Silicon photonic integrated devices and circuits have offered a promising means to revolutionalize information
processing and computing technologies. One important reason is that these devices are compatible with conventional
complementary metal oxide semiconductor (CMOS) processing technology that overwhelms current microelectronics
industry. Yet, the dream to build optical computers has yet to come without the breakthrough of several key elements
including optical diodes, isolators, and logic gates with low power, high signal contrast, and large bandwidth. Photonic
crystal has a great power to mold the flow of light in micrometer/nanometer scale and is a promising platform for optical
integration. In this paper we present our recent efforts of design, fabrication, and characterization of ultracompact, linear,
passive on-chip optical diodes, isolators and logic gates based on silicon two-dimensional photonic crystal slabs. Both
simulation and experiment results show high performance of these novel designed devices. These linear and passive
silicon devices have the unique properties of small fingerprint, low power request, large bandwidth, fast response speed,
easy for fabrication, and being compatible with COMS technology. Further improving their performance would open up
a road towards photonic logics and optical computing and help to construct nanophotonic on-chip processor architectures
for future optical computers.
One-dimensional PhC mirrors are constructed in a single-mode silica slab waveguide with a row of elliptical holes. The
photonic band gap (PBG) of the PhC structure is attained by fast eigen-mode calculations. Being aware that component radiated waves of the PhC mirror are generated at interfaces between different waveguide sections, when propagating guided waves impinge on these interfaces, we point out that the total radiation loss of the PhC mirror is consequence of interferometric interplays of component radiated waves. We visualize this radiation generation process with intuitive pictures. We also estimate total radiation losses of PhC mirrors by using an analytical model. For uniform PhC mirrors, our model explains the oscillations of the total radiation loss with the increase of the period number. The calculated results agree well with the numerical simulations in terms of the oscillation period, the damping speed, the initial phase, and the relative intensity. For non-uniform PhC mirrors, our model finds that the progressively tapered transition from the feeding waveguide to the PhC mirror does not yield the lowest radiation loss. This finding is against to the well known “impedance-matching” picture. The matching of our model with the simulated results certifies the interferometric nature of the radiation generation process in a PhC mirror especially when a low-index waveguide is considered.
This study demonstrates a method for measuring the optical absorption cross-sections (σ<sub>a</sub>) of Au-Ag nanocages and Au
nanorods using photoacoustic (PA) sensing. PA signals are directly proportional to the absorption coefficient (μ<sub>a</sub>) of the
nanostructure. For each type of nanostructure, we first obtained μa from the PA signal by benchmarking against a linear
calibration curve (PA signal vs. μ<sub>a</sub>) derived from a set of methylene blue solutions with different concentrations. We
then calculated σ<sub>a</sub> by dividing the μ<sub>a</sub> by the corresponding concentration of the Au nanostructure. Additionally, we
obtained the extinction cross-section (σ<sub>e</sub>, sum of absorption and scattering cross-sections) from the extinction spectrum
recorded using a conventional UV-vis-NIR spectrometer. From the measurements of σ<sub>a</sub> and σ<sub>e</sub>, we were able to easily
derive both the absorption and scattering cross-sections for each type of gold nanostructure. This method can potentially
provide the optical absorption and scattering properties of gold nanostructures and other types of nanomaterials.
In this paper, we introduce a plane-wave-based transfer-matrix method (TMM) in application to photonic crystal (PC) functional elements and integrated circuits. In this formulation, the electromagnetic fields are expanded into superposition of plane waves associated with the crystal lattice, which facilitates access to many advanced Fourier analysis techniques. In addition to the standard solution of transmission, reflection and absorption spectra for a finite PC slab and photonic band structures for an infinite PC, the TMM can be used to handle wave propagation in semi-infinite photonic crystals and related waveguide structures. This capability is particularly useful for accurate solution of the intrinsic optical properties of a variety of functional elements comprising a PC integrated circuit. The TMM possesses a great advantage over the popular finite-different time-domain approach in handling these structures that are embedded in an environment of periodic geometries. We have discussed several prominent examples to demonstrate the power and capability of the TMM in this new frontier of applications. These include 2D PC filters based on resonant waveguide-cavity coupling, analysis of 2D channel
add-drop filters that exhibit wideband continuous tunability, and discussion of the performance feature and radiation loss in resonant waveguide-cavity coupling based filters which are built on 2D slab PC platforms.
The design, fabrication and evaluation of photonic crystals (PhC) have attached more and more interests in recent decades. In this paper, a homemade femtosecond laser microfabrication system is described. The optimization of working parameters, especially for resolution power or 2-photon microfabrication and the spatial overlap ratio of scanning, is presented. After that, several log-pile type PhCs are made through 2-photon induced photopolymerization. And their reflection spectrums are got with an infrared spectrometer equipped with an infrared microscope. For comparison, simulation result of photonic bandgap (PBG) using a plane-wave based transfer-matrix method is shown. The measured reflection spectrum of our PhC is agreed with the simulation one quite well.
Proc. SPIE. 3276, Miniaturized Systems with Micro-Optics and Micromechanics III
KEYWORDS: Wafer-level optics, Diffraction, Dielectrics, Magnetism, Near field scanning optical microscopy, Near field, Electromagnetic coupling, Semiconducting wafers, Electromagnetism, Near field optics
The near-field scanning optical microscopy is widely applied in obtaining local optical information on the surface structures with subwavelength resolution. In the common illumination-transmission operation mode, the sample is illuminated by a near-field probe formed from an aluminum- coated, tapered optical fiber with subwavelength aperture and the transmitted light is collected by a conventional objective lens. Commonly the aperture tip is modeled according to Bethe's theory as the effective electric and magnetic dipoles whose magnitudes are only related to the incident electromagnetic fields. However, the coupling of the tip with the sample and the extended wafer can not be neglected as the tip is located in the proximity of the sample. In this work we treat the electromagnetic coupling of the tip with the sample and wafer in the real-space self- consistent approach and simplify the coupling of the wafer by the image method. The magnitudes of the effective dipoles are determined by the incident fields above the aperture as well as the perturbed fields reflected from below by the sample and wafer. When the coupling tip-sample-wafer system is solved in self-consistency, the transmitted optical signal collected by the lens can be derived straightforwardly, relating to the effective dipoles and the polarization of the sample. The simulation results show that the signal is sensitive to the polarization character of the incident fields.
An intersecting waveguide modulator which utilizes the carrier injection effects is presented and characterized. Using O<sup>+</sup> implantation to render the implanted region electrically inactive, a well confined injection carrier channel is formed. This area can be driven to function as waveguide or as antiwaveguide. A transversal electrode switches the modulator from the On-state to the Off-state or vice versa. By the use of carrier induced refractive index modeling and the finite difference beam propagation method (FD-BPM) simulation, good performance and small injection current ofthis modulator are predicted.