The characteristics of NRD waveguide gratings

The filter characteristic of NRD waveguide grating is investigated rigorously by combining network approach with mode matching theory. Numerical examples are shown and compared with experiment results.     

Arrayed waveguide gratings for wavelength routing

Wavelength routing can be performed in the optical domain for both long-haul and passive optical networks. Arrayed waveguide gratings (AWGs) can perform wavelength routing for a large number of optical channels and provide a high level of functionality on an integrated chip. The AWG guides light on a planar lightwave circuit into an array of waveguides that provide dispersion to separate the different wavelengths of light. Routing functions can be performed on individual wavelengths. With this technology, optical cross-connects, optical add/drop multiplexers, and passive optical routers have been demonstrated. Performance issues-such as insertion loss, polarization dependence, passband shape, passband position, crosstalk, and temperature dependence-are being addressed so that AWGs will be practical for deployment into systems     

阵列波导光栅的研究进展

综述了阵列波导光栅的研究进展,分析了其多功能和多应用的特性,展示了它在未来波分复用通信网中巨大的应用前景。     

Modeling and design of arrayed waveguide gratings

The purpose of this paper is twofold. First, a simple but comprehensive and powerful arrayed-waveguide grating (AWG) field model is presented which, based on Fourier optics, borrows some principles of that developed by Takeouchi and coworkers [see, Opt. Express, vol. 6, p. 124, 2000] for the analysis of reflective-type AWGs for optical signal processing, but at the same time adds more features, such as the calculation of device losses and the refinement of the mathematical model to obtain a simple expression for the output field for any input-output waveguide configuration where the meaning of the different high-level parameters of the AWG becomes very clear to the reader. Second, we elaborate on the model developed to present an useful design procedure of the AWG based on two steps illustrated by design flowcharts     

Apexes-linked circle gratings for low-loss waveguide bends

A low-loss waveguide bend with two apexes-linked circle gratings based on the concept of multiple phase compensation is designed. The apexes-linked circle gratings not only compensate the phase-difference in the bend corner, but also avoid distorting the eigenmode. Simulation results predict that the phase front of the modal field can be tilted correctly in the wide-angle waveguide bend. The transmitted power efficiency can be as high as 89% for bending angle up to 10°     

阵列波导光栅技术及其研究进展(本期优秀论文)

分析了AWG器件的基本原理,并介绍了近年来人们在研制小尺寸AWG、增加器件信道数量,改善器件的损耗、串扰、偏振敏感性和温度相关性等性能,以及AWG与其他器件集成等方面的最新研究进展.     

Temperature insensitive arrayed waveguide gratings on InPsubstrates

A temperature insensitive arrayed waveguide grating (TI-AWG) with an InGaAsP-InP material system is proposed. Less than 0.1 Å/°C temperature dependence for all eight channels was achieved for the first time even though we used the InGaAsP-InP material system. This novel characteristic is in good agreement with the design principle of the TI-AWG     

Evanescent-wave interferometric nanoscale photolithography using guided-mode resonant gratings

Generation of interference patterns of the evanescent electromagnetic waves with significantly subwavelength period using guided-mode resonant gratings is studied. The potential application field is the near-field interference lithography aimed at fabrication of periodic structures with nanoscale features. Calculations, based on the rigorous coupled-wave analysis of Maxwell’s equations, demonstrate the possibility of obtaining high-quality interference patterns by means of evanescent diffraction orders enhancement at the resonance conditions. The interference pattern feature size is up to 8 times smaller than the incident wavelength and the intensity at the interference maxima exceeds the incident wave intensity by an order-of-magnitude. The possibility of generating high-frequency interference patterns using low-frequency diffraction gratings is demonstrated. The 1D and 2D interference patterns with the periods 6 times smaller than those of the used diffraction gratings are generated.     

Analysis of a wide resonant strip in waveguide

An analysis has been developed to calculate the susceptance due to a wide resonant strip on the transverse plane of a rectangular waveguide. The theory is based upon a variational form for the susceptance, where the current distribution is determined by the moment method. Accurate results have been obtained for the wide strips as confirmed by the measurements     

Close coupled resonant aperture inserts for waveguide filteringapplications

A two-layer frequency selective surface (FSS) is used as a very compact and lightweight transverse waveguide filter element. A narrow-hand transmission response is produced from two layers, which, otherwise, in isolation would exhibit a broadband response. Measured results are compared with theoretical data obtained from a Transmission Line Matrix (TLM) based modeling method. Reduction in the passband bandwidth of a factor of four has been achieved using the proposed structure     

Generalized Bloch wave analysis for fiber and waveguide gratings

We have developed a generalized Bloch wave approach for the analysis of aperiodic gratings. This method yields both a macroscopic (i.e., reflection or transmission coefficient) as well as a microscopic (i.e., dispersion diagram and microstructure of the propagating internal field) characterization of fiber and waveguide aperiodic gratings     

Analysis of two narrow transverse resonant strips in waveguide

An analysis is made for the susceptance of two narrow transverse strips of differing widths and depths, unsymmetrically located in a rectangular waveguide. The analysis is based on extremization of the current-density ratio between the two strips, through use of the variational principle. The results are experimentally verified.     

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.     

Theoretical analysis of resonant waveguide optical second harmonicgeneration devices

Theoretical analysis of resonant waveguide SHG devices is presented. Mathematical expressions for SHG interaction in waveguides for arbitrary initial conditions were derived and applied to the analysis. Dependences of SHG efficiency on pump amplitude of singly and doubly resonant devices with various cavity mirror reflectivities, phase-mismatch, and propagation losses are compared with that of traveling-wave devices. It is shown that in resonant SHG devices much higher efficiency is obtained for low pumping power than in traveling-wave device. It is found, for the first time, that complete conversion can be attained for a finite input power in the doubly resonant devices. However, the efficiency is very sensitive to the propagation losses     

Surface morphology of refractive-index waveguide gratings fabricated in polymer films

The characteristic modifications are reported on the surface of polymeric waveguide film in the process of volume-grating fabrication. The light from a mode-locked 76 MHz femtosecond laser with pulse duration of 200 fs and wavelength of 800 nm is focused normal to the surface of the sample. The surface morphology modifications are ascribed to a fact that surface swelling occurs during the process. Periodic micro-structure is inscribed with increasing incident power. The laser-induced swelling threshold on the grating, which is higher than that of two-photon initiated photo-polymerization (TPIP) (8 mW), is verified to be about 20 mW. It is feasible to enhance the surface smoothness of integrated optics devices for further encapsulation. The variation of modulation depth is studied for different values of incident power and scan spacing. Ablation accompanied with surface swelling appears when the power is higher. By optimizing the laser carving parameters, highly efficient grating devices can be fabricated.     

Multiplexed computer-generated waveguide hologram using gratings with different spatial frequencies

We propose and experimentally demonstrate a multiplexed off-plane computer-generated waveguide hologram, using waveguide gratings with different spatial frequencies. Two spot arrays are produced at different deflection angles and simultaneously focused at different focal lengths above the waveguide. Electron-beam lithography and reactive ion beam etching were used in fabricating this device. The uniformity error and the diffraction efficiency were measured to be approximately 10% and 55%, respectively.     

Polymer waveguide notch filter using two stacked thermooptic long-period gratings

A polymer waveguide notch filter using two stacked thermooptic long-period gratings is proposed. It is a long-period waveguide grating whose transmission spectrum can be dynamically controlled. Thermooptic index perturbation, i.e., grating is temporarily induced by two groups of periodic heaters stacked vertically on the filter surface. The periods of the two groups are determined such that two different resonance bands are generated in the spectrum by the respective groups. Thus, the overall spectrum may be actively shaped by controlling the individual power applied to the two groups. Its feasibility is demonstrated experimentally by fabricating it with thermocurable polymers.     

Arrayed waveguide gratings based on perfluorocyclobutane polymers for CWDM applications

Compact wavelength-division multiplexers based on arrayed waveguide grating structures have been designed and fabricated for short-haul communication network applications using low-loss perfluorocyclobutane-containing polymers. The devices exhibit high thermal stability and low on-chip losses. The average on-chip loss was <6 dB, including the fiber-to-chip coupling loss. The output uniformity across five channels was typically /spl plusmn/0.5 dB, and the thermal sensitivity of the central wavelength was 0.045nm//spl deg/C. Optimization of devices through material properties and fabrication process parameters is discussed.     

Low switching threshold using nonlinearities in stopband-tapered waveguide Bragg gratings

We numerically study the nonlinear switching characteristics in a waveguide grating with a linearly tapered stopband. This type of design shows promising results in decreasing the threshold switching power, while simultaneously preserving a significant extinction ratio. We find that the switching threshold changes linearly with the tapering coefficient. The physical explanation for these phenomena is discussed. Potential applications for this type of device include all-optical switches and isolators.