Design Of Planar Lightwave Circuits Based Passive Optical Devices

With the advent of the information age, the bandwidth demand ofglobal communication exhibits an exponential growth trend, with anaverage rate of35%annually. In backbone network, optical fibers tookplace of coaxial cables, leaving the so-called “last-mile” optical accessnetwork the bottleneck of telecommunication system. Major functions ofthe optical access network includes establishing connections betweenoptical network and electrical end circuit, power distribution of opticalsignals, coupling control of various optical devices, multiplexing anddemultiplexing of optical signals. Via using highly efficent passiveoptical devices, bandwidth of the access network can be broadened, thusimproving the overall performance of the communication network.1×N power splitter is one of the most basic and the most importantpassive optical devices. It’s not only an integrate part of the optical accessnetwork, but also an indispensable component of many complex opticaldevices. Power splitters based on planar lightwave circuits possessesfeatures such as small size, low weight, high integration level, goodmechanical properties and environmental stability and therefore enjoy abroad application.The most widely adopted composition of1×N splitters is to cascade1×2power splitters via S-shaped waveguides in a tree-like pattern.Although this layout meets the general bandwidth requirements of PONnetworks, the device footprint and insertion loss is relatively large. In thispaper, we present a1×N optical power splitter with a new cascadingstrategy. The resulting device features a footprint reduction from24.80%to53.72%with the branching number ranging from4to64; as well as an insertion loss reduction from0.3dB to0.4dB within the1260nm~1610nmcommunication band.In our1×N splitter, arc-shaped waveguide segments are used toreplace the S-shaped waveguides to connect adjacent1×2power splitterunits. Therefore, the extra length and insertion loss introduced byconnecting waveguides are reduced. Moreover, we devised an intelligentoptimization algorithm based on direction-search, genetic algorithm andevolution programming to further improve the device structure. Thealgorithm takes the radian of each connection arc as parameters andregards the total device length as optimization target, and ensures that aglobal minimum can be reached.Finally, we designed an all-optical amplitude-phase equalizersuitable for the WDM network. The equalizer composes of an array ofvariable optical attenuators (VOAs) and tunable delay lines (TDLs)which can perform an power attenuation and phase adjustment of0~100ps within each channel.