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1.
A 90° phase switch in finline technique has been developed for application in a W-band homodyne network analyzer. It is realized on a 0.127 mm fibre reinforced teflon substrate in a standard WR 10-waveguide. It employs two low capacitance beam-lead PIN diodes mounted in series to the finline. The waveguides are connected via Dolph-Chebyshev tapers.The analysis of this circuit shows that the diode junction capacitance imposes certain constraints for the wave impedances which must be realized. They can only be met with overlapping antipodal finlines. There are several analytical solutions with different lengths and wave impedances of the transmission line sections. The choice has been taken with respect to bandwidth in the limits imposed by the range of wave impedances which can be realized. Between 90 and 105 GHz, the phase error of the realized modulator is below ±2.5°, and the amplitude imbalance is less than 0.5 dB. 相似文献
2.
The characteristics of slab waveguide tapers with finite-thickness cladding are investigated by approximating the tapered
section as a series of uniform five-layer waveguides with successive changes in the core and cladding thickness. The behaviour
of multimode coupling and transmission characteristics for typical tapers are studied in detail by computer simulation, employing
parameter values appropriate for practical systems. Strong coupling and efficient conversion between core and cladding modes
are demonstrated. In addition, it is shown that for tapers of moderate slopes, the nearest-neighbour coupling approximation
is quite adequate for the calculation of the individual mode amplitudes. For steeper tapers, however, additional neighbouring
modes have to be taken into account, and the modal energy tends to spread further towards the higher-order modes. It is also
demonstrated that relatively large step-size can be used in the iterative numerical calculations. This, in conjunction with
the choice of an appropriate coupling scheme (e.g., the nearest-neighbour approximation for mild tapers), makes it possible
to reduce the cost of computer simulation. The relevance of the present analysis to fiber tapers is also discussed.
Supported in part by the Department of Communications of Canada 相似文献
3.
基于深刻蚀SiO2脊型波导的紧凑型多模干涉功分器 总被引:2,自引:2,他引:0
采用深刻蚀SiO2脊型波导,利用其弯曲半径小的优点,设计了一种紧凑型1×2多模干涉功分器.在输入/输出波导与多模干涉区域之间引入了逆向锥形波导,有效地减小了输出波导间距,从而减小了多模干涉区域宽度及其长度,进一步实现了多模干涉器件的小型化(仅为150 μm×20 μm).并采用三维束传播方法对多模干涉区域及输入/输出波导中的光场传输进行了模拟仿真,得到了一组最优参量设计值,从而实现其结构优化. 相似文献
4.
《Photonics and Nanostructures》2009,7(1):19-25
One-dimensional (1D) photonic crystal (PC) microcavities can be readily embedded into silicon-on-insulator waveguides for photonic integration. Such structures are investigated by 2D Finite-Difference Time-Domain method to identify designs with high transmission which is essential for device integration. On-resonance transmission is found to decrease with the increasing mirror pairs, however, the quality factor (Q) increases to a saturated value. The addition to the Bragg mirrors of tapered periods optimized to produce a cavity mode with a near Gaussian shaped envelope results in a major reduction in vertical loss. Saturated Q up to 2.4 × 106 is feasible if the internal tapers are properly designed. The effect of increasing transmission is also demonstrated in a structure with the external tapers. 相似文献
5.
阵列波导光栅的平坦化在实际应用中有很重要的意义.本文系统地研究了阵列波导光栅的平坦化.在输入波导、输出波导、阵列波导输入端与输出端上分别引入了指数型锥形波导.通过改变锥形波导的形状和尺寸来实现平坦化的优化.本文首先从理论上论述了引入指数型锥形波导的输出光谱特性,给出了结构参量的关系表达式,阐明了输入波导处的锥形波导是影响输出光谱平坦化的主要因素,阵列波导和输出波导处的锥形波导对输出光谱的平坦化有一定的影响.其次采用数值模拟的方法模拟了输出光谱,优化了结构参量,总结出了指数型锥形波导对平坦化影响的趋势和规律.模拟结果显示,输出光谱1 dB带宽大于通道间隔的50%,插入损耗从5.2 dB减小到了4.0 dB,串扰小于-30 dB.最后,本文给出了实验结果,插入损耗减小了0.87 dB,串扰减小了3.67 dB,1 dB带宽增加0.1 nm,增加了54.7%.实验结果表明引入指数型锥形波导提高了阵列波导光栅器件的光谱性能. 相似文献
6.
We have demonstrated a hybrid Mach-Zehnder optical modulator consisting of a large-core, low-loss fluorinated passive polymer waveguide and an electro-optic (EO) polymer waveguide. The combination exhibits low fiber coupling loss to the passive waveguide and reduced transmission loss because the EO polymer waveguide is used only in the active region. The two waveguides are connected by vertical tapers that permit low-loss adiabatic coupling between the two modes. The half-wave voltage and the insertion loss of the fabricated modulator are 3.6 V and 6 dB, respectively, at a wavelength of 1.55 microm . The estimated coupling loss with the standard single-mode fiber is ~0.5 dB. 相似文献
7.
Eswarappa G. Costache W. J. R. Hoefer 《International Journal of Infrared and Millimeter Waves》1989,10(1):21-30
In this paper, a general finite element method as well as a graded-mesh TLM procedure for determining the dispersion characteristics, field distribution, pseudo-impedance and losses of generalized millimeter-wave transmission media are described. These methods cover arbitrary cross-sections and account for realistic features (finite metallization thickness, substrate mounting grooves etc.) that are often neglected in theoretical analysis. Dispersion characteristics and characteristic impedances obtained for dielectrically loaded ridged wave-guides compare well with the available data. Conductor and dielectric losses are also computed for these structures. A modified finline structure called ridged finline is also analysed. The main advantages of this structure are its large monomode bandwidth and reduced dispersion. The cutoff frequencies of bilateral finlines in circular waveguides are also computed. 相似文献
8.
Since the advent of three-dimensional photonic integrated circuits,the realization of efficient and compact optical interconnection between layers has become an important development direction.A vertical interlayer coupler between two silicon layers is presented in this paper.The coupling principle of the directional coupler is analyzed,and the traditional method of using a pair of vertically overlapping inverse taper structures is improved.For the coupling of two rectangular waveguide layers,a pair of nonlinear tapers with offset along the transmission direction is demonstrated.For the coupling of two ridge waveguide layers,a nonlinear taper in each layer is used to achieve high coupling efficiency.The simulation results show that the coupling efficiency of the two structures can reach more than 90%in a wavelength range from 1500 nm to 1650 nm.Moreover,the crosstalk is reduced to less than-50 d B by using multimode waveguides at intersections.The vertical interlayer coupler with a nonlinear taper is expected to realize the miniaturization and dense integration of photonic integrated chips. 相似文献
9.
Marcatili has proposed a class of graded-index (GRIN) tapers which do not radiate along their length. We investigated the splicing of such tapers to dissimilar waveguides, and derive a simple formula for the coupling efficiency, which clearly reveals the loss due to mismatch of spot-size and the curvature of the wavefronts. 相似文献
10.
A completely passive method of achieving phase delays inside multimode interference devices is presented. The desired relative phase is obtained by adjustment of the width of the waveguides in conjunction with the tapers to avoid interference inside the multimode section. One can generally apply the delay lines to avoid the use of active elements, and they are less sensitive to changes in wavelength than the traditional method with bends. Using this method, we have designed and analyzed a zero-to-one mode converter. The converter exhibits minimum excess loss of 0.100 and 0.102 for TE and TM polarization, respectively. A very large 1-dB bandwidth exceeding 350 nm is achieved. 相似文献
11.
《Optics Communications》1987,61(1):11-15
A method for the formation of gradient index tapered optical waveguides with predicted shape is proposed and described analytically. The method is applicable for structures fabricated by electric-field assisted ion-exchange in glass. The technique is based on the control of the taper shape by applying a non-uniform electrical field during the waveguide formation process. For experimental verification optical waveguides with tapers were formed by electrically induced migration of K+ ions. An optical coupler based on such a tapered waveguide has demonstrated 1.2° outcoupled beam divergence. The method proposed can be used to form different integrated optical elements, e.g. mode filters, horn structures etc. 相似文献
12.
A hybrid method combining the three-dimensional (3D) beam propagation method (BPM) and a 3D finite-difference time-domain (FDTD) method is presented for the simulation of multimode-interference (MMI) couplers based on silicon-on-insulator (SOI) nanowires. This hybrid method makes it possible to have a robust analysis for the reflection properties while avoiding a time-consumed computation with a simplex 3D-FDTD simulation. The reflected power is sensitive to both the length and the width of the MMI coupler and thus one should choose the optimal values for good self-imaging. Furthermore, the reflection could be reduced by introducing tapers between the MMI section and the access waveguides. 相似文献
13.
Two mode-evolution-based low-loss compact-size integrated polarization rotators and transformers are presented. They are designed to fulfill the tasks of rotating mode polarizations between Gaussian-like strip waveguide modes and non-Gaussian-like slotted waveguide modes, as well as the mode transforming between horizontal and vertical slotted waveguides. Consisting of several adiabatic tapers, the presented devices can achieve complete polarization rotations and transformations between different classes of waveguide modes with a device length of tens of micrometers and with a negligible insertion loss. 相似文献
14.
We present a highly efficient integratable waveguide transformer that is capable of converting Gaussian-like waveguide modes to much more complicated non-Gaussian-like slot-waveguide modes, and vice versa. The structure consists of several pairs of complementary tapers capable of making this mode conversion virtually lossless. The capability of extremely low-loss mode transformation between these two classes of waveguides has been demonstrated by means of single- and double-slot transformers. Our simulation has shown that the total transformation losses are less than 0.01 and 0.02 dB per transformer, respectively, and can be easily achieved, with a total device length of less than 100 microm. 相似文献
15.
C. Vassallo 《Optical and Quantum Electronics》1994,26(3):S235-S248
Abstact Numerical data are presented on the operation of field transformers consisting of down-tapered rectangular waveguides. The propagation is analysed through a classical finite difference 3-D BPM method. A new adiabaticity criterion is proposed. Adiabatic and nonadiabatic (linear or exponential) tapers are investigated, allowing one to increase the field radius from 0.5 to 1.5 or 2 m at =1.5 m, with a coupling loss to a Gaussian beam from 0.1 to 1 dB. For a given overall length, the more efficient field expansion (but also the larger coupling loss) is obtained with an adiabatic design. According to preliminary results on the effect of fabrication imperfections, it seems that linear tapers would be less sensitive to defects than optimized adiabatic tapers. 相似文献
16.
Cam Nguyen 《International Journal of Infrared and Millimeter Waves》1987,8(12):1581-1603
A very simple yet accurate design procedure for the finline bandpass filters at millimeter wavelengths is presented. The technique enables the geometry of finline bandpass filters to be obtained accurately from simple closed-form equations and curves. Using this graphical approach, various millimeter-wave finline bandpass filters have been designed. Results in V-band (50 to 75 GHz) and W-band (75 to 110 GHz) are presented and indicate a good agreement between the calculated and measured performances. 相似文献
17.
18.
Hettrick SJ Mackenzie JI Harris RD Wilkinson JS Shepherd DP Tropper AC 《Optics letters》2000,25(19):1433-1435
We report what is to our knowledge the first operation of a planar dielectric tapered-waveguide laser. The waveguide laser is fabricated by potassium-ion exchange in Nd(3+) -doped BK7 glass and consists of a single-mode channel waveguide of a few micrometers' width followed by a linear taper up to a broad region with a width of ~180microm . A slope efficiency of 42% is found both in the tapers and in standard channel waveguides fabricated upon the same substrate, indicating that the tapers and the channels have similar internal losses; hence the low-loss nature of the tapered beam expansion. The output from either end of the tapered structure is found to be nearly diffraction limited. 相似文献
19.
An electrooptically induced optical waveguide can be formed by applying a DC voltage between electrodes fabricated on the surface of a crystal with strong electrooptic coefficients (for example, strontium barium niobate). Calculations of the refractive index profile and the optical mode size for such waveguides are presented. Approximate solutions for the fundamental mode are used to analyse the power coupling between a single-mode step-profile fibre and these waveguides. The power transmission losses in the straight and S-shaped waveguides are estimated by using a finite-difference beam propagation method (FD-BPM). The calculations predict that a new kind of modulator/switch can be realized with the induced waveguides. The important characteristics of these devices are discussed and compared with LiNbO3 optical waveguide modulators. 相似文献
20.
André G. Edelmann Stefan F. Helfert Jürgen Jahns 《Optical and Quantum Electronics》2011,42(8):531-540
In this article, we examine spectral transmission characteristics based on the self-imaging effect in plasmonic multimode
waveguides. For the analysis, we calculate the correlation between an input field and the field in the self-imaging plane.
We perform full vectorial computations using the Method of Lines as numerical method. The resulting transmission profile is
discussed with regards to the attenuation, the even and odd mode sets and for several structural parameters of the plasmonic
waveguide. The introduced transmission characteristic may offer the opportunity for the implementation of filtering operations
in plasmonic waveguides. 相似文献