F. D. Muhammad

Graphene-Oxide-Based Saturable Absorber for All-Fiber Q-Switching With a Simple Optical Deposition Technique

A Q-switched erbium-doped fiber laser (EDFL) incorporating a graphene-oxide-based saturable absorber (SA) is proposed and demonstrated. The SA is fabricated by first dissolving graphene oxide nanopowder in water and subsequently using the thermophoresis effect to deposit it onto the fiber ferrule. The SA is integrated into a ring cavity EDFL, which uses a 3-m-long MetroGain Type-12 erbium-doped fiber (EDF) as the gain medium. The EDFL has a continuous-wave (CW) lasing threshold at a pump power of ~9 mW, with Q-switching behavior observed at pump powers ~18 mW and above. At the maximum pump power of ~100 mW, the Q-switched pulses generated by the EDFL have a repetition rate and pulsewidth of 61 kHz and 6.6 μs, respectively, along with an average output power of about 3.7 mW. Additionally, at the maximum power, the energy per pulse and peak power of the generated pulses are 61.3 nJ and 9.3 mW, respectively.

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.

Graphene-Based Saturable Absorber for Single-Longitudinal-Mode Operation of Highly Doped Erbium-Doped Fiber Laser

In this paper, a conventional wavelength band (C-band) fiber laser with a tunable single-longitudinal-mode (SLM) output using multilayer graphene as a saturable absorber is demonstrated. The proposed fiber laser uses a short length of highly doped erbium-doped fiber (EDF) as the gain medium and a fiber ferrule with graphene flakes adhered to it by index matching gel (IMG) that acts as the saturable absorber. The fiber laser is able to generate an adjustable wavelength output between 1547.88 and 1559.88 nm with an average peak power of -6.48 dBm with a measured signal-to-noise ratio between 66.0 and 68.3 dB. The SLM output is verified by the absence of frequency beating in the radio frequency (RF) spectrum output and by a measured linewidth of 206.25 kHz using the self-heterodyne technique. The deposition of graphene flakes on the fiber ferrule using the IMG is a new and effective technique to generate SLM operation in the fiber laser.

Graphene-Based Mode-Locked Spectrum-Tunable Fiber Laser Using Mach–Zehnder Filter

An ultrafast spectrum-tunable fiber laser using a tunable Mach-Zehnder filter (TMZF) and a graphene-based saturable absorber as a mode-locking element is proposed and demonstrated. The proposed laser uses a 2-m-long zirconia-erbium-doped fiber (Zr-EDF) as the primary gain medium. The Zr-EDF has a dopant concentration of 3800 ppm/wt and an absorption rate of 18.3 dB/m at 980 nm. The proposed laser is able to generate mode-locked solitons, with the central wavelength of the spectrum tunable from 1551 to 1570 nm and covering a wavelength range of about 19 nm. Sidebands are observed with 3-dB bandwidths and pulsewidths of between 3.4 and 3.6 nm and from 730 to 780 fs, respectively, as well as a time-bandwidth product between 0.32 and 0.33. The generated pulse yields an average output power value of ~ 1.4 mW, pulse energy of ~ 128 pJ, and repetition rate of ~ 10.9 MHz. This is the first time, to the knowledge of the authors, that a graphene-based mode-locked spectrum-tunable fiber laser is demonstrated using a TMZF.

Wideband tunable Q-switched fiber laser using graphene as a saturable absorber

An ultra-wide wavelength tuning range, which covers three different band regions consisting of the S-, C-, and L-bands, is proposed and demonstrated for a graphene-based Q-switched erbium-doped fiber laser using a tunable bandpass filter as the wavelength tuning and filtering mechanism. A 3 m length of erbium-doped fiber is used as the gain medium in a ring laser cavity configuration, with absorption coefficients of between 11 and 13 dB m−1 at 980 nm and about 18 dB m−1 at 1550 nm. The tuning range of the Q-switching pulses covers a wide wavelength range of 58 nm, which spans from 1512.5 nm to 1570.5 nm. In addition, the lasing and Q-switching thresholds are considerably low, with respective values of ∼11.0 mW and ∼18.4 mW. A repetition rate of 55.3 kHz is obtained at the maximum pump power of 100.4 mW, together with pulse width and pulse energy of 1.6 μs and 25.8 nJ, respectively.

S-band multiwavelength Brillouin/Raman distributed Bragg reflector fiber lasers.

A multiwavelength Brillouin/Raman distributed Bragg reflector fiber laser operating in the S-band region is proposed and demonstrated. The laser uses a 7.7 km long dispersion-shifted fiber with an effective mode area of 15 μm(2) as the Brillouin and Raman gain media simultaneously. Two 1420 nm laser diodes with a combined power of 372 mW are used as pump sources, while a fiber Bragg grating with a center wavelength of 1500 nm is used as a reflector in the cavity. The setup is capable of generating 6 clearly defined Stokes lines at the highest pump power, spanning from 1499.8 to 1500.3 nm with the even Stokes having relatively higher peak powers, between 1.4 and 3.5 dBm as compared to the odd Stokes, which have peak powers between -4.7 and -5.0 dBm. The output of the laser is very stable and shows little to no fluctuations over a monitoring period of 50 min.

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

This review describes the evolution of dual-wavelength fiber lasers (DWFLs), which provide a simple and cost-effective approach for the optical generation of microwave 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.

Temperature-Insensitive Bend Sensor Using Entirely Centered Erbium Doping in the Fiber Core

A fiber based bend sensor using a uniquely designed Bend-Sensitive Erbium Doped Fiber (BSEDF) is proposed and demonstrated. The BSEDF has two core regions, namely an undoped outer region with a diameter of about 9.38 μm encompassing a doped, inner core region with a diameter of 4.00 μm. The doped core region has about 400 ppm of an Er2O3 dopant. Pumping the BSEDF with a conventional 980 nm laser diode gives an Amplified Spontaneous Emission (ASE) spectrum spanning from 1,510 nm to over 1,560 nm at the output power level of about −58 dBm. The ASE spectrum has a peak power of −52 dBm at a central wavelength of 1,533 nm when not spooled. Spooling the BSEDF with diameters of 10 cm to 2 cm yields decreasing peak powers from −57.0 dBm to −61.8 dBm, while the central wavelength remains unchanged. The output is highly stable over time, with a low temperature sensitivity of around ∼0.005 dBm/°C, thus allowing for the development of a highly stable sensor system based in the change of the peak power alone.

Tunable Radio Frequency Generation Using a Graphene-Based Single Longitudinal Mode Fiber Laser

A novel, simple, and short cavity design of single longitudinal mode (SLM) tunable erbium-doped fiber ring laser using a graphene-based saturable absorber is proposed and demonstrated as a tunable signal source. The SLM output is then mixed with another output signal from a tunable laser source (TLS) to generate tunable radio frequency (RF) signals. The tunable SLM fiber ring laser uses a short length of 1 m highly doped erbium-doped fiber as the gain medium. Graphene is used as a saturable absorber to generate the SLM operation, as opposed to the commonly used unpumped erbium-doped fiber. The tuning range of the fiber ring laser is determined by a tunable fiber Bragg grating, which can be tuned from 1547.88 to 1559.88 nm. A continuous wavelength spacing tuning range of 0.020-0.050 nm is obtained between the output of the SLM fiber ring laser and the TLS which is then mixed in a 6 GHz bandwidth optical-to-electrical convertor. This generates a corresponding RF signal of between 2.4 and 5.9 GHz with a low variation in output power. The current RF signal generation is limited by the frequency bandwidth of the optical-to-electrical convertor.

S-band SLM distributed Bragg reflector fiber laser

Generation of single longitudinal mode operation based on distributed Bragg reflector (DBR) cavity configuration, using a depressed-cladding erbium-doped fiber as the gain medium collectively with fiber Bragg grating (FBG) and Faraday rotator mirror (FRM) performing as the end mirrors, is proposed and demonstrated in this work for operation in the S-band region. The FBG has a central wavelength of 1506 nm, which functions to restrict the lasing frequency. A small line-width value measured at 20 kHz has been achieved in this system. A graph of average pump power against output power establishes the measured slope efficiency at about 0.01%.