Scattering in twin-cavity narrow-band interference filters illuminated by a monochromatic beam

The scattering behavior of the all-dielectric twin-cavity narrow-band interference filter is studied both in theory and in experiment in two cases, l(1) = l(2) and l (1) not equal l(2), where l(1) and l(2) are the optical thicknesses of the two cavities. It has been shown that the scattering properties are determined mainly by the spacers in which the electric-field intensities are large because of the presence of large standing-wave fields. The scattered light cones are found on both sides of the filter illuminated by a monochromatic light of which the wavelength (lambda(L)) is shorter than the peak wavelength (lambda(0)?) of the filter. The scattering angle of each cone is equal to the tilted angle of the filter when the peak wavelength of the filter shifts to the illumination wavelength. For the case l(1) not equal l(2), the distributions of the scattered light on both sides of the filter are quite different. The analytical calculations are in good agreement with experimental results. The possible applications of scattering in the twin-cavity filter in determining the bandwidth of the peak transmittance and the optical thicknesses of two spacers are addressed.     

一种测量光学滤波器参数的低相干方法

在光纤通信网络中, 以微环为代表的光学滤波器是实现在波长频段选择功能的重要器件。测量该器件的物理参数不仅是实际应用的需求更有利于设计更加复杂的滤波器结构。本文基于低相干干涉测量技术, 给出一种通用数学方法, 可获得复杂结构微环滤波器的物理参数。该方法引入数字滤波器概念以及 Z变换分析法来对光学滤波器进行建模, 并用简洁的线性方程组将干涉图中峰值以及传输函数的系数关联起来。对于一个给定的滤波器结构, 根据传输函数与物理参数的内在关联, 物理参数就能被准确地计算出来, 从而为器件的激光修正提供关键参数。实验结果表明, 该方法实现了低成本并且准确可行。     

利用WDM光纤耦合器的光纤光栅传感解调技术

根据 WDM 光纤耦合器波长解调方案的工作原理、偏振特性以及影响系统波长分辨力的因素,提出一种改进的利用 WDM 光纤耦合器的光纤光栅传感解调技术。该技术在原技术的基础上,采用偏振控制器控制入射光偏振状态,提高了解调的精度和稳定性。对 WDM 光纤耦合器的多次波长扫描结果表明,采用偏振控制器后,其波长误差可减小到 5pm 左右。实验采用 1540/1560nm的 WDM 光纤耦合器对单点光纤光栅应变传感器进行静态解调,结果表明:按此技术开发的解调系统具有 0.01nm 波长分辨力和 10nm 的波长线性解调范围。     

Hybrid wavelength-division and optical time-division multiplexed multiwavelength mode-locked semiconductor laser

A multiwavelength laser source composed of a single semiconductor optical amplifier and a commercially available off-the-shelf wavelength-division multiplexed (WDM) filter is constructed and tested under actively mode-locking operation. Five independent mode-locked wavelength channels are generated simultaneously, with a wavelength spacing of 1.6 nm established by the WDM filter. In addition, to demonstrate the potential of this mixed time-frequency, or hybrid WDM-optical time-division multiplexed, signal, we demonstrate a simple parallel-to-serial wavelength conversion to increase the pulse repetition rate of the mode-locked laser by a number of output wavelengths for applications in high-performance optical sampling applications.     

Design of all-optical tunable filter based on two-dimensional photonic crystals for WDM (wave division multiplexing) applications

In this paper, all-optical tunable filters based on two-dimensional photonic crystals with very small dimensions for optical telecommunication of WDM technology are designed and simulated. The structure is made of air holes in a dielectric background. The tuning is done by changing resonant defect angle. The channels obtained for this structure will be set in wavelength range of 1550 nm. Created channels are at wavelengths of 1550, 1551, 1552, and 1565 (16 channels); the distance between adjacent channels is 1 nm. Design and simulation of this filter is done by RSOFT software. Quality factor, transmission efficiency, and band gap shows that filter performance is very good.     

Effect of stress on performance of dense wavelength division multiplexing filters: optical properties

Thin-film filters used for dense wavelength division multiplexing (DWDM) applications are processed by a variety of deposition techniques, including ion-beam sputtering. Ion-beam sputtering produces high-quality coatings and provides flexibility of coating materials. However, DWDM filters consisting of oxide films that are reactively deposited by ion-beam sputtering, as in most sputter techniques, typically exhibit high levels of compressive stress. This affects the optical characteristics of the filters. Details of the filter passband characteristics and wave-front distortion illustrate the influence of the stress. Spatial variation of the stress on the filter surface causes the filter center wavelength to have spatial variation, and it causes the filter to have an asymmetric passband characteristic.     

基于复合式微纳光纤锁模器件的单腔多光频梳技术研究

光纤滤波器与锁模器件作为实现波长复用式单腔双光频梳光源的核心组件受到了研究者们的广泛关注。针对传统滤波器对偏振敏感、制作工艺复杂的问题,研制了一种基于微纳光纤的复合式器件,采用熔融拉锥方式进行微纳器件的制作,利用模间干涉产生滤波效应,利用热泳效应实现光沉积。将该复合器件应用于环形腔中,实现了1532,1543,1555 nm 的多波长锁模,且在不同偏振态下,波长漂移均不高于0.2 nm。该复合器件为实现单腔双光频梳、单腔三光频梳提供了新的解决方案,对于促进多光频梳技术在精密测量等领域的应用具有重要意义。     

Automated design and sensitivity analysis of wavelengh-division multiplexing filters

An automated approach to the design of wavelength-division multiplexing (WDM) filters is based on the combination of ideas from classical design approaches with an integer optimization technique. This approach turns out to be extremely efficient from a computational point of view and makes it possible to construct a set of significantly different filter designs with nearly equivalent spectral properties. The sensitivity of WDM filters is analyzed by a computer simulation of the deposition process with turning-point optical monitoring. This analysis enables the designer to compare feasibility properties of various filter designs.     

Wavelength-division multiplexing free-space optical interconnect networks for massively parallel processing systems

Wavelength-division multiplexing (WDM) techniques provide many advantages for building optical interconnect networks for massively parallel processing (MPP) systems. A design for a 1024-channel network for MPP systems based on the interconnection-cached network with vertical-cavity surface-emitting laser (VCSEL) arrays with one wavelength is described. We then show how a WDM version with four different wavelengths can increase the channel density. We also show how a WDM system can reduce the fan-in loss by a factor of 4. All the VCSEL's in each array are of the same wavelength, while different arrays use different wavelengths. We describe our experimental WDM subsystem containing four VCSEL arrays, operating at wavelengths of 843, 950, 970, and 980 nm, and three different WDM filters for multiplexing-demultiplexing. We present the operational results of the subsystem at 1 Gbit/s per channel.     

Wavelength filtering and demultiplexing devices based on ultrathin corrugated MIM waveguides

We have numerically investigated the transmission properties of spoof surface plasmon polaritons on the ultrathin corrugated metal–insulator–metal (MIM) waveguides with different grooves. A band-pass plasmonic filter with T-shaped grooves and a compact 4-way wavelength division demultiplexing (WDM) incorporating the filter have been proposed. The whole 4-way WDM is more compact by the use of corrugated MIM waveguides with meander grooves. The near electric field distributions show that electromagnetic waves at different frequencies are guided and propagate along different branches with good isolation between branches. The experimental and numerical results have shown good agreements and validated the functions of the 4-way wavelength splitter. We also numerically investigate the 4-way WDM at terahertz frequencies by scaling down the whole structure. It is believed that the spoof plasmonic devices can find more applications in the plasmonic integration platform, such as optical communications, signal processing and spectral engineering.     

基于光纤光栅的波分复用系统设计

设计了两种基于光纤布拉格光栅的波分复用(WDM)系统,一种为基于光纤光栅的四路波分复用系统,另一种为结合光分插复用器(OADM)的四路波分复用系统。给出了基于Opti System的波分复用光传输系统仿真模型,对复用及解复用后的光信号进行仿真得出了光谱图,对传输性能及Q因子、误码率、眼图等参数进行分析。在第二种结构中光纤光栅作为色散补偿器、光反射器和滤波器使用,可以实现任一波长的上载和下路。两种波分复用系统眼图张开良好,误码率均低于10e-9。证明了波分复用系统的正确性和设计方案的可行性。     

Dünnschichtfilter in der Telekommunikation

Market forces are pushing the performance of optics to their limits. Optical components must be developed to provide the best possible combination of manufacturability, performance and price. One vital step to success in creating WDM optics lies in a discipline that is often overlooked or misunderstood – coating engineering. A key technology for controlling light in WDM systems is the optical filter, which performs functions from simple filtering in multiplexers and demultiplexers, to more sophisticated functions in optical amplifiers, modulators and test equipment. The basic tool of multiplexing and demultiplexing devices, thin film filters offer accurate center wavelength, broad flattop passband and high isolation from adjacent and nonadjacent channels. Thin film filters are widely used for gain flattening, band splitting, C and L band separation and combining amplifier‐pump beams. Choosing the right thin‐film‐deposition process is essential for the efficiency and productivity of vacuum coating systems. LEYBOLD OPTICS has developed and optimized a comprehensive range of vacuum coating processes and process tools. LEYBOLD OPTICS has been proven the ability of producing shift‐free coatings on large substrate areas by means of PIAD (Plasma Ion Assisted Deposition) in many applications over the past ten years. The low loss and stress values achieved, especially with silica and tantala films, allows besides the production of narrow band pass filters (DWDM, CWDM) also the production of gain flattening filters (GFF). PIAD is considerably improving the properties of evaporated thin films by high energy ion bombardment during the growing of the film. PIAD allows to produce dense shift free thin films with high refractive index, good adhesion and extremely low absorption. With the Advanced Plasma Source (APS) LEYBOLD OPTICS has developed a high power plasma source for PIAD. The APS provides high ion current densities over a large surface area in a neutral plasma to produce high quality layers at a high productivity.     

Thermally stable narrow-bandpass filter prepared by reactive ion-assisted sputtering

Thermal stabilities of three-cavity narrow-bandpass (NB) filters with high-index half-wave spacers and 78-102 layers of Ta(2)O(5) and SiO(2) prepared by reactive ion-assisted bipolar direct-current (dc) magnetron sputtering of tantalum and silicon targets, respectively, were investigated. Pure argon and pure oxygen were used as the sputtering gas and the reactant, respectively. The oxygen gas was introduced and ionized through the ion gun and toward the unheated BK7 glass substrate. The refractive indices of single-layer Ta(2)O(5) and SiO(2) films were 2.1 and 1.45, respectively, at 1550 nm, which were comparable with those of films prepared by other ion-assisted coating techniques. The moisture-resistant properties of the films were excellent as evidenced from the water-immersion test, implying that the packing density of the films was close to that of their bulk materials. The temperature-dependant wavelength shifts of the NB filters were <3 x 10(-3) nm/ degrees C at temperatures of <75 degrees C, indicating that the temperature-induced wavelength shift of the filter was <0.15 nm when the temperatures were raised from room temperature to 75 degrees C, which was compliant with Bellcore GR-1209-CORE generic requirements of NB filters used for optical-fiber communication systems.     

Effect of stress on performance of dense wavelength division multiplexing filters: thermal properties

Thin-film filters used for dense wavelength division multiplexing (DWDM) applications are processed by a variety of deposition techniques, including ion-beam sputtering. Ion-beam sputtering produces high-quality coatings and provides flexibility of coating materials. However, DWDM filters consisting of oxide films that are reactively deposited by ion-beam sputtering, as in most sputter techniques, typically exhibit high levels of compressive stress. This affects the thermal characteristics of the filters. We have identified three thermal effects: center wavelength drift with temperature, center wavelength creep, and permanent center wavelength shift. The latter two are strongly dependent on the stress state of the filter. Models are presented that support the data that were taken.     

Gain improvement in a dual-stage S-band EDFA by filtration of forward C-band ASE

Gain improvement in a dual-stage S-band erbium-doped fiber amplifier (S-band EDFA) is demonstrated using a broadband fiber Bragg grating (FBG) operating in the conventional-band (C-band) region or a C-band/S-band wavelength division multiplexing (WDM) coupler which filters out the forward C-band amplified spontaneous emission (ASE) in the amplifier system, thus increasing the population inversion in the S-band region. The gain for the amplifier with the WDM coupler increases by about 8.5 dB with an input signal power of ?40 dBm, compared to that of the conventional dual-stage amplifier. The gain improvement varies from 4.0–9.2 dB at a wavelength region between 1480 to 1512 nm without a significant noise figure penalty.     

Synthesis and tuning of high-order Solc-type birefringent filters

Multiple optical wavelength passbands of Solc-type filters can be reselected within each fixed half-period by a scheduled rotation of each birefringent filter element. No additional wave plates are needed, and wavelength channels can be switched on or off while others continue unaffected. Designs for high-order transfer functions suitable for wavelength multiplexing are given along with experimental results for a set of fifth-order filters. This tuning concept is verified and its application in fiber-optic multiplexers is discussed.     

Photonic Crystal Drop Filter Exploiting Resonant Cavity Configuration

Band dropping devices are widely used in WDM application. In this paper the design of a two-dimensional photonic crystal drop filter is proposed. Different from the configuration reported in literature which are realized by means of a photonic bandgap waveguide and one or more resonant cavities, able to select a signal at desired frequency, the proposed drop filters exploits a novel system of point defects. The design is based on the accurate analysis of higher order resonant modes supported by the system and their parities. The temporal and spectral behavior of the device is studied using plane wave expansion (PWE) and FDTD methods.     

Inductive cross-shaped metal meshes and dielectrics

The Micro-Stripes program has been used to calculate resonance wavelengths and the bandwidth of inductive cross-shaped metal meshes in contact with dielectric layers. The shift of the resonance wavelength, depending on the thickness of the dielectric layers, has been studied for two refractive indices. The transmittance of two mesh filters with dielectric spacers or embedded in a dielectric has been calculated for specific alignment of the crosses of one mesh with respect to the other. Transmission line theory has been used to calculate the transmittance of two mesh filters with nonaligned crosses and dielectric layers. A coupled oscillator model has been used for interpretation of the interaction of resonance and Fabry-Perot modes.     

High-performance and highly stable 0.3-nm-full-width-at-half-maximum interference optical filters

Fabrication of very-narrow-bandpass optical tunable filters [(0.3 nm full width at half-maximum) (FWHM)] is reported. To improve the film densities, the O(2) ion-assisted deposition-method is used in the fabrication. In the succession of high- and low-refractive-index layers, the commonly used TiO(2) material is replaced by Ta(2)O(5), which suits the ion-assisted fabrication technique. The relative thicknesses of the filter multilayer structure of 1/2/1 are modified to 0.998/2.007/0.998, which reduces the shift difference in the central wavelengths with regard to the p and s polarizations when the filter is tilted. These improvements enabled fabrication of 0.3-nm-FWHM optical tunable filters with improved stability characteristics.     

Beam displacement and distortion effects in narrowband optical thin-film filters

A three-dimensional model for beam propagation through optical interference filters is presented. The model predicts a wavelength-dependent lateral beam displacement of tens or hundreds of micrometers in narrowband filters at an angle of incidence of only 3 degrees to 5 degrees . The effects of filter bandwidth, wavelength offset, angle of incidence, and beam size are investigated. The effect is experimentally confirmed for a 100 GHz filter at a 3.5 degrees angle of incidence.