Dual-Wavelength Fiber Lasers for the Optical Generation of Microwave and Terahertz Radiation

Dual-Wavelength Fiber Lasers (DWFLs), which provide a simple and cost-effective approach for the optical generation of Microwave (MHz) and Terahertz (THz) radiation. The emphasis of this review is to trace the early development of DWFLs, including the issues and limitations faced by the various gain media right to the latest advancements in this field as well as their roles in generating the desired output. This review covers both the simple approaches of narrow-band filters and comb filters for microwave radiation generation, as well as the use of DWFLs with diethylaminosulfurtetrafluoride or LiNbO3 crystals for generating THz radiation

Highly stable graphene-assisted tunable dual-wavelength erbium-doped fiber laser

A highly stable tunable dual-wavelength fiber laser (TDWFL) using graphene as a means to generate a highly stable output is proposed and generated. The TDWFL comprises a 1 m long, highly doped erbiumdoped fiber (EDF) acting as the linear gain medium, with a 24-channel arrayed waveguide grating acting as a wavelength slicer as well as a tuning mechanism to generate different wavelength pairs. The tuned wavelength pairs can range from 0.8 to 18.2 nm. A few layers of graphene are incorporated into the laser cavity to induce the four-wave-mixing effect, which stabilizes the dual-wavelength output by suppressing the mode competition that arises as a result of homogenous broadening in the EDF. © 2013 Optical Society of Americ

S-band Q-switched fiber laser using MoSe2 saturable absorber

A passively Q-switched S-band fiber laser using Molybdenum Diselenide (MoSe2) saturable absorber (SA) is proposed and demonstrated. The SA is fabricated by depositing MoSe2 onto two fiber ferrules using the drop-cast method before heating and connecting the two fiber ferrules to form the SA. The passively Q-switched fiber laser designed using the MoSe2 SA has an operational range of 1491.0–1502.0 nm. The output pulse train has a pulse-width ranging from 2.0 μs to 1.0 μs and corresponding repetition rate of between 34.5 kHz and 90 kHz with increasing pump powers, as well as a signal-to-noise of about 35.97 dB. The peak performance of the proposed laser is between 1480.0 and 1490.0 nm, corresponding to the first peak gain region with the S-band

Passively Q-switched S+/S band fiber laser with copper telluride saturable absorber

A Q-switched S-band fiber laser based on a thulium-fluoride fiber gain medium and copper telluride (Cu2Te) based saturable absorber (SA) is demonstrated. The Cu2Te based SA is fabricated as a thin film and at the maximum pump power, the generated Q-switched output has a minimum pulse width of 3.2 µs and highest pulse energy of 56.7 nJ. The pulse train varies from 20.9 kHz to 30.2 kHz at the highest pump power. The wavelength of the generated output can be tuned over a range of 32 nm from 1470 nm to 1502 nm. The demonstrated laser has a high potential for industrial applications focusing on the S-band region

Zirconia-Yttria-Alumino silicate glass-based erbium-doped fibres as a medium for q-switched and mode-locked pulse generation / Kavintheran a/l Thambiratnam

In this research, the fabrication and characterization of zirconia–yttria–alumino silicate glassbased erbium-doped fibres as well as their application as the gain media for compact fast and ultra-fast pulsed sources is presented. The fabrication process is similar to that of a conventional erbium doped fibre, with the ZrO2 co-dopants incorporated into the silica host during solution doping. Morphological studies of the drawn fibres reveal a core with a diameter of approximately 10 μm. Tunneling electron microscope scanning shows the presence of ZrO2 rich micro-crystallites, while X-ray diffraction analysis indicates the formation of tetragonal ZrO2 structures. Spectral characterization of the fibres show attenuation peaks at 980 nm and 1550 nm, with sample designated ZEr-B having absorption rates of 22.0 dB/m and 53.0 dB/m at 980 and 1550 nm respectively as well as a fluorescence life-time of 10.86 ms, as well as a W-profile refractive index. A 3 m long ZEr-B fiber with a dopant concentration of about 3880 ppm/wt is used to generate an amplified spontaneous emission spectrum. The fibres amplified spontaneous emission spectrum output differs substantially from that of a conventional erbium doped fibre of the same length, rising to a peak region at 1530 nm, followed by a short ‘plateau’ before decreasing. As a fibre amplifier a gain of around 28.0 dB near 1530 nm and a relatively flat gain of between 22.0 to 25.0 dB at the plateau region is obtained, together with a noise figure of approximately 14.1 dB for an input signal of -30 dBm. The fiber can also generate a single-longitudinal mode output, ranging from 1533.8 nm to 1545.0 nm at output powers of more than -8.9 dBm with an average signal-to-noise ratio of more than 50 dB. Additionally, the fiber allows non-linear interactions to occur at lower signal intensities than normal, with a four-wave-mixing output adhering to theoretically predicted models. The average four-wavemixing power level is -45 dBm at approximately 1565 nm, with a non-linear coefficient of 14 W-1km-1 with chromatic and dispersion slopes of 28.45 ps/nm.km and 3.63 ps/nm2.km. The erbium-doped zirconia fiber is also used in conjunction with gaphene and singlewalled carbon nanotubes based passive saturable absorbers to generate fast and ultrafast pulses is examined. Using a 3 m long ZEr-B with single-walled carbon nanotubes suspended in a polymer host generates Q-switched pulses with a repetition rate of 14.20 kHz and corresponding pulse width of 8.6 μs at a maximum pump power of 141.8 mW, as well as an average pulses output power of 270.0 μW and maximum pulse energy of 19.02 nJ. Using the graphene based saturable absorber gives a 50.1 kHz pulse train with a pulse width, energy and peak power of 4.6 μs, 16.8 nJ and 3.6 mW respectively. When mode-locked, the ZEr-B combined with the graphene based saturable absorber generates ultrafast pulses with an average output power, pulse energy and peak power of approximately 1.6 mW, 23.1 pJ and 31.6 W respectively as well as a pulse width of 730 fs and repetition rate of the pulses is 69.3 MHz. Using the single-walled carbon nanotubes composite as a saturable absorber gives mode-locked pulses with a repetition rate and peak power of 17.74 MHz and 14.09 W as well as average output power of 180 μW and pulse duration of approximately 720 fs at the fullwidth at half maximum point, with a pulse energy of 0.01 nJ. The generated pulses are stable and consistent, and allow them to be deployed with a high degree of confidence and reliability in multiple practical applications

Q-switched erbium-doped fiber laser with molybdenum disulfide (MoS2) nanoparticles on D-shaped fiber as saturable absorber

In this study, short Q-switching laser pulses are generated by drop-casting two-dimensional Molybdenum Disulfide (MoS2) nanoparticles as saturable absorbers (SA) on a side polished optical fiber in a C-band laser cavity. The proposed laser is capable of generating highly stable Q-switched laser pulses at the wavelength of 1559.42nm with a maximum repetition rate of 73.96kHz, and a minimum pulse width of 1.93μs. The relatively high signal-to-noise ratio of 58.7dB indicates a highly stable output. The proposed SA can be applied in a variety of fields due to its ease of manufacturing and cost-effectiveness as well as its robust and compact design. © 2019 World Scientific Publishing Company

Dual characteristics of molybdenum disulfide based PN heterojunction photodetector prepared via drop-cast technique

A p-silicon/molybdenum disulfide (p-Si/MoS2) p-n heterojunction photodetector (PD) is proposed and fabricated using the drop-casting technique. The composition of elements in the localized surface morphology enables for excellent photoconduction under 380 nm illumination at various ultraviolet (UV) powers. The uneven and even distribution of the current-voltage I-V curve in the negative and positive bias regions indicate substantial dual characteristics in the fabricated device. A high responsivity of about 9.6 and 0.388 AW−1 is measured at the negative and positive bias regions respectively, allowing the p-Si/MoS2 p-n heterojunction PD to operate at UV powers lower than 830 μW. © 2019 Elsevier Gmb

Fabrication and characterization of tungsten disulphide/silicon heterojunction photodetector for near infrared illumination

Tungsten disulphide (WS 2 ), a member of the transition metal dichalcogenide (TMD) family that is known for its superior optoelectronic properties is used in this work to fabricate a low cost and highly efficient photodetector for operation in the near infrared (NIR) region. The WS 2 /Si heterojunction photodetector is fabricated using the drop cast method. Sample analysis shows Raman shifts at the E 1 2g and A 1g phonon modes located at 349.84 cm −1 and 419.62 cm −1 , validating the growth of monolayer 2H-WS 2 with a direct bandgap of 2.06 eV. Field emission scanning electron microscope (FESEM) analysis reveals an inhomogeneous surface on the film, while energy-dispersive X-ray (EDX) spectroscopy shows non-stoichiometric WS 2 layer growth on the Si wafer. Current-voltage (IV) measurements are performed in the NIR region with a 785 nm red laser source under dark and illuminated conditions. From the IV measurements, the threshold voltage is determined to be 2.2 V, and the photocurrent is found to be highly dependent on the laser power. The fabricated photodetector has a high responsivity of 10.46 mA/W and detectivity of 1.17 × 10 9 Jones for an incident light intensity of 11.696 mW.cm -2 . These results are promising as an alternative low-cost fabrication method with potential for the development of photovoltaic and optoelectronic applications. © 2019 Elsevier Gmb

85 nm wide-band tunable erbium doped fiber laser using a gallium selenide (GaSe)-based saturable absorber for passive optical modulation

A wide-band and tunable passively optically modulated fiber laser using a gallium selenide (GaSe) based saturable absorber (SA) is proposed and demonstrated. The GaSe-based SA is prepared by mechanical exfoliation and is able to generate self-starting pulses that have a maximum repetition rate of 57.9 kHz and minimum pulse width of 3.6 s. The highest pulse energy generated by the pulse laser is 30 nJ. The laser has wide-band tunability covering a broad wavelength range of 1501 nm to 1586 nm, giving a total tuning range of over 85 nm. The proposed laser would have potential for use in various optical telecommunications and measurement applications. © 2019 Astro Ltd

Infrared photodetectors based on reduced graphene oxide nanoparticles and graphene oxide

Two photodiode (PD) designs incorporating graphene oxide (GO) and reduced graphene oxide (rGO) are proposed and fabricated. Both PDs have 50 mm thick silver electrodes deposited on the active area, and another electrode consisting of either GO or rGO nanoparticles (NPs). The GO and rGO NPs are deposited onto the p-type silicon substrate by the drop casting method. Both fabricated PDs show good sensitivity and quick responses under 974 nm laser illumination at 150 mW. The photoresponsivity values and external quantum efficiency of both photodetectors are measured to be approximately 800 μAw-1 and 0.12% for the GO based PD and 1.6 m Aw-1 and 0.20% for the rGO based PD. Both PDs also have response and recovery times of 114 μs and 276 μs as well as 11 μs and 678 μs for the GO and rGO based PDs respectively. The proposed PDs would have significant applications in many optoelectronic devices as well as nanoelectronics