Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session X27: Optoelectronic Devices and Applications |
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Sponsoring Units: FIAP Chair: Nelson Tansu, Lehigh University Room: 329 |
Thursday, March 19, 2009 2:30PM - 2:42PM |
X27.00001: Optical Fiber Tapers for Characterization of Novel Photonic Crystal Devices Jenna Hagemeier, Jan Gudat, Susanna Thon, Dirk Bouwmeester Optical fiber tapers are a useful tool for near-field spectroscopy of solid state devices. There are advantages to using fiber tapers rather than other waveguides because they can be moved spatially with respect to the device being studied, a single taper can be used for both pumping and data collection, and they can be used to probe bare cavities. The experimental procedures and challenges for building these micron-scale tapers will be discussed, as well as their uses for probing new kinds of photonic crystal cavities. [Preview Abstract] |
Thursday, March 19, 2009 2:42PM - 2:54PM |
X27.00002: Temporal Wavelength Multiplexing of a Quantum Cascade Laser Fatima Toor, Amirali Shanechi, Jianxin Chen, Claire Gmachl Quantum cascade (QC) laser based sensor systems in the mid-infrared wavelength range (3-30 $\mu $m) have applications in environmental, industrial and medical trace gas sensing. QC laser- based spectroscopic techniques have been developed by several research groups. However, more research work is needed to make these techniques more compact and field deployable. One approach to compactness is to have spectral versatility from a single device. Here we report work on a QC laser based system that is both temporally and wavelength multiplexed, that is, it can emit two different wavelengths at two alternate time slots. A bi-directional and multi-wavelength QC laser source that emits at 10.2 $\mu $m wavelength for positive polarity current and 8.6 $\mu $m for negative polarity current is used. A system is designed so that a single pulsed current source is the input to a pulse-alternator circuit that flips the polarity of every other pulse. The output of the circuit is connected to the bi-directional and multi-wavelength QC laser to emit two different wavelengths for alternate pulses. Contributions by Gary Shu at the beginning of the work are acknowledged. [Preview Abstract] |
Thursday, March 19, 2009 2:54PM - 3:06PM |
X27.00003: Whispering-Gallery modes dynamics of GaAs-AlGaAs microdisk lasers Albert Heberle, Botao Zhang Semiconductor microdisk lasers are of great interest because of their low threshold, high Q-factor and potential for quantum optical effects. A microdisk laser consists of a disk with typically 100 nm thickness and several microns diameter freely standing on a pedestal. Total reflection induces high-Q whispering-gallery modes inside the circular outer edge of the disk-shaped cavity. We investigated the picoseconds dynamics of GaAs/AlGaAs microdisk lasers after ultrafast optical excitation at a sample temperature of 10 Kelvin. Surface recombination was prevented by passivation. The emission was measured temporally and spectrally resolved with a streak camera connected to a confocal microscope. The spatial emission patterns of the lasers varied significantly with the position of the exciting laser spot and shifted blue shift with increasing excitation power. The devices emitted in one or two optical modes with an excitation-dependent turn-on delay of the order of 15 picoseconds and a 5 meV red shift with two time constants during the typically 50 picosecond emission time. These effects show the balance between carrier cooling, diffusion and recombination in connection with band gap renormalization and refractive index changes [Preview Abstract] |
Thursday, March 19, 2009 3:06PM - 3:18PM |
X27.00004: Electrically Pumped Quantum Post Vertical Cavity Surface Emitting Lasers Hyochul Kim, Matthew Rakher, Dirk Bouwmeester, Pierre Petroff Quantum dot (QD) lasers based on high quality, small mode volume microcavities have shown low lasing current threshold. A novel MBE grown self assembled nanostructure, the quantum post (QP) is also a very good candidate as a gain medium for low threshold lasing. As opposed to the QD laser, the delta function density of states in the QP is associated with multiple vertically and laterally confined states. In addition, QPs have a large carrier capture cross section. We demonstrate very low threshold electrically pumped lasing in oxide apertured vertical cavity surface emitting lasers (VCSELs) with QPs as the active medium and compare their characteristics with similar structure with QDs as the active gain medium. [Preview Abstract] |
Thursday, March 19, 2009 3:18PM - 3:30PM |
X27.00005: Insitu Contact Resistance Evaluation of 2.6-2.9 THz Quantum Cascade Lasers Neelima Chandrayan, Krongtip Tremkoa, Jin Li, Xifeng Qian, Shivashankar Vangala, William Goodhue, Andriy Danylov, Jerry Waldman, Robert Giles, William Nixon The fabrication of THz Quantum Cascade Lasers (QCL) requires a strong understanding of the two electrical contacts of the device. Contact resistance as well as contact/semiconductor interdiffusion properties must be designed to minimize series resistance, free carrier absorption, and e-e scattering. Here, insitu measurement of contact resistance using Transmission Line Measurement (TLM) pads has been implemented in the fabrication of 2.6-2.9 THz quantum cascade lasers. The measurement of contact resistances as part of device processing also verifies the correct etch depth of laser structure, uniformity of the etching, and the ohmic nature of the contacts. For example, the procedure has been used to successfully fabricate 2.93 THz lasers with 5 mW of continuous wave output power. [Preview Abstract] |
Thursday, March 19, 2009 3:30PM - 3:42PM |
X27.00006: Magnetic Field Assisted sub-THz Quantum Cascade Lasers A. Wade, Y. Kim, D. Smirnov, S. Kumar, Q. Hu, B.S. Williams, J. Reno In THz QCLs radiative transitions take place between closely-spaced 2D electronic subbands (1THz~$\sim $~4meV) of a multi-QW semiconductor system. THz quantum cascade lasers now cover the frequency range from 1.2 THz to 5 THz, though cryogenic cooling is still required. Further progress towards the realization of devices emitting at longer wavelengths (sub-THz QCLs) and higher temperatures may be realized in a system with additional lateral confinement. Here we use strong magnetic fields to achieve quasi-0D confinement in THz QCL based on the resonance phonon design. We studied two designs: (a) 2-well injector/2 well active region, emitting at 3~THz at B=0; and (b) 1-well injector/3-well active region, emitting at 2~THz at B=0~T. By applying the appropriate electrical bias and strong magnetic fields, we achieved laser emission at 0.8-0.9~THz at B$>$16~T [1], and 0.6~THz at B$\sim $17~T, from devices a and b respectively. The ability to achieve sub-THz lasing is due to magnetic field enhanced population inversion in a quasi-0D QCL. [1] Wade, A et. al., \textit{Magnetic field assisted Terahertz quantum cascade laser operating up to 225K, }\textbf{Accepted for publication Nature Photonics} (2009) [Preview Abstract] |
Thursday, March 19, 2009 3:42PM - 3:54PM |
X27.00007: Conducting a wide-range single-transverse mode operation in a commercial multi-mode VCSEL by beam-profile transferred optical feedback Chuan-Pi Hsu, Tsu-Chiang Yen, Da-Long Cheng, Wang-Chuang Kuo In this research, a beam-profile transferred optical feedback (BTOF) method was employed to conduct a wide range single-transverse mode operation of a commercial multi-mode VCSEL. In BTOF, a spatial modulation optical system was used to reconfigure the spatial distribution of the feedback beam, and to control the laser's transverse mode. Experimental results indicated that, over a range of about 8.7 times of the laser's threshold current, BTOF could conduct the laser to output a single-transverse mode with high spectra purity and low intensity noise. While, without optical feedback, the solitary laser exhibited a multi-mode output with a complicate variation in mode distribution as the laser's current was tuned. More special features of BTOF will be presented in the report. [Preview Abstract] |
Thursday, March 19, 2009 3:54PM - 4:06PM |
X27.00008: Single mode operation in ultra-short cavity Quantum Cascade lasers Richard Cendejas, Wendy Sanchez-Vaynshteyn, Dongxia Qu, Claire Gmachl Single-mode continuous wave operation of a $\lambda $=5.3 $\mu $m Quantum Cascade laser (QCL) is achieved through the systematic shortening of the cavity length of ridge waveguide QCLs with lengths ranging from 800 to 100 $\mu $m. Increasing mirror loss was mitigated with highly reflective metallic facet coatings. With smaller cavity lengths, the power consumption of an ultra-short cavity QCL of 110 $\mu $m is $\sim $250 mW at 80K, or about 20 times lower than conventional QCLs. Shortening the cavity length increases the free spectral range of the longitudinal modes placing the side modes at the edge of the gain profile, thus deliberately reducing the number of lasing modes until single-mode operation is achieved. The dominant mode is placed on the gain peak via temperature tuning, increasing the gain margin between the dominant and side modes, further increasing the single-mode current range. Amplified spontaneous emission spectra at various temperatures show that an initial gain margin increase from 1.5:1 to 2:1 doubles the single-mode current range. Ultra-short cavity QCLs with lengths of 110 $\mu $m are shown to operate single mode with the best device having a 10 cm$^{-1 }$single-mode continuous tuning. [Preview Abstract] |
Thursday, March 19, 2009 4:06PM - 4:18PM |
X27.00009: Correlated Photon Noise at Threshold of an Interband Cascade Laser Patrick Folkes We report the observation of correlated photon fluctuations at threshold of an interband cascade laser at 30 K and 100 K. Away from threshold, the laser exhibits a frequency-independent photon noise spectral density. The correlated photon noise is manifested by large fluctuations in the low-frequency photon noise spectral density at certain frequencies over a narrow range of current near threshold. Concurrently, we observe the emergence and growth of the lasing mode over the same current range. The data indicates that the correlated photon noise is caused by the onset of laser coherence. [Preview Abstract] |
Thursday, March 19, 2009 4:18PM - 4:30PM |
X27.00010: Effect of free carrier absorption on the efficiency of nitride devices. Emmanouil Kioupakis, Andr\'e Schleife, Patrick Rinke, Friedhelm Bechstedt, Chris G. Van de Walle Indium gallium nitride alloys are successfully being used in the fabrication of optoelectronic devices, such as light emitting and laser diodes, in the green to ultraviolet part of the optical spectrum. The wider application of these devices, however, is limited by their reduced efficiency in the green part of the spectrum. Several mechanisms have been suggested as the cause of this efficiency loss, such as Auger recombination and free carrier absorption. We use the band structure and dipole matrix elements from highly accurate many-body perturbation theory calculations in the GW approach (P. Rinke et al., Phys. Rev. B77, 075202 (2008)) to determine the optical absorption coefficient due to free carriers in InGaN. From this we obtain the corresponding photon mean free path and examine the role of free carrier absorption as a possible energy loss mechanism at high carrier concentrations. The computed values indicate that the effect is weak in light emitting diodes but it may become relevant for laser devices that operate at higher current densities. [Preview Abstract] |
Thursday, March 19, 2009 4:30PM - 4:42PM |
X27.00011: Light Emission Polarization Properties of a-plane InGaN/GaN Quantum Wells Hung-Hsun Huang, Yuh-Renn Wu This paper discusses the optical characteristics for nonpolar a-plane InGaN/GaN quantum wells (QWs) with different indium compositions, QW well widths, and injection carrier densities. We compared it with the results of the conventional c-plane QWs and analyzed the characteristics of optical anisotropy polarization in (11$\bar{2}$0)-oriented wurtzite a-plane InGaN-based QWs. A self-consistent Poisson, Schrodinger $6 \times 6 $ k$\cdot$p method is used to calculate the electronic band structure including the effect of strain on QWs. We found that different indium compositions, QW well widths, and injection carrier densities have significant influences to polarization ratio of light. We find that the larger indium composition and smaller well width make the energy separation of $|Y\rangle$-like state to $|Z\rangle$-like state larger, and as a result enhance the polarization ratio of light. However, the polarization ratio decreases as the carrier injection increases, which might be a drawback for high power applications. We have studied the optimization condition for designing the a-plane InGaN quantum well LED for applications, such as LCD back light modules and lasers, which would be useful information for device designs. [Preview Abstract] |
Thursday, March 19, 2009 4:42PM - 4:54PM |
X27.00012: Auger recombination rates in nitrides from first principles Patrick Rinke, Kris T. Delaney, Chris G. Van de Walle Indium gallium nitride (InGaN) alloys are successfully being used for light emitting and laser diodes in the green to ultraviolet part of the spectrum, but increases in internal quantum efficiency (IQE) are still required to allow broader applications. The IQE of InGaN devices is limited by loss mechanisms that, at high drive currents (i.e., high carrier concentrations) lead to a decrease in IQE, a phenomenon commonly referred to as ``efficiency droop''. We demonstrate by means of rigorous first-principles calculations (density-functional and many-body-perturbation theory), in which individual loss processes can explicitly be isolated, that Auger recombination is a key loss mechanism in wurtzite InGaN. Auger recombination had previously been proposed by Shen {\it et al.} [1] as a loss mechanism in optically pumped InGaN LED devices, but it is difficult to discriminate between different radiationless processes experimentally. We examine two different mechanisms -- inter- and intra-band recombination -- that affect different parts of the spectrum. In the blue to green spectral region and at room temperature the Auger coefficient can be as large as 2$\times$10$^{-30}$cm$^{6}$s$^{-1}$ and in the infrared even larger. Since Auger recombination scales with the cubic power of the free-carrier concentration it becomes an important non-radiative loss mechanism at high current densities. [1] Shen \textit{et al.}, Appl.\ Phys.\ Lett. \textbf{91}, 141101 (2007). [Preview Abstract] |
Thursday, March 19, 2009 4:54PM - 5:06PM |
X27.00013: Enhancement of terahertz output power in terahertz parametric oscillator with recycled pump beam Dong Ho Wu, Tomofumi Ikari In the terahertz parametric technique the pump beam is used only once, and then dumped, regardless that the dumped pump beam still has substantial laser energy. So the energy efficiency of the technique is low. This paper reports a new parametric technique in which we recycle the pump beam (instead of dumping it) in order to increase the efficiency and enhance the terahertz beam output. Our experiments, in which we used a doped LiNbO$_{3}$ crystal with 5{\%} MgO, indicate that the terahertz beam output increases almost five times magnitude for a terahertz parametric oscillator with recycled pump beam. [Preview Abstract] |
Thursday, March 19, 2009 5:06PM - 5:18PM |
X27.00014: Electro-optic sensors for high power microwave measurements Anthony Garzarella, Dong Ho Wu Nonperturbative measurements of high power microwave fields utilizing electro-optic (EO) field sensors are described. Conventional metallic-based field probes (such as dipole antennas) perturb the very fields they measure and typically saturate for field strengths exceeding $\sim $1000 V/m. EO sensors are all-dielectric, have large intrinsic bandwidths (DC to THz), and measure the true waveform of the field noninvasively. Nonlinear EO crystals such as Lithium Niobate or Potassium Dideuterium Phosphate have half-wave retardation fields of the order 10$^{6}$ V/m, making them ideal for high power microwave applications. Initial field tests with our EO sensors revealed several sources of noise and instability which are normally not encountered in laboratory settings. In this presentation, we describe a newly-designed EO sensor and how it is configured to address the noise issues in high power microwave field tests. Using this improved sensor configuration, electric field measurements in the near and far field regions of a radiating microwave horn antenna are presented. [Preview Abstract] |
Thursday, March 19, 2009 5:18PM - 5:30PM |
X27.00015: Miniature Wireless BioSensor for Remote Endoscopic Monitoring Alex Nemiroski, Keith Brown, David Issadore, Robert Westervelt, Chris Thompson, Keith Obstein, Michael Laine We have built a miniature wireless biosensor with fluorescence detection capability that explores the miniaturization limit for a self-powered sensor device assembled from the latest off-the-shelf technology. The device is intended as a remote medical sensor to be inserted endoscopically and remain in a patient's gastrointestinal tract for a period of weeks, recording and transmitting data as necessary. A sensing network may be formed by using multiple such devices within the patient, routing information to an external receiver that communicates through existing mobile phone networks to relay data remotely. By using a monolithic IC chip with integrated processor, memory, and 2.4 GHz radio, combined with a photonic sensor and miniature battery, we have developed a fully functional computing device in a form factor compliant with insertion through the narrowest endoscopic channels (less than 3mm x 3mm x 20mm). We envision similar devices with various types of sensors to be used in many different areas of the human body. [Preview Abstract] |
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