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.
We propose a novel efficient dispersion compensating filter that is relatively simple and much less expensive to implement. It is a multicavity Gires-Tournois etalon based all-pass filter and the length of each of the cavities is slightly mismatched. We present a theoretical study of the filter for chromatic dispersion compensation. Our simulation results show that a linear group delay response can be obtained by properly choosing the mismatched cavity length and the chromatic dispersion value can be controlled by suitably adjusting the reflection coefficients of the mirrors. For applications in fiber disperison compensation, the disperson slope can be achieved by slightly modulating the reflection coefficients of the reflectors relative to wavelength.
A periodic optical filter based on a Michelson interferometer with a three-mirror Gire-Tournois resonator in one of the two arms is analyzed. We derive the general condition for the occurrence of flattop spectra. The results show that flattop spectra can be obtained by suitably choosing the reflective coefficients of individual mirrors.
Optical bandpass filters with ripple-free spectral response are highly desirable for dense wavelength-division-multiplexed (DWDM) systems. We study and analyze the transmission characteristics of an optical bandpass filter, based on a three-mirror Gires-Tournois resonator (GTR) in a Michelson interferometer (MI). The three-mirror GTR (R<sub>1</sub>, R<sub>2</sub>, R<sub>3</sub>) is actually an all-pass filter with the reflectivity of the end mirror R<sub>3</sub> being unity. In this paper, we present an analytical expression for the optimum design which has a ripple-free spectral response. The results show that flattop spectra can be obtained by suitably choosing the reflectivities R<sub>1</sub>, R<sub>2</sub> of the two mirrors. Whereas a two-mirror GTR-based bandpass filter has only one unique optimum reflectivity, a three-mirror GTR-based filter has many sets of optimum values, making it easier to be designed to give much better performance. The effects of the reflective coefficients of the mirrors on the optical performance were also discussed.
An erbium-doped fiber ring laser, with a single- longitudinal-mode, operating at 1548.5 nm, has achieved traveling wave operation without the use of an optical isolator. The unidirectional operation is guaranteed by a combination of an output coupler and an external fiber Bragg grating. The laser can provide up to 19.6 mW output power. The linewidth of the laser was measured to be < 24 kHz.