Single-mode Ti:LiNbO 3 Waveguide Crossings And Switches: Design Rules And Applications

Abstract

Lehrstuhl fur Hochfrequenztechnik, Universitat DortmundPostfach 500500, 4600 Dortmund 50, Federal Republic of GermanyAbstractThe operational principles of passive and active LiNb03 waveguide crossings are outlined.The radiation losses and crosstalk in large -angle passive wavequide crossings are calculatedusing the beam -propagation method. A detailed electrode analysis of an electrooptic X- switchis presented and compared with that of a directional coupler switch.Prospective applicationsof waveguide crossings are listed. As an example, the parameters of an integrated 4x4switching array with 16 X- switches are presented.IntroductionWaveguide crossings are becoming to be important components of integrated opticalcircuits1-8. Low -angle (% 1 °) crossings may find applications mode splitters2, electro-optic modulators and switches3,5 and wavelength -selective devices6 while large -angle (% 100)crossings are used to enhance the packing density of complicated waveguide structures7-8The properties of waveguide crossings have recently been studied both experimentally9,10and theoretically10 -12 with promising results. However, work is still to be done to revealall the features and to find the optimum performance of these components.Waveguide crossings are intrinsically longitudinally nonuniform devices, which makestheir analysis complicated. Local normal mode approach is useful to explain the behaviourof low -angle structures3-6'9. To analyse the radiation losses and crosstalk, mode conversioneffects must be taken into account. The beam propagation method13(BPM) is ideally suited tomodel the complex devices11,12,14 while analytical methods such as ,16 possess betterphysical insight. We first show, in analogy with9, the angular dependence of the powersplitting in diffused -waveguide crossings, using the local mode approach. For large anglesof intersection, where this approach fails, the splitting ratio is calculated by the BPM14.For electrooptic modulators and switches, one of the most important parameters is theswitching voltage. To have a clear comparison with the widely used directional couplerswitch 17-21, a voltage- length product of both the X- switch on the X -cut LiNb03 and Z -cut-directional coupler switch are calculated. The X -cut has been chosen for the X- switch