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In this work, fabrication of multilayers of colloidal CdSe/CdS/ZnCdS core/wings/shell nanoplatelets (NPls) on solid substrates by layer-by-layer deposition technology is successfully demonstrated for the first time. Integration of multilayers of nanoplatelets into polymeric waveguide resulted in strong dichroism in absorption and polarization effects in photoluminescence with preferable absorption and emission of TE (horizontal) mode that evidences about in-plane orientation of NPls relative to the planar waveguide. The propagation of the excitation and emission light along the waveguide was thoroughly investigated both theoretically and experimentally for different number of NPl layers. [ABSTRACT FROM PUBLISHER]

A polarization-insensitive quantum dot semiconductor optical amplifiers (QD-SOAs) have been studied for use in future optical communication systems. A part of our work shows that the optical polarization property in QDs depends on both their aspect ratio and strain. To control these two parameters, we propose the use of strain-controlled columnar QDs (SC-CQDs), which exhibit a high aspect ratio and have strain-controlled side barriers for polarization-insensitive operation in the 1.5-μ m wavelength band. QD-SOAs with these optimized SC-CQDs demonstrated polarization-insensitive characteristics. They showed a gain of 8.0 dB with polarization dependence of the gain as low as 0.4 dB, -3-dB saturation output power of 18.5 dBm at a wavelength of 1550 nm, and error-free amplification at a bit rate of 40 Gbit/s. [ABSTRACT FROM PUBLISHER]

A novel class of optical waveguides with a box-shaped cross section consisting of a low-index inner material surrounded by a thin high-index coating layer is presented. This original multilayered structure widens the traditional concept of index contrast for dielectric waveguides toward a more general concept of effective index contrast, which can be artificially tailored over a continuous range by properly choosing the thickness of the outer high-index layers. An electromagnetic analysis is reported, which shows that the transverse electric and transverse magnetic modes are spatially confined in different regions of the cross section and exhibit an almost 90degC rotational symmetry. Such unusual field distribution is demonstrated to open the way to new intriguing properties with respect to conventional waveguides. Design criteria are provided into details, which mainly focus on the polarization dependence of the waveguide on geometrical parameters. The possibility of achieving single-mode waveguides with either zero or high birefringence is discussed, and the bending capabilities are compared to conventional waveguides. The feasibility of the proposed waveguide is demonstrated by the realization of prototypal samples that are fabricated by using the emerging CMOS- compatible Si3N4-SiO2 TriPleX technology. An exhaustive experimental characterization is reported, which shows propagation loss as low as state-of-the-art low-index-contrast waveguides (< 0.1 dB/cm) together with enhanced flexibility in the optimization of polarization sensitivity and confirms the high potentialities of the proposed waveguides for large-scale integrated optics. [ABSTRACT FROM PUBLISHER]

A polarization-insensitive waveguide design featuring a novel asymmetric ridge structure is proposed. This design relaxes former stringent constraints imposed on material compositions (i.e., refractive indices) and geometrical dimensions in an attempt to reach low polarization sensitivity over a broad wavelength operating range. In conjunction with a bulk active region with an isotropic gain, such a design is highly desirable for its potential to eliminate the polarization dependence of the optical gain in semi-conductor optical amplifiers or output power in super luminescent light-emitting diodes. [ABSTRACT FROM AUTHOR]

An optical waveguide with multilayer films with the characteristics of 1.31µm reflection/1.55µm transmission is analyzed by means of the beam propagation method. First, the power-conservation wide-angle beam propagation method for TM wave analysis is derived. In the process, the evaluation equation for the power is presented and its effectiveness is demonstrated. Next, the characteristics of the filter structure in which the vertex angle of the input and output waveguides is 45° are discussed. After the location of the effective reflection point in the filter is investigated, the wavelength dependence is discussed. It is shown that the difference in the characteristics of the two polarizations can be kept small if the vertex angle is 45°. In order to obtain wavelength separation characteristics with small polarization dependence in a structure with a 90° crossing angle of the input and output waveguides, a structure is presented in which two waveguides with multilayer films and a vertex angle of 45° are cascaded. It is demonstrated that a reflectivity of 98% can be realized for the TE wave and 88% for the TM wave. Finally, it is shown that 98% reflection/98% transmission can be realized for the TE wave and 95% reflection/94% transmission for the TM wave by inserting a spacer layer (1/2 wavelength layer) into the multilayer filter. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 89(1): 11–18, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.20214 [ABSTRACT FROM AUTHOR]

We present a rigorous comparison of the unique characteristics of directional couplers and multimode interferometers based on the unique properties of high-index contrast ridge waveguides. The two devices are intimately related as the multimode interference (MMI) is derived from the directional couplers (DCs). We show for the first time the continuous evolution from the two-mode coupling characteristic of DC to the multimode mixing and interference characteristic of MMI, as the DC is structurally transformed into the MMI. We also show that DC can be designed to have the MMI features of compactness and polarization-insensitivity, two traits that reflect their shared lineage. The performance of MMI and DC are compared in terms of coupling length, polarization dependence, crosstalk, excess loss, and fabrication tolerances. We show that the DC, as long as it is designed to have nearly the same coupling length for transverse electric and transverse magnetic, can potentially have better performance than the MMI in terms of crosstalk and polarization sensitivity. Such a DC, however, requires careful control of many design parameters, while the MMI design is more robust and involves fewer design variables. Finally, the effect of higher-order modes and mode filtering are also considered. [ABSTRACT FROM PUBLISHER]

An intensity modulation using a hybrid electrooptic (EO) polymer/sol-gel straight channel waveguide, useful in the 1550-nm wavelength regime is demonstrated without using Mach-Zehnder interferometric waveguide. The sol-gel waveguide is selectively buried so that a vertical transition into and out of an EO polymer coated on the sol-gel waveguide is arranged. The throughput ratio for transverse electric (TE) and transverse magnetic (TM) modes of the light coupled out of the hybrid waveguide is improved up to 0.9 dB with the help of reduced birefringence of the EO polymer after corona poling. We show that the fabrication process of such hybrid-type waveguides enables production of a phase modulator operating at 1550-nm wavelength. The fabricated straight channel waveguide modulator exhibits stable- and high-intensity modulation efficiency (82%) using a simple cross-polarization setup after the polarization dependence is reduced. We demonstrate an all wet-etching process to fabricate polymeric EO modulators. [ABSTRACT FROM PUBLISHER]

A new and effective nonintrusive method for characterization of N coupled waveguides is presented. The method is able to furnish readily the coupling parameters of most significance, and furnishes in addition, a way of assessment of overall device quality and performance. The procedure is based on a semi-empirical implementation of coupled mode theory, by means of which different functions are defined for different input configurations. In a well-functioning device, all these function should attain a common single minimum, out of which the coupling coefficient and additional parameters of the device are deduced. Devices were fabricated on Z-cut LiNbO3 crystals by in-diffusion of titanium. The method was applied in order to measure the wavelength and polarization dependence of the coupling coefficient [ABSTRACT FROM PUBLISHER]

Birefringence modulators for controlling the phase retardation between transverse electric (TE) and transverse magnetic (TM) polarizations are demonstrated based on polymeric waveguides. Highly birefringent polymer material is incorporated to increase the polarization dependence of the thermo-optic (TO) effect. The TO coefficient for each polarization is measured using a Mach-Zehnder device, and the polarization dependence of the TO effect is found to be 1.0 × 10-5/°C. By applying 70 mW of heating power with an integrated heater, π-phase difference is achievable between the TE and TM polarizations. For 45° input polarization, the output polarization is successfully modulated to cover the entire Poincare sphere. [ABSTRACT FROM PUBLISHER]

We designed and fabricated benzocyclobutene-based polymer waveguide directional couplers and measured the polarization dependence of their splitting ratios. Wide-band polarization-insensitive operation and the possibility of using thermal tuning to maintain low polarization dependence were demonstrated. [ABSTRACT FROM PUBLISHER]

We report the fabrication of benzocyclobutene strip optical waveguides and the measurement of their birefringence properties. To take into account the stress-induced birefringence in the waveguide, we generalize the formulas reported previously for the analysis of strip waveguides. Our experimental results are shown to agree closely with the theoretical calculation. The condition for achieving zero modal birefringence by control of the aspect ratio of the strip of the waveguide is highlighted. The dependence of the birefringence in the waveguides on the temperature is also measured and discussed. [ABSTRACT FROM PUBLISHER]