Chia-Jean Wang

Modeling and simulation for a nano-photonic quantum dot waveguide fabricated by DNA-directed self-assembly

We propose a nano-photonic waveguide structure by DNA-directed self-assembled fabrication. In this paper, we focus on the study of quantum dot (QD) behavior under optical stimulation in terms of gain, absorption, and emission characteristics. Both continuous wave (CW) and pulsed operations are considered and the results are compared utilizing the CdSe/ZnS and In/sub 0.47/Ga/sub 0.53/As/InP core/shell material systems. Gain coefficients reach optima at pump powers of 0.055 and 0.05 nW for the former and 0.11 and 0.019 /spl mu/W for the latter in 100 ps pulsed and CW cases, respectively. Due to their unique properties and size, QDs provide a means to create integrated photonic circuits on the nanoscale. Accordingly, the optical propagation of a QD waveguide array in a single line formation is simulated and demonstrates a viable subdiffraction limit optical energy transfer for high coupling coefficient between adjacent QDs. A proposed fabrication process by DNA-directed self-assembly is also described.

Nanoscale waveguiding methods.

While 32 nm lithography technology is on the horizon for integrated circuit (IC) fabrication, matching the pace for miniaturization with optics has been hampered by the diffraction limit. However, development of nanoscale components and guiding methods is burgeoning through advances in fabrication techniques and materials processing. As waveguiding presents the fundamental issue and cornerstone for ultra-high density photonic ICs, we examine the current state of methods in the field. Namely, plasmonic, metal slot and negative dielectric based waveguides as well as a few sub-micrometer techniques such as nanoribbons, high-index contrast and photonic crystals waveguides are investigated in terms of construction, transmission, and limitations. Furthermore, we discuss in detail quantum dot (QD) arrays as a gain-enabled and flexible means to transmit energy through straight paths and sharp bends. Modeling, fabrication and test results are provided and show that the QD waveguide may be effective as an alternate means to transfer light on sub-diffraction dimensions.

Comparison of cross-talk effects between colloidal quantum dot and conventional waveguides.

We present cross-talk calculations for a subdiffraction nanophotonic waveguide that consists of a colloidal quantum dot (QD) array 10 nm in diameter and compare the results with conventional continuous dielectric waveguides, assuming the same 10 nm size as well as a 200 nm cutoff diameter for guided mode. We find that the QD cascade has much lower cross talk than 10 nm dielectric waveguides at an identical separation >30 nm. Moreover, results for 200 nm dielectric waveguides at a 280 nm gap are comparable with those of QD structures spaced 110 nm apart. Hence the proposed QD device is potentially superior to conventional waveguides in achieving lower cross talk in the subdiffraction regime and provides a new route to achieving high-density photonic integrated circuits.

100-nm quantum dot waveguides by two-layer self-assembly

We demonstrate for the first time fabrication of 100 nm and 500 nm quantum dot waveguides, whose design relies on stimulated emission to propagate energy and accordingly present the process, results and energy transfer model.

Quantum dot nanophotonics - from waveguiding to integration

Due to its unique optoelectronic properties, the quantum dot (QD) has become a promising material for realizing photonic components and devices with high quantum efficiencies. Quantum dots in colloidal form can have their surfaces modified with various molecules, which enables new fabrication process utilizing molecular self-assembly and can result in new QD photonic device structures in nano-scale. In this review paper, we describe our work on QD waveguides for sub-diffraction limit waveguiding that utilizies near-field optical coupling between QDs, nano-scale QD photodetectors with nanogaps for sensing with high spatial resolution and sensitivity, as well as integration of these two nanophotonic components. The QD waveguide achieved a transmission loss of 3 dB/4 Pm, which is lower than the experimental results from other sub-diffraction limit waveguides that have been reported. It also demonstrated a comparable waveguiding effect through a waveguide with a sharp bend. The QD photodetector showed a sensitivity of 60 pW over a device with a nano- gap of 25 nm for detection. The compatibility between the fabrication processes for these two components with colloidal QDs allows integration of them through self-assembly fabrications.

Nano-scale quantum dot optical transducers by self-assembly

We propose a nano-scale optical transducer for future all-optical quantum circuits. The device is comprised of an array of quantum dot islands between opposing electrodes, fabricated by self-assembly. The device operates under low bias and produces a measurable photocurrent in response to light. Modeling, fabrication, and preliminary experimental results are presented in this paper.

Nanophotonic waveguides by self-assembly of multiple-type quantum dots

We demonstrate the design and fabrication of optically pumped sub-diffraction nanophotonic waveguides using a self assembly process to attach two different types of quantum dots on a silicon dioxide substrate, thus enabling low crosstalk.

Nanocrystal Quantum Dot Waveguides and Photodetectors

Sub-diffraction nanophotonic waveguides are achieved via molecular self-assembly of quantum dots (QDs) and near-field interaction between the QDs. Nanoscale photodetectors with high spatial resolution and sensitivity are also demonstrated by compatible fabrication process.

Fabrication and Testing of Nano-Photonic Quantum Dot Waveguides

We present test results for straight and corner nanophotonic waveguides constructed from colloidal quantum dots. Elevated signal levels compared to control measurements on the substrate are observed across devices of 20 mum transmission length