Due to their negative permittivity, plasmonic materials have found increasing number of applications in advanced photonic devices and metamaterials, ranging from visible wavelength through microwave spectrum. In terms of intrinsic loss and permittivity dispersion, however, limitations on available plasmonic materials remain a serious bottleneck preventing practical applications of a few novel nano-photonic device and metamaterial concepts in visible and nearinfrared spectra. To overcome this obstacle, efforts have been made and reported in literature to engineer new plasmonic materials exploring metal alloys, superconductors, graphene, and heavily doped oxide semiconductors. Though promising progress in heavily doped oxide semiconductors was shown in the near-infrared spectrum, there is still no clear path to engineer new plasmonic materials in the visible spectrum that can outperform existing choices noble metals, e.g. gold and silver, due to extremely high free electron density required for high frequency plasma response. This study demonstrates a path to engineer new plasmonic materials in the visible spectrum by significantly altering the electronic properties in existing noble metals through high density charging/discharging and its associated strong local bias effects. A density functional theory model revealed that the optical properties of thin gold films (up to 7 nm thick) can be altered significantly in the visible, in terms of both plasma frequency (up to 12%) and optical permittivity (more than 50%). These corresponding effects were observed in our experiments on surface plasmon resonance of a gold film electrically charged via a high density double layer capacitor induced by a chemically non-reacting electrolyte.
We derive a light-intensity-dependent dielectric constant for gain medium based on
the conventional rate equation model. A scattering-matrix method in conjunction with
an efficient iteration procedure is proposed to simulate photonic crystal lasers (PCLs).
The light output vs pumping (L-I) curve, lasing mode profile, and chirping effect of
lasing wavelength can be calculated. We check our method in a 1D DBR laser and the
L-I curve agrees well with results by the rate equation model. Our method can be
extended to 3D systems. More complex 2D and 3D PCLs will be simulated in the
The planewave based transfer matrix method has been developed with rational function interpolation to efficiently simulate photonic crystal devices. Cavities embedded in three-dimensional layer-by-layer photonic crystal are systematically studied as an example to show the power of transfer matrix method with the relation between resonant frequencies and the cavity size obtained.
Photonic crystal microcavity lasers are potentially attractive optical sources for future communication systems. They operate at lithographically defined wavelengths and because of their small volumes they are expected to exhibit low operating powers. Much work remains to be done, however, in order for these sources to find mainstream applications. In this presentation we will report on our work on optically pumped photonic crystal lasers. Finite-difference time-domain and finite element simulations will be presented as part of a discussion of the resonant cavity design. The trade-offs in the design of photonic lattice hole radius and membrane thickness will also be included, and we will discuss strategies for minimizing the optical loss in these cavities. The photonic crystal laser cavities reported here are defined by electron beam lithography in pmma. The pmma is subsequently used as a mask to transfer the pattern into a Cr/Au layer in an ion beam milling step. This patterned metal layer is then used as a mask for a reactive ion etch that patterns a silicon nitride layer. Finally this layer is used as a mask to transfer the lattice into the InGaAsP semiconductor using an ECR etching step. Suspended membranes are formed by chemically undercutting the lattice. This provides strong optical confinement at the semiconductor/air interfaces at the top and bottom of the cavity.
We have demonstrated pulsed, optically pumped lasing at and above room temperature in these resonant cavities using a semiconductor diode laser as the pump. The resonant cavity in our demonstration is formed by removing 19 holes from a triangular lattice and is about 2.6 mm across. Incident threshold pump powers for this cavity size as low as 0.5 mW have been demonstrated at room temperature. The peak output power collected through an optical fiber is approximately 2 mW. Lasing is seen for pump pulses as long as 200 ns. We have also demonstrated lasing in these cavities at elevated substrate temperatures. This demonstration was done using an 860 nm top emitting VCSEL as the pumping source because we expect it to provide a direction towards monolithic, electrically addressable lasers. Input power versus output power lasing characteristics for substrate temperatures up to 50 °C have been obtained. We will also report on our work on lithographic fine-tuning of the lasing wavelength. This wavelength can be defined through the lattice constant or the hole radius. This feature of photonic crystal lasers allows the definition of multiwavelength arrays. We have built and characterized arrays in which the lattice constant varies 2 nm steps across the array. The lasing wavelength redshifts with increasing lattice constant with an average separation between adjacent lasing wavelengths of 4.6 nm. The lasing wavelength tunes through the gain spectrum before the laser mode hops. Finally, we will present data on the optical loss in these cavities obtained by varying the number of lattice periods. We observed a reduction in incident threshold pump powers with increasing number of lattice periods at least through 11 periods.