High-speed Silicon Optical Modulator Research Articles

Study on auto bias control of a silicon optical modulator in a four-level pulse amplitude modulation format.

Recently, the high-speed silicon optical modulator has played a greater and greater role in optic fiber communication. Due to the silicon material nonlinear electro-optic effect, the quadrature (Quad) bias point of the modulator is difficult to be locked precisely. In this paper, a novel automatic bias control (ABC) method for four-level pulse amplitude modulation format silicon modulator is presented. First, a sinusoidal dither signal is applied to the modulator DC bias, and the normalized output optical signal function, which is modulated by the dither signal, is obtained. Then, a pair of orthogonal reference functions is created, whose numerical size is equal to the absolute value of sinusoidal and cosine functions so that the frequency is the same as the dither signal. Through the cross-correlation integral operation between the normalized and reference functions above, we find that the zero point of the above integral operation is the best Quad bias point through numerical simulation and experiment. The phase accuracy error of ABC is lower than 2deg, and it satisfies the business specifications of a high-speed silicon optical modulator.

Forward bias operation of silicon photonic Mach Zehnder modulators for RF applications.

In this paper, we demonstrate that forward bias (+0.9V) of a high-speed silicon (Si) optical Mach-Zehnder modulator (MZM) increases the radio-frequency (RF) link gain by 30 dB when compared to reverse bias operation (-8V). RF applications require tunable, narrowband electro-optic conversion with high gain to mitigate noise of the optical receiver and realize high RF spur-free dynamic range. Compared to reverse bias, the forward bias gain rolls off more rapidly but offers higher RF link gain improvement of more than 13.2 dB at 20 GHz. Furthermore, forward bias is shown to result in comparable spurious-free dynamic range (SFDR: 104.5 dB.Hz2/3). We demonstrate through an analytical dc transfer curve the existence of simultaneous high gain and OIP3 and verify the theoretical results with measurement under forward bias at a bias point of around +0.9 V.

Calibration of a Circular HV Magnetron Sputtering Source for in-Situ RE Doping of Ecr-PECVD Si-Based Thin Films

Rare-Earth doped silicon based luminescent materials have become an attractive solution in some key areas of technological development. For instance, in the field of silicon photonics there is a drive to replace electronic on-chip components with photonic counterparts [1-2]. One of the major challenges thus far has been to provide the monolithic integration of an efficient reliable electrically driven light source. Such an element could also be used for solid state lighting, and avoid expensive III-V compounds that cannot be fully integrated into electronic drivers in a CMOS line [3]. In-situ doping of Eu3+ions in silicon oxides and oxynitrides fabricated by electron-cyclotron-resonance plasma enhanced chemical vapour deposition (ECR-PECVD) is performed. Doping is achieved by using a Circular High Vacuum Magnetron sputtering source attached to the ECR-PECVD tool. The doping concentration is varied by varying the distance of the sputtering source to the target. The hot matrix composition is varied through varying oxygen and nitrogen gas flows. The effects on the doping concentrations of the sputtering source distance to target is determined through Rutherford Backscattering Spectrometry and Variable Angle Spectroscopic Ellipsometry. Preliminary luminescence measurements are discussed. [1] Jalai, B., and Fothpour, S. “Silicon photonics,” Journal of Lightwave Technology 24, 4600-4615(2006) [2]Liu, A. Jones, R., Liao, L., Samarah-Rubio, Rubin, D., Cohen, O. Nicolaescu, R., and Paniccia, M., “A high-speed silicon optical modulator based on a metaloxide-semiconductor capacitor,” Nature 427, 615-618 (2004) [3] Ponce, F.A., Bour, D.P., “Nitride-based semiconductors for blue and green light-emitting devices”, Nature 386 (6623), 351-359 (1997)

Optimization and Demonstration of a Large-bandwidth Carrier-depletion Silicon Optical Modulator

We present the design, fabrication, and measurement of a high-speed carrier-depletion silicon optical modulator based on Mach-Zehnder Interferometer structure. Based on an equivalent circuit model, the traveling-wave electrode size and doping concentration of the PN junction are optimized to achieve a large modulation bandwidth. The modulation efficiency and optical loss at different positions of the PN junction are also simulated. The device is fabricated on silicon-on-insulator (SOI) with 0.13 μm CMOS technology. An insertion loss of 3.9 dB (resp. 6.2 dB) and a VπLπ of 1.62-2.05 V·cm (resp. 1.47-1.97 V·cm) are experimentally realized for 1 mm (resp. 2 mm) long phase shifter. By small signal measurement, the modulator exhibits a 3 dB bandwidth of 30 GHz and 19 GHz for 1 mm and 2 mm long phase shifter, respectively, which agrees well with the simulation results. The optical eye diagram with data rate up to 44 Gb/s is also demonstrated, showing potential in the application of high-speed optical interconnects.

10 Gbit/s Silicon modulator and germanium detector chip-to-chip optical link

Experimental results of a high-speed silicon optical modulator based on carrier depletion in a pipin diode and Germanium photodetectors are presented. 10 Gbit/s data transmission is obtained for both optoelectronic devices, with for the optical modulator an extinction ratio (ER) higher than 8 dB and insertion loss (IL) lower than 6 dB and for Ge photodetector, a zero-bias operating at 10 Gbit/s. Finally, a 10 Gbit/s optical link combining Si modulator and Ge photodetector is demonstrated.

Fabrication of low loss and high speed silicon optical modulator using doping compensation method

Compared with an optical modulator based on lithium niobate, the total loss of the current high speed silicon modulator is still too high for commercial use. Reduction of the total loss always comes along with the degradation of the other two characteristics including modulation efficiency or switching speed. In this paper, we reduce the phase shifter loss through optimizing the doping level out of the depletion region while keeping the modulation efficiency and switching speed at a high level. Compensated doping method is utilized to optimize the doping level on the cross section of the phase shift. With doping compensation, the Loss·Efficiency figure-of-merit (FOM) of 4 mm phase shifter is reduced from 25.8 dB·V to 19.4 dB·V while still keeping the small signal 3 dB-bandwidth at about 10 GHz. After doping profile optimizing, the measured bandwidth of the phase shifter with doping compensation can even reaches 17 GHz with a Loss·Efficiency FOM of about 25.4 dB·V.

High speed silicon optical modulator with self aligned fabrication process

With the imminent commercialisation of silicon photonic devices comes the requirement for a fabrication process capable of high yield and device performance repeatability. The precise alignment of the different elements of a device can be a major fabrication challenge for minimising performance variation or even device failure. In this paper a new design of high speed carrier depletion silicon optical modulator is introduced which features the use of a self-aligned fabrication process to form the pn junction. Experimental results are presented from an initial fabrication run, which has demonstrated a 6 dB modulation depth at 10 Gbit/s from a 3.5 m long device.

Wavelength Division Multiplexing Based Photonic Integrated Circuits on Silicon-on-Insulator Platform

We review recent advances in the development of silicon photonic integrated circuits for high-speed and high-capacity interconnect applications. We present detailed design, fabrication, and characterization of a silicon integrated chip based on wavelength division multiplexing. In such a chip, an array of eight high-speed silicon optical modulators is monolithically integrated with a silicon-based demultiplexer and a multiplexer. We demonstrate that each optical channel operates at 25 Gb/s. Our measurements suggest the integrated chip is capable of transmitting data at an aggregate rate of 200 Gb/s. This represents a key milestone on the way for fabricating terabit per second transceiver chips to meet the demand of future terascale computing.

Low V_pp, ultralow-energy, compact, high-speed silicon electro-optic modulator

We present a high-speed silicon optical modulator with a low V(pp) (peak-to-peak driving voltage) and ultralow energy consumption based on a microring resonator, with the refractive index modulation achieved by electric-field-induced carrier depletion in a reverse-biased lateral pn diode embedded in the ring structure. With a V(pp) of 2 V, we demonstrate a silicon modulator with a 3 dB bandwidth of 11 GHz, a modulation depth of 6.5 dB together with an insertion loss of 2 dB, ultralow energy consumption of 50 fJ per bit, and a small device active area of approximately 1000 microm(2).

Recent Progress in High-Speed Silicon-Based Optical Modulators

The evolution of silicon optical modulators is recalled, from the first effect demonstrations to the characterization of high-performance devices integrated in optical waveguides. Among possibilities to achieve optical modulation in silicon-based materials, the carrier depletion effect has demonstrated good capacities. Carrier depletion in Si and SiGe/Si structures has been theoretically and experimentally investigated. Large phase modulation efficiency, low optical loss, and large cutoff frequency are obtained by considering simultaneously optical and electrical structure performances. Integrated Mach-Zehnder interferometers and resonators are compared to convert phase modulation into intensity modulation. Finally, recent results on high-speed and low-loss silicon optical modulator using an asymmetric Mach-Zehnder interferometer are presented. It is based on a p-doped slit embedded in the intrinsic region of a lateral pin diode integrated in a silicon-on-insulator waveguide. This design allows a good overlap between the optical mode and carrier density variations. An insertion loss of 5 dB has been measured with a -3 dB bandwidth of 15 GHz.

Recent development in a high-speed silicon optical modulator based on reverse-biased pn diode in a silicon waveguide

We review the recent development of a high-speed silicon optical modulator based on electric-field-induced carrier depletion effect in a silicon-on-insulator waveguide containing a reverse-biased p–n junction. The device design, fabrication and characterization are presented. To obtain efficient optical modulation, we design a sub-micrometer size silicon waveguide phase shifter based on both semiconductor device modeling and photonic circuit modeling. By employing traveling-wave drive that allows co-propagation of electrical and optical signals along the waveguide, we demonstrate a high-frequency modulator with 3 dB optical response bandwidth of 30 GHz and data transmission up to 40 Gb s−1. Such a high-speed silicon modulator will be a key component for silicon-photonic-integrated circuits for future computing I/O applications.

Low loss and high speed silicon optical modulator based on a lateral carrier depletion structure

A high speed and low loss silicon optical modulator based on carrier depletion has been made using an original structure consisting of a p-doped slit embedded in the intrinsic region of a lateral pin diode. This design allows a good overlap between the optical mode and carrier density variations. Insertion loss of 5 dB has been measured with a contrast ratio of 14 dB for a 3 dB bandwidth of 10 GHz.

40 Gbit/s silicon optical modulator for high-speed applications

A high-speed silicon optical modulator based on the free carrier plasma dispersion effect is presented. It is based on carrier depletion of a pn diode embedded inside a silicon-on-insulator waveguide. To achieve high-speed performance, a travelling-wave design is used to allow co-propagation of the electrical and optical signals along the length of the device. The resulting modulator has a 3 dB bandwidth of ∼30 GHz and can transmit data up to 40 Gbit/s.

High-Speed Silicon Optical Modulator Developed

High-Speed Silicon Optical Modulator Developed

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 approximately 20 MHz (refs 10, 11), although it has been predicted theoretically that a approximately 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.