Setup of an Erbium-Fiber-Based Optical Frequency Comb

• Main Authors: Lin, Ying-Hsiu, 林盈秀
• Other Authors: Shy, Jow-Tsong
• Format: Others
• Language: zh-TW
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/10122744664652749944

碩士 === 國立清華大學 === 光電工程研究所 === 98 === The optical frequency comb (OFC) is the great contribution in optical frequency metrology by the 2005 Nobel physics winner J.L. Hall and T.W. Hänsch. The concept of the optical frequency comb was proposed as early as 1978, but it was first demonstrated 20 years later. During this period, the development of the Ti:sapphire Kerr lens mode locking laser, the invention of photonic crystal optical fiber as well as the proposal of the intelligent self reference technique bring the OFC to reality . At present, the Ti:sapphire laser based optical frequency comb has been well developed. In our laboratory, we have established a stable Ti:sapphire OFC. It has following disadvantages: it pumping laser needs long warm up time, the mode locking mechanism relies the external perturbation, the system volume is also quite huge, and the mobility is not high. The advantages of optical fiber OFC, lies in the reduction turn-on time, the self-starting mode locking, the small system volume, and the high mobility. The Ti:sapphire OFC provides reference wavelengths from 500 to 1600 nm, but the fiber OFC provides reference wavelengths from 1100 to 2200 nm, i.e., fiber OFC covers broader infrared region. The goal of this thesis is to setup an erbium-fiber-based OFC using the polarization additive mode locking (P-APM) technique. Its output pulse width is 50 fs at 1560 nm and repetition frequency is 100 MHz. After amplifying the output by an erbium fiber amplifier, its spectrum is extended by an 18 cm long HNLF (High NonLinear Fiber) to obtain a supercontinuum from 1100 to 2200 nm. The offset frequency is detected by the self-referencing technique and is then stabilized by controlling the laser pump power through a PLL (Phase-Locked Loop). The repetition frequency is stabilized by controlling the cavity length with a PZT through another PLL. At present, the perturbation frequency of 9th harmonics of repetition frequency is approximately 2.01 mHz, and the perturbation frequency of offset frequency is approximately 4.73 mHz. Therefore, our fiber OFC has a stability better than 2.3μ10-13 and it can be used to measure the optical frequency in the wavelength range of 1100 to 2200 nm.