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Novel fiber optic devices with strongly enhanced graphene-evanescent field interaction for ultrafast fiber laser applications
- Author(s)
- 박남훈
- Advisor
- 염동일
- Department
- 일반대학원 에너지시스템학과
- Publisher
- The Graduate School, Ajou University
- Publication Year
- 2020-08
- Language
- eng
- Keyword
- Electro-optic modulation; Fiber optic device; Graphene; Saturable absorber; Ultrafast fiber laser
- Alternative Abstract
- Graphene, a single atomic layer of carbon atoms forming a hexagonal lattice, has been regarded as a promising material for use as a building block for future photonic, optoelectronic, and plasmonic devices owing to its outstanding electrical and optical properties. In particular, its uniform linear band structure, huge nonlinearity and ease of integration into diverse optical systems allow graphene to be applied to nonlinear optic devices such as nonlinear wavelength converters, optical limiters, and saturable absorbers for ultrafast fiber laser applications. However, low optical absorption (2.3%) and very thin thickness (0.34 nm) of monolayer graphene often limits its practical application. The graphene-light interaction can be greatly enhanced through the lateral interaction scheme where the evanescent field of guided light in a waveguide or an optical fiber interacts with graphene along the direction parallel to the graphene layer. Although there have been several attempts to increase graphene-light interaction based on lateral interaction scheme with evanescent field, realization of efficient fiber optic devices by evanescent-field interaction with a monolayer graphene is still challenging. In this dissertation, we investigate highly efficient linear and nonlinear all-fiber graphene devices based on strongly enhanced evanescent-field interaction with graphene, and apply these to the ultrafast fiber laser system for robust and stable operation. First, we develop an all-fiber graphene saturable absorber (SA) where high quality monolayer graphene is transferred on a side-polished fiber and a matched overcladding structure is additionally applied to it, which allows strong optical absorption of monolayer graphene up to 13.3 dB at 1550 nm wavelength. Additionally, we develop a passively mode-locked Er-doped fiber laser using our in-line monolayer graphene SA, which stably generated ultrashort pulses with pulse duration of 377 fs at a repetition rate of 37.7 MHz. The corresponding 3-dB spectral bandwidth of the laser was measured to be 8.6 nm at the central wavelength of 1607.7 nm. Moreover, the performance of the developed all-fiber graphene SA and ultrafast fiber lasers is explored in space-like environments. The monolayer graphene SA-based laser showed stable CW mode-locking operation while the inserted graphene SA was irradiated with gamma-ray of 2 kGy at a 45 Gy/hr dose rate. Lastly, an efficient electro-optic modulation is demonstrated in all-fiber graphene devices over a broad spectral range from visible to near-infrared. The ion-liquid based gating device fabricated onto a side-polished fiber with high numerical aperture significantly enhances the light-matter interaction with graphene, resulting in strong and non-resonant electro-optic modulation of up to 25.5 dB in the wavelength ranging from 532 nm to 1950 nm. In this works, the remarkable optical and electrical properties of monolayer graphene was applied to various ultrafast fiber laser applications through strongly enhanced evanescent field interaction with graphene. We believe that our study provides an opportunity for graphene to be applied in various linear and nonlinear optical devices such as broadband photodetectors, efficient SAs and electro-optic modulator in an all-fiber format.
- Fulltext
- Appears in Collections:
- Graduate School of Ajou University > Department of Energy Systems > 4. Theses(Ph.D)
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