IIIA-3 Heterodyne Measurement of Linewidth, Tunability, and Frequency Synthesis of Vertical-Cavity Surface-Emitting

(7 nm thick). The strained MQW layers were composed of compressively strained InGaAs wells (34 nm thick). The barrier layers were InGaAsP (A, = 1.3 pm, 1015 nm thick). The K-factor and dg/dN were determined from the laser intrinsic response, which was measured using the optical modulation technique [4] modified by the present authors. We determined E from (1). Main results for the MQW lasers are as follows: when optical confinement factor r was increased from 0.05 (number of wells N,, = 4) to 0.17 (N,, = 15), I) K-factor was reduced from 0.9 to 0.25 ns, 2) dg/dN was increased from 2.5 X to 9 X m/s, and 3) E was almost constant (4-6 x m3). We should note that the r dependence of the K-factor does not result from the change in t but results from the change in dg/dN. The increase in dg/dN is caused by the decrease in the threshold carrier density. Similar results were obtained for the strained MQW lasers. When r was increased from 0.03 (N,, = 5) to 0.05 (N, = IO), the K-factor was decreased from 0.7 to 0.4 ns and dg/dN was increased from 3 x to 6 X IO-’’ m’/s. The K-factors in the strained MQW lasers were smaller than those in the MQW lasers when both lasers had the same r. This is due to the larger dg/dN for the strained MQW laser. E’S were almost the same as those of the MQW lasers. The most important conclusion of our studies is that the K-factors in the MQW and strained MQW lasers are reduced as the optical confinement factor is increased, which mainly results from the increase in the differential gain. Strained MQW lasers with large optical confinement factor is expected to achieve small K-factor and large modulation bandwidth.