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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

ABSTRACFAdditional development of the four areas identified in this paper would provide useful information to those modeling existing semiconductor lasers and to those that hope to design future high performance semiconductor lasers. These four problem areas are by no means unique, and there are numerous problems to fill any void left by thorough solutions to the issues raised herein. 1. FAR-FIELD SYMMETRY The farfield, or radiation pattern is one of the basic characteristics of a semiconductor laser which is both easily measured and easily predicted given the physical description of the device. Text book derivations of the farfield radiation pattern I (0) 1 result in a straightforward mathematical expression 2 I(O)=F(O)IY(k.,sth(O))I (1)where F (0) is the obliquity factor 1 (which is proportional to cos (0)) and 'I' (kr, 5i11 (s)) the Fourier Transform of the nearfield distribution at the laser facet.In all practical lasers, the nearfield distribution perpendicular to the plane of the junction is essentially a real function. Although it is true that real semiconductor lasers have losses, typically on the order 10 cm1, and that there is very high gain in the active region, the calculated and measured phase fronts are found to be very flat. This being the case, it is easy to argue that the far-field distribution should be symmetric, since 1) the obliquity factor is symmetric and 2) the Fourier Transform of any real function is symmetric.Indeed, the appearance of asymmetric far-fields in channel-substrate-planar (CSP) lasers was used to diagnose problems in the material growth of the devices2 that were correlated with poor performance of the lasers.However, there is occasionally data from high performance laser diodes showing some asymmetry in the perpendicular far-fields. In reviewing the literature, we note that the necessity of including radiation modes in the far-field calculation has been known for some time 3. A detailed calculation of the far-fields for lead-salt lasers4 included radiation modes for a symmetric waveguide. 276 / SPIE Vol. 2399 0-8194-1 746-7/95/$6.00 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/23/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx

AB STRACTA1GaTnAs semiconductor lasers operating at a wavelength of 13 jim show superior performance compared to InGaASP lasers. Ridge guide lasers are fabricated from both material systems by the same process. The characteristic temperaçure T0 for the A1GaInAS lasers (-100°K) is about twice that of the InGaAsP lasers (-500 }) resulting in substantially lower thresholds ( 34 mA compared to -56 mA) at 85°C. The 3-cIB modulation frequency of A1GaInAS lasersis about 25%higher than that of the InGaASP lasers.