High-speed guided-wave electro-optic modulators and polarization converters in III-V compound semiconductors

In the last few decades, the need for electronic communication has increased by several orders of magnitude. Due to the rapid growth of the demand for transmission bandwidth, development of very high-speed communication systems is crucial. This thesis describes integrated-optic electro-optic modulators using travelling-wave electrodes in compound semiconductors for ultra-high-speed guided-wave optical communications. Both Mach-Zehnder (MZ) interferometric modulators and polarization converters (PC) have been studied with particular emphasis on the latter ones. Slow-wave travelling-wave electrodes in compound semiconductors have previously been proposed and demonstrated. Here, a study of slow-wave, travelling-wave electrodes on compound semiconductors has been performed in order to significantly improve their use in ultra-wide-band guided-wave electrooptic devices. The most important factors limiting the high frequency performance of such devices, in general, are the microwave-lightwave velocity mismatch and the microwave loss on the electrodes. Based on the deeper understanding acquired through our study, we have designed, fabricated, and tested low-loss, slow-wave, travelling-wave electrodes on semiinsulating GaAs (SI-GaAs) and AlGaAs/GaAs substrates. Microwave-to-lightwave velocity matching within 1% was achieved using slow-wave coplanar strip electrodes; many of the electrodes had effective microwave indices in the range 3.3 to 3.4 (measured at frequencies up to 40 GHz). For the electrodes fabricated on SI-GaAs substrates, microwave losses of 0.22 Np/cm and 0.34 Np/cm (average values at 40 GHz) were measured for the slow-wave coplanar strip and the slow-wave coplanar waveguide electrodes, respectively. For the electrodes fabricated on the AlGaAs/GaAs substrates containing the modulators, the corresponding losses were, on average, 0.17 Np/cm higher at 40 GHz. For the first time, ultra-wide-band polarization converters using slow-wave electrodes have been designed, fabricated, and tested. A detailed analysis of the use of the slow-wave electrodes together with optical ridge waveguides as polarization converters has been provided. The effects of the modal birefringence of the optical waveguides, the microwave loss on the electrodes, and the residual microwave-lightwave velocity mismatch have all been taken into account in our study. Low frequency optical measurements showed very good qualitative agreement between the measured and the predicted results as regards the effect of the modal birefringence; it was also shown that the modal birefringence has to be kept to very small values to keep the efficiency of such modulators high. High-speed optical measurements were performed at frequencies up to 20 GHz (limited by the equipment bandwidth); the 3-dB optical bandwidths exceeded 20 GHz for both the MZ type and the PC type devices. The MZ modulators, however, had significantly larger half-wave voltages, -25 V, and their electrodes were significantly "over-slow" (by -15%). Evidence acquired through this study suggests that reducing the half-wave voltages below 5 volts and keeping the bandwidth in excess of 40 GHz is extremely difficult for these MZ type devices. The PC type devices using slow-wave coplanar strip electrodes, on the other hand, had lower half-wave voltages, as low as 7 V was measured, and had very good microwave-tolightwave velocity matching, within 1%. From this study we conclude that these devices can be designed to have bandwidths in excess of 100 GHz and half-wave voltages less than 2 V.Applied Science, Faculty ofElectrical and Computer Engineering, Department ofGraduat

Integrated optics pockels cell high voltage sensor

In this thesis an integrated optics version of the Pockels cell, to be used for the measurement of high voltage in power transmission systems, is described. The operation of the sensor is based on the electro-optic effect in lithium niobate. The sensing head consists of a waveguide formed by diffusing a strip of titanium in a y-cut lithium niobate substrate. This waveguide (z-propagating) supports two orthogonal modes. An electric field, in which the sensor is immersed, alters the difference in the phase velocities of the two modes and, in turn, alters the polarization state at the output of the waveguide. Polarization maintain ingoptical fibres transmit light to the sensor head and interrogate its output. The electric field in which the sensor head is immersed can be detected by measuring the change in the polarization state at the output of the sensor. Also, some of the technological problems encountered in realizing an integrated optics Pockels cell (IOPC) have been addressed and overcome. The photolithographic fabrication of the waveguides, waveguide end preparation, permanent fibre to waveguide butt-coupling, and other fabrication steps have been successfully completed. Fully connectorized systems have been fabricated and tested to characterize the performance of the IOPC. Various device parameters such as intrinsic phase, half-waveelectric field, and extinction ratio have been measured for several devices. The effects of waveguide width and length on the performance of the sensor have been studied. Test results indicate that useful devices, well biased, need to be at least 5 mm long. The linearity of sensor response and noise in the measurements have been investigated. The test results show that the sensor is capable of metering high voltage AC signals with less than 0.3% error and,therefore, is likely to meet the power industry standards, such as those proposed by Erickson in 1992, for optical high voltage transducers. The stability of the sensor under various conditions has been explored. The piezoelectric resonances of the sensor heads and their effects on the bandwidths of the sensors have been examined. Sensors with large enough bandwidths have been fabricated which have successfully measured the IEC (InternationalElectrotechnical Commission) standard lightning impulses with 1.2 As front time and 50 Astail time. The results indicate that one IOPC can be used as a high voltage sensor in several applications such as metering high voltage AC signals, protection, and time-resolved-fault-location.Applied Science, Faculty ofElectrical and Computer Engineering, Department ofGraduat

Bias of integrated optics Pockels cell high-voltage sensors.

The results of measurements of the intrinsic phase-differences of titanium- indiffused lithium niobate waveguides, for use in integrated optics Pockels cell high-voltage sensors, are presented. The dependencies of the intrinsic phase-differences of these waveguides on their lengths and widths are investigated; a change of between 4.9 and 5.9 degree(s)/micrometers /mm was obtained. Also, the change in the intrinsic phase-difference as a function of both temperature and time was investigated; a typical change of 0.02 degree(s)/ degree(s)C/mm was measured and, following a small initial change, the bias was found not to drift with time. Some suggestions for possible post-processing of the output signals, of the integrated optics Pockels cell high-voltage sensors, to increase the dynamic range and to compensate for small changes in the bias, are presented. Copyright 1994 Society of Photo-Optical Instrumentation Engineers. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited.Applied Science, Faculty ofElectrical and Computer Engineering, Department ofReviewedFacult

Success Factors for Sustainable Electrical Energy Delivery

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Integrated-optic voltage transducer for high-voltage applications.

This paper describes a novel voltage transducer. Its design is based on a mathematical procedure that enables a small numberof strategically positioned electric field sensors to accurately measure the voltage. The voltage transducer takes advantage ofexisting compact, non-intrusive optical electric field sensor technology, specifically, the integrated-optic Pockels cell (IOPC),but is not limited to optical technology. The key advantage of this voltage transducer over other existing optics-based voltagetransducer technologies is that it does not require any customized electrode structures and/or special insulation. A highvoltageintegrated-optic voltage transducer has been used to obtain measurements with metering class accuracies. Copyright 2000 Society of Photo-Optical Instrumentation Engineers. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited.Applied Science, Faculty ofElectrical and Computer Engineering, Department ofReviewedFacult