### Session L35: Optoelectronic Devices and Applications

 Tuesday, March 11, 2008 2:30PM - 2:42PM L35.00001: High Efficiency Quantum Cascade Lasers Matthew Escarra , Anthony Hoffman , Scott Howard , Kale Franz , Aishwarya Sridhar , Claire Gmachl Quantum cascade (QC) lasers have proven to be of great interest as powerful and versatile mid-infrared light sources. However, improvement in the wall-plug efficiency of these sources at room temperature and under continuous wave operation is critical to their development across a broad range of sensing applications. The internal, current, voltage, and optical efficiencies all must be maximized. Several different approaches must be taken in conjunction. We will focus primarily on several QC laser designs with low voltage defect. Low voltage defect quantum designs with heterogeneous injector regions have shown efficiencies as high as 13.9{\%} from a single facet in 80K, pulsed operation. Performance at high temperatures can be improved by better confinement of electrons in the upper laser level. The addition of high-reflection and anti-reflection coatings to opposing facets has greatly improved the optical efficiency. Temperature performance can also be improved through InP lateral regrowth, epi-side down mounting, and electroplated gold top contacts. Tuesday, March 11, 2008 2:42PM - 2:54PM L35.00002: High-speed wavelength conversion in quantum-dot and quantum-well semiconductor optical amplifiers David Nielsen , S. L. Chuang , N. J. Kim , D. Lee , S. H. Pyun , W. G. Jeong , C. Y. Chen , T. S. Lay All-optical wavelength conversion is an important technology for advanced wavelength division multiplexed networks. The carrier localization available in quantum dots, due to the relatively slow carrier capture and escape times compared to intersubband relaxation in quantum wells, makes it possible to achieve efficient wavelength conversion through the non-linear optical process of four-wave mixing due to enhanced spectral hole burning. To examine the various carrier dynamics we experimentally investigate four-wave mixing in both quantum-dot and quantum-well optical amplifiers. Our results show superior conversion efficiency in a quantum-dot device compared to a quantum well device with identical gain at pump-probe detunings between 100 GHz and 1 THz, and a small-signal modulation bandwidth $>$ 25 GHz. Cross-gain modulation measurements were performed as well and show a much smaller bandwidth of 1 GHz indicating that four-wave mixing is superior for high-speed signals. Tuesday, March 11, 2008 2:54PM - 3:06PM L35.00003: Magnetic field controlled sub-THz emission in Quantum Cascade Lasers A. Wade , G. Fedorov , D. Smirnov , S. Kumar , Q. Hu , B.S. Williams We report on the observance of strong multi-wavelength terahertz (THz) radiation in GaAs/AlGaAs based Quantum Cascade Lasers (QCL). The QCL was measured in a strong magnetic field, up to 31 T, applied parallel to the growth axis. The lasing intensity exhibits oscillations due to magnetophonon resonance and Landau Level interaction resulting in a strong increase in the optical power and reduction of the current threshold. By applying the appropriate magnetic field and bias, lasing emission is obtained between 3.27 to 2.61 and 1.53 to 0.68 THz. This demonstrates that a magnetic field offers the unprecedented possibility to control the QCL emission frequency and achieve lasing action as low as 0.68 THz. Tuesday, March 11, 2008 3:06PM - 3:18PM L35.00004: Effect of Waveguide Side-Wall Roughness on Quantum Cascade Laser Performance Fatima Toor , Hao Liu , Deborah Sivco , Claire Gmachl Waveguide loss in optical devices can be attributed to two main factors, intrinsic material loss (e.g. free carrier absorption) and scattering loss from imperfections (e.g. fabrication errors). To-date most work for determining the waveguide loss of quantum cascade lasers (QCLs) is concentrated on determining the intrinsic material loss, but there is very little research work done on determining the effect of fabrication errors such as side-wall roughness on QCL performance. Here we report on an experimental and modeling study to determine the effect of side-wall roughness on QC laser performance. The work involved designing and fabricating waveguides with different amounts of side-wall roughness. Measurements were then taken to determine the effect of waveguide side-wall roughness on laser performance parameters like threshold current density and slope efficiency. Tuesday, March 11, 2008 3:18PM - 3:30PM L35.00005: Optical coherence imaging using the phase coherent photorefractive effect in ZnSe quantum wells A. Kabir , M. Ajward , S. Tripathy , H.P. Wagner We have performed depth-resolved optical coherence imaging (OCI) of both stationary and moving objects using the exciton resonant phase coherent photorefractive (PCP) effect in ZnSe quantum wells (QWs). PCP QWs operate without electrical contacts thus avoiding elaborate sample processing and avoiding sample destruction due to Joule heating. In addition, the PCP effect exploits the coherence of excitons in OCI experiments thus enabling 3D images of reflecting objects with a depth resolution of $\sim$15 $\mu$m using 90 fs pulses. Due to the high diffraction efficiency of $\eta$ = 5x10$^{-4}$ in our PCP ZnSe QWs we are able to record still images at very low intensities ($\sim$500 $\mu$W/cm$^{-2})$. The OCI movies of moving objects were recorded using a camcorder with frame rates of 60 and 180 Hz. The shortest possible time resolution in these experiments is determined by the decay time of the PCP electron grating being in the $\sim$10 $\mu$s range. Tuesday, March 11, 2008 3:30PM - 3:42PM L35.00006: Integrated Plasmonic Terahertz Detector and a Gate Controlled Schottky Barrier$^{1}$ G.C. Dyer , E.A. Shaner , M.C. Wanke , J.L. Reno , G.R. Aizin , J.D. Crossno , S.J. Allen We have successfully fabricated and tested a plasmonic terahertz detector that integrates a gate controlled lateral Schottky diode$^{2}$. As demonstrated in prior work$^{3-4}$, a grating gated two dimensional electron gas can be the basis for a finely tuned terahertz detector. The addition of an independently biased gate adjacent to the drain yields striking Schottky-like behavior and offers increased sensitivity when biased to pinch off. We present measurements and models of the Schottky-like I-V characteristics, resonant plasmonic response ($\sim$50 GHz width), and bias-dependent terahertz rectification. The monolithic Schottky diode plasmonic detector points the way to a plasmonic detector with increased sensitivity. $^{1}$Supported through NSF NIRT Grant No. ECS0609146, and in collaboration with Sandia, a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. $^{2}$V. Ryzhii, et al., Jap. J. Appl. Phys. \textbf{45}, L1118 (2006). $^{3}$E.A. Shaner, et al., Appl. Phys. Lett. \textbf{90}, 181127 (2007). $^{4}$G.R. Aizin, et al., Appl. Phys. Lett. \textbf{91}, 163507 (2007). Tuesday, March 11, 2008 3:42PM - 3:54PM L35.00007: High precision frequency characterization of THz quantum cascade lasers by heterodyne mixing Mark Lee , Michael Wanke , Maytee Lerttamrab , Erik Young , Albert Grine , John Reno , Robert Dengler , Peter Siegel Terahertz quantum cascade lasers (QCLs) have been used together with a monolithic planar Schottky diode receiver to study the heterodyne mixing between dual internal modes of a QCL and between a single mode of a QCL and a known molecular line from a molecular gas laser. Dual mode mixing using a single QCL shows that the intrinsic linewidth of a free-running QCL is $<$ 30 kHz. Both standard and distributed feedback grating QCLs were mixed against known molecular gas laser lines. Resulting difference frequency spectra gave a high precision measurement of a QCL's absolute frequency against known references. Unusual slow transient turn-on behavior was also observed in a pulsed standard QCL. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. Tuesday, March 11, 2008 3:54PM - 4:06PM L35.00008: Electric Field and Polarization Dependent Spatial Fringe-Patterns in Electro-optic Crystals Randall Hinton , Anthony Garzarella , Dong Ho Wu Electro-optic (EO) crystals, such as LiNbO$_{3}$, are being widely used for high speed optical communication applications, which exploit their fast EO modulation capability. This EO modulation capability is also being used for the detection of an electric field over an extremely broad frequency band, namely DC through THz. It is known that most of EO crystals exhibit the photorefractive, pyroelectric, piezo and photo-elastic effects. While considered as parasitic effects and detrimental for most EO applications, our experimental results seem to suggest that some of these effects can increase the effective EO responsivity. To understand how these effects influence the EO responsivity we have carried out systematic investigations with LiNbO$_{3}$ and Sr$_{0.75}$Ba$_{0.25}$Nb$_{2}$O$_{6}$ crystals. When a linearly polarized laser beam (628 nm) passes through the crystal, to which an external low frequency AC field is applied, we observed a periodic interference pattern, which was dynamically modulated by the AC field. We also found that the interference pattern was produced by the reflected beam from the crystal's front and back surfaces. The patterns and dynamic modulation behaviors of the transmitted and reflected beams were noticeably different from each other. We will discuss the implications of these experimental results to the EO responsivity. Tuesday, March 11, 2008 4:06PM - 4:18PM L35.00009: A MHz-Rate High-Power UV Laser Source for High-Speed Planar Laser-Induced Fluorescence Spectroscopy Mikhail N. Slipchenko , Joseph D. Miller , Terrence R. Meyer , Naibo Jiang , Walter R. Lempert , James R. Gord We report on producing MHz-rate pulse burst tunable high energy UV radiation and its application to high-speed temperature measurements of combustion based on planar laser-induced fluorescence (PLIF) spectroscopy. The laser system consists of a narrowband high-speed tunable seeded OPO pumped by harmonics of a MHz-rate pulse-burst pump laser. The pump laser utilizes an AOM-based pulse slicer followed by a 5-stage Nd:YAG amplifier. The pump laser produces 4 bursts per second with a burst duration as long as 1.5 ms and total burst power up to 2 J. Each burst consists of 5 to 100 pulses with each pulse duration variable between 6 to 50 ns. The custom OPO produces up to 5 mJ per pulse in the range from 220 to 315 nm for exciting electronic transitions of species such as nitric oxide and the hydroxyl radical. The laser system performance is tested in well characterized flames and pulse-burst PLIF results are presented. Tuesday, March 11, 2008 4:18PM - 4:30PM L35.00010: Theory of THz rectification at a gate controlled Shottky barrier in a FET based plasmonic detector G.R. Aizin , J. Mikalopas , G.C. Dyer , E.A. Shaner , M.C. Wanke , S.J. Allen We present a theory of the resonant THz photoresponse in a grating gated FET with a gate controlled Shottky barrier [1]. We use theoretical modeling to show that the potential barrier induced in the 2D FET channel by an isolated gate finger, biased to pinch off, yields the Shottky-like $I-V$characteristics of the FET. The grating gate couples an external THz radiation to the plasmon excitations in the 2D electron channel. We calculate the photoresponse signal resulting from the THz rectification at the Schottky barrier and demonstrate that it has resonant peaks at plasmon frequencies. The results obtained are consistent with recent measurements [2]. This work is supported by ARO (Grant {\#} W911NF-05-1-0031) and The University at Buffalo NSF NIRT (Grant {\#}ECS0609146 ). Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. 1. E.A. Shaner et al, Appl. Phys. Lett., 90, 181127 (2007). 2. G. Dyer et al, this meeting presentation. Tuesday, March 11, 2008 4:30PM - 4:42PM L35.00011: Control of exciton fluxes Alex High , Aaron Hammack , E.E. Novitskaya , Leonid Butov , Micah Hanson , Arthur Gossard We present proof of principle for control of excitonic fluxes by gate in mesoscopic devices. Since excitons are bosonic particles, control of exciton fluxes can extend mesoscopics, the field which electron transport in potential reliefs, to bosons. Also, as are coupled to light, the control of exciton fluxes may lead to development of new optoelectronic devices. The demonstrated devices as a directional switch, star switch, and flux merger. Tuesday, March 11, 2008 4:42PM - 4:54PM L35.00012: Experimental Studies of Alignment Tolerance and High Temperature Performance of A Fabry-Perot Interferometric Pressure Sensor Ivan Padron , Anthony Fiory , Nuggehalli Ravindra Fabry-Perot interferometry is one of the most reliable of the several optical techniques that can be utilized to facilitate the fabrication of an optical sensor. Devices based on this technique can provide high degree of sensitivity, versatility and immunity to environmental noise. The Fabry-Perot Interferometric Sensor (FPIS), to be discussed in this presentation, consists of a Fabry-Perot cavity formed between two bonded surfaces: a corrugated diaphragm with a center rigid body (or boss) which deflects under external pressure and keeps a high alignment tolerance and a glass surface with an optical fiber insert. The Fabry-Perot cavity and optical fiber have been used as the sensing element and interconnect, respectively. The Fabry-Perot cavity has been fabricated using the MEMS technology. Micromachining techniques make Fabry-Perot sensors very attractive by reducing the size and cost of the sensing element. Tuesday, March 11, 2008 4:54PM - 5:06PM L35.00013: Growth and properties of wide band gap II-VI multi-quantum well structures for mid-infrared quantum cascade lasers William Charles , Kale Franz , Aidong Shen , Maria Tamargo , Claire Gmachl Mid-infrared emission based on intersubband transitions has been recently very actively pursued for the fabrication of quantum cascade lasers (QCLs) operating in that wavelength range. Highly efficient, ultra fast lasing can be achieved from engineered structures in which the emission wavelength is determined by the precisely controlled multi-layered structure rather than the specific materials of choice. However, operation at wavelengths shorter than 3.5 $\mu$m is limited by the conduction band offset of the materials currently available. To address this limitation, we have begun to explore wide band gap II-VI ZnCdMgSe materials grown lattice matched to InP substrates for these applications. Recently, we reported the growth and characterization of multi-quantum well structures that exhibit absorption in the 3-5 $\mu$m region. We have designed a structure consisting of the active/injector regions of a QCL and fabricated electroluminescent devices. Electroluminescence emission at 4.7 $\mu$m has been observed in these structures, suggesting that these materials hold great promise for the fabrication of short wavelength mid-IR QCLs. This work is supported by NSF Grant No. EEC-0540832 (MIRTHE-ERC). Tuesday, March 11, 2008 5:06PM - 5:18PM L35.00014: Behavior of laser diodes in the small particle number quantum limit. Kaushik Roy Choudhury , Anthony F.J. Levi We use master equations to model the steady-state and transient response of a laser diode in the small particle number quantum limit. In scaled laser diodes $n$ electrons and $s$ photons are correlated such that $<$\textit{ns}$>$ may not be factorized and there are significant differences in behavior compared to predictions of continuum mean-field theory. Quantization of photon number is found to supress lasing threshold and create a non-Poisson probability distribution for $n$ discrete electrons and $s$ discrete photons. The same correlation effect damps the transient dynamic response of laser emission. The predictions of conventional mean-field and Langevin theory are recovered in the large particle number limit.