Silicon Photonic Devices for Optical Computing

Abstract

The requirement for high performance computer will be significantly increased by the fast development of the internet. However, traditional CMOS computer will meet its bottleneck due to the miniaturization problem. Optical computer comes to be the leading candidate to solve this issue. Silicon photonic technology has tremendous developments and thus it becomes an ideal platform to implement optical computing system. In Chapter 1, I will first show the development of the optical computing and silicon photonic technology. I will also discuss some key nonlinear optical effects of silicon photonic devices. Based on the current silicon photonic technology, I will then make a brief introduction on the optical direct logic for the 2D optical computing and spatial light modulator for the 3D optical computing, both of which will be discussed in detail in the followed chapters. In Chapter 2, I will discuss micro-ring resonator which is the key element of optical directed logic circuit discussed in Chapter 3. I will give the analytical model based on photonic circuit to explain the performance of the micro-ring resonator. The group delay and the loss of the micro-ring resonator will be analyzed. And I will also show the active tuning of the transmission spectrum by using the nonlinear effect of silicon. In Chapter 3, I will show a revised optical direct-logic (DL) circuit for 2D optical computer that is well suited for complementary metal–oxide–semiconductor (CMOS)-compatible silicon photonics. It can significantly reduce the latency compared with traditional CMOS computers. For proof of concept, I demonstrated a scalable and reconfigurable optical directed-logic architecture consisting of a regular array of micro-ring resonator based optical on-off switches. The switches are controlled by electrical input logic signals through embedded p-i-n junctions. The circuit can be reconfigured to perform any 2×2 combinational logic operations by thermally tuning the operation modes of the switches. In Chapter 4, I will present a diffraction-based coupling scheme that for the first time allows silicon micro-resonator to directly manipulate a free-space optical beam at normal incidence. A high-Q micro-gear resonator with a 1.57-um radius is demonstrated whose vertical transmission and reflection change 40% over a wavelength range of only 0.3 nm. A dense 2D array of such resonators can also be integrated on a chip for spatial light modulation and parallel bio-sensing. In Chapter 5, I will demonstrate a spatial light modulator based on 1D photonics crystal cavity for 3D optical computing. It can control the free-space optical beam through perturbation coupling scheme as shown in Chapter 4. Compared with micro-gear resonator, it has much higher extinction ratio(ER) and quality factor. As the resonance of the silicon-based photonic crystal cavity can be rapidly tuned with an embedded p-i-n junction, a compact spatial light modulator is demonstrated with speed up to 150 MHz and extinction ratio of 9.5 dB. In Chapter 6, I will make a summary of my work and then talk about the future trend in our field.