New frontiers in quantum cascade lasers and applications

Federico Capasso, Claire Gmachl, Roberto Paiella, Alessandro Tredicucci, Albert L. Hutchinson, Deborah L. Sivco, James N. Baillargeon, Alfred Y. Cho, H. C. Liu

Research output: Contribution to journalArticlepeer-review

168 Scopus citations


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 μm by appropriately choosing the thickness of the quantum wells in the active region. Using strained AlInAs-GaInAs, wavelengths as short as 3.4 μm have been produced. New results on QC lasers emitting at 19 urn, 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 pm), with continuous-wave linewidths <1 MHz when freerunning and ∼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 with the high-speed operation of QC lasers. Gain switching with pulse widths ∼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.

Original languageEnglish (US)
Pages (from-to)931-946
Number of pages16
JournalIEEE Journal on Selected Topics in Quantum Electronics
Issue number6
StatePublished - 2000
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Atomic and Molecular Physics, and Optics
  • Electrical and Electronic Engineering


  • Chemical sensing
  • High-speed optoelectronic devices
  • Injection lasers
  • Intersubband transitions
  • Mid-infrared
  • Semiconductor heterostructures
  • Unipolar semiconductor lasers


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