach-Zehnder型热光开关.利用扫描电镜观测波导形貌,通过红外摄像机观测波导的近场输出光斑,在通信波段1 550 nm波长下测试了器件的输出光谱.在电极上施加直流信号,测得热光开关的消光比为－15 dB,驱动功率为16 mW.引入直流偏置网络,获得了器件的开关特性曲线,经测量开关上升时间为1.2 ms,下降时间为0.8 ms.     

Integrated optical Ti:Er:LiNbO3 distributed Bragg reflector laser with a fixed photorefractive grating

For the first time to the authors' knowledge, an integrated optical distributed Bragg reflector laser with a fixed photorefractive grating in LiNbO(3) is demonstrated. Sample preparation, grating fabrication, and laser characteristics are reported. The device is pumped by a fiber pigtailed laser diode (lambda(p) approximately 1480 nm) through the Bragg grating in a double-pass configuration, yielding an emission in the backward direction at lambda=1531.7nm . The laser threshold is 40 mW; as much as 5 mW of output power has been obtained at 110 mW of launched pump power in cw operation.     

Three-zone phase-only filter increasing the focal depth of optical storage systems with a solid immersion lens

The field distribution of a Weierstrass solid immersion lens (SIL) is presented, which shows that its focal depth is only in nanoscale. A novel filter design based on a three-zone binary phase pupil function is introduced for increasing the focal depth of a near-field Weierstrass SIL system and a procedure for designing a rotationally symmetric binary phase filter is presented. Numerical results show that an appropriate three-zone phase-only filter not only can evidently increase the focal depth of the SIL system, but also can effectively lower the spreading of the spot size with distance and suppress the side-lobe intensity. PACS 42.79.Ci; 42.40.Lx; 42.79.Vb; 42.25.-p     

Realization of a subwavelength focused spot without a longitudinal field component in a solid immersion lens-based system

In a solid immersion lens (SIL)-based system, we predict theoretically that, by using the illumination of an azimuthally polarized beam with helical phase (APH), the subwavelength focusing can be simultaneously realized both in SIL and the third medium in spite of the presence of an air gap between the SIL and the third medium, which is not easily achieved in the case of the illumination of linearly, circularly, and radially polarized beams. For the APH illumination, the field in the focal region of the multilayered medium has no longitudinal component, and the on-axis intensity of the focused spot is nonzero. The APH illumination extends the capacity of SIL in realizing a supersmall focused spot, which is useful in microscopy, near-field optics, recording optics, and lithographic optics.