Binglin Miao

Self-collimation in photonic crystal structures: a new paradigm for applications and device development

In this paper, we report on the development of the self-collimation phenomenon in photonic crystal structures for integrated optics applications. In addition, detailed numerical analysis, design procedures, fabrication and characterization techniques are included. Applications presented in this paper include: channelless waveguiding, orthogonal bending of light, tunable beam splitter, all-optical analog-to-digital converter, reconfigurable optical switch, chemical/gas sensor and a three-dimensional optical interconnect bus.

Photonic Crystal Structures and Applications: Perspective, Overview, and Development

In this paper, we present an overview of milestone achievements in the research and development of photonic crystal structures and their perspective applications. We highlight challenges in the analysis techniques, device design, efficient coupling techniques, and fabrication and characterization techniques for both planar and three-dimensional structures. We discuss extensively progress to date to overcome various aspects in the available modeling and simulation tools as well as the necessary fabrication procedures to produce functional photonic crystal structures and devices. Hence, the goal of the work presented in this paper is to present key building blocks, which will in turn facilitate the full utilization of the unique spatial and temporal properties of photonic crystal structures

A high-efficiency in-plane splitting coupler for planar photonic Crystal self-collimation devices

In this letter, we present the design, fabrication, and characterization of a high-efficiency in-plane splitting coupler for planar photonic crystal self-collimation devices. This splitting coupler consists of multiple concatenated in-plane reflective lenses and is capable of efficiently splitting and coupling a wide input beam into multiple narrow self-collimated beams. As an example, a one-to-two splitting coupler is simulated using the two-dimensional finite-difference time-domain method with an effective index used to account for the third dimension. The simulation shows a total coupling efficiency of 86% and a splitting ratio of two channels is 0.51 to 0.49. This device is also experimentally validated and the measured splitting ratio is 0.57 to 0.43.

High-efficiency broad-band transmission through a double-60/spl deg/ bend in a planar photonic Crystal single-line defect waveguide

We present two designs to improve the transmission of a conventional double-60/spl deg/ bend in a single-line defect planar photonic crystal waveguide by locally optimizing the shape and the size of air holes of a photonic crystal lattice at the corners. We fabricate these devices on a silicon-on-insulator substrate and characterized them using tunable laser sources over a wavelength range from /spl lambda/=1.259 /spl mu/m to /spl lambda/=1.641 /spl mu/m. As we show, over a 9% bandwidth, less than 1-dB loss/bend was observed. In order to theoretically validate these experimental results, the three-dimensional finite-difference time-domain simulations are performed and found to agree with the experimental results.

Multilayer three-dimensional photolithography with traditional planar method

We describe and demonstrate a method for the realization of three-dimensional lithography through the use of repeated planar photolithography processes. This process is based on the use of a commercially available resist system and consists of tailoring the resist response by controlling the exposure, development, and baking aspects of the process. In particular, postexposure bake is studied in detail as a primary working mechanism which, when combined with a small UV exposure and strong absorption, vertically confined photoacid is produced. As a result, the possibility of re-exposure in lower layers during top layer exposure is eliminated. In the course of this letter, we discuss issues related to this process and how they were overcome. Last, as a demonstration of the proposed method, we present three- and four-layer, three-dimensional “woodpile” photonic crystal structures.

Negative refraction imaging in a hybrid photonic-crystal device at near-infrared frequencies

We present the experimental demonstration of imaging of a point source by negative refraction at near-infrared frequencies using a hybrid photonic crystal device. The photonic crystal device, fabricated by patterning holes in 260nm silicon-on-insulator, integrates a triangular-lattice photonic crystal with a large photonic bandgap and square-lattice photonic crystal with negative refraction. Experimental results show that the output of a line-defect photonic bandgap waveguide provides a nearly ideal point source and then is imaged through the photonic crystal by negative refraction.

Ultralow-loss photonic crystal waveguides based on the self-collimation effect

In this paper, we review the confinement mechanism of self-collimation in planar photonic crystals. In this mechanism, an approximately flat equi-frequency contour (EFC) below the light cone of the planar photonic crystal can be used to laterally confine the light and total internal reflection (TIR) provides vertical confinement. To this end, self-collimation in both low-index and high-index planar photonic crystals are investigated using the three-dimensional (3D) finite-difference time-domain (FDTD) method and the 3D iterative plane wave method (PWM). It is found that low-loss self-guiding is achievable in both the valence and conduction bands for high-index planar photonic crystals. However, for low-index planar photonic crystals, low-loss self-guiding can be only observed in the valence band. Experimental results show a propagation loss of as low as 1.1 dB/mm for the self-guiding in a high-index planar photonic crystals.

Fabrication of silicon microring resonators with narrow coupling gaps

We demonstrate fabrication of silicon microring resonators with narrow coupling gaps using electron-beam lithography followed by lift-off process. Microring resonators of different diameters and 58 nm coupling gaps are fabricated in a silicon-on-insulator water. These devices are then characterized using a tunable laser source. For the microring resonator with a diameter of 7.5 µm, the measured maximum transmission is 88%, the free spectra range is 25 nm, the finesse is 28, and the Q factor is 1715.

Tunable Photonic Crystal Based on SOI

Self-collimation in photonic crystals (PhCs) has been demonstrated providing a very promising light-guiding mechanism. The fact that self-collimation allows light-guiding with- out any physical boundary is beneflcial in high-density photonic integrated circuits (PICs) in terms of e-cient coupling and arbitrary beam routing with no crosstalk. In this paper, we demon- strate a tunable photonic crystal device by combining the self-collimation lattice and band-gap lattice. DOI: 10.2529/PIERS060907215746

Self-collimation photonic crystal based modulator and switching elements in silicon

We design and characterize a photonic crystal (PhC) based silicon electro-optic modulator. The device is composed of a planar photonic crystal with associated input and output dielectric waveguides and a p-i-n diode to inject free carriers for index modulation. The photonic crystal, which confines light using the self-collimation phenomenon, has two regions of varying air hole diameters forming a defect area in a host self-collimation lattice. At the interface of the defect with the host lattice, an impedance mismatch is formed which is modulated using free carrier injection. With sufficient index modulation the impedance mismatch is large enough to decrease the transmission through the defect region, thus, modulation the overall transmission of the device. Our analysis shows that with a doping concentration in the range of 1020/cm3, the injected free carrier concentration can exceed 2.5*1019 with a drive voltage of 2.6 V. This free carrier concentration is sufficient to modulate the refractive index, Δn, greater than .05, which in turn produces a modulation depth greater than 75%. A fabricated device produces a modulation depth of 80% with a drive current of 4mA.