光纖光頻梳的架設

Setup of an Erbium-Fiber-Based Optical Frequency Comb

林盈秀(Ying-Hsiu Lin)

指導教授 ： 施宙聰

國立清華大學/電機資訊學院/光電工程研究所/碩士(2009年)

https://doi.org/10.6843/NTHU.2009.00783

摘要

本論文為架設一套摻鉺光纖光頻梳(erbium-fiber-based OFC)，以摻鉺光纖作為增益介質，使用980 nm半導體雷射作為幫補光源，利用非線性偏極旋轉鎖模機制(P-APM)得到鎖模雷射脈衝，輸出中心波長為1560 nm，脈衝寬度約為50 fs，脈衝重複率為100 MHz。其輸出經一光纖放大器放大後，使用一長18 cm的高非線性光纖(Highly NonLinear Fiber, HNLF)展頻，得到波長範圍為1100 到2200 nm的超連續光譜(supercontinuum)。我們使用自參考技術(self-referencing technique)量測偏差頻率，並且利用鎖相迴路(Phase-Locked Loop, PLL)回饋至幫浦雷射，控制幫浦雷射光功率即可穩定偏差頻率之頻率與相位。此外，將光偵測器量測到脈衝重複率訊號，利用鎖相迴路回饋給PZT，利用PZT隨電壓變化的延展特性控制共振腔腔長，作為穩定脈衝重複率之方法。目前，脈衝重複率的第九諧波(9th harmonics)的頻率擾動(frequency fluctuation)為2.01 mHz，偏差頻率的頻率擾動是4.73 mHz，此光纖光頻梳的穩定度已達2.31013，可作為光頻量測的標準。

關鍵字

光纖 ； 光頻梳 ； 鎖模雷射 ； 自參考技術 ； 脈衝重複率 ； 偏差頻率

並列摘要

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.

並列關鍵字

fiber ； optical frequency comb ； mode-locking laser ； self-referencing technique ； repetition frequency ； off-set frequency

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