3470 JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 28, NO. 23, DECEMBER 1, 2010 An All-Optical Switching Based on Resonance Breaking With a Transient Grating Osman Akin and Mehmet Salih Dinleyici Abstract—A new resonance breaking in-fiber switch as an all-op- tical network component is investigated and presented. A transient grating is applied to break the transverse resonance of the fun- damental waveguide mode and the power coupled into the higher order propagating mode is computed using coupled mode theory (CMT). The coupling of the modes with the grating forming beams in the evanescent region of the waveguide is investigated with four wave mixing (FWM). High conversion efficiency is calculated in the case of perfect phase matching at communication wavelength 1550 nm. The conversion efficiency of the proposed structure is consid- ered in terms of third-order nonlinear susceptibility, and the ef- fect of design and tuning parameters are investigated for grating forming geometry and laser beam intensity, respectively. Index Terms—Four wave mixing (FWM), nonlinear optics, op- tical Kerr effect, optical switches, transient gratings. I. INTRODUCTION D RAMATIC increase of data traffic in current communi- cation networks has steered the research interests in pho- tonics into all optical signal processing elements. Accordingly, the invention of high-power lasers made it possible to realize photonic components based on optical nonlinearities requiring high power densities. Designing a faster all-optical switching component using optical nonlinearity is one of the most desired goals in the field of all-optical information processing, and var- ious types of all optical elements have been proposed so far [1], [2]. All optical switches based on semiconductor optical amplifier and Mach–Zender interferometer [3], ring resonator [4] and plasmonics [5] have been demonstrated. However, most of these are far from being satisfactory for the current require- ments of optical packet switching, such as switching power re- quirement, scalability, switching efficiency, and switching rate, which make these components inadequate for future commu- nication networks. The implementation of all optical process of controlling light with light requires nonlinear medium. Al- though the material nonlinearity observed up to now is still quite low, third-order optical nonlinearity, namely, Kerr effect, is one of the fastest phenomenon that can be exploited to design a high-speed all-optical switching mechanism [6]. Furthermore, the modification of refractive index of Kerr-type medium in free Manuscript received February 16, 2010; revised May 15, 2010, September 13, 2010; accepted October 10, 2010. Date of publication October 25, 2010; date of current version November 29, 2010. This work was supported by Tubitak under Project 109E240 and IYTE Research Fund under Project 2008IYTE10. The authors are with Izmir Institute of Technology, Izmir 35430, Turkey (e-mail: osmanakin@iyte.edu.tr; salihdinleyici@iyte.edu.tr). 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.2010.2089599 space using holographic method was demonstrated experimen- tally, and a response time of few femtoseconds was reported [7], [8]. All optical devices comprising various forms of stationary gratings written in core region are widely used in fiber com- munication and sensing applications. There are numerous pub- lications for all-optical switching based on stationary gratings externally written on the fiber core [9]–[11]. However, Chen et al. discovered that a periodic perturbation created in cladding can affect the fundamental core mode and offer some advan- tages compared to the traditional methods [12]. In light of these developments, we propose a new in-fiber all optical switching device, which have not been realized yet to our knowledge. This device consists of a transient grating formed by control laser light according to the Kerr effect and another sta- tionary grating placed just after the transient grating. The sug- gested device is created by partial removal of the cladding and placing a material with high third-order nonlinearity instead of a cladding material. This process was previously investigated ex- perimentally by Dinleyici [13]. The nonlinear medium enables the interaction of propagating mode with the grating forming laser control light that results in all optical switching. The pro- posed waveguide structure can be analyzed by considering four wave mixing (FWM) of Gaussian beams and propagating mode in the region of core-cladding boundary, where fields of modes and grating forming fields are interacting in the evanescent re- gion of the waveguide and where nonlinear material is placed. Hereafter, the coupled wave equations for the propagation of higher order modes are obtained in the existence of the transient grating. In order to extract these modes out to another wave- guide, a second permanent grating may be placed after the tran- sient grating. By using this method, optical data packets can be transferred to another waveguide by means of transient grating and secondary stationary grating. Due to fast response time (fs) of Kerr-type materials, this method gives possibility to achieve high-optical switching rates of about tens of Gb/s for recent op- tical communication systems. In this method, the existence of transient grating satisfies the switching operation, while the laser beam intensity is the control parameter. The switching efficiency can be controlled via total intensity and the higher Kerr coefficient of the cladding mate- rial, the lower intensity is needed to obtain switching operation. Recent developments in polymer science can make it possible to realize this instantaneous switching with low-level control light [14], [15]. In the switching schematic, as shown in Fig. 1, two Gaussian laser beams are interfered at the cladding region of the wave- guide to create a transient grating using the Kerr effect. The formed structure is close enough to the core-cladding boundary 0733-8724/$26.00 © 2010 IEEE