Research

Polarization bistable VCSELs and its application to optical buffer memory

  We have demonstrated the polarization bistability in vertical-cavity surface-emitting lasers (VCSELs). When an optical pulse is injected into a polarization bistable VCSEL, the lasing polarization switches to the same polarization as the injected optical pulse. The switching time was about 7 ps, which is the fastest switching in the world. Using the polarization bistable VCSELs, we are conducting researches on optical signal processing such as all-optical DEMUX, RZ to NRZ or NRZ to RZ convertors, 3R (reamplification, reshaping, and retiming) repeaters, and optical buffer memory with a two-dimansional array of the VCSELs.
Bistable switching in a VCSEL by optical pulse injection
                  VCSEL array

Spintronics

  A new research field of Spintronics has been attracting much attention where the spin, another degree of freedom of electrons, is utilized. We measure the electron spin dynamics in semiconductors using ultra-short laser pulses in femto-second order.
  We focus on the very long electron spin relaxation time in quantum wells on GaAs(110), and have successfully fabricated a spin-VCSEL based on the (110)-QWs and demonstrated its circularly polarized lasing. We are also conducting researches on switching of the lasing circular polarizations by controlling the electron spin-polarization, injection of spin-polarized electrons from ferromagnetic metals into semiconductors, and control of spin-dynamics by applying electric field.
Femto-second laser & ultra-fast detection systems
 
      Spin-VCSEL on GaAs(110)
 
  Circularly polarized lasing spectra
  of the (110)-VCSEL