Axel Scherer

Photonic bandgap defect laser

We form a microcavity laser using two-dimensional photonic crystals embedded in a half wavelength thick waveguide. Modes localized to a single defect in the photonic crystal can be theoretically shown to have mode volumes as small 2(/spl lambda//2n)/sup 3/ and near unity spontaneous emission coupling factors. The flexibility in design of the photonic crystal enables one to tailor the device for vertical emission or for coupling into an in-plane waveguide. These type of devices may be useful for high density, low threshold optical sources in compact optical systems. The added versatility in being able to etch the laser cavity may also help develop low threshold laser sources in material systems in which high index contrast epitaxial mirrors do not exist. The defect laser cavities were formed in the InGaAsP material system in order to reduce the non-radiative surface recombination rate. The active region consists of four quantum wells (QW) designed for 1.55 /spl mu/m peak emission at room temperature.

Design of single-mode photonic crystal optical waveguides

Summary form only given. Photonic crystals have inspired a lot of interest recently due to their potential for controlling the propagation of light. Photonic crystals with line defects can be used for guiding light. A conventional method for making a two-dimensional (2D) dielectric-core photonic crystal (or PBG) waveguide is to remove one row of air columns. This usually results in a multimode waveguide. We present a more systematic way of making single-mode dielectric-core 2D PBG waveguides. It was recently shown that the main guiding mechanisms in dielectric-core PBG waveguides are total internal reflection and distributed Bragg reflection (DBR). The confinement of the guided mode in the center slab of the waveguide suggests that the properties of such modes can be modified by modifying the guiding structure in the vicinity of the center slab.

Design and implementation of the next generation electron beam resists for the production of EUVL photomasks

A new class of resist materials has been developed that is based on a family of heterometallic rings. The work is founded on a Monte Carlo simulation that utilizes a secondary and Auger electron generation model to design resist materials for high resolution electron beam lithography. The resist reduces the scattering of incident electrons to obtain line structures that have a width of 15 nm on a 40 nm pitch. This comes at the expense of lowering the sensitivity of the resist, which results in the need for large exposure doses. Low sensitivity can be dramatically improved by incorporating appropriate functional alkene groups around the metal-organic core, for example by replacing the pivalate component with a methacrylate molecule. This increases the resist sensitivity by a factor of 22.6 and demonstrates strong agreement between the Monte Carlo simulation and the experimental results. After the exposure and development processes, what remains of the resist material is a metal-oxide that is extremely resistant to silicon dry etch conditions; the etch selectivity has been measured to be 61:1.

Light-matter interaction in 2D material heterostructures (Conference Presentation)

Two-dimensional transition metal dichalcogenide (TMDC) heterostructures provide a unique platform for strong light-matter interaction in a wide wavelength range. Here, we report the formation of high-quality TMDC heterostructures through a dry transfer method along with the study of the detailed physical properties of heterostructures formed between MoS2 and MoSe2 (especially, simultaneous quenching of photoluminescence of both materials in the overlapping region, red shift and broadening of the MoSe2 photoluminescence) will be reported. We also report the formation of a thin tunable diode by depositing metal contacts on TMDCs and the back-gate.

Geometrically-induced loss suppression in plasmoelectronic nanostructures (Conference Presentation)

Nanostructured metals have utilized the strong spatial confinement of surface plasmon polaritons to harness enormous energy densities on their surfaces, and have demonstrated vast potential for the future of nano-optical systems and devices. While the spectral location of the plasmonic resonance can be tailored with relative ease, the control over the spectral linewidth associated with loss represents a more daunting task. In general, plasmonic resonances typically exhibit a spectral linewidth of ~50 nm, limited largely by the combined damping and radiative loss in nanometallic structures. Here, we present one of the sharpest resonance features demonstrated by any plasmonic system reported to date by introducing dark plasmonic modes in diatomic gratings. Each duty cycle of the diatomic grating consists of two nonequivalent metallic stripes, and the asymmetric design leads to the excitation of a dark plasmonic mode under normal incidence. The dark plasmonic mode in our structure, occurring at a prescribed wavelength of ~840 nm, features an ultra-narrow spectral linewidth of about 5 nm, which represents a small fraction of the value commonly seen in typical plasmonic resonances. We leverage the dark plasmonic mode in the metallic nanostructure and demonstrate a resonance enhanced plasmoelectric effect, where the photon-induced electric potential generated in the grating is shown to follow the resonance behavior in the spectral domain. The light concentrating ability of dark plasmonic modes in conjunction with the ultra-sharp resonance feature at a relatively low loss offers a novel route to enhanced light-matter interactions with high spectral sensitivity for diverse applications.

Hybrid Mach-Zehnder Racetrack Resonator for Fast, Low-Power Thermooptic Modulation and Coupling Control

An InGaAsP/InP optical modulator based on electrical control of waveguide-resonator coupling is demonstrated. Thermooptic switching with 18.5 dB contrast, switching power of 29 mW, and 1.8 μs rise time is measured.

Geometrical tuning of photonic crystal defect lasers

The lasing frequency of 2-D photonic crystal defect cavities is tuned by varying crystal geometry. A 10×10 array of photonic crystal defect cavity lasers is fabricated in a 100µm×100µm area, covering a wavelength span of 1480-1600nm.

Two-dimensional photonic bandgap defect laser

We form a new type of optical microcavity using 2D photonic crystals embedded in a half wavelength thick waveguide. Modes localized to a single defect in the photonic crystal can be theoretically shown to have small mode volumes. The flexibility in design of the photonic crystal enables one to tailor the device for vertical emission or for coupling into an in-plane waveguide. The added versatility in being able to etch the laser cavity may also help develop low threshold laser sources in material systems in which high index contrast epitaxial mirrors do not exist.