Study On The Optimization Of Modulation Performance Of 40Gb/s Integrated Light Source Module

In recent years, with the continuous growth of wideband wireless communications, video-on-demand, and other new network applications, the fiber-optic communication networks are evolving from 10 Gb/s to 40 Gb/s technology. Distributed feedback (DFB) semiconductor laser integrated with electroabsorption (EA) modulator plays an important role in 40 Gb/s fiber communications systems. Fabrication of high-speed integrated light source is challenging and is now a hot research topic in the world, as it involves epitaxial growth, device structure design, chip processing, as well as module packaging and measurement.This dissertation focuses on problems in large signal modulation performance of the prototype integrated light source module fabricated in our lab. Based on theoretical analysis of large signal modulation characteristics, the device structure, manufacturing process, module packaging and other aspects of the integrated light source are optimized. Integrated light source module with dynamic extinction ratio over 8.2 dB is fabricated, whose performance is comparable to that of commercialized 40 Gb/s transmitter products.Firstly, anti-reflection (AR) coating technique is optimization to suppress the relaxation oscillation of the DFB laser caused by optical reflection at the EA modulator facet. By adopting novel thickness control method based on chromaticity coordinates calculated from reflection spectrum, the residual reflectivity of single layer SiNx anti-reflective coating is reduced to 10-4, and low-frequency modulation response fluctuations of the integrated light source is effectively suppressed.Secondly, based on theoretical analysis of the resonance formation mechanism in microwave transmission line, grounded coplanar waveguide (GCPW) transmission line with metal-walled via holes is designed by numerical simulation. Microstrips like (MSL) modes in the GCPW have been suppressed and the high frequency resonance in integrated light source module is eliminated, resulting in a smoothed modulation response.Meanwhile, wire-bonding technique and polymer planarization technology based on benzocyclobutene (BCB) are developed to further reduce the modulator capacitance. As a result, extinction ratio of the modulator is increased by increasing the modulator length, while maintaining the modulation bandwidth for 40 Gb/s operation.Finally, by systematically optimizing the module packaging structure, a 40 Gb/s integrated light source module is successfully fabricated, and a series of tests are carried out to characterize its performance. According to the measurement results, the static extinction ratio of the integrated light module is as high as 27 dB, and clear eye-opening is demonstrated under 43 Gb/s non-return-to-zero (NRZ) modulation, with a dynamic extinction ratio in excess of 8.2 dB.