Simultaneous measurement of the linewidth, linewidth enhancement factor α, and FM and AM response of a semiconductor laser

Abstract

Using a commercially available computer controlled spectrum analyser with tracking generator, optical input section, and optical delay line it is possible to measure the linewidth, linewidth enhancement factor cy, and FM and AM response of a semiconductor laser in one process. The determination of the linewidth yields also information about the frequency noise density and the determination of cy delivers information about the nonlinear gain. Assuming an optical input power of 0 dBm, a laser linewidth < 50 MHz and a modulation response of the laser without cut-off, AM indices m > 0.01% and FM deviations of about > 10 MHz up to 20 GHz can be detected.

GaAs-Based Quantum Dot Lasers

“…Finally, the modified linewidth method relies on the measurement of SL's linewidth as a function of emitted power under and above the laser's threshold, and the ratio of the slopes of the curves linewidth as a function of the inverse power gives directly the a H -factor value (Villafranca et al, 2005). The ratio of the FM over AM components gives a direct measurement of the a H -factor (Harder et al, 1983;Kruger and Kruger, 1995;Shimpe et al, 1986;Zhang et al, 2007). Those methods based on the SL's linewidth both require a thorough characterization of the specific device under test and suffer from a poor accuracy due to the complex dependence of the laser's linewidth on several parameters.…”

Phase Shift Measurements Between Intensity and Frequency Modulations of a Self-Mixing Interferometer

“…It always leads to a mean value well in agreement with previous measurement (0.05 π), but it indicates for this laser an unpredicted dependence on other feedback parameters, to be further studied in future works. Measuring simultaneously AM and FM self-mixing signals unveils a straightforward method to measure the linewidth enhancement factor of a laser source, an important parameter of the semiconductor lasers [4,[14][15][16][17][18]. This is possible since it suffices to measure the phase shift of the waveforms to find out the α-factor.…”

“…This is possible since it suffices to measure the phase shift of the waveforms to find out the α-factor. We would like to highlight that different methods to determine the alpha factor based on SMI have been proposed; however, they require specific experimental conditions [14][15][16][17][18]. For instance, in [16] the interferometric signal in the AM channel must present a sawtooth shape, a condition that is achieved only in a moderate feedback regime.…”

Characterization of Optical Devices

“…Figure 3.2.15 shows an example of time-domain characterization of transmitter chirp using a setup based on a balanced Mach-zehnder interferometer [13]. However, since it is based on the swept-frequency smallsignal modulation, it usually provides only linear performance of the transmitter.…”