Proceedings Volume 3419

Optoelectronic Materials and Devices

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Proceedings Volume 3419

Optoelectronic Materials and Devices

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Volume Details

Date Published: 22 June 1998
Contents: 9 Sessions, 54 Papers, 0 Presentations
Conference: Asia Pacific Symposium on Optoelectronics '98 1998
Volume Number: 3419

Table of Contents

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Table of Contents

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  • Wide-Bandgap Group-III Nitride Materials
  • Short-Wavelength Light Emitters and Optical Properties of Wide-Bandgap Materials
  • Manufacturing Issues
  • Red Diode Lasers
  • Advanced Characterization of Optoelectronic Materials
  • Vertical-Cavity Surface-Emitting Lasers
  • MEMS and Photodetectors
  • Novel Optoelectronic Materials and Devices
  • Poster Session
Wide-Bandgap Group-III Nitride Materials
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Growth shape control of group-III nitrides by selective-area MOVPE
Naoki Kobayashi, Tetsuya Akasaka, Seigo Ando, et al.
In the selective area metal-organic vapor phase epitaxy, III-V micro-crystals surrounded by low-index crystallographic facets are grown on the open area of the masked substrate. The shape of grown crystal can be controlled by changing the growth condition and/or the mask pattern. On the B substrate, highly symmetrical tetrahedron, hexagonal and regular triangle prisms can be grown in a micrometers scale. The application to micro-lasers called 'facet laser' makes the most use of facet growth because flat and damage-free vertical-facets are best fitted to the laser resonator. Even in group III nitrides, which are extremely hard and chemically inactive, we succeeded in the growth of GaN hexagonal micro prisms and observed the optically pumped room-temperature lasing by ring-cavity mode.
Epitaxial lateral overgrowth of GaN by the sublimation method and by MOCVD
Jie Wang, Satoru Tottori, Maosheng Hao, et al.
Selective overgrowth method has been sued to grow GaN epitaxial layers by metalorganic chemical vapor deposition (MOCVD) and sublimation technology. MgO, Si and SiO2 which have different thermal conductivities and thermal expansion coefficients, have been chosen as mask materials. The microstructure and selectively grown GaN and the lateral growth mechanisms of sublimation and MOCVD have also ben investigated by transmission electron microscopy and scanning electron microscopy. The effect of different mask materials on reduction of dislocation density is discussed. The experimental results indicate that Si is the best mask material for GaN lateral overgrowth. The dislocation density is about 109 cm-2 above the window areas, and it is reduced to 106 cm-2 in the lateral overgrowth region above the Si mask.
Homoepitaxial growth of InGaN/GaN double-heterostructure light-emitting diode by low-pressure MOCVD
Yoon-Ho Choi, Sung-Woo Kim, Jae Hyung Yi, et al.
The homoepitaxial growth InGaN/GaN double heterostructure (DH) light emitting diode (LED) by low pressure metalorganic chemical vapor deposition is reported for the first time. Hydride Vapor Phase Epitaxy prepared 350micrometers -thick GaN single crystal was polished down to a surface roughness of 10 angstrom rms to serve as the substrate. The LED exhibited luminous intensity of 850mcd and forward voltage of 5V at a current of 20mA. The peak wavelength and full width at half maximum of electroluminescence were 490nm and 83nm, respectively.
Growth of high-quality cubic GaN on (001) GaAs by halide VPE with backside buffer
Fumio Hasegawa, Harutoshi Tsuchiya, Kenji Sunaba, et al.
It is reported that arsenic (As) act as a surfactant in growth of cubic GaN by GSMBE, and that it improves quality of cubic of the grown layer. In this paper, we report that it is true for Halide Vapor Phase Epitaxy (HVPE) of GaN, however, it deteriorates photoluminescence intensity of the grown layer very much. It was found that in order to get optically high quality cubic GaN, it is important to prevent incorporation of As. The As autodoping in HVPE was suppressed by growing GaN layer on back side of the substrate, too. The photoluminescence intensity was improved by more than one order to magnitude by preventing the As autodoping. In HVPE, we can grow thick and pure GaN layers, though it is said that when the grown thickness exceeds 1.5 micrometers , more than 10 percent hexagonal phase is introduced for gas source molecular beam epitaxy and metalorganic vapor phase epitaxy growth of cubic GaN. Best value of the cubic component for HVPE was 2 micrometers with the cubic component of more than 99 percent.
Phonon-assisted photoluminescence in wurtzite GaN epilayer
Wei Liu, Ming Fu Li, ShiJie Xu, et al.
Photoluminescence of wurztite GaN epilayer was measured in the range of 4K to 300K. At low temperature, the neutral- donor bound exciton emission dominates the spectra, while with increasing temperature, free exciton emissions grow rapidly and finally become the dominant lines. The exciton linewidth due to exciton-phonon interaction was studied.Lo phonon-assisted photoluminescence associated with both the bound exciton and the free exciton were also observed. The temperature dependence of LO phonon-assisted emissions can be well explained by the phonon-assisted free exciton emission theory established for II-VI compound semiconductors. In particular, the study of 2LO phonon replica can provide information of the temperature dependence of the concentration and recombination lifetime of free excitons in GaN.
High-temperature stimulated emission studies of MOCVD-grown GaN films
Sergiy Bidnyk, Brian D. Little, Theodore J. Schmidt, et al.
Edge and surface-emitted stimulated emission (SE) in optically pumped GaN thin films was studied in the temperature range of 20 K to 700 K. The single-crystal GaN films used in this work were grown by MOCVD on sapphire and 6H-SiC substrates. We have observed that the SE peak shifts from 360 nm at 20 K to 412 nm at 700 K, which is the highest temperature at which SE has been reported for this material. The temperature sensitivity of the SE threshold was studied over the entire temperature range. The characteristics temperature was found to be about 170 K over the temperature range of 300 K to 700 K for samples grown on both sapphire and SiC substrates. The energy position of the SE and spontaneous emission peaks were shown to shift linearly to longer wavelengths with increasing temperature and empirical expressions for this shift are given. We demonstrate that the energy separation between the spontaneous and SE peaks gradually increases from 90 meV at 300 K to 200 meV at 700 K indicating that an electron-hole plasma is responsible for the SE mechanisms above room temperature (RT). We demonstrate that the surface-emitted SE in GaN epilayers comes from cracks, burn spots, and other imperfections, and is due to the scattering centers and, under strong optical excitation, become points of origin for burning of the sample surface. This study shows that GaN has an extremely low temperature sensitivity compared to other semiconductors and is suitable for the development of light emitting devices that can operate significantly above RT.
Short-Wavelength Light Emitters and Optical Properties of Wide-Bandgap Materials
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MOCVD growth of AlGaN UV LEDs
Jung Han, Mary Hagerott Crawford
Issues related to the MOCVD growth of AlGaN, specifically the gas-phase parasitic reactions among TMG, TMA, and NH3, are studied using an in-situ optical reflectometer. It is observed that the presence of the well-known gas phase adduct could seriously hinder the incorporation behavior of TMGa. Relatively low reactor pressures are employed to grow an AlGaN/GaN SCH QW p-n diode structure. The UV emission at 360 nm represents the first report of LED operation from an indium-free GaN QW diode.
Comparison of the optical gain of wurtzite GaN/AlGaN quantum well lasers grown on (0001)- and (1010)-oriented substrates
Tow Chong Chong, Yee Chia Yeo, Ming Fu Li
We calculate the optical gain of wurtzite (WZ) GaN/AlGaN QWs grown on the (0001) and (1010) oriented substrates, taking into account the valence subband structure modification due to the crystal orientation effect and the pseudomorphic strain which is anisotropic in the QW plane. We show that, for the (1010) GaN/AlGaN quantum well (QW), the two topmost valence subbands are more widely separated than the HH1 and LH1 subbands in the (0001) GaN/AlGaN QW. The in-plane energy dispersion of the (1010) QW also becomes anisotropic, giving rise to a reduced band-edge density-of-states in comparison with the (0001) QW. Moreover, states constituting the topmost valence subband at the (Gamma) point favor TE mode gain. A combination of the reduced band-edge density-of- states and the existence of the preferred symmetry at the valence band maximum contributes to an improvement of the TE optical gain. A comparison of the QWs of both orientations shows that the (1010) QW is capable of achieving lower transparency current densities. Therefore, the (1010) orientation is promising in improving the threshold performance of WZ GaN-based QW lasers.
Large optical nonlinearities in the bandgap region of GaN thin films grown by MOCVD on sapphire
Theodore J. Schmidt, Yia-Chung Chang, Jin-Joo Song
We report the results of nanosecond non-degenerate optical pump-probe experiments and single-beam power dependent absorption experiments performed on metalorganic chemical vapor deposition grown GaN thin films. Changes in the optical transitions near the band gap due to excess photo- generated free carriers were studied as a function of excitation density at 10 K and room temperature using pump- probe spectroscopy. At 10 K, strong, well-resolved features are present in the absorption spectra corresponding to the 1s A and B free exciton transitions. These features are shown to broaden and decrease in intensify due to the presence of the high densities of photo-excited free carriers generated by the pump beam, resulting in extremely large values of induced transparency, exceeding 4 X 104 cm-1 as the excitation density (Iexc) approaches 3 MW/cm2. In addition, large values of induced absorption are observed with increasing pump density in the below-gap region where gain was expected. This induced absorption was also found to be extremely large, exceeding 4 X 104 cm-1 as Iexc was increased to over 3 MW/cm2. At room temperature the resulting induced transparency and induced absorption were found to approach 2 X 104 cm-1 as Iexc approached 3 MW/cm2. The single-beam power dependent absorption experiments show enhanced bleaching of the excitonic transitions with increasing Iexc compared to the pump-probe experiments, while the below-gap induced absorption is drastically reduced in the single-beam experiments. The large values of induced transparency/absorption observed in this work and the fact that excitons have been shown to persist to over 450 K in GaN1 suggest the possibility of new opto-electronic applications for the group III nitrides.
Manufacturing Issues
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MOCVD technology for the production of highly efficient GaAlP/GaAs/Ge solar cells
Rainer Beccard, Harry Protzmann, Dietmar A. Schmitz, et al.
Since the invention of the Planetary Reactors a reliable tool for mass production of various III-V compounds is existing. These reactors have proven to grow extremely uniform films together with a highly efficient utilization of the precursors. Now a new generation of Planetary Reactors is introduced: the so-called G3 systems. Their main features are: an inductive heating system with extremely low thermal mass for precise and fast heating, high flexibility in the reactor size and the option to use a fully automated cassette-to-cassette wafer loading system. The benefits of this new design are very short cycle times, extreme run-to- run stability and even further reduced cost of ownership. We will present comprehensive data concerning growth of GaAs, AlGaAs, GaInP, AlGaInP and other III-V materials. Special focus will be put on uniformity, efficiency and electrical and optical characteristics of films grown in these machines. The data prove that the G3 systems are the most flexible and efficient reactors to meet the demands of solar cell production for the next decade.
Ga2O3(Gd2O3) as a dielectric insulator for GaAs device applications
Tsong Sheng Lay, Minghwei Hong, J. P. Mannaerts, et al.
The novel deposition technique of Ga2O3(Gd2O3) film by using in-situ molecular beam epitaxy (MBE) has led to the first demonstration of enhancement mode GaAs metal oxide semiconductor field effect transistors. For sub- micron GaAs device applications, the current leakage in the gate dielectric of reduced thickness has been an important issue. In this work, we address this aspect for the Ga2O3(Gd2O3) thin films deposited on n-type GaAs and present the electrical characteristics of the GaAs MOS structures as a function of the gate dielectric thickness, varying from 16.6 nm to 7.7 nm. The as-deposited thin dielectric layers show, in dark an inversion layer formation as well as an excellent insulator performance: a gate leakage current density as low as 10-9 A/cm2 at low gate bias up to 2.5 V and the electrical breakdown field reaches above 10 MV/cm. The high resolution transmission electron microscopy measurements show a sharp and uniform dielectric/GaAs transition with interfacial roughness < 1 nm.
MPACVD processing technologies for planar integrated optics
Cheng-Chung Li, Robert Addison Boudreau, Terry P. Bowen
Optical circuits based on low-loss glass waveguide are the practical and promising approaches to integrate different functional components for optical communication system. Microwave plasma assisted chemical vapor deposition produces superior quality, low birefringence, low-loss, planar waveguides for integrated optical devices. A microwave plasma initiates the chemical vapor of SiCl4, GeCl4 and oxygen. A Ge-doped silica layer thus deposited on the substrates with reasonable high growth rate. Film properties are based on various parameters, such as chemical flow rates, chamber pressure and temperature, power level and injector design. The main emphasis has been on optimizing the deposition parameters and reproducibility. An uniform, low-loss film can be made by properly balancing the precursor flows. The refractive index of deposited film can also be controlled by adjusting the flow ratio of SiCl4 and GeCl4 bubblers. Deposited films was characterized by prism coupler, loss measurement, residual stress, and composition analysis. The resulted refractive index step can be varied between 1.46 to 1.60. Waveguide can be fabricated with any desired refractive index profile. Standard photolithography defines the waveguide pattern on mask layer. Core layer was remove by the plasma dry etch which has been investigated by both reactive ion etch (RIE) and inductively coupled plasma etch. Etch rate of 3000-4000 angstrom/min has been achieved by using ICP compared to typical etch rate of 200-300 angstrom/min by using conventional RIE.
Finite element analysis of thermal stresses in laser packaging
Maw-Tyan Sheen, Cheng-Huang Chen, Jao-Hwa Kuang, et al.
A finite -element method (FEM) analysis is performed on the calculation of residual stresses during spot -welding for Au- coated Invar materials. Numerical results show that the high residual tensile stresses of the phosphorus rich segregation layer generated by rapid solidification shrinkage is the possible cause for crack formation. This indicates that the FEM calculations may provide one of the effective methods for predicting the crack formation in laser -welded Au- coated materials Keywords: Crack, thermal stress, laser packaging, finite -element method 1. INTRODUCTION To enhance the solderability for chip and wire bonding, optoelectronic materials of Invar' or Kovar2 of very low coefficient of thermal expansion (CTE) are often coated with a Au thin film. There have been well documented in the area of thin film coating that an inadequate thickness of Au coating on optoelectronic materials in laser welding process can cause undesirable reactions such as crack defects in the welded joints34. Prior to Au plating on optoelectronic material, a Ni underlayer coating is often applied to improve adhesion. The Ni underlayer can be formed by P -free electroplating or P- containing electroless plating, denoted hereafter as Ni and Ni(P), respectively. However, the chemical reducing agent NaH2P02 is required in the electroless Ni(P) plating process, which introduces additional phosphorus (P) element in the Ni(P) underlayer. Recently comprehensive measurements of laser -welded Au -, Ni -, Ni(P), and Au/Ni- coated Invar have shown that the existence of the P element content in the Ni(P) underlayer instead of the Au element in the Au plating layer play a major role in determining the crack formation in laser welded Au- coated optoelectronic materials8. The purpose of this work is to study the solidification crack formation mechanism in laser -welded Au- coated optoelectronic materials due to P- containing underlayer by using finite- element method (FEM). This work has led to important result that the FEM provides an effective method for predicting the crack formation in laser -welded Au- coated optoelectronic materials. 2. LASER WELDING SYSTEM AND PACKAGE CONSTRUCTION 2.1 Laser Welding System: Fig. 1 (a) shows the experimental setup of the laser welding system. The system consisted of a pulsed Nd: YAG laser and a dual -beam fiber optic beam delivery. Two laser beams delivered from the Nd:YAG laser to the workpiece were accurately adjusted with the same energy and with the incident angles of (45° ± 1 0)9. The laser energy required to create the welds was delivered simultaneously through two fibers placed 180° apart. The simultaneous and equal energy delivery is designed to reduce the post -weld -shift (PWS) in the two components because the solidification- shrinkage of both welds can compensate each other, resulting in minimized displacement shifts9. 2.2 Package Construction: A top view of dual -in -line package (DIP) indicating the pigtail fiber to the laser chip is also shown in Fig. 1 (a). The DIP construction consisted of a 1.3 j.tm laser, the Invar housing materials, a thermoelectric cooler, W.H. Cheng (correspondence): E -mail: whcheng@eo.nsysu.edu.tw; Telephone: (886) 7 -525 -2000 ext. 4450; Fax: (886) 7 -525 -4499 Part of the SPIE Conference on Optoelectronic Materials and Devices Taipei, Taiwan July 1998 SPIE Vol. 3419 0277 -786X/98/$10.00 93 Finite-element analysis of thermal stresses in laser packaging Maw-Tyan Sheen#, Cheng-Huang Chen*, Jao-Hwa Kuang', and Wood-Hi Cheng* #Mh•c1 Engineering Department and *Jjj ofElectro—Optical Engineering, National Sun Yatsen University, Kaohsiung, Taiwan 804 Huang-Lon Chang, Szu-Chun Wang, Chungyung Wang, Chy-Ming Wang, and Jy-Wang Liaw Chunghwa Telecom Laboratories, 12, Lane 55 1, Min-Tsu Rd, Sec. 3, Yang-Mei, Taoyuan, Taiwan 326 ABSTRACT A finite-element method (FEM) analysis is performed on the calculation of residual stresses during spot-welding for Au- coated Invar materials. Numerical results show that the high residual tensile stresses of the phosphorus rich segregation layer generated by rapid solidification shrinkage is the possible cause for crack formation. This indicates that the FEM calculations may provide one of the effective methods for predicting the crack formation in laser-welded Au-coated materials
Fiber alignment shift in temperature cycling test
Yih-Cheng Sheu, Cheng-Huang Chen, Chy-Pen Chien, et al.
A finite-element method (FEM) analysis has been carried out on the fiber alignment shift in an optical fiber soldered into a ferule. Results show that the maximum fiber alignment shifts are strongly depend on the geometry of fiber offset from the center of the ferrule.Up to 0.24 and 0.27 micrometers of the maximum fiber alignment shifts were predicted in temperature cycling from -40 to +85 degrees C and -40 to +100 degrees C, respectively. Detailed knowledge of predicting the maximum fiber alignment shift in temperature cycling test is important for practical design and fabrication of high yield optoelectronic packaging.
Red Diode Lasers
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Laser diode for DVD pickup head
Man-Fang Huang, How-Chiang Lee, Jin-Kuo Ho, et al.
General requirements of AlGaInP/InGaP laser diode (LD) for digital versatile disk (DVD) optical pick-up head application, such as wavelength, output power, astigmatism, mode profile, and relative intensity noise will be discussed in this paper. Several efforts which have been made to develop AlGaInP/InGaP laser diodes suitable for DVD application will be reviewed. To record or erase signals in a DVD system, an output power of about 30 mW from AlGaInP/InGaP laser diode is required. Several methods which were proposed to increase catastrophic optical damage level will also be reviewed. Several methods which were proposed to increase catastrophic optical damage (COD) level will also be reviewed. A low-power 650-nm-band AlGaInP/InGaP laser diode utilizing double-channel ridge waveguide structure has been developed at OES/ITRI. Good characteristics of this laser diode such as very low operation current, small astigmatism, and stable fundamental transverse mode operation at a power level of more than 10 mW were obtained. A hybrid optical pick-up head utilizing this laser diode was incorporated in a commercial DVD-video player and functioned with a very good quality.
Characteristics of AlGaInP/InGaP broad-area laser diodes
Hung-Pin D. Yang, Chien Chia Chiu, Jin-Kuo Ho, et al.
We report the results of the AlGaInP/InGaP broad area laser diodes.the broad area lasers were made with laser cavity- lengths of 250 micrometers to 1.25 mm. The pulsed L-I characteristics of these broad area lasers were measured, as a function of the laser stripe width. The pulse width of the pulsed L-I measurements was 360 nsec and the pulse periods were 10 msec to 5 (mu) sec. The measured pulsed L-I characteristics of the AlGaInP/InGaP lasers were found to be strongly dependent on the duty cycles of the applied voltage pulses, which were attributed to heating effects within the broad area lasers. The threshold current increases with increasing pulse duty cycle, while the external quantum efficiency decreases with increasing duty cycle. Heating effects were negligible only at very low duty cycles of 0.1 percent or below. Similar pulsed L-I measurements were performed on the 850-nm AlGaAs/GaAs broad area lasers. Heating effect was not observed in those measurements because of better heat conduction properties of the AlGaAs cladding layers. The results were carefully analyzed.
650-nm GaInP/AlGaInP visible laser diode with buried tapered-ridge structure
Jun-Ho Jang, Young-Hak Chang, Hee-Suk Song, et al.
A new tapered ridge waveguide structure is employed in GaInP/AlGaInP laser diodes in order to increase (theta) PLL for digital versatile disk optical pick-up application. The dry-etched buried tapered ridge has been fabricated using BCl(subscript 3/Ar plasma in electron cyclotron resonance reactive ion etching system and chemical treatments. The parallel far-field angle was increased up to 9.7 degrees when the width of tapered ridge at the front facet was reduced down to 3.2 micrometers . The threshold current was 60mA and slope efficiency was 0.42W/A, which were comparable to the values of wet-etched lasers. The characteristics temperatures were estimated to be 154K at 25-60 degrees C and 60K at 60-100 degrees C. An operating time of over 1000 hours at the output power of 5mW at 70 degrees C was obtained without significant increase of operating current, which indicates a sufficient reliability for commercial purposes.
High-temperature operation of 650-nm AlGaInP quantum well laser diodes grown by LP-MOCVD
Xiaoyu Ma, Qing Cao, Guohong Wang, et al.
Low threshold current and high temperature operation of 650nm AlGaInP quantum well laser diodes grown by low pressure metal organic chemical vapor deposition are reported in this paper. 650nm laser diodes with threshold current as low as 22-24mA at room temperature, and the operating temperature over 90 degrees C at CW output power 5 mW were achieved in this study. These lasers are stable during 72 hours burn in under 5mW at 90 degrees C.
Advanced Characterization of Optoelectronic Materials
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Correlation between dislocations and luminescence in GaN
Maosheng Hao, Tamoya Sugahara, Satoru Tottori, et al.
A GaN film grown on sapphire substrate by metalorganic chemical vapor deposition have been investigated by the plan-view TEM and CL. Direct evidence of dislocation being a non-radiative recombination center, have been provided. A bulk GaN grown by the sublimation method and a homoepitaxial GaN grown by hydride vapor phase epitaxy have also been investigated by TEM, the x-ray diffraction and PL. The results confirm that it is not the dislocations but the point defects that are responsible for the yellow luminescence of the grown GaN. It was found, in a cross- section TEM image of a GaN/Al2O3 film, that there are many precipitates gathered around a mixed dislocation. The precipitates might be formed by the segregation of point defects around dislocations. The precipitates might be formed by the segregation of point defects around dislocations. Since most of the point defects in GaN seems to segregate around the dislocations, dislocations can reduce the local concentration of the point defects in the no dislocation region. In this case, the optical property of GaN might be improved by the existence of the dislocation.
Conduction-band mass determinations for n-type InGaAs/InAlAs single quantum wells
Eric D. Jones, Nobuo Kotera, John L. Reno, et al.
We report the measurement of the conduction band mass in n- type single 27-ML-wide InGaAs/InAlAs quantum well lattice matched to InP using two methods: (1) Magnetoluminescence spectroscopy and (2) far-IR cyclotron resonance. The magnetoluminescence method utilizes Landau level transitions between 0 and 14 T at 1.4 K. The far-IR cyclotron resonance measurements were made at 4.2 K and to fields as large up to 18 T. The 2D-carrier density N2D equals 3 X 1011 cm-2 at low temperatures. The magnetoluminescence technique yielded an effective conduction-band mass of mc equals 0.062m0 while the far-IR cyclotron resonance measurements gave mc equals 0.056m0. Both measurements show no evidence for any significant conduction-band nonparabolicity.
Characterization of heavy masses of two-dimensional conduction subband in InGaAs/InAlAs MQW structures by pulsed cyclotron resonance technology
Nobuo Kotera, H. Arimoto, Noboru Miura, et al.
Conduction-band effective masses in a direction parallel to the quantum well plane were investigated in n-type- modulation-doped InGaAs/InAlAs multi-quantum well system. Thicknesses of well and barrier were 5 and 10 nm. Three highly-doped specimens having about 1 X 1012 cm-2 per one quantum well were prepared by MBE. Double-crystal x-ray diffraction was used to check the crystal quality. Heavy electron effective masses, almost 50 percent bigger than the band edger mass of 0.041m0, were measured by far-IR and IR cyclotron resonances under pulse high magnetic fields up to 100 T. Nonparabolicity of this subband was less than 12 percent by comparing the two cyclotron resonances. Observed 2D subband structure was quite different from conduction band in a direction perpendicular to the same quantum well and from that of GaAs/GaAlAs quantum well system.
Temperature-dependence photoreflectance study of InAs/GaAs self-assembled quantum dots
Gwo-Jen Jan, S. M. Chang, ChihMing Lai, et al.
Temperature dependence photoreflectance has been used to study InAs/GaAs self-assembled quantum dots (QDs). The QDs samples were grown on (100) misoriented 7 degrees toward (110) GaAs semi-insulting substrate by a gas source molecular beam epitaxy with changing V/III ratio. The energy features of PR spectra from QDs and wetting layer (WL) were fitted by the first derivative Gaussian functional form and band-gap feature was fitted by the derivative-like Lorentian line shape function.THE blue-shift of optical transition energies responded from QDs has been characterized. The signals responded from an ultra-thin wetting layer of InAs/GaAs QDs samples and band-gap transition energy from GaAs portions were also observed. It demonstrates that the energy features of PR spectrum responded form QDs and WL section could provide the important information about QDs quality. The results show that the size, uniformity and density of QDs can be improved by the changing V/III ratio.
Formation of high-performance PtSi/p-Si Schottky barrier detector using high-resolution transmission electron microscope
Wen-Sheng Wang, Chia Ho, Tien-Ming Chuang
The effects of the discontinuity in thin PtSi layers on the performance of PtSi/p-Schottky-barrier detectors (SBDs) have been studied in detail in this paper. We have observed discontinuous PtSi film formed in large detector size and continuous PtSi film formed in smaller detector size when very thin PtSi is formed at temperature of 350 degrees C or below. For the SBDs with discontinuous PtSi film, the quantum efficiency is lower and barrier height is higher compared to those with continuous PtSi films. However, if the PtSi layer thickness is larger than 4 nm, the PtSi islands in the layer coalesce and the performance of the detector is similar to that of SBDs with continuous PtSi film. The formation of discontinuous PtSi layer results from the 3D growth of PtSi at preferential steps. However, the smaller area for PtSi formation can promote the 2D growth. When the PtSi formation temperature is 450 degrees C or above, thin PtSi forms in islands either in larger size test-key or in smaller size pixel. The results studied by transmission electron microscopy indicate that PtSi layer formed above 450 degrees C is preferentially oriented to (100) Si substrate. This results in the 3D PtSi growth. 256 X 244 PtSi/p-Si arrays monolithically integrated to read- out circuit have been fabricated using standard Si IC processes. From the measurement of uniformity and noise equivalent temperature difference of arrays, the PtSi/p-Si Schottky-barrier detector is shown to be operated under background limited condition.
Vertical-Cavity Surface-Emitting Lasers
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Surface-emitting lasers for parallel data transmission and data storage
Fumio Koyama, Kenichi Iga
Low threshold vertical cavity surface emitting lasers (VCSELs) have been developed for future parallel optoelectronics, including optical interconnects. The research field of surface emitting lasers is growing up rapidly and micro-amperes low threshold devices have been realized. In this paper, we present some of our results on 980 nm GaInAs/GaAs surface emitting lasers for parallel data transmission. Specifically, we describe some attempts to improved device performances, which include low electric resistance p-type DBRs and p-type delta doping in quantum wells. We demonstrate a penalty-free 10 Gbit/s data transmission. Also, VCSELs grown on (311) GaAs substrates have been developed for stable polarization control, which will give us low noise operations. In addition, we discuss a possibility of a novel VCSEL optical head toward Tera bytes optical memories using scanning near-field optics.
Progress in high-power VCSELs and arrays
Rainer Michalzik, Martin Grabherr, Roland Jaeger, et al.
Recent achievements in the design and fabrication of monolithic high power vertical cavity surface emitting lasers (VCSELs) are reviewed and major distinctions between the scaling properties of top and bottom emitting devices clarified. Although a few hundred milliwatts optical power can be extracted from a single bottom emitting laser, decreasing efficiencies with increasing device diameter suggest the investigation of 2D laser arrays. First experimental results are presented, featuring oxide confined VCSEL arrays at 980 nm wavelength with 3 X 3 elements and maximum output powers up to 650 mW, still delivering 270 mW with 25 percent conversion efficiency under continuous wave operation. With further optimizations of device size and array pitch, emitted power densities averaged over the entire chip area in excess of 1 kW/cm2 should be attainable.
Three-dimensional simulation of oxide-confined vertical-cavity surface-emitting semiconductor lasers
Several vertical-cavity surface-emitting laser (VCSEL) structures are investigated by means of 3D steady-state electrical-thermal-optical numerical modeling. Electrical and thermal models are coupled via: (i) heat generation by current passing through the diode; (ii) temperature dependence of the diffusion potential of the junction; and (iii) temperature dependence of the bulk resistivity of passive material at both sides of the junction. Optical waveguide model is coupled to electrical-thermal model through position-dependent carrier recombination lifetime and temperature-dependent refractive-index. Simulation is performed for cylindrically symmetric two-sided oxide- confined intracavity-contact VCSELs. For comparison purposes, numerical data are acquired for materially identical bottom-emitting mesa laser and p-side intracavity- contact VCSEL. Nonuniformity of the main device characteristics is studied. Several different phenomena are shown to contribute to nonuniformity: (i) current crowding due to device geometry; (ii) current crowding induced by stimulated emission processes; (iii) current spreading related to oxide positioning; (iv) temperature related effects.
Measurement of resonant-mode blueshifts in quantum-dot vertical-cavity surface-emitting lasers
James A. Lott, Michael J. Noble, John P. Loehr, et al.
We experimentally investigate the modal properties of vertical cavity surface emitting lasers with vertically coupled quantum dot active regions. Etched air-post structures with aluminum-gallium-oxide apertures and aluminum-oxide distributed Bragg reflectors are electrically-pumped below the lasing threshold. The wavelengths of the resonant cavity modes are revealed by room temperature electroluminescence measurements. In concert with our earlier theoretical predictions, we find that the resonant cavity modes blueshift as the radius of the oxide aperture decreases.
MEMS and Photodetectors
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Surface micromachined devices for microwave and photonic applications
M. Frank Chang, Ming C. Wu, JeyHsin Yao, et al.
As an enabling technology, Micro Electro Mechanical Systems (MEMS) have continuously provided new and improved design/implementation paradigms for a variety of scientific and engineering applications. In this paper, we review recent advances made in MEMS and its derivative MOEM devices for both microwave and photonic applications.
Two-dimensional micro-optical scanner excited by PZT thin-film microactuator
Hiroshi Goto
A silicon micromachined resonance type 2D micro optical scanner has been developed for miniaturization of optical scanning sensors such as a bar-code reader, a laser range finder, a shape recognition sensor and so on. A PZT thin film microactuator is adopted to the actuator of the micro scanner in order to miniaturize the actuator and decrease the operation voltage. The scanner, 2mm X 4mm in size, consisting of a resonator with two degrees of freedom and a PZT thin film microactuator for excitation of the resonator and the strain detector for scanning position detection is capable of 2D optical scanning with wide scanning angle at low applied voltage and detection of the scanning position. A miniature scanning image sensor and a range sensor could be realized using the micro scanner.
Performance evaluation of a lead-titanate (PbTiO3) pyroelectric thin-film infrared sensor with temperature isolation improvement structure by microelectromechanical system (MEMS) technologies
Jyh-Jier Ho, Yuen Keun Fang, Chin-Ying Chen, et al.
An IR sensor with the lead-titanate thin-film using the technology of micro-electro-mechanical systems to achieve a better thermal isolation structure has been fabricated and developed. The major IR-sensing part on the cantilever beam with dimensions of 200 X 100 X 2 micrometers 3 consists of a 500-angstrom lead-titanate layer deposited by RF sputtering, and an evaporated bismuth layer. This thermal isolation improved structure exhibits a much superior performance to that of a traditional IR-sensing bulk structure on the experimental results, which show a 200 percent and 300 percent improvement in current gain under the incident optical power 500 (mu) W and 6V applied bias at room temperature and 77 degrees K, respectively.
Sofradir IR detectors: today and tomorrow
Sofradir, the European company totally dedicated to second and third generation of IR detectors has focused its activities on development and production based on MCT material. As a matter of fact, Sofradir is one of the sole companies in the world able to master the MCT technology for SW, MW and LW and then to produce this type of arrays in good conditions allowing affordable prices. This activity covers TDI long linear arrays and staring arrays. Performances of TDI arrays like the 480 X 4 staring arrays like the 320 X 240 will be presented. Then the most advanced activities in France in the field of IR detectors will be presented.
Dark current mechanisms in HgCdTe photodiodes
Experimental and theoretical results are presented for current-voltage and dynamic resistance-voltage characteristics of Hg1-xCdxTe ion-implanted p-n junction photodiodes with x approximately equals 0.22. By measuring the temperature dependence of the dc characteristics in the temperature range 25-140K, the dark current mechanism are studied. At high temperature and in low reverse bias region, the diffusion current dominates. On the other hand, at medium temperature and medium reverse bias, trap-assisted tunneling plays an important role. At low temperature and in the medium reverse bias region, band-to-band tunneling is the key leakage current source.However, when the temperature is further lowed down to 25K and the applied reverse bias is very small, the band-to-band tunneling current will be ruled out and the trap-assisted tunneling mechanism dominates again. We have measured 1/f noise in HgCdTe photodiode as a function of temperature, diode bias, dark current. The dependence of 1/f noise on dark current was measured over a wide temperature range on devices. The temperature dependence of the 1/f noise was found to be the same as the temperature dependence of the surface generation and leakage currents. We obtained the maximum specific detectivity value and the maximum signal-to-noise ratio are about 3.51 X 1010 cm Hz1/2/W and 5096 respectively.
Novel Optoelectronic Materials and Devices
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Applications of photonic crystals in optoelectronics
Shawn-Yu Lin, Joel R. Wendt, G. Allen Vawter, et al.
In this paper, I describe realistic applications of photonic band gap (PBG) materials in optoelectronics at the mm-wave, IR and optical wavelength regimes. Examples are highly dispersive PBG-prisms and PBG-lasers. I will also describe our recent breakthrough at Sandia in the successful fabrication of 3D silicon photonic crystal operating at IR wavelengths.
High-power and high-efficiency mid-infrared type-II quantum well and interband cascade lasers
Shin Shem Pei, C.H. Thompson Lin, Bao Hua Yang, et al.
High power and high quantum efficiency operation of both diode-pumped and interband cascade lasers based on InAs/Ga(In)Sb type-II quantum well with a broken gap band alignment have been demonstrated. The interband cascade laser yielded 0.5 W peak and 16 mW average output per facet under 1- and 5-microsecond(s) long pulses at 80K, while the optically pumped 4-micrometers devices yielded 0.9-1.6 W peak and 90-150 mW average output per facet for 0.1- to 1-ms long pulses at 71K. These output powers are among the highest long-pulse results reported from any semiconductor laser at these wavelengths.
High-speed plastic optical fibers and amplifiers
Yasuhiro Koike, Takaaki Ishigure, Takeyuki Kobayashi, et al.
Recent progress of the graded-index polymer optical fiber (GI POF) and polymer optical fiber amplifier (POFA) are reviewed. Because the low attenuation of light transmission in the perfluorinated (PF) polymer base GI POF enables 500 to 1000 m transmission, more accurate analysis is required in the refractive index profile to realize the order of giga bit transmission. Furthermore, recent improvement of the thermal stability of the GI POF is introduced. We clarified that the stability of the refractive index profile and the attenuation under high temperature and high humidity atmosphere can be improved by selecting the suitable dopant material. We demonstrated that organic dye-doped POFA cover a wide spectral range in the visible with a best observed gain of 37 dB in a Rhodamine B-doped POFA pumped at 550 nm. Also, wit a GI POF doped with europium chelate of hexafluoroacetylacetone in tris form, we observed superfluorescence, evidenced by spectral narrowing and lifetime shortening. The prospect is that the wide choice of organic dyes and rare earth chelates offers optical amplifiers and superfluorescence sources for a variety of communication and sensor applications.
Antimonide-based interdiffused quantum wells
Steven K. H. Sim, E. Herbert Li, Kabula Mutamba, et al.
Antimonide (Sb) is said to be an emerging optoelectronic materials for both high speed and long wavelength electronics devices. Recently, there has been much research activities on antimonide based system. Among Group V elements, antimonide is of particular interest as its lattice parameter matches solid solutions of various ternary and quaternary III-V compounds whose band gap cover a wide spectral range from absorption in antimonide based superlattices, detection of longer wavelength of 8 to 14 micrometers is possible. With the technique of interdiffusion applying to an antimonide based quantum well, we will be able to obtain devices which are bias tunable. This technique of interdiffusion is a thermal process which induces an interdiffusion of the constituent atoms across the heterointerfaces of an as-grown quantum well, and results in modification of the composition and confinement profiles of the quantum well structures. Hence, the optical properties of the material can be modified to desire values. In this presentation, an antimonide based interdiffused quantum well structure is carefully examined including experimental results, with strong emphasis on its tunable properties and summarized with focus on its device applications and future development.
Poster Session
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Theoretical model for studying hot phonon effects and electron energy relaxation in GaN: the roles of A1-mode and E1-mode optical phonons
Chin-Yi Tsai, Chin-Yao Tsai, Jenkins C.H. Chen, et al.
The decay of a zone-center LO-phonon in GaN into a TO phonon and a LA phonon is theoretically investigated, because its decay into two LA phonons is forbidden in GaN. A theoretical model is presented to study the effect of nonequilibrium LO and TO phonons on the electron energy relaxation rate. The individual contributions of A1 mode and E1 optical phonons in the overall electron energy relaxation processes are also discussed.
Band structure of interdiffused InGaN/GaN quantum wells
Elaine M. T. Cheung, Michael C. Y. Chan, E. Herbert Li
Quantum well composition intermixing is a thermal induced interdiffusion of the constituent atoms through the hetero- interface. The intermixed structures created by both impurity induced and impurity-free vacancy promoted processes have recently attracted high attention. In recent years, blue green LED and laser of III-nitride semiconductors have attracted a large amount of interest. This is mainly due to its large bandgap range from 1.89eV to 3.44eV. InGaN/GaN single quantum well structures have been used to achieve high lumens blue and green light emitting diodes. In this paper, we will present the band structure of strained InGaN/GaN single quantum well under the influence of interdiffusion. Band structure is a fundamental aspect in determining the electronic and optical properties of the materials such as optical gain, refractive index, absorption, etc.
Near-band-edge optical properties of MBE-grown ZnSe epilayers on GaAs by modulation spectroscopy
Ru-Chin Tu, Yan-Kuin Su, Ying-Sheng Huang, et al.
A study of near-band-edge optical properties on ZnSe epilayers grown on GaAs substrates using various modulation techniques is presented. We compare the contactless electroreflectance (CER) and piezoereflectance (PzR) spectra to ascertain that our ZnSe epilayers of 1.2 micrometers in thickness grown on GaAs substrates are under a biaxial tensile strain. The defect-related transitions near the ZnSe/GaAs interface are also compared by identifying the photoreflectance (PR) and other spectra. In addition, in order to observe the temperature-dependent energy splitting and strains, we present a detailed investigation of the heavy and light-hole related transition energies as a function of temperature in the 15-200 K range by identifying the excitonic signatures in the CER spectra. We have also calculated the energy splitting between heavy and light-hole valence bands by utilizing the temperature-dependent elastic constants for ZnSe and the thermal-expansion coefficients for ZnSe and GaAs. Both the experimental result and the theoretical calculation have shown a similar trend that the biaxial tensile strains decrease in magnitude with increasing temperatures in the 1.2 micrometers ZnSe epilayer grown on a GaAs substrate.
Experimental Luttinger parameter determination by confined states in InGaAs/InAlAs multiple quantum well structures
Koichi Tanaka, Nobuo Kotera, H. Nakamura
In0.53Ga0.47As/In0.52Al0.48As multi-quantum well structures were studied with photocurrent spectroscopy. Based on the envelope function model in the effective mass approximation, effective mass and valence band offset were derived from the experimental eigen energies. The effective masses of the heavy hole and the light hole were 0.39 m0 and 0.051 m0 in a direction normal to the MQWs plane. The valence band offset was 0.22 eV. Luttinger parameters calculated from the effective masses were (gamma) 1 equals 11 and (gamma) 2 equals 4.3. The effective masses in the direction parallel estimated from the Luttinger parameters were 0.065 m0 and 0.14 m0. The parallel mass of the heavy hole estimated by this experiment agreed to the one by cyclotron resonance, 0.061 m0.
Formation mechanism of defects in annealed InP
Yujie Han, Xunlang Liu, Jinghua Jiao, et al.
Dynamical formation mechanism of defects in the annealed nominally undoped semi-insulating InP obtained by high pressure, high temperature annealing of high purity materials is proposed. Local vibrational modes in tenths of InP samples reveal clearly existence of complexes related to hydrogen. Complexes of vacancy at indium site with one to four hydrogen atoms and isolated hydrogen or hydrogen dimers, complexes of hydrogen with various impurities are investigated by FTIR. Hydrogen can act as an actuator for generation of antistructure defects. Fully hydrogenated indium vacancy dissociates leaving large lattice relaxation behind, deep donors, many larger complexes involving phosphorus at indium site and isolated hydrogen defects are created in nominally undoped InP after annealing. Also created are acceptor levels such as vacancy at indium site. Carrier charge compensation mechanism in nominally undoped InP upon annealing at high temperature is given. Microscopic models of hydrogen related defects are given. Structural, electronic and vibrational properties of LVMs related to hydrogen as well as their temperature effect are discussed.
Ion beam synthesis of beta-FeSi2 as an IR photosensitive material
Yoshihito Maeda, Tomoki Akita, Kenji Umezawa, et al.
The large sized and flat polycrystalline (beta) -FeSi2/n- Si heterojunction can be formed by a triple energy implantation method and the sample annealing at 800 degrees C. The polycrystalline (beta) -FeSi2 gains show good crystalline characteristics, a photoluminescence peak at 0.81 eV at 4.2 K and the optical direct band-gap of 0.84 eV. The (beta) -FeSi2/n-Si heterojunction shows good diode characteristics and high photovoltaic sensitivity for IR light. These results support that the ion beam synthesized (beta) -FeSi2/n-Si heterojunction is a promising IR sensitive materials.
Light-emitting devices made of Langmuir-Blodgett-deposited poly(3-hexadecylthiophene)
Antonio Vaz Cavalcanti, Clecio Gomes dos Santos, Celso Pinto de Melo
Organic LEDs are a promising class of optoelectronic devices which have advantages of cost, manipulation and emission spectrum over existing options in the market. The key to these advantages is the organic nature of the active layer prepared by the adequate deposition of a conjugated polymer. In this communication we present preliminary results of the preparation and characterization steps of a LED consisting of an ITO covered glass substrate as the anode, an active layer of poly(3-hexadecylthiophene) (P3HDT) and an evaporated aluminum layer as the cathode. Using the Langmuir-Blodgett technique, 20 organized monomolecular layers were transferred from a mixed Langmuir film of P3HDT and behenic acid. The devices were submitted to current- voltage and luminance-current test. Some of them have shown rectifying characteristics and luminance of about 1 cd/m2 at 25 volts and 4 mA. While the production yield was of the order of 25 percent, almost every device tested has shown rectifying characteristics.
Carrier distribution in asymmetric dual quantum wells
Ching-Fuh Lin, Bor-Lin Lee
The carrier density distribution in MQWs is investigated using asymmetric dual quantum wells (ADQWs). The ADQWs consist of a stake of double quantum wells with different well widths. The corresponding spontaneous emission for each well is centered on 0.8 micrometers and 0.83 micrometers , respectively. The carrier recombination in each quantum well can be distinguished by the EL spectrum. We theoretically calculate the EL spectrum of the ADQWs using the multi-band effective mass theory and density matrix formalism with different carrier distribution condition. In the multi-band effective mass theory, valence band mixing is taken into account by a 4 X 4 Luttinger-Kohn Hamiltonian. A Lorentzian lineshape function is used to include the intraband relaxation and lineshape broadening. The comparison of the calculated results with the experimentally measured EL spectrum and TE/TM mode ratio is given. At 200mA injection current,the theoretical EL spectrum shows very good agreement with the experimental results when the carrier density in the p-side well is 17 percent higher than that in the n-side well. Decreasing the injection current, the uniformity of the carrier density distribution becomes better. The reasons for the behavior of the carrier distributions are briefly discussed.
MBE-grown high-efficiency 808-nm laser diodes
Xinqiao Wang, Jun Wang, Geoffrey T. Burnham
High power semiconductor lasers operating at 808 nm lasing wavelength with high internal quantum efficiency and low internal loss have been fabricated by solid source MBE. Experimental results have shown as high as 65.5 percent maximum wall-plug efficiency at room temperature for 1.5 mm cavity length devices. The wall-plug efficiency maintains up to 58 percent even when the devices operate at 6 watts of CW output power.
Improved output beam quality using a hyperbolically flared semiconductor laser amplifier
Ching-Fuh Lin, Yu-Chia Chang, Jie-Wei Lai
Filament formation is widely observed in semiconductor laser amplifiers (SLAs). In this work, we propose a new flared structure that could significantly eliminate the filaments.Conventional tapered amplifiers consist of a linearly tailored gain region that serves as the spherical expansion of wave front, which is not ideal due to the diffraction of the nonzero beam size. The proposed hyperbolically flared structure analogizes the expansion of a Gaussian beam and therefore is better for the beam expansion. We use a theoretical model to analyze the beam amplification. This model takes into account the phenomena involved in rate equation, optically induced refractive- index change, paraxial beam propagation. Improved output beam profiles are obtained for the hyperbolically flared SLAs.
Theoretical characterization of feedback-induced noise in a self-sustained pulsation laser
Minoru Yamada
Theoretical calculations of the pulsing operation and the feeback induced noise are demonstrated. Dynamic equations of the photon number, the optical phase and the carrier density are formulated by counting the gain saturation effect as well as the optical injection for a laser having a saturable absorbing region to generate the self-sustained pulsation. Modulations on the pulsing operation due to the optical feedback are traced by performing the time integration of the equations. The feedback induced noise is also analyzed by adding the Langevin noise sources to these equations. Variations of the noise characteristics with the injection current level,the feedback distance and the feedback ratio are examined.
Thermal modeling in semiconductor lasers by incorporating the effects of carrier heating, nonequilibrium optical phonons, and thermal conduction of acoustic phonons
Chin-Yi Tsai, Fang-Ping Shih, Jenkins C.H. Chen, et al.
Theoretical models are outlined for studying energy transfer processes among electrons, holes, photons, optical phonons, and acoustic phonon is in order to theoretically investigate the effects of carrier and phonon heating in semiconductor lasers. The roles of nonequilibrium optical phonons, nonequilibrium acoustic phonons, and phonon bath sharing of optical phonons on the phonon dynamics are also discussed.
Precise automatic alignment of a pinhole integrated with photodiodes
Minoru Sasaki, Yuji Arai, Wataru Kamada, et al.
The spatial filter of a Si micromachined pinhole integrated with photodiodes is fabricated. The photodiode cells placed around the center pinhole can detect the relative position between the incident beam spot and the pinhole. In our previous study, the automatic alignment of the pinhole realized the accuracy of 1 micrometers using the feedback control based on the obtained position signal. To increase the alignment accuracy, the suitable design of the pinhole and the photodiode cell is necessary, since it decides the sensitivity to the laser spot position. The sensitivity is examined changing the separation length between the photodiode cells.
Silicon-based integrated Mach-Zehnder interferometer with acousto-optic modulation: a biosensor application
Christophe Gorecki, Eric Bonnotte, Kerstin Woerhoff, et al.
As a novel application of silicon-based integrated optics, the results of a compact Mach-Zehnder interferometer are presented. The deposition of a ZnO thin-film transducer on the reference arm of the interferometer transforms this optically passive device under an active sinusoidal phase modulation. This device will be used as an in situ biosensor.
Efficiency limit of multilevel spatially quantized Fourier-plane diffractive optical elements
Jeng-Feng Lin
For five selected diffraction patterns, the combing effect of phase and spatial quantization to diffraction efficiency is evaluated by checking the effectiveness of the proposed efficiency limit sinc2(1/Z)(eta) slim, where Z is the number of uniformly distributed phase levels and (eta) slim is the efficiency limit due to spatial quantization only. The simulation results show that the effectiveness of the above efficiency limit depends on the number of phase levels, diffraction pattern and the initial random phase. For some patterns, the above efficiency limit approximately holds for both Z equals 4 and Z equals 8.
Implementation of a holographic optical memory system using a new input and angular multiplexing method
Cheol Su Kim, SeungHee Lee, Seong-Wan Kim, et al.
In this paper, we implemented a holographic optical memory system which can store and reconstruct many image types using a new input and angular multiplexing methods. As a new input method, the phase information of an image is input in the recording material instead of the brightness information. To do so, we represented the images, which were captured with a CCD camera or displaced on a computer monitor, on a liquid crystal television (LCTV) without a polarizer/analyzer. Therefore, we could achieve a uniform beam power regardless of the total brightness of the input image, and could apply a conventional scheduled recording method for the determination of the recording time for all the images needing to be stored. The reconstructed image was acquired by transforming the phase information into brightness information using an analyzer. The reference beam was generated by a Fourier transform of a binary phase hologram which was designed with a simulated annealing algorithm on a LCTV. The LCTV was then interfaced with a computer. The proposed optical memory system is stable because the incident angle of the reference beam is controlled electronically by computer. We demonstrated the system using an optical experiment which stored and reconstructed various types of images in a 45 degree cut BaTiO3 using the proposed holographic memory system.
Optical Bayan network using layered thermally fixed holograms in a photorefractive LiNbO3 crystal
Xiaona Yan, Liren Liu, Guoqiang Li, et al.
The Banyan network belongs to the class of log, (N) stage networks like the perfect shuffle and the crossover networks. In our paper, an optical scheme for constructing the Banyan network in one single -block of photorefractive LiNbO, crystal is suggested. The photorefractive crystal is used to record layered holograms according to the structure of link stage of the network and repeatedly pulsed CO, laser beam is suggested to thermally fix the local layer holograms. Programmable electro -optic modulator array is selected as switches to implement the dynamic space- variant interconnect and the reflective elements as the cascading medium to implement the Banyan network in one single block LiNbO, crystal. Because the whole network can be implemented with one single block crystal and simple reflective elements, it has the properties of compactness and miniaturization.
Photorefractive two-beam coupling of time-modulated optical signals in Cu-KNSBN crystals
Nam Kim, Jun-Won An, Kwon-Yeon Lee, et al.
The interaction between two incident beams in a photorefractive Cu-doped (Cu-KNSBN) crystal is investigated at 632.8nm He-Ne laser wavelength. In addition, the coherent two-wave coupling properties of a photoinduced volume refractive-index phase grating in the presence of amplitude modulation on the signal beam are also experimentally investigated as a function of the intensity ratio of the two incident beams. Some preliminary experimental result are presented for use as a dynamic photorefractive beam-splitter and pulse shaping element in coherent optical communication systems and in optical signal processing.