Active Q-switched Fiber Lasers with Single and Dualwavelength Operation

A brief explanation on Q-switched fiber laser operating principle for active technique in terms of operation characteristics is presented. Experimental analysis of proposed pulsed fiber lasers by the active Q-switched technique is demonstrated. Experimental setups include the use of Er/Yb doped fiber as a gain medium and an acousto-optic modulator as cavity elements. Setup variations include the use of fiber Bragg gratings for wavelength selection and tuning and Sagnac interferometer for wavelength selection in single wavelength operation and for cavity loss adjustment in dual wavelength operation. The experimental analysis of principal characteristics of single-wavelength operation of the fiber laser and cavity loss adjustment method for dual-wavelength laser operation are discussed

Compact Narrow Linewidth Actively Q-Switched Er–Yb Double-Clad Fiber Laser

Abstract: Actively Q-switched laser operation of a narrow linewidth compact fiber laser based on an Er–Yb double-clad fiber is presented. The laser linewidth as a function of the repetition rate and the Q-switched pulses characteristics for different pump powers are experimentally analyzed. Stable Q-switched laser operation with spectral laser linewidth of 73 pm in a repetition rate range from 90 to 270 kHz is obtained. The minimum pulse duration of 178 ns, maximum peak power of 30.5 W, and maximum pulse energy of 5.4 µJ are observed. The maximum average power reached is 1.1 W. Keywords: fiber lasers; Q-switched lasers; Er–Yb double-clad fiber; fiber Bragg grating

Stimulated Raman Scattering for All Optical Switches

We theoretically and experimentally investigate an all optical switch based on stimulated Raman scattering in optical fibers. The experimental setup consists of a Raman circuit of two stages connected in series through a bandpass filter. In the first stage, we have a saturated amplifier, in this stage the pump pulses are saturated when pump and signal are launched to the input or the pump pulses remain without saturation when pump only is launched at the input. The second stage works as the Raman amplifier; for this stage amplification is directly dependent on the pump power entering from the first stage. For the case when pump pulse only is launched at the input pass to the second stage without saturation and amplifies the signal entering in the second stage, very intense signal pulses appear at the output of this stage. For the case when both pump and signal pulses are launched to the input, the pump pulse is saturated in the first stage and the filter rejected the amplified signal, so that only low power pump enters the second stage and consequently no signal pulses appear at the output. We show that the contrast can be improved when using fibers with normal and anomalous dispersion connected in series in the first stage. The best contrast (the ratio of energies) obtained was 15 dB at 6 W pump peak power

Experimental Investigation of Self-Starting Operation in a F8L Based on a Symmetrical NOLM

We experimentally analyze the self-starting operation of a figure-eight mode-locked fiber laser. The design is based on a power-balanced nonlinear optical loop mirror (NOLM) with highly twisted low-birefringence fiber and a quarter-wave (QW) retarder in the loop. The NOLM operates by nonlinear polarization rotation. Self-starting mode-locking requires a careful adjustment of the NOLM low-power transmission, which is easily realized with our setup by adjusting the angle of the QW retarder. The laser is capable of generating ∼20 ps pulses at the fundamental repetition frequency of 0.78 MHz

Mmi Filters Configuration For Dual-Wavelength Generation In A Ring Cavity Erbium-Doped Fibre Laser

Background: Dual wavelength laser generation has been of constant interest due to their applications in optical communications and teraheartz generation. A novel configuration for Dual-wavelength laser generation based on the use of a couple of multimode interference (MMI) filters is demonstrated in a ring cavity Erbium-doped fibre laser. Methods: The MMI filters consist of a segment of no-core fibre spliced between two SMF-28 single mode fibre segments. The MMI filters configured as a Mach-Zehnder interferometer, are used as transmission spectral filters for simultaneous generation of two laser wavelengths. An optical attenuator is used to adjust the intra-cavity losses for dual-wavelength laser generation. Results: Laser emission at 1540.4 and 1554 nm for a wavelength separation of ~13.6 nm is obtained. The laser wavelengths output power stability variations with the applied pump power is also experimentally discussed. Conclusions: The use of MMI filters in the proposed dual-wavelength laser filter is experimentally demonstrated as a reliable device for dual-wavelength generation in fibre lasers