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22 Jun 1998

Volume 72, Issue 25, pp. 3243-3383

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Uniform component of index structure induced in Ge-SiO2 fibers by spatially modulated ultraviolet light

Tsung-Ein Tsai, Glen M. Williams, and E. J. Friebele

Appl. Phys. Lett. 72, 3243 (1998); http://dx.doi.org/10.1063/1.121678 (3 pages) | Cited 8 times

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Experimental data are presented to show that Ge(1) and Ge(2) centers are induced by trapping photoinduced electrons from the conduction band, in agreement with our previous proposal that both are trapped electron centers. The spacing (Λ) dependence of ultraviolet (UV) light bleaching of the pre-existing Ge E′ centers illustrates that the electron diffusion length is greater than Λ of the spatially modulated UV light used in the fabrication of fiber Bragg gratings (FBGs) with Bragg wavelengths ⩽ 1.5 μm (short period grating) for laser powers as low as 25 mJ/cm2. The Ge(1) and Ge(2) centers are uniformly induced by the spatially modulated UV light and therefore contribute to the uniform component of the index structure of FBGs.
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42.81.Wg Other fiber-optical devices
42.79.Dj Gratings
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.55.-i Impurity and defect levels

1.5 μm asymmetric Fabry–Perot modulators with two distinct modulation and chirp characteristics

S. J. B. Yoo, M. A. Koza, Raj Bhat, and Catherine Caneau

Appl. Phys. Lett. 72, 3246 (1998); http://dx.doi.org/10.1063/1.121612 (3 pages) | Cited 6 times

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This letter discusses the design and the realization of asymmetric Fabry–Perot modulators with InP/InGaAsP distributed Bragg reflectors and 80 AlInGaAs quantum wells. We demonstrate two types of modulators utilizing two different top reflectors: an InP to air interface and a Si/SiO2/Si coating. The first modulator showed a monotonic reduction in the reflectivity as the bias voltage increased, and achieved a 2.2 dB insertion loss and a 15 dB contrast ratio at the resonant wavelength. The second modulator showed an initial reduction and then an increase in the reflectivity as the bias changed from 0 to −10 V. The chirp calculation based on the measured data reveals that the second modulator exhibits two distinct positive and negative chirp characteristics. © 1998 American Institute of Physics.
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42.79.Hp Optical processors, correlators, and modulators
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Dispersion correction of surface-normal optical interconnection using two compensated holograms

Charles C. Zhou, Zhenhai Fu, Ray T. Chen, and Brian M. Davies

Appl. Phys. Lett. 72, 3249 (1998); http://dx.doi.org/10.1063/1.121613 (3 pages) | Cited 3 times

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Performance of optical interconnects using volume holographic gratings and substrate-guided waves is subject to source wavelength detuning which originates from laser chirping and operating temperature changes. In this letter, we characterize and measure the dispersion of commonly used surface-normal volume holographic gratings. Dispersion characteristics of a 20 μm thick photopolymer volume holographic grating are evaluated. A dispersion correction method is demonstrated to provide a dispersion-free surface-normal optical interconnect using two dispersion-compensated volume holographic gratings and substrate-guided waves which automatically compensate the dispersion that results from detuning over a 5.7 nm bandwidth. © 1998 American Institute of Physics.
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42.82.Ds Interconnects, including holographic interconnects
42.40.Eq Holographic optical elements; holographic gratings
42.60.Fc Modulation, tuning, and mode locking

Inducing a large second-order optical nonlinearity in soft glasses by poling

F. C. Garcia, I. C. S. Carvalho, E. Hering, W. Margulis, and B. Lesche

Appl. Phys. Lett. 72, 3252 (1998); http://dx.doi.org/10.1063/1.121614 (3 pages) | Cited 21 times

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Electrothermal poling of soft glasses (soda lime and borosilicate glass) at relatively high currents led to the creation of a second-order optical nonlinearity. The second-harmonic generation efficiency decays in time, and the decay rate can be accelerated by exposure to intense infrared radiation. © 1998 American Institute of Physics.
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42.70.Ce Glasses, quartz
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Coupled-power theory of nonlinear distributed-feedback lasers, yielding reduced longitudinal spatial hole burning

Jing-Yi Wang, Michael Cada, and Toshihiko Makino

Appl. Phys. Lett. 72, 3255 (1998); http://dx.doi.org/10.1063/1.121615 (3 pages) | Cited 2 times

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An analysis of the nonlinear distributed-feedback (DFB) laser action is presented. A set of nonlinear coupled-power equations is derived. A general condition for a nonlinear DFB laser with reduced spatial hole burning (SHB) is obtained. It is shown that the elimination of SHB in DFB lasers can be achieved by introducing properly-chosen variations of the coupling strength along the longitudinal direction; a novel complex-coupling AR-coated DFB laser diode is proposed as a result. It is also shown that the optical nonlinearity must be considered for the design of high-power laser structures with reduced SHB. © 1998 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency

Laser plasma x-ray contact microscopy of living specimens using a chemically amplified epoxy resist

A. C. Cefalas, P. Argitis, Z. Kollia, E. Sarantopoulou, T. W. Ford, A. D. Stead, A. Marranca, C. N. Danson, J. Knott, and D. Neely

Appl. Phys. Lett. 72, 3258 (1998); http://dx.doi.org/10.1063/1.121616 (3 pages) | Cited 7 times

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We report on the use of an epoxy based chemically amplified resist, to produce x-ray images of living biological specimens, exposed with laser plasma generated soft x rays, in the water window (2.3–4.4 nm). The photoresist response was at least two orders of magnitude “faster” than polymethyl methacrylate, the standard resist used so far in soft x-ray contact microscopy. Atomic force and scanning electron microscopy of the biological specimen images, recorded in the resist, clearly showed the flagella of the motile green alga, chlamydomonas, suggesting a lateral resolution better than 150 nm. The resist was also capable of providing height features, as small as 20 nm, in atomic force microscope depth profiles and discriminating the flagella intersection areas. © 1998 American Institute of Physics.
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87.64.kd X-ray and EXAFS
87.80.-y Biophysical techniques (research methods)
07.85.-m X- and γ-ray instruments
87.64.Dz Scanning tunneling and atomic force microscopy
87.17.-d Cell processes

Determination of the optical constants of zinc oxide thin films by spectroscopic ellipsometry

P. L. Washington, H. C. Ong, J. Y. Dai, and R. P. H. Chang

Appl. Phys. Lett. 72, 3261 (1998); http://dx.doi.org/10.1063/1.121617 (3 pages) | Cited 69 times

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Spectroscopic ellipsometry (SE) has been used to determine the complex pseudo dielectric functions, ϵ1(E)+iϵ2(E), of ZnO films on (0001) Al2O3 substrates over the spectral range of 1.33 and 4.96 eV at room temperature. The SE measurements are carried out with E⊥c at angles of incidence of 60° and 65° with respect to the surface normal. Below the band gap, the refractive index n is found to follow the first order Sellmeir dispersion relationship n2(λ) = 1+1.881λ2/(λ2−0.05382). A free excitonic structure located at the band edge of 3.32 eV is clearly observed in the pseudo absorption spectrum. Elliott expression with Lorentzian broadening is used to model the pseudo absorption coefficient above the band edge. © 1998 American Institute of Physics.
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78.66.Hf II-VI semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
71.35.-y Excitons and related phenomena

Helicon plasma deposition of a TiO2/SiO2 multilayer optical filter with graded refractive index profiles

Xinrong Wang, Hiroshi Masumoto, Yoshihiro Someno, and Toshio Hirai

Appl. Phys. Lett. 72, 3264 (1998); http://dx.doi.org/10.1063/1.121618 (3 pages) | Cited 22 times

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Thirty one layer TiO2/SiO2 optical filters with graded refractive index profiles were fabricated by helicon plasma sputtering at room temperature. Multilayer films were deposited on glass (BK7) and Si (100) substrates simultaneously and sequentially. The measured transmittance spectrum exhibited a reflectance of 99.8% at a central wavelength of 730 nm and high transmittance over the wavelength region outside of the reflected band as a result of the suppression of the sidelobes. The experimental transmittance spectrum corresponded almost completely with that calculated based on the optical multilayer film theory and using the measured refractive indices of TiO2, SiO2 and TiO2–SiO2 composite films. Transmission electron microscopic observations confirmed the expected microstructure of the filter. © 1998 American Institute of Physics.
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42.79.Ci Filters, zone plates, and polarizers
81.15.Cd Deposition by sputtering
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
42.79.Ry Gradient-index (GRIN) devices
78.66.Nk Insulators
42.86.+b Optical workshop techniques
78.40.Ha Other nonmetallic inorganics
78.30.Hv Other nonmetallic inorganics

Catastrophic optical damage in GaInN multiple quantum wells

Daniel A. Cohen, Tal Margalith, Amber C. Abare, Michael P. Mack, L. A. Coldren, S. P. DenBaars, and David R. Clarke

Appl. Phys. Lett. 72, 3267 (1998); http://dx.doi.org/10.1063/1.121619 (3 pages) | Cited 2 times

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We have observed progressive damage due to reabsorption of stimulated emission in optically pumped laser-quality GaInN–GaN multiple quantum wells. The degradation occurred on a time scale consistent with the lifetime of electrically pumped lasers incorporating the same active region, suggesting that the failure mechanism was in part catastrophic optical damage, and not just heating in the p contact and p cladding as is often assumed. © 1998 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
78.66.Fd III-V semiconductors
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.45.+h Stimulated emission

Room-temperature ultraviolet laser emission from self-assembled ZnO microcrystallite thin films

Z. K. Tang, G. K. L. Wong, P. Yu, M. Kawasaki, A. Ohtomo, H. Koinuma, and Y. Segawa

Appl. Phys. Lett. 72, 3270 (1998); http://dx.doi.org/10.1063/1.121620 (3 pages) | Cited 728 times

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Room-temperature ultraviolet (UV) laser emission of ZnO microcrystallite thin films is reported. The hexagonal ZnO microcrystallites are grown by laser molecular beam epitaxy. They are self-assembled and parallelly arrayed on sapphire substrates. The facets of the hexagons form natural Fabry–Pérot lasing cavities. The optical gain for the room-temperature UV stimulated emission is of an excitonic nature and has a peak value an order of magnitude larger than that of bulk ZnO crystal. The observation of room-temperature UV lasing from the ordered, nano-sized ZnO crystals represents an important step towards the development of nanometer photoelectronics. © 1998 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
78.45.+h Stimulated emission
71.35.-y Excitons and related phenomena
78.66.Hf II-VI semiconductors

Eyesafe pulsed microchip laser using semiconductor saturable absorber mirrors

R. Fluck, R. Häring, R. Paschotta, E. Gini, H. Melchior, and U. Keller

Appl. Phys. Lett. 72, 3273 (1998); http://dx.doi.org/10.1063/1.121621 (3 pages) | Cited 26 times

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We passively Q-switched a diode-pumped Er/Yb:glass microchip laser at a 1.535 μm wavelength using semiconductor saturable absorber mirrors and demonstrated pulses as short as 1.2 ns. By varying the design parameters of the saturable absorber, the pump power, and the pump spot size, we achieved repetition rates from 300 Hz to 100 kHz with pulse energies up to 4 μJ. © 1998 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.55.Rz Doped-insulator lasers and other solid state lasers
42.79.Bh Lenses, prisms and mirrors
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency

Spectroscopic light scattering for real-time measurements of thin film and surface evolution

Eric Chason, Michael B. Sinclair, Jerry A. Floro, John A. Hunter, and Robert Q. Hwang

Appl. Phys. Lett. 72, 3276 (1998); http://dx.doi.org/10.1063/1.121622 (3 pages) | Cited 23 times

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We describe a light scattering technique for measuring the real-time evolution of thin film and surface morphology. By using spectroscopic detection, the technique requires no motion of the sample during the measurement, which makes it compatible with many processing geometries. Results from the growth of strained heteroepitaxial layers of SixGe1−x on Si(001) are presented to demonstrate the technique. © 1998 American Institute of Physics.
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78.66.Li Other semiconductors
78.35.+c Brillouin and Rayleigh scattering; other light scattering
68.55.-a Thin film structure and morphology
68.35.B- Structure of clean surfaces (and surface reconstruction)
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