新型1×N多模干涉分束器的三维设计与模拟

相比于传统的1×N对称型多模干涉（Mult-Mode Interference,MMI）分束器设计,提出了一种新型埋入式弱限制光波导分束器件.它的干涉区及输入输出波导采用倒锥形式,器件尺寸减小,且不均匀性与附加损耗也减小.以1×4的对称型MMI分束器为例,当只对干涉区采用倒锥形结构后,在TE偏振中心波长为1.55 μm时,器件长度减小了500 μm,均匀性增加了0.131 dB,而附加损耗仅增加了0.02 dB,波长响应较传统设计增加了40 nm.在此基础上,又在输入输出臂上也各增加倒锥形结构后,相比于传统设计附加损耗减小了0.02 dB,均匀性增加了0.139 dB,器件长度减小了500 μm.改进后的器件具有优越的容差性.器件采用掺氟型聚合物材料进行优化设计,通过在合理范围内偏离输出波导位置,使输出光强达到最大值.     

To analyse the performance of tapered and MMI assisted splitter on the basis of geographical parameters

A literal model using geometric examination was formulated to calculate the optimum width and length of multimode interference structure used in the 1 × 2 power splitter and plot electric field intensity for input and each output signal. Designing and simulation of the wavelength response of 1 × 2 splitter using Tapered and MMI assisted structure. Mechanism on the critical geographical parameters like length and width of MMI structure, separation distance between output ports ‘S’, arm angle ‘α’ which give the optimum power and electric field intensity for the considered necessary wavelength. Finite difference beam propagation methods have been used to simulate the conventional and tapered MMI device behaviour.     

多模干涉型GaAs光功分器的研制

采用导模传输分析法设计了多模干涉型１×４ 光功分器。根据所确定的器件结构参数, 结合器件设计和制作过程中可能遇到的因素, 详细分析了器件中自映像效应多模波导的宽度和长度、波导的折射率等结构参数对器件性能的影响。进行了多模干涉型 Ｇａ Ａｓ １×４ 光功分器的制作和测试。测试结果表明, 所研制的器件实现了１×４ 光功分器功能。针对实验过程和测试结果中遇到的问题进行了讨论, 并提出了进一步完善器件性能的方法。     

Experiment Research on a Highly Stable LD-pumped Solid State Laser

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Experiment Research on a Highly Stable LD-pumped Solid State Laser

In high power laser systems, the stability of the seed laser is vitally important. This paper presents the work on the design and manufacture of a highly stable LD pumped solid state seed laser which has the advantages of being all solid state, compact, easy to manufacture and low cost. The laser was composed of two parts. One was an LD pumped 0.5 mm thin Nd: YLF laser system in which the instability was around±6% (3σ). The other was a close-looped laser power control system using external cavity power feedback. Using an electro-optic modulator, a 1×2 optical fiber splitter and a signal processing circuit, we successfully realized the highly stable LD pumped Nd: YLF laser in which the instability of laser output power was lower than±0.2 %/hour (3σ). A digital PID (Proportion, Integration and Differentiation) control method was used with a control frequency of 40 kHz. The 3 mW of highly stable laser power through the optical fiber was obtained.     

基于1×4光子晶体波导分束器的特性研究

光子晶体波导分束器是集成光学电路的重要组成元件。设计一种线缺陷1×4光子晶体分束器,用时域有限差分法研究其特性。实验结果表明:输出端的透射传输特性随入射光的波长和分支的几何形状有关,并且入射波分别相等地流入4个输出端口。为了减少1×4分束器在3个Y型分支区的反射,通过调节分支区的可调介质柱的半径R,可使每个输出端口输出较高的透射率。     

Relaxed fabrication tolerance for self-imaging photonic crystal waveguide splitters using a tapered multimode interference region

The power imbalance between different waveguide outputs is compensated by manipulating the dispersion of the guided propagation in the multimode interference (MMI) region. This is attainable using a tapered region at the beginning of the MMI region that has been verified through simulation and experiment. From this, the fabrication tolerance for the diameters of holes in a tapered 1×3 photonic crystal waveguide (PhCW) splitter is relaxed up to a range of at least 27 nm. The output power is well-balanced to within 1 dB. The effective bandwidth of the splitters shifts only around 13 nm, for a reduction of 10 nm in the diameter of the PhCW holes. The optimized component is an outstanding ultracompact 1×3 splitter for the photonic integrated circuit (PIC).     

Splitting-on-demand optical power splitters using multimode interference (MMI) waveguide with programmed modulations

Reconfigurable multi-channel optical power splitter is proposed and its optical properties are calculated. The device can dynamically reconfigure the number of splitting channels by providing programmed refractive index modulations on a multimode interference (MMI) waveguide. A reconfigurable 3-channel optical power splitter is designed to work as 1 × 1, 1 × 2 or 1 × 3 optical power splitter depending on the state of the heat electrodes using thermo-optic modulation, and the input light can be distributed to three output channels with sequential orders. The device can work in the whole C-band (1530-1565 nm) with extinction ratio better than −29.0 dB, excess loss better than −0.45 dB, imbalance better than 0.08 dB and polarization dependent loss (PDL) better than 0.14 dB. The design conception is scalable to a multi-channel splitting-on-demand optical power splitter which can divide input light to 1, 2, …, N output channels equally by using the 3-channel reconfigurable optical power splitter as a building block.     

Higher diffraction order photorefractive optical beam splitter

A higher diffraction order photorefractive (PR) optical beam splitter has been realized based on a PR higher diffraction order grating. In the experiments, the beam splitter was produced by two-wave coupling at a small incident angle in Fe:LiNbO₃ using the output from a He–Ne laser at 632.8 nm. An incident signal beam containing three different wavelengths (632.8, 532.0 and 488.0 nm) was split into multi-output beams by the beam splitter. The size of higher diffraction order is given and the influence of crystal thickness is discussed. Results show that the higher diffraction order PR optical beam splitter provides a practical method to split a multi-wavelength signal beam.     

Measurement of absolute phase Shift on reflection of thin films using white-light spectral interferometry

A novel method to measure the absolute phase shift on reflection of thin film is presented utilizing a white-light interferometer in spectral domain. By applying Fourier transformation to the recorded spectral interference signal, we retrieve the spectral phase function Ф, which is induced by three parts： the path length difference in air L, the effective thickness of slightly dispersive cube beam splitter Teff and the nonlinear phase function due to multi-reflection of the thin film structure. We utilize the fact that the overall optical path difference （OPD） is linearly dependent on the refractive index of the beam splitter to determine both L and Teff. The spectral phase shift on reflection of thin film structure can be obtained by subtracting these two parts from Ф. We show theoretically and experimentally that our new method can provide a simple and fast solution in calculating the absolute spectral phase function of optical thin films, while still maintaining high accuracy.     

高反射光学薄膜激光损伤研究进展

激光诱导损伤阈值是大功率光学系统中重要参数,其数值大小对激光系统的输出功率与稳定性具有重要影响。为了突破损伤阈值对激光光学系统输出功率的限制,科研人员主要从制备薄膜工艺、激光特性、薄膜特性以及薄膜后工艺等方面开展研究。本文介绍了高反膜理论、制备工艺;综述了近十年来国内外对高反膜损伤研究的成果;阐述了激光特性、薄膜特性以及薄膜后工艺对薄膜损伤阈值的影响。在此基础上,对提高高反膜损伤阈值的研究和发展趋势进行了分析与展望。     

等离子体闪光法识别薄膜损伤的误判消除方法

传统的等离子体闪光法,是根据探测器是否接收到来自薄膜样片周围发射的闪光信号,对薄膜是否发生损伤进行评判,这样的评判方法极易把空气与薄膜的等离子体闪光混淆而发生误判。为了消除这种误判,提出通过比较空气和薄膜各自的等离子体闪光的点燃时间,利用两者时间上的差异,实现对传统等离子体闪光法误判现象的消除方法。为了验证新方法的可靠性,借助于多光子吸收和级联电离理论,建立了空气等离体子体点燃时间的计算模型,根据薄膜与激光的相互作用原理建立了薄膜被击穿时的等离子体点燃时间计算模型,利用建立的模型仿真计算了空气和薄膜的等离子体闪光点燃时间分别为1.856和7.843 ns;搭建实验装置以实现对传统等离子体闪光法的更新,在装置中的不同位置设置三个光电探测器分别采集入射激光信号、空气和薄膜等离子体闪光信号,采集入射激光信号的光电探测器置于聚焦透镜的侧面,另外两个探测器位于薄膜样片周围且左右对称放置,分别用于采集薄膜的等离子体闪光信号和空气的等离子体闪光信号,所有光电探测器采集的信号转换为电信号后同步传输至示波器,以入射激光信号为基准信号,其与空气和薄膜等离子体闪光信号的起始时刻之差,分别为空气和薄膜等离子体闪光点燃时间。脉宽为10 ns、波长为1 064 nm的Nd∶YAG脉冲激光以0.015 cm的聚焦光斑半径、82.4 mJ的入射能量作用于光学厚度为λ/4、直径为20 mm的单层Al₂O₃薄膜样片上后,采集上述激光作用条件下的各路信号,经处理后得到的空气和薄膜的等离子体闪光点燃时间测试值分别为2.7和7.8 ns;理论计算和实验测试结果表明,空气的点燃时间总是小于薄膜的点燃时间,二者有很好的一致性。说明当强激光作用于单层Al₂O₃薄膜表面时,空气等离子体闪光先于薄膜等离子体闪光发生。基于空气和薄膜等离子体闪光点燃时间上的这种差异,利用闪光信号时间上的差别就可准确分辨出薄膜是否发生损伤,从而获得识别薄膜损伤与否的判据,这种从时间差异上识别薄膜等离子体闪光损伤的新方法,无论从理论上还是实验上均为传统等离子体闪光法误判现象的消除提供了技术基础。     

新型小尺寸窄带偏振分光器在光纤通信中的应用

在光纤通信中,为了在不改变调制波长范围的基础上仍能实现更多数据通道的波分复用,设计了一种新型的小尺寸窄带偏振分光器,用于对现有的数据通信网络进行扩容以及提高光信号的信噪比。在该分光器上蒸镀了两种新设计的膜系,一层是窄带滤光膜,另一层是偏振分光膜。采用TFCalc软件仿真,设计结果中窄带滤光膜的带宽约为0.4 nm,偏振分光膜在1 530～1 560 nm范围内对p光的通透性能优于99.8%。基于以上膜系设计在BK7光学玻璃上实际制备两组膜系,实验采用Agilent 8164-A型光波测量系统对经过膜后的光进行光谱分析。结果显示,窄带滤光膜的实际带宽优于0.4 nm,增益平坦度小于-0.05 dB,相比现有常见的0.8 nm滤光膜具有更窄的带宽,可以实现在调制波长范围不变的条件下增大波分复用的数据通道总量。偏振滤光膜的实际p光透光率为99.6%,相比仿真值略低,但仍优于设计要求,相比传统分光器的光信号强度保留效果更好,具有更高的信噪比。综上所述,该分光器具有更好的应用价值和实用意义。     

弱导波导多模干涉耦合器结构参量优化设计

本文分析了以硅基底上二氧化硅波导为代表的弱导波导多模干涉(MMI)耦合器件输入(出)波导位置及宽度和MMI长度等结构参量对器件性能的影响.提出了参量空间法,在给定工艺材料参量和多模波导宽度情况下,通过匹配各结构参量,制出均匀性好、附加损耗低的弱导波导多模干涉耦合器件.     

Impact of waveguide sidewall roughness on the output uniformity and phase of MMI splitters

In this paper, we develop a model for the effects of waveguide sidewall roughness on the output uniformity and phase of a 3-dB MMI splitter. We achieve this by investigating analytically the effect of sidewall roughness on mode coupling in the MMI section of the splitter using the coupled mode and coupled power equations. Using these equations, the subsequent impact of mode coupling losses on the splitter output uniformity and phase is calculated and results for 1 × 2 and 2 × 2 splitters are presented and compared. Finally, to illustrate the impact of sidewall roughness on the operation of a waveguide device, the response of a Mach Zehnder interferometer comprising 2 × 2 splitters is investigated.     

Two-dimensional higher-diffraction-order optical beam splitter based on phenanthrenequinone-doped poly(methyl methacrylate) photopolymer

A two-dimensional optical beam splitter has been realized that uses the higher diffraction orders of a refractive-index grating. Gratings were recorded experimentally with light from a semiconductor laser incident at a small angle on phenanthrenequinone-doped poly(methyl methacrylate) photopolymer. The incident signal beam, which was made up of three different wavelengths (632.8, 532.0, and 488.0 nm), was split by the grating into multiple output beams with nearly equal size and separation. Results are given for when the sample grating was placed behind, in front of, and in the focal plane of a Fourier lens. The properties of higher-order-diffraction images have been discussed. The discussion shows that a two-dimensional higher-diffraction-order optical beam splitter provides a practical method for splitting a signal beam.     

Frequency quadrupling using an integrated Mach–Zehnder modulator with four arms

In this paper, a novel technique to realize frequency quadrupling in the radio over fiber system is proposed. The frequency quadrupling is achieved by using an integrated Mach–Zehnder modulator (MZM) consisting of a 1 × 4 multimode interference (MMI) coupler and four optical phase modulator arms. Due to the inherent optical splitting ratio and phase relations between the outputs of the MMI coupler, the optical harmonics at + 1 order and ? 3 order are generated corresponding to four times frequency of the microwave drive signal, only by setting the DC bias voltage of the main MZM at the minimum transmission point. That leads to the integrated MZM with reduced complexity compared with the conventional dual-parallel MZM. The effect of the nonideal integrated MZM, including the splitting imbalance and the bias drift, on all the sidebands is also analyzed theoretically. The following simulation results show that the slight deviation of the ideal values would not cause great degradation of the generated optical millimeter-wave signal.     

LaCaMnO3 thin film laser energy/power meter

A prototype laser energy/power meter was designed based on the anisotropic Seebeck effect of LaCaMnO₃ thin film grown on vicinal cut LaAlO₃ substrate. The optical response of this device to the pulsed laser and the chopped CW laser was measured from infrared to ultraviolet. The peak voltage of the measured signal shows a good linear relation to the laser energy and power in the measured range. It was shown that at 1064 nm wavelength, this prototype device demonstrates higher sensitivity than that of commercial device.     

1×4 MMI Splitter Based on Rib SOI Waveguide

In this paper, a 1×4 MMI splitter based on silicon-on-insulator (SOI) by effective index method and guide mode method is designed. The fabrication tolerance was analyzed. The device was fabricated and near-field output was obtained.     

1×4 MMI Splitter Based on Rib SOI Waveguide

In this paper, a 1×4 MMI splitter based on silicon-on-insulator (SOI) by effective index method and guide mode method is designed. The fabrication tolerance was analyzed. The device was fabricated and near-field output was obtained.