毫米波折叠波导行波管输入输出过渡波导设计

折叠波导以其宽频带、加工方便而成为一类重要的毫米波与太赫兹波段行波管慢波线。针对折叠波导慢波系统与标准波导的匹配过渡连接,通过等效电路分析与电磁计算软件模拟,设计出了直渐变波导、双曲圆弧渐变波导、切比雪夫阶梯渐变波导3种输入输出过渡波导结构,分析了各种过渡波导的优缺点及结构尺寸对性能的影响。计算表明,经过合理优化的设计,3种过渡结构均可以使反射系数在28~40 GHz波段小于0.05。     

小型铌酸锂多功能集成光学器件

为满足小型光纤陀螺对光学器件小体积的要求,对铌酸锂多功能集成光学小型化器件的结构做了分析和优化设计。采用BPM软件分析了Y形分支波导的S形波导损耗与弯曲长度及折射率差的关系。通过调整退火质子交换的工艺参数,增加了波导对光的束缚能力;降低了小型化芯片上S形波导的弯曲损耗;去掉了原有Y形波导的输出端直波导,直接由S形弯曲波导引至输出端,在更短的芯片上得到了更长的弯曲过渡区。设计制作的芯片长度由常规的20 mm减至12.5 mm,封装后的器件长度减小到20 mm,为目前同类常规器件尺寸的2/3。设计制作的器件插入损耗典型值小于2.5 dB,全温损耗变化量小于0.2 dB。     

Design of tunable surface mode waveguide based on photonic crystal composite structure using organic liquid

With the method of replacing the surface layer of photonic crystal with tubes, a novel photonic crystal composite structure used as a tunable surface mode waveguide is designed. The tubes support tunable surface states. The tunable propagation capabilities of the structure are investigated by using the finite-difference time-domain. Simulation results show that the beam transmission distributions of the composite structure are sensitive to the frequency range of incident light and the surface morphology which can be modified by filling the tubes with different organic liquids. By adjusting the filler in tubes, the T-shaped, Y-shaped, and L-shaped propagations can be realized. The property can be applied to the tunable surface mode waveguide. Compared with a traditional single function photonic crystal waveguide, our designed structure not only has a small size, but also is a tunable device.     

Design of short length and C+L-band mismatched optical coupler with waveguide weighted by the Blackman function

A mismatched optical coupler with waveguide weighted by the Blackman function is numerically investigated in the demand of short length, C+L-band, and low crosstalk. Utilizing the full factorial design, the structure parameters of coupling waveguide are obtained by beam propagation method. In the condition of crosstalk of −35 dB, the mismatched optical coupler with proper selected waveguide structure parameters is found to have a coupling length of 3.60 mm in the transmission wavelength ranges of C+L-band (1.53-1.61 μm). Obviously, the selection and design of waveguide structure are very important to satisfy the qualities of a mismatched optical coupler for the demand of short length, broad bandwidth, and low crosstalk.     

High-power multibeam CO2 laser for industrial applications

Multibeam CO₂ lasers consist of a large number of closely packed parallel glass discharge tubes, all sharing a common plane parallel resonator. This paper describes construction and operation of a CW multibeam CO₂ laser consisting 20 discharge tubes and cooled length of 1500 mm, delivering 1 kW power. A high-frequency pulser is used for producing preionization in all discharge sections for initiating the main DC discharge simultaneously in all discharge tubes. Plane parallel resonator consists of a plane ZnSe mirror of 90 mm diameter having 60% reflectivity and a gold-coated copper mirror of same diameter. This laser operates in waveguide regime and laser power is not critically sensitive to mirror misalignment.     

Short-length and broadband mismatched optical couplers with tapered Hamming function for C- and L-band

Mismatched optical couplers with variable widths of waveguide tapered by Hamming function are numerically investigated in the demand of short-length, broadband, and low crosstalk. We used global search algorithm and beam propagation method to seek optimal structure parameters of coupling waveguide. The coupler length is 3.6 mm within the C+L-band (1.53-1.61 μm) for variable widths of waveguide at crosstalk level of −35 dB. Comparison with constant width of waveguide, the constant width of waveguide has a coupler length of 4.4 mm and can only achieve −20 dB of crosstalk within the C-band (1.53-1.565 μm). Obviously, the waveguide with variable widths has the advantage over constant width for the demand of short-length, bandwidth, and low-crosstalk.     

Compact waveguide CO2 laser excited by a RF power supply

The design and performance of radio frequency (RF) excited partial Z-fold waveguide CO2 laser with two channels are exposed. The length of the partial Z-fold channel is 3×460 mm and that of the single channel is 460 mm. The electrodes for the two channels are common and excited by a same RF source. According to our analysis, this kind of structure can greatly improve the laser offset frequency stability. In the experiments, we studied the variation of laser output power with gas pressure for two different channels.The maximum laser output power is about 23 W for the partial Z-fold channel and about 6 W for the single channel.     

A design for a nonreciprocal phase shifter

A design is described for a nonreciprocal phase shifter, which is the key element in the constitution of a Mach-Zehnder interferometric isolator consisting of a magneto-optical channel waveguide. A four-layered structure waveguide is dealt with in which a cover layer having a larger refractive index than that of the film is placed on the magneto-optic thin film; it is revealed that the phase shifter length can be shortened by up to 6 mm at the 1.15 m wavelength, which is half the length of a nonreciprocal phase shifter constructed of a three-layered waveguide without a large refractive index cover layer. Two types of channel waveguides are investigated: a rib waveguide and a strip-loaded waveguide; they are found to have the same phase shifter length for the optimum condition.     

Structure design and performance simulation on monolithic integrated chaotic-optical transmitter with photonic crystal waveguide in external cavity

A novel monolithic integrated chaotic-optical transmitter structure is proposed in this paper. It consists of a distributed feedback laser, a semiconductor optical amplifier, a passive waveguide, and a photonic crystal waveguide. The length of external cavity is shorten to 1.125 mm by the slow light effect in photonic crystal waveguide. The performance of the integrated chaotic-optical transmitter is simulated. A series of dynamic states transiting from steady state, period state, and finally to chaotic laser is obtained. The size and power consumption of the chaotic-optical transmitter are both reduced by introduction of photonic crystal waveguide.     

折叠矩形槽波导行波管输入输出过渡波导

为了将槽波导端与标准矩形波导相连接,设计了一种适用于折叠槽波导结构行波管的输入输出过渡波导, 可将其视为槽宽渐变的双槽加载矩形波导。利用电磁仿真软件CST微波工作室对该结构进行仿真计算,讨论了各个结构参数对其性能的影响。对比了直线渐变、抛物线渐变和指数渐变3种槽宽渐变规律在W波段对其传输特性及损耗特性的影响。研究结果表明:指数渐变结构的驻波系数小于1.15的带宽比其他两种结构都要宽,且在90~99 GHz、驻波系数小于1.25时,该结构的整体长度也远小于另外两种结构,能够实现良好的过渡效果; 而直线渐变结构的损耗在90~97 GHz为最低。     

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The structure and its optimization of 2.45GHz high power microwave ceramic window are introduced in this paper. The structure optimization includes optimization of structure dimensions and coolant flowing rate. The microwave properties are sufficient when the thickness of ceramic disk is 4.4mm and the length of cylindrical waveguide is 52.3mm. The maximum thermal stress on the ceramic disk is far less than the limitation that ceramic disk could sustainable stress when the coolant flowing rate is 0.4t×h^-1 . Optimized ceramic window did not appear crack problem after several runs of experiments.     

基于平板波导的小型红外光栅光谱仪光学设计

为实现红外光谱仪器的小型化,通过分析现有小型光谱仪,提出了一种基于平板波导的小型红外光栅光谱仪的设计方法。平板波导光谱仪的小型化原理与一般的微小型光谱仪不同。在平板波导光谱仪中,光束被限制在一层薄薄的平板波导介质中传播,看起来像是整个光学系统被压扁了。在垂直于平板波导的方向上光学元件的尺寸可以做到很小,从而显著减小光学系统的尺寸。该系统的设计可分为Czerny-Turner结构设计、波导结构设计。先根据像差理论设计Czerny-Turner结构,目标是保证光谱分辨率及校正像差;然后根据几何光学理论设计波导结构,包括平板波导和两个柱面透镜,目标是压缩光束并校正像散;最后将它们输入Zemax软件中进行综合优化,以获得最优的光学系统。据此方法设计了一个平板波导红外光栅光谱仪,工作波段为8~12 μm,数值孔径为0.22,采用线阵探测器。通过Zemax软件对结果进行分析和评价,表明仪器光学系统的尺寸为130 mm×125 mm×20 mm,工作波段内光谱分辨率达到80 nm,满足设计指标要求。证明了该优化设计方法是可行的,所得系统尺寸小、性能高。     

Analysis of Oversized Sliding Waveguide by Mode Matching and Multi-Mode Network Theory

Transmission and reflection coefficients of hybrid modes in the sliding waveguide are discussed on the basis of mode matching method and multi-mode network theory. It is confirmed that the decrease in power of < 0.2% at 84 GHz is obtained for 2 cm in gap of the sliding waveguide which is composed of the corrugated waveguide with 88.9 mm diam. and the smooth-wall waveguide with 110 mm diam. At the sliding length near multi-half-wavelength in vacuum, transmission and reflection powers in the sliding waveguide change slightly, because the very small amount of standing wave in high higher-mode is produced resonantly in the gap.     

Waveguide electro-optic modulator in fused silica fabricated by femtosecond laser direct writing and thermal poling

An integrated electro-optic waveguide modulator is demonstrated in bulk fused silica. A Mach-Zehnder interferometer waveguide structure is fabricated by direct writing with a femtosecond laser followed by thermal poling. A 20 degrees electro-optic phase shift is achieved at an operating wavelength of 1.55 microm with an applied voltage of 400 V and an interaction length of 25.6 mm, which correspond to an estimated effective electro-optic coefficient of 0.17 pm/V for the TE-polarized mode.     

脊加载同轴交错圆盘波导的高频特性

提出脊加载同轴交错圆盘波导慢波结构,并用电磁场仿真软件HFSS对其色散特性和耦合阻抗进行了计算,分析了不同结构参数对其高频特性的影响。研究表明:脊加载同轴交错圆盘波导有较好的色散特性,它比非同轴结构的带宽有明显增加,同时可以降低慢波结构的相速,用作行波管慢波结构时可以降低工作电压。脊加载同轴交错圆盘波导是一种全金属结构,散热性能好,损耗低,在毫米波及亚毫米波段的行波管中有较好的应用前景。     

A smart optical liquid level sensor based on Hg cladding optical waveguide

A smart optical liquid level sensor based on the theory of connected vessels is introduced. The Hg cladding optical waveguide (HCOW) is taken as its probe, and the change of liquid level is presented by the change of the HCOW length. Both the theoretical analysis and experiments show that when the waveguide diameter and the light wavelength are certain, the optical power loss decreased linearly with the increase of the HCOW length. By detecting the power loss of HCOW, optimizing the structure of probe and selecting the appropriate apparatus for detection, the real time detection of liquid level with high precision can be got. The experimental results show that the measurement accuracy is 5.2 mm within 10 m liquid level, and its theoretical precision can be up to 0.02%.     

Millimeter-wave mode conversions at dielectric waveguide steps

The conversion of guided modes (TE₀ and TE₁) at a rectangular step on a dielectric slab waveguide is investigated with mm microwaves. The power of the modes is measured from their interference patterns in the evanescent field outside the waveguide slab. The relative power of two modes changes periodically when the length of the step is varied. In the experiments a change of up to three orders of magnitude was measured. The step is considered as a sequence of three waveguide sections of different thickness. At the discontinuities the modal fields are assumed to illuminate the next section. The calculation based on this model agrees with the experimental results.     

Propagation Modes in Periodically Poled Lithium Niobate Waveguides Exploiting Cascaded Second Order Nonlinearity

The improvement of cascaded second-order nonlinearity ≤(2) : ≤(2) effects in a quasiphase-matching (QPM) structure constituted by a periodically poled lithium niobate (PPLN) waveguide is obtained utilizing an integrated metal mirror placed after an additional waveguide segment. The resulting double-pass device, which can be employed for wavelength conversion, is refined by choosing the most advantageous length of the segment waveguide and by taking into account both the thermal and electro-optic effects. In the ideal case of perfect QPM, for a grating length z G4 = 25 mm, the calculated double-pass maximum efficiency is eta dp = 22.86 dB, which is almost the triple of eta sp = 8.20 dB, calculated for the single-pass version (without mirror) for the same value of the pump and signal powers.     

一种基于不平坦基底结构的混合等离子体波导

提出了一种工作于太赫兹波段的、基于半圆柱形"不平坦"InSb基底结构的混合等离子体波导.分析了半导体材料InSb的相对介电常量随工作频率的变化特性,重点研究了该混合波导以及两种不同形变结构的有效模场面积、传播长度、品质因数、能量分布等随波导工作频率、波导尺寸的变化情况.结果表明,本文提出的"不平坦"基底结构波导可以达到与传统结构几乎相同的传播长度,有效模场面积较传统结构减小了一个数量级以上,具有非常强的模场约束性,适合于太赫兹频段高密度集成电路中的应用.     

曲折圆形槽波导慢波系统的高频特性

 对曲折圆形槽波导新型慢波系统的高频特性进行了研究，通过理论分析和数值计算，得到了它的色散曲线和耦合阻抗表达式，并分析了结构参数变化对色散特性和耦合阻抗的影响。研究表明：当周期变小时色散减弱，耦合阻抗增加；而增大直波导长度时色散变弱，但同时耦合阻抗也会下降。因此较小的周期有利于改善曲折圆形槽波导慢波电路的高频特性。鉴于这种电路的耦合阻抗较低，可以适当地减小直波导长度来提高耦合阻抗。曲折槽波导结合了曲折波导散热能力强、色散特性好、容易加工和槽波导单模工作、低损耗、大尺寸等优点，在毫米波及亚毫米波段的行波管中具有较好的发展前景。