Home >  About ISSP >  Publications > Activity Report 2018 > Xxxx Group

Direct Short-Pulse Generation from Gain-Switched Semiconductor Lasers

Akiyama Group

The compact, inexpensive, and easy-to-operate gain-switched semiconductor lasers have wide potential applications as pulse light sources in industries and medical treatments [1]. However, it was very difficult to obtain short pulses with duration shorter than 10 ps through gain-switching technique. We investigated gain-switching dynamics in various semiconductor lasers [2-4], and successfully achieved Fourier-transform limited picosecond optical pulses via spectral filtering technique from gain-switched semiconductor lasers [5, 6].

Fig. 1. (a) Lasing spectra of a single-mode DFB-LD at room temperature with various current densities, showing the significant spectral broadening towards short wavelength side with increasing current density. Dashed line shows the down chirp during gain switching of the DFB-LD with the highest excitation density. (b) Spectrum of the short wavelength component after spectral filtering of the one with the highest excitation in (a). The FWHM of the peak is measured to be 0.56 nm. (c) The autocorrelation trace of the spectrally filtered short wavelength component. Fitting result shows that the pulse has a sech2 shape with a pulse width of 4.7 ps. The time-bandwidth product (0.33) of the obtained short pulse demonstrates that the obtained short pulses at short-wavelength side are Fourier-transform-limited pulses.

Excitation-power-dependent lasing spectra from a gain-switched distributed feedback (DFB) laser diode (LD) driven by pulsed current injection with duration of nanosecond are shown in Fig. 1(a). The spectral broadening as well as the down chirping (shown as the dashed line in Fig. 1(a)) on short wavelength side are typical phenomena reflecting the large variation of carrier density during pulse generation by gain switching [6], which in turn is an important reason that results in the broadening of the gain-switched output pulses. By utilizing spectral filtering technique to extract the transient short wavelength components (Fig. 1(b)) in the lasing spectra, we have successfully generated Fourier-transform limited 4.7-ps short pulses (Fig. 1(c)) from a gain-switched DFB-LD. The present technique provides a simple and practical method for short pulse generation and brings new insights for ultrafast nonlinear dynamics producing picosecond optical pulses by gain switching.


References
  • [1] H. Yokoyama, et al., Opt. Express 14, 3467 (2006).
  • [2] S. Q. Chen, et al., Jpn. J. Appl. Phys. 51, 098001 (2012).
  • [3] S. Q. Chen, et al., Appl. Phys. Lett. 101, 191108 (2012).
  • [4] S. Q. Chen, et al., Opt. Express 21, 7570 (2013).
  • [5] S. Q. Chen, et al., Opt. Express 20, 24843 (2012).
  • [6] S. Q. Chen, et al., Opt. Express 21, 10597 (2013).
Authors
  • S. Q. Chen, M. Yoshita, T. Ito, T. Mochizuki, C. Kim, H. Akiyama, A. Satoa, and H, Yokoyamaa
  • aTohoku University