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A tunable dual-wavelength with two separated twin-pulse dissipative solitons (DSs) of Yb-doped mode-locked fiber laser in the all-normal-dispersion (ANDi) regime is firstly reported and demonstrated in this paper. A Sagnac loop is used as an all-fiber format spectral filter in the laser cavity, and stable twin-pulse DSs with different wavelength mode-locked lasers are achieved by the nonlinear polarization evolution (NPE) effect. By adjusting the polarization state of the Sagnac loop, the spectral ranges of the dual-wavelength can be tuned from 1031.3 nm to 1041.5 nm and from 1067.1 nm to 1080.9 nm, respectively. However, the pulse space between the two separated twin-pulse DSs is maintained, i.e., 41.63 ns. Furthermore, the twin-pulse can regress to the single-pulse when the pump power keeps dropping. It has been observed that the highest energy of the two twin-pulse DSs output is 23.36 nJ at a repetition rate of 2.282 MHz with a maximum pump power of 560 mW. [ABSTRACT FROM AUTHOR]

A tunable triple dissipative solitons (DSs) mode-locked laser without a spectral filter in the all-normal dispersion (ANDi) system is reported and demonstrated. The nonlinear polarization evolution (NPE) acted as an artificial bandwidth filter for formatting the pulses with multiple DSs hysteresis phenomenon and adjusting the output wavelength with tuning. The spectral range can be adjusted from 1036.24 to 1043.44 nm, and the temporal distances between adjacent pulses are all equal to 33.9 ns. With the pump power of 560 mW, the highest output energy of the triple DSs is 48.8 nJ at a repetition rate of 2.541 MHz. Besides, the mode-locking states were stabilized during the wavelength tuning process. [ABSTRACT FROM AUTHOR]

A tunable all-fiber optical attenuator (AOA) based on microfiber with adjustable coupling angle is reported and demonstrated. The AOA is fabricated of a microfiber probe coupled to a tapered fiber on the waist region through van der Waals and electrostatic forces. The attenuation can be tuned by adjusting the coupling angle of the two microfibers. When the coupling is fabricated of angles adjust from 8 0 o to 1 0 o , the optical attenuation can be tuned in a large range from 5.7 dB to 40.1 dB with low insertion loss. The simulation and experimental show that the coupling length can be changed by increasing the coupling angle, which results in decreasing the attenuation of AOA. The attenuation of AOA is decreased linearly by increasing the coupling angle. It provides a feasible approach to achieve attenuators with miniature volume, low cost, and multiple functions in optical communication and fiber lasers. • The AOA is fabricated by a microfiber probe coupled to a tapered fiber on the waist region through van der Waals and electrostatic force. • The optical attenuation can be linearly tuned in a large range with low insertion loss by adjusting the coupling angles. • The all-fiber structure of AOA excludes a difficult alignment between end-faces of two fibers and includes an easy connection to SMFs. • The AOA has the advantages of miniature volume, low cost, and multiple functions. [ABSTRACT FROM AUTHOR]

Abstract We have demonstrated the generation of widely tunable spectral multi-wavelength all-normal-dispersion (ANDi) Yb-doped fiber laser based on nonlinear polarization evolution (NPE) as the passively mode-locking mechanism. An easy-controlling tunable passband filter fabricated through a phase-shift long-period grating (PS-LPG) is employed to tune and control the wavelength in the laser cavity. By combining the character of the emission cross section of Yb-doped fiber, the tunable spectral ranges of the dual- and triple-wavelength pulses output is up to ∼20 nm and ∼7 nm, respectively. To our knowledge, it's the widest of tuning spectral range in the both dual- and triple-wavelength ANDi Yb-doped fiber laser with controllable and all-fiber format filter. The proposed method may provide a simple way to obtain a broad spectral range with multi-wavelength output in fiber laser systems. [ABSTRACT FROM AUTHOR]