Tunable spectral slicing filter utilizing sparse grating in Ti:LiNbO 3 Renato C. Rabelo* a , Ohannes Eknoyan b and Henry F. Taylor b a Instituto de Estudos Avançados (IEAv), Rod. Tamoios km 5,5, S. J. Campos, SP Brazil 12228-001; b Deptartment of Electrical and Computer Engineering, Texas A&M University, College Station, TX, USA 77843-3128 ABSTRACT A new type of tunable guided-wave spectral slicing filter at the 1530nm wavelength regime is reported. The design allows the selection of equally spaced frequency channels and simultaneously produces nulls that are equally spaced between the selected channels. This makes it attractive for minimizing crosstalk in dense wavelength division multiplexing (DWDM) applications. The spectral selection of the filter is based on co-directional polarization coupling between transverse electric (TE) and transverse magnetic (TM) orthogonal modes in a waveguide by means of a static strain induced index grating. An etalon-like response results from the sparse arrangement of the grating sections as N individual coupling regions in tandem with equal spacing between their centers, yielding N-1 equally spaced nulls between adjacent selected frequencies. Adjustments of the resulting filtering function may be obtained by proper choice of coupling regions’ lengths and spacing. Devices were fabricated using single mode channel waveguides formed by Ti diffusion on x-cut y-propagating LiNbO 3 substrates. Static strain from a periodically delineated surface film was used for making N = 6 polarization coupling regions. Electrode patterns centered about the optical waveguide and defined by liftoff were used to tune the filter electrooptically. Experimental results are in good agreement with design theory. Keywords: Integrated optics, Lithium niobate, Tunable filters, Sparse gratings. 1. INTRODUCTION A DWDM optical network demands devices capable of filtering individual channels respecting strictly defined pass bands and stop bands. Among the optical tunable filters, those with smallest response time to a tuning excitation are the ones attracting more interest because they would enable a future dynamically varying DWDM network, in which packet switching and wavelength routing will be routine operations. The electro-optically tunable filter places as one of the fastest response time devices and there is still ongoing research on devices of that category as well as on the competing technologies aimed at satisfying DWDM requirements. Research activities at Texas A&M University have demonstrated electro-optic tunable filters employing Ti-diffused waveguides in lithium niobate substrate (Ti:LiNbO 3 ) [1]. These devices perform optical filtering by using co-directional TE-TM mode conversion. The coupling between these two modes is accomplished by using a phasematched strain- induced overlay grating of a silica (SiO 2 ), deposited at high temperature and patterned at room temperature. The difference in SiO 2 and LiNbO 3 thermal expansion coefficients builds up a strain field that generates a periodic refractive index grating in the waveguide through the strain-optic effect. By properly choosing the SiO 2 film deposition parameters as well as waveguide fabrication parameters and grating period, the polarization conversion is made efficient. When uniform gratings are used, the polarization conversion efficiency has a well known spectral response and even though the resulting filtering function is periodic, it is not with respect to the desired parameter (frequency). The filtering function periodicity in the frequency domain would translate into presenting equally spaced nulls and maxima through the spectrum of interest, making it easier to define channel regions in the spectrum and avoid crosstalk between those. In order to circumvent the uniform grating characteristic of unequally spaced nulls and maxima, a new topology of sparse strain gratings was proposed [2]. It is capable of placing the nulls of the spectrum at well known, equally spaced positions, defining channel spectral regions in the stop band and pass band of the filter. This paper reports the first realization of spectral slicing filters that uses sparse strain gratings on Titanium difused Lithium niobate waveguides (Ti:LiNbO 3 ). *rcrabelo@ieav.cta.br; phone 55 12 3947-5460; fax 55 12 3944-1177 Integrated Optics: Devices, Materials, and Technologies XIII, edited by Jean-Emmanuel Broquin, Christoph M. Greiner, Proc. of SPIE Vol. 7218, 72180F · © 2009 SPIE · CCC code: 0277-786X/09/$18 · doi: 10.1117/12.808659 Proc. of SPIE Vol. 7218 72180F-1