Adam Mock

Padé approximant spectral fit for FDTD simulation of graphene in the near infrared

A parameterization of the dispersive conductivity of highly-doped graphene has been developed and is presented for use in finite-difference time-domain simulation of near infrared graphene-based photonic and plasmonic devices. The parameterization is based on fitting a Pade approximant to the conductivity arising from interband electronic transitions. The resulting parameterization provides an accurate spectral representation of the conductivity in the wavelength range 1.3 – 2.3μm which is important for near infrared graphene plasmonics. Finite-difference time-domain simulations of straight graphene plasmonic waveguides of infinite and finite width are presented.

High-quality-factor photonic crystal heterostructure laser

A high-quality-factor (Q) photonic crystal heterostructure laser was designed and characterized. Good agreement was obtained between the experimental lasing data and three-dimensional finite-difference time-domain numerical predictions.

Propagation Loss of Line-Defect Photonic Crystal Slab Waveguides

Photonic crystal slab waveguides are created by inserting a linear defect in two-dimensional (2-D) periodic dielectric structures of finite height. Photonic crystals provide 2-D in-plane bandgaps through which light cannot propagate, however, the fact that the waveguide modes must be index-confined in the vertical direction implies that the propagation loss is strongly dependent on the out-of-plane radiation loss. We present a fully three-dimensional finite-difference time-domain numerical model for calculating the out-of-plane radiation loss in photonic crystal slab waveguides. The propagation loss of the single-line defect waveguide in 2-D triangular lattice photonic crystals is calculated for suspended membranes, oxidized lower claddings, and deeply etched structures. The results show that low-loss waveguides are achievable for sufficiently suspended membranes and oxidized lower cladding structures. The roles of the photonic crystal in out-of-plane loss of the waveguide modes are further analyzed. It is predicted that the out-of-plane radiation loss can be reduced by shifting one side of the photonic crystal cladding by one-half period with respect to the other sides along the propagation direction

Modal Analysis of Photonic Crystal Double-Heterostructure Laser Cavities

A detailed 3-D finite-difference time-domain analysis of photonic crystal double-heterostructure bound state resonances is presented along with supporting experimental results. The connection between different photonic crystal waveguide bands and the associated photonic crystal double-heterostructure bound states is made, and mode profiles are presented. We analyze the quality factors using the Pade interpolation method and directional radiation properties by calculating the time-averaged Poynting vector. We also present field profiles of higher order bound states and discuss cavity geometries to enhance a given bound state mode relative to neighboring modes. Experimental lasing results are presented demonstrating the utility of our approach.

Spectral properties of photonic crystal double heterostructure resonant cavities

Spectral properties of photonic crystal double-heterostructure resonant cavities were investigated using the three-dimensional finite-difference time-domain method. Bound state formation associated with dispersion minima is observed as well as Fabry-Perot resonances associated with the waveguide cladding

Edge-emitting photonic crystal double-heterostructure nanocavity lasers with InAs quantum dot active material

We report what is, to the best of our knowledge, the first demonstration of an edge-emitting photonic crystal nanocavity laser that is integrated with a photonic crystal waveguide. This demonstration is achieved with a double-heterostructure photonic crystal nanocavity incorporating an InAs quantum dot active region.

Photonic crystal lasers in InGaAsP on a SiO 2 /Si substrate and its thermal impedance

Two-dimensional photonic crystal defect lasers in InGaAsP membranes directly bonded to a SiO(2)/Si substrate have been demonstrated. Lasing at wavelengths near 1550 nm was obtained with incident threshold pump powers as low as 1.5 mW. Good agreement between experimental data and three-dimensional finite-difference time-domain (FDTD) simulation was achieved. The thermal impedance of this laser is also characterized.

120μW peak output power from edge-emitting photonic crystal double-heterostructure nanocavity lasers

As an attempt to collect more in-plane emission power out of wavelength size two-dimensional photonic crystal defect lasers, edge-emitting photonic crystal double-heterostructure quantum well membrane lasers were fabricated by shortening the number of cladding periods on one side. 120μW peak output power was collected from the facet of the single mode laser at room temperature. Laser efficiencies were analyzed and agree very well with three-dimensional finite-difference time-domain modeling.

A portable optical human sweat sensor

We describe the use of HNQ (2-hydroxy-1,4-naphthoquinone or Lawsone) as a potential sweat sensor material to detect the hydration levels of human beings. We have conducted optical measurements using both artificial and human sweat to validate our approach. We have determined that the dominant compound that affects HNQ absorbance in artificial sweat is sodium. The presence of lactate decreases the reactivity of HNQ while urea promotes more interactions of sodium and potassium ions with HNQ. The interactions between the hydroxyl group of HNQ and the artificial sweat components (salts, lactic acid, and urea) were investigated comprehensively. We have also proposed and developed a portable diode laser absorption sensor system that converts the absorbance at a particular wavelength range (at 455 ± 5 nm, where HNQ has an absorbance peak) into light intensity measurements via a photocell. The absorbance intensity values obtained from our portable sensor system agrees within 10.4% with measurements from a laboratory based ultraviolet-visible spectrometer. Findings of this research will provide significant information for researchers who are focusing on real-time, in-situ hydration level detection.

Low-Power All-Optical Switch Based on Time-Reversed Microring Laser

An all-optical switch based on an absorbing microring resonator laterally coupled to two waveguides is described theoretically using the coupling of modes in time formalism and numerically using the finite-difference time-domain method. The operating principle of the device is based on the recently published time-reversed laser concept. The proposed switch relies on a combination of coherent interference and absorption in the microring and does not require nonlinear refractive index changes. It has a smaller footprint than other approaches, and it is capable of converting frequency- or phase-shift-keyed digital signals to amplitude-shift-keyed signals for direct detection.