Used In The Full Light Of The Optical Analog-to-digital Converter Comparator Study

Firstly, a comprehensive analysis on the conversion rate, bit-resolution, architecture feature, and performance enhancement of electronic analog-to-digital converters (EADC) and optical analog-to-digital converters (OADC), is presented. Low rate, high bit-resolution EADCs and high rate, low bit-resolution OADCs can be used in different fields complementarily. It is pointed out that three important research topics in OADCs are: 1) all-optical comparators without opto-electronic conversion for all-optical quantization; 2) novel optical encoding schemes for lowering demand upon preceding circuits, such as pre-amplification, and enhancing the conversion number of bits; 3) consideration of both voltage, or current, and light pulses for input analog and output digital signals, for the convenience of future high-speed hybrid opto-electronic circuit interfacing. Based on the analysis on physic process of realizing comparator, an all-optical differentiator is proposed using two-beam interference; thus an all-optical intensity comparator is realized by combining interference with injection locking of a laser.Secondly, the semiclassical theory of semiconductor laser injection locking is studied by means of taking into account the spontaneous emission and non-linear gain effect with the definitions of several new physic parameters. Locked output power, phase, static and dynamic locking regions, transient process, as well as noise effect on locking, are discussed. The intensity and phase relation among light fields in the two-beam interference are analyzed, and embodiment of optical differentiation, by destructive interference with phase difference of odd times ofπ, is emphasized. The phase of the interference output is the result of differentiation. When this differentiated field injection-locks a semiconductor laser, the locked output phase is controlled by the injection, and intensity signal is regenerated from this phase information under second interference. The optical comparison is thus achieved. Taking the interference as the driving item in the injection-locking rate equation, numerical calculation is performed, yielding the output waveform of the second interference under altemate input light intensity. The discussion on the non-idealness of the phase condition before interferences and their impacts on the output waveform of the comparator are presented. Thirdly, an experiment system is devised to study the optic fiber interference and semiconductor laser injection-locking, where an electrooptic M-Z intensity modulator is used. Based on the power budget and optical length calculation, the parameters of fibers and couplers are chosen. Piezoelectric fiber phase shifters and laser drive circuits are designed and fabricated. Intensity modulation signal is obtained by applying appropriate sinusoidal voltage on the electrooptic M-Z modulator, and the outputs of optical differentiator and comparator are observed using an oscilloscope. The experiment waveforms are compared with theoretical calculations with the jams under experimental conditions taken into consideration, showing that the main factors affecting all-optical comparator performance are: phase conditions and state of polarization stability before interferences, linewidths of injected and free-running laser light fields, frequency detuning and width of locking region.Finally, the enhancement approaches of the high-speed performance of all-optical comparator are discussed, which mainly cover utilizations of laser with broader longitudinal mode spacing and opto-electronically integrated circuit interference system immune from noise affection. A conclusion is drawn with indication of the main following work.