This paper investigates optical properties of few-mode fiber with non-uniform refractive index, namely: the few mode fiber with U-shape refractive index and the two-mode and four-mode few-mode fiber with bent radius. Finite element method is used to analyze the mode distributions based on their non-uniform refractive index. Effective mode control can be achieved through these few mode fibers to achieve vector beam generation. Finally, reflection spectra of a few-mode fiber Bragg grating are calculated theoretically and then measured under different bending conditions. Experimental results are in good accordance with the theoretical ones. These few mode fibers show potential applications in generation of cylindrical vector beam both for optical lasing and sensing systems.
We demonstrate an ultra-narrow-band mode-selection method based on a hybrid-microsphere-cavity which consists of a coated silica microsphere. Optical field distribution and narrow-band transmission spectrum of the whispering gallery modes (WGM) are investigated by finite-difference time-domain method. WGM transmission spectra are measured for microsphere and tapered fibers with different diameters. A high refractive index layer coated on the microsphere-cavity make the Q factor increased, the transmission spectrum bandwidth compressed and the side-mode suppression ratio increased. Parameters of the hybrid-microsphere-cavity, namely, the coated shell thickness and its refractive index are optimized under different excitation light source as to investigate the whispering-gallery-modes’ transmission spectrum. The 3dB bandwidth of the proposed filter can be less than MHz which will have great potential for applications in all-optical sensing and communication systems.
A fiber-wireless sensor system based on a power-over-fiber technique is developed to offer a flexible, distributed sensing ability over a middle distance, especially under environments that are sensitive to electromagnetic interference. In this system, the optical energy of a high-power laser in the base station is transmitted via a fiber and then converted into electrical energy by a photovoltaic power converter (PPC) in the remote unit. This optically power-supplied remote unit operates as the coordinator in the wireless sensor network (WSN) and exchanges the sensing information with the base station via another fiber. In our demonstration system, the sensing information can be collected by a WSN 2 km away and be transmitted back. In order to improve the power supply ability of PPC, a maximum power point tracking technique is applied. More than 80% of PPC’s maximum output power can be obtained. Moreover, to reduce the power consumption of the remote unit and the sensor nodes, a simple and stable low-power communication protocol is designed.
We report on the construction of a pulse-pumped fiber laser using highly doped gain fiber within a ring-shaped all-fiber
resonator. The pump laser is pulse modulated and coupled into a segment of highly doped Erbium doped fiber. The ring
cavity is close-looped in an all-fiber manner. The pulsed-lasing in kHz repetition rate down to single-shot operation are
tunable by pulsed-modulation of the pump laser and tuning of an intracavity variable optical coupler. The lasing power
increases for a higher pump pulse energy and repetition rate which sets the limit of the output pulse energy. We measure
the time-domain characteristics of the lasing pulses and analyze the dynamical property of the pulsed-pumping process
theoretically based on time-dependent rate equation.
Internet Of Things (IOT) drives a significant increase in the extent and type of sensing technology and equipment.
Sensors, instrumentation, control electronics, data logging and transmission units comprising such sensing systems will
all require to be powered. Conventionally, electrical powering is supplied by batteries or/and electric power cables. The
power supply by batteries usually has a limited lifetime, while the electric power cables are susceptible to
electromagnetic interference. In fact, the electromagnetic interference is the key issue limiting the power supply in the
strong electromagnetic radiation area and other extreme environments. The novel alternative method of power supply is
power over fiber (PoF) technique. As fibers are used as power supply lines instead, the delivery of the power is
inherently immune to electromagnetic radiation, and avoids cumbersome shielding of power lines. Such a safer power
supply mode would be a promising candidate for applications in IOT. In this work, we built up optically powered active
sensing system, supplying uninterrupted power for the remote active sensors and communication modules. Also, we
proposed a novel maximum power point tracking technique for photovoltaic power convertors. In our system, the actual
output efficiency greater than 40% within 1W laser power. After 1km fiber transmission and opto-electric power
conversion, a stable electric power of 210mW was obtained, which is sufficient for operating an active sensing system.
We demonstrate a low noise fiber laser (LN-FL) based on gain feedback controlled high efficiency fiber amplifier chain
(FAC) which connect with other optical devices in a circle manner. The FAC contains two cascaded fiber amplifiers
with core pumped and double-clad pumped Erbium and Erbium-Ytterbium co-doped fibers. Gain saturation effect and
amplified spontaneous emission noise in the FAC is analyzed and suppressed through gain control method. Lasing mode
in the LN-FL is stabilized with fiber pigtails setting in special orbits and ensuring fiber device splicing loss low without
any filters. For continuous wave operation, mode-hopping free laser spectrum with output power of 2W and SNR of
50dB is achieved. The narrowest bandwidths are about 0.2nm and 0.01nm for lasing cavity without and with filters,
respectively. Lasing wavelength can be tuned in a wavelength span of 7nm by adjusting of a fiber pigtailed polarization
controller. Pulsed operation of the laser under different pump seeds injection is experimental investigated and analyzed.
For the thermal stability of mean wavelength of erbium-doped super-fluorescent fiber source (SFS), particularly, from a
different viewpoint, we analyzed the variation of spectrum of SFS at different temperature and wavelength range. Firstly,
the spectrum of a SFS at 10 °C is selected as a standard data (STDD), then at the different temperatures from -40 °C to
+60 °C (10 °C per step), the spectrums subtract the STDD for the spectral temperature dependent instability. It is found
that the variation of spectrum from short wavelength to long wavelength can be divided into three regions. In the middle
wavelength region from 1540nm to 1565nm, the dBm values of the spectrum are decreased with increasing temperature,
and with wavelength-flattened characteristics. On the other hand, at the short and long wavelength region, the dBm
values of the spectrum change inversely with temperature, and the variations are larger than that of the middle region.
Based on this characteristics, we design a new configuration of SFS, the mean-wavelength stability can be achieved
2.10ppm/mA and 1.75ppm/ °C in the range of pump current from 100mAto 250mA and in the range of temperature from
-40 to +60 °C, respectively.