Wanzhuo Ma

Wavelength-Spacing Switchable Dual-Wavelength Single Longitudinal Mode Thulium-Doped Fiber Laser at 1.9 μm

We propose and demonstrate a spacing switchable dual-wavelength single longitudinal mode thulium-doped fiber laser at 1.9 μm. The fiber laser employs a ring cavity and a segment of 4-m thulium-doped fiber pumped by a 1563 nm laser. A fiber Sagnac loop is used as a comb filter to generate a stable dual-wavelength laser. A multimode interference filter consisting of a single-mode-multimode-single-mode fiber and a rotary fiber squeezer is used to adjust the wavelength spacing. When pump power is fixed at 260 mW, a stable dual-wavelength laser at 1.9 μm is obtained by adjusting the polarization controller in the Sagnac filter, and the wavelength spacing can be tuned from 6.7 to 26.7 nm by adjusting the rotary fiber squeezer in the multimode interference filter. Each wavelength of the dual-wavelength laser operates at a single longitudinal mode state, and the maximum linewidth is 7.5 MHz analyzed by a Fabry-Perot scanning interferometer.

Tunable ultra-narrow linewidth microwave generation from a double-loop Brillouin fiber laser

A simple photonic approach to generate an ultra-narrow linewidth microwave signal is proposed and experimentally demonstrated. In this scheme, a multi-wavelength Brillouin fiber laser (BFL) with a double-loop and un-pumped polarization maintaining erbium doped fiber (PM-EDF) is used. The double-loop configuration includes a 50 m long single-mode fiber (SMF) and a 10 m long SMF as Brillouin gain. The threshold and linewidth of the microwave source can be improved by using a double loop, while a 4 m long un-pumped PM-EDF is used to suppress unwanted side-modes. A dual-wavelength optical signal is heterodyned at the high-speed photo detector to produce a microwave signal by adjusting the polarization controller and the wavelength of the Brillouin pump. As a result, a tunable microwave signal from 10.605 to 10.887 GHz can be obtained. The linewidth of the microwave signal is about 14.4 kHz, and the side-mode suppression ratio is about 30 dB.

1.9 μm square-wave passively Q-witched mode-locked fiber laser

We propose and demonstrate the operation of Q-switched mode-locked square-wave pulses in a thulium-holmium co-doped fiber laser. By using a nonlinear amplifying loop mirror, continuous square-wave dissipative soliton resonance pulse is obtained with 4.4 MHz repetition rate. With the increasing pump power, square-wave pulse duration can be broadened from 1.7 ns to 3.2 ns. On such basis Q-switched mode-locked operation is achieved by properly setting the pump power and the polarization controllers. The internal mode-locked pulses in Q-switched envelope still keep square-wave type. The Q-switched repetition rate can be varied from 41.6 kHz to 74 kHz by increasing pump power. The corresponding average single-pulse energy increases from 2.67 nJ to 5.2 nJ. The average peak power is also improved from 0.6 W to 1.1 W when continuous square-wave operation is changed into Q-switched mode-locked operation. It indicates that Q-switched mode-locked operation is an effective method to increase the square-wave pulse energy and peak power.

Dual square-wave pulse passively mode-locked fiber laser

We study a passively mode-locked square-wave pulse (SWP) fiber laser with a nonlinear amplifying loop mirror in the cavity. The net dispersion of the cavity is about 0.68  ps2 and the SWP mode-locked fiber laser can be realized. The peak power of the SWP hardly varies and the pulse duration gets expanded with the increasing pump power. SWPs breaking in the low nonlinear cavity can be observed and the stable dual SWP can be achieved in the experiment. When the total pump power stays at 800 mW, the interval of dual pulses is 41 ns. The widths of dual SWPs are both 1.5 ns. The output power rises linearly with the increasing of the pump power, while the interval of dual SWPs is almost constant. Then, the physical mechanism of the SWP breaking and vector nature of the pulse are analyzed.

Triple Brillouin frequency spacing multiwavelength fiber laser with double Brillouin cavities and its application in microwave signal generation

We propose and experimentally investigate a multiwavelength Brillouin fiber laser (MBFL) with triple frequency spacing by employing a modular structure. In this scheme, we obtain nine channels optimized with frequency spacing of 0.259 nm. The single, double, and triple Brillouin frequency spacing for the MBFL can be easily realized by utilizing this modular structure. The impact of Brillouin pump (BP) power, BP wavelength, and erbium-ytterbium-doped fiber amplifier (EYDFA) output power on the performance of the MBFL is investigated, respectively. We also study the generation of beating frequency microwave signals based on single, double, and triple frequency spacing MBFL. 10.5 GHz, 21.48 GHz, and 31.77 GHz microwave signals with 3 dB linewidth of 16.4 MHz, 15.2 MHz, and 12.8 MHz are generated, respectively.

Passively harmonic mode-locked pulses in thulium-doped fiber laser based on nonlinear polarization rotation

Abstract. A simple approach to generate passively harmonic mode-locked pulse trains in thulium-doped fiber laser based on nonlinear polarization rotation is proposed and demonstrated. Three different ways of mode-locked techniques have been employed in our structure to generate passively high-order harmonic mode-locked pulse trains; 128th-order passively harmonic mode-locked pulse train is achieved in the experiment and the repetition rate is 406.8 MHz. With the increase of the pump power, multiwavelength output can be tuned. A segment of dispersion compensation fiber is used to compensate the dispersion in the cavity; thus, the single pulse width is compressed from 617 to 48 ps.

Experimental research on thulium-doped fiber ASE characteristics pumped by 976nm LD

In this paper, a segment of thulium-doped fiber is pumped by a 976nm laser diode.Broadband gain at centerwavelength of 1953nm is achieved. The maximum amplified spontaneous emission bandwidth is 8nm. Simultaneously, self- oscillation of wavelength spacing 0.073nm is observed. The output power and self- oscillation modes increase with pump power increasing and wavelength spacing of self-oscillation is unchanged.The relation between fiber length and output power at pump power 400mW is analyzed. Higher output power can be abtained by selecting a appropriate fiber length when pump power is unchanged. Through the experiment, a weak absorption band of thulium-doped fiber near 976nm is verified. The structure can be used as narrow linewidth broadband source near 1950nm with the characteristic of low cost, simple structure and good stability.