篇題：Low-frequency-drop of electroabsorption modulated lasers and the improvement with partially corrugated grating based DFB lasers
文章出處：IEEE Photon. J., vol. 14, no. 2, Apr. 2022, Art. no. 1515409
作者：S. Sulikhah, S. L. Lee, L. W. Chung, and H. W. Tsao
任職單位及部門：臺灣科技大學電子系/台灣大學電機系
Electroabsorption modulated lasers (EMLs) is sensitive to the residual facet reflection (RFR), which can cause a low-frequency drop (LFD) in the modulation response. The LFD may result in output waveform distortion, especially for high-data rate and multi-level modulation. We verify by simulation and experiments that the effect of LFD on the EML performance and propose to use LFD as one of the key performance indices for qualifying EMLs in high-speed optical transceivers. LFD can be suppressed by incorporating partial-corrugated-grating (PCG) in the laser section. With PCG-DFB structure, the EMLs can maintain high single-mode yield (SMY) and an excellent quality factor even with a strong modulator reflection from EAM section. This provides the robustness in applying the PCG-DFB to achieve a flat intensity modulation response or to enhance the output waveform under large signal modulation. By designing the PCG-EML to have about 60% of grating region, it can reach >80% of SMY and improve the average Q-value from the reduced LFD in the modulation response. The PCG-EML with reduced LFD can enhance the eye-opening through reduced waveform undershoot and overshoot for transmitting 56-Gbaud/s or beyond PAM-4 signals.
文章摘要：
電吸收調制雷射 (EML) 對殘餘端面反射 (RFR) 很敏感，這會導致調制響應中的低頻陷落或突起 (LFD)。 LFD 可能導致輸出波形失真，特別是對於高資料速率和多準位調制訊號會是決定效能的一個主要因素。我們通過模擬和實驗驗證了 LFD 對 EML 性能的影響，並建議將 LFD 作為驗證EML高速光收發器的關鍵性能指標之一。 LFD 可以通過在雷射部分加入部分光柵 (PCG) 來抑制。採用 PCG-DFB 結構，EML 可以保持高單模良率 (SMY) 和出色的品質因數，即使來自 EAM 部分的調制器反射很強，仍可獲得平坦的調制響應。通過將 PCG-EML 設計為具有約 60% 的光柵區域，它可以達到 >80% 的 SMY，並從調制響應中降低的 LFD 中提高Q 值。具有減少 LFD 能力的 PCG-EML 可以減少波形失真來增強眼圖，以傳輸 56 Gbaud/s 以上的 PAM-4 信號。