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High-power laser diodes at various wavelengths

Description: High power laser diodes at various wavelengths are described. First, performance and reliability of an optimized large transverse mode diode structure at 808 and 941 nm are presented. Next, data are presented on a 9.5 kW peak power array at 900 nm having a narrow emission bandwidth suitable for pumping Yb:S-FAP laser materials. Finally, results on a fiber-coupled laser diode array at {approx}730 nm are presented.
Date: February 19, 1997
Creator: Emanuel, M.A.
Partner: UNT Libraries Government Documents Department

Intracavity Frequency Doubling of a Diode-Pumped, External Cavity, Surface Emitting Semiconductor Laser

Description: The authors present a compact, robust, solid-state blue light (490 nm) source capable of greater than 5 mW of output in a TEM{sub 00} mode. This device is an optically pumped, vertical external-cavity surface-emitting laser (VECSEL) with an intracavity frequency doubling crystal.
Date: April 22, 1999
Creator: Alford, W.J.; Allerman, A.A.; Crawford, M.H. & Raymond, T.D.
Partner: UNT Libraries Government Documents Department

Plasma Heating in Highly Excited GaN/AlGaN Multiple Quantum Wells

Description: Plasma Heating in Highly Excited GaN/AIGaN Multiple Quantum @@lvEu Wells w f + 1998 %p, K. C. Zeng, R. Mair, J. Y. Liz and H. X. Jiang a) ` fabrication and understanding of MQW lasers [2-5]. For the design of these lasers, one on RT optical studies. Our results revealed that in the GaN/AIGaN MQWS, plasma heating strongly effects the carrier distribution between the confined and unconfined band-to-band and fke excitonic transitions [7]. In the MQW sample under low the unconfined states as determined from the band structure. sample under high Lxc, we varied the excitation intensity by one order of magnitude from 0.110 to IO. The carrier density is estimated to be about N=1012/cm2 (at UC= 0.1 Io) to 1013/cm2 (at 1=== l.). We plotted the PL spectra for four representative excitation fimction of injected carrier density N (open squares). The ratio starts at a value of about 18% for N=1012/cm2 (& = O. lb), and reaches a value over 64 `XO for N=1013/cm2 (& = regions is a loss to optical gain. The carrier density is ve~ high in our experiment and an electron-hole plasma (EHP) state is expected. Because the carrier transfer process plasma temperature. The laser pump energy is about 4.3 eV, which is far above the energy band gap of the sample studied here. This may result in a hot carrier population carrier densities and plasma temperatures. Using a phenomenological expression based The calculated ratio of carriers in the unconfked to the confined states (Ima~ kf) as a finction of carrier density at different temperatures are plotted in Fig. 3 (solid lines). The figure shows that the experiment results can only be explained by plasma heating of the injected carriers at high & ( TP > TJ. The transparency carrier densities for GaN/AIXGal.XN MQW structures ...
Date: October 9, 1998
Creator: Botchkarev, A.; Chow, W.W.; Jiang, H.X.; Lin, J.Y.; Mair, R.; Morkoc, H. et al.
Partner: UNT Libraries Government Documents Department

Ball lens reflections by direct solution of Maxwell`s equations

Description: Ball lenses are important for many applications. For example, ball lenses can be used to match the mode of a laser diode (LD) to a single mode fiber (SMF), essential for low-loss, high bit rate communication systems. Modeling the propagation of LD light through a ball lens presents a challenge due to the large angular divergence of the LD field (typically > 20{degrees} HWHM) and the subsequent significant effect of spherical aberration. Accurately calculating the reflected power is also difficult, but essential, since reflections as small as {minus}30 dB can destabilize the LID. A full-wave analysis of this system using, e.g., a finite-difference time-domain method is not practical because of the size of the ball lens, typically hundreds of wavelengths in diameter. Approximate scalar methods can give good results in some cases, but fail to calculate reflected power and miss polarization effects entirely. The authors` approach exploits the fact that the scattering of an arbitrary electromagnetic beam from a sphere is an exactly solvable problem. The scattering of a plane wave from a sphere is a classical problem which was solved by Mie in 1908. More recently, various workers have considered the scattering of a Gaussian beam from a sphere and its numerical implementation for other applications. To the authors knowledge, this is the first time this approach has been applied to a problem in optical design. They are able to calculate reflection and transmission accurately with modest computational effort.
Date: February 15, 1995
Creator: Ratowsky, R.P.; Deri, R.J. & Kallman, J.S.
Partner: UNT Libraries Government Documents Department

Advanced Concepts for High-Power VCSELS and 2-Dimensional VCSEL Arrays

Description: We have developed high power vertical cavity surface emitting lasers (VCSELS) for multimode or single mode operation. We have characterized new cavity designs for individual lasers and 2-dimensional VCSEL arrays to maximize output power. Using broad area high power VCSELS under pulsed excitation, we have demonstrated the triggering of a photoconductive semiconductor switch (PCSS) with a VCSEL. We also have developed designs for high output power in a single mode. The first approach is to engineer the oxide aperture profile to influence the optical confinement and thus modal properties. A second approach focuses on "leaky-mode" concepts using lateral modification of the cavity resonance to provide the lateral refractive index difference. To this end, we have developed a regrowth process to fabricate single-mode VCSELS. The overall objective of this work was to develop high-power single-mode or multimode sources appropriate for many applications leveraging the many inherent advantages of VCSELS.
Date: April 1, 1999
Creator: Allerman, A.A.; Choquette, Kent D.; Chow, W.W.; Geib, K.M.; Hadley, R.; Hou, H.Q. et al.
Partner: UNT Libraries Government Documents Department

Theory of gain in group-III nitride lasers

Description: A microscopic theory of gain in a group-III nitride quantum well laser is presented. The approach, which treats carrier correlations at the level of quantum kinetic theory, gives a consistent account of plasma and excitonic effects in an inhomogeneously broadened system.
Date: June 1, 1997
Creator: Chow, W.W.; Wright, A.F. & Girndt, A.
Partner: UNT Libraries Government Documents Department

Advances in oxide-confined vertical cavity lasers

Description: We review the advances made in device fabrication, structure, and performance of vertical-cavity surface emitting lasers (VCSELs) which incorporate the selective oxidation of AlGaAs.
Date: February 1, 1996
Creator: Choquette, K.D.; Schneider, R.P. Jr.; Lear, K.L.; Geib, K.M.; Hou, H.Q.; Chui, H.C. et al.
Partner: UNT Libraries Government Documents Department

Interband cascade light emitting devices based on type-II quantum wells

Description: The authors discuss physical processes in the newly developed type-II interband cascade light emitting devices, and review their recent progress in the demonstration of the first type-II interband cascade lasers and the observation of interband cascade electroluminescence up to room temperature in a broad mid-infrared wavelength region (extended to 9 {mu}m).
Date: June 1, 1997
Creator: Yang, Rui Q.; Lin, C.H. & Murry, S.J.
Partner: UNT Libraries Government Documents Department

Fabrication issues of oxide-confined VCSELs

Description: To insert high-performance oxide-confined vertical-cavity surface- emitting lasers (VCSELs) into the manufacturing arena, we have examined the critical parameters that must be controlled to establish a repeatable and uniform wet thermal oxidation process for AlGaAs. These parameters include the AlAs mole fraction, sample temperature, carrier gas flow, and bubbler water temperature. Knowledge of these parameters has enable the compilation of oxidation rate data for AlGaAs which exhibits an Arrhenius rate dependence. The compositionally dependent activation energies for Al{sub x}Ga{sub 1-x}As layers of x=1.00, 0.98, and 0.92 are found to be 1.24, 1.75, and 1.88 eV, respectively. 7 figs, 1 tab, 14 refs.
Date: April 1, 1997
Creator: Geib, K.M.; Choquette, K.D.; Hou, H.Q. & Hammons, B.E.
Partner: UNT Libraries Government Documents Department

Current trends in the packaging of photonic devices

Description: Optoelectronic and photonic devices hold great promise for high data-rate communication and computing. Their wide implementation was limited first by the device technologies and now suffers due to the need for high-precision packaging that is mass-produced. The use of photons as a medium of communication and control implies a unique set of packaging constraints that are highly driven by the need for micron and even sub-micron alignments between photonic devices and their transmission media. Current trends in optoelectronic device packaging are reviewed and future directions are identified both for free-space (3-dimensional) and guided-wave (2-dimensional) photonics. Emphasis will be placed on the special needs generated by increasing levels of device integration.
Date: April 1, 1995
Creator: Carson, R.F.
Partner: UNT Libraries Government Documents Department

Incorporating many-body effects into modeling of semiconductor lasers and amplifiers

Description: Major many-body effects that are important for semiconductor laser modeling are summarized. The authors adopt a bottom-up approach to incorporate these many-body effects into a model for semiconductor lasers and amplifiers. The optical susceptibility function ({Chi}) computed from the semiconductor Bloch equations (SBEs) is approximated by a single Lorentzian, or a superposition of a few Lorentzians in the frequency domain. Their approach leads to a set of effective Bloch equations (EBEs). The authors compare this approach with the full microscopic SBEs for the case of pulse propagation. Good agreement between the two is obtained for pulse widths longer than tens of picoseconds.
Date: June 1, 1997
Creator: Ning, C.Z.; Moloney, J.V. & Indik, R.A.
Partner: UNT Libraries Government Documents Department

High-speed modulation of vertical cavity surface emitting lasers

Description: This report summarizes work on the development of high-speed vertical cavity surface emitting lasers (VCSELs) for multi-gigabit per second optical data communications applications (LDRD case number 3506.010). The program resulted in VCSELs that operate with an electrical bandwidth of 20 GHz along with a simultaneous conversion efficiency (DC to light) of about 20%. To achieve the large electrical bandwidth, conventional VCSELs were appropriately modified to reduce electrical parasitics and adapted for microwave probing for high-speed operation.
Date: March 1, 1998
Creator: Hietala, V.M.; Armendariz, M.G.; Choquette, K.D. & Lear, K.L.
Partner: UNT Libraries Government Documents Department

Engineering high-performance vertical cavity lasers

Description: The cw and high-speed performance of vertical cavity surface emitting laser diodes (VCSELs) are affected by both electrical and optical issues arising from the geometry and fabrication of these devices. Structures with low resistance semiconductor mirrors and Al-oxide confinement layers address these issues and have produced record performance including 50% power conversion efficiency and modulation bandwidths up to 20 GHz at small bias currents.
Date: December 31, 1996
Creator: Lear, K.L.; Hou, H.Q.; Hietala, V.M.; Choquette, K.D. & Schneider, R.P. Jr.
Partner: UNT Libraries Government Documents Department

Technical report on task orders no. B239703 and B239705: Development of technology of Al-free high-power laser diodes

Description: Our investigations of InGaAsP/GaAs system have shown that it is in many ways superior to the conventional AlGaAs/GaAs system. Lasers fabricated from InGaAsP/GaAs exhibit low facet overheating, high efficiency, good degradation characteristics, and high catastrophic optical damage (COD) limit. Our postgrowth technology provides stripe- contact lasers having very low series resistance and, therefore, high electrical-to-optical efficiency.
Date: June 1, 1996
Creator: Alferov, Zh.I. & Tarasov, I.S.
Partner: UNT Libraries Government Documents Department

Performance of a diode-end-pumped Yb:YAG laser

Description: Using an end-pumped technology developed at LLNL we have demonstrated a Yb:YAG laser capable of delivering up to 434 W of CW power and 280 W of Q-switched power. In addition, we have frequency doubled the output to 515 nm using a dual crystal scheme to produce 76 W at 10 kHz in a 30 ns pulse length.
Date: May 5, 1997
Creator: Bibeau, C.; Beach, R.; Ebbers, C. & Emanuel, M.
Partner: UNT Libraries Government Documents Department

Coupled resonator vertical cavity laser

Description: The monolithic integration of coupled resonators within a vertical cavity laser opens up new possibilities due to the unique ability to tailor the interaction between the cavities. The authors report the first electrically injected coupled resonator vertical-cavity laser diode and demonstrate novel characteristics arising from the cavity coupling, including methods for external modulation of the laser. A coupled mode theory is used model the output modulation of the coupled resonator vertical cavity laser.
Date: January 1, 1998
Creator: Choquette, K.D.; Chow, W.W.; Hou, H.Q.; Geib, K.M. & Hammons, B.E.
Partner: UNT Libraries Government Documents Department

Analysis of lateral mode behavior in broad-area InGaN quantum well lasers

Description: A wave-optical model that is coupled to a microscopic gain theory is used to investigate lateral mode behavior in group III nitride quantum well lasers. Beam filamentation due to self-focusing in the gain medium is found to limit fundamental-mode output to narrow stripe lasers or to operation close to lasing threshold. Differences between nitride and conventional near-infrared semiconductor lasers arise because of band structure differences, in particular, the presence of a strong quantum-confined Stark effect in the former. Increasing mirror reflectivities in plane-plane resonators to reduce lasing threshold current tends to exacerbate the filamentation problem. On the other hand, a negative-branch unstable resonator is found to mitigate filament effects, enabling fundamental-mode operation far above threshold in broad-area lasers.
Date: June 1, 2000
Creator: CHOW,WENG W. & AMANO,H.
Partner: UNT Libraries Government Documents Department

Fully confined photonic band gap and guided modes in a two-dimensional photonic crystal slab

Description: A new two-dimensional photonic crystal (2D PC) slab structure was created with a full three-dimensional light confinement. Guided modes with broad bandwidth and high transmission within the band gap are also observed. As an optical analog to electronic crystals, PC promises a revolution in the photonic world similar to the electronic revolution created by the electronic band gap engineering in semiconductor. 2D PC has an advantage of being easier to fabricate at optical wavelength ({lambda}) comparing with 3D PC. However, the light leakage in the vertical direction has been the main problem for using 2D PC in opto-electronic application. In this study, the authors solve this problem by combining traditional 2D PC with strong vertical index guiding between the waveguide layer (GaAs) and the cladding layer (Al{sub x}O{sub y}). A set of triangular lattice holes 2D PC's were fabricated with lattice constant a=460nm, hole diameter (d=0.6a) and waveguide layer thickness (t = 0.5a). Those parameters were chosen to maximize the TE photonic band gap (PBG) around {lambda} = 1.55{micro}m. The depth of etched holes is {approximately}0.6{micro}m and the 2{micro}m thick Al{sub x}O{sub y} cladding layer is obtained by thermal oxidation of Al{sub 0.9}Ga{sub 0.1}As. PC waveguides were also created by introducing line defects along {Gamma}K direction. The authors perform transmission measurement by coupling light to PC with 3{micro}m wide waveguides which extends {approximately}0.6mm on both sides of PC. An aspheric lens with NA = 0.4 is used to focus the collimated light from tunable diode laser into the input waveguide. Another identical lens is used to collect the transmitted light and focus to an infrared (IR) camera and a calibrated photo-detector with a beamsplitter. The Gaussian waveguide mode indicates that the signal detected by the photodetector comes only from the light interacting with PC and propagating along the waveguide. The ...
Date: December 15, 1999
Creator: Chow, K.C.; Lin, S.Y.; Johnson, S.G.; Villeneuve, P.R. & Joannopoulos, J.D.
Partner: UNT Libraries Government Documents Department

Single transverse mode selectively oxidized vertical cavity lasers

Description: Vertical cavity surface emitting lasers (VCSELs) which operate in multiple transverse optical modes have been rapidly adopted into present data communication applications which rely on multi-mode optical fiber. However, operation only in the fundamental mode is required for free space interconnects and numerous other emerging VCSEL applications. Two device design strategies for obtaining single mode lasing in VCSELs based on mode selective loss or mode selective gain are reviewed and compared. Mode discrimination is attained with the use of a thick tapered oxide aperture positioned at a longitudinal field null. Mode selective gain is achieved by defining a gain aperture within the VCSEL active region to preferentially support the fundamental mode. VCSELs which exhibit greater than 3 mW of single mode output power at 850 nm with mode suppression ratio greater than 30 dB are reported.
Date: April 26, 2000
Partner: UNT Libraries Government Documents Department

Effective index model predicts modal frequencies of vertical-cavity lasers

Description: Previously, an effective index optical model was introduced for the analysis of lateral waveguiding effects in vertical-cavity surface-emitting lasers. The authors show that the resultant transverse equation is almost identical to the one typically obtained in the analysis of dielectric waveguide problems, such as a step-index optical fiber. The solution to the transverse equation yields the lateral dependence of the optical field and, as is recognized in this paper, the discrete frequencies of the microcavity modes. As an example, they apply this technique to the analysis of vertical-cavity lasers that contain thin-oxide apertures. The model intuitively explains the experimental data and makes quantitative predictions in good agreement with a highly accurate numerical model.
Date: April 18, 2000
Partner: UNT Libraries Government Documents Department