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ABSTRACT: We studied experimentally and theoretically the substrate-orientation impact on carrier transport and capture in InGaN multiple quantum well (MQW) laser diodes (LDs) with emission in the aquamarine-green spectral range. A new simulation approach was developed to analyze this behavior of LEDs and LDs emitting at these wavelengths. We show that due to deep carrier confinement, the thermal escape from a QW in such devices is negligible. The carrier distribution among QWs is therefore determined by the carrier transport and capture rates. We also show that the ballistic transport mechanism is dominant in this type of MQW active region. In c-plane structures, this mechanism is tunneling-assisted, and therefore, the transport is much slower than in nonpolar and semipolar structures. Because of this, a strong carrier injection nonuniformity observed in c-plane LDs, causes the threshold current increase when number of QWs is >;2. This effect is not observed in semipolar LDs because the carrier transport rate is faster than the capture rate.
IEEE Journal of Selected Topics in Quantum Electronics 11/2011; · 3.78 Impact Factor
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ABSTRACT: Semiconductor quantum cascade lasers that emit mid-infrared light in the wavelength range of 4 to 9 μm are unipolar and the laser emission is due to intersubband transitions in a repeated stack of multiple quantum wells. The thermal management of these devices is a challenge. The overheating of the active region (referred to as `core' throughout this paper) in these lasers decreases the optical power and ultimately results in laser failure. In this work, we present a detailed finite element (FE) based numerical modeling of the thermal behavior of these devices and the measurements performed to validate the models. The studies include the effect of submount material, mounting schemes such as epi-side down or epi-side up mounting and finally, the effect of core geometry on the thermal impedance. We have also looked at various core designs such as split core. We conducted various experiments to correlate the results with the numerical modeling by measuring the thermal impedance between the laser diode's core and the bottom of the substrate and measuring the temperature change within a pulse of a distributed-feedback (DFB) QCL which emits in a single longitudinal mode of narrow linewidth. The temperature of the active core of a DFB QCL can be determined by measuring the lasing frequency, which changes with the temperature of the active core as: v=v<sub>0</sub>+βvT<sub>core</sub>=v<sub>0</sub>+βvT<sub>submount</sub>+βvR<sub>th</sub>P<sub>dec</sub>, where v is the lasing wavenumber, R<sub>th</sub> is the thermal resistance, P<sub>elec</sub> is the electric power loading, and β is the thermal tuning coefficient. By measuring the lasing frequency as a function of time within a pump current pulse, we can determine the temperature change, and the thermal conductance of a laser structure. In the conclusion, we provide various recommendations for efficient thermal performance of these quantum cascade lasers.
Electronic Components and Technology Conference (ECTC), 2010 Proceedings 60th; 07/2010
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ABSTRACT: Using varied stripe length method we systematically studied optical gain properties of blue-green 3 nm InGaN QWs grown on c-plane and (11−22) semipolar substrates. We determined that for such structures when the product of modal net gain at peak and stripe length exceeds factor 5 the gain saturation occurs due to depletion of pumped carriers. We then focused our attention on the gain in unsaturated conditions. We observed strong gain peak position blue shift with increase of pumping power for both substrate orientations due to quantum well state filling and for c-plane due to piezoelectric field screening. Thus in order to increase lasing wavelength, minimizing optical losses, and maximizing modal gain are essential. We then found that for the semipolar QWs the gain at ∼500 nm was 2× higher with the stripe along [−1−123] direction despite the fact that at low pumping level the polarization switching of spontaneous emission resulted predominant E||[−1−123]. Finally we compared the semipolar and c-plane QWs and found that the gain increase with pumping power of c-plane QW is slower than that for semipolar QW in high gain direction while the transparency pumping power is lower for c-plane.
Physica Status Solidi (A) Applications and Materials 05/2010; 207(6):1309 - 1312. · 1.46 Impact Factor
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ABSTRACT: Continuous-wave operation of a distributed-feedback quantum-cascade laser in a packaged module is demonstrated up to a heat sink temperature of 80 °C with an output power of greater than 10 mW and a power consumption of less than 3.8 W. Single longitudinal mode emission near 5.24 μm is observed over a temperature range from 10 to 80 °C with a side mode suppression ratio greater than 20 dB limited by the instrumentation. A single spatial mode is determined with far-field pattern measurement. The above performance is achieved using a buried heterostructure and a small cavity of 7.6 μm×1.5 mm.
Applied Physics Letters 09/2009; 95(9):091110-091110-3. · 3.84 Impact Factor
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ABSTRACT: Using the variable stripe length method we demonstrated positive net optical gain around 500 nm for an optically pumped laser with InGaN/GaN multiple quantum wells grown on c-plane freestanding GaN substrates. We found that owing to low optical gain, reducing optical losses is crucial to increasing lasing wavelength. We demonstrated lasing at 502 nm by using a 3-mm-long cavity with cleaved facets.
Optics Letters 03/2009; 34(3):328-30. · 3.40 Impact Factor
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ABSTRACT: We demonstrate bandwidth enhancement of external- and direct-modulated lasers using a tunable optical equalizer. Modulation bandwidth of >50 GHz for LiNbO<sub>3</sub> modulators was obtained. Also, the equalizer permits the increased-speed and chirp-reduction simultaneously for direct-modulated VCSELs.
Lasers and Electro-Optics, 2008 and 2008 Conference on Quantum Electronics and Laser Science. CLEO/QELS 2008. Conference on; 06/2008
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ABSTRACT: We report highly reliable 1060-nm DBR lasers with a single-wavelength output power larger than 350 mW and a failure rate as low as 3.2 kFITs at a heat-sink temperature of 25degC and a gain current of 500 mA. The reliability data of the high-power 1060-nm DBR lasers under longest aging tests at the highest level of current and temperature stress have been obtained for the first time, to the best of our knowledge
Lasers and Electro-Optics Society, 2006. LEOS 2006. 19th Annual Meeting of the IEEE; 11/2006
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ABSTRACT: High-power semiconductor lasers have found increasing applications in industrial, military, commercial, and consumer products. The thermal management of high-power lasers is critical since the junction temperature rise resulting from large heat fluxes strongly affects the device characteristics, such as wavelength, kink power, threshold current and efficiency, and reliability. The epitaxial-side metallization structure has significant impact on the thermal performance of a junction-down bonded high-power semiconductor laser. In this paper, the influence of the epitaxial-side metal (p-metal) on the thermal behavior of a junction-down mounted GaAs-based high-power single-mode laser is studied using finite-element analysis. It is shown that a metallization structure with thick Au layer can significantly reduce the thermal resistance by distributing the heat flow to wider area laterally, and the thermal resistance of a junction-down bonded laser with thick Au metallization is much less sensitive to the voiding in the die attachment solder interface than a laser with thin Au metallization. A metallization structure of Ti-Pt-thick Au-Ti-Cr-Au is designed and implemented, and the metallurgical stability of this metallization scheme is reported. It was found that, without a diffusion barrier, the thick Au layer in the epi-side metallization would be mostly consumed and form intermetallics with the Sn from the AuSn solder during soldering and thermal aging. The Ti-Pt-thick Au-Ti-Cr-Au metallization scheme prevents the diffusion of Sn into the thick Au layer and preserves the integrity of the metallization system. It is a promising candidate for junction-down bonding of high-power semiconductor lasers for improved thermal management and reliability
IEEE Transactions on Advanced Packaging 09/2006; · 1.12 Impact Factor
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ABSTRACT: Semiconductor pump lasers are an important component in erbium-doped fiber amplifiers and Raman amplifiers. Thermal management has become one of the major obstacles of pump laser development. Understanding of the thermal behavior of high-power laser packages is crucial to the thermal design and optimization of pump lasers. In this paper, we report on the thermal characteristics of a high-power pump laser and discuss the issues associated with heat dissipation. The thermal management of high-power pump laser modules mainly consists of three aspects. One is the thermal resistance reduction which reduces bulk temperature rise in the laser diode chip. The second is facet temperature control, and the third is the thermoelectric cooler (TEC) coefficient of performance improvement. In this paper, the approaches to reduce thermal resistance and facet temperature at the chip level and package level will be reviewed, and the thermal design and optimization of the package assembly to improve the TEC coefficient of performance will be discussed. The thermal resistance of a pump laser could be reduced up to 40% by the proper design of the laser chip and epi-down bonding. An unpumped window design in the pump laser diode is proven to be very effective in reducing the facet temperature and increasing the catastrophic optical mirror damage level. Assembly and package optimization can provide more uniform temperature distribution on TEC cold plate which is critical in improving the TEC coefficient of performance
IEEE Transactions on Components and Packaging Technologies 07/2006; · 0.94 Impact Factor
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Hong Ky Nguyen,
M.H. Hu,
N. Nishiyama,
N.J. Visovsky,
Yabo Li,
Kechang Song,
Xingsheng Liu,
J. Gollier,
Jr. L.C. Hughes,
R. Bhat, Chung-En Zah
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ABSTRACT: We have generated 107-mW green-light emission by frequency doubling of a reliable 1060-nm distributed feedback (DFB) laser diode using a periodically poled MgO-doped lithium niobate waveguide in the most compact single-pass configuration. The green power variation is lower than 1% at frequencies below 82 kHz. The relative intensity noise of -150 dB/Hz has been measured at 100 MHz. We also report 5000-h life-test results of 1060-nm DFB lasers at 80°C.
IEEE Photonics Technology Letters 02/2006; · 2.19 Impact Factor
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M.H. Hu,
Hong Ky Nguyen,
Kechang Song,
Yabo Li,
N.J. Visovsky,
Xingsheng Liu,
N. Nishiyama,
S. Coleman,
L.C. Hughes,
J. Gollier,
W. Miller,
R. Bhat, Chung-En Zah
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ABSTRACT: We report on the static and dynamic performance of high-power and high-modulation-speed 1060-nm distributed Bragg reflector (DBR) lasers for green-light emission by second-harmonic generation. Single-wavelength power of 387 mW at 1060-nm wavelength and green power as high as 99.5 mW were achieved. A thermally induced wavelength tuning of 2.4 nm and a carrier-induced wavelength tuning of -0.85 nm were obtained by injecting current into the DBR section. Measured rise-fall times of 0.2 ns for direct intensity modulation and 0.6 ns for wavelength modulation make the lasers suitable for >50-MHz green-light modulation applications
IEEE Photonics Technology Letters 02/2006; · 2.19 Impact Factor
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Kechang Song,
Yabo Li,
N. Visovsky,
M. Hu,
Hong Ky Nguyen,
Xingsheng Liu,
S. Coleman,
B. Paddock,
M. Turner,
C. Catherine,
R. Bhat, Chung-En Zah
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ABSTRACT: We report a single-wavelength 1060 nm distributed Bragg reflector laser with a record high single lateral mode optical power of 400 mW. These lasers are fabricated using a quantum well intermixing technique for the non-absorbing phase and DBR sections.
Lasers and Electro-Optics Society, 2005. LEOS 2005. The 18th Annual Meeting of the IEEE; 11/2005
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ABSTRACT: An all-optical inverter using transverse mode switching in a 1.5-μm vertical-cavity surface-emitting laser (VCSEL) was demonstrated theoretically and experimentally. The fundamental mode in a single-mode VCSEL was strongly suppressed when external light was injected into an LP02 high-order mode, resulting in an on-off ratio of over 20 dB. The polarization dependence of the static optical input--output characteristics of inverter operations was as low as ∼13%. The VCSEL-based optical inverter operated with a 5-Gb/s nonreturn-to-zero (NRZ) input signal. A theoretical result using two-mode rate equations is in good agreement with experimental results.
IEEE Journal of Selected Topics in Quantum Electronics 10/2005; · 3.78 Impact Factor
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ABSTRACT: 1.3-μm InP-based VCSELs with high optical reflection resistance for optical isolator-free 10-Gbps operation have been demonstrated. The 13-GHz relaxation frequency increased the critical feedback level of those VCSELs and allowed 10-km, 10-Gbps error free transmission without isolator, even with -13dB optical reflection.
Lasers and Electro-Optics, 2005. CLEO/Pacific Rim 2005. Pacific Rim Conference on; 09/2005
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ABSTRACT: Error-free transmission through 10-km single-mode fiber at 10 Gb/s under -13-dB optical reflections has been demonstrated for the first time using a directly modulated 1.3-μm InP-based VCSEL without any optical isolator. The 13-GHz relaxation oscillation frequency and stable polarization suppresses relative intensity noise degradation under optical reflection. Only 1-dB error-free power penalty has been observed with optical reflection set with the worst polarization direction.
IEEE Photonics Technology Letters 09/2005; · 2.19 Impact Factor
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ABSTRACT: A measurement system called laser bar prober for characterizing high-power semiconductor edge-emitting laser bars is described. The laser bar prober is fully automated to handle testing of large numbers of lasers, is multifunctional to measure various laser characteristics and is accurate in predicting performance of fully mounted lasers. The bar prober has been proven to be an effective instrument for screening lasers during manufacturing process as well as an indispensable tool for providing rapid feedback to the development of new laser structures. In this paper, the design of the laser bar prober is described and a few examples of its applications are given; in particular, a time-resolved technique to correlate the measurement data of a laser within a laser bar to those of a fully mounted laser is demonstrated.
Journal of Lightwave Technology 03/2005; 23(2):573- 581. · 2.78 Impact Factor
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ABSTRACT: We report on highly reliable, high-power, and high-performance 980-nm quantum-well laser chips and modules. Ridge waveguide laser diode chips with 750-mW output power and 500-mW fiber Bragg grating stabilized modules have been achieved and Telcordia-qualified. Long-term reliability tests show a very low failure rate of 400 FIT (failures in time) at 900-mA operating current or 500-mW module power. The kink-free fiber coupled module output power can be as high as 640 mW with grating stabilization, which produces very good wavelength stability and power stability. A further improved structure shows a record continuous-wave rollover chip power of 1.6 W for the 5-μm-wide ridge waveguide laser diodes.
IEEE Photonics Technology Letters 12/2004; · 2.19 Impact Factor
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ABSTRACT: Epi-down and epi-up bonded high-power single-mode 980-nm lasers have been studied in terms of bonding process, thermal behavior, optical performances, and long-term laser reliability. We demonstrated that epi-down bonding can offer lower thermal resistance and improved optical performance without degrading the long-term laser reliability. An optical power of 630 mW was obtained for the first time from an epi-down bonded 980-nm pump module. Our studies have shown that epi-down bonding of single-mode 980-nm lasers can reduce junction temperature and thermal resistance by up to 30%. Experimental measurements showed over 20% in thermal rollover power improvement and over 25% reduction in wavelength shift versus current in epi-down mounted lasers compared to epi-up mounted lasers. Lifetime test over 14 000 h at 500 mA and 80°C of the epi-down bonded lasers is reported for the first time.
IEEE Transactions on Advanced Packaging 12/2004; · 1.12 Impact Factor
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ABSTRACT: We report a high kink-free facet power of 852 mW and a high single-wavelength facet power of 350 mW for 1060-nm raised-ridge Fabry-Perot (FP) and distributed-feedback (DFB) lasers, respectively.
Semiconductor Laser Conference, 2004. Conference Digest. 2004 IEEE 19th International; 10/2004
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ABSTRACT: Lasing operation up to 125 °C of 1.3 μm InP-based VCSELs with AlGaInAs/InP DBR has been demonstrated. A single mode power of 0.6 mW at 85 °C, 10 Gbit/s transmission through 10 km and >2500 hours lifetime have been achieved.
Semiconductor Laser Conference, 2004. Conference Digest. 2004 IEEE 19th International; 10/2004
