The refractive index changes induced by stimulated Brillouin scattering in an optical fiber are measured experimentally by polarization-decoupled four-wave mixing. Under undepleted pump approximation, net phase-matching condition depends on pump power and frequency detuning from Brillouin frequency. By investigating this net phase-matching condition, one can measure spectral change in the refractive index which is responsible for the slow light effect based on stimulated Brillouin scattering. Due to the high sensitivity of the measurement, very small refractive index changes (on the order of 10-8) versus frequency detuning can be determined experimentally, which is the lowest index change reported so far.
A high-spatial-resolution distributed optical fiber vibration sensor is demonstrated. The distributed dynamic strain or
vibration information can be obtained using time-resolved optical frequency-domain reflectometry (OFDR). Time-domain
information is resolved by measuring Rayleigh backscatter spectrum in different wavelength ranges which fall in
successive time sequence due to the linear wavelength sweep of the tunable laser source with a constant sweeping rate.
This time-resolved local Rayleigh backscatter spectrum shift of the vibrated state with respect to that of the non-vibrated
state along the fiber length provides dynamic strain information in a distributed manner. The measurable frequency range
of 0-32 Hz with the spatial resolution of 10 cm can be achieved
An all-fiber passively Q-switched erbium/ytterbium co-doped cladding pumped fiber laser is presented. A section of
erbium/ytterbium co-doped fiber is used as both gain medium and saturable absorber, which makes the laser
configuration simple and compact. By properly choosing the splitting ratio of the laser output coupler, stable Q-switching
could be achieved. It has been found that the splitting ratio of the output coupler is very important for
generating stable Q-switching pulses. The operation range of stable Q-switching is different for different lengths of
the erbium/ytterbium co-doped fiber. Self-mode-locking effect is also observed accompanying with the Q-switched
pulses. The characteristics of the laser output against the pump power and the splitting ratio of the output coupler are
studied in detail.
A novel temperature-independent multi-mode fiber (MMF) lateral strain sensor based on a core-offset interferometer is
presented and demonstrated experimentally. Slightly misaligning a splice between an MMF and a single-mode fiber
(SMF), high extinction ratio of the interferometer based on SMF-MMF-SMF structure can be obtained. When the lateral
strain is applied to a short section of the MMF, the extinction ratio of the interferometer will decrease accordingly while
the interference phase remains almost constant. Temperature variation only leads to shift in the transmission power
spectrum of the interferometer and does not affect the extinction ratio. Experimental results show that there is a good
quadratic relationship between the lateral strain and the extinction ratio. The proposed strain sensor has the advantages of
temperature-independency, high extinction ratio sensitivity, good repeatability, low cost, and simplicity in structure.
A novel lateral force sensor based on a core-offset multimode fiber interferometer with intensity-based interrogation
technique is reported. An offset between the cores of the single-mode fiber and multimode fiber is made to produce high
extinction ratio. When a lateral force is applied to a short section of the multimode fiber, the extinction ratio decreases
with the interference phase almost unchanged. In addition to serving as a sensing head, the multimode fiber can also act
as a filter to realize lateral force measurement by determining the power change from a power meter. Experimental
results show that the power ratio change has a linear relationship with respect to the applied lateral force, and the
resolution of the sensor configuration is about 0.01 N.