Arman Zarei

Nonlinear Polarization Rotation-Based Mode-Locked Erbium-Doped Fiber Laser with Three Switchable Operation States

A simple mode-locked erbium-doped fiber laser (EDFL) with three switchable operation states is proposed and demonstrated based on nonlinear polarization rotation. The EDFL generates a stable square pulse at a third harmonic pulse repetition rate of 87 kHz as the 1480 nm pump power increases from the threshold of 17.5 mW to 34.3 mW. The square pulse duration increases from 105 ns to 245 ns as the pump power increases within this region. The pulse operation switches to the second operation state as the pump power is varied from 48.2 mW to 116.7 mW. The laser operates at a fundamental repetition rate of 29 kHz with a fixed pulse width of 8.5 μs within the pump power region. At a pump power of 116.7 mW, the average output power is 3.84 mW, which corresponds to the pulse energy of 131.5 nJ. When the pump power continues to increase, the pulse train experiences unstable oscillation before it reaches the third stable operation state within a pump power region of 138.9 mW to 145.0 mW. Within this region, the EDFL produces a fixed pulse width of 2.8 μs and a harmonic pulse repetition rate of 58 kHz.

Analytical Model for Broadband Thulium-Bismuth-Doped Fiber Amplifier

Due to the tremendous growth in applications for fiber laser in medical science, sensor solution, and light detection and ranging system at 1.8 to 2-μm region, more research efforts have been directed toward developing highly efficient broadband fiber amplifiers in this range. In order to amplify this region, Thulium-Bismuth-doped fiber amplifier (TBDFA) is proposed in conjunction with 800-nm pumping. Optimal Thulium ion concentration of 4.17 × 1026 ion/m3 and Bismuth ion concentration of 2.08 × 1026 ion/m3 together with low phonon energy of germanate glass lead to the highest energy transfer rates. Effective energy transfer mechanism from Bismuth to Thulium in addition to the cross relaxation process between Thulium ions results in higher amplification, efficiency, and super broadband amplification in TBDFA. We analytically solve the rate equations of TBDFA including the effect of energy transfer in order to calculate the broadband amplifier gain.

Multi-wavelength Q-switched Erbium-doped fiber laser with photonic crystal fiber and multi-walled carbon nanotubes

A simple multi-wavelength passively Q-switched Erbium-doped fiber laser (EDFL) is demonstrated using low-cost multi-walled carbon nanotubes (MWCNTs)-based saturable absorber, which is prepared using polyvinyl alcohol as a host polymer. The multi-wavelength operation is achieved based on non-linear polarization rotation effect by incorporating 50 m long photonic crystal fiber in the ring cavity. The EDFL produces a stable multi-wavelength comb spectrum for more than 14 lines with a fixed spacing of 0.48 nm. The laser also demonstrates a stable pulse train with the repetition rate increasing from 14.9 to 25.4 kHz as the pump power increases from the threshold power of 69.0 mW to the maximum pump power of 133.8 mW. The minimum pulse width of 4.4 μs was obtained at the maximum pump power of 133.8 mW while the highest energy of 0.74 nJ was obtained at the pump power of 69.0 mW.

Proposal and performance evaluation of an efficient RZ-DQPSK modulation scheme in all-optical OFDM transmission systems

A return-to-zero differential quadrature phase-shift keying (DQPSK) modulation scheme is proposed for all-optical orthogonal frequency-division multiplexing transmission systems. The system uses coupler-based inverse fast Fourier transform/fast Fourier transform to support a 700 km single-mode fiber link and a transmission rate of 40 Gb/s without any nonlinear compensation. The performance of the proposed system is evaluated using simulation and four performance measures are obtained, namely, the eye diagram, the eye-opening penalty (EOP), the power spectral broadening, and the bit error rate(BER). The effect of self-phase modulation is taken into account in the performance evaluation. In addition, the performance of the proposed system is compared to that of a traditional one adopting a non-return-to-zero DQPSK scheme. Our results reveal that the proposed system outperforms the traditional one in all four aforementioned performance measures, yet the spectral efficiency is almost preserved. Specifically, for an input average power of 12 dBm, a reduction in both the required optical-signal-to-noise ratio of about 4 dB (to achieve a BER of 10-6) and the EOP of about 5 dB are reported when adopting the proposed system, as compared to the traditional one.

Investigation of spontaneous Brillouin scattering generation based on non-adiabatic microfibres

Brillouin Stokes and anti-Stokes generation is successfully demonstrated in backward direction using a non-adiabatic microfibre as the gain medium. The Stokes light wavelength is up-shifted by 0.088 nm (10 GHz) from the BP wavelength as monitored by using an optical spectrum analyzer. The Brillouin scattering can also be enhanced by employing a microfibre based inline Mach–Zehnder interferometer (IMZI) as the gain medium due to its stronger multimode interference effect. It is shown that the microfibre geometry plays an important role in the spontaneous Brillouin scattering generation and gain bandwidth broadening due to its effect on irritation of the acoustic modes inside the microfibre.

Q-Switching Pulse Generation with Thulium-Doped Fiber Saturable Absorber

A simple Q-switched erbium-doped fiber laser (EDFL) is proposed and demonstrated by using a 2-m-long thulium-doped fiber (TDF) as a passive saturable absorber (SA). The EDFL generates a Q-switching pulse operating at 1557.6 nm at a threshold pump power as low as 20.0 mW. The Q-switching operation is maintained before disappearance when the pump power is above 33.7 mW. This is due to the fact that the TDF SA could not fully recover in time after a pulse and less gain population is excited before the next pulsing. With the SA, the laser produces a stable pulse train with repetition rate ranging from 3.9 to 12.7 kHz and the pulse width reduces from 20.6 to 7.4 μs while varying the 1480 nm pump power from 20 mW to 33.7 mW. The maximum pulse energy of 22.8 nJ is obtained at a pump power of 20.0 mW. The laser is perspective for technology processes and medicine.

Generation of Q-Switched Mode-Locked Erbium-Doped Fiber Laser Operating in Dark Regime*

We demonstrate a stable Q-switched mode-locked erbium-doped fiber laser (EDFL) operating in dark regime based on the nonlinear polarization rotation technique. The EDFL produces a pulse train where the Q-switching envelope is formed by multiple dark pulses. The repetition rate of the Q-switched envelope can be increased from 0.96 kHz to 3.26 kHz, whereas the pulse width reduces from 211 μs to 86 μs. The highest pulse of 479 nJ is obtained at the pump power of 55 mW. It is also observed that the dark pulses inside the Q-switching envelope consist of two parts: square and trailing dark pulses. The shortest pulse width of the dark square pulse is obtained at 40.5 μs when the pump power is fixed at 145 mW. The repetition rate of trailing dark pulses can be increased from 27.62 kHz to 50 kHz as the pump power increases from 55 mW to 145 mW.

Fundamental and harmonic soliton mode-locked erbium-doped fiber laser using a single-walled carbon nanotubes embedded in poly (ethylene oxide) film saturable absorber

This paper presents a simple, compact and low cost mode-locked Erbium-doped fiber laser (EDFL) using a single-walled carbon nanotubes (SWCNTs) embedded in poly(ethylene oxide) (PEO) film as a passive saturable absorber. The film was fabricated using a prepared homogeneous SWCNT solution, which was mixed with a diluted PEO solution and casted onto a glass petri dish to form a thin film by evaporation technique. The film, with a thickness of 50 μm, is sandwiched between two fiber connectors to construct a saturable absorber, which is then integrated in an EDFL cavity to generate a self-started stable soliton pulses operating at 1560.8 nm. The soliton pulse starts to lase at 1480 nm pup power threshold of 12.3 mW to produce pulse train with repetition rate of 11.21 MHz, pulse width of 1.02 ps, average output power of 0.65 mW and pulse energy of 57.98 pJ. Then, we observed the 4th, 7th and 15th harmonic of fundamental cavity frequency start to occur when the pump powers are further increased to 14.9, 17.5 and 20.1 mW, respectively. The 4th harmonic pulses are characterized in detail with a repetition rate of 44.84 MHz, a transform-limited pulse width of 1.19 ps, side-mode suppression ratio of larger than 20 dB and pulse energy of 9.14 pJ.

Brillouin Lasing with a Reduced Self-Pulsing Characteristic Using a Short-Length Erbium-Doped Fiber as the Nonlinear Gain Medium

A single-wavelength Brillouin laser is demonstrated by using a 3-m-long erbium doped fiber (EDF) in a ring cavity. The EDF is used to provide both nonlinear and linear gains to generate a stimulated Brillouin scattering (SBS) and to amplify the generated SBS, respectively. The Brillouin erbium fiber laser (BEFL) operates at 1561.5 nm, where the operating wavelength is up-shifted by 0.08nm from the Brillouin pump. The operation wavelength is also tunable within 1560.6–1562.6 nm. The BEFL also shows a self-pulsing characteristic with repetition of 66.7 kHz when the BP is set around the threshold pump power of 13mW. Compared to the conventional Brillouin fiber laser with a long cavity length, the proposed BEFL exhibits a significantly lower amplitude of pulse. This laser has many potential applications, such as in optical communication and sensors.

System tolerance of NRZ-DQPSK all-optical OFDM in long-haul transmission system using DCF

This paper presents the analysis of a coupler based NRZ-DQPSK all-optical orthogonal frequency division multiplexing system with a rate of 80 Gb/s. The transmission line used is SSMF that is over 1000 km long with 21 km DCF for each span. The performance of the system is characterized in terms of BER, eye diagram and Q values. The power tolerance of the system as a function of fiber dispersion is also surveyed.