Ting Feng

A multiwavelength thulium-doped silica fiber laser incorporating a highly nonlinear fiber

A multiwavelength Tm3+-doped silica fiber laser incorporating a highly nonlinear fiber is presented. In the laser cavity, a nonlinear polarization rotation (NPR) based fiber loop mirror is used to overcome the mode competition and a polarization-maintaining fiber Sagnac loop mirror is used as the filter. The 150 m highly nonlinear fiber can improve the NPR effect in the laser cavity, which can increase the number of output channels. By adjusting the polarization state of the polarization controllers properly, stable multiwavelength operation at the 2 μm spectrum can be obtained at room temperature. It can achieve 15 output channels within a 10 dB bandwidth from 1990 to 2007.5 nm. The channel spacing of the multiwavelength Tm3+-doped silica fiber laser is 1.22 nm. Moreover, the performance of the laser is investigated for different pump powers and fibers.

Switchable and tunable dual-wavelength single-longitudinal-mode erbium-doped fiber laser with special subring-cavity and superimposed fiber Bragg gratings

A switchable and tunable dual-wavelength single-longitudinal-mode (SLM) erbium-doped fiber laser (EDFL) has been proposed and demonstrated. Two superimposed fiber Bragg gratings (SI-FBG) have been used as one original wavelength selection component. A special subring-cavity was employed to select the SLM. By properly adjusting a polarization controller, single- and dual-wavelength switchable operations with high wavelength and power stability were realized experimentally. Regardless of which work mode, the signal to noise ratio was higher than 60 dB and the polarization extinction ratio was higher than 20 dB. The wavelength-spacing was 9.96 nm, indicating that it can be used to generate continuous-wave terahertz waves. The linewidth of each lasing wavelength measured by the delayed self-heterodyne method was approximately 1.25 kHz and 1 kHz, respectively. By stretching the SI-FBG, the EDFL had a wavelength-tunable range of 5.96 nm in both the single- and dual-wavelength operations.

Widely tunable single-/dual-wavelength fiber lasers with ultra-narrow linewidth and high OSNR using high quality passive subring cavity and novel tuning method

High stability single- and dual-wavelength compound cavity erbium-doped fiber lasers (EDFLs) with ultra-narrow linewidth, high optical signal to noise ratio (OSNR) and widely tunable range are demonstrated. Different from using traditional cascaded Type-1/Type-2 fiber rings as secondary cavities, we nest a Type-1 ring inside a Type-2 ring to form a passive subring cavity to achieve single-longitudinal-mode (SLM) lasing with ultra-narrow linewidth for the first time. We also show that the SLM lasing stability can be further improved by inserting a length of polarization maintaining fiber in the Type-2 ring. Using a uniform fiber Bragg grating (FBG) and two superimposed FBGs as mode restricting elements, respectively, we obtain a single-wavelength EDFL with a linewidth as narrow as 715 Hz and an OSNR as high as 73 dB, and a dual-wavelength EDFL with linewidths less than 1 kHz and OSNRs higher than 68 dB for both lasing wavelengths. Finally, by employing a novel self-designed strain adjustment device capable of applying both the compression and tension forces to the FBGs for wavelength tuning, we achieve the tuning range larger than 10 nm for both of the EDFLs.

Switchable 10 nm-spaced dual-wavelength SLM fiber laser with sub-kHz linewidth and high OSNR using a novel multiple-ring configuration

A switchable dual-wavelength (10 nm spacing) single-longitudinal-mode (SLM) erbium-doped fiber laser (EDFL) that uses a multiple-ring configuration was demonstrated experimentally. A novel theoretically lossless triple-ring passive secondary cavity composed of three optical couplers was utilized to select the SLM from the dense main cavity longitudinal modes for the first time. Using two superimposed fiber Bragg gratings as one compact mode-restricting element and introducing the nonlinear polarization rotation effect to alleviate the strong mode competition for the fiber laser, a highly stable dual-wavelength mode-hop-free SLM operation with sub-kHz linewidths and optical signal to noise ratios (OSNRs) of >69 dB was achieved for both lasing wavelengths. By adjusting the polarization controllers, the dual-wavelength operation could be easily switched to single-wavelength lasing with a linewidth of 72 dB. The proposed EDFL may find many important applications, such as the generation of very pure terahertz waves.

Demonstration of distributed fiber-optic temperature sensing with PM fiber using polarization crosstalk analysis technique

Polarization crosstalk is a phenomenon that the powers of two orthogonal polarization modes propagating in a polarization maintaining (PM) fiber couple into each other. Because there is certain mathematical relationship between the polarization crosstalk signals and external perturbations such as stress and temperature variations, stress and temperature sensing in PM fiber can be simultaneously achieved by measuring the strengths and locations of polarization crosstalk signals. In this paper, we report what we believe the first distributed temperature sensing demonstration using polarization crosstalk analysis in PM fibers. Firstly, by measuring the spacing changes between two crosstalk peaks at different fiber length locations, we obtained the temperature sensing coefficient (TSC) of approximately −0.73 μm/(°C•m), which means that the spacing between two crosstalk peaks induced at two locations changes by 0.73 μm when the temperature changes by 1 °C over a fiber length of 1 meter. Secondly, in order to bring different temperature values at different axial locations along a PM fiber to verify the distributed temperature sensing, four heating-strips are used to heat different fiber sections of the PM fiber under test, and the temperatures measured by the proposed fiber sensing method according to the obtained TSC are almost consistent with those of heating-strips measured by a thermoelectric thermometer. As a new type of distributed fiber temperature sensing technique, we believe that our method will find broad applications in the near future.