Femtosecond mode-locked fiber lasers incorporating graphene-based saturable absorbers
The advancement of mode-locked fiber laser (MLFL) in femtosecond range has wide applications especially in biomedical sciences. For instance, femtosecond lasers are employed for cancer treatment at cellular level. MLFL is achieved by mode-locking regime with an appropriate mode-locker. Over th...
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| Main Author: | |
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| Format: | Thesis |
| Language: | English |
| Published: |
2017
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| Subjects: | |
| Online Access: | http://psasir.upm.edu.my/id/eprint/68513/1/FK%202018%2014%20-%20IR.pdf |
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| Summary: | The advancement of mode-locked fiber laser (MLFL) in femtosecond range has
wide applications especially in biomedical sciences. For instance, femtosecond
lasers are employed for cancer treatment at cellular level. MLFL is achieved by
mode-locking regime with an appropriate mode-locker. Over the past few years,
researchers have shown substantial interest in fabricating efficient saturable
absorbers (SAs) as passive mode-locker due to its minimal weight, mechanically
stable and highly nonlinear properties. Two-dimensional materials are popular for
SA fabrication due to broadband and almost wavelength independent absorption.
However, fabrication techniques to incorporate two-dimensional material in SAs
involve tedious procedures especially wet chemicals. This research work focuses
on the generation of femtosecond pulses utilizing two different types of sandwichstructured
SA; graphene-polymethyl-methacrylate (PMMA) thin-film and
graphene nanoplatelet (GNP) powder. The graphene/PMMA-SA is made through
simple transfer procedure of the thin-film on a fiber ferrule. On the other hand, the
GNP-SA is realized by mechanical exfoliation technique of GNP powder on a fiber
ferrule. The optical characterization shows that graphene/PMMA-SA possesses
larger modulation depth and lower insertion loss as compared to GNP-SA, thus
leading to stronger saturable absorption for pulse shaping mechanism. The main
aspect of the study is to validate the fabrication techniques through enhanced laser
architectures in erbium-doped fiber laser (EDFL); single- and dual-lasing output.
The cavity optimization is carried out for both lasing operation in order to achieve
stable mode-locking operation in femtosecond range. For the optimized setup, the
EDFL with graphene/PMMA saturable absorber is able to generate around 700 fs
at approximately 1556 nm wavelength range. For dual-lasing MLFL generation, its
main challenge is to have a balance net cavity gain at different wavelengths. For
erbium materials, the interested lasing wavelengths are about 1530 nm and 1560
nm within its emission range. In order to minimize the complexity of configuration,most of the optical components are shared between these two lasing wavelengths.
This research work proposes laser architectures that utilize common gain medium
and SA. Two red/blue wavelength division multiplexers are employed to provide a
mechanism to split/combine these two wavelength ranges. Based on the proposed
laser architectures, lasing directions are also investigated; unidirectional and
bidirectional. The optimized pulse width of 730 fs and 870 fs are obtained at 1530
nm and 1560 nm, respectively. These findings are achieved with the bidirectional
MLFL architecture incorporating graphene/PMMA-SA. The achievement of this
research work solves the limitation of optical pulses measured in picosecond range
from previous works, while new architectures of dual-lasing mode-locked EDFLs
are successfully designed and executed. |
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