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A multi-wavelength erbium-doped fiber laser based on a Sagnac loop filter which is formed by a birefringent and highly nonlinear photonic crystal fiber (PCF), a 3-dB optical coupler and two polarization controllers is proposed. The PCF Sagnac loop filter is used as a comb filter and power-stabilizing and -equilibrizing component in the multi-wavelength erbiumdoped fiber laser. Stable multi-wavelength lasing at room temperature is achieved, owing to the contributions of both the birefringent property and the four-wave mixing effect of the PCF.Output power, dBm

In this paper, we experimentally demonstrated the fabrication and hydrostatic pressure characteristics of a twin-core photonic crystal fiber (TC-PCF). Mode couplings in the TC-PCF for x- and y-polarizations were analyzed simultaneously using group effective index of guiding modes. The output spectrum of the TC-PCF was modulated due to the combined couplings of the two polarizations. To the best of our knowledge, it is the first time to measure hydrostatic pressure through the dual-polarization mode coupling in a TC-PCF. The measured sensitivity of the pressure sensor was -21 pm/MPa. The length of the TC-PCF used for pressure measurement was 20 cm, which is much shorter than pressure sensor based on PM-PCF, and does not require any external polarizing components, meaning that it is a good candidate for compact pressure sensor.

We propose a kind of novel low-loss Terahertz (THz) waveguide, a polymer tube with a cross section of ring structure. Low-loss property of the polymer tube for THz guiding is achieved due to the effect of the air core inside the polymer tube which traps a large part of mode power and, at the same time, enlarges the mode area of the fundamental mode. Both the polymer tube and a solid polymer fiber are comparatively investigated, considering effective indexes, mode area, power fraction, relative absorption loss and mode profile. Simulation results show that the proposed polymer tube exhibits better loss property and confinement property than the solid polymer fiber. As an example, we finally show the experimentally measured property of a Polytetrafluoroethylene (PTFE) tube.

A novel fiber Bragg grating (FBG) sensing system based on a spectrum-limited Fourier domain mode-locking (SL-FDML) fiber laser is proposed. Multiple FBGs cascaded in a long fiber are utilized as both the sensors in the system and the wavelength-selected components in the SL-FDML fiber laser. Both wavelength-division multiplexing and spatial-division multiplexing techniques are demonstrated for interrogation of multiple FBGs by mapping the wavelength measurement to the time measurement and by adjusting the driving frequency of the SL-FDML fiber laser. The proposed FBG sensing system, employing techniques of the wavelength- and spatial-domain interrogation of multiple FBGs, can be used in remote and quasi-distributed multipoint sensing.

A stable and uniform multi-wavelength fiber laser based on the hybrid gain of a dispersion compensating fiber (as the Raman gain medium) and an Erbium-doped fiber (EDF) is introduced. The gain competition effects in the fiber Raman amplification (FRA) and EDF amplification are analyzed and compared experimentally. The FRA gain mechanism can suppress the gain competition effectively and make the present multi-wavelength laser stable at room temperature. The hybrid gain medium can also increase the lasing bandwidth (as compared with a pure EDF laser) and the power conversion efficiency (as compared with a pure fiber Raman laser).

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A multi-wavelength fiber ring laser of tunable channel spacing is proposed by employing an optical variable delay line (OVDL) in a Mach-Zehnder interferometer. Stable lasing is achieved at room temperature with the hybrid gains of a single mode fiber (as the Raman gain medium) and an Erbium-doped fiber (EDF) in a ring structure. The channel spacing of the present multi-wavelength fiber ring laser can be continuously tuned by adjusting the computer-controlled OVDL.