Bruno Vinouze

APPLICATION OF POLYMER DISPERSED LIQUID CRYSTAL (PDLC) NEMATIC: OPTICAL-FIBER VARIABLE ATTENUATOR

Dispersions of liquid crystals in polymeric matrices (PDLC) are used as light Variable Optical Attenuators (VOAs). Electronically controllable VOAs play a crucial role for channel power equalizers in WDM systems. This article describes the theoretical model optimizing PDLC performance and the fabrication process utilizing the polymerization-induced phase separation (PIPS) method, and presents the optical attenuation (OA) and polarization dependence loss (PDL) characteristics versus fabrication conditions. Fabricated VOAs have a large attenuation range (10–30 dB) and low insertion loss (IL) at a 1.55 µm wavelength (0.5 dB). Depending on the fabrication parameters, the OA, IL, and PDL are optimized. This device needs an applied voltage V90 of 10 to 70 Vrms for 10–100 µm PDLC thickness. The flatness of the optical characteristics of this device has also been measured in the C+L band.

Channel Equalization and Bandwidth Tuning Using a LC-Based Tunable Hybrid Birefringent Filter

We propose and demonstrate a new modified Lyot filter to independently ensure the channel amplitude equalization and the bandwidth tuning functions. The device consists of hybrid liquid crystal interferometers. We show numerically and experimentally that for a modified four-stage Lyot filter, the two first interferometers ensure equalization function with a maximum extinction ratio, while the last interferometer allows full-width at half-maximum tuning function by using, in particular, the optical canceling approach. Such a device is highly desirable in optical telecommunications, especially where in the core network the optical filters must perform several other functions in addition to their basic amplitude filtering action.

Phase-shifting VOA with polymer dispersed liquid crystal

A polymer containing fine droplets of liquid crystal (LC) is investigated for obtaining an optical phase-shifting attenuator at 1550-nm wavelength. Two mixtures of liquid crystals and monomers are compared for a cell thickness of 15 /spl mu/m. The first method uses nanosized LC droplets to achieve 2.29-rad phase shifting for an applied voltage of 230 Vrms. The second method uses microsized LC droplets to achieve 2.35-rad phase shifting for an applied voltage of 15 Vrms. Theoretical analysis of the phase shifting is developed. This optical property is used to achieve a variable optical attenuator (VOA) between two single-mode fibers. An optical architecture using graded index rod lenses and a pattern of photoresist polymer is presented. Typical characteristics of such VOA are: 12-dB range of attenuation, a maximum polarization dependence loss of 0.5 dB, 1.1-dB insertion loss, and a saturation voltage of 20 Vrms.

Contrast and Finesse Enhancement in a Birefringent Filter

We propose and demonstrate a novel optical implementation to simultaneously improve the contrast and increase the finesse of a classical N-stage Lyot filter. The new device based on the multiple-passage concept uses two mirrors placed at the extremities of the filter. The light beam passes through the structure back and forth and each passage has a significant influence in reducing the sidelobes and the bandwidth of the filter transmittance. We show that for a two-stage Lyot filter, the contrast is increased by 100% after each passage and the finesse is improved by over 50% after four passages and more. Such a device is highly desirable in a wide field where the filtering function requires high performances in term of contrast and finesse.

Multiplexer and Variable Optical Attenuator Based on PDLC for Polymer Optical Fiber Networks

In this work, a combination of a multiplexer and a variable optical attenuator in the same device (VMUX) for use in Polymer Optical Fiber is proposed. Polymer Dispersed Liquid Crystals (PDLC) are polarization independent, have high contrast and gray scale capability. For these reasons, PDLC cells with pixels can be used as switching elements in the device. Characterization of the PDLC has been carried out at two wavelengths. VMUX Complete switching is reached for driving voltages of 20 Vrms, with insertion losses less than 1.6 dB, attenuation larger than 31 dB, rise time less than 2.6 ms and decay time better than 12.4 ms have been obtained.

Multi-channel amplitude equalization based on liquid crystal polarization interference filters

We propose the design of a multi-channel amplitude-equalizing polarization interference filter based on stacked liquid crystal birefringent blocks. Each block, which is optimized to control a predefined wavelength channel, consists of three components. The wavelength blocking/transmitting and the equalizing actions are provided by the liquid crystal component whose optical path difference varies between two particular values when its birefringence is electrically controlled. For a typical three-channel equalizing filter, the three liquid crystal cells provide all eight possible combinations to block/transmit channels and also allow us to independently equalize their corresponding levels. The benefit of such a polarization-based filter is that it operates without free-space demultiplexing optics and with no moving parts. It can be used as a key element in the present reconfigurable optical networks.

A starter activity design process to deepen student's understanding of outcome-related project learning objectives

Engineering educational programs increasingly rely on project-based learning. Within, it is crucial to early present to students intended learning outcomes from the outset of large projects. However, even if well formulated, many outcome-related project learning objectives are not properly understood by students out of experiences. Thus, some students struggled to identify objectives throughout activities and tended to distance themselves from acquisitions. Short concrete activities could advantageously help student self-recognize learning objectives. For such, we propose a systematic insertion of authentic starter activities in the front-end of large projects, so as to give students a better insight and deeper understanding of the knowledge, skills, and abilities they are expected to acquire. Properly designed starter activities promote enthusiasm, motivation, and increase project involvement. For program developments, this paper proposes a three-phase process, from design to improvement, for integrating starter activities and to favor a coherent treatment throughout a curriculum. This process is based on our six years of experiences with large semester projects.

Liquid crystal optical switches

Abstract: This chapter describes the potential of liquid crystal (LC) in switching, from LC materials properties and principles to switching parameters and applications, including the advantages and limitations of LC technology in optical switching. A description of the main types of switches based on the mechanisms used for steering the light with LCs such as reflection, waveguide, polarization management or volume beam-steering is summarized with special emphasis on their parameters as switches and their applications. Apart from previous configurations, there are growing technologies such as ring resonators, holograms and microstructures fibers, which use LC as electro-optical elements for controlling optical switching status. These promising technologies will also be analyzed.

A novel 1×2 wavelength routing switch based on a tunable hybrid liquid-crystal solc filter

A novel 1×2 wavelength routing switch is introduced and analyzed. It is based on a tunable hybrid liquid-crystal Solc filter and a polarization beamsplitter. The device can be set into the bar state for an arbitrary subset of WDM channels while remaining in the cross state for the rest of channels. This is achieved via a tuning voltage applied to liquid-crystal cells. Interchannel crosstalk and its reduction are discussed. Application of the switch includes coarse and dense WDM.