Design and Simulation of Broadband IR integrated Waveguide Amplifiers with Long - Period Waveguide Grating Filter

A novel broadband IR integrated Er-Yb codoped phosphate glass waveguide amplifier with a long-period waveguide grating is proposed. The long-period waveguide grating, which is used as a gain equalizer, is directly fabricated in the waveguide. The amplifier model is based on propagation and population-rate equations and includes both uniform and pair-induced up-conversion mechanisms. It is solved numerically by combining overlapping integral and Runge-Kutta(RK) algorithm. The intrinsical gain spectrum of the proposed amplifier is obtained by solving a set of rate and power propagation equations and, the deleterious gain peaking is reduced by the long-period waveguide grating filter. The effects of transmission spectrum of the proposed long-period grating on flattening gain are discussed. An average gain  ~ 20dB between 1532 nm and 1565 nm with gain difference of  < 3dB is achieved.     

Silicon Photonic Wire Filter Using Asymmetric Sidewall Long-Period Waveguide Grating in a Two-Mode Waveguide

We demonstrate a silicon photonic wire filter using asymmetric sidewall long-period waveguide gratings for the first time. The proposed device consists of single-mode waveguide sections, a two-mode section with corrugated gratings, and taper sections to connect them. The operation of this device is based on the codirectional coupling between two core modes. By adopting a high refractive index contrast waveguide, the period and depth of grating are given as 4.44 m and 5 nm, respectively. Thus, the total length of long-period grating is significantly reduced to 260 m. The measured maximum attenuation at the center wavelength is about 13 dB. The bandwidth of the transmission dip is 15 nm. Finally, issues on the design and the performance of our device are discussed.     

Design and Simulation of a Narrow Passband Electro-Optical Tunable Filter with Band-pass and Band-rejection Output

An electro-optical tunable filter comprised of two paralleled identical long-period waveguide gratings is proposed in this paper. The filter has one input port and two separate output ports, outputting band-pass and band-rejection light respectively. Using poled electro-optical polymer material to fabricate its waveguide cores enable the filter’s tuning speed to approach nanosecond order. With the aid of long-period waveguide gratings, the tuning range of the filter is Λ times larger than the conventional electro-optical filters. We built up a model to design and simulate the proposed tunable optical filter. We investigate the relationship between the parameters of the long-period waveguide grating and the characteristics of the tunable filter, such as tuning range and FWHM. The simulation results show that the tunable optical filter can realize high-speed tuning in the wavelength range of 1530 nm to 1560 nm, and the FWHM width can reach 0.8 nm. Compared with the conventional optical filters, the results show that a high-speed widely tunable optical filter with narrow pass band can be achieved.     

基于长周期光栅的宽带磷酸盐玻璃波导放大器

提出一种基于长周期波导光栅的宽带集成Er-Yb掺杂磷酸盐玻璃集成波导放大器,其中增益平坦光栅滤波器直接刻蚀在有源波导上.放大器模型建立在考虑了上转换之后的传输与速率方程基础上,利用重叠积分与龙格-库塔相结合的方法进行求解.放大器的本征增益谱通过求解重叠积分龙格-库塔方程得到,放大器的有害增益峰由长周期波导光栅滤波器来消除.讨论了长周期波导光栅透射谱对放大器增益平坦的影响.数值计算结果表明,在1 532～1 565 nm范围内,放大器的平均增益约为20 dB,增益抖动小于3 dB.研究结果表明,该结构可有效地消除本征增益谱中的峰值增益,提高放大器的增益平坦带宽.     

Fabrication and characterization of annealed proton exchanged long period waveguide grating in x-cut LiNbO3

In this paper, a long-period waveguide grating was fabricated in x-cut lithium niobate substrate by patterned annealed proton exchange waveguide fabrication process. The waveguide mode characteristic was evaluated using a charge-coupled device (CCD) camera. It shows that the waveguide is single mode transmission at a wavelength of 1 550 nm. The transmission spectra of the long period waveguide gratings were measured by optical spectrum analyzer (OSA) and show an extinction ratio of ~17 dB and a 3 dB bandwidth of ~10 nm at the resonant wavelength. The resonant wavelength moves toward to the long wavelength direction as the waveguide width-difference increases in the same period, and also shifts toward to the long wavelength direction with the increase of the period in the case of the same waveguide width-difference. The method of fabricating a long period waveguide grating based on a patterned annealed proton exchange technique simplifies the fabrication process, and at the same time, reduces the fabrication cost.     

Phase-shifted Bragg grating filters in polymer waveguides

We fabricated a very narrow-band 0.03-nm (5-GHz) phase-shifted Bragg grating filter at 1290 nm on an LD-3 polymer ridge waveguide. The grating was post processed onto the waveguide by photobleaching using a 457-nm argon ion laser with a phase mask. We present the details of the fabrication process and a measurement of the filter spectrum with an analysis.     

Tunable notch filter using a thermooptic long-period grating

This paper proposes a tunable notch filter using a thermooptic long-period grating and investigates it theoretically. This notch filter is in the form of an integrated optical device and is based on a simple structure as compared with existing integrated optical notch filters. The thermooptic grating denotes a thermooptic index perturbation induced by periodic heaters. The attenuation of a resonance band in the transmission spectrum of the proposed notch filter can be controlled by adjusting the electric power applied to the periodic heaters. Employing the heat transfer theory and the coupled-mode theory, the proposed filter is designed and analyzed. The paper also presents analytic expressions for the temperature change due to a heater and the coupling coefficients due to the thermooptic grating. This filter may have potential as a compact dynamically controllable device like a tunable gain flattening filter.     

在光纤拼接处刻写长周期光纤光栅及其传感应用

在"单模光纤-细芯光纤"拼接处刻写了 Type Ⅱ 型长周期光纤光栅,构成一种高温光纤传感器.该传感器实际由2 段不同的长周期光纤光栅级联构成,在第二个光栅形成了 Mach-Zehnder 干涉,因此,传感器透射谱由长周期光纤光栅与Mach-Zehnder 干涉仪共同作用形成.利用传感器的透射谱与环境温度的线性变化关系...     

探测波导全息光栅傅里叶变换光谱的新方法

提出一种利用波导全息光栅分光元件 ,通过测量波导光栅附近区干涉条纹 ,经快速傅里叶变换达到测量光谱的新方法。讨论了波长测量范围和光谱分辨率。给出了在设计波导光栅、确定探测器时应该考虑的几个问题。对系统测量误差进行了分析。该光谱探测方法具有光谱分辨率高、波长范围宽和结构简单等优点。     

Gain-flattening filter using long-period fiber gratings

We propose a novel structure for a gain-flattening filter, in which a conventional long-period fiber grating (LPFG) and a phase-shifted LPFG are written closely. The transmission characteristics are investigated in the case of a closely arranged configuration. For the fabrication of a phase-shifted LPFG, a UV-trimming method to control the amount of the phase shift is examined theoretically and experimentally. Finally, a 67-mm-long LPFG gain-flattening filter designed for an erbium-doped fiber amplifier is fabricated and the measured spectrum is shown     

Realization of Long-Period Corrugated Grating in Silica-on-Silicon-Based Channel Waveguide

Long-period corrugated grating in silica-on-silicon-based channel waveguide is realized by making periodic corrugation on top of a relatively high-indexed (contrast ap.8%) Ge-doped silica waveguide, which is sandwiched between undoped silica undercladding and boro-phospho-silicate-glass overcladding layers. Resonance wavelength of the 15-mm-long grating is found at ~1581 nm, having negligible polarization dependency at room temperature, with a grating strength of ~11 dB and 3-dB bandwidth of 7 nm. The temperature characteristic of the grating is also investigated, which is found to be similar to that of the long-period fiber grating. This device has significant potential for various integrated-optic communication and sensing applications.     

Flattened Broadband Notch Filters Using Guided-Mode Resonance Associated With Asymmetric Binary Gratings

In this letter, the broadband notch filter exhibiting a flattened bandstop spectral response is experimentally demonstrated for the first time by using the guided-mode resonance associated with the periodic subwavelength structure possessing asymmetric binary grating profiles. The proposed filter consisting of grating and waveguide structures is realized by utilizing a single-layer poly-silicon film deposited on a quartz substrate. The asymmetric grating profile is carried out by dividing the one-filling-factor binary structure into the one with two distinct filling factors within one identical period. A flat bandstop spectral response at the central wavelength of 1.22 mum is obtained under normal incidence for transverse-electric polarization. Its transmittance of bandstop spectrum can be suppressed as low as -20dB within a broad spectral range of 85 nm and its corresponding Deltalambda/lambda is larger than 6%. The spectra under oblique incidence are demonstrated to verify the proposed filter has a high immunity for the angular deviation up to 20deg     

基于表面等离子波耦合的流体波导光栅耦合器

提出了一种由金属光栅和流体光波导结构组成的,基于表面等离子波耦合的光栅耦合器。利用光栅的衍射效应,将金属光栅与介质分界面之间产生的表面等离子波耦合到流体光波导中,并且能够沿着流体光波导稳定地向前传播。通过采用基于有限时域差分算法的FDTD Solutions软件对光栅耦合器进行了参数优化及特性分析,通过优化使该结构在650 nm波长下的耦合效率达到56%。此外,由于该结构对TE偏振光和TM偏振光的选择比达到70∶1,因此具有偏振器的功能。同时由于TE偏振光耦合频谱的频带宽度仅为20 nm,该结构还具有窄带滤波的作用。此外,还研究了光栅结构参数、入射角以及流体折射率对耦合频谱的影响。     

Lithium–Niobate Channel Waveguide for the Realization of Long-Period Gratings

We propose a special lithium-niobate (LiNbO₃) single-mode waveguide for the realization of long-period gratings, which consists of a channel core embedded in a thin slab cladding. We fabricated the waveguide on a z-cut LiNbO₃ substrate with a two-step proton-exchange process and demonstrated its suitability for grating application with a number of removable photoresist long-period gratings deposited on the waveguide surface. The waveguide fabrication process and the LiNbO₃ waveguide structure could be further explored for the development of electrooptic gratings for high-speed applications.     

Tunable waveguide transmission gratings based on active gain control

Mode loss or gain can have a significant effect on the operation of waveguide transmission gratings as optical filters. Taking for example a long-period grating (LPG), we present a computer simulation that accounts for these effects. We show that cladding loss or gain result in qualitatively different LPG spectral behavior that can be used as a tuning mechanism in guiding structures where cladding mode properties can be controlled. One possible control mechanism is to have pump-driven gain in a doped cladding, which can perform gradual loss compensation and eventually gain excitement. Based on simulation results, we propose new approaches to tuneable amplifying filter designs in special fibers, as well as grating assisted co-directional couplers for integrated optics platforms.     

级联长周期光纤光栅和Bragg光纤光栅的光学特性

基于耦合模理论及传输矩阵法,给出了级联长周期光纤光栅和Bragg光纤光栅系统(CLBG)的耦合模方程与总传输矩阵,理论模拟了CLBG的反射谱,得到的反射峰位置与已知文献中所给出的两个反射峰的位置关系相吻合。在此基础上,模拟了镀膜CLBG之间的光纤长度、薄膜折射率、薄膜厚度等参数对反射谱的影响。由仿真结果可知,CLBG反射峰中受长周期光纤光栅和Bragg光纤光栅共同影响产生的反射峰对外界环境的变化非常敏感,其对薄膜折射率的分辨率较单个镀膜长周期光纤光栅高2个数量级,表明CLBG在薄膜传感领域具有重要的应用价值。     

一种新型四级叠层波导带通滤波器

提出一种新型四级叠层介质波导谐振器滤波器的结构及其设计方法。建立三维有限分析模型讨论了二级介质波导滤波器耦合特性,设计出二级片式介质波导谐振器滤波器。采用LTCC工艺叠加两块二级片式波导滤波器得到四级叠层波导滤波器,通过三维有限元分析模型绘制出四级叠层波导滤波器耦合特性曲线。最终设计出的四级叠层波导滤波器长8.8mm、宽6.2mm、厚1.6mm,中心频率5.2GHz,带宽300MHz,带内波动0.1 dB,插损0.8dB。其具有小型化、低插损以及适合表面帖装等特点,能满足下一代WLAN系统应用要求。     

Widely tunable polymer long-period waveguide grating with polarisation-insensitive resonance wavelength

A long-period waveguide grating in a polymer channel waveguide, which consisted of a benzocyclobutene core and an epoxy cladding, has been fabricated. By changing the stress in the waveguide through etching of the cladding width, a polarisation-insensitive resonance wavelength thermo-tunable from 1520 to 1610 nm with a temperature range of only 8/spl deg/C was achieved.     

传输矩阵法求解长短周期级联光纤光栅传输谱

基于光纤光栅的模式耦合理论,用传输矩阵法对长短周期级联光纤光栅的传输谱特性进行分析。先由耦合模方程分别得到长周期光纤光栅(LPFG)、连接光纤段和短周期光纤光栅(FBG)的传输矩阵,然后将它们相乘得到总的传输矩阵,最后再结合边界条件求得长短周期级联光纤光栅(CLBG)的传输谱。进一步对CLBG的传输谱进行了数值模拟,并通过实验进行了验证。实验结果表明,CLBG的传输谱中出现了由纤芯模和包层模耦合形成的两个谐振峰,与模拟计算的结果一致,证明了传输矩阵法求解CLBG传输谱的可行性,为CLBG在多参量传感和测量领域的广泛应用提供了理论支持。     

Miniaturized Bandpass Filters With Double-Folded Substrate Integrated Waveguide Resonators in LTCC

This paper proposes miniaturized bandpass filters with double-folded substrate integrated waveguide (SIW) resonators using multilayer low-temperature co-fired ceramic (LTCC) technology. Formed by inserting a metal plate with two orthogonal slots into the cavity, the double-folded SIW resonator is used for the circuit size reduction with its footprint about a quarter of the conventional ${rm TE}_{101}$ mode. With LTCC technology, there is more flexibility to organize the cavities of filters because of the 3-D arrangement. The vertically stacked cavities are coupled by “L”- or “U”-shaped slots, and if arranged horizontally, by an inductive window on the common sidewall or a suspended stripline between the cavities. Through experimental measurements and simulations at both the $Ka$- $V$ -bands, it has been demonstrated that the proposed filter has compact sizes and good frequency responses. The area of the fully stacked Chebyshev filter has 88% size reduction in comparison with a three-pole planar waveguide filter, while the vertically stacked quasi-elliptic filter has 74% size reduction in comparison with a four-pole planar waveguide filter.