The bandwidth of a distributed feedback (DFB) directly modulated laser (DML) is limited by its carrier–photon resonance (CPR) frequency. A viable approach to break the bottleneck is to introduce a photon–photon resonance (PPR), since the PPR can happen at a much higher frequency than the CPR. Among the many structures that can possibly generate the PPR, the dual-sectional push–pull modulated (PPM) DFB is of particular interest for its fabrication cost-effectiveness as no regrowth is required. The PPR in the PPM DFB, however, usually shows a rapid roll-off on both edges, which brings in an indentation on the lower frequency side of the PPR peak and, consequently, cuts off the bandwidth. To compensate for this dip, we introduce a detuned PPR and restart the CPR response by exploiting a time delay between the differential signals applied to the PPM DFB. Our simulation result shows that the broadened PPR peak and the restarted CPR response indeed mitigate the dip and effectively expand the PPM-DFB’s bandwidth to approximately 50 GHz, a value double that of the conventional (single-sectional) DFB DML.
Extracting the parameters of a laser from the measured results is critical for laser design, modeling and optimization. This work presents a parameter extraction method for quantum well distributed feedback (DFB) lasers based on the one-dimensional traveling wave model (1D TWM). Facet reflectivities, grating coupling coefficient and the other parameters can be extracted by fitting the lasing spectrum, lightcurrent (L-I) curve, intensity modulation (IM) response and largesignal chirp. During the extraction progress, the 1D TWM is simplified to improve the extraction efficiency. The feasibility of this extraction method is verified by extracting parameters from preset simulation results and experimental results, respectively. The 1D TWM can reflect the physical properties of the laser profoundly and the parameter extraction method based on 1D TWM will be a valuable tool for laser design, optimization or processing improvement.
Disordered waveguides mediated by transverseAnderson localization (TAL) can be used as mode division multiplexing system. The whole cross-section of the disordered waveguides is covered by all localized modes, which function as independent space channels. The localized modes are independent of the boundary and external excitation. The numerical results reveal that the average width tends to be steady in one particular realization of the disordered waveguide with a sufficient number of localized modes. In this paper, we proposed that localization length can be measured by the average width of localized modes. Besides, we explore the impact of the disordered waveguide design parameters, such as refractive index contrast, fill-fraction, and feature size, on the average width of localized modes.
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