High impact shock testing of fiber-optic components

MIL-S-901 High Impact Shock tests were performed on commercial-grade and ruggedized fiber-optic connectors, splices, and switches. Both single-mode and multimode connectors and splices were tested. Only multimode switches were tested. Transient losses of varying magnitudes and durations were observed. Most components suffered no permanent degradation.     

A modal cutoff approach to the study of buried channel waveguide couplers

We investigate the higher-order supermodes of symmetric buried channel waveguide (BCW) couplers with cores of square, rectangular, and trapezoidal geometries. We show how the cutoff wavelengths of these supermodes can be used to interpret the spectral response of a practical single-mode BCW coupler. Our results highlight the design constraints imposed by second-order supermodes. We also compare the behaviour of these couplers with that of circular-core couplers to illustrate how the geometry of each core affects the coupler cutoff characteristics.     

Finite element analysis of optically controlled non-linear directional coupler switches

Optically controlled two-way optical switches are useful for high-speed photonic switches and rapidly reconfigurable optical interconnection networks. A directional coupler forms such a switch because the field can be switched from one waveguide to the other by altering the optical length of the waveguide. Nonlinear materials are incorporated in the waveguide so that the optical path length may be altered by using an optical control beam to vary the intensity of light. A finite element method is described that enables the modelling of the non-linear dual waveguide structure for arbitrary waveguide shapes. Spurious modes are avoided in the transverse magnetic field method and non-linearity is handled by iteration and assuming an equivalent non-linear relative permittivity.     

Novel multimode interference devices for low index contrast materials systems featuring deeply etched air trenches

A novel design of multimode interference (MMI) device is proposed for photonic integrated circuits fabricated in low index contrast materials. In this design, deeply etched air trenches are used to define the boundaries of the multimode section to achieve strong lateral confinement. This results in superior imaging quality and therefore lower loss and imbalance, which can only be achieved in strongly guiding MMIs. However, the access waveguides remain weakly guiding, which is essential for low loss fibre connection. We demonstrate the merit of the design in 1 × 4 MMI power splitters. By introducing air trenches, loss decreases from 0.45 to 0.053 dB and imbalance decreases from 0.15 to 0.058 dB for TE polarization. For TM polarization, loss decreases from 0.46 to 0.003 dB and imbalance decreases from 0.16 to 0.067 dB.     

New Criterion for Designing Silica Multimode Interference Power Splitters

We introduce a new criterion for designing 1 × N silica multimode interference power splitters using overlapping-image multimode interference analysis. This criterion requires that widths of multimode waveguides in the devices should be greater than 2 times the product of port number N and effective widths of output waveguides. Better device uniformity can be achieved when the new criterion is satisfied.     

A 1 × 2 optical switch using one multimode interference region

A 1 × 2 optical switch using only one multimode interference (MMI) region is designed and demonstrated in GaAs/AlGaAs. This design makes a single MMI region works as MMI coupler using paired interference at “off” state and symmetric interference at “on” state. By injecting a current of 110 mA, the measured on/off ratio and crosstalk are 23 dB and 33 dB, respectively in the demonstrated device with GaAs/GaAlAs.     

New Criterion for Designing Silica Multimode Interference Power Splitters

We introduce a new criterion for designing 1 × N silica multimode interference power splitters using overlapping-image multimode interference analysis. This criterion requires that widths of multimode waveguides in the devices should be greater than 2 times the product of port number N and effective widths of output waveguides. Better device uniformity can be achieved when the new criterion is satisfied.     

Numerical characterization of nanopillar photonic crystal waveguides and directional couplers

We numerically characterize a novel type of a photonic crystal waveguide, which consists of several rows of periodically arranged dielectric cylinders. In such a nanopillar photonic crystal waveguide, light confinement is due to the total internal reflection. A nanopillar waveguide is a multimode waveguide, where the number of modes is equal to the number of rows building the waveguide. The strong coupling between individual waveguides leads to the proposal of an ultrashort directional coupler based on nanopillar waveguides. We present a systematic analysis of the dispersion and transmission efficiency of nanopillar photonic crystal waveguides and directional couplers. Plane wave expansion and finite difference time domain methods were used to characterize numerically nanopillar photonic crystal structures both in two- and three-dimensional spaces.     

Influence of dispersion on spectral characteristics of GADC optical filters

This text deals with the study of the characteristics of GADC filters by taking into account the dispersion. After having defined the characteristics of the filter, the influence of separation between the guides and filter length on the characteristics of the filter are studied. It is shown that dispersion plays a very important role in the evaluation of spectral features of the filter and can not be neglected.     

光束传播法分析硅交叉波导光开关的光学效应

运用光束传播法对硅交叉波导全内反射光开关中的光学效应进行了详细分析。结果表明：１）光学表面衰减波和泄漏波所引发的光遂道效应对开关特性有重要影响；２）反射端功率的相对大小于与反射区界面位置密切相关，其起因是古斯－汉欣位移；３）合理考虑这些因素的影响可以大大降低器件对折射率变化的要求。     

Switching and Fano resonance via exciton–plasmon interaction

We fnrther study theoretically the properties of switching and Fano resonance in a hybrid nanosystem consisting of two quantum dots （QDs） and a metal nanowire via exciton-plasmon interaction. The transmission of the single plasmon can be switched on or off in a wide-frequency region by adjusting the transition frequencies of the QDs and the phase of the propagating plasmon. Specifically, the dynamical mechanism of Fano-type transmission is further revealed and analyzed in detail.     

Polymer-silica hybrid 1 × 2 thermooptic switch with low crosstalk

A new polymer-silica hybrid 1 × 2 thermooptic switch with significantly low crosstalk is demonstrated. The top cladding and the core layers are composed of polymer, while the bottom cladding layer is made of silica. Since polymer and silica have algebraic signs of their thermooptic coefficients that are opposite to each other, the refractive index of the core changes in the opposite direction to that of the bottom cladding as the temperature is increased. Thus, switching operation is initially done through adiabatic mode evolution in the Y-branch, and then a heated waveguide arm in the Y-branch can enter into the optical cut-off region if the temperature is sufficiently high. Using this phenomenon, low crosstalk performance is achieved. The proposed device has a crosstalk of −35 dB, while most integrated-optic switches with a single stage have a relatively high crosstalk in the region of −20 dB. The switching power of the proposed device is about 70 mW.     

用有效折射率／有限元法设计1．55μmTi：LiNbO_3单模条波导及其方向耦合器

应用有效折射率／有限元法（ＥＩ－ＦＥＭ），考虑到ＬｉＮｂＯ３晶体和Ｔｉ扩散的各向异性，折射率增量与寻常光、非寻常光及波长色散的关系，设计了１．５５μｍ光波长下工作的ｚ切ｙ传播Ｔｉ：ＬｉＮｂＯ３单模条波导的制备参数，计算和分析了其单模特性、模式场分布及其变化规律．扩展了ＥＩ－ＦＥＭ，将其用于求解耦合波导系统，确定了方向耦合器的耦合长度及其波长色散特性．     

All-optical logic gates using semiconductor-based three-coupled waveguides nonlinear directional coupler

All-optical logic gates with nonlinear optical (NLO) properties of three-coupled identical waveguides have been proposed and designed theoretically in a unique semiconductor-based symmetric structure. The model uses the NLO interactions of the coupled waveguides, like Kerr effect and Two Photon Absorption (TPA). Unlike the previous studies, we take into account higher order NLO effects of semiconductors such as Free Carriers (FC) and loss to control the switching operation. These NLO phenomena lead to high functionality in a simple unique structure. Therefore, in this work, by setting the input intensity of the waveguides, the logic AND, OR, NAND, and NOR gates are designed in a unique structure with different lengths. Our analysis deals with continuous waves (CW) region and the results are valid for the ranges of short optical pulses with time duration longer than FC life time.     

A comparative numerical study of soliton switching in a nonlinear directional coupler with saturating nonlinearity

A detailed numerical study of soliton switching in a nonlinear directional coupler with saturating nonlinearity is carried out. All commonly used models have been studied. Relevant physical characteristics for switching have been determined, compared and discussed.     

Modeling of circular integrated optical microresonators by 2-D frequency domain coupled mode theory

Circular integrated optical (ring or disk) microresonators are increasingly employed as compact and versatile wavelength filters. In this paper, we investigate a 2-D frequency domain model for these devices, based on spatial coupled mode theory. The microresonators are functionally represented in terms of two couplers with appropriate connections using bent and straight waveguides. The abstract scattering matrices of the couplers and the propagation constants of the cavity bends allow to compute the spectral responses of the resonators. Capitalizing on the availability of rigorous analytical modal solutions for bent waveguides, the constituent bent-straight waveguide couplers are modeled using a spatial coupled mode formalism derived by means of a variational principle. The resulting scattering matrices show reciprocity properties as expected according to the symmetry of the coupler structures. We present results for the spectral response and field examples for microresonators with mono- and multi-modal cavities for TE and TM polarizations. Comparisons with finite difference time domain simulations show very good overall agreement.     

Passive fiber-optic components made by the fused biconical taper process

The rapid development and deployment of optical fiber for a variety of applications has resulted in a similarly rapid development of myriad components to effectively utilize the fiber. Thus, for example, significant work has been done over the past several years in the development of sources and detectors, connectors, and splices. These components share the common trait of being external to the fiber and hence not part of the fiber per se. Another class of components, however, is made from the fiber itself. A number of components, such as polarizers, analyzers, and mode or wavelength filters, require only simple bending of the fiber in a specified manner. On the other hand, such techniques as polishing, etching, and heating can also be used to alter the transmission properties of the fiber.

While a number of interesting devices have been made by these procedures, the present paper is limited to devices made by the biconical taper process. If a fiber is heated and stretched, a biconical taper is formed, which can significantly alter the transmission characteristics of the fiber. Interesting wavelength filters and sensors can be made with single tapers or combinations of tapers. Moreover, if two or more tapered fibers are fused, then coupling of light from one fiber to another can be achieved. The tapering and fusing processes can be used to make wavelength-enhanced couplers, which can be used as wavelength-division multiplexers or nearly wavelength-independent couplers or splitters.

In this paper, we discuss the components made by the biconical taper process, their fabrication, in both theory and practice, and their performance. Practical implementations of these components are also discussed, including their manufacturability and reliability.     

Waveguide sub‐wavelength structures: a review of principles and applications

Periodic structures with a sub‐wavelength pitch have been known since Hertz conducted his first experiments on the polarization of electromagnetic waves. While the use of these structures in waveguide optics was proposed in the 1990s, it has been with the more recent developments of silicon photonics and high‐precision lithography techniques that sub‐wavelength structures have found widespread application in the field of photonics. This review first provides an introduction to the physics of sub‐wavelength structures. An overview of the applications of sub‐wavelength structures is then given including: anti‐reflective coatings, polarization rotators, high‐efficiency fiber–chip couplers, spectrometers, high‐reflectivity mirrors, athermal waveguides, multimode interference couplers, and dispersion engineered, ultra‐broadband waveguide couplers among others. Particular attention is paid to providing insight into the design strategies for these devices. The concluding remarks provide an outlook on the future development of sub‐wavelength structures and their impact in photonics.

     

Absorption and transmission spectral measurement of fiber-optic components using supercontinuum radiation

We report on broadband absorption and transmission measurements using supercontinuum sources generated in microstructured fibers. The advantages of this measurement technique include high brightness and broad bandwidth. Furthermore, the high spatial coherence of the supercontinuum source allows for efficient coupling into the device under test compared to standard light bulbs. Employing this technique, we measure the impurity absorption spectrum of Erbium-doped fibers with both low and high dopant concentration. The transmission spectra of a photonic bandgap fiber and a high-finesse fiber cavity are also characterized.     

切伦科夫型级联二阶非线性效应的解析优化

在考虑传输损耗的基础上，用解析的方法详细分析和优化了平板波导中切伦科夫型级联二阶非线性效应引起的基波非线性相位移动和基波功率的变化，结果表明，基波非线性相位移动和基波功率变化对波导参数和光波波长有强烈的依赖关系。另外，即使不引入周期畸反转，只要对波导厚度和入射光波波长合理选择，就可以在基波功率消耗很小的情况下得到相当大的基波非线性相位移动（＞2π）。不引入畸反转可以避免制作高质量反转结构的技术困难，对该结构在全光开关器件中的实际应用有重要的价值。