7 research outputs found
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
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