JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 29, NO. 1, JANUARY 1, 2011 69 Insertion Loss and Crosstalk Analysis of a Fiber Switch Based on a Pixelized Phase Modulator David Sinefeld and Dan M. Marom, Senior Member, IEEE Abstract—We analyze the performance of a spatial fiber switching system when using a pixelized mirror, such as a LCoS or MEMS spatial light modulator, in place of a large tilting mi- cromirror. Our findings demonstrate the dependence of insertion losses on tilt angles or fiber counts, and the dependence of the crosstalk in the number of phase quantization levels and random phase errors. The former effects can be minimized by satisfying a relationship between the tilt angle to a fiber, the pitch of the array, and the optical wavelength. Index Terms—Microelectromechanical devices, multiplexers, optical fiber communication, optical switches, spatial light modu- lators (SLMs). I. INTRODUCTION O PTICAL switching between a single input fiber and multiple output fibers is often implemented with a free-space arrange- ment using a single tilting mirror that performs the task of beam steering [1] [see Fig. 1(Top)]. A diffraction grating may be inserted into the optical path to construct a wavelength-selective switch version [2] [see Fig. 1(Bottom)], in which case a 1-D array of tilting micromir- rors is required, one for every wavelength channel. Both the single tilting mirror and the micromirror array are usually implemented using microelectromechanical system (MEMS) technology, which is based on processing of silicon to construct moving structures. However, some system vendors are averse to using MEMS tilting micromirrors in telecom components and subsystems, due to concerns of stability, repeatability, fatigue, and aging. While it has been shown that by proper design such concerns can be laid to rest [3], there is still intense interest in alternative beam-steering solutions [4]. Recent technological advances in large, 2-D array, spatial light mod- ulators (SLMs)—which were originally developed for high-resolution image projection application—can also be utilized for beam steering. The SLM has to be configured to modulate phase instead of ampli- tude, and beam steering is achieved by prescribing a linear phase ramp. Modern SLM panels are often based on a liquid--crystal on silicon (LCoS) device, which utilizes a silicon chip for defining and electri- cally addressing the individual pixels of the array, with no moving parts [5]. MEMS-based panels are also available, where pixel modulation is achieved with piston motion pixels [6]. Manuscript received July 04, 2010; revised September 08, 2010; accepted October 25, 2010. Date of publication November 11, 2010; date of current ver- sion January 05, 2011. This work was supported in part by the Israel Science Foundation under Grant 1359/07 and in part by The Peter Brojde Center for In- novative Engineering. The authors are with the Applied Physics Department, The Hebrew Uni- versity of Jerusalem, Jerusalem 91904, Israel (e-mail: sinefeld@gmail.com; danmarom@cc.huji.ac.il). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org Digital Object Identifier 10.1109/JLT.2010.2091623 Fig. 1. Switches based on beam-steering architecture. Top: Switching from an input fiber to any output fiber, as determined by the mirror tilt angle. Bottom: Fiber switching on a wavelength-basis, as determined by the mirror tilt angle in the mirror array, where each mirror is assigned for each wavelength. In this paper, we offer a rigorous analysis of the performance asso- ciated with beam scanning switches, when the mirror is implemented with a phase SLM instead of a tilting mirror. We analytically calculate the fiber coupling integral to the desired fiber to which the optical signal is routed, as well as to the other fibers giving rise to crosstalk. We take into account the effects of pixel size and phase level quantization. We find that the insertion loss to the desired fiber increases as the number of pixels spanning the full phase period decreases. Additionally, we find that the crosstalk to the other fibers increases as the number of discrete phase levels that can be prescribed decreases. A statistical analysis of random phase errors was also performed, showing the im- pact of phase errors on the crosstalk. Hence, the ideal SLM should have infinitesimally-small pixels and continuous, as opposed to dis- crete, gray level representation, hence approaching the performance of a bulk tilting mirror. Due to the generality of the discussion, we avoid including effects that are typical to a specific SLM type. LCOS SLM suffer mostly from the fringe-field effect between pixels [7] , whereas MEMS modulators have a lower fill factor, which reduces the diffraction efficiency; both effects were omitted from our analysis. The paper is structured as follows: in Section II, we describe the system model and our method of calculation, in Section III, the per- formance (e.g., fiber coupling and crosstalk) of a simple system with a continuous mirror as the phase deflector is discussed, in Section IV, the mirror is replaced with a phase SLM where the pixelization effect is being taken into account. Finally in Section V, the addition of random 0733-8724/$26.00 © 2011 IEEE