International Journal of Optics and Applications 2012, 2(3): 15-19 DOI: 10.5923/j.optics.20120203.01 Comparative Analysis of Optical Ring Resonators with Cross- and Direct-Coupled Configurations Faramarz E. Seraji 1, 2, * , Fatemeh Asgahri 3 1 Optical Communication Group, Iran Telecom Research Center, Tehran, Iran 2 Electrical Eng. Dept., Ghiasodin Jamshid Kashani Institute of Higher Edu., Abyek, Qazvin, Iran 3 Physics Group, Payam Noor University, Shahr Rey, Iran Abstract This paper presents a proposed alternate configuration for optical ring resonator (ORR) having a resonance loop made of single-mode optical fiber. Under steady state condition, the responses of the proposed ORR are formulated by considering the output and loop intensities for various conditions of transmission coefficient, power coupling coefficient, and compared the results with the previous reported ORR configuration. The analyses have shown that the main difference be- tween two ORRs is due to the values of power coupling coefficients of the couplers used in their configurations. Another major point, that is to be considered in design of ORR for a maximum output power is that the transmission coefficient and power coupling coefficient in the proposed configuration are not required to be equal, as the case of the previously reported configuration. The analytical results given in this article can be useful for selection of ORR configuration for particular applications, specially in case of nonlinear use of ORR configuration. Keywords Comparative analysis, Optical ring resonator, Alternate configurations 1. Introduction With increasing demands in optical communication and sensing systems, optical ring resonators (ORR) with differ- ent structures[1-6], have been analyzed and proposed for several applications such as polarization sensing[7], bio- sensing[8], optical filters[9-14], optical fiber dispersion compensation devices[15,16], optical integration/ differen- tiation and optical triggering[2]. optical bistability[17,18], add/ drop multiplexer[19], optical switching[20-23], and various other applications[24-30]. In early work, steady state[2,31] and dynamic responses of ORR built on fiber were analyzed[32,33] for applications in polarization sens- ing[7], FM deviation measurement of a laser diode[33], optical triggering, optical integration/differentiation and fiber dispersion compensation[2], and rotation sensing[31]. Recently, dynamic resonance characteristic of fiber ring resonator has been analyzed for gyro system[34]. A basic structure of an ORR consists of a 2×2 directional coupler where one of the input port is connected to one of the output port, making a closed loop to configure a ring resonator. To operate an ORR at resonance, the loop length could be of the order of few micrometers[10] to tens of me- ters[32]. Recently, a full steady-state analysis of the ORR is * Corresponding author: feseraji@itrc.ac.ir (Faramarz E. Seraji) Published online at http://journal.sapub.org/optics Copyright © 2012 Scientific & Academic Publishing. All Rights Reserved reported where characteristic parameters such as coupling coefficient of the coupler and transmission parameters of the loop fiber affecting the response are investigated[35]. In another report, the dynamic behavior of the ORR, by con- sidering the influences of light-source parameters on the response, is presented[36]. An ORR may be realized mainly by two types of con- figurations: Cross-coupled and direct-coupled. To the best of our knowledge, in the reported analyses of the ORR in the literatures, the importance and difference of these con- figurations have not been addressed with application point of views. With respect to the type of high power applica- tions of ORR, variety of configuration may play an impor- tant role[37-39]. In this paper, we analyze the two ORR configurations and compare their characteristic intensities at the output and in the resonance loop[35]. It is shown that in one configura- tion the, the resonance loop intensity is about twice the other one. 2. ORR Configurations and Response Formulation 2.1. Intensities of Output and Resonance Loop The two ORR configurations, which are considered for analysis, are shown in Fig. 1. In Fig. 1(a), a previously re- ported configuration[35] is shown in which the resonance loop is made by connecting two cross-coupled ports (2) and (3), whereas the resonance loop of our suggested ORR con-