We present a novel hybrid silicon-polymer dual slot waveguide for high speed and ultra-low driving voltage electro-optic (EO) modulation. The proposed design utilizes the unique properties of ferroelectric materials such as LiNbO3 to achieve dual RF and optical modes within a low index nanoslot. The tight mode concentration and overlap in the slot allow the infiltrated organic EO polymers to experience enhanced nonlinear interaction with the applied electric field. Half-wavelength voltage-length product and electro-optic response are rigorously simulated to characterize the proposed design, which reveals ultrabroadband operation, up to 250？GHz, and subvolt driving voltage for a 1？cm long modulator. 1. Introduction Low driving voltage and high-speed electro-optic (EO) modulators are of great interest due to their wide variety of applications including broadband communication, RF photonic links, millimeter wave imaging, and phased-array radars. In order to attain optical modulation at low driving voltages, a strong mode concentration and a tight mode overlap between optical and radio-frequency (RF) modes in the nonlinear EO material are required. Typically, to maintain a single mode operation in optical domain, the optical mode size is on an order of wavelength, that is, 2？um at telecommunication region. As a result, to match with the optical mode, the RF guiding structure essentially has to reduce a factor of three orders of magnitude. Conventional traveling wave EO modulators are usually driven by RF transmission lines, such as coplanar waveguides (CPWs) and microstrip lines. These electrode designs provide not only high speed operation but also a strong overlap between optical and RF modes. While the device operates at very high frequency, that is, over 20？GHz, the RF wave propagation attenuation attributed from both conduction loss and dielectric loss becomes the key issue that prevents the device from operating over a wide bandwidth. Physically, a small mode size provides a strong RF field concentration, or a small mode volume, however, leads to a significant increase in propagation loss. As a result, an optimal design of RF electrode design including signal electrode and gap between signal and ground is required to minimize the overall RF propagation loss. To date, many high speed traveling wave EO modulators have been designed, fabricated, and characterized, leading to operation at speeds as high as 140？GHz. Most of these modulators were developed using crystalline EO materials, such as LiNbO3 [1–5] and GaAs [6, 7]. Recently, tremendous efforts
References
[1]
J. Macario, P. Yao, R. Shireen, C. A. Schuetz, S. Y. Shi, and D. W. Prather, “Development of electro-optic phase modulator for 94 GHz imaging system,” Journal of Lightwave Technology, vol. 27, pp. 5698–5703, 2009.
[2]
K. Noguchi, O. Mitomi, and H. Miyazawa, “Millimeter-wave Ti:LiNbO3 optical modulators,” Journal of Lightwave Technology, vol. 16, no. 4, pp. 615–619, 1998.
[3]
Y. Liao, H. Zhou, and Z. Meng, “Modulation efficiency of a LiNbO3 waveguide electro-optic intensity modulator operating at high microwave frequency,” Optics Letters, vol. 34, no. 12, pp. 1822–1824, 2009.
[4]
Y.-Q. Lu, M. Xiao, and G. J. Salamo, “Wide-bandwidth high-frequency electro-optic modulator based on periodically poled LiNbO3,” Applied Physics Letters, vol. 78, no. 8, pp. 1035–1037, 2001.
[5]
D. Janner, M. Belmonte, and V. Pruneri, “Tailoring the electrooptic response and improving the performance of integrated LiNbO3 modulators by domain engineering,” Journal of Lightwave Technology, vol. 25, no. 9, pp. 2402–2409, 2007.
[6]
Q. Y. Lu, W. H. Guo, D. Byrne, and J. F. Donegan, “Design of low V-pi high-speed GaAs travelling-wave electrooptic phase modulators using an n-i-p-n structure,” IEEE Photonics Technology Letters, vol. 20, pp. 1805–1807, 2008.
[7]
M. Jarrahi, T. H. Lee, and D. A.B. Miller, “Wideband, low driving voltage traveling-wave Mach-Zehnder modulator for RF photonics,” IEEE Photonics Technology Letters, vol. 20, no. 7, pp. 517–519, 2008.
[8]
Y. Enami, C. T. Derose, and C. T. Derose, “Hybrid polymersol-gel waveguide modulators with exceptionally large electro-optic coefficients,” Nature Photonics, vol. 1, no. 3, pp. 180–185, 2007.
[9]
Y. Enami, D. Mathine, C. T. Derose, R. A. Norwood, J. Luo, A. K.-Y. Jen, and N. Peyghambarian, “Hybrid cross-linkable polymer/sol-gel waveguide modulators with 0.65 v half wave voltage at 1550 nm,” Applied Physics Letters, vol. 91, no. 9, Article ID 093505, 3 pages, 2007.
[10]
M. Lee, H. E. Katz, C. Erben, D. M. Gill, P. Gopalan, J. D. Heber, and D. J. McGee, “Broadband modulation of light by using an electro-optic polymer,” Science, vol. 298, no. 5597, pp. 1401–1403, 2002.
[11]
C. T. DeRose, D. Mathine, Y. Enami, R. A. Norwood, J. Luo, A.K.-Y. Jen, and N. Peyghambarian, “Electrooptic polymer modulator with single-mode to multimode waveguide transitions,” IEEE Photonics Technology Letters, vol. 20, no. 12, pp. 1051–1053, 2008.
[12]
E. M. McKenna, A. S. Lin, A. R. Mickelson, R. Dinu, and D. Jin, “Comparison of r33 values for AJ404 films prepared with parallel plate and corona poling,” Journal of the Optical Society of America B, vol. 24, no. 11, pp. 2888–2892, 2007.
[13]
T. Gorman, S. Haxha, and J. J. Ju, “Ultra-high-speed deeply etched electrooptic polymer modulator with profiled cross section,” Journal of Lightwave Technology, vol. 27, no. 1, pp. 68–76, 2009.
[14]
L. R. Dalton, P. A. Sullivan, and D. H. Bale, “Electric field poled organic electro-optic materials: state of the art and future prospects,” Chemical Reviews, vol. 110, no. 1, pp. 25–55, 2010.
[15]
V. R. Almeida, Q. Xu, C. A. Barrios, and M. Lipson, “Guiding and confining light in void nanostructure,” Optics Letters, vol. 29, no. 11, pp. 1209–1211, 2004.
[16]
R. Sun, P. Dong, N.-N. Feng, C.-Y. Hong, J. Michel, M. Lipson, and L. Kimerling, “Horizontal single and multiple slot waveguides: optical transmission at λ = 1550 nm,” Optics Express, vol. 15, no. 26, pp. 17967–17972, 2007.
[17]
C. Koos, P. Vorreau, and P. Vorreau, “All-optical high-speed signal processing with silicon-organic hybrid slot waveguides,” Nature Photonics, vol. 3, no. 4, pp. 216–219, 2009.
[18]
F. Dell'Olio and V. M. N. Passaro, “Optical sensing by optimized silicon slot waveguides,” Optics Express, vol. 15, no. 8, pp. 4977–4993, 2007.
[19]
J.-M. Brosi, C. Koos, L. C. Andreani, M. Waldow, J. Leuthold, and W. Freude, “High-speed low-voltage electro-optic modulator with a polymer-infiltrated silicon photonic crystal waveguide,” Optics Express, vol. 16, no. 6, pp. 4177–4191, 2008.
[20]
C. A. Barrios, “Ultrasensitive nanomechanical photonic sensor based on horizontal slot-waveguide resonator,” IEEE Photonics Technology Letters, vol. 18, no. 22, pp. 2419–2421, 2006.
[21]
G. Wang, T. Baehr-Jones, M. Hochberg, and A. Scherer, “Design and fabrication of segmented, slotted waveguides for electro-optic modulation,” Applied Physics Letters, vol. 91, no. 14, 2007.
[22]
T. Baehr-Jones, B. Penkov, and B. Penkov, “Nonlinear polymer-clad silicon slot waveguide modulator with a half wave voltage of 0.25 v,” Applied Physics Letters, vol. 92, no. 16, Article ID 163303, 2008.
[23]
M. Hochberg, T. Baehr-Jones, G. Wang, J. Huang, P. Sullivan, L. Dalton, and A. Scherer, “Towards a millivolt optical modulator with nano-slot waveguides,” Optics Express, vol. 15, no. 13, pp. 8401–8410, 2007.
[24]
K. K. McLauchlan and S. T. Dunham, “Analysis of a compact modulator incorporating a hybrid silicon/electro- optic polymer waveguide,” IEEE Journal on Selected Topics in Quantum Electronics, vol. 12, no. 6, pp. 1455–1460, 2006.
[25]
S. Shi and D. W. Prather, “Dual rf-optical slot waveguide for ultrabroadband modulation with a subvolt Vp,” Applied Physics Letters, vol. 96, Article ID 201107, 2010.
[26]
Z. Zhu and T. G. Brown, “Full-vectorial finite-difference analysis of microstructured optical fibers,” Optics Express, vol. 10, no. 17, pp. 853–864, 2002.
[27]
R. C. Alferness, “Waveguide electrooptic modulators,” IEEE Transactions on Microwave Theory and Techniques, vol. 30, no. 8, pp. 1121–1137, 1982.
[28]
S.-K. Kim, Y.-C. Hung, and Y.-C. Hung, “Metal-slotted polymer optical waveguide device,” Applied Physics Letters, vol. 90, no. 24, Article ID 243507, 3 pages, 2007.
