Chip-scale frequency combs

A frequency comb is a light source whose lines are evenly spaced. Their regularity and ability to make precise measurements have revolutionized many fields, and for that reason the Nobel Prize in Physics was awarded for their development. Until recently, frequency combs were primarily based on mode-locked lasers, and could not be used in applications requiring compactness. However, this changed with the introduction of semiconductor frequency combs, which use a technology similar to what you might find in a laser pointer.

Although it is possible to naturally form combs in semiconductor lasers, this mode of operation is difficult to produce reliably or predictably over a wide dynamic range, since the dispersion could not be controlled by material growth to the necessary precision. We demonstrated that the concept of dispersion engineering, which had previously been well-established in ultrafast optics, was also valuable for semiconductor quantum cascade lasers. In doing this, we were able to demonstrate the first laser-based terahertz combs, and also the first deliberately-designed combs in semiconductor lasers. We also showed how the temporal profile of these combs could be directly measured, solving a problem that had been standing in the field since 2000.

Schematic of a frequency comb in a quantum cascade laser. A multimode laser is synchronized into a comb by an optical nonlinearity.

Double-chirped mirrors that compensate dispersion. Long wavelengths penetrate further into the cavity than short wavelengths. [3]

Picture of a MEMS-actuated mid-infrared QCL comb, which allows for chip-scale tuning of the comb. [1]

Select publications

  1. D. Burghoff, N. Han, F. Kapsalidis, N. Henry, M. Beck, J. Khurgin, J. Faist, and Q. Hu, “Microelectromechanical control of the state of quantum cascade laser frequency combs,” Appl. Phys. Lett., vol. 115, no. 2, p. 021105, Jul. 2019. (pdf)
  2. D. Burghoff, Y. Yang, D. J. Hayton, J.-R. Gao, J. L. Reno, and Q. Hu, “Evaluating the coherence and time-domain profile of quantum cascade laser frequency combs,” Opt. Express, vol. 23, no. 2, p. 1190, Jan. 2015. (pdf, notes on SWIFTS)
  3. D. Burghoff et al., “Terahertz laser frequency combs,” Nature Photon, vol. 8, no. 6, pp. 462–467, Jun. 2014. (pdf, supplementarycover image)

Other publications

  1. N. Henry, D. Burghoff, Q. Hu, and J. Khurgin, “Study of Spatio-temporal Character of Frequency Combs Generated by Quantum Cascade Lasers,” IEEE Journal of Selected Topics in Quantum Electronics, pp. 1–1, 2019.
  2. J. B. Khurgin, N. Henry, D. Burghoff, and Q. Hu, “Linewidth of the laser optical frequency comb with arbitrary temporal profile,” Appl. Phys. Lett., vol. 113, no. 13, p. 131104, Sep. 2018.
  3. N. Henry, D. Burghoff, Q. Hu, and J. B. Khurgin, “Temporal characteristics of quantum cascade laser frequency modulated combs in long wave infrared and THz regions,” Opt. Express, vol. 26, no. 11, p. 14201, May 2018.
  4. Y. Yang, D. Burghoff, J. Reno, and Q. Hu, “Achieving comb formation over the entire lasing range of quantum cascade lasers,” Opt. Lett., vol. 42, no. 19, pp. 3888–3891, Oct. 2017.
  5. P. Tzenov, D. Burghoff, Q. Hu, and C. Jirauschek, “Analysis of Operating Regimes of Terahertz Quantum Cascade Laser Frequency Combs,” IEEE Trans. THz Sci. Technol., vol. 7, no. 4, pp. 351–359, Jul. 2017.
  6. N. Henry, D. Burghoff, Y. Yang, Q. Hu, and J. B. Khurgin, “Pseudorandom dynamics of frequency combs in free-running quantum cascade lasers,” Opt. Eng, vol. 57, no. 01, p. 1, Sep. 2017.
  7. Y. Yang, D. Burghoff, D. J. Hayton, J.-R. Gao, J. L. Reno, and Q. Hu, “Terahertz multiheterodyne spectroscopy using laser frequency combs,” Optica, vol. 3, no. 5, p. 499, May 2016.
  8. P. Tzenov, D. Burghoff, Q. Hu, and C. Jirauschek, “Time domain modeling of terahertz quantum cascade lasers for frequency comb generation,” Opt. Express, vol. 24, no. 20, p. 23232, Oct. 2016.