基于整形飞秒激光脉冲的三维微纳制备

飞秒激光脉冲加工具有热效应小、加工精度突破衍射极限、三维内部加工能力等特性,在微纳制备领域独具优势。综述了利用飞秒激光脉冲整形技术结合飞秒激光三维直写进行透明介质中微纳制备的最新进展,这些技术有望在新型集成光学和微纳光学中发挥重要的作用。     

6H-SiC的飞秒激光超衍射加工

利用飞秒激光直写微纳加工平台, 对6H-SiC材料进行了突破衍射极限的微纳结构加工研究. 使用中心波长和脉宽分别为800 nm和130 fs的钛蓝宝石激光器和荧光倒置显微镜搭建了飞秒激光直写微纳加工平台, 研究了在不同的实验条件下对6H-SiC的光学加工情况, 采用扫描电子显微镜对加工结构进行表征. 通过分析不同的激光功率和不同的曝光时间等实验条件下加工的分辨率, 发现分辨率随着激光功率的减小而提高, 随扫描速度的增大而提高, 且能突破光学衍射极限. 最终获得125 nm的加工线宽, 并加工了加工线宽240 nm, 周期1.0 μm的线阵列. 研究结果为微机电系统(MEMS)的微器件设计开创了新的思路, 对发展MEMS器件具有重要意义. 关键词： 飞秒激光直写 超衍射加工 6H-SiC 微机电系统     

微球激光的最新研究进展

 利用回音壁模式微球腔的高Q谐振原理，可以获得微球激光。研究了微球腔的特点和微球激光产生的原理，介绍了单量子点、表面栅耦合和光纤耦合三种微球激光器，讨论了获得高Q值微球腔的方法，提出采用半导体纳米微球及通过旋转电弧或者旋涂方式制成的玻璃微球，给出了微球激光器的几种应用以及当前国内外最新进展。     

飞秒激光直写偏振转换器件和几何相位器件(特邀)

光学器件的微型化和集成化是当前研究的热点,其中利用微纳结构实现局域电磁改性的超构光学更是引人关注。本文从微纳结构的制备出发,总结了利用超衍射精密加工的飞秒激光直写技术,制备偏振转换器件和几何相位器件的工作。介绍了微纳结构改性的物理机制,飞秒激光直写光刻胶、飞秒激光烧蚀金属薄膜、飞秒激光诱导纳米光栅等手段在偏振转换器件和几何相位器件制备方面的进展,展望了飞秒激光微纳加工技术在超构光学器件制备方面的挑战。     

柱形微腔回音壁激光光谱模式的精确标定

由柱形微腔中回音壁模式满足的本征值方程,得到确定回音壁模式位置和间距的近似解析公式。以此近似解析公式,首次对直径在215～328 μm间的5个柱形微腔回音壁激光光谱做了模式标定。在用近似解析公式对柱形微腔激光光谱的数值作拟合的计算中,除了回音壁模的径向模式数(l)和角动量模式数(n)外无需其他拟合参数,解析公式的拟合值和实验激光光谱波长值间的偏差小于0.05 nm,拟合结果精确可靠。柱形微腔回音壁激光光谱模式的精确标定在模式的场分布计算以及频移型微腔生物传感器的研究应用中具有重要作用,文章介绍的方法亦可应用于柱形微腔直径和折射率的精密测量。     

飞秒激光直写光量子逻辑门

量子比特在同一时刻可处于所有可能状态上的叠加特性使得量子计算机具有天然的并行计算能力,在处理某些特定问题时具有超越经典计算机的明显优势.飞秒激光直写技术因其具有单步骤高效加工真三维光波导回路的能力,在制备通用型集成光量子计算机的基本单元—量子逻辑门中发挥着越来越重要的作用.本文综述了飞秒激光直写由定向耦合器构成的光量子比特逻辑门的进展.主要包括定向耦合器的功能、构成、直写和性能表征,集成波片、哈达玛门和泡利交换门等单量子比特逻辑门、受控非门和受控相位门等两量子比特逻辑门的直写加工,并对飞秒激光加工三量子比特逻辑门进行了展望.     

回音壁模式光学微腔器件的封装与集成

回音壁模式微腔器件在现代光学中扮演着十分重要的角色,在高灵敏度传感、低阈值激光器等领域具有广泛的应用前景.然而基于回音壁模式微腔的光学系统容易受到振动、温湿度变化等外界环境干扰,这些问题为其实用化带来巨大挑战.近年来回音壁模式微腔器件的实用化问题日益受到关注,大量相关研究被报道.本文简要介绍了关于回音壁模式光学微腔器件封装和集成的最新研究进展.     

基于回音壁微腔拉曼激光的纳米粒子探测

回音壁模式光学微腔由于其品质因子高、模式体积小等优点, 近年来在非标记性的纳米粒子探测方面得到了广泛的重视, 开展了大量的研究, 取得了重要的进展. 利用回音壁微腔的拉曼激光, 通过测量纳米粒子造成的模式劈裂的拍频, 可以实现不同环境下纳米粒子的实时探测. 与传统的稀土离子掺杂法不同, 这种方法采用腔的内禀增益, 不仅提高了应用回音壁模式微腔进行纳米粒子探测的极限, 而且避免了传统方法中稀土离子能级对泵浦光的限制, 拓展了应用范围. 这种方法还可以应用于其他材料的回音壁微腔, 如硅基微环腔等, 以及光子晶体结构、超材料等受损耗限制的系统中. 本文简单介绍了回音壁模式光学微腔进行纳米粒子探测的基本原理以及最新研究进展.     

光纤回音壁模式的三波段激光辐射研究

将石英光纤浸入低折射率的激光染料溶液中构成圆柱形微腔.采用沿光纤轴向光抽运的消逝波激励增益方式,获得了沿光纤轴向长距离的激光染料增益,受激辐射光在圆柱形微腔中回音壁模式的支持下形成激光振荡.在直径为288 μm的同一根光纤外分三段分别填入罗丹明6G、罗丹明610和罗丹明640激光染料乙二醇溶液,实现了波长分别在567～575 nm、605～614 nm和656～666 nm三个不同波段的回音壁模式激光振荡,用一根光纤同时获得了红、橙、黄三种不同颜色的激光辐射.对实验所获得的回音壁模式激光光谱做了模式标定,依据标定的模式数计算了各种模式以及抽运光在光纤截面的强度分布.计算结果表明,激光增益区域总是局限在圆柱形微腔回音壁模式的模场区域内,由此可以显著地提高抽运效率,增加抽运光沿光纤轴向的增益长度.     

基于光场调控的飞秒激光直写光波导研究进展(特邀)

飞秒激光直写是一种无掩模、高效、灵活的三维加工技术,可以对材料实现微纳米级加工,已经成为应用最广泛的材料精密加工技术之一.基于光波导的微纳光子器件(如分束器、频率转换器和电光调制器等),不但可以保持块体材料本身的优异特性,还能极大提高器件的性能和集成度,具有块体材料器件所不具备的特点和优势.因此,对集成光波导和光波导器...     

Whispering‐gallery microcavities with unidirectional laser emission

Optical whispering‐gallery mode (WGM) microcavities featuring ultrahigh Q factors and small mode volumes enhance significantly the interaction between light and matter, becoming an excellent platform for achieving ultralow‐threshold microlasers. However, the emission of traditional WGMs is isotropic due to the rotational symmetry of cavity geometries, which hinders the potential photonics applications. In this review, the progress in WGM microcavities towards unidirectional laser emission is summarized. When a subwavelength scatterer is placed on the boundary of the microcavity, the unidirectional emission occurs due to the collimation effect of the microcavity‐enhanced scattering field. Furthermore, microcavities deformed from the circular shapes can not only produce the chaos‐assisted unidirectional emission, but also maintain high Q factors by special design and fabrication processes. Finally, gratings along the circumference of the WGM microdisk or microring can scatter the WGMs in the vertical direction. The review also lists several important applications of these types of microcavities, such as wide‐band laser illumination source, free‐space coupling, evanescent‐field enhancement, optical energy storage, and sensing.

     

Silica-based microcavity fabricated by wet etching

Silica whispering gallery mode(WGM) microcavities were fabricated by the buffered oxide etcher and potassium hydroxide wet etching technique without any subsequent chemical or laser treatments. The silicon pedestal underneath was an octagonal pyramid, thus providing a pointed connection area with the top silica microdisk while weakly influencing the resonance modes. The sidewalls of our microdisks were wedge shaped, which was believed to be an advantage for the mode confinement. Efficient coupling from and to the 60 μm diameter microdisk structure was achieved using tapered optical fibres, exhibiting a quality factor of 1.5×10~4 near a wavelength of 1550 nm. Many resonance modes were observed, and double transverse electric modes were identified by theoretical calculations. The quality factor of the microdisks was also analysed to deduce the cavity roughness. The wet etching technique provides a more convenient avenue to fabricate WGM microdisks than conventional fabrication methods.     

Lasing in microdisks with an active region based on lattice-matched InP/AlInAs nanostructures

The emissivity of unstrained quantum-dimensional InP/AlInAs nanostructures and their lasing properties in microdisk cavities prepared by wet etching have been studied. For as-prepared structures, it has been found that they radiate owing to quantum-dimensional InP islands 50–300 nm in diameter. At temperatures below 160 K, whispering gallery modes have been observed in the microdisks. Experimental data on the PL intensity for microcavity modes versus the pump power, which were obtained at liquid helium temperature, have made it possible to find the lasing threshold, 50 W/cm². The half-width of the laser line at above-threshold powers equals 0.06 nm, which corresponds to a Q factor of 15 000.     

Single-mode lasing in a coupled twin circular-side-octagon microcavity

We demonstrate the curvature of coupled twin circular-side-octagon microcavity (TCOM) lasers as the degree of freedom to realize manipulation of mode quality ($Q$) factor and lasing characteristics. Numerical simulation results indicate that mode $Q$ factors varying from 10$^{4 }$ to 10$^{8}$, wavelength intervals of different transverse modes, and mode numbers for four-bounce modes can be manipulated for five different deformations. Global mode distributes throughout coupled microcavity with mode $Q$ factor around the order of 10$^{4 }$ or 10$^{5}$. Four-bounce modes lase with injection currents applied single microcavity. By pumping both microcavities simultaneously, single-mode lasing for global modes with side mode suppression ratios (SMSRs) of 30, 32, 32, 31, and 36 dB is achieved at the deformation of 0, 0.5, 1, 1.5, and 2 with four-bounce modes suppressed, respectively. Moreover, the linewidths less than 11 MHz for the single mode are obtained with the deformation of 2. The results show that the lasing modes can be efficiently manipulated considering variable curvature for TCOM lasers, which can promote practical applications of microcavity lasers.     

Wavelength and intensity switching in directly coupled semiconductor microdisk lasers

We demonstrate output wavelength and intensity switching in a three-element directly coupled microdisk device consisting of one spiral microdisk coupled to two semicircle microdisks. The gapless coupling mechanism used allows individual elements to achieve lasing while achieving optimal transfer of optical power between adjacent microdisks. By controlling the transparency of the center element via injection current, the edge elements can be allowed to exchange their amplified spontaneous emission. In this manner, on-off-on switching of the output intensity, as well as discontinuous shifts in the output wavelength, can be achieved as a function of increasing injection current.     

Whispering gallery microcavity lasers

Whispering gallery mode (WGM) optical microresonators have attracted intense interests in the past decades. The combination of high quality factors (Q) and small mode volumes of modes in WGM resonators significantly enhances the light‐matter interactions, making them excellent cavities for achieving low threshold and narrow linewidth lasers. In this Review, the progress in WGM microcavity lasers is summarized, and the laser performance considering resonator geometries and materials as well as lasing mechanisms is discussed. Label‐free detection using WGM resonators has emerged as highly sensitive detection schemes. However, the resolution is mainly limited by the cavity Q factor which determines the mode linewidth. Microcavity lasers, due to their narrow laser spectral width, could greatly improve the detection resolution. Some recent developments in sensing using microcavity lasers are discussed.     

Investigation of resonant modes in thin microcavities by using electromagnetic theory

A biharmonic differential equation for 3D thin microcavities with uniform thickness is investigated by use of electromagnetic theory, whose exact solution is determined to govern the electromagnetic field distribution inside the thin microcavities. The resonant field patterns of a thin microdisk and thin rectangular microcavity are obtained accordingly. The governing equation can be verified by comparing the results of the thin microdisk presented with the approximate ones in the literature. The fourth-order partial differential equation and its exact solution should be useful in possible applications of the thin microcavities for optical resonators in laser optics and optical devices.     

Photoinduced whispering gallery mode microcavity resonator in a chalcogenide microfiber

We demonstrate an approach to creating localized whispering gallery mode (WGM) microcavities by exploiting the photosensitivity of a chalcogenide (As2S3) microfiber. A highly prolate WGM microcavity with cavity quality factors (Q) exceeding 2×10(5) is fabricated and characterized. Without the need for geometrical shaping, our approach enables the cavity properties to be monitored during fabrication for the first time.     

Whispering‐gallery mode lasing from patterned molecular single‐crystalline microcavity array

Organic single‐crystalline materials have attracted great attention for laser applications. However, the fabrication of laser resonators and pattern of crystals are still intractable problems. Organic single crystals have been limited to fundamental property studies despite their superior photonic characteristics. In this work, whispering‐gallery mode (WGM) resonators of BP1T and BP2T crystalline materials have been fabricated through a combination method with improved lithography and dry etching. Crystalline microresonators with different geometries over a large area are top‐down fabricated with submicrometer spatial resolution. WGM lasing oscillation from circular, hexagonal, pentagonal and square resonators is definitively observed. The BP1T and BP2T crystals are characterized with high refractive index, and stable lasing in aqueous solution is demonstrated besides in the air environment. It is expected that organic crystalline materials would be used for the practical applications in a variety of organic electronic and optical devices.     

Controlling spontaneous emission and threshold-less laser oscillation with optical microcavities

We describe the alteration of spontaneous emission of materials in optical microcavities having dimensions on the order of the emitted wavelength. Particular attention is paid to one-dimensional optical confinement structures with pairs of planar reflectors (planar microcavities). The presence of the cavity causes great modifications in the emission spectrum and spatial emission intensity distribution accompanied by changes in the spontaneous emission lifetime. Experimental results are shown for planar microcavities containing GaAs quantum wells or organic dye-embedded Langmuir-Brodgett films as light emitting layers. Also discussed are the laser oscillation properties of microcavities. A remarkable increase in the spontaneous emission coupling into the laser oscillation mode is expected in microcavity lasers. A rate equation analysis shows that increasing the coupling of spontaneous emission into the cavity mode causes the disappearance of the lasing threshold in the input-output curve. Experimentally verification is presented using planar optical microcavities confining an organic dye solution. The coupling ratio of spontaneous emission into a laser mode increases to be as large as 0.2 for a cavity having a half wavelength distance between a pair of mirrors. At this point, the threshold becomes quite fuzzy. Differences between the spontaneous emission dominant regime and the stimulated emission dominant regime are examined with emission spectra and emission lifetime analyses.