We demonstrate an all-fiber figure-eight mode-locked thulium-doped fiber laser with a wide tunable range in both pulsewidth and wavelength. A 45-m-long ultrahigh numerical aperture fiber is used to manage the cavity dispersion, and the net cavity dispersion is calculated to be 0.8585 ps 2 at 1900 nm. With net-normal dispersion, the experimental laser, operating in a dissipative soliton resonance region, generates stable rectangular pulses. The pulsewidth varies from 480 ps to 6.19 ns with the increasing pump power, and its center wavelength has a 28.95-nm tunable range (from 1940.22 to 1969.17 nm) by properly adjusting the polarization controllers. The maximum of average output power and pulse energy is 60.73 mW and 19.51 nJ, respectively. The rectangular pulses have a clamped peak power of about 3.16 W. The wavelength-tunable fiber laser with high-energy output operating at 2 "m has great potential in various application fields.

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Starting from Maxwell's equations and taking the nonlinearity of linear electro-optic effect as a perturbation, we derive general wave coupling equations of quasi-phase-matched (QPM) linear electro-optic effect. And then we use the equations to study the electro-optic effect in PPLN. The numerical results indicate that the QPM condition plays an important role in electro-optic coupling. In addition, the coupling is very sensitive to the temperature and incident light wavelength, but it has a large tolerance to the direction of incident light.

We experimentally report on the soliton dynamics in a passively mode-locked thulium-doped fiber laser based on the nonlinear amplifying loop mirror with all-abnormal dispersion. In fundamental mode-locked regime, stable soliton mode-locked pulses, with central wavelength of 1965.67 nm and repetition rate of 1.72 MHz, have been observed. In addition, by changing the pump power and appropriately rotating the intra-cavity polarization controllers, several distinctive multi-soliton operations and interactions have been observed, such as different types of soliton rain, the release of solitons, the conversion between soliton rain and soliton release, and the emission of quasi-rectangular pulses.

Spin is an intrinsic property of the photon. A method for using an externally applied dc electric field to manipulate the transfer of spin angular momentum of light in an optically active medium is presented. To discuss this, we first develop a wave coupling theory of the mutual action of natural optical activity and the linear electro-optic effect. Besides being used for analyzing the electrically controlled transfer of spin angular momentum of light, the theory can also be used to describe the propagation of light traveling along an arbitrary direction in any optically active medium with an external dc electric field along an arbitrary direction.