Faculty of Engineering, Blk EA, 02-11 Seminar Executive Room

Speaker :Chen Ao
Singapore- MIT, National University of Singapore

Topic: Two- dimensional Photonic Crystals Fabricated by Nanoimprint Lithography

Abstract:
We report on the process parameters of nanoimprint lithography (NIL) for the fabrication of two-dimensional (2-D) photonic crystals. The nickel mould with 2-D photonic crystal patterns covering the area up to 20mm2 is produced by electron-beam lithography (EBL) and electroplating. Periodic pillars as high as 200nm to 250nm are produced on the mould with the diameters ranging from 180nm to 400nm. The mould is employed for nanoimprinting on the poly-methyl-methacrylate (PMMA) layer spin-coated on the silicon substrate. Periodic air holes are formed in PMMA above its glass-transition temperature and the patterns on the mould are well transferred. This process can be utilized for commercial applications of photonic crystal devices.

Speaker: Wang YaDong
Singapore -MIT, National University of Singapore

Topic: High density nitride nanostructures fabrication

Abstract:
Semiconductor materials with ordered nanostructures have generated considerable interest in both basic research field and commercial applications because of their new electronic, optical, magnetic, or biological properties. Self organized nanoporous anodic aluminum oxide templates can form ordered nano-size pores with tunable diameter and pore spacing under the appropriated anodization conditions. Here we reported the fabrication of ordered nano-scale nitride structures including nanopores, nanodots by integrating this self-assembly electrochemical process with conventional semiconductor microfabrication technologies.

Speaker: Dr Xiang Ning
Assistant Professor ,Department of Electrical and Computer Engineering

Topic: Semiconductor Saturable Absorber Mirrors for Generating Ultrashort Optical Pulses

Abstract:
Semiconductor saturable absorber mirrors (SESAMs) are novel components in passively mode-locked lasers used for ultra-short optical pulse generation. Ultra-short optical pulses have pulse widths of femto-second (10-15 s) to pico-second (10-12 s) range, and such ultra-short optical pulses have many applications in physics, chemistry, biology, medicine, micro-machining, optical communications and so on. In a SESAM, nano-meter scale quantum wells (QWs) act as the saturable absorber. The non-linear behavior in QW absorption vs. light input makes SESAM an ideal passive device for mode-locking with flexible wavelength design. We will discuss the fabrication of SESAMs operating at around 1.55 mm wavelength. Femto-second optical pulses were generated using such SESAMs by mode-locking an Er-doped fiber laser.

Speaker: Li HePing
Department of Physics, National University of Singapore

Topic: Nonlinear optical properties of carbon nanotubes

Abstract:
In this presentation, we report our efforts in investigating nonlinear optical properties of carbon nanotubes (CNTs), including: (i) ultrafast absorptive and refractive nonlinearities in CNTs; (ii) broadband optical limiting with CNTs; and (iii) Optical diffraction of CNT dispersions. Possible mechanisms responsible for the observed optical nonlinearities are discussed. Such understanding is of direct relevance to developments of CNT-based photonic devices.

Speaker: Dr Yan Qingfeng
Department of Chemical and Biomolecular Engineering, NUS

Topic: Embedding Linear Defects in Self-Assembled 3D Photonic Crystals

Abstract:
Photonic crystals (PCs) or photonic band gap (PBG) materials have gained a steadily growing interest for their potential for photonic applications.Self-assembly of colloidal spheres offers a simple and inexpensive route to the fabrication of three-dimensional (3D) PCs. Device applications of PCs require exact placement of well-defined defects (planar, line or point defect) in the interior of the PCs. However, the introduction of these defects is not so straightforward in the case of PCs from self-assembly approach. In this presentation, a simple and straightforward method for engineering micron-scale linear defects within self-assembled 3D photonic crystals will be demonstrated. The method combines the techniques of self-assembly of colloidal spheres, patterns defining, template-directed colloidal crystal growth, sequential growth of colloidal crystal, and template replica. Linear defects with desired shapes can be embedded in the interior of a self-assembled system. 3D PCs containing such artificial defects may act as the elementary building blocks of next-generation photonic and optoelectronic devices based on photonic crystals and find possible application in photonic networking, optical computing and optical communications. In addition, extrinsic defects in such 3D ordered porous systems may also act as buried micro-channels and find potential applications in fluidics systems.