The generalized Mach-Zehnder interferometer using multimode interference couplers for optical communications networks

The explosive growth in telecommunications traffic in recent years has hastened the emergence of optical communications networks. As the volume and complexity of network traffic increases, efficient, flexible, and cost-effective methods of routing and distributing optical signals are being sought. One method for meeting these requirements is through the use of integrated optics technology, which enables the realization of miniaturized optical components and circuitry on a planar substrate surface.; In this work the integrated optic multiple-arm or generalized Mach-Zehnder interferometer (GMZI) using multimode interference (MMI) couplers is studied. Through an investigation into the principles governing the operation of this device, a mathematical theory describing both its idealized and observed properties is developed. This theory predicts the operation of the GMZI as a variable-ratio optical power splitter, which in specific instances functions as an optical switch. Both the power splitting and switching functions of the GMZI are useful for efficient optical signal distribution, routing, and protection switching applications in emerging optical communications networks.; The variable-ratio optical power splitting function allows an input optical signal to be distributed in a controlled, dynamic manner to a number of output channels. This provides an efficient and flexible means of broadcasting an optical signal to multiple users. The method of operating this novel device is described and its strengths and limitations are assessed.; A consideration of the optical switch function reveals that various levels of symmetry are present in the operation of the GMZI. This symmetry is used to develop new designs for 1 x N optical switches with reduced operational requirements. Further consideration of the multiple-input switch properties leads to new designs for non-blocking N x N optical switches that possess the benefits of compactness and a simple design and fabrication procedure. The switches enable optical signal routing and network protection and reconfiguration switching to be realized with compact components exhibiting low power consumption levels. The operation and performance issues of these switches are examined in detail.; To demonstrate the feasibility of the manufacture and operation of the GMZI and the validity of the theory upon which it is based, a number of integrated optical waveguide components including MMI couplers and GMZI devices have been realized. The devices were fabricated in a high refractive index contrast silicon oxynitride (SiON) based planar waveguide system, utilizing the thermo-optic effect for active operation.; The measured device performance is reported, and demonstrations of efficient thermo-optic operation, 1 x N switching in 2 x 2 and 4 x 4 GMZI devices, and variable-ratio power splitting and multi-port switching in a 4 x 4 GMZI device have been achieved. The observed device characteristics validate the tenets of the mathematical theory developed in this work, and demonstrate the feasibility of using the GMZI to perform the complex optical functions required for state-of-the-art optical communications networks.