The application of a cascaded phase shift to a fully integrated nonlinear directional coupler (NLDC) and Mach-Zehnder interferometer (MZI) is presented. It shows that for MZI, the input power was increased and the throughput was modulated between 80% and 20% of the input. For the NLDC, the switching from the cross to the bar states is clear

Baek, Yongsoon

Baumann, I.

Krijnen, Gijs

Schiek, Roland

Sohler, W.

Stegeman, George I.

English

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Applications of cascading nonlinear optics to all-optical devices

Stegeman, G.I.

Schiek, R.

Baek, Y.

Krijnen, Gijsbertus J.M.

University of Twente Research Information

10:30am-l1:00an (Invited) ThWl Applications of Cascading Nonlinear Optics to All-Optical Devices George I. Stegeman, Roland Schiek, Yongsoon Baek and Gijs Krijnenz CREOL, University of Central Florida, P.O.Box 162700 4000 Central Florida Blvd., Orlando, Fl32816-2700 I. Baumann and W. Solder Angewandte Physik, Universitat- Gesamthochschule- Paderbom Warburger Strasse 100, D-33098 Paderborn, Germany Current address: $Lightwave Devices Group, University of Twente, 7500 E, Enschede, The Netherlands Cascading is the process by which second order nonlinearities, when used near phase- matching for parametric mixing processes such as second harmonic generation (SHG), can be used to mimic some effects normally associated with third order nonlinearities, more specifically with an intensity-dependent refractive index. The findmental beam on transmission through a x(2)-active medium has the form: away from the phase-matching condition there is a nonlinear phase shift +m(z> induced whose magnitude and sign depends on the detuning from phase-matching. (There are also interesting effects associated with the amplitudes of the fundamental and second harmonic, includmg the formation of solitary waves - these will not be discussed here.) It is well-known that nonlinear phase shifts in general are needed for all-optical switching devices and in this paper we will describe the application of such cascaded phase shifts to a klly integrated nonlinear directional coupler and Mach-Zehnder interferometer. [ 1-41 The devices utilized Type I phase matching in a Somm long Titanium indiffused symmetrical channel waveguide with propagation along the X-axis on a Y-cut LiNbOj crystal. Temperature tuning is required at 1320 nm to implement SHG and the experiments were conducted in an oven around 34OoC. The key to the successll implementation of devices in these waveguides was the temperature distribution in the oven ( d o r m  in the middle and decreasing towards the input and output windows) which allowed large phase shifts (>1.5x) to be obtained with minimal net losses in the findmental throughput due to SHG (- 10%)).[23 were made on a LiNbO3 substrate.[3,4] The modelling of the devices was complicated by the presence of four coupled fields and the spatial distribution of the wavevector mismatch was optimized so that SHG is minimized at both outputs siiultaneously. The final designs were fabricated and tested with a Nd:YAG laser operating with 90psec pulses. The results are shown in Figs. 1 and 2. For the MZI it is clear that as the input power is increased, the throughput is modulated between >80% to less than 20% of the input. Similarly, for the NLDC, the switching Both a nonlinear directional coupler (NLDC) and Mach-Zehnder interferometer (NMZI) 322 Authorized licensed use limited to: IEEE Xplore. Downloaded on October 10, 2008 at 04:07 from IEEE Xplore.  Restrictions apply.from the CROSS to the BAR states with increasing power is clear. I . I . , . I . , . -  Fig. 1: Measured transmittance of a 88 - - Limo3 integrated Mach Zehnder interferometer as a hnction of the peak input power with initial phase difference of -IT between the two arms (solid curves, experiment; dotted curves, theory). g 6o - 4 01 " " " * I " ' I Input Power (W) 0 1000 2000 3000 4000 5000 6000 Fig. 2: Power-dependence of a NLDC findamental output for a crystal temperature of 343 "C. Smooth curves are theory. 100 80 60 40 20 POWER DN] The switching powers in these Go applications are in the KW range. These waveguides have large modal areas ( A e f f  75 pn2) and utilize small second order nonlinearities (5  p"). There are materials now available with d(2)s of 600 mN, and in which waveguide containment can be optimized. The switching power varies as I J2)IZAeff and we expect that milliwatt switching powers will ultimately be possible. References: [ 11 1852,7 (1993). [2] Sohler, Opt. Lett., 19, 1949 (1994). [3] press [4] Lett., 68,2055 (1996) G.I. Stegeman, SPIE Proceedings on Nonlinear Optical Properties of Advanced Materials, R. Schiek, M.L. Sundheimer, D.Y. Kim, Y. Baek, G.I. Stegeman, H. Suche and W. R. Schiek, Y. Baek, G. Krijnen, G.I. Stegeman, I. Baumann and W. Sohler, Opt. Lett., in Y. Baek, R. Schiek, G. Krijnen, G.I. Stegemaq I. Baumann and W. Sohler, Appl. Phys. 323 Authorized licensed use limited to: IEEE Xplore. Downloaded on October 10, 2008 at 04:07 from IEEE Xplore.  Restrictions apply.

[2] Sohler,

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Applications of cascading nonlinear optics to all-optical devices

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