High-power, continuous-wave, current-tunable, single-mode quantum-cascade distributed-feedback lasers at lambda congruent to 5.2 and lambda congruent to 7.95 mu m

Quantum-cascade distributed-feedback lasers with high-power, continuous-wave (cw), tunable, single-mode emission are reported. The emission wavelengths are near 5.2 and 7.95 mu m. The lasers are operated at liquid-nitrogen temperature and above. A maximum output power of >100 mW is obtained per facet at 80 K for both wavelengths, which is the result of careful positioning of the peak gain with respect to the Bragg wavelength. Continuous tuning with either heat-sink temperature or cw current is demonstrated. The tuning coefficients are 0.35 nm/K (5.2 mu m) and 0.51 nm/K (7.95 mu m) for thermal tuning and vary from 20 to 40 nm/A for tuning with current. The lasers are being used in high-resolution and high-sensitivity gas-sensing applications. (C) 2000 Optical Society of America OCIS codes: 140.3070, 140.3600, 140.5960

High-power gimel approximate to 8 mu m quantum cascade lasers with near optimum performance

Quantum cascade (QC) lasers emitting at lambda approximate to 8 mu m with a power performance equal to short-wavelength (lambda approximate to 5 mu m) QC lasers are reported. The device improvement is mainly achieved by a design of the injector/relaxation region, which at laser threshold allows resonant carrier injection between the ground state of the preceding and the upper laser level of the subsequent active region. In pulsed operation a peak output power of 1.3 W per facet has been measured at 100 K. At room temperature a record peak power of 325 mW and a record slope efficiency of 180 mW/A have been measured. In continuous-wave operation the maximum power at 30 K was 510 mW per facet and still 200 mW per facet at 80 K. The high values of the output power and slope efficiency demonstrate the validity of the cascading scheme, in which electrons above threshold,generate one photon per each active region they successively traverse. (C) 1998 American Institute of Physics

High power and tunable single-mode quantum cascade lasers

Quantum cascade (QC) lasers are a fundamentally new semiconductor laser source designed by methods of 'bandstructure engineering' and realized by molecular beam epitaxy (MBE). One of their most intriguing features is the cascading scheme, which results in the lasers' intrinsic potential for high optical output power. QC-lasers with varying numbers, from one to 75, of cascaded active regions and injectors have been studied. Pulsed peak output power levers of greater than or equal to 500 mW at room temperature and greater than or equal to 1 W at 200 K have been obtained for a 2.25 mm long and approximate to 12 mu m wide Fabry-Perot laser-stripe with 75 cascades. In continuous wave operation, 200 mW have been measured from one facet at 80 K and still 60 mW at 110 K, both from lasers with 30 stages. These lasers have an InP top cladding layer grown by MBE using solid source phosphorous. Widely tunable single-mode QC-distributed feedback (DFB) lasers have been fabricated in the wavelength range around 8.5 mu m. A side-mode suppression ratio of 30 dB and a 140 nm single-mode tuning range (thermal tuning between 10 and 320 K for lasers operated in pulsed mode) have been obtained. QC-DFB lasers driven in cw-mode display a tunability of approximate to 70 nm as a result of thermal tuning between 20 and 120 K. (C) 2000 Elsevier Science S.A. All rights reserved

High-power continuous-wave quantum cascade lasers

High-power continuous-wave (CW) laser action is reported for a quantum cascade structure operating in the midinfrared (lambda similar or equal to 5 mu m). Gain optimization and reduced heating effects have been achieved by employing a modulation-doped funnel injector with a three-well vertical-transition active region and by adopting InP as the waveguide cladding material to improve thermal dissipation and lateral conductance, A CW optical power as high as 0.7 W per facet has been obtained at 20 K with a slope efficiency of 582 mW/A, which corresponds to a value of the differential quantum efficiency eta(d) = 4.78 much larger than unity, proving that each electron injected above threshold contributes to the optical field a number of photons equal to the number of periods in the structure, The lasers have been operated CW up to 110 K and more than 200 mW per facet have still been measured at liquid nitrogen temperature, The high overall performance of the lasers is also attested by the large "wall plug" efficiency, which, for the best device, has been computed to be more than 8.5% at 20 K, The spectral analysis has shown finally that the emission is single-mode for some devices up to more than 300 mW at low temperature

New frontiers in quantum cascade lasers and applications

Recent advances and new directions in quantum cascade (QC) lasers are discussed in this paper. Invented in 1994 following many years of research on band-structure engineered semiconductors and devices grown by molecular beam epitaxy, this fundamentally new laser has rapidly advanced to a leading position among midinfrared semiconductor lasers in terms of wavelength agility as well as power and temperature performance. Because of the cascaded structure, QC lasers have a slope efficiency proportional to the number of stages. Devices with 100 stages having a record peak power of 0.6 W at room temperature are reported here. QC lasers in the AlInAs-GaInAs lattice matched to InP material system can now be designed to emit in the whole midinfrared range from 4 to 20 mum by appropriately choosing the thickness of the quantum wells in the active region. Using strained AlInAs-GaInAs, wavelengths as short as 3.4 mum have been produced, New results on QC lasers emitting at 19 mum, the longest ever realized in a III-V semiconductor laser, are reported. These devices use innovative plasmon waveguides to greatly enhance the mode confinement factor, thereby reducing the thickness of the epitaxial material. By use of a distributed feedback (DFB) geometry, QC lasers show single-mode emission with a 30-dB side-mode suppression ratio. Broad continuous single-mode tuning by either temperature or current has been demonstrated in these DFB QC lasers at wavelengths in two atmospheric windows (3-5 and 8-13 mum), with continuous-wave linewidths 10 KHz with suitable locking to the side of a molecular transition. These devices have been used in a number of chemical sensing and spectroscopic applications, demonstrating the capability of detecting parts per billion in volume of several trace gases. Sophisticated band-structure engineering has allowed the design and demonstration of bidirectional lasers, These devices emit different wavelengths for opposite bias polarities. The last section of the paper deals,vith the high-speed operation of QC lasers, Gain switching with pulse widths similar to 50 ps and active modelocking with a few picosecond-long pulses have been demonstrated. Finally a new type of passive modelocking has been demonstrated in QC lasers, which relies on the giant and ultrafast optical Kerr effect of intersubband transitions

Improved CW operation of quantum cascade lasers with epitaxial-side heat-sinking

First results on the epilayer-side mounting of quantum cascade (QC) lasers are presented. Operated;in continuous-wave (CW) mode, these lasers are superior to substrate-bonded devices. The maximum CW temperature is raised by 20 K (up to 175 K), and, at comparable heat sink temperatures, the performance with respect to threshold current, output power, and slope efficiency is greatly improved for the epilayer-side mounted devices. QC-laser-specific mounting procedures are discussed in this letter, such as the high reflectivity coating of the back-facet and the front-facet cleaving after mounting, Modeling of the temperature distribution inside the QC laser shows a strong temperature gradient within the active waveguide core, which partly explains the still low maximum CW operating temperatures

Continuous-wave and high-power pulsed operation of index-coupled distributed feedback quantum cascade laser at lambda approximate to 8.5 mu m

High performance index-coupled quantum cascade distributed feedback (QC-DFB) lasers operating at lambda approximate to 8.5 mu m are reported. Reliable dynamic single-mode emission with a side mode suppression ratio greater than or equal to 30 dB is obtained. The continuous single-mode tuning range is 140 nm. In pulsed operation a record high peak output power of 60 mW at 300 K is achieved. We further report on the first continuous-wave QC-DFB lasers. These devices display an output power of 10 mW at 120 K