Modulation (nW) 10 Modulation P 1/2 1 0.1 0.01 1E-3 0.01 0.1 1 10 100 RF power, P RF (mW) Fig. 9: Modulationamplitude at SAW frequency vs. RF power to the IDT, PRF. Δφs = ωnΔx/c as mentioned above. This results in a sinusoidally varying DC transmission spectrum of the device (fig. 8). The overall transmission of the device at constructive interference at the exit port was about –20 dB. This poor performance is primarily ascribed to the two T-splitters in the MZI. These topology-optimized ridge-waveguide splitters [7] were designed without ZnO coverage in mind. We also believe that the deviations from a sinusoidal transmission spectrum are due to the T-splitters. The MZI had an arm separation of D=4.5λSAW corresponding to an out-of-phase phase-change in the two interferometer arms when SAW modulation is applied to the device. It follows from eq. 1 that the modulation spectrum at the SAW frequency will display minima at both the DC transmission maxima and minima in agreement with fig. 8 (minima marked with arrows). Furthermore it is concluded from eq. 1, that the observed modulation at the SAW fundamental frequency is consistent with a refractive change of 2.3×10 -5 . This value is also consistent with the absence of measurable higher harmonics in the modulated light at all wavelengths. The relative modulation in the investigated wavelength range varied from 0% to 8%. Finally, we mention that the modulation amplitude vs. RF power was measured, and a reasonable agreement with the expected PSAW 1/2 dependency, as demonstrated in fig. 9. Conclusion SAW-driven MZI is a promising technology for compact light modulators in integrated semiconductor platforms such as Si and GaAs. Acknowledgments This project is supported by the EU network of excellence ePIXnet. Mike van der Poel acknowledges support from the Danish Research Council. References 1 M. M. de Lima, Jr., M. Beck, R. Hey, and P. V. Santos, Appl. Phys. Lett., vol. 89, p. 121104, 2006. 2 E. A. Camargo, H. M. H. Chong, and R. M. De La Rue, Opt. Express, vol. 12, p. 588, 2004. 3 R. S. Jacobsen et al., Nature, vol. 44, p. 199, 2006. 4 M. Hochberg et al., Nature Mater., vol. 5, p. 703, 2006. 5 M. Lipson, J. Lightwave Techn., vol. 23, p. 4222, 2005. 6 U. Basu and A. K. Chopra,, Comput. Methods Appl. Mech. Engrg., vol. 192, p. 1337 (2003). 7 L. H. Frandsen, paper CMV4, Conference of Lasers and Electro-Optics (CLEO), 2006.
Publication [P4] Improving the acousto-optical interaction in a Mach-Zehnder interferometer
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