Design, Fabrication And Measurement Of Ion-exchanged Four Branch Waveguide

Optical waveguides are the base of the integrated optical circuits. They are carriers for rapidly transmitting optical signals in large quantities. Waveguides and fibers connect all parts of optical systems. As the elements for restricting and guiding the lights, their essential is that the refractive index of waveguides is higher than that of external medium. In the integrated optical devices, structure and transmission characteristics of channel waveguides are similar to ones of single-mode fiber. Compared with other waveguides, when coupled with fibers channel waveguides have lower coupling loss. Four branch waveguides are also important in integrated circuits. Although new type four branch waveguides could have wide angle, low loss, the technics used here are very complicated. It is useful to study how to use simple technics to fabricate four branch waveguides.Many methods have been proposed to analysis the propagation characteristics of the dielectric optical waveguides. The beam propagation method (BPM) is the most widely used propagation technique for modeling integrated and fiber-optic photonic devices. In addition to its relative simplicity, the BPM is generally an efficient method and can be applied to complex geometries without having to develop specialized versions of the method. Furthermore, the approach automatically includes the effects of both guided and radiating fields as well as mode coupling and conversion. There are several reasons for the popularity of BPM: perhaps the most significant being that it is conceptually straightforward, allowing rapid implementation of the basic technique. In this thesis, the FD-BPM is used to study the propagation characteristics of four branch waveguides. For the fabrication of an integrated glass waveguide, the ion-exchange technology is widely used. This simple technich is not only suitable for mass production, but also cheap. It enables us to create a region of higher refractive index in the glass substrate by a simple thermal diffusion. In addition, its refractive index profile can be made symmetric to match the modal field profile of an optical fiber and thus to reduce waveguide-to-fiber coupling losses.In order to test waveguides we make, we built a set of coupling and testing system between the optical fiber and the optical waveguide. It is precisely measuring instrument in the optical communication. It is proved to be effective. The testing result indicated that our laboratory has already had the ability to manufacture channel and four branch optical waveguides. It provides us a solid basis and great values to optimize the design of ion-exchange waveguides. It also makes a good foundation for our following work, such as the light branch and the optical waveguide amplifier.Index Profile Simulation of Ion exchange waveguideThe increment of index ?n (λ, x ,y)have direct ratio with the Ag+ ion concentration. ?n (λ, x , y ) =d e(λ) g ( x ) f ( y) ( )d eλis the dispersion gene; g ( x ) and f ( y )are distribution function of index towards width and depth.Here we use the error fuction model: ?n e( x) is the index increment of the ion waveguide, ?n es( x) is the largest index increment, d e is the diffused depth. After numeration, we can get the index formula of ion-exchange waveguide:Simulation and design of four branch waveguideWhen we simulate the 3D waveguide model, considering the practical experiment, here are values used in simulation.Light wavelength is 1.55um. Index of the substrate, K9 glass under wavelength 1.55um is 1.50. Index of air is 1. Increment of index ?n =0. 03. Diffusion width d x= 2.4um. Diffusion depth d y= 2.4um. Computing length on Z direction is 1.5um. The length of waveguide is 16000um.we have three type of four branch waveguide, the branch space is 100um,150um,200um. For example: four branch waveguide with 100um branch space.the refractive index profile is fig1The design of four branch waveguide:We use 63mm×63mmchrome board to make a four branch mask, mainly including 13 group of four branch waveguides and four right-angle L model,thereinto:(1) four right-angle L model is illuminating, the width id 1mm,the length is 2mm.(2) the 13 groups of four branch waveguides is illluminting ,the width of waveguide is 6um. Fabrication of four branch waveguideFirstly, channel waveguides were fabricated in prepared K9 glass using a conventional procedure. To localize the diffusion in specific regions in the substrate, the photolithography technique is used to create an aluminum mask on the glass substrate to prevent the exchange in the masked region. Lastly, the diffusion in a melt mixture was carried out under settled high temperature and for 1 hour. Then light can pass through the waveguide zone. We use the same process to fabricate four branch waveguides. Fig 3 shows the process of thermal ion-exchange waveguide. We built a set of coupling and testing system between the optical fiber and the optical waveguide to detect the four branch waveguide. It is precisely measuring instrument in the optical communication. The laser beam emerging from the Single-Mode fiber shoots into the sample waveguide and a CCD camera is used to monitor the output light. Here we use the end coupling method to achieve the coupling between the channel waveguide and tapered optical fiber. Fig.4 shows the coupling and testing system between the optical fiber and the optical waveguide. The test systerm are shown fig4 The test result of the different branch space waveguideWe have design waveguide with three type of space branch width using Ledit.100um,150um,200um,respectively.in our test we only see the facula of 100um and 150umbecause of our experiment restriction. The facula are in fig6 and fig7The testing result indicated that our laboratory has already had the ability to manufacture the four branch optical waveguide. It provides us important basis and great values to optimize the design of optical waveguides. We make a good foundation for the following work, such as the light branch and the optical waveguide amplifier.