Farzin Amzajerdian NASA/Langley Research Center
Astrid Aksnes Norwegian University of Science and Technology
Nasser Peyghambarian University of Arizona
K1: Fiber Optics Lasers and Amplifiers
Tuesday PM, March 25, 2008
Room 2010 (Moscone West)
9:30 AM - **K1.1
Enhancing Light-Matter Interactions with Photonic Crystal Fibres and Related Structures
Philip Russell 1 Show Abstract
1 , University of Erlangen, Erlangen, Bavaria, Germany
Hollow photonic crystal fibre (HC-PCF) – a hair-thin thread of glass with a lattice of hollow channels running along its length – allows light to be trapped and guided inside an empty micro-tube that can be loaded with particles, liquids or gases. Before the arrival of HC-PCF, there was simply no practical way to do this at visible and near-infrared frequencies because no cladding material exists that has a refractive index less than unity (one has to move to other spectral regions for this to happen) and metals, which could perhaps be used to form a mirror around a hollow core, have extremely high absorption losses. An entirely new guidance mechanism had to be found. HC-PCFs guide light by the photonic band gap effect. The concept is simple. If a two-dimensional lattice of hollow nano-channels can be suitably arranged, an absence of photonic states might be arranged in the cladding, and light might be trapped within a central hollow core because it is simply not allowed to exist in the cladding. The periodic cladding would become a “dark space” within which light could not, in a fundamental sense, exist. The latest versions of HC-PCF have transmission losses as low as 1 dB/km at wavelength 1550 nm, approaching those of the best telecommunications fibres. This has prepared the ground for new developments in several areas of nano-photonics, the first results of which are beginning to emerge.One such development involves greatly enhanced nonlinear laser interactions with gases and vapours. In recent work, we were able to reduce the threshold for stimulated Raman scattering by a factor of ten million in a single pass along a 30 m length HC-PCF filled with hydrogen gas. For nonlinear optics – a traditionally “difficult” field – such a scale of improvement is simply unprecedented. Many other applications are emerging, for example ultrahigh sensitivity gas/vapour monitoring and absorption-based optical frequency references. In the second of these, HC-PCF gas-cells are filled with acetylene at low pressure, yielding a cluster of narrow absorption peaks in the 1550 nm band. These can then be used for frequency measurement in telecommunications, a possibility made all the more attractive by the fact that the device can be joined hermetically to standard all-solid telecommunications fibres. Photonic crystal fibres have created a renaissance of new possibilities in many diverse areas of research and technology. There is already a gradual take-up of PCFs in many fields of application including optical sensing, medical physics, high power fibre lasers, supercontinuum sources, frequency metrology, fibre-based laser delivery for manufacturing and gas-based nonlinear wavelength converters.
10:00 AM - **K1.2
Microstructured Soft Glass Fibers for Advanced Fiber Lasers.
Axel Schulzgen 1 , Li Li 1 , Shigeru Suzuki 1 , Xiushan Zhu 1 , Valery Temyanko 1 , Jacques Albert 2 , Nasser Peyghambarian 1 Show Abstract
1 College of Optical Sciences, University of Arizona, Tucson, Arizona, United States, 2 Department of Electronics, Carleton University, Ottawa, Ontario, Canada
A review of our efforts to advance the performance of compact fiber lasers based on microstructured phosphate glass fiber will be presented. Such fiber lasers find applications in fiber optics sensing and can also be envisioned as building blocks for laser systems with scalable output power. Combining novel highly-doped phosphate glasses and advanced fiber drawing techniques, we fabricated and tested single-frequency fiber lasers that generate powers of more than 2-W. We demonstrate enhanced performance employing active photonic crystal fiber compared to more conventional devices that are based on large core step-index fiber.We also present results on phase-locking and coherently combining the output of up to 37 fiber cores into a single, near-Gaussian laser beam. To achieve exclusive oscillation of the fundamental in-phase supermode, several all-fiber laser cavities have been designed, numerically analyzed, fabricated, and tested. We will report on a 10-cm long monolithic all-fiber laser that emits more than 12-W of optical power and is based on combining the output of 19 active cores. All the cores are integrated within the same cladding and arranged in a two-dimensional isometric array. Our truly all-fiber approach that omits any free-space optical elements let to a multi-emitter laser device that is free of optical alignment and robust against external perturbations. In addition, we will discuss our efforts to fabricate photosensitive phosphate glasses and write gratings into them through illumination with UV light. Novel UV-photosensitive phosphate glasses and initial grating formation will be reported. Through the integration of phosphate glass fiber gratings and highly-doped active phosphate glass fiber, we improve on optical, thermal and mechanical behavior of our compact fiber lasers. Powerful and widely tunable phosphate glass distributed fiber lasers will be presented and the possibility of cascading several grating structure for multiple wavelength generation will be demonstrated.
10:30 AM - **K1.3
Current Progress in 2-Micron Fiber Lasers.
Shibin Jiang 1 Show Abstract
1 , AdValue Photonics Inc, Tucson, Arizona, United States
2-micron fiber lasers can be used for materials processing, medical applications, laser remote sensing, and direct energy sources for defense. Recently, highly efficient high power 2-mciorn fiber lasers with slope efficiency greater than 65% and output power greater than hundreds watts were demonstrated. In this presentation, we will summarize the current progress of Tm-doped 2-micron fiber laser in both silica glass fiber and multi-component glass fibers.
11:30 AM - K1.4
Efficient High Power ns Pulsed Fiber Laser for Lidar and Laser Communications.
Jian Liu 1 Show Abstract
1 , PolarOnyx, Inc., Sunnyvale, California, United States
In laser radars and laser communications, fiber laser is becoming an enabling technology due to its high efficiency, compact size and reliable operation. In these applications, high extinction rate and high OSNR are musts for a fiber laser. However, current Q-switched fiber lasers and solid state lasers can not meet these criteria. Innovative approach has to be conceived to meet the requirements. PolarOnyx has invented and demonstrated several types of fiber lasers that the repetition rate can be adjusted from 10’s kHz to 10’s MHz and the pulse width from 10 to 1 ns at wavelengths of 1550 nm and 1064 nm. The extinction ratio has been demonstrated over 30 dB and OSNR over 45 dB. The output average power can be scaled to over 100 W with a peak power up to 10 kW. The fiber grating based pulse shaping technology allows us to reduce the noise level and nonlinear effect in the high power laser. The pulse shaping allows us in manipulate the pulse shape into a Gaussian shape. The stability of the pulse intensity is controlled within 3%. In this presentation, we will discuss our research on both 1550 nm and 1064 nm results on high energy/power ns pulsed fiber lasers. Modulation schemes for seed laser in getting various optical waveforms, high power operation of fiber amplifiers, nonlinearity mitigation in high power fiber lasers, and trade-offs among the parameters such as OSNR, power/energy scaling, extinction ratio, interpulses background noise (contrast ratio), and efficiency will be discussed.
11:45 AM - **K1.5
High Power Ultrafast Fiber Lasers.
Martin Fermann 1 Show Abstract
1 , IMRA America Inc., 1044 Woodridge Av., Michigan, United States
We review the key developments that have led to the introduction of the first industrially qualified femtosecond lasers. These systems are based on a highly integrated fiber optic system architecture and have enabled femtosecond material processing to reach the industrial realm. Current systems generate average powers of 1 W and pulse energies up to 10 microJoules at wavelengths of 1040 nm. Research activities aimed at further improving industrial femtosecond laser technology are also disucssed.
K3: Photodetection Devices II
Tuesday PM, March 25, 2008
Room 2010 (Moscone West)
2:30 PM - **K3.1
HgCdTe Electron-Initiated Avalanche Photodiodes (e-APDs)
Marion Reine 1 Show Abstract
1 , BAE Systems, Lexington, Massachusetts, United States
The success of the semiconductor alloy HgCdTe as today’s most broadly applicable high-performance infrared detector material is due to three features of its energy band structure: (1) tailorable band gap over the 1-30 µm range; (2) large optical absorption coefficients that enable high quantum efficiencies; (3) favorable inherent recombination mechanisms that lead to long carrier lifetimes, low thermal generation rates, and high operating temperatures.This band structure, together with a unique set of technologically favorable material properties, has enabled a diverse family of high-performance quantum infrared detectors, including photoconductors and both single-color and two-color photodiodes, which has led to large-format back-illuminated photovoltaic arrays that are the basis for a widely-applicable hybrid Focal Plane Array (FPA) technology.Moreover, in the past several years, it has become clear that unique features of the HgCdTe energy band structure also make it an ideal material for avalanche photodiodes (APDs) over a wide range of useful wavelengths.The key characteristics and highly desirable properties of electron-initiated HgCdTe avalanche photodiodes (e-APDs) were first reported by Beck of DRS. In HgCdTe, the electron ionization coefficient is much larger than that of the hole, so e-APDs exhibit true single-carrier multiplication. Gain increases exponentially with reverse bias, with highest values reported as 5300. There is negligible excess noise; F(M) is basically unity. Shortly thereafter, Kinch of DRS theoretically related the key features and benefits of the e-APD directly to HgCdTe band structure. The electron effective mass is much smaller than the heavy hole mass, so that electrons have higher mobility, lower phonon scattering rate, and lower ionization threshold energy. There are no nearby subsidiary minima in conduction band to which electrons can scatter and loose energy. And the light holes are not important.Since then, the ideal properties of HgCdTe e-APD have been substantiated by other laboratories, and progress has been rapid. FPAs with HgCdTe e-APD arrays as large as 128x128 with 40 µm x40 µm unit cells and 320x256 with 24 µm x 24 µm unit cells have been reported for MWIR 3D imaging. Large-area MWIR HgCdTe e-APD 4x4 arrays with 250 µm x 250 µm elements have been reported. This paper will review the physics and characteristics of HgCdTe e-APDs, and the progress made since the seminal paper of Beck. The theory of operation of HgCdTe e-APDs will be summarized. The various device architectures that have been used to realize HgCdTe e-APDs in both single-element and array formats will be reviewed and compared. The FPAs utilizing HgCdTe e-APD arrays will be described.1. J.D. Beck et al., Proc. SPIE 4454, 188 (2001)2. M.A. Kinch et al., J. Electronic Mat. 33, 630 (2004)
3:00 PM - **K3.2
Quantum Well and Quantum Dot Based Detector Arrays for Infrared Imaging.
Sarath Gunapala 1 Show Abstract
1 Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, United States
A mid-wavelength infrared (MWIR) and long-wavelength infrared (LWIR) 1024x1024 pixel quantum well infrared photodetector (QWIP) focal plane arrays (FPAs) have been demonstrated with excellent imagery. MWIR FPA has given noise equivalent differential temperature (NETD) of 19 mK at 95K operating temperature with f/2.5 optics at 300K background and LWIR FPA has given NEDT of 13 mK at 70K operating temperature with same optical and background conditions as MWIR array. Both of these FPAs have shown background limited performance (BLIP) at 90K and 70K operating temperatures with the same optics and background conditions.In addition, epitaxially grown self-assembled InAs/InGaAs/GaAs quantum dots (QDs) are exploited for the development of large-format FPAs. The Dot-in-a-Well (DWELL) structures were experimentally shown to absorb both 45o and normal incident light, therefore a reflection grating structure was used to enhance the quantum efficiency. The devices exhibit peak responsivity out to 8.1 microns, with peak detectivity reaching ~ 1 x 1010 Jones at 77 K. The devices were fabricated into the first LWIR 640x512 pixel QDIP FPA, which has produced excellent infrared imagery with NETD of 40 mK at 60K operating temperature. In this presentation, we will discuss FPA performance in quantum efficiency, NETD, uniformity, and operability.
3:30 PM - K3.3
Solution Processed Quantum Dot Photodetectors for Visible and Short Infrared Wavelength Applications.
Gerasimos Konstantatos 1 , Jason Clifford 1 , Larissa Levina 1 , Edward Sargent 1 Show Abstract
1 Electrical and Computer Engineering, University of Toronto, Toronto, Ontario, Canada
Sensing in the visible and short wavelength infrared part of spectrum is of utmost importance in a plethora of applications in biomedical imaging, night vision and surveillance. Today's imaging applications in the visible part is well represented by silicon photodiodes that exhibit high sensitivity but suffer from poor integration in the case of charge coupled device architectures and poor filling factors in CMOS architectures. Further more silicon sensors are not compatible with flexible electronics technology. Detection in the short infrared wavelength spectrum is facilitated by InGaAs photodetectors that are not compatible with CMOS electronics leading in low pixel resolution and high cost and are very expensive to fabricate due to the epitaxial techniques required. In this work an alternative approach is presented where colloidal quantum dots are employed as the photoconductive material. Solution processibilty enables for CMOS compatibility and no loss in filling factors thanks to the top-surface architecture. We present herein the first demonstration of solution processed photodetectors with high internal photoconductive gain and low noise performance that yielded specific detectivity in the order of 1013 Jones at 1300 nm  , superior to InGaAs sensitivity of ~1012 Jones. This was achieved by simultaneous removal of long ligands to increase mobility, oxidation of the nanocrystal surface to form long-lived sensitizing centers and control of the oxidation process to minimize noise current. Sequentially we present the development of high sensitivity visible-only photodetectors based on small PbS nanocrystals. A modified ligand exchange technique was employed to preserve the sharpness of the absorption onset of the material as well as to increase mobility. The combination of photoconductive gain with low noise yielded in specific detectivity of 1012 Jones comparable to that of silicon photodiodes . We then provide further characterization of the optoelectronic properties of the devices and correlation of the performance with trap state identification via photocurrent temperature spectroscopy . Multiple sensitizing centers are discovered in the range of 0.1 - 0.3 eV below the conduction band edge. We finally propose a device architecture that exploits the ease of fabrication of these devices to demonstrate a dual-spectral detector in the visible and short infrared wavelength.  Gerasimos Konstantatos, et al., “Ultrasensitive solution-cast quantum dot photodetectors”, Nature, Vol 442, 180-183, 2006. Gerasimos Konstantatos, et al., “Sensitive Solution-processed Visible-Wavelength Photodetectors”, Nature Photonics, Vol 1 531-534, 2007. Gerasimos Konstantatos, Edward H. Sargent, “PbS colloidal quantum dot photoconductive photodetectors: transport, traps and gain”, Applied Physics Letters, 91, 173505, 2007.
3:45 PM - **K3.4
Infrared detector activities at NASA Langley Research Center.
M. Nurul Abedin 1 , Tamer Refaat 2 , Oleg Sulima 3 , Farzin Amzajerdian 1 Show Abstract
1 , NASA Langley Research Center, Hampton , Virginia, United States, 2 , Old Dominion University, Norfolk, Virginia, United States, 3 , University of Delaware, Newark, Delaware, United States
We will review the detector technology development activities over a wide spectral-range at NASA Langley Research Center, for use in space-based and airborne remote sensing applications. Discussions will be focused on current and the most recently developed single-element infrared detector and future development of near-infrared focal plane arrays (FPA) for applications to next generation space-based instruments. Most of these activities are based on phototransistor and avalanche photodiode technologies offering high internal gain and low noise operation. These novel detector components will improve the sensitivity of the laser remote sensing instruments while eliminating the need for high power laser transmitter.
4:45 PM - K3.5
Enhancing the Dynamic Photo-response Property of ZnO Based Ultraviolet-detecting Transistor with Polymer Gate Dielectric by UV Treatment.
Kimoon Lee 1 , Ki-tae Kim 1 , Min Suk Oh 1 , Jeong Min Choi 1 , Do Kyung Hwang 1 , Seongil Im 1 Show Abstract
1 Institute of Physics and Applied Physics, Yonsei University , Seoul Korea (the Republic of)
ZnO-based thin-film transistors (TFTs) have attracted much attention over the last several years because of several potentials toward future electronic and optoelectronic applications. Especially, ZnO-based photo-transistor has recently been one of the candidates as a ultraviolet (UV)-detectable device for its high responsivity compared with diode structure, but the insufficiency of studies about possible applications with ZnO-TFTs as a photo-detector makes needs for further researches about that. In this meeting, we report on the fabrication of UV-detecting top-gate ZnO-TFTs which adopt poly-4-vinylphenol (PVP) polymer gate dielectric and the enhanced property of dynamic photo-response by ZnO surface treatment with UV (wavelength of 352 nm) illumination.The field-effect mobility and on/off current ratio of our pristine device in the saturation region are ~0.1 cm2/Vs and ~104 respectively while those properties change to be ~0.004 cm2/Vs and ~3×102 with 352 nm UV treatment (1 hr, 6 mW) on ZnO surface. When devices are illuminated by UV (wavelength of 364 nm) for the UV detection measurements, the photo-induced current of the both un-treated and UV treated ZnO-TFTs generates to be about 104 times higher than their general off-state level. In contrast, the dynamic photo-response of un-treated and UV-treated ZnO-TFTs appears quite different each other. The photo-current rising time of un-treated device was ~120 msec which was much longer than that of UV treated device (~58 msec), so that it is regarded that the UV treatment of ZnO surface enhances the dynamic photo-response property of UV-detecting device, probably because the intense UV effectively diminishes the trap density at the ZnO/PVP interface.By applying this type of photo-transistor, we set up a photo-inverter device which operates by optical signal and it shows fast UV-response (optical gating) under low voltage-operation (VDD = 5V). Our top-gate ZnO-TFTs may be optimally engineered by UV treatment on active ZnO surface to be detectors or photo-inverter component. More and advanced details will be discussed in the meeting.
5:00 PM - K3.6
Theoretical Analysis and Preliminary Experimental Results on the Suitability of InNxSb1-x for the Long-wavelength Infrared Detector Applications.
Alex Freundlich 1 , L. Bhusal 1 , A. Fotkatzikis 1 , A. Alemu 1 , C. Rajapaksha 1 Show Abstract
1 Center for Advanced Materials, University of Houston, Houston, Texas, United States
5:15 PM - K3.7
Novel Intra-band Photodetectors for Standing Electro-magnetic Wave Sampling.
Sindy Hauguth-Frank 1 , Vadim Lebedev 1 , Katja Tonisch 1 , Florentina Niebelschutz 1 , Hans-Joachim Buechner 2 , Gerd Jaeger 2 , Oliver Ambacher 3 Show Abstract
1 Institute of Micro- and Nanotechnologies, Technical University Ilmenau, Ilmenau Germany, 2 Institute of Measurement and Sensor Technology, Technical University Ilmenau, Ilmenau Germany, 3 , Fraunhofer Institute for Solid State Physics, Freiburg Germany
5:30 PM - K3.8
Recent Development in High Performance APD and ROIC at Raytheon Vision Systems.
Jinxue Wang 1 , Michael Jack 1 , Steven Bailey 1 , James Asbrock 1 Show Abstract
1 , Raytheon Vision Systems, Goleta, California, United States
Farzin Amzajerdian NASA/Langley Research Center
Astrid Aksnes Norwegian University of Science and Technology
Nasser Peyghambarian University of Arizona
K7: Semiconductor Lasers and Pump Arrays I
Thursday AM, March 27, 2008
Room 2010 (Moscone West)
9:30 AM - **K7.1
Electrically Pumped Photonic Crystal Distributed Feedback Quantum Cascade Lasers.
Manijeh Razeghi 1 , Yanbo Bai 1 , Philippe Sung 1 , Steven Slivken 1 , Shaban Darvish 1 Show Abstract
1 Electrical Engineering and Computer Science, Northwestern University, Evanston, Illinois, United States
In parallel with the effort to improve the efficiency of Quantum cascade lasers (QCL) for high power continuous wave (CW) operations, the peak power in pulsed mode operation can be easily scaled up with larger emitting volumes, i.e., processing QCLs into broad area lasers. However, as the emitter width increases, multi-mode operation happens due to poorer lateral mode distinguishability. By putting a two dimensional photonic crystal distributed feedback (PCDFB) layer evanescently coupled to the main optical mode, both longitudinal and lateral beam coherence can be greatly enhanced, which makes single mode operation possible for broad area devices. For PCDFB laser performance, the linewidth enhancement factor (LEF) plays an important role in controlling the optical coherence. Being intersubband devices, QCLs have an intrinsically small LEF, thus serves better candidates over interband lasers for PCDFB applications. We experimentally demonstrate electrically pumped, room temperature, single mode operation of PCDFB quantum cascade lasers emitting at l ~ 4.75 µm. Ridge waveguides of 100 mm width were fabricated with both PCDFB and Fabry-Perot feedback mechanisms. The Fabry-Perot device has a broad emitting spectrum and a double lobed far-field character. The PCDFB device, as expected, has primarily a single spectral mode and a diffraction limited far field characteristic with a full angular width at half-maximum of 2.4 degrees. The superior beam quality of the PCDFB quantum cascade laser over its Fabry-Perot counterpart opens the possibility of making single-mode, high-power broad area mid-infrared semiconductor lasers.
10:00 AM - **K7.2
Mid-ir to THz Quantum Cascade Lasers: State-of-the-art and Applications to Chemical Sensing.
Federico Capasso 1 Show Abstract
1 SEAS, Harvard University, Cambridge , Massachusetts, United States
The richness of the underlying basic physics of Quantum Cascade Lasers (QCL) combined with the capabilities of bandstructure engineering has led to unprecedented design flexibility and functionality compared to other lasers1,2. State-of-the-art performance in the mid-ir and Terahertz will be reviewed. A broad range of applications (chembio sensing, trace gas analysis, atmospheric chemistry, medical and combustion diagnostics, THz imaging, etc.) and their ongoing commercial development will be discussed. In particular the talk will focus on broad band QCL based spectrometers, optofluidic lasers for chem-bio sensing as well as QC plasmonic laser antennas for sub-wavelength resolution chemical imaging. Finally I will also discuss recent important developments such as new THz light-sources that use the giant resonant nonlinear susceptibilities of quantum engineered structures to achieve for the first time THz generation in semiconductor laser at Peltier cooler temperatures ( 250 K).1.F. Capasso et al., IEEE J. Quantum Elect. 38, 511-532 (2002).2.F. Capasso, C. Gmachl, D. L. Sivco, and A. Y. Cho, Physics Today 55, 34 (May 2002
10:30 AM - **K7.3
Development of Low-Cost Multi-Watt Yellow Lasers using InGaAs/GaAs Vertical External-Cavity Surface-Emitting Lasers
Mahmoud Fallahi 1 , Li Fan 1 , Chris Hessenius 1 , Joerg Hader 2 , Hongbo Li 2 , Jerome Moloney 2 , Wolfgang Stolz 3 , Stephan Kock 3 , James Murray 4 , Robert Bedford 5 Show Abstract
1 College of Optical Sciences, University of Arizona, Tucson, Arizona, United States, 2 Arizona Center for Mathematical Science, University of Arizona, Tucson, Arizona, United States, 3 , Philipps Universität Marburg, Marburg Germany, 4 , Areté Associates, Longmont, Colorado, United States, 5 , Air Force Research Laboratory, Dayton, Ohio, United States
11:30 AM - **K7.4
Quantum Design of Active Semiconductor Materials for Targeted Wavelengths.
Jerome Moloney 1 3 4 , Joerg Hader 1 3 , Stephan Koch 2 Show Abstract
1 , Nonlinear Control Strategies, Tucson, Arizona, United States, 3 College of Optical Sciences, University of Arizona, Tucson, Arizona, United States, 4 Department of Mathematics, University of Arizona, Tucson, Arizona, United States, 2 Physics Department, University of Marburg, Marburg Germany
The culmination of a series of basic research breakthroughs over the past decade on the first principles calculation of semiconductor optical properties has led to the first ever prediction of an end-packaged semiconductor multiple quantum well (MQW) laser device performance without resorting to the use of adjustable fit parameters. Performance metrics of every class of semiconductor amplifier or laser system depend critically on semiconductor quantum well (QW) optical properties such as photoluminescence (PL), gain and recombination losses (radiative and nonradiative). Photoluminescence spectra provide direct feedback to the material’s grower on wafer growth accuracy and quality. Gain spectra and recombination losses yield key operating parameters of a running laser and determine laser threshold, slope efficiency, modulation characteristics and other critical dynamical responses. Current practice in amplifier or laser design assumes phenomenological parameterized models with parameters extracted from prior experimental measurement on packaged devices. We will present an overview of a sophisticated first-principles microscopic quantum design approach that allows one to extract these critical optical properties without relying on prior experimental measurement. Full band structure and many body calculations of the semiconductor optical response for a broad variety of material systems that yield lasing emission from the UV/Visible to mid IR have shown quantitative agreement with experimental measurements. Optimized epi designs can be calculated for a target operating laser wavelength allowing one to fast track to an end device thereby avoiding wasteful, time consuming and costly growth, re-growth and packaging cycles. This quantum design approach is not material specific and can, in principle, be used for any material combination and structural arrangement emitting from the UV to far-IR as long as input bandstructure parameters are reliably known.Applications of this microscopic quantum approach include design of all classes of semiconductor amplifiers and lasers ranging from low power surface (VCSEL) and edge emitters to high power edge-emitting diode bars and optically-pumped surface emitters (OPSLs).As specific applications we will discuss the design of an Optically-Pumped-Semiconductor-Laser (OPSL) sub-cavity and recent extensions of the theory to antimonide-based QW structures. The latter have been shown to lase in the mid IR from 2 - 10 microns. Our OPSL design focused on a highly strained MQW InGaAs resonant periodic gain structure and only required a single wafer growth to achieve greater than 10 Watts of near TEM00 emission at the targeted 1178nm wavelength. Intra-cavity second harmonic generation yielded greater than 5 Watts of yellow light at 589 nm as a first step in developing a compact, cost effective laser guidestar source.
12:00 PM - **K7.5
> 1 Watt, 1550 nm and 1064 nm, Single Mode Semiconductor Lasers with Single Frequency Performance for LIDAR and Communications Applications
Paul Rudy 1 , Mark Osowski 1 , Robert Lammert 1 , Jeffrey Ungar 1 Show Abstract
1 , QPC Lasers, Inc., Sylmar, California, United States
We will present results on high power > 1 Watt single mode semiconductor lasers in the 1064 - 1550 nm regimes. The devices operate with single frequency performance and can be directly modulated for short pulse length and high speed applications.
12:30 PM - K7.6
Advanced Laser Diode Cooling Concepts
Ryan Feeler 1 , Jeremy Junghans 1 , Greg Kemner 1 , Ed Stephens 1 , Fred Barlow 2 , Aicha Elshabini 2 , Jared Wood 2 Show Abstract
1 , Cutting Edge Optronics, St. Charles, Missouri, United States, 2 Department of Electrical and Computer Engineering, University of Idaho, Moscow, Idaho, United States
A new, patent-pending method of cooling high-power laser diode arrays has been developed which leverages advances in several areas of materials science and manufacturing. This method utilizes multi-layer ceramic microchannel coolers with small (100’s of microns) integral water channels to cool the laser diode bar. This approach is similar to the current state-of-the-art method of cooling laser diode bars with copper microchannel coolers. However, the multi-layer ceramic coolers offer many advantages over the copper coolers, including reliability and manufacturing flexibility. The ceramic coolers do not require the use of deionized water as is mandatory of high-thermal-performance copper coolers.Experimental and modeled data is presented that demonstrates thermal performance equal to or better than copper microchannel coolers that are commercially available. Results of long-term, high-flow tests are also presented to demonstrate the resistance of the ceramic coolers to erosion. Data is presented based upon several multi-layer ceramic approaches, including LTCC, HTCC, and multi-layer AlN. The materials selected for these coolers allow for the laser diode bars to be mounted using eutectic AuSn solder. This approach allows for maximum solder bond integrity over the life of the part.
12:45 PM - K7.7
High Performance Optically Pumped Antimonide Lasers Operating in the 2.2 to 9.5 μm Range.
Andrew Ongstad 1 , Michael Tilton 2 1 , Greg Dente 3 2 1 , Ron Kaspi 1 Show Abstract
1 , Air Force Research Laboratory, Albuquerque, New Mexico, United States, 2 , Boeing, LTS, Albuquerque, New Mexico, United States, 3 , GCD Associates, Albuquerque, New Mexico, United States
Many applications, including remote chemical sensing as well as infrared counter measures (IRCM) require lasers that operate in the 2-10 micron wavelength range. This wavelength region is important in that there are several atmospheric transmission windows suitable for IRCM applications. This region also constitutes the fingerprint region of molecular absorbance where pumping of molecular vibrational transitions can lead to sensitive spectroscopic detection methods. Clearly, it would be advantageous to use a single semiconductor material system and quantum well laser design to provide CW laser sources to cover this entire region. Indeed, the antimonide based III-V compounds can be used in this capacity.In practice this is accomplished by imbedding type-II InAs/InGaSb/InAs quantum wells into thick lattice-matched InGaAsSb layers. These four constituents, InGaAsSb/InAs/InGaSb/InAs, can then be used as one period of the superlattice active region of an optically pumped mid-infrared laser. The InGaSb layer provides a well for holes and is typically fixed at 8 monolayers (~24 angstrom) thickness. The InAs layers then provide coupled quantum wells for electrons. The radiative transition is type-II and occurs across the InAs to InGaSb interfaces. This ”broken-gap” band alignment allows the emission wavelength to be tuned from 2.2 microns out to, in principle, extremely long wavelengths by simply increasing the thickness of the electronically coupled InAs layers. The thickness of the other epitaxial layers is not normally changed.When the superlattice active region is pumped by a 1.95 μm high-power diode laser array, the photo-generated electrons and holes transport from the quaternary layer into the type-II wells, providing optical gain anywhere within a 2.2 to approximately 9.5 um region. These optically pumped lasers have demonstrated high quantum efficiencies with high power output and excellent beam quality. For example, quantum efficiencies remain > 0.64 for wavelengths up to ≈ 7.5 μm. The maximum peak output power of lasers operating near 84 K and at 2.85 μm, 3.4 μm, and 7.2 μm were 12 W, 12.4 W and 4.3 W, respectively.In this paper we will provide an overview of these optically pumped antimonide based type-II lasers. In particular, we will show the wavelength tuning ability of the material system to provide high brightness lasers that cover the range from 2.2 to nearly 10 μm. We will present measurements of the subband energies for a large number of lasers with differing InAs thicknesses. Further, we will compare these results with those calculated by a superlattice empirical pseudopotential method, SEPM. A brief introduction to superlattice subband calculations utilizing the SEPM will be given. Finally, we will show that the ability of the superlattice material system to provide lasing action beyond ≈ 9.5 μm is constrained by high waveguide losses induced at the longer wavelengths by such process as free-carrier absorbance.
K9: Photonic Structures and Quantum Dot Devices
Thursday PM, March 27, 2008
Room 2010 (Moscone West)
4:00 PM - **K9.1
MEMS for Space.
Nico de Rooij 1 , Wilfried Noell 1 , Urs Staufer 1 , Danick Briand 1 Show Abstract
1 University of Neuchatel, Institute of Microtechnology, Neuchatel Switzerland
Our knowledge about the universe is mostly based on earthbound experiments and observation. Space research aims at supplementing this knowledge with extra-terrestrial observations in the interplanetary and interstellar space and on the surface of planets. Due to costs and physical constrains, conducting experiments in space require low-mass and low-volume systems. Hence, compact instruments based on small, reliable, and light-weight MEMS's are extremely attractive for space research. Proven MEMS sensors measure pressure, temperature, acceleration, liquid flow rates, and electrical potentials. MEMS implemented in ultra-miniaturized spacecraft subsystems can potentially address the requirements for shock survivability, radiation tolerance, low-power consumption and volume constraints. They will be the key for new commercial space activities since they enhance the payload/total mass ratio at launch for instance of telecommunication satellites. Today’s commercial satellites have a total mass of several thousands of kilograms. Future satellites will be smaller but with potentially increased functionality. The goal is to batch process these pico- and nanosatellites and have them communicate in a distributed network. MEMS can play a key role because it is inherently oriented towards batch fabrication.Two distinct examples of MEMS for space research developed by IMT are described in the following paragraphs. In both applications the design of the MEMS-based instruments had to be tailored towards space applications from the beginning.The first example is a miniature bioreactor for the cultivation of yeast cells that has been flown three times (1994, 1996 and 2003) aboard Spacelab and the space shuttle. The objective was to evaluate the effects of mixing and stirring on cell growth characteristics in a controlled bioreactor experiment in micro-gravity. This experiment was performed in collaboration with the Space Biology Group of ETH Zurich and the company Mecanex SA. The liquid handling technology for low-volume liquid dispensing used in high-throughput screening has led to the creation of the start-up, Seyonic SA, in Neuchâtel.The second example is an atomic force microscope (AFM), which is a tool for characterizing the surface topography of a sample with nanometer resolution. Micro-fabrication technology combined with innovative design ideas allowed IMT to build an error tolerant system. The instrument is part of the Phoenix Mission headed by JPL landing on Mars in May 2008. The instrument development was headed by IMT and realized in close collaboration with the company Nanosurf AG and the Institute of Physics of the University of Basel.Current MEMS developments dedicated to space applications aim at micro thrusters, initiated by LAAS/CNRS and micro-optical components and systems intended for optical cross connectors aboard future telecom satellites, where IMT is subcontractor of Sercalo Microtechnology and collaborates with the LMTS of the EPFL.
4:30 PM - K9.2
Wavelength-division Multiplexing/demultiplexing Devices using a-SiC:H Multilayer Heterostuctures.
Manuela Vieira 1 2 , Miguel Fernandes 1 , Paula Louro 1 2 , Alessandro Fantoni 1 , Manuel Vieira 1 3 , Manuel Barata 1 2 Show Abstract
1 DEETC, ISEL, Lisbon Portugal, 2 CTS, UNINOVA, Lisbon Portugal, 3 Traffic Dept., CML, Lisbon Portugal
In this paper we present results on the optimization of multilayered a-SiC:H heterostructures for wavelength-division multiplexing/demultiplexing applications. The WDM device is a double heterostructure and consists of a glass/ITO/a-SiC:H (p-i-n) photodiode which faces the incoming modulated light followed by an a-SiC:H(-p) /Si:H(-i’)/SiC:H (-n’)/ITO heterostructure that allows the optical readout. The single (monochromatic) or the multiple (polychromatic) wavelength beams are passed through the device, and absorbed accordingly to its wavelength, giving rise to a time dependent wavelength electrical field modulation across it. The effect of single or multiple input signals is converted to an electrical signal to regain the information (wavelength, intensity and frequency) of the incoming carriers.In the device the thickness and the absorption coefficient of the front photodiode are optimized for blue collection and red transmittance and the thickness of the back one adjusted to achieve full absorption in the green and high collection in the red spectral range. Both front and back diodes act as optical filters confining the blue and the red optical carriers, respectively inside the front and back diodes while the greens are absorbed across both. Results show that by reading out, under reverse bias, the photocurrent generated simultaneously by all the incoming monochromatic optical carriers the input information is multiplexed together by the device, acting as a multiplexer. Then, the different wavelengths (the color) which jointly can be transmitted over a POF (Polymer optical fiber) need to be separated to regain all information. This separator, the demultiplexer, is the same WDM device, but uses a different optical readout to regain the information. Here, a pulsed laser beam is used, from the back side, to fulfill the single wavelength channels.The devices were characterized through responsivity measurements (400-700nm), under different electrical bias (-10V to +1V) and frequencies (150 Hz to 20KHz). The responsivity was analyzed using either the light coming from multiple wavelength combinations or from a monochromator. Results show that, under demultiplexer operation the photocurrent generated by a modulated probe decreases almost linearly with the wavelength, and reverses in sign around 550 nm. When compared with the signal without visible light the red and blue signals have opposite signs and the green is almost suppressed, allowing blue, green and red recognition. Under multiplexer operation the output signal is balanced by the wavelength of each incoming optical carrier and modulated by there frequencies allowing the multiplexing of the information without losing the input information.An electrical model is presented and supported by a SPICE simulation.Digital home appliance interfaces, home and car network and traffic control applications are foreseen due to the low cost associated to the amorphous a-SiC:H technology.
4:45 PM - K9.3
Embedding Colloidal CdSe/ZnS Quantum Dots in TiO2 Thin Films by Metalorganic Chemical Vapor Deposition.
Sueng-Hee Kang 1 , Young-Soo Park 1 , Eui-Tae Kim 1 Show Abstract
1 School of Nano Science & Engineering, Chungnam National University, Daejeon Korea (the Republic of)
Semiconductor nanocrystal quantum dots (QDs) synthesized via colloidal solution chemistry have been studied extensively for the physics and potential device applications of zero-dimensional (0-D) semiconductor systems. Colloidal nanocrystal QDs are particularly suitable for applications in solution environments such as biological labelling. On the other hand, there have been intensive research efforts to integrate nanocrystal QDs into solid-state based device technology, i.e., light-emitting diodes, lasers, memory devices, etc. Such device applications have mainly used hybrids of nanocrystal QDs and soft-material (e.g., polymer) matrix as a vehicle. Few results have been reported on the system of nanocrystal QDs embedded in solid materials such as oxide. Nanocrystal QDs embedded in oxide can be more electronically and chemically stable and mechanically robust than those in polymer matrix. In this presentation, we report some results on our approach to embed colloidal CdSe/ZnS nanocrystal QDs into TiO2 thin films by plasma-enhanced metalorganic chemical vapor deposition (PEMOCVD). Colloidal CdSe/ZnS core-shell QDs were spread on Si wafers via spin coating. After drying the solvent of QDs, TiO2 thin films were deposited at the thickness of ~100 nm using PEMOCVD. The titanium-isopropoxide was used as a titanium precursor and bubbled at 30 oC with the argon gas flow rate at 50 SCCM (sccm denotes cubic centimeter per minute at STP). The chamber pressure and the RF plasma power were fixed at 1.2 Torr and 40 W, respectively. The average size and the photoluminescence (PL) peak of CdSe/ZnS QDs were ~5 nm and ~550 nm, respectively. We first investigated the thermal stability of QDs as a function of deposition temperature. Up to 250 oC of deposition temperature, the PL intensity and the peak position of QD-embedded films were not significantly changed with respect to those of QDs. The PL intensity of the QD-embedded film grown at 300 oC was dramatically dropped while the PL peak position was not changed. Above 400oC, the PL peak position was remarkably blueshifted with respect to that of QDs. Hydrogen (H2)-plasma treatment was also performed to remove organic surfactants of QDs. QDs were unstable above 300 oC during H2-plasma treatment. We will further discuss characteristics of QDs-embedded TiO2 thin films and their potentials for device applications such as light-emitting diodes and lasers.
5:00 PM - K9.4
Tailoring Quantum Dot Saturable Absorber Mirrors forUltra-Short Pulse Generation.
Matthew Lumb 1 , Edmund Clarke 1 , Raymond Murray 1 Show Abstract
1 EXSS Physics, Imperial College London, London United Kingdom
We have designed and grown a series of quantum dot semiconductor saturable absorber mirrors (QD-SESAMs) for a range of operating wavelengths, incorporating innovative design and processing features to optimise the device performance. SESAMs are well suited as passive modelocking elements in lasers due to their ultrafast carrier dynamics, high spectral tunability and low toxicity compared with dye based saturable absorbers. Structures incorporating a dielectric distributed Bragg reflector (DBR) and semiconductor absorber layers have been used to produce mirrors with non-linear reflectivity which facilitate passive mode-locking for a wide variety of laser gain media. Recently, self-assembled InAs/GaAs quantum dots (QDs) have been employed as the absorber region in such structures for use in the nearinfrared. Careful control of growth parameters allows very wide tunability of the ground state (GS) emission of QD layers, with room temperature emission ranging from around 1 μm in single QD layers to as far as 1515nm in strain-coupled QD bilayers. This range encompasses a large selection of gain media and also allows us to target the important telecommunications wavelengths of 1300 and 1550 nm, enabling the production of ultrashort pulses at important wavelengths for both research and commercial applications.We have grown a range of QD-SESAM structures to different design specifications and using a range of reflectivity studies, ellipsometric measurements and both CW and time-resolved spectroscopic studies, we have conducted detailed investigations of device performance and the physics underpinning the saturable absorption in QDs. Extensive modelling work of dielectric multilayers has been undertaken, including the reflectivity, dispersive characteristics and field distributions inside the samples at variable angles of incidence. This supports our experimental findings and allows us to understand and design novel structures in order to improve and tailor device characteristics.We present SESAMs incorporating electronically coupled QD bilayers, allowing us to achieve long wavelength operation. We also demonstrate samples designed for operation with the higher excited states of the QD dot electronic structure, offering several potential advantages over traditional GS devices, including improved absorption recovery times and modulation depths. We also report on the use of rapid thermal annealing (RTA) as a means of tailoring QD-SESAM characteristics, and discuss the consequences of RTA on the performance of the devices. We demonstrate that RTA can be used to shift the GS or excited states of dots into resonance with the DBR stop-band region without degradation of the DBR reflectivity whilst significantly reducing the luminescence lifetime of the dots, which consequently reduces the absorption recovery time of the dots.