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

Modeling and characterization of capacitively coupled interdigital-gated HEMT plasma device for terahertz wave amplification

A capacitively coupled interdigital-gated HEMT structure was used to investigate the occurrence of uniformity of electric field distribution along the structure. The structure was designed and simulated using Commercial Electromagnetic Sonnet Suites software. The return loss characteristics were analyzed and evaluated. The comparison of the admittance characteristics from simulation between dc connected structure and capacitively coupled structure is carried out in order to evaluate electromagnetic wave propagation. This structure kept uniform electric field in the channel when the dc biased is applied to the interdigital gate, which modulates the potential in the channel

Acrylate polymer coated side-polished fiber with graphene oxide nanoparticles for ultrafast fiber laser operation

In this work, a mode-locked fiber laser with a side-polished fiber coated with graphene oxide nanoparticles as a saturable absorber (SA) is proposed and demonstrated. The SA is further coated with an acrylate polymer layer to add strength and durability, thus enabling real-world applications to be realized. The coated SA is capable of generated a pulsed output with a pulse width, pulse energy and pulse peak power of 1.09 ps, 0.013 nJ and 0.012 kW respectively. The cavity has a threshold power of 131.7 mW, and the output signals have a constant signal-to-noise ratio of about 33 dB over a test period of 1 h, indicating a highly stable output. The protective polymer coating allows a simple way to manufacture a rugged device with no penalty to performance

Q-switched dual-wavelength fiber laser using a graphene oxide saturable absorber and singlemode–multimode–singlemode fiber structure

A Q-switched dual-wavelength fiber laser using a graphene oxide-based saturable absorber to generate the desired output pulses is proposed and demonstrated. The system utilizes a singlemode-multimode-singlemode fiber structure to control the net losses in the cavity so that only two dominant wavelengths are allowed to oscillate. The proposed system is capable of generating an output with a high repetition rate of 27.1 kHz and a narrow pulse width of 4.03 μs. The output pulses also have average output power and pulse energy of up to 0.5 mW and 18.5 nJ, respectively. The 1st harmonic obtained has a high signal-to-noise ratio of 33.2 dB, indicating a highly stable pulse output with minimum mode hopping

Tunable graphene-based Q-switched erbium-doped fiber laser using fiber Bragg grating

A graphene-based Q-switched erbium-doped fiber laser (EDFL) with a tunable fiber Bragg grating (TFBG) acting as a wavelength tuning mechanism is proposed and demonstrated. The proposed setup utilizes a newly-developed ‘ferrule-to-ferrule transfer’ technique to obtain a single graphene layer that allows for Q-switch operation in the EDFL using a highly doped-gain medium. A TFBG is used as a wavelength tuning mechanism with a tuning range of 10 nm, covering the wavelength range from 1547.66 nm to 1557.66 nm. The system has a wide repetition rate range of over 206.613 kHz from 1.387 kHz to 208.000 kHz with pulse durations of between 94.80 μs to 0.412 μs. The laser output is dependent on the pump power, with energy per pulse of 4.56 nJ to 16.26 nJ. The system is stable, with power and wavelength variations of less than 0.47 dBm and 0.067 nm. The output pulse train is free from self-mode locking and pulse jitters

2.0- \mu\hbox {m} Q-Switched Thulium-Doped Fiber Laser With Graphene Oxide Saturable Absorber

A compact Q-switched thulium-doped fiber laser (TDFL) operating near the 2.0- μm region is proposed and demonstrated. The proposed laser uses a 2-m-long thulium-doped fiber with a core absorption of 27 dB/m at 793 nm as the active medium and a graphene oxide (GO)-based saturable absorber (SA) as the Q-switching element. The SA is fabricated by optically depositing GO particles dissolved in distilled water onto the face of a fiber ferrule, which is then used to assemble the SA. The proposed TDFL is capable of generating pulses with a maximum repetition rate of 16.0 kHz and pulsewidths as narrow as 9.8 μs, as well as having maximum average output power and pulse energy of 0.3 mW and 18.8 nJ, respectively. The combination of the easily fabricated GO-based SA, together with the TDFL's ability to operate in the eye-safe region of 2.0 μm, gives the proposed Q-switched TDFL a high potential for a multitude of real-world applications, including range-finding, medicine, and spectroscopy

Mode-locked L-band bismuth–erbium fiber laser using carbon nanotubes

A passively mode-locked, bismuth–erbium-co-doped fiber (Bi-EDF) with a pulse width of 460 fs is proposed and demonstrated. A highly doped, 180-cm Bi-EDF with an erbium concentration of 3,250 ppm/wt and an absorption rate of 133 dB/m at 1,530 nm serves as the gain medium. The cavity is 11.6 m long with an overall group velocity dispersion of +0.063 ps2. The output pulses have a repetition rate, average output power, pulse energy and peak power of 11.18 MHz, 5 mW, 448 pJ and 1 kW, respectively. The system has a high beam quality and a narrow pulse width output in the L-band region

Q-switched Zr-EDF laser using single-walled CNT/PEO polymer composite as a saturable absorber

In this work, we propose and demonstrate a compact, Zirconia–Erbium Doped Fiber (Zr-EDF), a new type of fiber with zirconia dopants added to the silica glass host to significantly increase erbium ion concentrations in the glass matrix. Q-switched behavior is obtained by using a Single-Walled Carbon Nanotube/Polyethylene Oxide composite sandwiched between two fiber ferrules as a saturable absorber. The Zr-EDF fiber laser has a nearly flat amplified spontaneous emission spectrum from 1545 to 1565 nm, unlike conventional erbium doped fibers. The pulse train generated has a maximum repetition rate and pulse width of 14.20 kHz and 8.6 μs respectively. The highest average output power of the system is 270.0 μW, with a corresponding pulse energy of 19.02 nJ. The proposed system is compact, cost-effective and rugged and has applications in range-finding, medicine and in industry

Q-switched fibre laser using 21 cm Bismuth-erbium doped fibre and graphene oxide as saturable absorber

A compact, Q-switched fibre laser is proposed and demonstrated using a compact Bismuth-based erbium doped fibre (Bi-EDF) together with a Graphene Oxide (GO) Saturable Absorber (SA). The 21 cm long Bi-EDF has an erbium dopant concentration of 6300 ppm with absorption rates of about 83 and 133 dB/m at 1480 and 1530 nm. The SA is fabricated from graphene flakes dissolved in water, forming a GO film that is sandwiched between two FC/PC connectors. The Q-switched Bi-EDF laser has an Amplified Spontaneous Emission (ASE) spectrum of 120 nm, stretching from 1490 to 1610 nm and a Q-switching threshold power of about 65 mW. At the maximum pump power of 118 mW, the pulses are generated with an average output power and pulse energy of 0.11 mW and 4.3 nJ, with a repetition rate and pulse width of 27.2 kHz and 7.7 μs. The output can be tuned over the amplified spontaneous emission spectrum with an average peak power of about −16.8 dBm, and observation under a radio frequency spectrum analyser shows a highly stable output at 21.8 kHz. The proposed Bi-EDF laser will have substantial uses in applications requiring short and stable pulses such as rangefinding and sensing

A new compact micro-ball lens structure at the cleaved tip of microfiber coupler for displacement sensing

A compact micro-ball lens structure is fabricated at the cleaved tip of microfiber coupler (MFC) waist for displacement sensor application. The MFC is made by fusing and tapering two optical fibers using a flame brushing technique. It is then cleaved at the center of the minimum waist region. Then a micro-ball lens is formed at the tip of the microfiber by an arcing technique using a fusion splicing machine. The proposed displacement sensor uses the micro-ball lens as a probe and a reflector as a target. As the target is moved from the micro-ball lens, an interference fringe is obtained due to the interference between two reflected beams from the micro-ball lens and the reflector. At the smallest displacement of 0.6 mm, the output spectrum shows the interference fringes with highest extinction ratio and largest free spectral range (FSR). Both extinction ratio and FSR reduces following the power trend line with correlation coefficient of 0.99 as the displacement increases. The Q resonant factor of the comb spectrum increases from 1628 to 38,286 as the displacement increases from 0.6 to 3.6 mm