Design And Fabrication Of LN Y-branch Waveguide Modulator

Fiber optical gyroscope has already been the most popular instrument in the inertialtechnology area, and widely used in both millitary and civil. Fiber optical gyroscope isconsist of optic source, lithom niobate Y-branch modulator, fibre ring and ect.In the fiberoptical gyroscope, lithom niobate Y-branch waveguide is being commonly used aspolarizer, beam splitter and phase modulator. The main factor which may effect the lithomniobate Y-branch waveguide is its fabrication progress. So it is very important to test theindex profile of lithom niobate waveguide to improve the fabrication progress.Lithom niobate Y-branch waveguide, which is fabricated by annealing and protonexchange process, is the main part of lithom niobate Y-branch modulator. After fabricatingprocess, the lithom niobate Y-branch waveguide gets a gradual index profile, whichdirectly effects on the transition optical field of the waveguide. So it is important to controlits index profile to get a high quality waveguide. The main researches as follows:1. Fabricated the LN waveguide by annealing proton exchange, and describe itstheory and equations in details.2. By using the prism coupler method, the index profile of a lithom niobate (LN)waveguide can be get. And by testing the index profile under different fabricate conditions,the relationship between index profile and the fabrication parameters can also bedetermined. Combined the theory with the test result, a better performance waveguide canbe achieved by changing the parameters, such as the time of proton exchange, the time ofannealing, etc.3. Combining the Y-branch structure with the index profile, we can get the threedimensional optical propogation path and propogation loss in the device by using the FiniteDifference Beam Propagation Method (FD-BPM).4. A set of coupling and testing system have been designed and built to test the LNwaveguide.Through coupling, solidification and package, the final device can be get andalso the related character can be tested such as propagation loss, extinction ratio, etc. 5. The related definitions of lithom niobate Y-branch waveguide’s characteristicparameter, such as propagation loss, instinction ratio, half wave voltage and etc, have beendefined and caculating methods have been described. And also, the technical parameters,which may cause effct in FOG, have been analised. The parameters under differenttemperature have been tested and the result has been regulared.The testing result indicates that we have already had the ability to manufactureY-branch waveguides, which has the index profile approximate the Gaussian profile. Also,we have already had the ability to test the waveguide’s characteristic such as propagationloss, half wave voltage etc. And we have achieved the business standard with propagationloss is less than3.5dB, and half wave voltage lower than5V. This builds a good fundationfor optimization waveguide’s fabrication process and future’s work.