Comparison of Uniform Grating and Partially Corrugated Grating DFB Structures for High-Speed Directly Modulated Lasers

• Main Author: SITI SULIKHAH
• Other Authors: San-Liang Lee
• Format: Others
• Language: en_US
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/99093290057512742918

碩士 === 國立臺灣科技大學 === 電子工程系 === 105 === Future data center optical networks desired a high-speed laser to meet IEEE 802.3bs standard, which is defining an Ethernet speed of 400 Gb/s (4x100 Gb/s or 8x50 Gb/s) for network aggregation applications. The objectives of designing high-speed lasers are low-cost, reliable, and high performance. Direct-modulation of semiconductor lasers (DML) was proposing an attractive choice for large-capacity transmission. However, DMLs have some disadvantages, including a relatively small direct modulation bandwidth and the modulation induced chirp effects that prevent their high-speed applications. One of the solutions for enhancing modulation bandwidth of DMLs is using short cavity length. Practically, a shorter cavity length (L< 200 µm) is difficult to cleave and handle. The partially corrugated grating (PCG) structure is able to improve the resonance frequency of laser and provide a high immunity to external reflections. In this thesis, the characteristics of DMLs with a uniform grating (UG) and partially corrugated grating (PCG) structures were analyzed and compared in various aspects. The simulated frequency response of DMLs agreed with the calculated results in terms of smaller modulation bandwidth for longer laser lengths. We have achieved a better dynamic performance by using PCG-DMLs against UG-DMLs for a data rate up to 50Gbps. PCG-DFB structures have obtained -3dB bandwidth of >30 GHz with a side-mode suppression ratio (SMSR) of>45dB by using a grating length of 150 µm for 200-µm long lasers. These enhancements make PCG-DMLs attractive as high-speed light sources for future broadband access networks.