We propose a novel structure of single-polarization single-mode(SPSM) holey fiber designed based on resonant coupling
effect. The proposed fiber is able to achieve SPSM operation over an ultra-broad bandwidth as large as 920nm ranging
from 1.48μm to 2.4μm, within which only one polarization state of the fundamental mode can be effectively guided.
With the aid of six smaller holes around the central core, the effective mode area of the fiber is enlarged and the
chromatic dispersion curve is flattened. The numerical results indicate that the proposed fiber achieves nearly zero
ultra-flattened dispersion over a wide spectral range and the effective mode area is approaching ~78μm2 at 1550nm.
Moreover, the structure shows superiority in output beam quality owing to the symmetry of the central core region, and
also exhibits great modal compatibility with SMF.
A compact in-fiber Mach-Zehnder interferometer comb-filter is demonstrated by splicing a section of twin-core fiber
(TCF) between two single mode fibers (SMFs). The temperature and strain induced wavelength shifts of the interference
fringes are experimentally monitored. Redshift (i.e., wavelength shifts to the longer wavelength side) is observed with
sensitivity of about 0.037 nm/°C for increased temperature, whereas blueshift (i.e., wavelength shifts to the shorter
wavelength side) is observed with sensitivity of about 0.866 pm/με for applied strain changes. This device is relatively
simple to fabricate and expected to have applications in high temperature or strain fiber optic sensors and the multiwavelength
fiber lasers.
Switchable dual-wavelength fiber laser with photonic crystal fiber (PCF) Sagnac loop and broadband fiber Bragg grating
(BFBG) at room temperature is demonstrated. By adjusting the polarization controller (PC) appropriately, the laser can
be switched between the stable single- and dual-wavelength lasing operations by exploiting polarization hole burning
(PHB) and spectral hole burning effects (SHB).
A vectorial finite element method is adopted to investigate this novel single-mode single-polarization (SPSM) photonic
crystal fiber coupler which has asymmetric dual-core and two lines of enlarged air holes. we demonstrate that the SPSM
region of the designed fiber can be more than 250nm wide for a set of optimized air-hole parameters and show that the
width of the SPSM region could change slightly by little adjustment of the large inner air holes. The coupling length
between the odd and even x-polarization modes are also investigated through fine-tuning the large and small air-hole
diameters.
A highly negative dispersion photonic crystal fibre with less germanium doped core and central index dip is numerically
investigated by fully vectorial finite element method. By adjusting the pitch, the depths and radius of the central index
dip and the diameter of six small air holes in the third ring, Highly negative dispersion value (-1325.5ps/nm.km) and
large mode effective area (71.4um2) DCPCF around the wavelength of 1.55μm is obtained.
A fully vectorial effective index method and multiple-cladding method (FVEIM&MCM) is developed for modeling
photonic crystal fibers. Large negative dispersion photonic crystal fibers can be designed by changing the diameters of
the first, second and third ring of air-holes.
Dual-wavelength with orthogonal polarizations erbium-doped fiber ring laser at room temperature is proposed. One
polarization-maintaining fiber Bragg grating (PMFBG) in a Sagnac loop interferometer is used as the wavelength-selective
filter. Due to the polarization hole burning (PHB) enhanced by the PMFBG, the laser can operate in stable dual-wavelength
operation with wavelength spacing of 0.336 nm at room temperature by adjusting a polarization controller
(PC). The optical signal-to-noise ratio (OSNR) is over 52 dB. The amplitude variation in nearly one and half an hour is
less than 0.6 dB for both wavelengths.
The very high dispersive dual-core photonic crystal fiber is analyzed by the full-vector finite element method. The
dependence of the phase-matching wavelength (PMW) and the full width at half-maximum (FWHM) on the refractive
index of the doped inner core, the diameter of air holes and the hole pitch is demonstrated. The dispersion value is as
large as -1427 ps/(nm km) and the effective mode area of the fundamental mode, 82.06 um2 are obtained.
The temperature dependence of fluorescence in erbium-doped silica fiber between ~-30 and ~150°C is discussed.
980nm pumping configuration is used in our experiment. 1450nm and 1531nm wavelengths are chosen to calculate the
FIR (fluorescence intensity ratio) at the first time instead of the mostly used wavelengths 525nm and 550nm. It shows
that as the temperature increases, the fluorescence intensity increases obviously at short wavelengths but changes a little
at long wavelengths. The temperature coefficient can achieve ~0.023dB/°C, and its resolution is improved as the
temperature decreases. Because there are many effects in our experiments, so it shows a deviation from the behavior of
simulation.
Highly nonlinear fibers with nearly zero flattened dispersion over a wide band range has very wide applications in future
high-capacity, all-optical networks. Because of its flexibility of structure design and much larger index contrast between
the core and effective cladding than the conventional fibers, photonic crystal fibers (PCFs) are becoming to be an
attractive candidate to form this kind of highly nonlinear fibers. Based on quantitative analysis on the effect of the
difference of hole-sizes between the first ring and the other's, and the effect of Ge-doped concentration in the core region
on the PCF's dispersion curve, a new way to design PCF with high nonlinear coefficient and nearly zero flattened
dispersion is proposed. Based on this, a PCF is designed, which has dispersion values between ±0.8ps/nm/km over
S+C+L wavelength bands, and the dispersion slope of 0.005ps/nm2/km, nonlinear coefficient of 46.6W-1km-1 at 1.55μm.
Through introducing two sizes of hole in the cladding of PCF, a kind of highly birefringent two-mode photonic crystal
fiber (PCF) is proposed. Modal properties are analyzed numerically by the plane wave expansion method. Numerical
results demonstrate that only two-mode, i.e. LP01 and LP11even can propagate in the wavelength range from 500nm to
1890nm in the two-mode PCF which is nine times as wide as that in elliptical core fibers. The theory of highly
birefringence two-mode PCF for constituting fiber sensor is also discussed. According to the structure proposed, we
successfully fabricate the highly birefringent two-mode PCF with stack-drawing technique and gas-inert pressurization
control at furnace temperature 1900°C and gas-inert pressure 900pa. They could extend significantly the application
range of these two-mode devices and open up new possibilities.
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