The polarization maintaining fiber has been playing an important role in the fields of optical fiber sensing, communication, and so on. The beat length is one of the main parameters of polarization maintaining fiber, and it usually represents its polarization maintaining performance. In this paper, the beat length variation of Panda fiber with external force is investigated. The simulation results indicate that the beat length variation was determined both by the external force value F and the angle θ between the external force direction and the slow axis of Panda fiber. When F is a constant, the beat length of polarization maintaining fiber is changed in sinusoidal form whose various cycle is π with the variation of θ. Meanwhile, the minimum and maximum values of beat length will be obtained when the angles are even multiple of π/2 or odd multiple of π/2, respectively. When θ is a constant, the beat length is changed in linear form with the increasing of external force value. Finally, the experimental system of beat length measurement based on Sagnac interferometer loop is illustrated, and the result shows an excellent agreement with the theoretical analysis.
A novel method of narrow line-width Er3+-doped fiber ring laser based on FBG F-P etalon and FBG Sagnac loop is
presented in this paper. The all-fiber single frequency and narrow line-width Er3+-doped fiber ring laser has been
designed in which two 976 nm laser diodes are used as the pump sources, the high concentration Er3+-doped fiber as the
gain medium, the fiber Faraday rotator is adopted to eliminate the spatial hole burning effect, the FBG F-P etalon and
FBG Sagnac loop filter can discriminate and select laser longitudinal modes efficiently. The experiment system using 3m
long Er3+-doped fibers is presented, when the maximum pump power of two 976nm laser diodes is 146mW, the fiber
laser exhibits 16mW threshold and stable single frequency 1550nm laser with the output powers of 45mW is acquired,
and the slope efficiency is about 34.6%. The 3dB line-width is less than 9.3 kHz, measured by the delayed selfheterodyne
method with 15km single-mode fiber, and no mode hopping is observed. The fiber laser has the advantages
of simple structure, high efficiency and high reliability and it has great potential applications in the fields of optical fiber
sensing system.
How to determine the parameters of thin film precisely and rapidly becomes more and more important. In this paper, a
new method based on reflectance spectrum combining complex-shape method to determine multi parameters of thin film
simultaneously by dwindling the polyhedron is first presented. On the one hand, this new method fix out the problem of
multiple solutions well. On the other hand, for there is no dependence on interferential spectrum and transparent area, the
method can be applied to diverse sorts of reflectance spectrum with a fast speed, nice convergence, and high precision. In
the meantime, the metrology system based on this method is built up and measured experiment for standard thin film
sample is implemented also. Comparing the measured results to the standard values of the standard thin film sample, the
results show that the error degree is about ± 3%. The experimental results prove this method has a nice application
value.
Self- and cross-phase modulation (SPM, XPM) in fiber is expected to play a major role in ultrafast all-optical analog-todigital
conversion(ADC), which can overcome the obstacles of inherently limited operating speed of electronic ADC. In
this paper, we propose an optical quantizing and coding method for all-optical ADC based on asymmetrical nonlinear
optical-loop mirrors . The multiperiod transfer function, which is the key to quantizing and coding, is achieved through a
careful design of the asymmetrical nonlinear optical-loop mirrors. We conducted proof-of-principle numerical simulation
and successfully demonstrated 3-bits all optical ADC with Gray code output, it is ready for experiments in future. The
proposed optical quantizing and coding, combined with existing optical sampling techniques, will enable ultrafast
photonic ADC without electronics.
In this paper, an early warning monitoring system for landslides, based on high spatial resolution distributed fiber optic
stress sensing and monitoring the intra-stress distribution and changes in landslide bodies, was first presented. The
principle of distributed fiber optic stress sensing and the monitoring method for landslides were described in detail.
Through measuring the distributed polarization mode coupling in the polarization-maintaining fiber, the distributed fiber
stress sensor with stress measuring range 0-15Mpa, 10cm spatial resolutions and measuring range 0.5km, was designed.
The warning system was investigated in detail through the field test also.
A novel method for direct optical detection of spontaneous Brillouin scattering in optical fiber by using a fiber Bragg
grating (FBG) Sagnac loop is introduced. The transmission character as an optical filter of FBG Sagnac loop is
investigated theoretically. The filter which is based on an asymmetric grating Sagnac loop is manufactured and used in
the measurement of spontaneous Brillouin scattering sensing system, and the separation of backscattered spontaneous
Brillouin from Rayleigh is achieved effectively. It is demonstrated that the fiber grating Sagnac loop filter can be applied
in the distributed sensing system based on spontaneous Brillouin scattering.
Self- and cross-phase modulation (SPM, XPM) in fiber is expected to play a major role in ultrafast all-optical analog-to-digital conversion(ADC), which can overcome the obstacles of inherently limited operating speed of electronic ADC.
In this paper, we propose novel optical coding method for all-optical ADC using nonlinear optical switches based on the
Sagnac interferometer. The multiperiod transfer function, which is the key to coding, is achieved through an exact design
of the Sagnac interferometer. We conducted proof-of-principle experiments and successfully demonstrated 2.6-bit all
optical ADC with Gray code output. The proposed optical coding, combined with existing optical sampling and
quantizing techniques, will enable ultrafast photonic ADC without electronics.
We report on an optical fiber Raman temperature Sensor with a backscattering nonlinear mirror. four ports of one 2×2 coupler link the two sensing optical fiber, one incident optical fiber, one output optical fiber respectively and the two sensing fiber make a bunch. On the condition that the quasi-continuous wave input, the 1:1 2×2 coupler forms the backscattering nonlinear mirror, so the signals received by the detector will take four times of what a single sensing optical fiber does. We make up the experimental system and the agreement with the theory is reasonable.
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