利用矽波導非線性現象產生中紅外超連續光譜

超連續光譜最早是在1969年由Alfano與Shapiro提出，因為有著高功率、寬頻譜與高同調特性，在近紅外光通訊波段已被應用於許多領域，如光學斷層攝影、光頻量測數及非線性光譜學等等。相較於近紅外光，中紅外光則在無線通訊、環境偵測與醫學等方面具有不錯之優異性及潛力。本實驗提出利用矽波導，打入高能量之超短脈衝，藉由自相位調變與色散的交互作用，在單一晶片上產生超連續光譜。選擇矽波導是因為它比起光纖擁有許多的優勢，如光侷限性佳與非線性係數高，元件只需數公分長度，加上和CMOS製程相符合，能把元件積體化；最重要的是，光纖在中紅外波段的吸收損耗是近紅外光好幾個數量級，而矽材料在1.3–9 μm則擁有高穿透性，較適合中紅外光傳播。本論文研究包含矽波導的非線性理論與模擬，矽波導結構設計，以及元件的製作與量測分析。量測原先使用的超短脈衝雷射波長為2.2 μm，但是此光源重覆率只有1 kHz，使的峰值功率太大造成元件損壞。最後我們改用近紅外光光源，觀察在高功率超短脈衝雷射的激發下，頻譜從原先的40 nm擴展至55 nm，證明元件是可以作用且產生超連續光譜。

關鍵字

超連續光譜；中紅外光

並列摘要

Supercontinuum (SC) is a broadband light source first observed by Alfano and Shapiro in 1970. Due to high brightness and high coherence, SC has been applied in optical coherence tomography, frequency metrology and nonlinear spectroscopy within near-IR spectrum. Apart from near-IR, mid-IR radiation can be used for free space communication, environmental sensing, and Medicine. We propose launching an optical ultra-short pulse into a silicon rib waveguide to generate mid-IR SC. The SC generation on Si waveguides relies on the third-order nonlinear optics, such as self-phase modulation, interplaying with chromatic dispersion. Compared with silica-based optical fibers, silicon has attracted the generation of SC due to high confinement and nonlinear coefficient. Meanwhile, along with the rapid development of silicon photonic technologies, a compact nonlinear optic chip is feasible to be implemented by those silicon photonic waveguides. Most importantly, silica is very lossy in the mid-IR spectrum window but silicon is transparent from 1.3μm to 9μm. Therefore, nonlinear silicon waveguides could be a promising platform to generate mid-IR SC due to its low optical loss and strong optical nonlinearity. This study includes the analysis of nonlinear optical effects in silicon, simulation, device design, device fabrication and experiment results. The wavelength of pump mid-IR pulse in the experiment was 2.2 μm. However, the repetition rate of pump only 1 kHz, causing the chip easily damaged because of too strong peak power but weak averaged power. We then alter the light source to near-IR and observed the spectral broadening from 40 nm to 55 nm. It is demonstrated that we can use such a short silicon waveguide to generate SC.

並列關鍵字

supercontinuum ； Mid-IR

參考文獻

[1] James G. Fujimoto and Costas Pitris, “Optical coherence tomography: an emerging technology for biomedical imaging and optical biopsy,” Neoplasia, Vol. 2, 2000, pp. 9-25.

[3] Jinendra K. Ranka, Robert S. Windeler, and Andrew J. Stentz, “Visible continuum generation in air-silica microstructure optical fibers with anomalous dispersion at 800 nm,” Opt Lett, Vol. 25, No. 1, 2000, pp.391-393..

[4] Boyraz, O., Indukuri, T., and Jalali, B. “Self-phase-modulation induced spectral broadening in silicon waveguides,” Opt. Express 12, 2004, pp.829-834.

[5] Hsieh, I. W. et al., “Cross-phase modulation-induced spectral and temporal effects on co-propagating femtosecond pulses in silicon photonic wires,” Opt. Express 15, 2007, pp. 1135-1146.

[6] Salem, R. et al. “Signal regeneration using low-power four-wave mixing on silicon chip," Nat Photon 2, 2008, pp. 35-38.

國際替代計量

利用矽波導非線性現象產生中紅外超連續光譜

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