High power ultrafast all-fiber lasers using saturable absorbers based on low-dimensional materials
High power ultrafast all-fiber lasers using saturable absorbers based on low-dimensional materials
- 주제(키워드) Fiber laser , Mode-locking , SWCNT , graphene
- 발행기관 아주대학교
- 지도교수 염동일
- 발행년도 2017
- 학위수여년월 2017. 8
- 학위명 박사
- 학과 및 전공 일반대학원 에너지시스템학과
- 실제URI http://www.dcollection.net/handler/ajou/000000025993
- 본문언어 영어
- 저작권 아주대학교 논문은 저작권에 의해 보호받습니다.
초록/요약
Ultrafast all-fiber laser has advantages such as alignment-free structure, high gain, cost-effectiveness, efficient heat dissipation, excellent spatial beam quality, and compact size. It can be potentially applied in fields of material processing, medical, military, and optical metrology. In an ultrafast fiber laser, real saturable absorbers (SAs) are used for passive mode-locking for self-starting and environmentally stable operation. A commercial semiconductor saturable absorber mirror (SESAM) is widely used as a saturable absorber. However, it has narrow operation wavelength and complicated fabrication process. Recently, single-walled carbon nanotube (SWCNT) and graphene SAs were proposed as an alternative SA because of their unique optical features such as broad operation range, high 3rd order nonlinearity, and simple fabrication. Until now several types of in-line SA based on graphene or SWCNT SA are reported. Among previous platforms, a side-polished fiber (SPF) type SA has advantages such as moderate interaction length, high optical damage threshold, compatible with single mode fiber (SMF) and robust structure. Thus, SPF type SA is suitable for high power operation of the ultrafast fiber laser. Although the ultrafast fiber lasers have been intensively studied at the wavelength of 1.0, 1.5, and 2.0 μm, to realize all-fiber ultrafast laser with high output power is still challenging. In this thesis, the high quality SWCNT and graphene SAs based on the SPF platform were carefully fabricated under optimized condition for passive mode-locking at high power. Linear and nonlinear transmission of the SAs were characterized by using lab-built experimental setup. In addition, we measured the optical damage threshold of SWCNT-SAs. In case of graphene SA, the index matched over-cladding was applied onto the polished surface to obtain strongly enhance nonlinear properties of the SA. We also proposed polarization maintaining (PM) SWCNT-SPF-SA for mode-locked all-PM fiber laser. We investigate the performance of high power passively mode-locked all-fiber lasers operating at the wavelength from 1 μm to the 2 μm by employing our fabricated SAs. We firstly constructed the high-power Tm-doped soliton all-fiber laser using a high quality monolayer graphene SA on the SPF. The laser output stably delivers the soliton pulse with 3-dB spectral bandwidth of 5.1 nm at the central wavelength of 1910 nm. The pulse duration was measured as 773 fs when fitted by sech2-shape. The measured average output power was 115 mW and the estimated pulse energy was 6 nJ. We then built an Er-doped fiber laser operating at net normal dispersion regime. An all-fiber dissipative soliton laser was successfully fabricated by employing our SWCNT-SA at 1.55 μm. The dispersion compensating fiber with large normal dispersion (DCF, β2 ~ 162 ps2/km) was used to shift the net cavity dispersion to normal value. In the normal dispersion, the mode-locked laser can support the pulse with higher pulse energy. The generated dissipative soliton laser stably delivered high average output power of 335 mW and high pulse energy of 34 nJ, which is highest value to our knowledge ever reported in all-fiber passively mode-locked laser. The linearly chirped pulse of 12.7 ps was measured at the laser output. After pulse compression by single mode fiber (SMF), we could obtain the pulse with to be 369 fs pulse duration. The estimated peak power was 81 kW. In case of Yb-doped fiber laser, we first conducted numerical simulation for optimal design of the laser cavity. Based on numerical result, we fabricated graphene SA having large modulation depth, which is necessary in the all-normal dispersion ultrafast fiber laser. We successfully realize all-normal fiber Yb-doped dissipative soliton laser by including our graphene SA. The measured central wavelength and 3-dB spectral bandwidth were 1055 nm and 11 nm, respectively in the laser output. The maximum average output power was 199 mW where calculated pulse energy was 7.2 nJ. The laser delivers a linearly chirped pulse with pulse duration of 12.5 ps. The chirped pulse was then compressed to be 336 fs by grating pairs (1400 grooves) where the maximum peak power of the pulse was estimated to be 20 kW. We expect our works could be contributed to high power ultrafast fiber laser development particularly for the application to the fields including laser-based non-thermal material processing, medical surgery and environmental sensing at military.
more목차
Chapter 1 Introduction
Chapter 2 Passively mode-locked lasers
2.1 Passive mode-locking
2.2 Saturable absorber
2.3 Saturable absorbers based on low-dimensional carbon materials
2.3.1 Single-walled carbon nanotube (SWCNT)
2.3.2 Graphene
2.3.3 Types of saturable absorber in fiber laser
2.4 Mode-locked regimes in fiber laser
Chapter 3 SWCNT and graphene side-polished fiber saturable absorber
3.1 Introduction
3.2 Fabrications of saturable absorbers
3.3 Optical characteristics of SWCNT SA
3.3.1 Nonlinear properties of SWCNT SA
3.3.2 Optical damage threshold value of SWCNT SA
3.4 Characteristics of graphene SA
3.4.1 Nonlinear properties of graphene SA
Chapter 4 All-fiber soliton fiber lasers
4.1 Introduction
4.2 All-polarization maintaining Er-doped soliton fiber laser
4.3 All-fiber Tm-doped soliton laser
Chapter 5 High power dissipative soliton all-fiber lasers
5.1 Introduction
5.2 Dissipative soliton all-fiber laser with pulse energy of 34 nJ
5.3 All-normal dispersion fiber laser with average output power of 200 mW
5.3.1 Numerical simulation of mode-locked laser
5.3.2 Experimental results of fiber laser
Conclusion
References
Publications list
국문 요약
