Tunable and dual-wavelength passive Q-switched pulse generation with fiber-optic interferometers / Siti Fazilah Shaik Mohd Noor

Siti Fazilah , Shaik Mohd Noor (2024) Tunable and dual-wavelength passive Q-switched pulse generation with fiber-optic interferometers / Siti Fazilah Shaik Mohd Noor. PhD thesis, Universiti Malaya.

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Abstract

Tunable and multi-wavelength Q-switched Erbium doped fiber laser (EDFLs) operating in 1.5-micron region have gained tremendous interests in recent years due to their important applications in many areas including material processing, optical communication and biomedical. These lasers are normally realized by using an interference filter in conjunction with saturable absorber (SA). The filter functions to enable tunability and multi-wavelength operation while SA functions to initiate pulses by passive means. Up to date, plenty of works have been reported on developing new SA devices which have a good optical characteristic to produce high performance pulse lasers and on finding new applications for various interference filters. This work was aimed to explore the use of two types of fiber-optic interferometer: sagnac loop mirror (SLM) and single-mode fiber (SMF) – multimode fiber (MMF) – single-mode fiber (SMF) or SMS structure for demonstrating a tunable or dual-wavelength Q-switched EDFL using graphene oxide (GO) and aluminum oxide (Al2O3) thin film as SA. Both GO and Al2O3, thin films have been successfully fabricated by embedding in PVA thin film and characterized with modulation depths of 24.1% and 3.5 %, respectively. Wavelength tunable Q-switched EDFLs have been successfully demonstrated using the SLM in figure-of-eight laser cavity as a tunable filter and GO or Al2O3, thin film as SA. For instance, a stable passively Q-switched EDFL tunable by Sagnac interferometer operation was realized with a GO. By tuning the temperature of SLM from 30oC to 70 oC, the central wavelength of the Q-switched EDFL could be tuned continuously from 1566.3 nm to 1559.3 nm. At 1566.3 nm operation, the maximum repetition rate and minimum pulse width was recorded at 41.5 kHz and 7.3 μs, respectively. A dual-wavelength Q-switched pulse generation has been successfully demonstrated in an EDFL cavity using GO SA and SMS filter to operate at wavelengths of 1549.6 nm and 1558.6 nm. The maximum pulse repetition rate and the shortest pulse width are obtained at 65.27 kHz and 2.9 μs, respectively. At 225.1 mW pump power, the maximum output power and pulse energy were obtained at 0.99 mW and 15.17 nJ, respectively. This study revealed the promising potential of GO and Al2O3 based SA to be used in pulse generation. Both SLM and SMS could also be used as filters for tunable or multi-wavelength laser generation. The fabrication of the SAs and filters are simple, hence reducing the cost of the laser itself. Simple and low-cost fiber lasers are required in various applications including medical diagnostics and environmental sensing.

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