Browsing by Author "Qiu, Ciyuan"

Now showing 1 - 4 of 4
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    Active dielectric antenna on chip for spatial light modulation
    (Nature Publishing Group, 2012-11-14) Qiu, Ciyuan; Chen, Jianbo; Xia, Yang; Xu, Qianfan
    Integrated photonic resonators are widely used to manipulate light propagation in an evanescently-coupled waveguide. While the evanescent coupling scheme works well for planar optical systems that are naturally waveguide based, many optical applications are free-space based, such as imaging, display, holographics, metrology and remote sensing. Here we demonstrate an active dielectric antenna as the interface device that allows the large-scale integration capability of silicon photonics to serve the free-space applications. We show a novel perturbation-base diffractive coupling scheme that allows a high-Q planer resonator to directly interact with and manipulate free-space waves. Using a silicon-based photonic crystal cavity whose resonance can be rapidly tuned with a p-i-n junction, a compact spatial light modulator with an extinction ratio of 9.5 dB and a modulation speed of 150 MHz is demonstrated. Method to improve the modulation speed is discussed.
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    Device and method for modulating transmission of terahertz waves
    (2015-08-11) Xu, Quinfan; Shu, Jie; Mittleman, Daniel M.; Qiu, Ciyuan; Rice University; United States Patent and Trademark Office
    A device for modulating terahertz waves includes a metal layer (703) including a continuous metal portion (705) and island metal portions (707). The metal portions (705, 707) are separated by apertures (709). The device further includes a semiconductor layer (715) affixed to a bottom surface of the metal layer (703). The semiconductor layer (715) includes carrier regions (717) located below the apertures (709). The transmission of terahertz waves through the apertures (709) is modulated by changing a voltage applied across the aperture via voltage source (715). By injecting free carriers into carrier regions (717) due to a change of the voltage an extraordinary terahertz transmission effect of the metal layer (703) can be switched off. A small increase in the free-carrier absorption is significantly enhanced by the Fabry-Perot resonance, resulting in a substantial decrease in transmission. The disclosed ring aperture terahertz modulator allows for electrical control of the carrier density only in the area underneath the aperture. This design minimizes the power consumption and maximizes the operation speed.
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    Efficient Modulation of 1.55 μm Radiation with Gated Graphene on a Silicon Microring Resonator
    (American Chemical Society, 2014) Qiu, Ciyuan; Gao, Weilu; Vajtai, Robert; Ajayan, Pulickel M.; Kono, Junichiro; Xu, Qianfan
    The gate-controllability of the Fermi-edge onset of interband absorption in graphene can be utilized to modulate near-infrared radiation in the telecommunication band. However, a high modulation efficiency has not been demonstrated to date, because of the small amount of light absorption in graphene. Here, we demonstrate a ~40% amplitude modulation of 1.55 μm radiation with gated single-layer graphene that is coupled with a silicon microring resonator. Both the quality factor and resonance wavelength of the silicon microring resonator were strongly modulated through gate tuning of the Fermi level in graphene. These results promise an efficient electro-optic modulator, ideal for applications in large-scale on-chip optical interconnects that are compatible with complementary metal-oxide-semiconductor technology
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    Silicon Photonic Devices for Optical Computing
    (2013-11-26) Qiu, Ciyuan; Xu, Qianfan; Tittel, Frank K.; Lou, Jun
    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.