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.
To develop 1.55μm high power lasers with compactness, narrow spectral line-width and high wavelength stability
suitable for practical applications, EY-DCFLs built in all-fiber configuration are investigated. The experimental setups
are composed of Er3+/Yb3+ co-doped double-clad gain fiber, multimode 976nm pump laser diode, double-clad fiber
Bragg gratings (FBGs) and (1+1)x1 side pump couplers. FBGs with different reflectivity are applied as output
reflectors, and forward-pump scheme and backward-pump scheme are performed respectively. As the efficiency and the
spectral stability are considered simultaneously, EY-DCFL with low reflective FBG mirror and in backward-pump
manner is more desirable. In the optimized all-fiber EY-DCFL, the maximum output power with an optical-optical
efficiency of more than 17% is up to 1.5 W, and the wavelength is defined at 1550.8nm with a line-width about 0.03nm.
We study the quantum interference in three-photon resonant nondegenerate six-wave mixing (NSWM) in a five-level
system in which the middle level of six-wave mixing and other level are coupled by a strong laser field. The coupling
field-dependence of the NSWM signal intensity and the spectrum of the NSWM with a coupling field are discussed. We
find that in the presence of a strong coupling field, the three-photon resonant NSWM spectrum exhibits Autler-Townes
splitting, which reflects the levels of the dressed states. It also leads to either suppression or enhancement of the NSWM
To understand the physical process of SRS lasing in SOI waveguides and to optimize the performance of continuouswave Raman silicon lasers, in this paper numerical simulation on the output characteristics of continuous-wave Raman silicon lasers with different parameters is performed. Based on power propagation equations in SOI waveguides and boundary conditions, the output powers as functions of the launched pump power, the gain length, the reflectivity of the output end, and the effective mode area of the SOI waveguide are presented. It is shown that two-photon absorption (TPA) and free-carrier absorption (FCA) lead to a significant reduction to the output power of continuous-wave Raman silicon lasers, which is in good agreement with the experimental reports. Numerical analysis predicts that in the absence of TPA and FCA there are optimum values for the silicon waveguide length, the effective mode area and the output reflectivity, respectively.
In this paper, we demonstrate the output characteristics of a kind of all-fiber optical source based on Er3+/Yb3+ co-doped double-clad fiber (EY-DCF) in a master oscillator-power amplifier (MOPA) configuration. The amplifier is composed of a 10m long EYDCF, two isolators at both input and output terminals, and a 976nm pump diode connecting with the EYDCF via a side-pump fiber coupler. A DFB diode laser operating at 1547.8nm serves as the master oscillator. A maximum output power of 1.16W is obtained. The gain of the fiber amplifiers is up to 30.7dB. The wavelength centered at 1547.8nm with a spectral width no more than 0.02nm shows longtime stability.
To optimize the performance of Er3+/Yb3+ co-doped double cladding fiber laser (EY-DCFL), the output characteristics of
DBR EY-DCFLs with different parameters are investigated theoretically and experimentally. The output powers as
functions of the launched pump power, the gain fiber length, as well as the reflectivity of the output mirror are presented
by numerical simulation based on rate equations and power propagation equations. Experimental study on the output
power, the spectral properties and the time-domain stability of DBR EY-DCFLs with different reflectivity is carried out.
In the optimum condition, up to 2W output power at 1550.8nm is obtained with a slope-efficiency of 53.8% and a 3dB
bandwidth of about 0.02nm.
The output characteristics of fiber lasers built with large-mode-area(LMA) Yb3+-doped double-clad PCF are
experimentally investigated. The gain fiber used in the experimental setup is a LMA Yb3+-doped double-clad PCF,
which contains an Yb3+-doped core of 23μm in diameter and a holy inner clad of 420μm in diameter. In the forwardoutput
configuration the maximum output is 3.43W and the slope efficiency is 34.6%. At the same pump power, the
maximum output in the backward-output configuration is 3.63W and the slope efficiency is 38%. The spectra show that
the fiber lasers in both forward-output and backward-output configurations produce multi-wavelength output in a range
from 1067nm to 1076nm and unstable. Single wavelength output at 1067.5 nm with a FWHM of about 0.2nm is
demonstrated by using a dual-end-output configuration, and a maximum output of 4.25W with a slope efficiency of
44.1% is obtained.
Wavelength tunable high power lasers are desired for many applications, such as spectroscopy, sensing and nonlinear
optics, etc. A tunable Yb3+-doped photonic crystal fiber laser based on a blazed grating in Littrow configuration is
demonstrated. The active fiber used in the experiment is a double-clad Yb3+-doped PCF which contains an Yb3+-doped
core of 23 μm in diameter and a holy inner clad of 420 μm in diameter. The laser resonator is composed of a dichroic
reflective mirror and a blazed grating which is set in Littrow configuration. To reduce reflection the fiber end near to the
grating is polished into an angle of 8 degree. Wavelength tunable output with a range form 1035.425 nm to 1111.770nm
is realized. The output power of the laser at different wavelengths is flatten within 0.8 dB. At the available maximum
pump power of 12.11 W, the maximum output power of 3.45 W is obtained at 1064.085 nm, which corresponds to a
slope efficiency of 35.9%. Degree of polarization of the output at different pump level are all more than 0.87.
In this paper the SRS characteristic of a phosphorus-doped fiber made for RFLs is experimentally investigated. At an averaged pump power of 0.5W we observe three spectral lines in the output spectrum, which correspond to the first order Stokes of silica at 1.12μm, the third order Stokes of silica or the first order Stokes of P2O5 at 1.24μm, and the fourth order Stokes of silica at 1.31μm, respectively. When the pump power is increased to the maximum value of 2W, there in the spectrum appears a continuum near 1.54μm with a FWHM of more than 50nm. The expected fifth Stokes of silica at 1.39μm and the second Stokes of P2O5 at 1.48μm are not observed. We demonstrate that the fiber loss in the region of 1-1.5μm plays an important role in the development of SRS in phosphorus-doped fibers.
The output characteristics of a large-core double clad fiber (DCF) laser are experimentally investigated in this paper. The fiber laser is fabricated with 5m Yb-doped DCF that consists of a 30μm diameter core and a 400/340μm D-shape inner clad. The measured spectra show that the wavelength of laser is not stable at low pump levels, and the wavelength tends to be stabilized at 1074nm until the pump power is increased to a level far over the threshold. The maximum output power of 7.2W is obtained at an input pump of 11W with a FWHM of about 6nm. The slope efficiency and the total conversion efficiency are 84% and 65.5%, respectively.
An all-fiber Yb-doped double-clad fiber laser based on distributed Bragg reflection (DBR) with fiber Bragg gratings (FBGs) is demonstrated. The single transverse-mode wavelength-stable output at 1 .06 µ m is up to 1.18W, with a slope efficiency of 68% and an optical-to-optical conversion efficiency of more than 50%