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Extended precision in video-bandwidth analogue/digital convertors using optical techniques
Electronics Letters
Abstract
A new design for analogue/digital convertors (ADCs) which make use of electro-optic modulators and optical sampling in conjunction with conventional electronic ADCs is proposed. By taking advantage of the periodic response characteristic of the optical modulators, a significant increase in precision over purely electronic conversion is expected.
Research in the use of guided wave optics for signal processing is reviewed, and advantages and limitations of the technology are discussed. The signal processors employ electrooptic and fiber optic components to perform such functions as spectral analysis of radio-frequency signals, correlation and matched filtering, code and waveform synthesis, signal delay and storage, and analog-to-digital and digital-to-analog conversion. In most cases the guided-wave approach is distinguished by the ability to perform a particular function at very high analog bandwidths or digital data rates. In concluding remarks, an effort is made to provide some perspective on competing technologies and to indicate some areas where future research might prove fruitful.
This thesis develops an efficient and effective method for designing and analyzing the performance of various integrated optical waveguide structures using the beam propagation method of analysis. Modifications in the physical layout of an optical device through changes in coupling connection design, splitting angles and waveguide dimensions may have significant effects on device performance. The beam propagation method is initially developed for a symmetric Mach-Zehnder interferometer for baseline validation of the accuracy and applicability of the propagation scheme. A major validation is achieved through modeling an asymmetric device designed and built by the Naval Research Laboratory. The validated simulation model is used to analyze the performance and design characteristics of complex parallel configurations of interferometers. The beam propagation method allows quantitative analysis of the performance of these integrated optical devices. The propagation model developed implements a new global propagator scheme that substantially reduces computational requirements and introduces a design methodology that ensures compatibility between the discrete implementation and the physical structure. Also identified are areas in which continued research can provide a complete modeling system that may be implemented as a stand-alone design and analysis. (AN)
Research in the use of guided-wave optics for signal processing and sensing is reviewed, and advantages and limitations of the technology are discussed. The signal processors employ electrooptic, acoustooptic, and fiber-optic components to perform such functions as spectral analysis of radio-frequency signals, correlation and matched filtering, code and waveform synthesis, signal delay and storage, and analog-to-digital and digital-to-analog conversion. In most cases, the guided-wave approach is distinguished by the ability to perform a particular function at very high analog bandwidths or digital data rates. The second part of the review is concerned with sensor applications for guided-wave elements fabricated on planar substrates ("integrated optics"). Waveguides on an integrated optics chip have been used for sensing temperature, humidity, electric field, wavefront angle, and optical disc reflectivity. Also described are integrated optic phase and frequency shifters developed for use in fiber-optic sensors. In concluding remarks, an effort is made to provide some perspective on competing technologies and to indicate some areas where future research might prove fruitful.
Individual bit channels of a 4‐bit guided‐wave electro‐optic analog‐to‐digital converter have been demonstrated at 276 and 828 megasamples per second. The converter consists of a mode‐locked Nd: yttrium aluminum garnet (YAG) laser for sampling, a LiNbO 3 Ti‐indiffused waveguide interferometric modulator array for conversion, a Ge avalanche photodiode (APD), and a special 1‐GHz Si integrated circuit for digital processing. Beat‐frequency tests with a 413‐MHz test signal, representing the highest frequency analog waveform converted, are reported.
One‐bit electro‐optical analog‐to‐digital conversions of up to 100‐MHz signals were carried out in a system using a Ti‐diffused LiNbO 3 balanced bridge modulator and a 1.15‐μm cw He‐Ne laser. The modulators have a new configuration with a phase shifter formed by Ti double diffusants and revealed relatively low half‐wave voltages and high extinction ratios.
An electro-optic analogue-to-digital convertor system has been demonstrated at 1 Gsample/s. This system has been tested with low-frequency waveforms and by means of a beat-frequency technique with a 499 MHz test signal. Digital outputs are slowed in time and then fed into 125 MHz digital-to-analogue convertors which accurately reconstruct the beat signal, proving the compatibility of electro-optic signal processing with digital circuits. © 1983, The Institution of Electrical Engineers. All rights reserved.
The design, fabrication and performance of integrated electro-optic Mach-Zehnder interferometers is described. Operation of a 4-bit analogue-to-digital convertor comprising an array of interferometers with an integral optical input distributor has been demonstrated. Good high-frequency performance is indicated by the results of signal/noise measurements on the output signal.
A Ti-diffused LiNbO3 waveguide optical circuit, whose element is a balanced bridge modulator, was fabricated for application in a 2-bit analogue-digital (AD) conversion system. Using this device with a 0.8 ¿m wavelength pulsed laser diode, up to 240 Msamples/s high bit rate AD conversion operations were successfully achieved.
A new type of analog-to-digital converter, the basic element of which is an array of electrooptic waveguide modulators, is described. Higher conversion rates and simplicity are potential advantages in comparison with conventional electronic conversion techniques.
Describes a 20 MHz conversion speed, fully parallel, analog-to-digital converter device which has been designed for use at video speed. Laser trimming technology has been adopted to improve nonlinearity errors brought about by reference voltage distortion to less than 1 mV to realize a /SUP 1///SUB 2/ LSB accuracy for the 10-bit A/D converter. The large number of comparator stages required by a parallel converter leads to a high number of components and large power dissipation. Therefore, a circuit with a reduced number of components and optimized power has been used. The process employed is a 3 /spl mu/m bipolar process, which integrates about 40000 elements onto a 9.2/spl times/9.8 mm chip.
A design for an optical analog-to-digital converter using channel waveguide modulators is described. Optical and electrical power requirements and factors which limit the speed of operation are analyzed, and the implications of signal sampling with a repetitively pulsed light source are discussed.