Dynamics of ridge-guide strained-layer multiple quantum well 1.3- and 1.55-μm semiconductor lasers

Abstract

In this paper we report the observation of spikes in the intensity power spectra of strained-layer multiple quantum well (MQW) lasers emitting at wavelengths of 1.3 im and 1.5 rim. The spacing between the spikes on fiber-pigtailed lasers was equal to the mode spacing of the fiber resonator EVfir c/(2 Ng L) where c is the speed of light, Ng is the group index, and L is the length of the fiber. 1 . LASER DESIGN AND STATIC PERFORMANCE Cross sections of the MQW ridge-guide lasers are shown in Figs. 1 and 2. The quantum wells have a width of 100 A and 0.5% compressive strain. The corresponding theoretical and experimental lightcurrent curves are shown in Figs. 3 and 4. A 500 A etch stop layer was used to determine the lateral index step. Thicknesses of the p-spacer layer ranged from 0. 1 .tm to 0.3 rim, resulting in a lateral index step of 0.025 to 0.0075. The ridge widths ranged from 2.5 pmto 4.0 p.m. DYNAMIC BEHAVJThe intensity power spectra for a 1.3 p.m MQW ridge-guide laser with a 2 meter fiber pigtail is shown in Fig. 5 at drive currents of 15 mA, 17 mA, 21 mA, and 28 mA. The length of the semiconductor laser cavity is 250 p.m and the ridge width is 4 p.m. The -50 MHz spacing of the spikes remain constant, but the frequency location where the intensity of the peaks are maximum increases with increasing drive current. Figure 6 shows the intensity power spectrum for an identical laser with a fiber pigtail length of 1 meter. The measured spacing of -100 MHz between the spikes agrees with the calculated resonances of the shorter fiber cavity. Such spiking is not observed in commercial 1.3 p.m and 1.55 p.m bulk active layer laser diodes grown by liquid phase epitaxy at LDI with a buried crescent geometry (Fig. 7). We also looked at the intensity power spectra of a fiber pigtailed bulk active layer 1.3 p.m laser and a fiber pigtailed MQW buried ridge guide laser from another commercial manufacturer and again observed no spiking in the bulk active layer device but similar spiking in the MQW laser.Finally, we looked at the dynamic behavior of MQW ridgeguide lasers without fiber pigtails. As shown in Fig. 8, the bare lasers also exhibited spiking but of lower amplitude and spaced between 33 to 41 MHz. These spikes exhibit maximums near 75 to 100 MHz and also around 1.6 to 2.0 GHz. The spiking behavior of all of these devices are summarized in Table 1. O-8194-1744-O/95/$6.OO SPIE Vol. 2397 / 59 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/20/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx