A CCD fiber Bragg grating sensor demodulation system based on FPGA is proposed. The system is divided into three
units: spectral imaging unit, signal detection unit and signal acquisition and processing unit. The spectral imaging unit
uses reflective imaging system, which has few aberration, small size, simple structure and low cost. In the signal
detection unit, information of spectrum are accessed by CCD detector, the measurement of spectral line is converted into
the measurement of the pixel position of spot, multi point can be simultaneously measured, so the system's reusability,
stability and reliability are improved. In the signal acquisition and processing unit, drive circuit and signal acquisition
and processing circuit are designed by programmable logic device FPGA, fully use of programmable and high real-time
features, simplified system design, improved the system's real-time monitoring capabilities and demodulation speed.
Double-grating coupler based on two fiber Bragg gratings(FBGs) has the advantages of compact structure and enhanced
filtering efficiency. The influences of different gratings' position in the coupling region and grating length on the
filtering spectra were investigated based on the unified coupled-mode theory. The results show that, the coupling region
on the left of the graing mostly affects the drop channel characteristic;the length of the grating mostly affects the drop
efficiency;the transmission characteristic is best with the whole length of the coupling region Lc integral multiple of
coupling lengthπ /(2Kf ) .A coupler with uniform coupling region making of two photoconductive fibers was fabricated
by improved fused taper technology,then two Bragg gratings were written in the coupling region with 248nm ultraviolet
laser, and a grating reflecton coupler with maximum drop reflectivity 20dB and bandwidth 0.8nm was achieved.
The unified coupled-mode formalism derived from Maxwell's equation is employed to analyze the add/drop filters using
a Bragg grating assisted mismatched coupler. An add/drop filter using a Bragg grating-assisted mismatched coupler is
fabricated and tested. The maximum reflectivity, 3dB bandwidth, insert loss at the drop port and reflective loss at the
input port of the filter are measured to be about 12 dB, 0.2 nm, 3.91 dB and - 7.39 dB, respectively.
The unified coupled-mode formalism derived from Maxwell's equation is employed to analyze the add/drop filters using
a Bragg grating assisted mismatched coupler. By writing a linearly chirped Bragg grating over the uniform coupling
region of the coupler, a filter with maximum reflectivity and 3dB bandwidth at the drop port about 20 dB and 0.8 nm,
respectively, is obtained. The experimentally measured results are in good agreement with the numerical calculations. A
broadband add/drop filter using a Bragg grating-assisted mismatched coupler can be obtained by writing a linearly
chirped Bragg grating over the uniform coupling region of the coupler.
A simple multi-wavelength erbium-doped fiber laser with narrow-line-width lasing output was proposed and
demonstrated using fiber Bragg gratings and Arrayed-Waveguide Gratings (AWG). Wavelength competition was
naturally prevented in this kind of laser by using AWG in the linear-cavity. As an example, a triple-wavelength erbium-doped
fiber laser was experimentally investigated. Using the laser scheme, the proposed laser can laser three
wavelengths simultaneously. The fiber laser retrieved the optical side-mode suppression ratio of over 50dB and the
average output power of -10.714, -10.649 and -10.578dBm at 1554.710, 1555.516 and 1556.421nm, respectively. And
the 3-dB bandwidth of each laser was less than 0.010nm. Moreover, the output power stability of the laser had also been
measured and analyzed. Experiment results showed that the laser can be operated stably in narrow-line-width with
single- and triple-wavelength output at room temperature.
Influence of stress area mismatched Panda erbium-doped polarization-maintaining fibre on the birefringence is analyzed
and compared by finite element method and approximate analytical expression educed by the complex variable method
of elasticity with superposition techniques.
A new method of fabricating Panda-type photosensitive polarization-maintaining erbium-doped fiber(PM-EDF) is
proposed and demonstrated. A sample of PM-EDF is fabricated using this method and an exhaustive analysis is made
about the characteristics of PM-EDF, the results shows that this method is practicable. Two fiber Bragg Gratings (FBGs)
are written into PM-EDF directly as the lasers reflectors, a three-states-tuned fiber laser is then obtained using a
polarization controller (PC).
The finite element method is applied for solving the modal field of erbium-doped hole-assisted lightguide fiber
(EDHALF). The modified average population inversion iteration method is proposed for simulating the gain coefficients
of EDHALF amplifiers. The relation between the structural parameters of EDHALFs and the gain coefficient of L band
EDHALF amplifiers is investigated by means of the finite element method combined with the modified average
population inversion method. Four structural parameters of EDHALF-core diameter, the refractive index difference
between the core and silica cladding, the relative hole-to-core spacing and the relative size of air holes are optimized in
terms of the design criteria of L band erbium-doped fiber, which take into account the cutoff wavelengths, the gain
coefficients of L band fiber amplifiers and the splice loss between the EDHALF and the conventional single-mode fiber.
At last, the comparisons between the EDHALF and the conventional erbium-doped fiber for L band applications are
made.
A novel design of M-Profile Ytterbium doped Fibers (YDFs) for high power fiber Lasers was given. The output power
was two times higher than that in standard double-cladding fiber under the same threshold of damage.
A linear cavity photonics crystal fiber (PCF) laser has been fabricated. The
home-made polarization-maintaining PCF is acted as active material, and
polarization-maintaining fiber Bragg grating (PMF-FBG) is used as filter. The stabile
two-wavelength laser, which has high degree of polarization (DOP), has been exported. The
output power is 0.3mW, and DOP is about 98%. In this paper, we discuss the characteristics
of PCF laser and PMF-FBG. in detail.
The dispersion properties of the index-step higher order mode dispersion-compensating fibers (HOM-DCFs) are
simulated using an unequal interval finite difference method in this paper. Large negative dispersion of the first few
higher order modes (HOMs) near cutoff are studied comparatively, which is helpful for designing the dispersion
compensator based HOM-DCFs.
The relationship between the gain flatness performances with the pump wavelength spacing in single-stage backward-pumped
distributed fiber Raman amplifiers (B-DFRAs) were demonstrated theoretically. It was shown that the gain
spectrum of B-DFRA which pump wavelengths were arranged in a geometric proportion interval sequence were flatter
than one which pump wavelengths were arranged in an equal interval sequence in the same conditions.
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