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 QD waveguides for sub-diffraction-limit waveguiding, nano-scale QD photodetectors for sensing with high spatial resolution and sensitivity, as well as integration of these two nanophotonic components. The paper will provide an overview on the operating principles, fabrications and characterizations of the devices. The QD waveguide achieved a transmission loss of 3 dB/4 micron, 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.
Building photonic integrated circuits, which overcome the quantum limitation of the uncertainty principle, requires a new paradigm for optical waveguide design that is fundamentally different from the conventional approach. With recent advances in creating nanomaterials, quantum dots made of semiconductor compounds have enabled manipulation of electron and photon interaction in the presence of optical or electrical stimulus. In this paper, we explore the frontier of using quantum dots in new waveguide structures to pave the way for devices whose dimensions are below the diffraction limit of light. These components handle signals in the optical domain, and exploit the high-speed and transparency advantages of light. We first calculate the gain spectrum for pulsed optically-pumped quantum dots and derive the gain coefficient for waveguides. Then, a new model for a quantum dot waveguide is presented and optimum waveguide structure for propagation is determined. The results for two material systems, CdSe and CdTe quantum dots operating in free space, are given throughout. The model may be applied and extended to other compounds and establishes a foundation for quantum dot nano-scale photonic integrated circuits. By utilizing the non-linear properties of quantum dots, the proposed device forms a basis for applications in sensing, computing, and signal processing.