First observation of the short-pulsing Q-switching mode in a double-heterostructure laser diode without ion implantation

Abstract

A double heterostructure (DH) laser has been developed and tested with the aim of achieving high-power picosecond optical pulses in the near-infrared range for use in advanced laser radars and other applications. The physical idea consists of achieving fast gain control by means of temporal evolution of the electric field in the active region. The gain is controlled by the variation in current due to transformation in the built-in electric field across the active region, provided that a high current density is used for pumping. This transformation broadens the carrier energy distribution in the active region, thus suppressing lasing until the current pulse stops. The resulting carrier accumulation causes an enlargement in the power of the short-pulsing Q-switching mode. One of the most important features of the laser structure is the placement of the electron injector well outside the two hetero-barriers forming the active region. Three transient lasing modes were observed simultaneously in this laser diode, with a maximum difference in wavelength as large as 60 nm. One of them, a 45 W/ 25 ps Q-switching mode which appears near the trailing edge of the current pulse, being spectrally separated from the other two. A significant further increase in the power of the Q-switching mode can be expected from an optimized laser structure with two parasitic modes completely suppressed. The new laser structure produces much more powerful picosecond pulses than are obtainable from gain-switched lasers and allows lasing wavelength control by means of bandgap engineering.