| The integrated acoustooptic tunable filters (IAOTFs) have demonstratedpotential applications and exhibit their enormous potential in economy inwavelength-division multiplexed (WDM) optical fiber communication systems fortheir large tunability, narrow bandwidth, low drive power requirement, uniqueproperties of simultaneous multiwavelength filtering and as gain equalizers. In thispaper, the crucial technologies of IAOTFs such as optical waveguide design,polarization-independent, sidelobe suppression as well as wide tunability have beenstudied experimentally and theoretically. A IAOTF has been fabricated with itsperformance at the top place in the world. To enhance its performance, somecomponents of IAOTF such as wideband acoustooptic interdigital transducer,integrated optical reflection mirror and Si-coated polarizer have been investigated.Some innovations in the paper are as follows: 1. Waveguide design 1) The theory of Ti:LiNbO3 waveguide is studied by using modified Airyfunction in WKB method for the first time. The cutoff phase shift is testified as aconstant number, i.e., π / 6, which can provide an exact normalization frequencyand processing parameters for designing the single-mode waveguides. 2) A novel set of vector basis functions is presented for the first time. The weightof such basis functions is vanished at the edge of finite elements, and also its curlvaries with the position within finite element. These two properties make up theabsent characteristics of the primary tangential vector basis functions. At the sametime, the zero-divergence property of the primary tangential vector basis function iskept in the center of elements. The compute efficiency is improved obviously sincethese basis functions are orthogonal each other. 2. Sidelobe suppression & Dopple shift eliminating 1) To overcome the drawbacks of high power requirement, inefficient sidelobesuppression and complex configuration, the concept of quasi-collinear acoustoopticalcouple is presented for the first time. The acoustooptical couple is closed to Hammingfunction, which leads to high efficiency of sidelobe suppression, simple configurationand fabrication process and narrow bandwidth. The influence of SiO2/In2O3 film SAWguide on the mode index of optical waveguide has been investigated for the first time.The prototype has been fabricated, the measured FWHM is 1.46 nm and the measured iiABSTRACTsidelobes level is -13.2 dB, as compared to theoretical values of 1.44nm and -13.4 dB,respectively. Nowadays, it is the best performance in such kind of IAOTFsinternationally. 2) To overcome the drawbacks of frequency shift imposed in single-stage devicesand to achieve a higher sidelobe suppression, the concept of cascading of two stagesby an integrated reflection mirror is put forward and this mirror has been fabricated aswell. 3.Widening tunability & Enhancing the purity of polarization 1) A novel bouble-tapezia-electrode interdigital transducer (IDT) to compensatehigh-frequency component of the slanted single-electrode IDT is presented for thefirst time. It makes flatter amplitude response and wider bandwidth than those of thelatter. At the same time, the external compensating network is eliminated. The deviceis expected to be a integrated optics acoustooptical spectroscope in spectrometer for1.15~1.65 μm..2) To overcome the drawbacks of the frequency characteristic of the polarizationsplitter in IAOTFs, a novel design of a TE-pass waveguide polarizer based on Si on aTi:LiNbO3 waveguide is presented. This polarizer is fabricated and itspolarization-dependent measurements lead to the best polarization extinction ratio~34dB and the insertion loss< 0.4 dB. By splashing a Si film on mode splitter at theoutput of IAOTFs with simple processing steps, the performance of IAOTF will befurther improved.
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