Dual-wavelength thulium fluoride fiber laser based on SMF-TMSIF-SMF interferometer as potential source for microwave generationin 100-GHz region

A dual-wavelength thulium-doped fluoride fiber (TDFF) laser is presented. The generation of the TDFF laser is achieved with the incorporation of a single modemultimode- single mode (SMS) interferometer in the laser cavity. The simple SMS interferometer is fabricated using the combination of two-mode step index fiber and single-mode fiber. With this proposed design, as many as eight stable laser lines are experimentally demonstrated. Moreover, when a tunable bandpass filter is inserted in the laser cavity, a dual-wavelength TDFF laser can be achieved in a 1.5-μm region. By heterodyning the dual-wavelength laser, simulation results suggest that the generated microwave signals can be tuned from 105.678 to 106.524 GHz with a constant step of �0.14 GHz. The presented photonics-based microwave generation method could provide alternative solution for 5G signal sources in 100-GHz region

Switchable 10, 20, and 30 GHz region photonics-based microwave generation using thulium-doped fluoride fiber laser

In this work, switchable 10, 20, and 30 GHz region photonics-based microwave generation in a fiber laser cavity is proposed and demonstrated. The microwave generation is based on the beating of a dual-wavelength thuliumdoped fluoride fiber laser. With the aid of a micro-air gap in an adapter, single, double, and triple Brillouin spacing can be generated in a single fiber laser cavity without re-routing the cavity. The wavelength spacing of the dual wavelengths that are induced by the single, double, and triple Brillouin spacing are 0.084, 0.166, and 0.254 nm, respectively, at a center wavelength of 1490 nm. In addition, a numerical calculation is performed using MATLAB to prove the generation of microwave signals at 11.34, 22.44, and 34.3 GHz. With the advantage of switchability among the 10, 20, and 30 GHz regions, the proposed photonics-based microwave generation is promising for the advancement of 5G technologies

Q-switched brillouin fibre laser with multi-wall carbon nanotube saturable absorber

A Q-switched Brillouin fibre laser (BFL) is successfully demonstrated using multi-walled carbon nanotubes (MWCNTs) embedded in polyvinyl alcohol (PVA) film as a passive saturable absorber (SA) for the first time. The SA is obtained by sandwiching the developed MWCNTs-PVA film between two FC/PC fibre connectors after depositing index-matching gel onto the fibre ends. The proposed Q-switched BFL incorporates a 5 km long dispersion shifted fibre in a ring cavity structure to generate Stokes shifted by 0.08 nm from the Brillouin pump wavelength. The BFL starts to generate a Q-switching pulse train at threshold pump power of 5 dBm. As the BP power is varied from 5.0 to 6.0 dBm, the repetition rate of the Q-switched BFL exhibits an increasing trend from 27.75 to 30.21 kHz, whereas the pulse width exhibits a decreasing trend from 3.25 mu s to 1.11 mu s. The maximum pulse energy of 0.13 nJ is obtained at maximum BP power of 6.0 dBm

Dual-wavelength thulium fluoride fiber laser based on SMF-TMSIF-SMF interferometer as potential source for microwave generation in 100-g hz region

A dual-wavelength thulium-doped fluoride fiber (TDFF) laser is presented. The generation of the TDFF laser is achieved with the incorporation of a single modemultimode-single mode (SMS) interferometer in the laser cavity. The simple SMS interferometer is fabricated using the combination of two-mode step index fiber and single-mode fiber. With this proposed design, as many as eight stable laser lines are experimentally demonstrated. Moreover, when a tunable bandpass filter is inserted in the laser cavity, a dual-wavelength TDFF laser can be achieved in a 1.5-µm region. By heterodyning the dual-wavelength laser, simulation results suggest that the generated microwave signals can be tuned from 105.678 to 106.524 GHz with a constant step of ∼0.14 GHz. The presented photonics-based microwave generation method could provide alternative solution for 5G signal sources in 100-GHz region

Temporal and amplitude modulation at C-band region using Bi2Te3-based optical modulator

A temporal and amplitude modulator based on few-layers bismuth telluride (Bi2Te3) flakes is demonstrated for C-band operation. The few-layers thick Bi2Te3 flakes are prepared by mechanically exfoliating a Bi2Te3 crystal. As an optical pulse modulator, the Bi2Te3-based saturable absorber (SA) provides stable Q-switching operation at 1561.1 nm with a maximum repetition rate of 70.92 kHz and minimum pulse width of 2.38 µs. As an optical amplitude modulator, two linear regions at different pump power ranges are obtained in the regression line of the peak intensity. The first linear region covers a pump power range from 0.0 to 80.32 mW and corresponds to a modulation efficiency of 0.05 dB/mW, while the second linear region covers a pump power range of 80.32–98.64 mW with a modulation efficiency of 0.81 dB/mW

Formaldehyde sensing using tapered u-shape plastic optical fiber coated with zinc oxide nanorods

Continuous exposure to formaldehyde may cause injury to the central nervous, respiratory, blood, and immunological systems. Tapered U-shape plastic optical fiber (POF) coated with zinc oxide nanorods was evaluated at wavelength of 645 nm for formaldehyde vapor sensing within a concentration range from 5% to 20%. The tapered POF with 500 µm waist diameter was prepared using chemical etching technique. Zinc oxide nanorods were synthesized using hydrothermal method and growth for 12 hours on the tapered POF. The proposed sensor exhibited a good response to formaldehyde concentration ranging from 5% to 20% with sensitivity and linearity measured to be 0.00543V/% and 98.58%, respectively. Excellent measurement stability was observed when the concentrations from 5% and above are maintain over a 600 second period. Highest difference voltage was produced by 0.0958V due to the more scattering effect of ZnO nanorods at 20% of formaldehyde concentration. This proposed sensor might be also used to detect air pollution produced not just by formaldehyde vapor, but also by other dangerous or poisonous vapors or gases

ZnO nanorods coated tapered u-shape plastic optical fiber for relative humidity detection

A relative humidity sensor was fabricated by exploiting an evanescent wave (EW) on a U-bent tapered plastic optical fiber (POF) coated with zinc oxide (ZnO) nanorods. The POF was tapered manually using a polishing method to a diameter of 0.5 mm, a length of 5 cm, and a radius of 5 cm. ZnO nanorods were synthesized using a hydrothermal method and grown on the POF by a seeding process for 12 h. A significant response of the sensor was observed when the sensor was exposed to 35 to 90%RH due to the intense chemisorption process and changeable relative index in the POF. The sensitivity and resolution of the sensor have been improved by factors of 1.23 and 2.18, respectively, compared to the conventional tapered POF sensor without ZnO coating. Besides, the ZnO-coated sensor also exhibited better repeatability properties in terms of output voltage when exposed to 35 to 90%RH for three repeated measurements. The obtained results revealed that the proposed new POF sensor has an excellent sensing performance as an RH sensor in terms of sensitivity, repeatability, and stability propertie

Development of bright and dark pulsed fiber laser based on nonlinear polarization rotation / Tiu Zian Cheak

Pulsed lasers have many practical applications in both communication and sensing. This thesis describes in detail the generation of bright pulses and dark pulses lasers based on nonlinear polarization rotation (NPR). The passive techniques are explored for pulse generation as they are reliable, compact, producing high beam quality and do not require an external modulator. Various techniques such as film saturable absorber (SAs), fiber SA and NPR techniques are studied to generate pulse. Performance of graphene SA in Erbium-doped fiber laser (EDFL) with three different gain mediums is successfully demonstrated. Q-switched EDFL are also demonstrated using thulium-doped fiber as a SA. NPR technique is adopted in a ring EDFL to generate Q-switched with low pump power. Besides the Q-switching operation, NPR technique is also explored to generate mode-locked, harmonic mode-locked, and multi-wavelength mode-locked. On the other hand, nonlinear Schrödinger equation (NLSE) dark pulse, cubic-quintic nonlinear Schrödinger equation (CQNLSE) dark pulse and domain wall (DW) dark pulse are demonstrated under different EDFL cavities based on NPR technique. Furthermore, multi-wavelength dark pulse is achieved using PCF in figure-of-eight cavity to slice the dark pulse spectrum. Besides, Q-switched dark pulse is achieved in an unstable mode-locking operation, in which the Q-switching operation modulated the dark pulses

Multi-wavelength Praseodymium fiber laser using stimulated Brillouin scattering

A multi-wavelength Brillouin Praseodymium fiber laser (MWBPFL) operating at 1300 nm region is demonstrated based on the hybrid scheme by utilizing Brillouin gain medium and Praseodymium-doped fluoride fiber as linear gain medium. A 15 µm air gap is incorporated into the cavity to allow the switching of Brillouin frequency spacing from double to single spacing. Under the Brillouin pump of 8 dBm and the 1020 nm pump power of 567.2 mW, 36 Stokes lines with a wavelength spacing of 0.16 nm and 24 Stokes lines with a wavelength spacing of 0.08 nm are achieved. The wavelength tunability of 8 nm is realized for both MWBPFLs by shifting the Brillouin pump wavelength. The MWBPFLs exhibit an excellent stability in the number of generated Stokes and power level over one-hour period