Dean Samara-Rubio

A high-speed silicon optical modulator based on a metal–oxide–semiconductor capacitor

Silicon has long been the optimal material for electronics, but it is only relatively recently that it has been considered as a material option for photonics. One of the key limitations for using silicon as a photonic material has been the relatively low speed of silicon optical modulators compared to those fabricated from III–V semiconductor compounds and/or electro-optic materials such as lithium niobate. To date, the fastest silicon-waveguide-based optical modulator that has been demonstrated experimentally has a modulation frequency of only ∼20 MHz (refs 10, 11), although it has been predicted theoretically that a ∼1-GHz modulation frequency might be achievable in some device structures. Here we describe an approach based on a metal–oxide–semiconductor (MOS) capacitor structure embedded in a silicon waveguide that can produce high-speed optical phase modulation: we demonstrate an all-silicon optical modulator with a modulation bandwidth exceeding 1 GHz. As this technology is compatible with conventional complementary MOS (CMOS) processing, monolithic integration of the silicon modulator with advanced electronics on a single silicon substrate becomes possible.

High speed silicon Mach-Zehnder modulator

We demonstrate a silicon modulator with an intrinsic bandwidth of 10 GHz and data transmission from 6 Gbps to 10 Gbps. Such unprecedented bandwidth performance in silicon is achieved through improvements in material quality, device design, and driver circuitry.

Scaling the modulation bandwidth and phase efficiency of a silicon optical modulator

We present an optimized design and detailed simulation of an all-silicon optical modulator based on a silicon waveguide phase shifter containing a metal-oxide-semiconductor (MOS) capacitor. Based on a fully vectorial Maxwell mode solver, we analyze the modal characteristics of the silicon waveguide. We show that shrinking the waveguide size and reducing gate oxide thickness significantly enhances the phase modulation efficiency because of the optical field enhancement in the voltage induced charge layers of the MOS capacitor, which, in turn, induce refractive index modulation in silicon due to free carrier dispersion effects. We also analyze the device speed by transient semiconductor device modeling. As both optical absorption and modulation bandwidth increase with increasing doping concentration, we show that, with a nonuniform doping profile in the waveguide, balance between the device operation speed and optical loss can be realized. Our simulation suggests that a TE-polarized optical phase modulator with a bandwidth of 10 GHz and an on-chip optical loss less than 2 dB is achievable in silicon.

Developments in Gigascale Silicon Optical Modulators Using Free Carrier Dispersion Mechanisms

This paper describes the recent advances made in silicon optical modulators employing the free carrier dispersion effect, specifically those governed by majority carrier dynamics. The design, fabrication, and measurements for two different devices are discussed in detail. We present an MOS capacitor-based modulator delivering 10 Gbps data with an extinction ratio of ∼ 4 dB and a pn-diode-based device with high-speed transmission of 40 Gbps and bandwidth greater than 30 GHz. Device improvements for achieving higher extinction ratios, as required for certain applications, are also discussed. These devices are key components of integrated silicon photonic chips which could enable optical interconnects in future terascale processors.

Customized drive electronics to extend silicon optical modulators to 4 gb/s

The data transmission bandwidth of a metal oxide semiconductor (MOS) capacitor Si optical modulator is extended from 1 to 4 Gb/s through the introduction of custom-designed low-impedance drive circuitry. Two distinct drive circuits were produced and tested-the first targeting 2.5 Gb/s data rate and 3 dB extinction ratio (ER), and the second having reduced voltage swing (1.3 V single-ended swing) while achieving an open eye at 4 Gb/s. The speed, power, and ER data collected are used to build a quantitative discussion of the challenges in achieving a power-efficient free-carrier modulator at bit rates above 1 Gb/s.

Phase modulation efficiency and transmission loss of silicon optical phase shifters

This paper focuses on understanding the phase efficiency and optical loss of MOS-capacitor-based silicon waveguide phase shifters. A total of nine designs have been fabricated using poly-silicon and characterized at wavelengths around 1.55 /spl mu/m. Detailed comparison of design parameters shows that scaling down the waveguide dimensions, placing the capacitor gate oxide near the center of the optical mode, and reducing the oxide thickness significantly enhance phase modulation efficiency. Our best design to date demonstrates a /spl pi/-radian phase shift with 0.8-cm device length and 3-V drive. This phase shifter has a transmission loss of 15 dB, the primary source of which is the poly-silicon regions inside the device. An improved material can reduce loss to as little as 4 dB.

Sputtered A1N Thin Films for Piezoelectric MEMS Devices

Piezoelectric films have been demonstrated to be attractive for micromechanical systems (MEMS) devices. Among the piezoelectric films used, AlN film has been less explored. In this study, AlN resonators and accelerometers, utilizing longitudinal and transverse piezoelectric effects respectively, were demonstrated. Resonators with Q of 1000 and electromechanical coupling (kt 2) of 6.5% were achieved at ~2 GHz. Accelerometers were fabricated and tested with charge sensitivities ranging between 0.06 to 0.45 pC/g depending on device designs. Important material properties of sputtered AlN films - C33 of 435 GPa, e33 of 1.55 C/m2, and e31 of -0.58 C/m2 - were extracted by fitting finite element analysis (FEA) simulated values to measured results.

Fast silicon optical modulator

We present design, fabrication, and testing of a high-speed all-silicon optical phase modulator in silicon-on-insulator (SOI). The optical modulator is based on a novel silicon waveguide phase shifter containing a metal-oxide-semiconductor (MOS) capacitor. We show that, under the accumulation condition, the drive voltage induced charge density change in the silicon waveguide having a MOS capacitor can be used to modulate the phase of the optical mode due to the free-carrier plasma dispersion effect. We experimentally determined the phase modulation efficiency of the individual phase shifter and compared measurements with simulations. A good agreement between theory and experiment was obtained for various phase shifter lengths. We also characterized both the low- and high-frequency performance of the integrated Mach-Zehnder interferometer (MZI) modulator. For a MZI device containing two identical phase shifters of 10 mm, we obtained a DC extinction ratio above 16 dB. For a MZI modulator containing a single-phase shifter of 2.5 mm in one of the two arms, the frequency dependence of the optical response was obtained by a small signal measurement. A 3-dB bandwidth exceeding 1 GHz was demonstrated. This modulation frequency is two orders of magnitude higher than has been demonstrated in any silicon modulators based on current injection in SOI.

High Speed Metal?Oxide?Semiconductor Capacitor-Based Silicon Optical Modulators

Silicon photonics has recently attracted a great deal of attention because it offers an opportunity for low cost opto-electronic solutions for applications ranging from telecommunications down to chip-to-chip interconnect. One area of silicon photonics research that has seen an exceptional increase in activity and advancement is high speed silicon optical modulation. Within three years, modulation bandwidth has increased nearly three orders of magnitude from MHz range to 10 GHz range. This paper reviews two high speed silicon optical modulators with GHz bandwidth. It discusses in detail their design, performance, and limitations; and it outlines a path that can enable realization of further device improvements.

Recent development in silicon photonics: 2.5 Gb/s silicon optical modulator and silicon Raman laser

Due to the mature silicon fabrication technology and vast existing infrastructures, silicon photonics has a chance to offer low cost solutions to telecommunications and data communications. It could also enable a chip-scale platform for monolithic integration of optics and microelectronics circuits for applications of optical interconnects for which high data streams are required in a very small footprint. Two key building blocks needed for any silicon based optoelectronics are silicon based light source and high-speed optical modulator. This paper gives an overview of recent results for a fast (>1GHz) silicon modulator and a silicon Raman laser. We present optical characterization of a high speed metal-oxide-semiconductor (MOS) capacitor-based silicon optical modulator. We show that a Mach-Zehnder interferometer (MZI) structure with a custom-designed driver circuit results in the realization of a silicon modulator transmitting data at 2.5 Gb/s with an extinction ratio of up to 2.8 dB. In addition we show that by reducing the waveguide dimensions one can improve the phase efficiency. In addition, as single crystal silicon possesses higher (four orders of magnitude) Raman gain coefficient as compared to silica, it is possible to achieve sizeable gain in chip-scale silicon waveguide for optical amplification and lasing. With a 4.8 cm long waveguide containing a reverse biased p-i-n diode, we demonstrate lasing operation using a pulsed pump laser. We achieve ~10% slope efficiency. We in addition model a continuous-wave silicon Raman laser and show that higher conversion efficiency and lower threshold power can be realized with optimised cavity device design.