Electro-optic modulation in slotted resonant photonic crystal heterostructures

Abstract

Two dimensional photonic crystal waveguides in high index materials enable integrated optical devices with an extremely small geometrical footprint on the scale of micrometers. Slotted waveguides are based on the guiding of light in low refractive index materials and a field enhancement in this particular region of the device. In this letter we experimentally demonstrate electro-optic modulation in slotted photonic crystal waveguides based on silicon-on-insulator substrates covered and infiltrated with nonlinear optical polymers. A photonic crystal heterostructure is used to create a cavity, while simultaneously serving as an electrical connection from the slot to the metal electrodes that carry the modulation signal. © 2009 American Institute of Physics. ͓DOI: 10.1063/1.3156033͔Electrically driven optical modulation in silicon photonics typically relies on interactions between the optical mode and a free carrier plasma via either carrier depletion, injection, or accumulation. 1-3 The achievable modulation speed using these methods is limited by the time constants related to the injection or removal of carriers from the optical waveguide. In contrast, modulation via nonlinear optical ͑NLO͒ polymers accesses the electronic polarization of the organic molecules, which allows extremely high modulation speeds extending up to frequencies in the terahertz range. 4 Furthermore, molecular engineering of organic molecules has led to extremely high Pockels-coefficients in polymers exceeding 300 pm/V, 5 which is ten times the value available in lithiumniobate, the standard inorganic material used in electro-optic ͑EO͒ applications. Photonic devices based on a hybrid material system merging silicon and polymer are therefore attractive since they combine the strong light confining abilities of silicon with the superior NLO properties of polymers.All-optical and EO-modulation in such hybrid silicon and NLO-polymer systems has been demonstrated for slotted photonic wire based Mach-Zehnder and ring-resonator modulators. 6-8 Concepts based on slotted photonic crystal ͑PhC͒ waveguides can exploit slow light mechanisms or high quality factor cavities to achieve very compact device dimensions and have been discussed recently. 9-11 We propose a concept using a double heterostructure cavity 11-13 in a slotted silicon PhC waveguide, infiltrated with NLO-polymer to operate as an EO-modulator. Figure 1 shows a scanning electron micrograph of the structure. The 150 nm wide slot in the center of the waveguide is filled with NLO-polymer ͑n poly = 1.63͒ and the strong overlap between the optical field and the polymer makes the effective index of the propagating mode very sensitive to any refractive index changes in EOpolymer. The PhC features a background doping density of 10 15 cm −1 and therefore serves as an electrical conductor from the metallic contact pads to the slot, while keeping the optical field away from the metal regions and hence preventing additional losses. The double heterostructure design of the PhC ͑a = 410 nm, r / a = 0....

Exact solution to the steady-state dynamics of a periodically modulated resonator

“…2 The electro-optic modulator 3,4 is one of the most important components in silicon photonics, and CMOS-compatible, micrometer-scale devices based on a modulated cavity resonance have been a central focus of research. [5][6][7][8][9][10][11][12][13][14][15][16][17][18] Typically in these systems, a local refractive index change of the silicon results in a change of the transmission through the cavity. This is intuitively understood in the adiabatic limit, in which the modulation happens on a time scale that is much slower than the one given by the photon lifetime, but the phenomenology is in general much richer.…”

40 GHz electro-optic modulation in hybrid silicon–organic slotted photonic crystal waveguides

“…The calculated in-device Pockels coefficient of the NLO polymer is 12 pm=V, using the technique described in [15]. This value is nearly 1 order of magnitude below the value reported for thin film samples of the same material [13] or other NLO polymers.…”

“…by experiments at kilohertz modulation frequencies employing the lock-in measurement technique as explained in [15].…”

Compact and Temperature Independent Electro-optic Switch Based on Slotted Silicon Photonic Crystal Directional Coupler

“…The centrosymmetric crystal structure of silicon prohibits native silicon from possessing the Pockels effect, with the result that switches tend to be either very long or require high powers to operate. This problem limits the use of silicon in photonic integrated circuits (PICs) [6]. The thermo-optic effect in silicon is comparatively higher than EO effect, but the switching time above 1 μs is an important limitation in thermo-optic devices [2,8].…”