Multi-wavelength Brillouin-Raman fiber laser utilizing enhanced nonlinear amplifying loop mirror design

We demonstrate a single-spacing, multi-wavelength Brillouin-Raman fiber laser utilizing an enhanced cavity of nonlinear amplifying loop mirror. In this structure, the optimization of multi-wavelength lasing is done with proper adjustments of coupling ratio and Brillouin pump power. When setting the Raman pump power to 300 mW, up to 28 channels with an average 17 dB optical signal-to-noise ratio are achieved. In this case, the Brillouin pump power is maintained at -2.6 dBm when the splitting ratio and Brillouin pump wavelength are fixed at 99/1 and 1555 nm, correspondingly. Our achievements present high numbers of Stokes channels with an acceptable optical signal-to-noise ratio at low pump power operation

Enhanced flatness of 20 Ghz channel spacing multiwavelength Brillouin-Raman fiber laser with sub-millimeter air gap

We discover the technique of controlling the flatness in signal amplitude of a multiwavelength Brillouin-Raman fiber laser by employing an air-gap outside of the cavity. The structure that is adjustable within sub-millimeter length behaves as flexible optical feedback that provides modifiable portions of multiple Fresnel reflectivities. This is the main benchmark that allows the efficient management of gain competition between self-lasing modes and Brillouin Stokes waves that is vital for self-flattening initiation. When setting the Brillouin pump wavelength at 1529 nm and the air-gap distance to 0.4 mm, 296 Stokes lines are produced with a channel spacing of 0.158 nm. The lasing bandwidth is 46.60 nm that covers from 1529.16 to 1575.76 nm wavelength. In this case at Raman power of 950 mW, the intense Brillouin pump power of 2 dBm saturates the cascaded higher-orders lasing lines. As a result, the overall peak power discrepancy is maintained at just 1.8 dB where an average optical-signal-to-noise ratio of 20 dB is realized. To date, this is the widest bandwidth with the flattest spectrum attained in multiwavelength fiber lasers that incorporate a single Raman pump unit

Spectral broadening in tight confinement geometry of a random fiber laser

We present a random Raman fiber laser pumped by a continuous-wave 1480nm source where neither a visible saturable absorber nor a fiber Bragg grating were incorporated. The backward pumping feedback loop allows a single direction of 1584nm wave propagation under tighter confinement of a dispersion compensating fiber (DCF). This geometry that implies a stronger Kerr-lensing effect supports two types of nonlinear broadening that were achieved in the stable output power generation. The first that agrees well to wave kinetics theory favors 1.76 to 3.53nm spectral progress. Against this flow, another type of wider broadening begun at 4.88nm before reducing gradually to 4.05nm with the increase in pump power. The former corresponds to a maximum of 6.3 times broadening ratio with respect to the pump linewidth. To date, this is the best achievement in the world at just below 1.7 W pump power level especially without utilizing pump-pulse synchronization or any external mode-locking modulations. In contrast without the tighter confinement geometry, the initiation of 4.25nm bandwidth was realized in the unstable power zone. These ascertain the double roles of dispersion compensating fiber as a stabilizing factor as well as for dispersion management

20 GHz spacing multi-wavelength generation of Brillouin-Raman fiber laser in a hybrid linear cavity

We demonstrate a tunable multi-wavelength Brillouin-Raman fiber laser with 20 GHz wavelength spacing. The setup is arranged in a linear cavity by employing 7.2 and 11 km dispersion compensating fibers (DCF) in addition to a 30 cm Bismuth-oxide erbium doped fiber. In this experiment, for the purpose of increasing the Stokes lines, it is necessary to optimize Raman pump power and Brillouin pump power together with its corresponding wavelengths. At the specific Brillouin pump wavelength, it is found that the longer length of 11 km DCF with optimized parameters results in larger number of Stokes combs and optical signal to noise ratios (OSNRs). In this case, a total of 195 Brillouin Stokes combs are produced across 28 nm bandwidth at Brillouin pump power of −2 dBm and Raman pump power of 1000 mW. In addition, all Brillouin Stokes signals exhibit an average OSNR of 26 dB

Flat amplitude and wide multiwavelength Brillouin/erbium fiber laser based on Fresnel reflection in a micro-air cavity design

In this report, we demonstrate a wide multiwavelength Brillouin-erbium fiber laser (MBEFL) with improved flatness that integrates a micro-air cavity. This air-gap introduces a cavity loss to overcome the gain saturation as well as providing efficient pump recycling scheme through Fresnel back-reflection. In addition, the efficient four-wave mixing in the highly nonlinear fiber contributes to the self-flattening of the output spectra. During operation, the optimized pumping values are set at 13 dBm Brillouin power and 600 mW erbium-ytterbium doped fiber amplifier when the air-gap length is fixed at 10 µm. A total of 180 Stokes lines are produced with a channel spacing of 0.08 nm. The flat lasing bandwith is 14 nm that consists of 1557 to 1571 nm wavelengths within 3-dB span. The average optical signal-to-noise ratio is 18 dB, having high peak power of −8 dBm. To our knowledge, this is the best result attained in MBEFLs with respect to the spectral flatness. In fact, the power stability of 0.76 dB order over 45 minute durations merits it applications in optical fiber sensing and communications

Penilaian kualiti air bawah tanah di Kelantan dan Pahang, Malaysia

Air bawah tanah yang menjadi sumber kegunaan domestik kepada pengguna memerlukan penilaian air bawah tanah bagi mengelakkan berlakunya isu kesihatan. Kajian ini dijalankan untuk menilai kualiti air telaga tiub dalam aspek kandungan logam berat, bahan radioaktif semula jadi (NORM) dan bakteria patogen di Kelantan dan Pahang, Malaysia. Hasil kajian ini menunjukkan kandungan Fe (90-42100 µg/L) dan Mn (3-478 µg/L) yang diperoleh adalah tinggi dan boleh menjejaskan kualiti air secara keseluruhan. Kandungan NORM yang terkandung dalam air telaga adalah 0.02-0.08 Bq/L bagi jumlah pengaktifan Alpha dan 0.02-0.15 Bq/L bagi jumlah pengaktifan beta, yang berada di bawah paras selamat yang telah ditetapkan oleh WHO. Kandungan NORM dalam sampel tanah adalah dalam julat 401-1348 Bq/kg untuk 40K, 19-175 Bq/kg untuk 232Th dan 28-318 Bq/kg untuk 238U yang boleh diterima di Malaysia. Anggaran dos sinaran tahunan adalah antara 52 µSv/tahun hingga 379 µSv/tahun dan berada dalam julat selamat untuk orang ramai. Kesemua sampel air dari Kelantan dan dua sampel air dari Pahang mengandungi bakteria enteropatogen terutamanya Escherichia coli dan Salmonella sp. yang melebihi piawaian Kualiti Air Kebangsaan. Boleh disimpulkan bahawa kualiti air bawah tanah selamat untuk digunakan semasa kecemasan, tetapi ia perlu dirawat sebelum diminum

Effect of high concentration of ZnO on the structural and optical properties of silicate glass system

An investigation was conducted to explore the optimum composition to fabricate a zinc silicate glass substrate for optoelectronic device applications. The composition was determined based on the empirical formula (ZnO)x-(SiO2)1-x, where x = 0.40, 0.50, 0.60 and 0.70 wt, which was prepared by the conventional melt quenching technique. The focus is on characterizing the physical and structural aspects as well as the optical properties of the glass substrate. The physical properties of zinc silicate samples were assessed using the densitometer and their physical appearance. In addition, the materials' amorphous and glassy characteristics were verified using X-ray diffraction (XRD) and Fourier transform infrared (FTIR) techniques. Finally, ultraviolet–visible (UV–Vis) spectroscopy and photoluminescence spectrometer were used to study the optical properties of samples. The density of the samples was observed to increase from 2805 to 3878 kg/m3 as the percentage of ZnO in the glass composition increased. X-ray diffraction analysis indicated the absence of sharp peaks in the samples containing up to 0.60 wt of ZnO, suggesting the presence of an amorphous phase. Furthermore, the results of this study indicate that ZnO-SiO2 glass substrate samples favor direct forbidden transitions, with an increase in ZnO leading to higher absorption and consequently a lower band gap. The photoluminescence spectrum showed blue light emissions at 422 nm, associating with the variation of band gaps in the ZnO phase. Overall, from the interesting results achieved, this zinc silicate-based composite material at 0.60 wt ZnO can be a potent candidate in optoelectronic applications, among other concentrations used in this study

Yb-doped femtosecond lasers and their frequency doubling

Ultralow threshold, compact and highly efficient femtosecond lasers based on Yb³⁺-doped potassium yttrium tungstate (Yb:KYW) and Yb³⁺-doped vanadium yttrium oxide (Yb:YVO 4 ) have been demonstrated within this PhD-research project. For a continuous wave unmode-locked Yb:KYW laser a threshold as low as 101 mW was obtained with a slope efficiency of 74%. By employing a single prism for dispersion control, the laser was tunable between 1012 nm to 1069 nm. When operated in the mode-locked regime, this laser produced transform-limited pulses having durations of 210 fs at a central wavelength of 1044 nm. Stable mode locking was observed for an optimised incident pulse fluence on the SESAM between 140 μJ/cm² to 160 μJ/cm² which was 2-3 times higher than the designed energy pulse fluence of the SESAM (70 μJ/cm²). The employment of several combinations of chirped mirror designs for control of intracavity group velocity dispersion led to excellent results. The threshold for mode locking was satisfied for a pump power of 255 mW where the slope efficiency was measured to be 62%. This is the most efficient SESAM-assisted femtosecond laser yet reported and the highest optical-to-optical efficiency of 37% is exceptional. Transform-limited pulses with durations as short as 90 fs were produced in a spectral region centred on 1052 nm. The success of this research thus represents a good foundation on which to design and build more compact configurations that will incorporate just one chirped mirror for dispersion compensation. A relatively high nonlinear refractive index, n₂ , of 15 x 10⁻¹⁶ cm²/W was measured in Yb:YVO₄ and this affords particular potential for this candidate material in Kerr-lens mode locking. In fact, for operation in the femtosecond domain, the threshold power was 190 mW with a slope efficiency of 26% and near-transform-limited pulses as short as 61fs were generated at a centre wavelength of 1050 nm. The main objectives in developing this type of laser relate to a demonstration of high peak power operation in thin disc laser configurations. The deployment of a diode-pumped Yb:KYW femtosecond laser as a pump source for frequency doubling in a periodically-poled LiTaO₃ crystal was realised. The maximum realized output power of 150 mW corresponded to an impressive second harmonic conversion efficiency of 43%. 225-fs duration green pulses (centred at 525 nm) were generated under the condition of strong focusing in the nonlinear crystal

Yb-doped femtosecond lasers and their frequency doubling

Ultralow threshold, compact and highly efficient femtosecond lasers based on Yb³⁺ -doped potassium yttrium tungstate (Yb:KYW) and Yb³⁺ -doped vanadium yttrium oxide (Yb:YVO 4 ) have been demonstrated within this PhD-research project. For a continuous wave unmode-locked Yb:KYW laser a threshold as low as 101 mW was obtained with a slope efficiency of 74 %. By employing a single prism for dispersion control, the laser was tunable between 1012 nm to 1069 nm. When operated in the mode-locked regime, this laser produced transform-limited pulses having durations of 210 fs at a central wavelength of 1044 nm. Stable mode locking was observed for an optimised incident pulse fluence on the SESAM between 140 μJ/cm² to 160 μJ/cm² which was 2-3 times higher than the designed energy pulse fluence of the SESAM (70 μJ/cm² ). The employment of several combinations of chirped mirror designs for control of intracavity group velocity dispersion led to excellent results. The threshold for mode locking was satisfied for a pump power of 255 mW where the slope efficiency was measured to be 62 %. This is the most efficient SESAM-assisted femtosecond laser yet reported and the highest optical-to-optical efficiency of 37 % is exceptional. Transform- limited pulses with durations as short as 90 fs were produced in a spectral region centred on 1052 nm. The success of this research thus represents a good foundation on which to design and build more compact configurations that will incorporate just one chirped mirror for dispersion compensation. A relatively high nonlinear refractive index, n₂ , of 15 x 10⁻¹⁶ cm² /W was measured in Yb:YVO 4 and this affords particular potential for this candidate material in Kerr-lens mode locking. In fact, for operation in the femtosecond domain, the threshold power was 190 mW with a slope efficiency of 26 % and near-transform-limited pulses as short as 61 fs were generated at a centre wavelength of 1050 nm. The main objectives in developing this type of laser relate to a demonstration of high peak power operation in thin disc laser configurations. The deployment of a diode-pumped Yb:KYW femtosecond laser as a pump source for frequency doubling in a periodically-poled LiTaO₃ crystal was realised. The maximum realized output power of 150 mW corresponded to an impressive second harmonic conversion efficiency of 43 %. 225-fs duration green pulses (centred at 525 nm) were generated under the condition of strong focusing in the nonlinear crystal.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Switchable multiwavelength Brillouin-Raman fiber laser utilizing an enhanced nonlinear amplifying fiber loop design

We propose and demonstrate a new multiwavelength Brillouin-Raman fiber laser with switchable 10 and 20 GHz spacing. This is achieved by proper adjustments of optical coupling ratios that are incorporated in the design that consists of an enhanced nonlinear amplifying fiber loop. By utilizing a 50/50 coupler, 443 flat amplitude channels with 10 GHz spacing is realized. On the other hand, a 99/1 coupler is feasible for 20 GHz spacing that yields 215 lasing lines. In both cases, the average optical signal-to-noise ratios (OSNR) are 16.5 dB (50/50 coupler) and 24 dB (99/1 coupler). Wide multiwavelength bandwidth, flexible wavelength spacing, and high number of channels with excellent OSNRs are achieved using only a single Raman pump unit through a simple construction