A New Synthesis Procedure for Designing Digital Filters Based on Optical Fiber Structures

Since the advent of digital systems, digital filter design has seen an explosion of innovations driven by the ubiquity of microcontrollers and programmable digital systems. Digital filters are not limited by the non-linearities of analog filters and thus are stable and predictable. Traditionally, digital filters design relays on continuous ideal configurations with analytical approximations in the regions of transitions and require mapping using transformation approximations. Additionally, a digital filter will introduce noise during sample/hold, conversion, and quantization. The noise worsens as the filter complexity increases. Furthermore, digital filters introduce a higher fundamental latency that limits their applications to audio and video frequency range. In this paper, we present a new design procedure that will enhance the versatility of digital filters in optical communications and signal processing. We explore the physical structure of fiber optical filters that takes advantage of the single mode fiber properties and the inherent parallelism of the light. We will examine the optical fibers and their filtering properties in optical signal processing. In particular, we explore the modular structure of fiber optic interferometers for the design of digital filters using the cascade approach. Since the single mode optical fiber has an extremely high bandwidth and very low attenuation transmission medium, a short time-delay bandwidth can be realized. We propose a new approach for designing digital filters based on the single mode optical fiber. The approach demonstrates that a proper nesting or feedback in the optical structure can simplify the filter design. The procedure is a particular case of the theory of low sensitivity discrete time filters structures. Moreover, these digital filters are typical cases where the filters are designed in the z-domain without having the trouble to go through the continuous prototype design. We will implement the new procedure and present simulation design for all-pass and notch digital filters.